Effect of composition changes on the structure and properties of phosphate glasses in the pyrophosphate region

The structures of phosphate glasses in the ultra- and polyphosphate region are well-investigated. Discontinuous changes of the properties in the composition ränge around 50 mol% P₂O₅ (transition from network to chain-like structures) are known. The present work is concerned with the structural transition of chain-like phosphate glasses to pyrophosphate glasses. ³¹P MAS N M R in vestigations were used for the quantitative structural analyses of pyrophosphate and mixed pyrophosphate/orthophosphate glasses. Several chemical and physical properties of these glasses were determined in dependence on composition and structure. The in vestigated phosphate invert glasses are very sensitive to additives. Therefore, some important properties of phosphate invert glasses and glass-ceramics can be controlled by addition of relatively small and highly charged cations

Phosphate glasses and glass-ceramics for medical applications

Modified calcium phosphate glass Systems meet the requirements for the development of different biomaterials. Bioactive, longterm stable phosphate glass-ceramics and resorbable phosphate glasses were prepared in the Systems P₂O₅ - CaO - Al₂O₃ - Na₂O and P₂O₅ - CaO - MgO - Na₂O . Due to their high thermal expansion coefficients the bioactive phosphate glass-ceramics are excellently suited for coating metals. Using a salt-sintering process, porous resorbable glasses can be obtained. The properties of glassceramic coatings on cobalt/chromium alloys and the production of porous resorbable phosphate invert glasses are described

Effect of TiO2 , ZrO2 and ZnO addition on the hydrolytic durability, viscosity and crystallization behaviour of fibre glasses

Glasses of the System Na2O-K2O-MgO-CaO-BaO-AI2O3-SiO2-B2O3 with additions of TiO2, ZrO2 and ZnO were melted from the raw materials. The glasses were characterized with respect to their hydrolytic durabilities, the working ranges (difference of temperatures attributed to viscosities of 10^2 and 10^4 dPa s), the temperatures attributed to the working point (η = 10^3.5 dPa s), and the crystal growth velocities. In the most cases, the additions led to an increase in viscosity and to a slight decrease in the workability range. The crystal growth velocities decreased with the addition of Ti02 and/or Zr02, while they increased if adding ZnO. The addition of ZnO or of TiO2 and ZrO2 resulted in better chemical durability

Chemical solubility of phosphate glasses in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 in aqueous solutions of different pH values

Phosphate glasses of different composition ranges show very different solubility behaviour in aqueous solutions of pH 4 and 5.8. With inereasing P2O5 concentrations between 38 and 52 mol% , in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 , the dissolution rate generally increases, however, the most notable increase is observed at P2O5 concentrations larger than 48 mol%. Additives of TiO2 and AI2O3 increase the stability to corrosion. Glasses with compositions in the metaphosphate range show larger dissolution rates in slightly acidic medium than glasses near the invert glass range. Glasses in the invert glass range show a stronger increase in the dissolution rates with decreasing pH value and also deceleration of the dissolution with time

Crystallization and vicosity of phosphate melts in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2

Glasses in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 were studied with respeet to their crystallization and viscosity. Glasses in the metaphosphate range are composed of phosphate chains, and possess a comparably small tendeney to crystallization. Here, AlPO4 in a cristobalite-like modification and Ca2P2O7 are formed. Glasses in the intermediate range between metaphosphate and invert glass structures are composed of smaller phosphate units and show higher erystal growth velocities as well as higher viscosities. Additions of MgO, AI2O3 and TiO2 result in a strengthening of the glass network, and hence, inereasing viscosities and a notably smaller tendeney to crystallization

Bioactive coatings of glass-ceramics on metals

To combine the mechanical properties of high-strength base metals with the biological properties of bioactive materials, coatings of BIOVERIT® glasses and glass-ceramics on CoCr alloys and titanium have been produced. Different kinds of coating processes have been used: dipping, sputtering, plasma spraying, sintering and pasting. Dipping and pasting seem not to be suitable to produce layers because of cracks and low adhesion strength of the coatings (dipping) and the limitations in relation to the implant shape and the thickness of the layers (pasting). Using sputter techniques it is possible to produce dense layers ( < 10µim) with a high adhesion strength. Plasma spraying resuhed in layers with a thickness of 50 to 300µim, but during the plasma spraying process there is a partial evaporation of the highly volatile glass components. Sintering processes are very suitable to produce layers with a high adhesion strength; these layers are long term stable in simulated body fluid

Alumina and zirconia as inhibitors of crystallization during sintering of borosilicate glasses

The glass composition (in mol%) 16 Na2O ∙ 24 B2O3 ∙ 60 SiO2 has suitable viscosity and dilatometric properties to be used as sealing material for the gas manifolds of molten carbonate fuel cells (MCFC). Nevertheless, quartz crystallization takes place during sintering of the borosilicate glass powder at temperatures between 600 and 700 °C. The quartz crystallization leads to the formation of pores and a variation in the thermal expansion coefficient; both giving rise to defects and tensions in the seal. In this work, the possibility of inhibition of quartz crystallization by substituting AI2O3 or ZrO2 for 2 or 5 mol% of SiO2 is described. The thermal properties and the viscosity-temperature curve of the new compositions, especially those containing alumina do not differ much from the original glass

Processability, crystallization and mechanical strength of P₂O₅-modified glasses and glass-ceramics in the system MgO-Al₂O₃-SiO₂-TiO₂

The crystallization behaviour and the processability of P₂O₅-modified glasses in the MgO-Al₂O₃-SiO₂-TiO₂ system were investigated. The hot-press furnace system "Empress IPS 500" was used to estimate the processability of the glasses. The crystallization process of the glasses was changed with increasing P₂O₅ content. The stability range of the α-quartz solid solution crystal phase decreases and cristobalite becomes the main crystalline phase in glass-ceramics with high P₂O₅ amounts. Magnesium orthophosphate was detected as a phosphorus-containing crystal phase. Glass-ceramics with high mechanical strength crystallize from these modified glasses. The investigations show that the high mechanical strength of the glass-ceramics is related to the crystallization of crystal phases with a high coefficient of thermal expansion

Increased Surgical Delays Seen During the COVID-19 Pandemic in a Regional Referral Hospital in Soroti, Uganda: Perspective from a Low-Resource Setting.

INTRODUCTION: The impact of COVID-19 on low-resource surgical systems is concerning but there are limited studies examining the effect in low- and middle-income countries. This study assesses changes in surgical capacity during the COVID-19 pandemic at Soroti Regional Referral Hospital, a tertiary healthcare facility in Soroti, Uganda. METHODS: Patients from a prospective general surgery registry at SRRH were divided into cohorts admitted prior to the pandemic (January 2017 to February 2020) and during the pandemic (March 2020 to May 2021). Demographics, pre-hospital characteristics, in-hospital characteristics, provider-reported delays in care, and adverse events were compared between cohorts. RESULTS: Of the 1547 general surgery patients, 1159 were admitted prior to the pandemic and 388 were admitted during the pandemic. There was no difference in the median number of elective (24.5 vs. 20.0, p value = 0.16) or emergent (6.0 vs. 6.0, p value = 0.36) surgeries per month. Patients were more likely to have a delay in surgical care during the pandemic (22.6% vs. 46.6%, p &lt; 0.01), particularly from lack of operating space (16.9% vs. 46.3%, p &lt; 0.01) and lack of a surgeon (1.6% vs. 4.4%, p &lt; 0.01). Increased proportion of delays in care appear correlated with waves of COVID-19 cases at SRRH. There were no changes in rates of adverse events (5.7% vs. 7.7%, p = 0.18). DISCUSSION: The COVID-19 pandemic caused significant increases in surgical care delays and emergency surgery at SRRH. Strengthening surgical systems when not in crisis and including provisions for safe, timely surgical delivery during epidemic resource allocation is needed to strengthen the overall healthcare system

In-Hospital Obstetric Delays in Rural Uganda: A Cross-Sectional Analysis of a Hospital Cohort.

BACKGROUND: Deaths related to pregnancy and childbirth are extremely high in low-resource countries such as Uganda. Maternal mortality in low- and middle-income countries is related to delays in seeking, reaching, and receiving adequate health care. This study aimed to investigate the in-hospital delays to surgical care for women in labor arriving to Soroti Regional Referral Hospital (SRRH). METHODS: From January 2017 to August 2020, we collected data on obstetric surgical patients in labor using a locally developed, context-specific obstetrics surgical registry. Data regarding patient demographics, clinical and operative characteristics, as well as delays in care and outcomes were documented. Descriptive and multivariate statistical analyses were conducted. RESULTS: A total of 3189 patients were treated during our study period. Median age was 23&nbsp;years, most gestations were at term (97%) at the time of operation, and nearly all patients underwent Cesarean Section&nbsp;(98.8%). Notably, 61.7% of patients experienced at least one delay in their surgical care at SRRH. Lack of surgical space was the greatest contributor to delay (59.9%), followed by lack of supplies or personnel. The significant independent predictors of delayed care were having a prenatal acquired infection (AOR 1.73, 95% CI 1.43-2.09) and length of symptoms less than 12&nbsp;h (AOR 0.32, 95% CI 0.26-0.39) or greater than 24&nbsp;h (AOR 2.61, 95% CI 2.18-3.12). CONCLUSION: In rural Uganda, there is a significant need for financial investment and commitment of resources to expand surgical infrastructure and improve care for mothers and neonates