Key Engineering Materials Vols. 368-372

Abstract: The crystallization behaviors and microstructural developments in the CaO-MgO- Al2O3-SiO2 glass with Fe2O3, ZrO2 and F as additives were investigated by using scanning electron microscopy, X-ray diffraction and differential scanning calorimetry techniques. In the glass sample with 1.0wt% Fe2O3, only surface crystallization were observed, in which a three-layer compound surface containing the fine dendrite, finer fibrous morphology and particle-shaped crystals was formed respectively from the near free surface to the inner region. The crystalline phases precipitated were anorthite and wollastonite at 1000°C, and diopside at 1040°C. The addition of ZrO2 suppressed the nucleation and growth of the crystalline phases. The addition of another 4.0wt% fluorine into the glass with a pair of 1.0wt% Fe2O3 and 2.0wt% ZrO2 induced the bulk crystallization, the surface and bulk crystallizations were both observed at 1040°C. At the surface, a three-layer morphology, which had similar morphology to the glass with 1.0wt% Fe2O3 was formed. In the bulk region, the block-shaped crystalline phases were precipitated homogeneously in the residual glass.

Abstract: CaO-A12O3-SiO2 (CAS) system glass-ceramics were prepared by sintering with certain amount of yellow phosphorus slag. The effects of phosphorus and fluorine on the nucleation, crystallization and structure of CAS system glass-ceramics were investigated by differential thermal analysis, X-ray diffraction, scanning electron microscopy and other measuring methods. Glass-ceramics of CAS system with 42.32wt% yellow phosphorus slag were obtained by nucleating at 615°C for 1 hour and crystallizing at 926°C for 2 hours. The results showed that the introduction of phosphorus and fluorine promoted the nucleation and crystallization of glass-ceramics, lowering the crystallizing temperature. The main crystal phase of glass-ceramics was β-wollastonite. The density of the glass-ceramic was 2.695g/cm3.

Abstract: The effect of alkali earth metal oxides MO (M=Mg, Ca, Ba) on the crystallizing behavior and the microstructure of B2O3-Al2O3-SiO2 system (BAS) were studied. DSC, XRD and SEM were used to analyze the crystallization kinetics and to characterize the crystal phases and microstructures of the glass-ceramics. MO can effectively facilitate the formation of BAS glass, and the crystallinity of the glass increases in the order of MgO < BaO < CaO. For one given MO, the crystallinity of the glass is dependent on B2O3/SiO2 ratio: the lower the ratio is, the weaker the crystallinity of the glass will be. It was found that the early crystallization is aluminum metaborate (Al4B2O9) when the glass is heated at 800 °C, and it would transfer into aluminum borate(Al18B4O33) at temperatures over 1000 °C. The activation energy and the Avrami exponent of Al4B2O9 were calculated by Ozawa formulation.

Abstract: The basic compositions of the samples were selected inside and outside of Na2O-B2O3-SiO2 glass phase separation region, respectively. Nanocrystalline TiO2 was crystallized by melt-phase separation process. The results showed that the phase separation of Na2O-B2O3-SiO2-TiO2 glass system was advantaged to TiO2 nucleation and growth, and then the formation of the nanocrystalline. The main mechanism of TiO2 crystallization is that the rich alkali-boron phase has the lower viscidity and higher particles moving ability than that of parent phase glass. Therefore, the movement rate of TiO2 particle can be promoted and TiO2 crystallization can be accelerated. Moreover, the formation of non-homogeneous nucleus situation and the centralization function of TiO2 have less contribution to TiO2 crystallization.

Abstract: Calcium borosilicate (CaO-B2O3-SiO2, CBS) glass based glass-ceramic composites were prepared by introducing borosilicate glass. The effects of borosilicate glass and firing temperature on the microstructure and properties of the glass-ceramic composites were investigated. The results showed that the composites containing 0~40% (in mass fraction, the same below) borosilicate glass can be sintered at 850°C. The dielectric constant (εr) decreases with the increase of borosilicate glass content and can be adjusted in the range of 5.6~6.6. The coefficient of thermal expansion (CTE) increases with the increase of borosilicate glass content. Increasing sintering temperature favors the precipitations of crystal phases, which have lower εr than CBS glass, resulting in the decrease of εr for the composites.

Abstract: The characteristic of Angang blast furnace slag was studied by X-ray fluorescence spectrometry, DSC, X-ray diffraction and SEM. SiO2-Al2O3-CaO system glass-ceramics have been obtained successfully from slag with other additives. The properties of slag-based glass-ceramics were analyzed in this paper. It has been found that nucleation temperature is in the range of 600~700 °C, and crystallization temperature is in the range of 850~950 °C. The crystals phase is 2 CaO⋅ Al2O3⋅ SiO2. The chemical and mechanical properties of slag-based glass-ceramics are superior to the properties of clay brick.

Abstract: The effect of ZrO2 addition on mechanical and biological properties of bioactive glass-ceramics with chemical compositions of 60CaO-30P2O5-3TiO2-xZrO2-(7-x)Na2O (x=0,1,3) was investigated. It was found that ZrO2 addition up to 3 mol% contributes to monotonical increase of the glass transition temperature. The micro-hardness increases slightly by 1 mol% ZrO2 addition and keeps constant with further addition whereas 1 mol% ZrO2 addition results in ~20% increase of three-point bending strength. When the specimens were soaked in simulated body fluid, complete apatite layers were formed on the specimens regardless of the ZrO2 addition. It is therefore concluded that the toughening contribution of 1 mol% ZrO2 addition has no adverse effect on the bioactivity of calcium phosphate glass-ceramics.

Abstract: The effect of coordination number on glass properties was investigated by measuring the glass forming region, glass transition temperature, dilatometric softening temperature, density and chemical durability of the glasses. The coordination number of B and Zn in the system 20BaO-xZnO-(80-x) B2O3 glasses (x=0~40mol%) was measured by IR, respectively. No change in the coordination number (CN) of B was revealed, and the coordination of Zn was 4 at ZnO 10mol%, which increased the properties of glasses. On the other hand, the coordination number (CN) of B and Zn changed from CN4 to CN3, CN4 to CN6 over ZnO 20 and 10mol% respectively, which decreased the properties of glasses.

Abstract: The glass-ceramics, whose coefficient of thermal expansion approximately matched to that of silicon, were studied to replace conventional heat-resistant glass as substrate material for anodic bonding. The basic glasses of the Li2O-Al2O3-SiO2 system with TiO2 and ZrO2 as nucleation agents were prepared by melting technology, and the temperatures of nucleation and crystallization were determined. The glass-ceramics were obtained by two-step heat-treatment method. The oriented crystallization of glasses in gradient temperature field was studied. The crystal phases and microstructures of glass- ceramics were analyzed. Effect of heat-treatment schedule on the coefficient of thermal expansion was discussed. The results showed that the most of the main crystal phases of the samples were β-spodumene. The coefficient of thermal expansion of sample was about 32.5×10-7/°C, which was approach to that of silicon.

Abstract: Laser induced Crystallized glasses including nonlinear optical crystals have been taken attention, because of a high potential for laser host, tunable waveguide, tunable fiber grating, etc.. Laser irradiation of glass has been regarded as a process for selective structure modification and crystallization in glass, various researches of laser-induced structural changes have been progressed so far. In this work, Li2O–Al2O3–SiO2 (LAS) glass was irradiated by Nd: YAG laser with a wavelength of 1064nm by increasing Sm2O3 contents as a dopant which induces heat processing in a glass. Crystallized glasses by irradiation of Nd: YAG laser has been compared with conventional crystallization heat-treated in an electric furnace from x-ray diffraction analyses. Finally, we could achieve results which laser irradiation affect crystallization of glass by changing crystallinity between Tx and Tp.