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  • 1. Abram, Emese
    et al.
    Gajdatsy, Gabor
    Hermann, Peter
    Ujhelyi, Ferenc
    Borbely, Judit
    Shen, James Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The colour of monolithic zirconia restorations determined by spectrophotometric examination2019In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 118, no 1-2, p. 3-8Article in journal (Refereed)
    Abstract [en]

    Objective: The aim of this in vitro study is to examine the optical effects of monolithic zirconia of different translucency and thickness, combined with substrates of different colours. Materials and methods: Zirconia specimens of two colours (A2P1, WHITE) were used for the study, three try-in pastes (Variolink Esthetic); substrates were prepared from nine types of materials (six VITA SIMULATE, three metals). Measurements were carried out at the Faculty of Atomic Physics of the Technical University of Budapest with the state-of-the-art PerkinElmer (R) Lambda 1050 spectrophotometer. Results: The colouring of zirconia has a major effect on dE values resulting in different colour perceptibility and acceptability. Try-in pastes, however, have no significant effects overall. Conclusion: Applying coloured zirconia is highly eligible for preparing aesthetic crowns as their substrate-covering effect makes it possible to reproduce the desired colour. Uncoloured zirconia nonetheless is unaffected by the substrate material, especially above a certain layer thickness.

  • 2. Abram, Emese
    et al.
    Gajtdatsy, Gabor
    Feher, Dora
    Salata, Jozsef
    Beleznai, Szabolcs
    Hermann, Peter
    Borbely, Judit
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Spectrophotometric examination of the optical effects of monolithic multilayered zirconia with different substrates2020In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 119, no 5-6, p. 261-266Article in journal (Refereed)
    Abstract [en]

    The goal of this study is to examine specific optical effects of multilayered and coloured monolithic zirconia considering thickness and substrates of different colours using one of the most advanced spectrophotometers of the world. Multilayered zirconia specimens were used for the study with the thickness range of 0.5-2.5 mm and six types of substrate materials and three types of metal substrates. Measurements were carried out at Budapest Technical University with a PerkinElmer (R) Lambda1050UV/Vis/NIR spectrophotometer. The substrate colour and the thickness of zirconia affects the optical results, with special regard to colour perceptibility and acceptability. Monochromatic and multilayer zirconia show both similarities and discrepancies in behaviour, i.e. spectral reflectance and Delta E. Owing to the multi-coloured characteristics of multilayered zirconia the optical effect of the substrate less predictable than in the case of monochromatic zirconia thus requiring more detailed planning and implementation.

  • 3. Adolfsson, E
    et al.
    Shen, Z
    Stockholm University.
    Densification of zirconia-hydroxyapatite ceramics without phase changes2006In: Bioceramics 18 PTS 1 and PTS 2, Vol. 309-311, p. 1141-1144Article in journal (Refereed)
  • 4. Adolfsson, Erik
    et al.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Effects of granule density on strength and granule related defects in zirconia2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 11, p. 2653-2659Article in journal (Refereed)
    Abstract [en]

    A suspension of zirconia powder (TZ3YSE) with a solids loading of 50 vol% was prepared by ball milling. Binders were added and some of the suspension was diluted to 40, 30 and 20 vol% before freeze granulation was performed. A spray dried material (TZ3YSEB) was used as a reference. The pore size distribution of the different granules was evaluated and from the microstructure it was shown that inhomogeneities were present in both the freeze granulated as well as in the spray dried granules. In addition, the density, microstructure as well as the strength of sintered materials prepared from the granules were studied. The results showed that a high green density or sintered density was not sufficient in order to achieve a high strength material. It was further shown that the strength was significantly influenced by the granule density and not by the inhomogeneities found in the granules.

  • 5. Ahmed, Istaq
    et al.
    Kinyanjui, Francis G.
    Steegstra, Patrick
    Shen, Zhijian J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eriksson, Sten-G.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Improved Proton Conductivity in Spark-Plasma Sintered Dense Ceramic BaZr0.5In0.5O3-delta2010In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 13, no 11, p. b130-B134Article in journal (Refereed)
    Abstract [en]

    Spark-plasma sintering method was used to prepare dense proton conducting perovskite oxide BaZr0.5In0.5O3-delta. Analysis of X-ray powder diffraction data showed that the sample adopt the cubic crystal structure having the space group Pm3m. Thermogravimetric analysis of prehydrated samples showed significant mass losses beyond 300 degrees C due to loss of protons as water vapor. Scanning electron microscope images show that the grain size of the spark-plasma sintered dense sample was smaller than that of solid-state sintered porous sample. The highest total proton conductivity (2 X 10(-3) S cm(-1) at 450 degrees C) was found for dense spark-plasma sintered sample under wet H-2 than the samples prepared by other routes.

  • 6. Ahmed, Shafique
    et al.
    Zhang, Man
    Koval, Vladimir
    Zou, Lifong
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Chen, Riqing
    Yang, Bin
    Yan, Haixue
    Terahertz probing of low-temperature degradation in zirconia bioceramics2022In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 105, no 2, p. 1106-1115Article in journal (Refereed)
    Abstract [en]

    ZrO2-based ceramics are widely used in biomedical applications due to its color, biocompatibility, and excellent mechanical properties. However, low-temperature degradation (LTD) introduces a potential risk for long-term reliability of these materials. The development of innovative nondestructive techniques, which can explore LTD in zirconia-derived compounds, is strongly required. Yttria stabilized zirconia, 3Y-TZP, is one of the well-developed ZrO2-based ceramics with improved resistance to LTD for dental crown and implant applications. Here, 3Y-TZP ceramic powders were pressed and sintered to study the LTD phenomenon by phase transition behavior. The LTD-driven tetragonal-to-monoclinic phase transition was confirmed by XRD. XPS analysis demonstrated that induced LTD reduced the oxygen vacancies which supports these findings. It is proved that after the degradation, the 3Y-TZP ceramics show the decreased dielectric permittivity at terahertz frequencies due to the crystallographic phase transformation. Terahertz nondestructive probe is a promising method to investigate LTD in zirconia ceramics.

  • 7. An, Di
    et al.
    Li, Hezhen
    Xie, Zhipeng
    Zhu, Tianbin
    Luo, Xudong
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Ma, Jing
    Additive manufacturing and characterization of complex Al2O3 parts based on a novel stereolithography method2017In: International Journal of Applied Ceramic Technology, ISSN 1546-542X, E-ISSN 1744-7402, Vol. 14, no 5, p. 836-844Article in journal (Refereed)
    Abstract [en]

    In this work, we prepared Al2O3 ceramic green parts with complex geometry and architecture using an additive manufacturing process based on stereolithography. The rheological and thermal behavior of Al2O3 slurry was firstly examined and used to establish the conditions for molding and debinding. As opposed to previous researches that only focused on manufacture techniques, the sintering behavior and densification process were systematically investigated. In addition, special attentions were paid to the evolution of microstructure between green bodies and sintered parts. The results showed that debound parts were equipped with uniform particle packing and narrow pore size distribution. The dimensions of the Al2O3 parts changed anisotropically with the different processing steps. The densification process was greatly accelerated by the decrease in pore size and annihilating of interconnected pores in which significant grain growth was observed above 1450 degrees C. The sintered part also had a homogeneous microstructure and no interface between adjacent layers. High densification (relative density of 99.1%) and much desirable Vickers hardness (17.9 GPa) of Al2O3 parts were achieved at the sintering temperature of 1650 degrees C.

  • 8. Balazsi, C
    et al.
    Weber, F
    Kover, Z
    Shen, Z
    Stockholm University.
    Konya, Z
    Kasztovszky, Z
    Vertesy, Z
    Biro, LP
    Kiricsi, I
    Arato, P
    Application of carbon nanotubes to silicon nitride matrix reinforcements2006In: Current Applied Physics, Vol. 6, p. 124-130Article in journal (Refereed)
  • 9. Buixaderas, E.
    et al.
    Bovtun, V.
    Kempa, M.
    Savinov, M.
    Nuzhnyy, D.
    Kadlec, F.
    Vanek, P.
    Petzelt, J.
    Eriksson, M.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Broadband dielectric response and grain-size effect in K0.5Na0.5NbO3 ceramics2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 1, p. 14111-Article in journal (Refereed)
    Abstract [en]

    Dielectric spectra of two K0.5Na0.5NbO3 ceramics with different grain sizes (10 and 0.5 mu m) were measured from 10(2) to 10(14) Hz in a broad temperature range. The sequence of first-order phase transitions (cubic-tetragonal-orthorhombic-rhombohedral) was detected by differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy. The grain size affects all the phase transitions, which are more smeared in the small-grain sample. In the large-grain ceramics, two well-separated near-Debye relaxations are seen in the tetragonal phase, which suddenly merge on cooling across the tetragonal-orthorhombic transition, and on further cooling the lower-frequency relaxation strongly broadens. On reducing the grain size, the higher-frequency relaxation shifts from similar to 1 to similar to 20 GHz and the lower-frequency one strongly broadens. Without quantitative understanding, these effects could be assigned to domain-wall dynamics and its temperature and grain-size dependences. Similar to pure KNbO3, an overlapped central-mode-soft-mode type excitation was detected in the terahertz range related to the effective hopping and oscillations of the off-centered Nb ions in a multiwell potential.

  • 10.
    Cai, Yanbing
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Esmaeilzadeh, Saeid
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Thermal Properties of Nitrogen-Rich Ca-α-Sialons2009In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 29, no 16, p. 3409-3417Article in journal (Refereed)
    Abstract [en]

    Nitrogen-rich Ca-α-Sialon (CaxSi12−2xAl2xN16 with x = 0.2, 0.4, and 0.8, 1.2 and 1.6) ceramics were prepared from the mixtures of Si3N4, AlN and CaH2 powders in a hot press at 1800 °C using a pressure of 35 MPa and a holding time of 4 h, and then were investigated with respect to reaction mechanism, phase stability and oxidation resistance. In addition the sample with x = 1.6 was prepared in the temperature range 600–1800 °C using a pressure of 35 MPa and a holding time of 2 h. The α-Sialon phase was first observed at 1400 °C but the α-Si3N4 and AlN phases were still present at 1700 °C. Phase pure Ca-α-Sialon ceramics could not be obtained until the sintering temperature reached 1800 °C. The phase pure nitrogen-rich Ca-α-Sialon exhibited no phase transformation in the temperature range 1400–1600 °C. In general, mixed α/β-Sialon showed better oxidation resistance than pure α-Sialon in the low temperature range (1250–1325 °C), while α-Sialons with compositions located at α/β-Sialon border-line showed significant weight gains over the entire temperature range tested (1250–1400 °C). The phases formed upon oxidation were characterized by X-ray, SEM and TEM studies.

  • 11.
    Cai, Yanbing
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Saeid, Esmaeilzadeh
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sialon Ceramics Prepared by Using CaH2 as a Sintering Additive2008In: Journal of the American Ceramic Society, ISSN 0002-7820, Vol. 91, no 9, p. 2997-3004Article in journal (Refereed)
    Abstract [en]

    In developing elongated a-sialon grains, a nitrogen-rich liquidphase sintering method was introduced by using CaH2 as asintering aid, so as to vary the N/O ratio of the liquid phaseformed in the sintering process while keeping the Si/Al ratiosconstant. With increasing addition the phase contents changedfrom single b-sialon to dual b/a-sialons and to single Ca-a-sialon.At low N/O ratios the microstructures contained mainlyequiaxed b-sialon grains, and at high N/O ratios well facetedelongated Ca-a-sialon grains. The improved toughness(KIC57.8 MPa .m1/2) and hardness (HV10517.5 GPa) propertiescan be attributed to the formation of interlocked microstructures.High-temperature compressive deformation testsindicated that the deformation onset temperature is determinedmainly by the Si/Al and N/O ratios, whereas the deformationrate is affected by the microstructure, i.e., the morphology andamounts of elongated a-sialon grains and residual glass phase,especially for the sialons with low N/O ratios.

  • 12. Candelario, Victor M.
    et al.
    Moreno, Rodrigo
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Guiberteau, Fernando
    Ortiz, Angel L.
    Liquid-phase assisted spark-plasma sintering of SiC nanoceramics and their nanocomposites with carbon nanotubes2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 5, p. 1929-1936Article in journal (Refereed)
    Abstract [en]

    The appropriate conditions for liquid-phase assisted spark-plasma sintering (SPS) were identified for the fabrication of both SiC nanoceramics and their nanocomposites with carbon nanotubes (CNTs). A parametric study of the nanoceramics and nanocomposites with a given type of CNTs showed that the SPS temperature (as measured by the radial optical pyrometer) optimizing their densification, nanograin size, and mechanical properties is 1700 degrees C (soaking for a few minutes), below which there is incomplete densification, and above which there is obvious grain growth with no benefit in hardness or toughness in the case of the nanoceramics, and prejudicial to both properties in the case of the nanocomposites due to the CNT degradation. It was also shown that the nanocomposites have smaller nanograins than their nanoceramic counterparts, and are softer but tougher. Extension to nanocomposites with different types of CNTs confirmed these trends, and showed that the CNT features do not condition the densification, microstructure or mechanical properties of these nanocomposites.

  • 13. Candelario, Victor M.
    et al.
    Moreno, Rodrigo
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ortiz, Angel L.
    Aqueous colloidal processing of nano-SiC and its nano-Y3Al5O12 liquid-phase sintering additives with carbon nanotubes2015In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, no 13, p. 3363-3368Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes (CNTs) have occasionally been observed to benefit the aqueous colloidal processing of nano-SiC with its nano-Y3Al5O12 liquid-phase-sintering additives. Experimental evidence is here presented for a broad set of CNTs with different morphology and/or surface functionalization confirming that CNTs (7 vol.% addition), regardless of their features, prevent the coagulation of these nanoceramic suspensions, whence it is inferred that aqueous colloidal processing is well-suited for the environmentally friendly preparation of the homogeneous mixtures of nanoceramic particles and CNTs required for the fabrication of CNT-reinforced ceramic matrix nanocomposites. Furthermore, it is shown that surface-functionalized CNTs seem to work better than deflocculated CNTs for the preparation of stable concentrated colloidal suspensions, whose rheological properties are in general very close, but with thinner CNTs being nonetheless preferable. Finally, the feasibility is demonstrated of fabricating SiC/CNT nanocomposites by aqueous colloidal processing followed by liquid-phase assisted spark-plasma sintering.

  • 14. Chaim, R.
    et al.
    Marder, R.
    Estournes, C.
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Densification and preservation of ceramic nanocrystalline character by spark plasma sintering2012In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 111, no 5-6, p. 280-285Article in journal (Refereed)
    Abstract [en]

    Spark plasma sintering is a hot pressing technique where rapid heating by dc electric pulses is used simultaneously with applied pressure. Thus, spark plasma sintering is highly suitable for rapid densification of ceramic nanoparticles and preservation of the final nanostructure. A considerable portion of the shrinkage during densification of the green compact of nanoparticles in the first and intermediate stages of sintering occurs during heating by particle rearrangement by sliding and rotation. Further densification to the final stage of sintering takes place by either plastic yield or diffusional processes. Full densification in the final stage of sintering is associated with diffusional processes only. Nanoparticle sliding and rotation during heating may also lead to grain coalescence, with much faster kinetics than normal grain growth at higher temperatures. Based on existing models for particle rearrangement and sliding, the contributions of these processes in conjunction with nanoparticle properties and process parameters were highlighted.

  • 15. Chaim, Rachman
    et al.
    Kalina, Michael
    Shen, James Z.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Transparent yttrium aluminum garnet (YAG) ceramics by spark plasma sintering2007In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 27, no 11, p. 3331-3337Article in journal (Refereed)
    Abstract [en]

    Commercial nanocrystalline yttrium aluminum garnet (nc-YAG) powders were used for fabrication of dense and transparent YAG by spark plasma sintering (SPS). Spherical 34 nm size particles were densified by SPS between 1200 and 1500 degrees C using 50 and 100 MPa pressures for 3, 6, and 9 min durations. Fully dense and transparent polycrystalline cubic YAG with micrometer grain size were fabricated at very moderate SPS conditions, i.e. 1375 degrees C, 100 MPa for 3 min. Increase in the SPS duration and pressure significantly increased the density especially at the lower temperature range. The observed microstructure is in agreement with densification by nano-grain rotation and sliding at lower densities, followed by curvature driven grain boundary migration and normal grain growth at higher densities. Residual nanosize pores at the grain boundary junctions are an inherent microstructure feature due to the SPS process.

  • 16. Chaim, Rachman
    et al.
    Reshef, Ram
    Liu, Guanghua
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Low-temperature spark plasma sintering of NiO nanoparticles2011In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, no 6, p. 2936-2940Article in journal (Refereed)
    Abstract [en]

    NiO nanoparticles of 20 nm in diameter were spark plasma sintered between 400 °C and 600 °C for 5 and 10 min durations. Application of 100 MPa pressure from room temperature resulted in densities between 75% and 92%. The final grain size was between 26 nm and 68 nm. Lower densities were recorded when 100 MPa was applied at the SPS temperature. Two shrinkage rate maxima of 3.4 × 10−3 s−1 and 2 × 10−3 s−1 were observed around 390 ± 10 °C and at the SPS temperature. The two shrinkage rate maxima were related to densification by particle sliding followed by diffusional grain boundary sliding during the heating. The strong effects of the surface and interfacial processes which are active during the SPS were highlighted.

  • 17. Chen, Jinhan
    et al.
    Li, Kailun
    Wang, Yafei
    Xing, Leilei
    Yu, Chenfan
    Liu, Hailong
    Ma, Jing
    Liu, Wei
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    The effect of hot isostatic pressing on thermal conductivity of additively manufactured pure tungsten2020In: International journal of refractory metals & hard materials, ISSN 0263-4368, Vol. 87, article id 105135Article in journal (Refereed)
    Abstract [en]

    The crack-healing behaviors and microstructure evolution of pure tungsten produced by laser powder bed fusion (LPBF) were studied and compared before and after post hot isostatic pressing (post-HIP) treatment. An average thermal conductivity of 133 W.m(-1).K-1 at room temperature (RT) was obtained after HIP, which was 16% higher than that of as-built sample (115 W.m(-1).K-1). Although the HIP process had little effect on density, it resulted in a large grain size of > 300 mu m accompanied by a decrease in dislocation density and crack healing, which led to a substantial improvement of thermal conductivity of pure tungsten. The positive correlation between relative density and thermal conductivity of as-built tungsten was reported.

  • 18. Chen, Nan
    et al.
    Ma, Guoqiang
    Zhu, Wanquan
    Godfrey, Andrew
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wu, Guilin
    Huang, Xiaoxu
    Enhancement of an additive-manufactured austenitic stainless steel by post-manufacture heat-treatment2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, p. 65-69Article in journal (Refereed)
    Abstract [en]

    The effect of post-manufacture heat-treatment on the mechanical strength of an additively-manufactured austenitic stainless steel has been investigated. Microstructural investigations revealed that the as-manufactured material exhibited a multi-scale structure, composed of grains, cells, dislocations and nano-sized particles. Annealing at 400 degrees C resulted in a 10% increase in yield strength, associated with the additional precipitation of a population of nano-sized silicates. Annealing at higher temperatures resulted in a decrease in strength, attributed primarily to the thermal instability of the cell structure in the as-manufactured material. The results demonstrate that by careful control of annealing conditions the structure and mechanical properties of additively-manufactured austenitic stainless steel can be optimized by post-manufacture heat-treatment.

  • 19. Cui, Xinyue
    et al.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Xinzhi
    Esthetic appearances of anatomic contour zirconia crowns made by additive wet deposition and subtractive dry milling: A self-controlled clinical trial2020In: The Journal of prosthetic dentistry (Print), ISSN 0022-3913, E-ISSN 1097-6841, Vol. 123, no 3, p. 442-448Article in journal (Refereed)
    Abstract [en]

    Statement of problem. Anatomic contour zirconia crowns are widely used in clinical dental practice because of their mechanical reliability and improved appearance. However, few studies have performed clinical evaluations of the esthetics of these crowns in terms of color and translucency gradient.

    Purpose. The purpose of this clinical trial was to compare the esthetic effect and color-matching behaviors of anatomic contour zirconia crowns manufactured with 3-dimensional (3D) gel deposition and dry milling methods.

    Material and methods. Twenty-seven premolar teeth of 27 participants received 2 identical anatomic contour zirconia crowns fabricated by additive 3D gel deposition or dry milling. Color differences (Delta E) between the crown and natural control teeth were measured by a dental shadematching device. Subjective color matching was rated by professionals using an extended visual rating scale for appearance match (EVRSAM) and by participants using a visual analog scale (VAS). Data were analyzed by using repeated measures ANOVA, the Bonferroni test, paired Student t test, Pearson chi-square test, and Wilcoxon test (alpha=.05).

    Results. Significant differences were found in SE between zirconia crown and core types (P<.05); however, there was no significant interaction between these factors (P>.05). The average SE of crowns made by wet deposition and dry milling were 2.45 +/- 1.60 and 4.55 +/- 1.54 (P<.05). The mean crown Delta E was significantly higher if a gold cast post-and-core was placed rather than a prefabricated fiber post and composite core (P<.05). Consistent with these findings, subjective color matching was significantly higher in the wet deposition group than in the dry milling group as rated by EVRSAM and VAS (P<.05).

    Conclusion. Anatomic contour zirconia crowns fabricated by additive wet deposition were better matched to adjacent teeth and had excellent esthetics in terms of color and translucency gradient.

  • 20. de Moraes, Elisangela Guzi
    et al.
    Li, Duan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Colombo, Paolo
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Silicon nitride foams from emulsions sintered by rapid intense thermal radiation2015In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, no 12, p. 3263-3272Article in journal (Refereed)
    Abstract [en]

    Open cell Si3N4 foams were fabricated by an emulsification process and subsequent sintering. Emulsification took place in an aqueous environment by using octane as alkane phase and a surfactant as stabilizer. Effects of different octane concentrations (50 vol% and 70 vol%) and stirring velocities (700 rpm and 1000 rpm) on porosity and pore size distribution were investigated. The shaped foams were pressureless sintered at 1600 degrees C inside a modified SPS set-up. Si3N4 foams decorated with SiC nanowires and with an average cell size of 8-41 mu m and total porosity of 80-86 vol% were obtained. The compressive strength ranged from 2.0 MPa up to 9.9 MPa. Both the foaming and sintering processes contributed to the development of different microstructures.

  • 21. Dominguez-Rodriguez, Arturo
    et al.
    Gomez-Garcia, Diego
    Zapata-Solvas, Eugenio
    Shen, James Z.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Chaim, Rachman
    Making ceramics ductile at low homologous temperatures2007In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 56, no 2, p. 89-91Article in journal (Refereed)
    Abstract [en]

    Polycrystalline ceramics are brittle at room temperature but may deform by dislocation slip processes at higher temperatures, where T >= 0.5 T-M (T-M, the melting temperature), leading to strain hardening, i.e. the total strain to rupture is limited. We show that mutual sliding of nanometer grains and atomic transport along their boundaries enables low-temperature metal-like plasticity in nanocrystalline ceramics. Compression of fully dense MgO nanoceramics at temperatures as low as 700 degrees C (0.31 T-M) exhibited stress-strain curves with no strain hardening.

  • 22.
    Eden, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Physical Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Al and O substitutions in BaS-phases, Ba2AlxSi12-xN16-xO2+x: A TEM, XRD and solid-state NMR study2008In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 10, no 1, p. 50-60Article in journal (Refereed)
    Abstract [en]

    In a series of Ba-based oxonitrido-silicate S-phases (Ba2AlxSi12-xN16-xO2+x) spanning a compositional range up to x approximate to 3, we examine the incorporation of Al and O by Si-29 and Al-27 magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) and Al-27 triple-quantum MAS (3QMAS). The 3QMAS spectra reveal Al-27 signals from two distinct structural environments, assigned to AlN4 or AlN3O tetrahedra, respectively, and with their relative amounts depending on the S-phase substitution parameter x. Si-29 NMR show variable fractions of SiN4 and SiN3O environments. The NMR results accord overall with a structural substitution model for which O enters at one crystallographic position (occupied according to N4-xOx), in conjunction with a random Al for Si substitution at two distinct crystallographic positions. This leads to S-phase frameworks built from SiN4, SiN3O, AlN4 and AlN3O tetrahedra.

  • 23.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Yi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hu, Jiangfeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gao, Lian
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Transparent hydroxyapatite ceramics with nanograin structure prepared by high pressure spark plasma sintering at the minimized sintering temperature2011In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 31, no 9, p. 1533-1540Article in journal (Refereed)
    Abstract [en]

    A hydrothermally processed bulky powder composed of loosely aggregated nano-sized rods was consolidated by spark plasma sintering. The use of a high pressure cell allows the application of pressure up to 500 MPa. It was found that applying of high pressure is beneficial for widening up the kinetic window for attaining dense HAp nanoceramics. The high transparency of HAp nanoceramics obtained in this study is ascribed to the high density and homogeneous nano-grained structure achieved besides the unique intrinsic optical properties of the HAp crystal itself, i.e. its low refractive index and very small birefringence. Achieving full densification at the minimized sintering temperature allows for the first time the preparation of transparent HAp nanoceramics with stoichiometric composition, i.e. avoiding the loss of structural water that commonly takes place during the conventional ways of sintering.

  • 24.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Radwan, Mohamed
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Spark plasma sintering of wc, cemented carbide and functional graded materials2013In: International journal of refractory metals & hard materials, ISSN 0263-4368, ISSN 0263-4368, Vol. 36, p. 31-37Article in journal (Refereed)
    Abstract [en]

    Spark plasma sintering (SPS) is an extremely fast solidification technique for compounds that are difficult to sinter within the material group's metals, ceramics, or composites thereof. SPS uses a uniaxial pressure and a very rapid heating cycle to consolidate these materials. The heating is generated by Joule effect when a strong, pulsed electric current passes the conductive graphite die and also through the sample, if conductive. Cemented carbides (hard metals) are mostly used for metal cutting and drilling, wood cutting or rock drilling tools and are consolidated either by pressureless sintering (PLS), hot pressing (HP), or hot isostatic pressing (HIP). With SPS the main benefit is the ability to control the WC grain size due to the short sintering times at high temperature. In addition, unwished reactions between WC and cobalt to form other phases are minimized. By SPS the amount of cobalt can be reduced towards zero in fully dense WC materials. With this technique it is easy to prepare gradient materials where a ductile weldable metal can be joined with the cemented carbide part.

  • 25.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Salamon, David
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Spark plasma sintering and deformation of Ti-TiB2 composites.2008In: Materials Science & Engineering, A: Structural Materials: Properties, Microstructure and Processing, ISSN 0921-5093, Vol. 1-2, no A475, p. 101-104Article in journal (Refereed)
    Abstract [en]

    Spark plasma sintering (SPS) was used to investigate the densification and deformation behaviour of Ti–TiB2 composites. Fully densified samples were prepared with Ti addition larger than 5%. The prepared composites can be deformed under compression at 1700 °C to achieve a strain of 50% without cracking. At lower temperatures, cracks were initiated due to low ductility of TiB2 and low content of Ti. During the sintering and deformation, TiB is formed via a reaction between Ti and TiB2. To elucidate the formation mechanism of TiB in the SPS process, reactive sintering of TiB using element precursors was also performed. Fully dense samples were prepared but it was not possible to prepare pure uniphase TiB. The reactive sintering resulted in the formation of TiB and TiB2 mixtures at low temperatures and a mixture of TiB2 and Ti3B4 at high temperature

  • 26.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Fast densification and deformation of titanium powder2005In: Powder Metallurgy, ISSN 0032-5899, Vol. 48, no 3, p. 231-236Article in journal (Refereed)
    Abstract [en]

     A coarse titanium powder containing 0.2 wt-% oxygen with an average particle size of 45 micrometers was rapidly densified using the spark plasma sintering (SPS) technique. The fully consolidated specimens were also deformed in compression in the SPS unit and in a conventional hot pressing (HP) furnace. The densification and deformation behaviours were investigated by microstructural observation and examining the shrinkage and shrinkage rate recorded in real time. The efforts were focused on clarifying to what extent the possible spark discharging and intensive Joule heating at the particle contact points contribute to the densification, and what effect if any the pulsed electrical heating has on the densification. The results showed that what contributed to the densification were neither spark discharging nor anisotropic heating, but the particle deformation. Deformation occurs throughout the entire particle both in SPS and HP conditions, with a higher strain rate under SPS condition especially in the a phase region.

  • 27.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Yan, Haixue
    School of Engineering and Materials Science, Queen Mary University of London,.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Reece, Mike J
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Low temperature consolidated lead-free ferroelectric niobateceramics with improved electrical properties2010In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 25, no 2, p. 240-247Article in journal (Refereed)
    Abstract [en]

    There is a concerted effort to develop lead-free piezoelectric ceramics. ((Na0.5K0.5)NbO3 based ceramics have good electrical properties, and are a potential replacement material for lead zirconate titanate piezoelectric ceramics. In this work a commercial powder based on (Na0.5K0.5)NbO3 with an initial particle size of 260 nm was consolidated by plasma sintering (SPS). To avoid volatilization, high mechanical pressures were used to minimize the densification temperature. It was found that under a uniaxial pressure of 100 MPa, fully densified compacts can be prepared at 850. Ceramics densified at such a low temperature demonstrate an unusually high remanent polarization (30 mC/cm2) and high d33 (146 pC/N). The improved ferroelectric properties are ascribed to the homogeneous, dense, and submicron grained microstructure achieved.

  • 28.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Yan, Haixue
    School of Engineering and Materials Science and Nanoforce Technology Ltd, Queen Mary University of London, London, United Kingdom.
    Viola, Giuseppe
    School of Engineering and Materials Science and Nanoforce Technology Ltd, Queen Mary University of London, London, United Kingdom.
    Ning, Huanpo
    School of Engineering and Materials Science and Nanoforce Technology Ltd, Queen Mary University of London, London, United Kingdom.
    Gruner, Daniel
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Reece, Mike
    School of Engineering and Materials Science and Nanoforce Technology Ltd, Queen Mary University of London, London, United Kingdom.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
    Effect of grain size on ferroelectric domain and electrical properties of submicron sized sodium potassium niobate ceramicsManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    Piezoelectric ceramics of the composition Na0.5K0.5NbO3 (NKN) with grain sizes in the range of 0.2 - 1 mm were fabricated by Spark Plasma Sintering using normal pressure dies and a high pressure cell designed for pressures up to 500 MPa  with the purpose of investigating the effect of grain size on domain structures and electrical properties. Optimized processing conditions enabled ceramics of high densities (>99.5%TD) to be made at T≥850°C. It was found that domain size decreases with decreasing grain size and that non-180° ferroelectric domains walls were still visible in 200 nm sized grains. The room temperature dielectric constant firstly increased with decreasing grain size and then decreased in the low grain size regime. The materials with finer grain size displayed a broad ferro-paraelectric phase transition and a depression of the dielectric maximum at the Curie point. They also displayed an increase in the coercive field and approximately unchanged remnant polarization. The material sintered at 850°C represents a very good candidate for lead-free piezoelectric applications, because of its high piezoelectric constant (d33 = 160±2 pC/N).

  • 29.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yan, Haixue
    Viola, Giuseppe
    Ning, Huanpo
    Grunér, Daniel
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Reece, Mike J.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ferroelectric Domain Structures and Electrical Properties of Fine-Grained Lead-Free Sodium Potassium Niobate Ceramics2011In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, no 10, p. 3391-3396Article in journal (Refereed)
    Abstract [en]

    Piezoelectric ceramics of the composition Na(0.5)K(0.5)NbO(3) (NKN) with grain sizes in the range of 0.2-1 mu m were fabricated by spark plasma sintering. Ferroelectric domain size decreases with decreasing grain size and non-180 degrees ferroelectric domains walls were still visible in 200 nm sized grains. The Curie point of the ceramics was grain size independent. This suggests that the critical grain size for a single domain single grain structure for NKN is <200 nm. Optimized processing conditions enabled ceramics of high densities (>99.5% theoretical density) to be made at T >= 850 degrees C. For the dense ceramics (grain size >= 350 nm), the room temperature dielectric constant and coercive field increased with decreasing grain size. The remnant polarization was grain size independent. The material sintered at 850 degrees C is a very good candidate for lead-free piezoelectric applications because of its high piezoelectric constant (d(33) = 160 +/- 2 pC/N).

  • 30. Gan, Dianne
    et al.
    Iqbal, Muhammad Naeem
    Xu, Qianhui
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ramos, Van
    Chung, Kwok-Hung
    Effect of airborne-particle abrasion with a novel spherical abrasive on the zirconia surface2023In: The Journal of prosthetic dentistry (Print), ISSN 0022-3913, E-ISSN 1097-6841, Vol. 130, no 6, p. 866-876Article in journal (Refereed)
    Abstract [en]

    Statement of problem. A novel zirconia-alumina composite (ZAC) particle has yet to be studied for airborne-particle abrasion in a bonding protocol for the zirconia surface.

    Purpose. The purpose of this in vitro study was to evaluate the shear bond force of resin cement to yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) when using spherical ZAC particles to conduct airborne-particle abrasion and modify the topography of Y-TZP.

    Material and methods. Spherical 30- to 70-μm ZAC particles were fabricated by using a hybrid gel technique. A total of 160 Ø6.6×4.0-mm zirconia disks were fabricated from 4 commercially available zirconia blanks, e.max ZirCAD zirconia (EM), NexxZr T zirconia (NE), Lava Plus High Translucency zirconia (LP), and Imagine High Translucency Zirconia (IM), by using computer-aided manufacturing technology. As-sintered specimens without further surface treatment were used as controls (ZR0). Surface treatment groups included sharp-edged alumina airborne-particle abrasion (ABC), 50 μm, 0.2 MPa; airborne-particle abrasion with ZAC particle at 0.2 MPa (2ZA); and airborne-particle abrasion with spherical ZAC particle at 0.4 MPa (4ZA). All surface treatment groups were airborne-particle abraded at the specified pressures for 10 seconds at a standardized distance of 10 mm. The surface roughness (Ra) and area roughness (Sa) of specimens from each group were measured. Following the application of an adhesive (Scotchbond Universal), Ø6.6×4.0-mm resin cement (RelyX Ultimate) buttons were fabricated for shear bond testing by using a universal testing machine at a 5-mm/min crosshead speed (n=10). The data were analyzed by using a 2-way ANOVA, Tukey HSD test, and regression analysis (α=0.05). Scanning electron microscopy (SEM) was performed to observe changes of the zirconia surface and the failure modes of each group before and after shear bond testing.

    Results. The mean ±standard deviation shear bond force values ranged from 272.6 ±41.4 N to 686.7 ±152.8 N. Statistically significant higher force values than those of the controls (P<.05) were obtained by using airborne-particle abrasion. No significant differences were found among any of the airborne-particle abrasion treatment groups (P>.05). The mean of Ra values ranged from 0.27 μm to 0.74 μm, and the mean of Sa values, from 0.48 μm to 1.48 μm. SEM observation revealed that the zirconia surface was made jagged by abrasion with sharp-edged alumina particles. The spherical ZAC particles create microcraters on the zirconia surface. Fractographic observation disclosed that failures were adhesive-cohesive failure modes with residual resin cement attached on the zirconia surface.

    Conclusions. The surface treatment of zirconia with sharp-edged alumina or the spherical ZAC abrasives improved the bonding force between the zirconia and resin cement. No statistically significant differences in shear bond force values were found between airborne-particle abrasion surface treatment groups.

  • 31.
    Grins, Jekab
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Esmaeilzadeh, Saeid
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    High-resolution electron microscopy of a Sr-containing sialon polytypoid phase1999In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 19, p. 2723-2730Article in journal (Refereed)
    Abstract [en]

    A new type of Sr-containing sialon polytypoid phase with the structural formula SrSi10-xAl18+xN32-xOx (x approximate to l) has been found in the Sr-Si-Al-O-N system. The phase was characterised by X-ray powder diffraction (XRPD), and its structure was investigated by electron diffraction (ED) and high resolution electron microscopy (HREM). It is considerably disordered, but the average structure has a rhombohedral unit cell with a=5.335(5)approximate to root 3.a(AIN) and c= 79.1(1)Angstrom approximate to 30.c(AIN). The Sr atoms ave located in layers M-Sr-M, M=(Si/Al), at the origin of the unit cell with 12 X= (O,N) atoms around it, at distances of similar to 3 Angstrom, forming a cubo-octahedron. The X atoms that form a hexagon around the Sr atom in the ab plane are corner shared by M = (Si/Al) tetrahedra with opposite polarity in adjacent layers in which 2/3 of the tetrahedra are occupied. The M-Sr-M layers alternate with normally eight-layer-thick AIN type blocks, although the thickness of these blocks frequently varies. The structural model obtained from the HREM images includes a polarity reversal of the tetrahedra in the AIN blocks, similar to that proposed to occur in Si-Al-O-N polytypoid phases. The model with one Sr layer and 10 M = (Si,Al) layers per 1/3 of the repeat unit agrees with the composition of the phase and experimental HREM images.

  • 32.
    Gruner, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Direct Scanning Electron Microscopy Imaging of Ferroelectric Domains After Ion Milling2010In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 93, no 1, p. 48-50Article in journal (Refereed)
    Abstract [en]

    A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O-3. Stable high-resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain- and defect-free surface generated by gentle ion milling, pronounced orientation contrast is observed.

  • 33.
    Gryksa, Maximilian
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eriksson, Mirva
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    De Basso, Noran
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Phosphate dental cements agedin vivoup to 25 years2020In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 119, no 5-6, p. 338-347Article in journal (Refereed)
    Abstract [en]

    Phosphates particularly zinc phosphates is a family of conventional dental cements that was developed a century ago and has been in use until today despite the fact that a number of new resin composite cements have been introduced in the market through the years. A close inspection of thein vivoaged samples provides insides to the margins and to the micro-leakage thus would sharpen the understanding and inspire the future development of the cements and cementation interfaces between the dental restorations and the natural tooth or implant abutment. This study highlights the cementation interface and its structural change duringin vivoaging. Besides the focused studies on phosphate cements, limited investigation has also been performed on resin composite cements as references.

  • 34.
    Grüner, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fäldt, Jenny
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Argon Ion Beam Polishing: A Preparation Technique for Evaluating the Interface of Osseointegrated Implants with High Resolution2011In: International Journal of Oral & Maxillofacial Implants, ISSN 0882-2786, E-ISSN 1942-4434, Vol. 26, no 3, p. 547-552Article in journal (Refereed)
    Abstract [en]

    Purpose: The objective of this study was to assess the use of ion beam polishing for preparing cross sections suitable for high-resolution scanning electron microscope (SEM) investigation of dental implants with a brittle porous oxide layer and of bone/implant interfaces. Materials and Methods: Thirteen Nobel Biocare TiUnite implants were placed in minipigs. After 4 weeks, the implant and surrounding bone were removed en bloc and the implant was cut axially into two halves. The cross section was then polished with an argon ion beam. Additionally, ion beam-polished cross sections were prepared from four as-received implants. Ion beam-polished surfaces were studied with a field emission SEM (FE-SEM). Results: With FE-SEM, up to 1 mm along the interface of ion beam-polished implant surfaces can be studied with a resolution of a few nanometers. Filled and unfilled pores of the porous TiUnite coating can be distinguished, providing information on pore accessibility. Implant-bone interfaces can be analyzed using backscattered electron images, where titanium, the oxide layer, mineralized extracellular matrix, and osteocyte lacunae/resin/soft tissue can easily be distinguished as a result of atomic number contrast and the sharp boundaries between the different materials. Filled and unfilled pores can be distinguished. Characterization of local chemistry is possible with energy dispersive X-ray spectrometry, and bone growth into small pores (< 1 mu m) can be unambiguously confirmed. Conclusion: FE-SEM complements the established methods for the characterization of interfaces and bridges the wide gap in accessible length scale and resolution between the observations of mechanically polished interfaces by optical or scanning electron microscopes and the observation of focused ion beam-milled sections in a transmission electron microscope.

  • 35.
    Grüner, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Ordered coalescence of nano-crystals during rapid solidification of ceramic melts2011In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 13, no 17, p. 5303-5305Article in journal (Refereed)
    Abstract [en]

    Rapid cooling of an aluminosilicate-zirconia melt after laser sintering results in the formation of zirconia nano-crystals and dendritic zirconia crystals embedded in a glass matrix. The nano-crystals act as building blocks for the formation of non-faceted secondary crystals. Several secondary crystals built from two or a few nano-crystals with perfect structural coherence across the interface have been observed. Thus, the earliest states of these secondary crystals have been preserved by rapid cooling. Crystal growth can be described by a mechanism, ordered coalescence, which is characterized by self-assembly of nano-crystals combined with atom-by-atom growth and links classical and non-classical crystallization.

  • 36. Gu, Shijia
    et al.
    Zhang, Xin
    Wang, Lianjun
    Gan, Xuehui
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jiang, Wan
    Direct indication of a higher central temperature achieved during spark plasma sintering process of a zeolite2015In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, no 5, p. 1599-1603Article in journal (Refereed)
    Abstract [en]

    The transition between transparent and opaque of as-sintered zeolite samples is employed to study the temperature distribution of non-conducting samples during spark plasma sintering (SPS) process in this paper. The results show that temperature gradients exist in both radial and axial directions, which provide direct evidence of temperature distribution in the SPS process. The sample prepared at 1325 degrees C is transparent in the center and opaque in the edge, which suggests that the temperature of the center is higher than the edge and the temperature differential is about 26 degrees C by the thermal analysis model based on the experimental data in ANSYS code. The axial temperature gradient is also present in the as-sintered sample obtained at 1315 degrees C. The transparent part of the upper surface is larger than the lower surface, which illustrates that the temperature of the upper surface was higher than the lower surface and the difference is about 5 degrees C.

  • 37.
    Hakeem, A. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Daucé, R.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Leonova, E.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Edén, M.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Z.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, J.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Esmaeilzadeh, S.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Silicate glasses with unprecedented high nitrogen and electropositive metal contents obtained by using metals as precursors2005In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 17, p. 2214-2216Article in journal (Refereed)
    Abstract [en]

     

     

  • 38.
    Han, Guang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Müller, Werner E. G.
    Wang, Xiaohong
    Lilja, Louise
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization2015In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 47, p. 376-383Article in journal (Refereed)
    Abstract [en]

    Titanium received a macroporous titania surface layer by anodization, which contains open pores with average pore diameter around 5 gm. An additional mesoporous titania top layer following the contour of the macropores, of 100-200 nm thickness and with a pore diameter of 10 nm, was formed by using the evaporation-induced self-assembly (EISA) method with titanium (IV) tetraethoxide as the precursor. A coherent laminar titania surface layer was thus obtained, creating a hierarchical macro- and mesoporous surface that was characterized by high-resolution electron microscopy. The interfacial bonding between the surface layers and the titanium matrix was characterized by the scratch test that confirmed a stable and strong bonding of titania surface layers on titanium. The wettability to water and the effects on the osteosarcoma cell line (SaOS-2) proliferation and mineralization of the formed titania surface layers were studied systematically by cell culture and scanning electron microscopy. The results proved that the porous titania surface with hierarchical macro- and mesoporosities was hydrophilic that significantly promoted cell attachment and spreading. A synergistic role of the hierarchical macro- and mesoporosities was revealed in terms of enhancing cell adhesion, proliferation and mineralization, compared with the titania surface with solo scale topography.

  • 39.
    Han, Guang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Microscopic view of osseointegration and functional mechanisms of implant surfaces2015In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 56, p. 380-385Article in journal (Refereed)
    Abstract [en]

    Argon ion beam polishing technique was applied to prepare the cross sections of implants feasible for high resolution scanning electron microscope investigation. The interfacial microstructure between newly formed bone and implants with three modified surfaces retrieved after in vivo test using three different animal models was characterized. By this approach it has become possible to directly observe early bone formation, the increase of bone density, and the evolution of bone structure. The two bone growth mechanisms, distant osteogenesis and contact osteogenesis, can also be distinguished. These direct observations give, at microscopic level, a better view of osseointegration and expound the functional mechanisms of various implant surfaces for osseointegration.

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  • 40.
    Han, Guang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Quartz crystal microbalance titanium sensor with mesoporous poresManuscript (preprint) (Other academic)
    Abstract [en]

    The quartz crystal microbalance (QCM) is an effective tool for the surface study in real time. But mesoporous coating materials usually is thin layer and stick to the substrates, and its properties cannot be studied by conventional methods as other mesoporous materials. A new QCM sensor with mesoporous pores is expected. The new mesoporous QCM sensor has mesoporous titania coating with 200 nm thickness only on the active electrode side by the method with masking counter electrode side during dip-coating. The new mesoporous QCM sensor works well in Q-Sense E1 equipment.

  • 41.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Taiyuan University of Technology, China.
    Liu, Yongsheng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Neagu, Alexandra
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Core-Shell and Hollow Particles of Carbon and SiC Prepared from Hydrochar2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 11, article id 1835Article in journal (Refereed)
    Abstract [en]

    The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (-SiC) but also significant amounts of the 2H or the 6H polytypes (-SiC) in the SiC.

  • 42. He, Qinglong
    et al.
    Jiang, Jie
    Yang, Xianfeng
    Zhang, Li
    Zhou, Zhe
    Zhong, Yuan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Additive manufacturing of dense zirconia ceramics by fused deposition modeling via screw extrusion2021In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 41, no 1, p. 1033-1040Article in journal (Refereed)
    Abstract [en]

    A fused deposition modeling(FDM)system via screw extrusion suitable for feeding granular feedstocks with high solid loading was developed. Key parameters included aspect ratio of the screw, the compression ratio and pitch etc. In order to get constant extruded mass flow and wire diameter a processing window was determined by optimizing the barrel temperature, the nozzle diameter and the screwing speed. Microstructural characterization coupled with flexural strength measurement revealed that a higher printing temperature was beneficial to the inter layer bonding. The sintered zirconia ceramic samples with 99% of theoretical density of the 3 mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP) and flexural strength of 890 +/- 60 MPa was obtained. A set of zirconia ceramic parts with complex geometries and controllable dimensional accuracy was also successfully prepared for demonstrating the potential of the technique.

  • 43. Hedberg, Yolanda S.
    et al.
    Qian, Bin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Virtanen, Sannakaisa
    Odnevall Wallinder, Inger
    In-vitro biocompatibility of CoCrMo dental alloys fabricated by selective laser melting2014In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 30, no 5, p. 525-534Article in journal (Refereed)
    Abstract [en]

    Objectives: Selective laser melting (SLM) is increasingly used for the fabrication of customized dental components made of metal alloys such as CoCrMo. The main aim of the present study is to elucidate the influence of the non-equilibrium microstructure obtained by SLM on corrosion susceptibility and extent of metal release (measure of biocompatibility).Methods: A multi-analytical approach has been employed by combining microscopic and bulk compositional tools with electrochemical techniques and chemical analyses of metals in biologically relevant fluids for three differently SLM fabricated CoCrMo alloys and one cast CoCrMo alloy used for comparison.Results: Rapid cooling and strong temperature gradients during laser melting resulted in the formation of a fine cellular structure with cell boundaries enriched in Mo (Co depleted), and suppression of carbide precipitation and formation of a martensitic ε (hcp) phase at the surface. These features were shown to improve the corrosion and metal release susceptibility of the SLM alloys compared with the cast alloy. Unique textures formed in the pattern of the melting pools of the three different laser melted CoCrMo alloys predominantly explain observed small, though significant, differences. The susceptibility for corrosion and metal release increased with an increased number (area) of laser melt pool boundaries.Significance: This study shows that integrative and interdisciplinary studies of microstructural characteristics, corrosion, and metal release are essential to combine and consider during the design and fabrication of CoCrMo dental components of optimal biocompatibility. The reason is that metal release from CoCrMo alloys is dependent on the fabrication procedure.

  • 44. Herrmann, Mathias
    et al.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Schulz, Ingrid
    Hu, Jianfeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Jancar, Bostjan
    Silicon nitride nanoceramics densified by dynamic grain sliding2010In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 25, p. 2354-2361Article in journal (Refereed)
    Abstract [en]

    The densification behaviors of two silicon nitride nanopowder mixtures based respectively on a-Si3N4 and ß-Si3N4 as the major phase constituent were studied by spark plasma sintering. Sintering conditions were established where a low viscous liquid not in equilibrium with the main crystalline constituent(s) stimulated the grain sliding yet did not activate the reprecipitation mechanism that unavoidably yields grain growth. By this way of dynamic grain sliding full densification of silicon nitride nanoceramics was achieved with no noticeable involvement of a- to ß-Si3N4 phase transformation and grain growth. This processing principle opens the way toward flexible and precise tailoring of the microstructures and properties of Si3N4 ceramics. The obtained silicon nitride nanoceramics showed improved wear resistance, particularly under higher Hertzian stresses.

     

  • 45.
    Hu, Jianfeng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grain growth by multiple ordered coalescence of nanocrystals during spark plasma sintering of SrTiO3 nanopowders2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 18, p. 6405-6412Article in journal (Refereed)
    Abstract [en]

    Sintering is the most widely applied densification process for manufacturing polycrystalline materials in powder metallurgy and ceramic industries. Grain growth behavior during sintering has a crucial influence on the final microstructure and thus the achieved performance. So far, it has been accepted that grain growth, based on classic crystal growth theory, takes place via atomic diffusion driven by excess interfacial energy. This paper presents a novel grain growth mechanism resulting from multiple ordered coalescence of nanocrystals via the activation of rapid grain motions. In rapid solid-state sintering of a strontium titanate (SrTiO3) nanopowder, individual SrTiO3 nanocrystals can act as the building blocks and self-assemble to form larger grains. A quasi-liquid interfacial film achieved by surface melting of the nanocrystals plays an essential role in this new process by facilitating the grain motion and ordered coalescence of nanocrystals. The imperfect ordered coalescence of nanocrystals introduce deep structural heterogeneities characterized by the unique quasi-interfaces inside grown grains of single crystal signature. The quasi-interfaces consist of the vacancy arrays and/or aggregated line defects.

  • 46. Hu, Jianfeng
    et al.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grain growth competition during sintering of SrTiO3 nanocrystals: Ordered coalescence of nanocrystals versus conventional mechanism2021In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 194, article id 113703Article in journal (Refereed)
    Abstract [en]

    Grain growth plays a crucial role in developing the microstructures of polycrystalline materials during heating treatment. In this work, SrTiO3 ceramics sintered at different heating rates (10 degrees C/min and 100 degrees C/min) display the distinctly different grain growth behaviors and microstructures between them. The onset temperature of rapid grain growth and mechanical-performance-related fracture mode are apparently different between these two sets of samples. Two grain growth mechanisms are demonstrated to dominate separately the sintering of SrTiO3 nanocrystals at different heating rates, i.e. conventional mechanism of atom-by-atom additions for grain growth at 10 degrees C/min and ordered coalescence of nanocrystals for grain growth at 100 degrees C/min. It is demonstrated that the switch of growth mechanisms is determined by the competition between the activation of grain motions and the formation of steady neck among grains.

  • 47.
    Hu, Jianfeng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grain growth kinetics determined by the heating rate during spark plasma sintering: 2Dnucleation versus ordered coalescence of nanocrystals2013Article in journal (Refereed)
  • 48.
    Hu, Jianfeng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Intragranular heterojunctions formed by ordered coalescence of strontium and barium titanate nanocrystals2015In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 107, p. 14-17Article in journal (Refereed)
    Abstract [en]

    Crystal growth by nanocrystal-assembly plays an important role in the synthesis and preparation of nanostructural materials. In most cases, this crystal-growth mechanism is reported to occur in unary nanocrystal systems and in solution environment. Here, we report a new observation of grain growth by ordered coalescence of nanocrystals occurring in SrTiO3-BaTiO3 binary system during solid-state sintering, which also results in unique oxide heterostructures inside coarsened grains in bulk polycrystalline materials.

  • 49.
    Hu, Jianfeng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mosaic-like structure in Barium Strotium Titanate solid solutionManuscript (preprint) (Other academic)
  • 50.
    Hu, Jianfeng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ordered coalescence of nano crystallites contributing to the rapid anisotropic grain growth in silicon nitride ceramics2013In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, no 3, p. 270-273Article in journal (Refereed)
    Abstract [en]

    Microstructural characterization is performed on two dense Si3N4 ceramic samples consolidated by spark plasma sintering (SPS): one fabricated using alpha-Si3N4 and the other using beta-Si3N4 as the starting powder. A novel mechanism is revealed where ordered coalescence of nano beta-crystallites accelerate the rapid beta-Si3N4 anisotropic grain growth. The rapid alpha- to beta-Si3N4 phase transformation via a high supersaturation of dissolved Si3N4 in the melt favors this mechanism. The high heating rate by SPS is essential for achieving such supersaturation.

12345 1 - 50 of 220
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