A coupled phase diagram experimental study and thermodynamic optimization of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems,and prediction of the phase diagrams of the Li2O-CaO-Al2O3-SiO2 system

A coupled experimental phase diagram study and thermodynamic modeling of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was conducted at 1 atm total pressure. Differential scanning calorimetry (DSC) measurements were performed in the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems. In addition, the phase relations in the Li₂O-CaO-Al₂O₃ system were determined by equilibration/quenching experiments at 1643 and 1743 K, and the phases were characterized with X-ray diffraction (XRD) and Electron-probe micro analysis-wavelength dispersive spectroscopy (EPMA-WDS). The absence of ternary compounds or solid solutions was confirmed. Congruent melting of Li₂CaSiO₄ compound in the Li₂O-CaO-SiO₂ system was determined at 1350 ± 5 K. Thermodynamic optimization of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was carried out based on new phase diagram experiments and critically evaluated literature data. The phase diagrams of the quaternary Li₂O-CaO-Al₂O₃-SiO₂ system were predicted using the thermodynamic models with optimized model parameters.     

Critical evaluation and thermodynamic optimization of the Li-O,and Li2O-SiO2 systems

A critical evaluation and thermodynamic optimization of all available experimental data of the Li-O and Li₂O-SiO₂ systems were performed to obtain one set of consistent Gibbs energy functions for all phases in the systems. The obtained Gibbs energy functions can reproduce all available and reliable experimental data from 298 K to above liquidus temperatures at one atm total pressure. It is the first time, to the best of our knowledge that the Gibbs energy of stoichiometric phases like Li₂O, Li₄SiO₄, Li₂SiO₃, and Li₂Si₂O₅ was comprehensively evaluated and optimized. The liquid oxide solution was modeled using the Modified Quasichemical Model to describe its thermodynamic behavior accurately considering the short range ordering. Discrepancies observed in the metastable liquid immiscibility and the liquidus in the SiO₂-rich region of the Li₂O-SiO₂ system was resolved. The phase diagram and thermodynamic data of all the solid and liquid phases were well reproduced within experimental error limits.     

锂铝硅透明微晶玻璃着色研究

引入Cr2O3、CoO、NiO、MnO2等过渡金属氧化物对低膨胀锂铝硅透明微晶玻璃进行着色研究,结果表明,微晶玻璃与其母体玻璃相比,颜色有明显的不同,主波长向长波方向移动。研究还发现,在从核化阶段到晶化阶段的过程中颜色变化最为明显,而在核化阶段和晶化阶段颜色没有发生明显的变化。同时运用配位场理论和光散射原理来解释这种颜色变化的原因。     

Low Li2O content study in Li2O-Al2O3-SiO2 glass-ceramics

The price of lithium-containing minerals and other chemical materials continues to increase, resulting in an increase in the production cost of Li₂O-Al₂O₃-SiO₂ (LAS) system glass-ceramics. In the LAS glass-ceramics component, the reduction in the amount of Li₂O used can reduce the cost of the product. It is worthwhile to study whether it is possible to prepare glass-ceramics with low expansion properties under low Li₂O content. The effect of Li₂O content on the glass-ceramics of LAS system was studied. In this paper, spodumene was used as the main raw material, and TiO₂ and ZrO₂ were added as crystal nucleating agents to prepare transparent glass-ceramics with low expansion coefficient. The effects of the change of Li₂O content on the crystal phase and microstructure of glass-ceramics were investigated by XRD, DSC, FTIR and SEM. The results show that the main crystalline phase of the low expansion transparent glass-ceramics is β-quartz solid solution. When Li₂O content is in the range of 2.99 wt% to 4.13 wt%, low expansion glass ceramics can be prepared by an appropriate method. With the increase of Li₂O content, the average coefficient of thermal expansion (CTE) in the temperature range of 30 °C–300 °C shows a decreasing trend. When Li₂O content is in the range of 3.51 wt% to 4.13 wt%, the thermal expansion coefficient of the glass ceramics is extremely small, and even a negative expansion coefficient occurs.     

Li2O-Al2O3-SiO2系统玻璃的晶化和烧结

采用差热分析（DTA）,X射线衍射分析（XRD）和扫描电子显微镜（SEM）等分析手段研究了Li2O-Al2O3—SiO2 （LAS）系统玻璃的烧结和析晶.通过实验确定了最佳烧结温度,并获得主晶相为β—锂辉石的Li2O-Al2O3—SiO2 （LAS）的微晶玻璃.结合烧结体的体积密度、显气孔率和吸水率的数据,分析说明了粘结剂PVA的加入对玻璃粉烧结体性能的影响.     

Phase equilibria in the La2O3-Sm2O3-ZrO2 system: Experimental studies and thermodynamic modeling

A series of ceramic samples were prepared to experimentally investigate sub-solidus phase relations in the La₂O₃-Sm₂O₃-ZrO₂ system at 1873 K and 1673 K. No ternary compounds have been observed, while the binary La₂Zr₂O₇ and Sm₂Zr₂O₇ pyrochlore phases form a continuous solid solution La_2?xSm_xZr₂O₇ in the ternary system at the selected temperatures. X-ray diffraction and microstructure results demonstrated that the pyrochlore phase is stable in the ZrO₂-rich corner. The homogeneity range of the pyrochlore phase was carefully determined and the phase boundary of the cubic ZrO₂ (fluorite phase) which extends into the ternary system was also constructed via electron probe microanalysis. The as-obtained data were adopted to determine the mixing parameters for the pyrochlore and fluorite phases in the present thermodynamic modeling. A self-consistent database of the La₂O₃-Sm₂O₃-ZrO₂ system was accordingly established for the first time and the calculations agree well with the experimental data in the current work.     

Phase diagram study and thermodynamic modeling of the MgO-Y2O3-MgF2-YF3 system

The phase diagram of the MgO-Y₂O₃-MgF₂-YF₃ system (Mg,Y//O,F reciprocal system) at 1273–1773 K was investigated for the very first time using a classical equilibrium/quenching and differential thermal analysis (DTA) experiments followed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analyses. No ternary or quaternary crystalline phase was found, and the eutectic reactions in the reciprocal system were identified. The overall phase diagram of the reciprocal system was also calculated based on the thermodynamic modeling using the CALculation of PHAse Diagram (CALPHAD) method.     

Li2O-Al2O3-SiO2高强度半透光微晶玻璃晶化及机械性能研究

设计玻璃组成及晶化工艺提高Li₂O-Al₂O₃-SiO₂微晶玻璃的强度是当前亟需解决的问题。本文通过熔融浇铸法制备了具有特定组成的Li₂O-Al₂O₃-SiO₂玻璃,通过两步热处理方法制备了高强度半透光微晶玻璃。差示扫描热分析结果显示玻璃的转变温度为532 ℃,且有多个析晶峰。热处理后,X射线衍射证明了玻璃中析出以Li₂Si₂O₅、LiAlSi₃O₈、LiAlSi₄O₁₀为主晶相的晶体,且随着热处理温度的上升或时间延长,透锂长石逐渐转变为锂辉石晶相,晶粒尺寸也从70 nm(热处理条件为:750 ℃,0.5 h和780 ℃,10 h)生长至340 nm(热处理条件为:820 ℃,0.5 h和850 ℃,4 h),微晶玻璃从半透光转变为完全乳浊。微晶玻璃具有优异的机械性能,维氏硬度最大可达9.15 GPa,环上环的最大负载可达1 335 N,最大整机跌落高度可达162 cm。此微晶玻璃可用于手机等电子器件的背板保护玻璃。     

Phase diagram study and thermodynamic assessment of the Y2O3-YF3 system

The phase diagram of the Y₂O₃-YF₃ system up to 1973 K was investigated using a classical equilibration/quenching experiment and differential thermal analysis (DTA). Equilibrium phases were confirmed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analysis. For the very first time, the entire range of the phase diagram of yttrium oxy-fluoride system up to 1973 K was experimentally determined. Cubic-Y₂O₃ phase dissolves more than 5 mol% of YF₃ at 1973 K. The melting points of YOF and vernier phases are found to be higher than 1973 K and their steep liquidus in the YF₃-rich region are determined. Based on new experimental phase diagram data and thermodynamic property data in the literature, the Y₂O₃-YF₃ system was thermodynamically modeled by the CALculation of PHAse Diagram (CALPHAD) method. As applications of the thermodynamic database, metastable solubilities of YF₃ in Y₂O₃ during plasma etching process were calculated.     

R2O-Al2O3-B2O3-SiO2系统玻璃对羟基磷灰石的烧结及其相转变的影响

系统地研究了R2O－Al2O3-B2O3-SiO2系统玻璃对羟基磷灰石（HAP，Hydroxyapatite)的烧结和相转变的影响。其中玻璃组成为Na2O5-12,K2O 7-15,Al2O3 3-5,ZnO 0-5,B2O3 15-25,SiO2 65-75(wt%).结果表明R2O－Al2O3-B2O3-SiO2系统玻璃有较强的促进HAP烧结能力，但在较高温度下会促使HAP分解；合适的添加量为30wt%，烧结温度为1000℃。     

Thermodynamic modeling of the CaO-SiO2-ZrO2 system coupled with key phase diagram experiments

Thermodynamic modeling coupled with key phase diagram experiments of the ternary CaO-SiO₂-ZrO₂ system was carried out. The isothermal phase diagram of the CaO-SiO₂-ZrO₂ system at 1873 K was established by using a classical phase equilibration and quenching technique followed by EPMA phase analysis. The Gibbs energy of each phase was optimized through critical evaluation of all available thermodynamic properties and phase diagram data in literature with new experimental data. The discrepancies between experimental phase diagram data and possible errors in the existing thermodynamic data were resolved in this study.     

Impact of recently discovered sodium calcium silicate solutions on the phase diagrams of relevance for glass-ceramics in the Na2O-CaO-SiO2 system

Although phase relations in the Na₂O-CaO-SiO₂ system are vital to melting and thermal treatments in glass and glass-ceramics industries, the available data for thermodynamic modeling are mostly based on reports published in 1920s and 1950s. The present investigation verifies the formation of solid solutions of Na₂CaSiO₄ and Na₂Ca₂Si₂O₇ which have previously assumed to be stoichiometric compounds. The impact of these solid solutions on the features of the phase diagram were investigated using the equilibration-quenching-EDS/EPMA technique. The data were reported as liquidus projections and in isothermal sections within the temperature range of 1000 and 1400 °C. Ten primary phase fields were identified, namely SiO₂, Na₂Ca₃Si₆O₁₆, combeite, Na₄CaSi₃O₉ss, CaSiO₃, Na₂CaSiO₄ss, Na₂Ca₂Si₂O₇ss, Na₂Ca₆Si₄O₁₅, Ca₃Si₂O₇ and Ca₂SiO₄. In addition, some novel liquidus data and invariants points were examined in more detail. The fundamental data obtained can be employed for the thermodynamic reassessment of the Na₂O-CaO-SiO₂ system. The present study also discusses the findings and their impact on melting and annealing processes during the manufacture of glass and glass-ceramics.     

Al-TiO2-C体系热力学分析及Al2O3-TiC复相陶瓷的燃烧合成

对Al-TiO2-C燃烧合成体系进行了热力学计算,并利用Al-O-N、Ti-O-N、C-O-N三个体系的叠加优势区相图分析了该燃烧合成体系的平衡产物相.结果表明,Al-TiO2-C燃烧合成体系的绝热燃烧温度为2398 K,燃烧合成平衡相为Al2O3和TiC.XRD检测结果与热力学分析结果相吻合,说明该燃烧合成反应进行得较为彻底,证实热力学分析结果可信.原位生成的Al2O3和TiC两相分布较均匀,燃烧合成产物疏松多孔,易于通过球磨方式达到破碎、磨细的目的.     

热处理对Li2O-Al2O3-SiO2微晶玻璃的影响

本文对Li2O-Al2O3-SiO2（LAS）微晶玻璃的热处理制度、光学性能和热膨胀性能进行了分析,分析结果表明：应根据DTA曲线来确定最佳的成核温度范围和晶化温度范围并合理制定热处理制度;晶核密度和晶核尺寸随保温时间逐渐增加具有相反的趋势;晶粒尺寸大小将很大程度上影响微晶玻璃的光学性能;由于β-石英固溶体和β-锂辉石固溶体具有各向异性特点和螺旋链状结构,使其具有低的热膨胀系数和自由恢复形状特性。     

Preparation of fully dense and magnetically controllable CaO-Al2O3-SiO2-Na2O-Fe3O4 glass ceramics by hot pressing

Fully dense and magnetically controllable glass ceramics was successfully synthesized by method of hot pressing using CaO-Al₂O₃-SiO₂-Na₂O glass powder and Fe₃O₄ powder as raw materials. The influences of sintering temperature and time, content and particle size of Fe₃O₄, as well as particle size of glass powder on the densification and magnetic properties of samples were investigated. It was found that the saturation magnetization gradually increased with increasing magnetite content. In addition, the samples containing smaller size magnetite particles had a higher coercivity. However, for samples using smaller size glass powder, magnetite particles could partially dissolve into the glass matrix, which led to the decrease of saturation magnetization and the increase of coercivity. It was also concluded that the precipitation of crystalline phase from smaller size glass powder caused the decrease of degree of densification, and after decreasing the sintering temperature, the degree of densification of product was enhanced.     

Synthesis and characterization of LTCC compositions with middle permittivity based on CaO-B2O3-SiO2 glass/CaTiO3 system

CaTiO₃ ceramics with the addition of CaO-B₂O₃-SiO₂ (CBS) glass (45–55 wt%) composites were sintered at 830 °C, 850 °C, 875 °C and 900 °C. To illustrate influence mechanism of the different glass contents and sintering temperatures on the properties of the composites, we focused on the multiple performances of the composites by employing different qualitative and quantitative instruments. Composites with 50 wt% glass sintered at 875 °C presented fairly ideal performance: the bulk density was 3.20 g/cm³, the dielectric constant was 25.7 and the dielectric loss was 0.0009 at 7 GHz. Micro-Structure analysis of the composites showed a dense and pore-less microstructure except for few pores with size around 1 μm. In addition, the composite could meet the shrinkage requirement of Ag electrodes and could not possibly react with Ag electrodes any more. This makes them suitable for various dielectric applications at low sintering temperature.     

Effect of atmosphere control on magnetic properties of CaO-Al2O3-SiO2-Fe3O4 glass ceramics

The influences of atmosphere during processes of melting and heat treatment, heat treatment temperature, Fe₃O₄ content and basicity on the magnetic properties of magnetite-based glass ceramics were investigated. For sample containing 20 % Fe₃O₄ melted in different atmospheres, the highest saturation magnetisation was realized in 20vol% air + 80 vol% Ar, due to the fact that ratio of Fe³⁺ to Fe²⁺ in melt obtained in this atmosphere was close to 2. However, it was found that the coercivity of glass ceramics was not affected by the melting atmosphere. A high sintering temperature led to the decrease of saturation magnetisation and the increase of coercivity. As increasing Fe₃O₄ content, the main crystal phase transformed from CaSiO₃ to CaFe_0.6Al_1.3Si_1.08O₆ and finally to magnetite phase, accompanied by the increase of saturation magnetisation and coercivity. In addition, the increase of basicity caused the decrease of saturation magnetisation and the increase of coercivity.