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。     

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.     

晶化温度对MgO—Al2O3-SiO2系微晶玻璃显微结构及性能的影响

通过差热分析（DTA）、X射线衍射分析（XRD）、扫描电子显微镜（SEM）研究了3种不同晶化温度对MgO-Al2O3-SiO2系微晶玻璃析晶性能、微观结构及抗弯强度的影响。研究结果表明，随着晶化温度逐步升高，晶粒尺寸逐步增大，抗弯强度逐渐增高。     

核化温度对CaO—Al2O3-SiO2-Fe2O3系微晶玻璃微观结构及性能的影响

本文以钢渣和赤泥为主料,采用熔融法制备了CaO对微晶玻璃物相、微观结构及性能的影响。分析测试结果表明,化温度的升高,主晶相衍射峰先增高后降低,晶相析出量增加,晶玻璃的抗弯强度和耐腐蚀性最好。CaO-Al2O3-SiO2-Fe2O3系微晶玻璃,探讨了不同核化温度微晶玻璃的结晶物相不随核化温度的变化而改变。随着核且析出的晶粒尺寸逐渐增大。当核化温度为770℃时,微     

ZrO2/钙铝硅系微晶玻璃复合材料热处理制度研究

采用Sol-gel法制备ZrO2/CaO-Al2O3-SiO2系微晶玻璃复合材料,通过差热分析、X射线衍射和扫描电镜等对材料进行表征.结果表明:烧结温度范围为1035～1065℃,晶化温度约为870℃条件下所制得的复合微晶玻璃材料主晶相为t-ZrO2和β-CaSiO3,具有较高的抗折强度,可以用于制备高强度牙科材料.     

BaO-Al2O3-SiO2系微晶玻璃的研究进展和应用

以钡长石(BaAl2Si2O8)为主晶相的BaO-AlO3-SiO2(BAS)系微晶玻璃具有高的耐热温度、机械强度,具有较好的抗氧化性能和抗碱蚀能力,具有高的化学稳定性,与多种热、机械增强材料都有良好的化学相容性.而且,单斜钡长石的电绝缘和介电性能良好.因此,BAS系微晶玻璃作为高温结构材料和功能陶瓷材料均有相当多的应用.本文在评述BAS系微晶玻璃的不同制备工艺、加速六方钡长石→单斜钡长石晶型转变的不同手段与机理的基础上,介绍了BAS系微晶玻璃作为结构材料和功能材料的多种应用,指出了国内外的研究差距,并作出了研究展望.     

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.     

堇青石微晶玻璃与银电极的共烧兼容性

通过在MgO-Al2O3-SiO2(MAS)凝胶玻璃中引入少量银,研究了共烧过程中银对凝胶玻璃的析晶过程、烧结特性和介电性能的影响,以及微晶玻璃与银电极的共烧匹配性。结果表明,银的引入可促进α-堇青石析晶,并使微晶玻璃的烧结温度和介电常数降低。微晶玻璃和电极存在明显共烧失配,从而导致界面缺陷。     

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.     

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.     

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.     

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.     

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.     

SiO2—TiO2—ZrO2系涂层的制备及其特性

用溶胶－凝胶法（sol-gel method）在不锈钢表面制备了SiO2-TiO2-ZrO2系无机氧化膜（STZ）。用DTA／TG、IR、XRD和SEM等手段研究了涂层制备时由凝胶向玻璃态的转变以及涂层薄膜的显微结构特点，考察了涂层对基体的保护效果。试验结果表明，在溶胶至凝胶最终转变为无机氧化物的过程中形成了无机网络，Si^4 和Zr^4 充当了网络骨架的形成离子。涂层为无定型玻璃态，其间混有石英、锐钛矿或金红石等微晶。     

Structure of Na2O·2TiO2 glass

X-ray radial distribution analysis and Raman spectroscopic measurement were carried out on Na₂O-2TiO₂ glass prepared by twin-roller quenching method. It is found that four-coordinated Ti⁴⁺ ions may be predominant over six-coordinated ones in the present glass. It is also found that the fraction of six-coordinated Ti⁴⁺ ions is larger in the present glass than in K₂O·2TiO₂ and Cs₂O·2TiO₂ glasses. Poorer glass-forming ability of the Na₂O-TiO₂ system compared with the K₂O-TiO₂ and Cs₂O-TiO₂ systems is ascribed to a larger fraction of TiO₆ octahedron for the former system.     

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.     

掺杂Bi_2Ti_2O_7对Y_2O_3-2TiO_2系微波介质陶瓷材料性能的影响

目前国内外对εr范围在40～80左右的中介电常数微波介质陶瓷体系的研究还很缺乏。为适应现代微波通讯技术发展需求,本实验研究开发了新型中介电常数Y2O3-2TiO2系微波介质陶瓷,并在此基础上添加Bi2Ti2O7陶瓷粉料进行复相掺杂。利用网络分析仪,阻抗分析仪,XRD,SEM等方法,本文重点研究了不同Bi2Ti2O7掺杂量对Y2O3-2TiO2系微波介质陶瓷材料烧结性能和介电性能的影响。通过分析发现适量掺杂能够有效降低材料的烧结温度,并使材料致密化。同时由于Bi3+置换主晶相中的Y3+形成了固溶体,材料主晶相为烧绿石结构并未改变。当添加质量分数为8wt%时获得介电性能较好的陶瓷材料,烧结温度从未掺杂的1460℃降低到1320℃。在1M下:εr≈62.14,tanδ≈1.22×10-3,微波频率(4.55GHz)下εr≈62.85,Q.f=4122.8GHz,τf=-7ppm/℃。     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.