Dilshat U. Tulyaganov

Development of glass-ceramics by sintering and crystallization of fine powders of calcium-magnesium-aluminosilicate glass

Abstract Natural raw materials normally used in the ceramic and glass industry were studied for the production of calcium–magnesium–aluminosilicate glass or glass-ceramic materials. Sintering and crystallization processes of fine powders of parent glass with chemical composition (wt.%) 46.00 SiO 2 , 15.90 Al 2 O 3 , 1.20 Fe 2 O 3 , 0.42 TiO 2 , 23.50 CaO, 9.37 MgO, 0.04 Na 2 O, 0.98 K 2 O, 1.95 P 2 O 5 and 0.35 CaF 2 were studied. Crystallization kinetics of glass-ceramics was carefully examined by DTA, XRD, and SEM techniques and by dilatometric studies. The desired sequence of events, i.e. nucleation, sintering and devitrification occurred by heat-treating the glassy powder. However, crystallization of the parent glass did not follow phase diagram predictions, since anomalous appearance of akermanite phase was detected along with expected anorthite and diopside precipitation. A reasonable explanation for this unexpected observation is given.

The fluorapatite–anorthite system in biomedicine

Glasses and glass ceramics of fluorapatite-anorthite (eutectic composition) were produced and characterized in order to evaluate their potential application in biomedicine. Bio-reactivity was determined by in vitro tests by immersion of powders in simulated plasma liquids as well as by in vivo experiments by implantation in rabbits. According to the results, the investigated materials are bio-acceptable since no toxic or other harmful evidence was detected. Glass-ceramics showed remarkable inertness, whereas glasses spontaneously dissolved in SBF and after 1 week moderate formation of apatite was observed, that however ceased within a month.

Processing of cordierite based ceramics from alkaline-earth-aluminosilicate glass, kaolin, alumina and magnesite

Abstract Microstructural changes, porosity evolution and properties of cordierite based composites have been studied as a function of cordierite–anorthite ratio in modelled ceramic systems. The model systems were composed of alkaline-earth-aluminosilicate glass powder, kaolin, alumina and magnesite. Suitable densification levels of investigated compositions are attained in a narrow temperature range and relatively high residual porosity levels are observed. These features were attributed to the role of the liquid phase during high temperature sintering. Cordierite, anorthite or mixtures of each with mullite are the formed crystalline phases when maximum densification levels are achieved. Their properties are correlated to the processing route and to the composition of sintered materials. Control of the porous structure through manipulation of heating rate was found feasible and easy to implement.

Mullite-Alumina Refractory Ceramics Obtained from Mixtures of Natural Common Materials and Recycled Al-Rich Anodizing Sludge

This work describes attempts to reuse Al-rich sludge produced from industrial anodizing and surface treatment processes in the fabrication of mullite-based refractory materials. The complete characterization of the residue is reported, including physical and compositional parameters. Mixtures with common natural silica-containing materials, like ball clay, kaolin, and/or diatomite were prepared in order to achieve interesting final fired compositions. Rheological characterization of the suspensions, their slip casting performance, the thermal behavior of the consolidated bodies, and crystalline phase evolution are also detailed. From the knowledge acquired, pretreatment operations have been suggested to facilitate the recycling of the Al-rich sludge and to improve the characteristics of mullite-based materials.

Structure, surface reactivity and physico-chemical degradation of fluoride containing phospho-silicate glasses

We report on the structure, apatite-forming ability and physicochemical degradation of glasses along the fluorapatite [FA; Ca5(PO4)3F]–diopside (Di; CaMgSi2O6) join. A series of glasses with varying FA/Di ratio have been synthesised by melt-quenching technique. The amorphous glasses could be obtained only for compositions up to 40 wt.% of FA. The detailed structural analysis of the glasses has been made by infrared spectroscopy (FTIR), Raman spectroscopy and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in an orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of the glass powders in simulated body fluid (SBF) for times varying between 1 h–28 days. An extensive precipitation of calcite (CaCO3) after immersion in SBF was found in all the glasses, which considerably masked the formation of hydroxyapatite [HA; Ca5(PO4)3OH]. The possible mechanism favouring the formation of calcite instead of HA has been explained on the basis of experimental results obtained for the structure of the glasses, leaching profile of glass powders in SBF solution and pH variation in SBF solution. Furthermore, the physico-chemical degradation of the glasses has been studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris HCl and citric acid buffer. All the FA containing glasses exhibited a weight gain (instead of weight loss) after immersion in citric acid buffer due to the formation of different crystalline products.

Synthesis, bioactivity and preliminary biocompatibility studies of glasses in the system CaO–MgO–SiO2–Na2O–P2O5–CaF2

New compositions of bioactive glasses are proposed in the CaO–MgO–SiO2–Na2O–P2O5–CaF2 system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO4) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts’ cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).

Diopside (CaO·MgO·2SiO2)–fluorapatite (9CaO·3P2O5·CaF2) glass-ceramics: potential materials for bone tissue engineering

Glass-ceramics in the diopside (CaMgSi2O6)–fluorapatite [Ca5(PO4)3F] system are potential candidates for restorative dental and bone implant materials. In the present study, a series of glasses along the diopside–fluorapatite binary system have been prepared with varying diopside/fluorapatite ratios for their potential applications in bone tissue engineering. The glasses were obtained from compositions with fluorapatite contents varying between 0 and 40 wt%. The sintering ability and crystallization kinetics of as obtained amorphous glasses have been studied through hot-stage microscopy (HSM) and differential thermal analysis (DTA), respectively, while crystalline phase evolution in sintered GCs has been followed by X-ray diffraction (XRD) adjoined with the Rietveld-R.I.R. technique and scanning electron microscopy (SEM). Further, biodegradation and apatite forming ability of glass-ceramics were investigated by immersion of glass-ceramic discs in simulated body fluid (SBF) solution while chemical degradation and weight loss of glass-ceramics were studied by immersion in Tris–HCl in accordance with the ISO 10993-14 standard. The addition of fluorapatite (10–25 wt%) in the diopside glass system significantly enhanced the sintering ability of glass-ceramics and improved their apatite forming ability along with their biodegradation behaviour. Moreover, the in vitro cellular responses to glass-ceramics showed good cell viability and significant stimulation of osteoblastic differentiation, suggesting the possible use of the glass-ceramics for bone regeneration.

Production and characterisation of glass ceramic foams from recycled raw materials

Abstract Glass foams were produced exclusively from industrial residues, namely from sheet glass cullet and fly ashes from thermal power plant as the main components, and from burned wastes of silicon carbide (SiC) abrasive papers. The experimental results showed that homogenous microstructures of large pores could be obtained by adding an optimum amount (1 wt-%) of a commercial SiC powder (SiCC) after sintering at 950°C. The SiCC was then replaced by equivalent amounts of SiC abrasive paper ashes of different grain sizes. The SiC containing foams led to apparent density and compressive strength values of about 0⋅18–0⋅35 g cm–3 and 0⋅9–1⋅8 MPa. Good correlations between compressive strength, apparent density and microstructure (pore size, strut thickness and internal porosity) were observed.

Influence of ZnO on the crystallization kinetics and properties of diopside-Ca-Tschermak based glasses and glass-ceramics

We report on the influence of ZnO on the structural, thermal, and crystallization behavior of the diopside-Ca-Tschermak based glasses, and on the processing, microstructure, and the properties of the sintered glass ceramics. Four glasses with nominal compositions of CaMg0.8Al0.4Si1.8O6, CaMg0.75Zn0.05Al0.4Si1.8O6, CaMg0.70Zn0.10Al0.4Si1.8O6, and CaMg0.60Zn0.20Al0.4Si1.8O6 were obtained by melting at 1580 °C for 1 h. Structural and thermal behavior of the glasses was investigated by Fourier-transform infrared spectroscopy, density measurements, dilatometry, and differential thermal analysis. Nonisothermal crystallization kinetics has been employed to study the crystallization mechanism in the glasses. Sintering, crystallization, microstructure, and properties of the glass ceramics were investigated under nonisothermal heating conditions in the temperature range of 850–1000 °C.

Thermal and mechanical stability of lanthanide-containing glass–ceramic sealants for solid oxide fuel cells

Thermal stability of lanthanide (Ln = La, Nd, Gd, Yb) containing glass and glass–ceramics (GCs) was characterized for their application as sealants for solid oxide fuel cells (SOFCs). X-ray diffraction (XRD) in conjunction with the Rietveld-RIR and solid-state NMR techniques was employed to quantify the crystalline and amorphous fractions in the glasses sintered/heat treated at 850 °C in air for 1–1000 h. The structure and crystalline phase evolution of Ln containing aluminosilicate glasses depend markedly on the Ln3+ cation field strength over both short and intermediate length scales. Along with diopside, Ln containing silicate apatites, with general formula Ln9.33+2x(Si1−xAlxO4)6O2 (Ln = La, Nd and Gd; with x varying between 0 and 0.33), were observed in the GCs after the heat treatment periods of 1 to 1000 h at 850 °C, leading to moderately higher electrical conductivity. The substantial amount of the remaining glassy phase in Gd2O3-containing GC after 1000 h at 850 °C is likely to confer self-healing properties to this composition, in accord with the oxygen leakage measurements on thermal cycling. 29Si, 27Al and 11B magic-angle spinning (MAS) NMR spectra confirmed the results of the XRD RIR analysis. The values of Weibull characteristic strength and of average flexural strengths for all the GCs are higher than those reported for G-18 commercial glass (51 MPa), with Weibull modulus varying in the range 11.6–34.4 towards good mechanical reliability. Thermal shock resistance of model electrochemical cells made of yttria-stabilized zirconia (YSZ) was evaluated employing quenching from 800 °C in air and water. All the GC seals bonded well to YSZ and Sanergy HT metallic interconnects without gap formation. Suitable thermal expansion coefficient (9.7–11.1 × 10−6 K−1), mechanical reliability, high electrical resistivity, strong adhesion to Sanergy HT interconnects and YSZ, and sufficient thermal shock resistance indicate good suitability of the lanthanide-containing sealants for SOFC applications.