Models for the Structure of Amorphous Solids

Melt quenched silicate glasses containing calcium, phosphorus and alkali metals have the ability to promote bone regeneration and to fuse to living bone. Of these glasses 45S5 Bioglass s is the most widely used being sold in over 35 countries as a bone graft product for medical and dental applications; particulate 45S5 is also incorporated into toothpastes to help remineralize the surface of teeth. Recently it has been suggested that adding titanium dioxide can increase the bioactivity of these materials. This work investigates the structural consequences of incorporating 4 mol% TiO 2 into Bioglass s using isotopic substitution (of the Ti) applied to neutron diffraction and X-ray Absorption Near Edge Structure (XANES). We present the first isotopic substitution data applied to melt quench derived Bioglass or its derivatives. Results show that titanium is on average surrounded by 5.2(1) nearest neighbor oxygen atoms. This implies an upper limit of 40% four-fold coordinated titanium and shows that the network connectivity is reduced from 2.11 to 1.97 for small quantities of titanium. Titanium XANES micro-fluorescence confirms the titanium environment is homogenous on the micron length scale within these glasses. Solid state magic angle spinning (MAS) NMR confirms the network connectivity model proposed. Furthermore, the results show the intermediate range order containing Na-O, Ca-O, O-P-O and O-Si-O correlations are unaffected by the addition of small quantities of TiO 2 into these systems.

show abstract

“…[60][61][62] The program Correct was used to perform the data reduction and corrections. 63,64 The total structure factor is given by 65 iðQÞ¼…”

Section: Neutron Diffraction Methods and Analysismentioning

confidence: 99%

Structural characterization of titanium-doped Bioglass using isotopic substitution neutron diffraction

Martin

Moss

Lakhkar

et al. 2012

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…Studies clearly showed that metallic glass structures were, indeed, efficiently packed 11 12 13 14 , but none were able to explain how glass structures accomplished this feat. Reviews of the first 30 years of metallic glass structural modelling are available 15 16 17 .…”

mentioning

confidence: 99%

A predictive structural model for bulk metallic glasses

2015

View full text Add to dashboard Cite

Great progress has been made in understanding the atomic structure of metallic glasses, but there is still no clear connection between atomic structure and glass-forming ability. Here we give new insights into perhaps the most important question in the field of amorphous metals: how can glass-forming ability be predicted from atomic structure? We give a new approach to modelling metallic glass atomic structures by solving three long-standing problems: we discover a new family of structural defects that discourage glass formation; we impose efficient local packing around all atoms simultaneously; and we enforce structural self-consistency. Fewer than a dozen binary structures satisfy these constraints, but extra degrees of freedom in structures with three or more different atom sizes significantly expand the number of relatively stable, ‘bulk' metallic glasses. The present work gives a new approach towards achieving the long-sought goal of a predictive capability for bulk metallic glasses.

show abstract

“…(Notably, if there exists in the literature an overall agreement about a Na-O coordination number of 5 in soda-silica glass, the values of the Debye-Waller factor, which range from 0.004 to 0.02 nm, are much more scattered. 6 ) A careful study at different temperatures would be needed to derive values of that factor with a certain degree of confidence.…”

Section: (3) Sodium Dissolution At Room Temperaturementioning

confidence: 99%

“…A first difficulty stems from the fact that, at variance with the network formers such as Si, P, and B, whose covalent bondings with oxygen result in a local order dictated by the geometry of their hybridized orbitals, modifying ions produce only isotropic interactions with oxygen and are not expected to show any particular directional links. 6 Using extended X-ray absorption fine structure (EXAFS) analysis, Greaves has demonstrated that sodium cations are surrounded by a first oxygen shell involving five oxygen atoms at 0.23 nm. 7,8 Based on the idea that this environment compares with that encountered in binary silicates Na 2 SiO 3 and Na 2 SiO 5 where sodium is surrounded by a trigonal biprism of five nonbridging oxygen atoms, Greaves inferred that the binary silicate glass network comprises two interlacing sublattices.…”

Section: Introductionmentioning

confidence: 99%

“…12 In X-ray diffraction, the use of heavy atoms as network modifiers has long been used to improve the resolution of the Me-Si and Me-Me pair contributions with respect to the always intense Si-O and O-O peaks. 6 Direct evidence for a medium-range ordering of the modifying cations came from an energy dispersive X-ray diffraction 13 study of cesium silicate glasses. Peaks at 0.405, 0.69, and 0.8 nm in the radial distribution function were assigned to cesium ions in dense random packing.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Sodium Coordination Environments in Silica Films

Jupille

Flank

Lagarde

2002

Journal of the American Ceramic Society

View full text Add to dashboard Cite

The local structure centered on sodium after diffusion in silica (Na-SiO 2 samples) has been determined by means of extended X-ray absorption fine structure (EXAFS) studies. The Na-SiO 2 samples are of particular interest because (i) their sodium content can be varied over a wide range of concentration and (ii) their local structure is representative of that of soda-silica glass. EXAFS analyses reveal the existence of a well-defined local structure involving oxygen, sodium, and silicon neighbors. The Na-O, Na-Na, and Na-Si bonds lengths, which amount to 0.23, 0.30, and 0.38 nm, respectively, do not depend on sodium concentration. This environment closely resembles that found in soda-silica glass. Moreover, it is compatible with the "target site" and "the site memory effect" suggested by recent theories of the ionic conductivity in oxide glasses.

show abstract

Models for the Structure of Amorphous Solids

Cited by 4 publications

References 184 publications

Structural characterization of titanium-doped Bioglass using isotopic substitution neutron diffraction

Structural characterization of titanium-doped Bioglass using isotopic substitution neutron diffraction

A predictive structural model for bulk metallic glasses

Sodium Coordination Environments in Silica Films

Contact Info

Product

Resources

About