ZrO2对低温烧结 BaO-Al2O3-SiO2系微晶玻璃析晶和晶型转变的影响

用烧结法制备了化学计量比和高Ba含量的两组BaO-Al2O3-SiO2(BAS)系微晶玻璃,采用差示扫描量热法(DSC)和X射线衍射分析(XRD)等手段研究了ZrO2对BAS系微晶玻璃中六方钡长石析晶和六方钡长石向单斜钡长石晶型转变的影响.研究表明,两组BAS系玻璃的烧结温度低于850℃,晶化温度低于900℃.六方钡长石的析出为整体析晶.不加形核剂晶型转变为整体析晶;添加ZrO2晶型转变为表面析晶.提高Ba含量或添加ZrO2促进六方钡长石的析出和晶粒细化.化学计量比的BAS系微晶玻璃中添加ZrO2明显促进晶型转变.高Ba含量的BAS系微晶玻璃中添加ZrO2表现为抑制晶型转变,850℃保温100h不发生转变.     

Cr2O3的添加对MgO-Al2O3-SiO2-TiO2系统微晶玻璃析晶行为的影响

利用DTA、XRD、SEM和TEM等实验手段,研究了Cr2O3的添加对于MgO-Al2O3-SiO2-TiO2系统微晶玻璃析晶行为的影响.同时,通过Ozawa和Kissinger方法计算出系统中α-堇青石的析晶活化能E.研究结果表明,少量Cr2O3的添加并不改变MgO-Al2O3-SiO2-TiO2系统玻璃析出的晶相类型,但是提高了玻璃转化温度Tg,降低了α-堇青石的析晶活化能.由于析晶活化能的降低,促进了α-堇青石的析出,最终获得了一种有实用价值的微波介质材料.该材料在微波频率下(10GHz)的相对介电常数约5.5,介电损耗＜7×10-4.     

MgO-Al2O3-SiO2系堇青石微晶玻璃的制备及性能研究

采用高温熔融法制备了MgO-Al2O3-SiO2系堇青石微晶玻璃,采用DTA、XRD等对试样的热处理工艺和力学性能进行了分析,详细讨论了晶化温度、晶化时间、核化温度及核化时间对该系微晶玻璃力学性能及显微结构的影响。结果表明,对于实验研究的MgO-Al2O3-SiO2系玻璃,于600℃核化处理4h,于1100℃晶化处理2h,可以得到具有较好性能的堇青石基微晶玻璃,其抗弯强度可达182MPa。     

TiO2对CaO-MgO-P2O5-SiO2系玻璃晶化影响的研究

CaO-MgO-P2O5-SiO2系微晶玻璃是一种新型医学生物材料，该材料洋仅具有良好的生物相溶性，还具有一定的力学性能，本文采用热热分析（DTA）方法对以TiO2作为晶核剂的该系生物微晶玻璃的析晶动力学参数进行了测定，所得数据经计算机拟合后，其结果表明，在一定范围内引入TiO2（≤8.7wt%)能降低该系玻璃的析晶活化能E，有促进玻璃析晶的作用，当TiO2含量达到8.7wt%时，E达到最小值，当TiO2含量＞8.7wt%时，E值反而回升，晶化指数n与该玻璃体系中加入TiO2的变化规律与E值随TiO2的变化规律是一致的。     

掺P2O5氟化镓铟基玻璃微晶化可控性机理的探讨

用熔融法制备掺少量P2O5氟化镓铟基玻璃(20GaF3-15InF3-17CdF2-15ZnF2-10SnF2-20PbF2-3P2O5),玻璃的析晶动力学分析结果表明:掺入P2O5能使氟化镓铟基玻璃的析晶双峰间温度差△Tp(△Tp=Tp1-Tp2)增大,使可控微晶化变为可能。同时利用X射线衍射分析方法(XRD)和扫描电镜讨论了该微晶化玻璃的晶相和析晶形貌,并在593 K下保温1 h能得到透明度较好、含四方晶相ZnF2的微晶玻璃。     

晶种对低温烧结BaO-Al2O3-SiO2系微晶玻璃析晶的影响

用烧结法制备了化学计量比和高Ba含量的两组BaO-Al2O3-SiO2(BAS)系微晶玻璃,研究了晶种对低温烧结BaO-Al2O3-SiO2系微晶玻璃析晶的影响.结果表明,玻璃的软化温度随着品种含量的增加而提高.在两组玻璃粉中添加晶种有助于降低析晶活化能,促进六方钡长石和单斜钡长石的析出;晶种含量为1%时活化能最小,成分为化学计量比的玻璃析晶峰值温度也最低.在850℃保温时间2 h,添加1%晶种的BAS系微品玻璃全部转变为单斜钡长石.在两组成分的BAS系微晶玻璃中,六方钡长石的析出表现为整体析晶.不加晶种时,单斜钡长石通过六方钡长石一单斜钡长石的晶型转变析出,表现为整体析晶;添加晶种后,单斜钡长石主要因"同构"效应直接从基础玻璃中析出,表现为表面析晶.     

La2O3在MgO-Al2O3-SiO2-TiO2微晶玻璃中的作用

在MgO-Al2O3-SiO2-TiO2玻璃中添加不同数量的氧化镧，采用差热分析，X射线衍射及电子显微镜等技术研究了氧化镧对玻璃析晶过程与力学性能的影响。氧化镧的加入使玻璃中析出α－堇青石相的温度降低，同时避免了高膨胀方石英相的析出。随着氧化镧加入量的增加，玻璃整体析晶能力下降，微晶玻璃中晶相含量减少，晶粒尺寸增大，微晶玻璃的弹性模量与硬度减小，断裂韧性增加，体现出大尺寸长柱状金红石晶粒的增韧作用。     

亚微米Li2O-Al2O3-SiO2微晶玻璃制备

本文利用DTA、XRD和SEM对Li2O-Al2O3-SiO2(以下简称LAS)微晶玻璃核化晶化热处理制度及氟离子在该玻璃体系中的作用进行研究.通过分析得出:含氟LAS玻璃核化温度和晶化温度分别为620℃和710℃,比相同组份的不含氟Li2O-Al2O3-SiO2玻璃核化、晶化温度分别降低了40℃和160℃左右;引入氟离子明显降低LAS玻璃析晶温度,系统的活化能降低约54kJ/mol,当含氟LAS玻璃的核化时间为1h、晶化时间为4hrs,平均微晶颗粒尺寸在50nm左右.     

FeO-Fe2O3-CaO-SiO2体系铁磁微晶玻璃的磁性及生物活性

具有生物活性和磁性的微晶玻璃材料被认为是温热疗法治疗癌症的有效热种子材料.本文制备了添加少量B2O3和P2O5后的FeO-Fe2O3-CaO-SiO2体系铁磁微晶玻璃,并进行了微观结构分析、XRD分析、磁性检测以及生理模拟液的浸泡实验.实验结果表明,制备的微晶玻璃材料同时具备磁性和生物活性这两种重要性能.不经过核化处理在1000℃晶化2h能够获得较理想的磁铁矿主晶相和硅灰石次晶相均匀致密分布的微观组织,所得微晶玻璃具有最佳的磁性能.铁含量提高能够增加微晶玻璃的磁性,然而会抑制微晶玻璃表面羟基磷灰石的形成,从而降低其生物活性.     

ZnO和CaO含量对CaO-Al2O3-SiO2系泡沫微晶玻璃析晶与发泡的影响

以CaO-Al2O3-SiO2玻璃为基体,以石墨为发泡剂,制备硅灰石基泡沫微晶玻璃,研究了玻璃中引入ZnO和增加CaO含量对析晶与发泡的影响.结果表明,ZnO可降低发泡过程中假硅灰石晶相的析出量,促进玻璃粉与发泡剂混合物的烧结,降低发泡剂在较低温度下的损耗.提高CaO含量,样品结晶度增大,相同温度下玻璃的粘度增加,发泡效率降低.原料中ZnO加入量6wt%、CaO含量为18wt%的CaO-Al2O3-SiO2玻璃粉,较低温度下烧结充分,发泡剂损耗相对较少,在1000℃的发泡温度下可获得气孔率高的泡沫微晶玻璃.     

VLE data for CO2-CF2Cl2, N2-CO2, N2-CF2Cl2 and N2-CO2-CF2Cl

Knowledge about vapour-liquid (VLE) is required as a basis of reliable calculations for separation processes. Correlations available for the prediction of T, p, x, y data are less accurate for mixtures at high pressures and mixtures containing supercritical components. The results of VLE experiments are reported and compared with data calculated with equations of state.     

Preparation of ZrO2-CeO2 and HfO2-CeO2 nanopowders

We prepared weakly agglomerated powders of ZrO₂-CeO₂ and HfO₂-CeO₂ solid solutions 5–8 nm in particle size, consisting of monoclinic and tetragonal phases. After heat treatment at 1200°C, the crystallite size was 30 and 14 nm, respectively. We also examined the effect of precipitate freeze drying on the crystallization of hafnia-based solid solutions containing up to 20 mol % CeO₂.     

Thermal diffusion in binary mixtures H2-CCl2F2 and H2-CHClF2

Thermal diffusion coefficients were measured in two gaseous mixtures, in which one component was close to the critical temperature, in the pressure range (19.6–127.4)·10⁴ N/m² and at a freon concentration of 0.25–0.8.     

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

First-principles cluster calculations are reported of the local electronic structure of the three compounds: La₂CuO₄, Sr₂CuO₂Cl₂, and Sr₂CuO₂F₂. The copper ${\text{3d}}_{x^2 - y^2 } $ and the planar oxygen 2p _σ atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the ${\text{3}}d_{3z^2 - r^2 } $ atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.     

Radial GRIN glasses in Li2O-Na2O-Al2O3-TiO2-SiO2 systems

A series of GRIN glass rods have been developed in Li2O-Na2O-Al2O3-TiO2-SiO2 systems. Negative radial refractive index profiles were generated by exchanging Na+ for Li+ ions in these glass rods. It has been observed that TiO2 plays a vital role in increase in the profile depth and maximum change in the refractive index because of its ambivalent nature. Change in the refractive index can be further increased by increasing the concentration of exchanging cation in the base glass.     

Thermoelectric power of single-phase samples of Tl2CaBa2Cu2O y and Ba2CaSr2Cu2O y

Single-phase 2122 samples of thallium and bismuth superconductors were made by the precursor matrix method. The thermopower of these samples was measured in the temperature range 250 K-T _c . The thermopower was positive and decreased linearly with increasing temperature aboveT _c (onset). The exponential enhancement of thermopower seen in the undoped and doped YBCO was not observed in these samples. The linear variation of thermopower can be explained on the basis of either a two-band model or a narrow band model.     

Si_2N_2O-Al_2O_3-La_2O_3和Si_2N_2O-Al_2O_3-CaO系统的亚固相关系

本文给出了 Si_2N_2O-Al_2O_3-La_2O_3和 Si_2N_2O-Al_2O_3-CaO 系统的亚固相图。实验结果表明:在 Si_2N_2O-Al_2O_3-CaO 系统中有一个未知结构的新化合物 CaO·Si_2N_2O,在3CaO·Si_2N_2O 和3CaO·Al_2O_3两化合物之间形成连续立方固溶体。而 Si_2N_2O-Al_2O_3-La_2O_3系统中则没有发现新化合物。在两个系统的富 Si_2N_2O区,过量的 Si_2N_2O 与 La_2O_3和 CaO 分别反应形成 Si_3N_4与 La_(10)[SiO_4]_(?)N_2(H-相)(和 CaSiO_3。所研究的这两个三元系统中,分别形成了如下几个四元相容性区。在 Si_2N_2O-Al_2O_3-La_2O_3系统内有:H-Si_3N_4-La_2O_3·Si_2N_2O-La_2O_3·Al_2O_3;H-Si_3N_4-La_2O_3·Al_2O_3-La_2O_3·11 Al_2O_3;H-Si_3N_4-La_2O_3·11 Al_2O_3-Al_2O_3;H-Si_3N_4-Al_2O_3-O′s.s;H-Si_3N_4-O′s.s-Si_2N_2O在 Si_2N_2O-Al_2O_3-CaO 系统内有:Si_3N_4-CaSiO_3-CaO·Si_2N_2O-3CaO·Al_2O_3;Si_3N_3-CaSiO_3-3CaO·Al_2O_3-2CaO·Al_2O_3·SiO_(?);Si_(?)N_(?)-CaSiO_3-2CaO·Al_2O_3·SiO_2-Al_2O_3;Si_3N_4-CaSiO_3-Al_2O_(?)-O′s.s;Si_3N_4-CaSiO_3-O′s.s-Si_(?)N_(?)O     

Elastic and Electronic Properties of Superconducting CaPd 2 As 2 and SrPd 2 As 2 vs. Non-superconducting BaPd 2 As 2

The first-principles calculations were performed to predict the elastic and electronic properties of the superconducting ThCr₂Si₂-type phases CaPd₂As₂ and SrPd₂As₂ in comparison with the non-superconducting CeMg₂Si₂-type phase BaPd₂As₂. Besides, the same properties were compared for CeMg₂Si₂- and ThCr₂Si₂-type polymorphs of BaPd₂As₂. We found that all these phases are mechanically stable and belong to soft materials with low hardness. The near-Fermi region is formed by the valence states of the blocks [Pd₂As₂] with decisive contributions of Pd 4d states. The values of N(E _F) increase in the sequence: CaPd₂As₂ < SrPd₂As₂ < BaPd₂As₂, i.e. in the reverse sequence relative to the transition temperatures T _C. Thus, the change in T _C cannot be explained by the electronic factor, i.e. by the simple correlation T _C～N(E _F). Most likely the decrease in T _C in the sequence CaPd₂As₂ → SrPd₂As₂ and the absence of a superconducting transition in BaPd₂As₂ are related to the structural factors and the peculiarities of the electron–phonon coupling mechanism.