Investigation of the Mixed Alkali Effect in a Range of Phosphate Glasses

2007 ◽  
Vol 330-332 ◽  
pp. 161-164 ◽  
Author(s):  
E. A. Abou Neel ◽  
I. Ahmed ◽  
Jonathan C. Knowles
Keyword(s):  
Degradation Rate ◽  
Potassium Phosphate ◽  
Phosphate Glasses ◽  
Oxide Content ◽  
Ion Release ◽  
Scanning Calorimetry ◽  
Degradation Behaviour ◽  
Mixed Alkali ◽  
Alkali Glass ◽  
Mixed Alkali Effect

This study investigated the mixed alkali effect in a series of phosphate based glasses. These glasses were of the composition 0.5P2O5-0.2CaO-0.3-xNa2O-xK2O where x=0 to 0.3 in steps of 0.05. This study considered density measurements using Archimedes’s principle, thermal characterisation using differential scanning calorimetry, phase analysis following crystallisation using X-ray powder diffraction (XRD), and degradation studies combined with ion release. The results showed that these mixed alkali glasses showed a linear decrease in density, with the ternary single alkali glass with 0.3mol K2O showing a 3% reduction in density as compared to that with 0.3mol Na2O which correlated well with the difference in ionic diameter and atomic weight of both cations. These glasses also showed intermediate glass transition temperature (Tg) values, compared to those of the ternary single alkali glasses having the same alkali oxide content, and the minimum Tg value was recorded for equimolar amounts of both alkali oxides. However, they did not show any significant change in the degradation rate compared to the glass with 0.3mol Na2O with the exception of the 0.25mol K2O glass. The single alkali glass with 0.3mol K2O showed a significant increase in the degradation rate by an approximate one order of magnitude. For the mixed alkali glasses with low molar concentration of K2O, only sodium phosphate-rich phases [NaCa(PO3)3 and Na4Ca(PO3)6] were detected from XRD; at high molar concentrations however, potassium phosphate-rich phases [KCa(PO3)3 and KPO3] were detected. At equimolar concentration of both alkali cations, KCa(PO3)3 and Na4Ca(PO3)6 were identified. K+, Ca2+, and P3O9 3- release followed the degradation behaviour where the highly degrading glasses with 0.25 and 0.3mol K2O released the highest amount of these ions; however, there was no definite trend in the remaining glass compositions.

Degradation Behaviour of Metallic Biomaterials for Degradable Stents

2006 ◽  
Vol 15-17 ◽  
pp. 113-118 ◽  
Author(s):  
Hendra Hermawan ◽  
Maryam Moravej ◽  
Dominique Dubé ◽  
Michel Fiset ◽  
D. Mantovani
Keyword(s):  
Potentiodynamic Polarization ◽  
Degradation Rate ◽  
Corrosion Behaviour ◽  
Dynamic Test ◽  
Potential Candidate ◽  
Human Coronary Artery ◽  
Ion Release ◽  
Degradation Behaviour ◽  
Static Immersion

The short-term need of scaffolding function of stent and the prevention of potential longterm complication of permanently implanted stent have directed to the original idea of biodegradable stent. Selecting and developing materials showing appropriate mechanical and degradation properties are key steps for the development of this new class of medical devices. Therefore, the study of their in vitro degradation behaviour is mandatory for the selection of potential candidate materials suited in vivo. In this work, the degradation behaviour of current studied biodegradable metals including three magnesium alloys (Mg, AM60B and AZ91D), pure iron and Fe-35Mn was investigated. The tests were performed in a simulated blood plasma solution at 37±0.1 oC, using three different methods; potentiodynamic polarization, static immersion, and dynamic test in a test-bench which mimics the flow condition in human coronary artery. Degradation rate was determined as ion release rate measured by using atomic adsorption spectroscopy (AAS) and also estimated from weight loss and corrosion current. Surface morphology and chemical composition of corroded specimens were analyzed by using SEM/EDS. The three degradation methods provide consistent results in corrosion tendency, where Mg showed the highest corrosion rate followed by AZ91D, AM60B, Fe-35Mn and iron. Potentiodynamic polarization gives a rapid estimation of corrosion behaviour and rate. Static immersion test shows the effect of time on the degradation rate and behaviour. Dynamic test provides the closest approach to the environment after stent implantation and its results show the effect of the flow on the materials degradation. In conclusion, the three investigated methods can be applied for screening, selecting and validating materials for degradable stent application before going further to in vivo assessments.

scholarly journals OPTICAL PROPERTIES ON Li2O-K2O-WO3-B2O3 GLASS SYSTEM

2013 ◽  
Vol 22 ◽  
pp. 278-283
Author(s):  
A. EDUKONDALU ◽  
M. A. SAMEE ◽  
SHAIKH KAREEM AHMMAD ◽  
SAIR MD. TAQIULLAH ◽  
SYED RAHMAN ◽  
...  
Keyword(s):  
Glass Structure ◽  
Glass System ◽  
Alkali Concentration ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Mixed Alkali ◽  
Absorption Studies ◽  
Mixed Alkali Effect ◽  
Oxide Ion ◽  
B2o3 Glass

Mixed alkali tungsten borate glasses xLi2O–(30–x) K2O–10WO3–60B2O3 (0 < x < 30) were prepared from the melts. These glasses were characterized using X-ray diffraction, differential scanning calorimetry and density measurements. Optical absorption studies were carried out as a function of alkali content to look for mixed alkali effect (MAE) on the spectral properties of these glasses. From the study of ultraviolet absorption edge, the optical band gap energies and Urbach energies were evaluated. The average electronic polarizability of the oxide ion, optical basicity and the interaction parameters were also evaluated for all the glasses. Many of these parameters vary non-linearly exhibiting a minima or maxima with increasing alkali concentration, indicating the mixed alkali effect. An attempt is made to interpret MAE in this glass system in terms of its glass structure.

Structural Features and the Effect of Two Alkalis in Chalcogenide and Phosphate Glasses

2019 ◽  
Vol 822 ◽  
pp. 824-833
Author(s):  
Viktor A. Markov ◽  
Ivan Sokolov ◽  
Alexey Povolotskiy
Keyword(s):  
Ionic Conductivity ◽  
Electric Current ◽  
Structural Features ◽  
Phosphate Glasses ◽  
Electrical Parameters ◽  
Mixed Alkali ◽  
Mixed Alkali Effect

This paper presents data on the mixed alkali effect in two fundamentally different systems: chalcogenide and oxide (phosphate). In the first system (Ag – Cu)0.44AsSe1.5, the predominantly ionic conductivity of silver-containing glasses is replaced by purely electronic in copper-containing, in the second - 0.5(Li2O-Na2O) – 0.4P2O5 – 0.1Nb2O5 carriers of electric current are alkaline ions and the extreme dependences of the electrical parameters associated with their joint migration.

scholarly journals Sodium-free mixed alkali bioactive glasses

2016 ◽  
Vol 2 (1) ◽  
Author(s):  
Delia S. Brauer ◽  
Raika Brückner ◽  
Maxi Tylkowski ◽  
Leena Hupa
Keyword(s):  
Coefficient Of Thermal Expansion ◽  
Release Rates ◽  
Ion Release ◽  
Bioactive Glasses ◽  
Ionic Radii ◽  
Alkali Ions ◽  
Processing Window ◽  
Mixed Alkali ◽  
Mixed Alkali Effect ◽  
High Temperature Processing

AbstractTwo sodium-free mixed alkali series of bioactive glasses based on compositions Bioglass 45S5 and ICIE1, containing lithium and/or potassium as alkali ions, were prepared by a melt-quench route. Thermal properties showed the well-known mixed alkali effect, with glass transition and crystallisation temperatures and the coefficient of thermal expansion going either through a minimum or a maximum for the mixed alkali composition, resulting in a wider processing window. Ion release, by contrast, was controlled by the modifier ionic radius, with ion release rates in dynamic and static dissolution studies increasing for potassium-substituted glasses compared to the composition containing lithium as the only alkali ion. This was caused by pronounced changes in oxygen packing density and molar volume of the glasses owing to the differences in ionic radii (76 pm for Li+ and 138 pm for K+). Partially substituting one alkali for another therefore helps to improve high temperature processing of bioactive glasses and can also be used to control or tailor ion release.

Molybdenum Influence on the Mixed-Alkali Effect of Lithium–Sodium Phosphate Glasses

2018 ◽  
Vol 122 (28) ◽  
pp. 15886-15891 ◽  
Author(s):  
Luiz F. P. Pereira ◽  
Kadiali Bodiang ◽  
Eduardo H. M. Nunes ◽  
François O. Mear ◽  
Laurent Delevoye ◽  
...  
Keyword(s):  
Sodium Phosphate ◽  
Phosphate Glasses ◽  
Mixed Alkali ◽  
Mixed Alkali Effect

Mixed Alkali Effect as a Retarding Effect of Secondary Diffusion Processes in Glass

1998 ◽  
Vol 548 ◽  
Author(s):  
Vladimir Belostotsky
Keyword(s):  
Ion Mobility ◽  
Oxygen Diffusion ◽  
Diffusion Processes ◽  
Monovalent Cations ◽  
Alkali Ions ◽  
Mixed Alkali ◽  
Retarding Effect ◽  
Alkali Glass ◽  
Mixed Alkali Effect ◽  
Mobile Ions

ABSTRACTIon mobility in mixed alkali glass is discussed in the context of the recent experimental observation that oxygen diffusion from molten salt into glass accompanies the replacement of smaller alkali ions for larger alkali ions during ion exchange. The assumption is made that simultaneous migration of two unlike monovalent cations induces, among other things, oxygenexchange diffusion between sites. Diffusing oxygen molecules form additional fluctuating sites or traps lying along the ion pathways between regular ionic sites. Instead of jumping directly to the regular ionic site, mobile ions are forced to execute several additional hops between fluctuating sites, and this results in significant reduction in ion mobility.

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