Crystallization behavior and properties of K2O–CaO–Al2O3–SiO2 glass-ceramics

In order to obtain high-strength anorthite glass-ceramics, K₂O–CaO–Al₂O₃–SiO₂ quaternary glass and relevant glass-ceramics were prepared and investigated. The results show that anorthite along with kalsilite or leucite was precipitated from the parent glass. Kalsilite crystals were formed firstly and then converted into leucite through reacting with SiO₂ in the glass phase. The morphology of the crystals was dependent on the heat-treatment temperature. Column crystals were transformed into fine granular grains when the sintering temperature changed from 900 °C to 1100 °C. The activation energy (E_α) and avrami constant (n) were also calculated as 463.81 KJ/mol and 3.74 respectively, indicating that bulk nucleation and three-dimensional crystal growth were the dominating mechanisms in the temperature range 1000–1100 °C. The maximum value of the flexural strength for the glass-ceramics containing leucite was 248 MPa and the coefficient of thermal expansion (CTE) was in the range 5.69~11.94×10⁻⁶ K⁻¹. The leucite is the main reason for the high CTEs and high flexural strength of glass-ceramics.     

溶胶-凝胶法制备CaAl_2SiO_8粉末及其结晶行为研究

以正硅酸乙酯、硝酸钙及异丙醇铝为原料，用溶胶-凝胶法制备了钙长石粉末．为调节铝酸盐的水解动力学，采用乙酰乙酸乙酯作为化学螯合剂，研究结果表明，不同的螯合剂和水的加入量对溶胶的聚合过程和所得凝胶特性有重要影响．在选定的实验条件下，制备的凝胶均匀透明，易于形成Al－O－Si网络，使结晶过程明显加快     

Preparation of anorthite ceramics using SPS

A mixture of kaolin (92 wt.% of kaolinite) and laboratory-grade CaCO₃ was used for anorthite preparation using the spark plasma sintering (SPS) technique. The powder was heated up to the maximum temperature (850 °C–1100 °C with a step of 50 °C, heating rate 50 °C/min) using the SPS device. The as-prepared samples were compared with a reference sample produced by dry pressing and conventional firing. Rietveld refinement performed on the X-ray diffraction data revealed that before anorthite formation, gehlenite and Ca-feldspar appeared, which gradually transformed into anorthite with increasing temperature. The sample prepared by SPS at 1100 °C contained 90 wt.% of anorthite, while the anorthite content in the reference sample reached only 47 wt.%. The porosity of the samples prepared by SPS reached significantly lower values compared to that of the reference sample. Therefore, SPS can be considered as a promising technique in the preparation of anorthite ceramics at lower temperatures.     

结晶系列釉研制过程中值得注意的几个问题

本文就结晶系列釉研制过程中值得注意的三个方面即:釉层厚度、烧成制度、配方试验作了初步的探讨。     

Microstructure and ion-exchange properties of transparent glass-ceramics containing Zn2TiO4/α-Zn2SiO4 nanocrystals

Transparent glass-ceramics have particular properties compared with their precursor glasses, and have promising potential applications in many fields. Titanium-relative phases are frequently employed as nucleation agents for crystallization of glass-ceramics, and rarely been precipitated as functional nanocrystalline phases in glass-ceramics. In this work, transparent glass-ceramics containing Zn₂TiO₄ and/or α-Zn₂SiO₄ nanocrystals are investigated. It turns out that Vickers hardness of these glass-ceramics increases with the precipitation of Zn₂TiO₄ and α-Zn₂SiO₄ nanocrystals. Despite the blocking effect of nanocrystals precipitated in the glass-ceramics, structural and compositional modification of the residual glass induced by the precipitation of these nanocrystalline phases facilitates the K-Na ion-exchange, leading to the enhanced depth of layer and further improved Vickers hardness of the glass-ceramics.     

Highly translucent nanostructured glass-ceramic

Transparent and translucent glass-ceramics (GCs) are found in an increasing number of domestic and high-technology applications. In this paper, we evaluated and optimized the effects of two-stage heat treatments on the resulting crystalline phases and microstructure of a glass of the SiO₂–Li₂O–P₂O₅–TiO₂–CaO–ZnO–Al₂O₃ system. The objective was to develop a transparent nanostructured glass-ceramic (GC). After numerous heat treatment trials, we found that a long nucleation period of 72 h at 455 °C followed by a crystal growth treatment at 660 °C for 2 h resulted in a highly translucent GC having homogenously distributed nanocrystals. The relatively high amount of P₂O₅ (2.5 mol%) induced the formation of lithium disilicate as the main crystal phase. We thus developed a GC having crystals under 50 nm, with a high crystallized fraction (52%vol. Li₂Si₂O₅ and 26% vol Li₂SiO₃), transmittance of approximately 80% in the visible spectrum for 1.2 mm thick specimens, nano hardness of 8.7 ± 0.1 GPa (load of 400 mN), a high elastic modulus of 138 ± 3 GPa as measured by nanoindentation, and good flexural strength (350 ± 40 MPa) as measured by ball-on-3 balls tests. Due to its high content of Li⁺, this GC has the potential to be chemically strengthened and can be further developed to be used in a number of applications, such as on displays of electronic devices.     

NKMCAS系辉石型白瓷釉的化学组成与晶相结构的关系

本文利用OM、TEM、XRD等技术研究了辉石型白瓷釉的化学组成与晶相结构之间的关系及其对艺术外观的影响。揭示了辉石型白瓷釉的非平衡态下的晶相规律。找出了辉石型白瓷釉的较佳的组成范围,发现了晶间玻璃相发生了液相分离,指出了辉石型白瓷釉属于析晶—分相釉。     

Nanocrystallization of α-CsPbI3 perovskite nanocrystals in GeS2-Sb2S3 based chalcogenide glass

Black α-phase CsPbI₃ of cubic perovskite structure receives intense attentions recently for its unique combination of high photoluminescence quantum yield, suitable bandgap, and long lifetime. However, α-CsPbI₃ presents poor chemical and thermodynamic stability under atmosphere condition. Here, we report a strategy for confining the α-CsPbI₃ perovskite into chalcogenide glassy matrix through controllable glass nanocrystallization. In the chalcogenide glass with an elaborately designed composition of 80GeS₂·16Sb₂S₃·4CsPbI₃, spherical α-CsPbI₃ nanocrystals were formed and observed clearly, which present good red photoluminescence centered at 701 nm. With the increasing heat-treated temperature, the size of α-CsPbI₃ nanospheres increases, while the crystal quantity decreases. It is found that the nanocrystallization of α-CsPbI₃ nanospheres in chalcogenide glass is controlled by Ostwald-ripening process.     

Influence of Cr2O3, LiF, CaF2 and TiO2 nucleants on the crystallization behavior and microstructure of glass-ceramics based on blast-furnace slag

Glass-ceramics based on blast-furnace slag (56.78 wt%) were prepared by mixing quartz sand, dolomite, limestone, clay as other batch constituents.The nucleating agents Cr₂O_3, LiF, CaF₂ and TiO₂ were added to the batches to study their effects on the crystallization, phase assemblages, and microstructure. Glass-ceramics were obtained by single and double heat-treatment schedules and examined by DTA, XRD and polarizing microscope. The presence of Cr₂O_3, TiO_2, CaF₂ and LiF was found to enhance the crystallizability of the glass. Cr₂O₃ and TiO₂ are much better than LiF and CaF₂ in promoting homogeneous nucleation and the formation of extremely fine-grained microstructure of aluminous pyroxene and magnetite.     

Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li₂O–MgO–Al₂O₃–SiO₂ glass-ceramic for the application of joining Si₃N₄ ceramics. We investigated the influence of the MgO/Al₂O₃ composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi₂O₆ and Mg₂SiO₄ were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg₂SiO₄. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10^?6/°C, which was very close to that of Si₃N₄ ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si₃N₄ ceramic surface was 32° and the interface was well bonded.     

Raman imaging as a useful tool to describe crystallization of aluminum/iron-containing polyphosphate glasses

Polyphosphate glasses are materials of a wide spectrum of applications in many fields. The subject of the work is polyphosphate glasses containing aluminum and iron. Three compositions of the glasses were obtained and the materials have been characterized in terms of their crystallization. The differences in crystallization behavior between powder and bulk materials were compared. The crystallized materials were analyzed by Raman scattering spectroscopy and X-ray diffraction method. It was evidenced that depending on the glass composition the main crystalline phases were Al(PO₃)₃, AlPO₄, FePO₄, Fe₃(P₂O₇), Fe₄(P₂O₇)₃, FePO₄. The glass crystallization leads to enrichment of the residual glassy phase in P₂O₅ and increases its polymerization. Thus, it was observed the glass inhomogeneities are being increased due to crystallization. The two dimensions spectral maps of the bulk crystallized samples were executed to describe the mechanism and type of crystallization. The depth profiling proves the differences between surface and interior phase composition.     

彩色金属反应釉的研制

通过对日本和英国的釉料分析,结合两者共同的优点,经过系列实验,证实了彩色钨金属反应釉的可行性,并对其形成机理进行了探讨。     

利用工业废渣制备微晶玻璃进展

工业废渣大量排放造成了严重的环境污染,利用工业废渣制备矿渣微晶玻璃受到国内外的广泛关注.本文总结了目前已研究过用来制备微晶玻璃的工业废渣,并对其制备工艺、矿渣微晶玻璃成核和晶体长大等关键技术进行了阐述.认为工业废渣转制微晶玻璃是一项很有前景的材料开发和环保技术.     

Rheology,Crystallization Kinetics and Mechanical Properties of HDPE/Vinyl-POSS Nanocomposites

Polyhedral oligomeric silsesquioxane (POSS) is usually prepared from the hydrolytic condensation of organotrialkoxysilanes. The rheology, non-isothermal crystallization kinetics and mechanical properties of high density polyethylene (HDPE)/vinyl-containing POSS (V-POSS) nanocomposites were investigated. The results show that the molten HDPE/V-POSS belong to pseudoplastic fluid. The V-POSS can accelerate the nucleation of HDPE at starting stage of crystallization. However, it will decrease the crystallization ability of HDPE in the subsequent crystallization process. The modified Avrami analysis by Jeziorny can well explain the crystallization behaviour of HDPE/V-POSS. The yield strength and tensile modulus of nanocomposites both increase when V-POSS content is 6%.