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Structural Investigations of Complex Glasses by Solid-state NMR
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This PhD thesis presents structural investigations of amorphous inorganic materials: oxide and oxynitride glasses and mesoporous bioactive glasses (MBGs), by solid-state Nuclear Magnetic Resonance (NMR).

Lanthanum oxide and oxynitride [La-Si-(Al)-O-(N)] glasses have a large number of potential applications due to their physical properties. In our work we have studied, compared to previous investigations, significantly expanded ranges of glass compositions (for oxynitride glasses, including samples of very high nitrogen content, up to 53 % out of the anions). We have estimated local environments of 29Si and 27Al structural units (their coordination, polymerization degree and number of N incorporated into tetrahedral units) in the materials. We have suggested a random Al/Si distribution along with almost uniform non-bridging oxygen atoms distribution in aluminosilicate glasses.

Silicon nitride was used as precursor in the oxynitride glass synthesis. We studied both α- and β-modifications of silicon nitride, 15N-enriched, as well as fully (29Si, 15N)-enriched samples. We have shown that the linewidths of 15N NMR spectra are dominated by J(29Si-15N) coupling in 29Si315N4 sample.

Mesoporous bioactive glasses in the CaO-SiO2-P2O5 system show superior bioactivity (the ability to form a hydroxycarbonate apatite layer on the glass surface when exposed to body fluids) compared to conventional bioactive glasses due to their large surface area and uniform pore-size distribution. Previous studies suggested a homogeneous cation distribution over the MBG samples on a 10−20 nm length-scale. From our results, on the other hand, we may conclude that Si and P is not intimately mixed. We propose a structural model, in which the pore walls of MBGs are composed of a silica network, and a phosphate phase is present as nanometer-sized clusters that are dispersed on the pore wall.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi , 2009. , 62 p.
Keyword [en]
glass, glass structure and properties, NMR, magic angle spinning, chemical shift
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:su:diva-8565ISBN: 978-91-7155-816-9 (print)OAI: oai:DiVA.org:su-8565DiVA: diva2:200487
Public defence
2009-03-19, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-02-26 Created: 2009-02-18 Last updated: 2010-01-26Bibliographically approved
List of papers
1. Structural Characterizations of Lanthanum Aluminosilicate Glasses by 27Al and 29Si Solid State NMR
Open this publication in new window or tab >>Structural Characterizations of Lanthanum Aluminosilicate Glasses by 27Al and 29Si Solid State NMR
2009 (English)In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 355, no 43-44, 2165-2174 p.Article in journal (Refereed) Published
Abstract [en]

We investigate the network structures of LaSiAlO glasses by 29Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR). Their compositions span most of the glass-forming region of the ternary La2O3Al2O3SiO2 system at 1600 °C. The 29Si NMR resonances narrow and become progressively deshielded when Al substitutes for Si in the network, as well as for increasing La-content of the glass, which leads to network depolymerization. We compare experimental and calculated center of gravities of the 29Si NMR peaks, the latter generated from different simplified models for the distributions of Al and Si as well as bridging oxygen (BO) and non-bridging oxygen (NBO) atoms over the networks. The data do not permit accurate quantifications and may only be interpreted in limiting scenarios. However, they indicate that both distributions are essentially randomized, implying a clear deviation of the Al/Si ordering from that according to a Loewenstein Al-avoidance, coupled with a nearly uniform partitioning of the NBO atoms between Al and Si tetrahedra.

National Category
Chemical Sciences
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-25761 (URN)10.1016/j.jnoncrysol.2009.06.031 (DOI)000271347000011 ()
Available from: 2009-02-26 Created: 2009-02-18 Last updated: 2017-12-13Bibliographically approved
2. Silicate glasses with unprecedented high nitrogen and electropositive metal contents obtained by using metals as precursors
Open this publication in new window or tab >>Silicate glasses with unprecedented high nitrogen and electropositive metal contents obtained by using metals as precursors
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2005 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 17, 2214-2216 p.Article in journal (Refereed) Published
Abstract [en]

 

 

Identifiers
urn:nbn:se:su:diva-24536 (URN)10.1002/adma.200500715 (DOI)
Note
Part of urn:nbn:se:su:diva-7169Available from: 2007-11-06 Created: 2007-11-06 Last updated: 2017-12-13Bibliographically approved
3. Nitrogenrich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR
Open this publication in new window or tab >>Nitrogenrich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR
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2008 (English)In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 354, no 1, 49-60 p.Article in journal (Refereed) Published
Abstract [en]

We investigate the local structures of oxynitride La–Si–(Al)–O–N glasses by 29Si and 27Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, 29Si NMR evidenced a progressive formation of Si–N bonds, with SiO2N2 tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO4, whereas the glasses with highest nitrogen contents have a major fraction of AlO3N structural units. Trends in isotropic 29Si and 27Al chemical shifts and 27Al quadrupolar couplings are compared with results of La–Si–Al–O glasses and are discussed in relation to the glass compositions and their proposed structures.

Place, publisher, year, edition, pages
Elsevier, 2008
Keyword
Oxynitride glass, La–Si–Al–O glass, Glass structure, Rare-earth Silicate, 29Si NMR, 27Al NMR, TEM, Cross-polarization, Cation distributions
National Category
Inorganic Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-24539 (URN)10.1016/j.jnoncrysol.2007.07.027 (DOI)000252686600007 ()
Note
Part of urn:nbn:se:su:diva-7169Available from: 2007-11-06 Created: 2007-11-06 Last updated: 2017-12-13Bibliographically approved
4. Solid-state NMR investigations of Si-29 and N-15 enriched silicon nitride
Open this publication in new window or tab >>Solid-state NMR investigations of Si-29 and N-15 enriched silicon nitride
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2009 (English)In: Solid State Nuclear Magnetic Resonance, ISSN 0926-2040, E-ISSN 1527-3326, Vol. 36, no 1, 11-18 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-35157 (URN)10.1016/j.ssnmr.2009.03.001 (DOI)000268919900002 ()
Available from: 2010-01-18 Created: 2010-01-14 Last updated: 2017-12-12Bibliographically approved
5. Multinuclear Solid-State NMR Studies of Ordered Mesoporous Bioactive Glasses
Open this publication in new window or tab >>Multinuclear Solid-State NMR Studies of Ordered Mesoporous Bioactive Glasses
Show others...
2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 14, 5552-5562 p.Article in journal (Refereed) Published
Abstract [en]

The local structures of highly ordered mesoporous bioactive CaO-SiO2-P2O5 glasses were investigated for variable Ca contents. 1H NMR revealed a diversity of hydrogen-bonded and "isolated" surface silanols as well as adsorbed water molecules. The structural roles of Si and P were explored using a combination of 29Si and 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) techniques; the proximities of Si and P to protons were studied through cross-polarization-based experiments, including 1H-29Si and 1H-31P hetero-nuclear two-dimensional correlation spectroscopy. The results are consistent with SiO2 being the main pore-wall component, whereas P is present as a separate amorphous calcium orthophosphate phase, which is dispersed over the pore wall as nanometer-sized clusters. The excess Ca that is not consumed in the phosphate phase modifies the silica glass network where it associates at/near the mesoporous surface. This biphasic structural model of the pore wall leads to the high accessibility of both Ca and P to body fluids, and its relation to the experimentally demonstrated high in vitro bioactivities of these materials is discussed.

Keyword
Nuclear-Magnetic-Resonance, H-1 MAS NMR, IN-Vitro, Calcium-Phosphate, Gel Glasses, Silica Nanoparticles, Cross-Polarization, Apatite Formation, Spinning NMR, System
Identifiers
urn:nbn:se:su:diva-15705 (URN)10.1021/jp7107973 (DOI)000254710800045 ()
Available from: 2008-12-08 Created: 2008-12-08 Last updated: 2017-12-13Bibliographically approved

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