Na2O-TeO2系统玻璃形成液体脆性的研究

通过测量Na2O-TeO2系统玻璃转化区的热容曲线，对该系统不同成分玻璃形成液体的热力学和动力学脆性进行研究。结果表明：该系统玻璃形成液体从热力学和动力学综合看脆性程度介于强弱之间，为中性偏脆性。随着氧化钠含量的升高，玻璃形成液体的脆性增强。用Kissinger方程和Ritland-Bartanev方程，得到的在玻璃转变区的结构松弛激活能十分接近。对该系统玻璃形成液体脆性参数的计算也得到该玻璃形成液体脆性分类的相同结果。     

玻璃的脆性(一)

评述了玻璃脆性的特征。维氏硬度和断裂韧性的比例可方便地确定玻璃脆性,并计算了不同成分玻璃的脆性。石英玻璃的脆性最大,氧化物玻璃次之,金属玻璃最小。而在氧化物玻璃中,微晶玻璃脆性最小,铝硅酸盐玻璃次之,钠钙玻璃又次之。     

玻璃的脆性(一)

评述了玻璃脆性的特征。维氏硬度和断裂韧性的比例可方便地确定玻璃脆性,并计算了不同成分玻璃的脆性。石英玻璃的脆性最大,氧化物玻璃次之,金属玻璃最小。而在氧化物玻璃中,微晶玻璃脆性最小,铝硅酸盐玻璃次之,钠钙玻璃又次之。     

新型GeSe2-Ga2Se3-KI系统硫卤玻璃形成的研究

开发了有高含量碱金属离子的新型硫化物玻璃.合成了GeSe2-Ga2Se3-KI系统的玻璃样品.研究了该系统的玻璃形成区并用孤对电子理论进行了解释.讨论了Ga2Se3和KI对玻璃形成能力的影响.给出了该系统玻璃的密度、特性温度、Raman和可见一红外光谱等.实验结果表明:该系统具有较广的玻璃形成区,某些组成,如摩尔组成为50 GeSe2 25Ga2Se3 25KI的样品具有良好的热学和光学性质,其表征热稳定性的特征温度差大于120K,玻璃透光范围从590nm到14.2μm.     

Na2O-CaO-Al2O3-SiO2系统微晶玻璃的析晶动力学研究

Na2O-CaO-Al2O3-SiO2系统微晶玻璃是一种新型建筑材料,该材料不仅具有一定的力学性能,还具有良好的装饰效果.本文采用差热分析 (DTA)方法对 Na2O-CaO-Al2O3-SiO2系统微晶玻璃的析晶动力学参数进行了测定,研究了该系统微晶玻璃析晶动力学.其结果表明:随着CaO含量的增加,该系统微晶玻璃的析晶活化能E和动力学析晶参数k(Tp)总体上是上升的.晶化指数n均小于3,表明该系统微晶玻璃以表面析晶的方式析晶.     

B_2O_3-PbO-Al_2O_3-SiO_2玻璃在醋酸中侵蚀动力学的研究

本文研究了B_2O_3-PbO-Al_2O_3-SiO_2玻璃在醋酸中侵蚀速度与溶液酸度、温度及时间散的关系。讨论了玻璃侵蚀机理和动力学方程。实验结果证明该玻璃的酸侵蚀具有扩动力学特征。     

GeSe2-As2Se3-CdSe系红外玻璃形成的研究

为研究GeSe2-As2Se3-CdSe系统的玻璃形成区,制备了该系统系列的透红外玻璃样品,并用差示扫描量热法对玻璃样品进行了测试。以玻璃析晶峰的形状以及玻璃析晶温度Tx玻璃转变Tg的差△T为参数,确定了具有较好析晶稳定性的组成区。结果表明：富GeSe2组成区能允许添加更多的CdSe。GeSe2摩尔分数在20%以上时,该三元系统有较大的玻璃形成区,并可对该区域内组成的玻璃进行微晶化处理。红外透射光谱的测试结果表明：所研究的玻璃样品在波长8～12μm区域均具有较好的透过性。     

玻璃的脆性(二)

玻璃的脆性受玻璃成分和结构、玻璃的微观和宏观缺陷、表面环境影响。玻璃原子结构聚合程度的减少和各向异性结构(层、链)的形成,提供了剪切变形,降低了无机玻璃脆性。此外,较高的摩尔体积表示结构较开放,使形变容易,造成较小的脆性。     

Bi_2O_3-SiO_2系统玻璃非等温析晶动力学

利用高温熔体冷却法制备了Bi2O3-SiO2(BS)系统玻璃,通过差热分析和X射线衍射,并借助Kissinger方程和Augis-Bennett方程,研究了BS系统玻璃的非等温析晶动力学和玻璃相转变动力学行为。结果表明:在热处理过程中,BS系统基础玻璃依次产生了3种主晶相:Bi12SiO20,Bi2SiO5和Bi4Si3O12;对应的活化能Ep1=150.6kJ/mol,Ep2=474.9kJ/mol,Ep3=340.3kJ/mol;平均析晶指数m1=2.5,m2=2.1,m3=2.2,所产生晶相均为体积成核,一维空间生长;系统中产生的亚稳定相Bi2SiO5易于向稳定的Bi4Si3O12相转变,通过Kissinger方程计算出该相转变的活化能Eg为90.5kJ/mol。     

花生壳活性炭对Cu~(2+)的吸附性能研究

以花生壳为原料,磷酸为活化剂制备花生壳活性炭,采用高分辨电子扫描电镜(SEM)对花生壳活性炭进行了表征。从热力学和动力学的角度,研究了花生壳活性炭对Cu2+的吸附行为。热力学研究表明:花生壳活性炭对Cu2+的吸附符合Langmuir等温吸附方程,该吸附是自发吸热过程。动力学研究表明:花生壳活性炭对Cu2+的吸附符合二级反应动力学方程反应特征,颗粒内扩散为主要控速步骤。     

Dilatometric fragility and prediction of the viscosity curve of glass-forming liquids

Viscosity and coefficient of thermal expansion (CTE) are both crucial properties in the design of new glasses for various applications. In this work, we extend the application of dilatometry to measure two important parameters governing the viscosity of glass-forming systems, viz., glass transition temperature and fragility index. We also describe a method to determine the dilatometric fictive temperature (T_f,DIL) and present data for five unique glass compositions covering a range of fragilities spanning 38-96, which are subjected to cooling and reheating rates in the range 1-30 K/min. The results show that the glass transition temperature obtained from the dilatometric method at 10 K/min (T_g,DIL) is consistent with both viscosity-based (T_g,vis) and DSC-based measurements (T_g,DSC). It is shown that the fragility of a liquid (m_vis) can be determined by calibrating the dilatometric fragility (m_DIL) with the same empirical model as in the calorimetric approach. Put together, we have developed a reliable method to measure the fragility and predict the viscosity curves of glass-forming liquids over a wide range (eg, 10¹-10¹⁶ Pa·s) without direct viscosity measurements, while simultaneously obtaining the CTE of the glass. However, this method is not suitable for glasses with a strong tendency toward phase separation or crystallization.     

Nucleation and Crystallization Kinetics in Fragile Glass-Forming Liquids

Isothermal kinetics of crystallization in the "fragile" Ca(NO₃)₂─KNO₃ melts and in AgI─Ag₂SO₄─Ag₂WO₄ melts of intermediate fragility have been investigated using singlestep and multistep calorimetric techniques. Time-temperature-transformation curves for crystal nucleation and growth have been delineated and the temperature for maximum nucleation rate ( T _NN) identified. The results are compared with the kinetics of nucleation observed in other fragile systems, such as fluoride glass melts, and with classical oxide melts (such as Li₂Si₂O₅) which have "strong" liquid characteristics. Reduced-temperature presentations of nucleation-rate data show qualitative correlations between T _NN/ T _L ( T _L is liquidus temperature) and liquid fragility. These correlations show that strong-liquid glass formers survive much larger supercoolings without nucleation than do fragile liquids.     

Sintering of Si3N4 with liquid in the system Ce2O3---AIN---SiO2

Liquid phase sintering of Si₃N₄ with melts from the system Ce₂O₃---AIN---SiO₂ has been studied. The glass forming region in this system and the reaction products formed during sintering at 1750–1800°C were analysed. Sintering of Si₃N₄ with two melt compositions selected from outside the glass forming region yields fully dense Si₃N₄. Post sintering treatment at 1300°C resulted in devitrification with consequent improvement of high temperature mechanical properties. The mechanical properties of Si₃N₄ sintered with liquids in the system Ce₂O₃---AIN---SiO₂ were found to be inferior to those of liquids selected from Y₂O₃---AIN---SiO₂, but superior to those selected from the system MgO---AIN---SiO₂.     

Viscosity of glass‐forming systems

As one of the most important properties of glass‐forming liquids, viscosity has drawn significant attention in both glass manufacturing and fundamental research. We review the recent scientific progress in viscosity of glass‐forming systems, including both the liquid and glassy states. After the Vogel‐Fulcher‐Tammann (VFT) equation was introduced, many more efforts have been made to develop more accurate models to describe the temperature dependence of viscosity. In addition to the VFT equation, we also discuss three other viscosity models, viz., the Adam‐Gibbs, Avramov‐Milchev, and Mauro‐Yue‐Ellison‐Gupta‐Allan models. We compare the four viscosity models in terms of their theoretical underpinnings and ability to fit measured viscosity curves. The concept of fragility and the universality of the high‐temperature viscosity limit are also discussed. Temperature‐dependent constraint theory is introduced in detail as a powerful tool for predicting the composition dependence of viscosity. Some examples of the application of this approach to predict the glass transition temperature and fragility of various glass systems are shown. Topological constraint theory is not only of scientific interest, but also has important industrial applicability. We also discuss the thermal history dependence of viscosity in the glassy state. Some phenomenological models are briefly reviewed, while the main focus is given to the modified Mauro‐Allan‐Potuzak model, which can accurately predict the nonequilibrium viscosity as a function of temperature, thermal history, and composition. The correlation of viscosity with elasticity is described in terms of the shoving model. Some theoretical implications of the various viscosity models are discussed, including the concepts of the Kauzmann paradox and the ideal glass transition. Some of the evidence against the existence of these phenomena are discussed. We also review the link between glass relaxation and viscosity, that is, emphasizing that the viscosity equations presented in this review can also be used to model different types of relaxation effects based on the Maxwell relation.     

Na2O-Al2O3-B2O3系统低熔点玻璃的热学性质研究

介绍了Na2O-Al2O3-B2O3系统玻璃的制备，确定了Na2O-Al2O3-B2O3系统玻璃的成玻范围，研究了玻璃的转变温度（Tg）、软化温度（Tf）和热膨胀系数（α），以及玻璃的Tg、Tf、α与玻璃组成的关系。     

The glass transition and the glassy state in isotropic and liquid crystalline polymers

PVT-measurements on atactic polystyrene shows that the Ehrenfest equations, which describe a thermodynamic transformation of the second order, are not applicable for the glass transition. The introduction of one internal ordering parameter ζ in addition to the conventional variables T and P, is sufficient to describe the behaviour in case of atactic PS in the isotropic glassy state. The usually observed way dependences in the glassy state can be explained by the concept of ordering parameters. In recent years liquid crystalline side chain polymers were developed. The liquid crystalline phases of these polymers can be supercooled and frozen-in like isotropic liquids. As the nematic or smectic liquid crystalline structure freezes-in, and can be conserved by this process, glasses with anisotropic properties are obtained. These glasses show e.g. a high optical birefringence. The glass transition of the liquid crystalline polymers can only be described by the assumption of at least two parameters ζ_i. Therefore the Ehrenfest equations are not applicable for the glass transition of isotropic as well as anisotropic glasses.     

Na2O-Al2O3-B2O3玻璃的热学性质和红外光谱

制备了Na2OAl2O3B2O3系统低熔点玻璃,确定了Na2OAl2O3B2O3系统玻璃成玻范围,研究了玻璃的转变温度(Tg)、热膨胀系数(α)和玻璃的红外光谱,表明这种玻璃的熔化温度低、转变温度也较低、玻璃的热膨胀系数较大,在近红外区有一水分的吸收带,在中红外区有BO、AlO的特征吸收带,以及玻璃的Tg、α与玻璃组成的关系。     

Crystallization and relaxation dynamics of glass-forming liquids at the Kauzmann temperature

If the entropy extrapolation of supercooled liquids (SCL) suggested by Kauzmann was correct, then they would have the same entropy as their stable crystalline phase at a certain low temperature, below the laboratory glass transition (T_g), known as the Kauzmann temperature (T_K). Extrapolating even further, the liquid entropy would be null at a temperature above absolute zero, violating the Third Law of Thermodynamics and constituting a paradox. Several possibilities have been proposed over the past 70 years to solve this paradox with different degrees of success. Our objective here is to access liquid dynamics at deep supercoolings to test the so-called crystallization solution to the paradox. By comparing the relaxation and crystallization kinetics determined above T_g and extrapolated down to T_K, a possible solution would be that the crystallization time is shorter than the relaxation time, which would mean that a SCL cannot reach the T_K. In this case, the liquid stability limit or kinetic spinodal temperature (T_ks) should be higher than T_K. We tested two fragile glass-forming liquids (diopside and wollastonite) and two strong liquids (silica and germania). For the fragile substances, T_ks ? T_K, hence such a supercooled liquid cannot exist at T_K, and the entropy crisis is averted. On the other hand, the results for the strong liquids were inconclusive. We hope the findings of this work encourage researchers to further investigate the liquid dynamics of different strong glass-forming systems at deep supercoolings.     

The apparent activation energy and dynamic fragility of ancient ambers

According to the literature, different types of materials have different glass transition temperature (T_g) dependences of apparent activation energy (E_g) and dynamic fragility (m). In previous work we found that for different ambers, there were different glass transition temperatures. These same samples provide an opportunity to study the T_g dependence of E_g and m for amber, which has not been reported previously in the literature. In this work, nine pieces of amber from different locations and having different ages were investigated by differential scanning calorimetry. Six cooling rates were used to provide the different thermal histories, and the corresponding limiting fictive temperatures were determined using Moynihan's area matching method. From the cooling rate dependence of the limiting fictive temperature both the apparent activation energy and dynamic fragility were calculated. We find that as glass transition temperature increases, both the apparent activation energy and dynamic fragility increase. The T_g dependence of m for amber shows a similar trend with temperature as do the metallic glass formers and compares favorably with the m–T_g dependence of other aromatic polymers.