锂铝硅微晶玻璃结构与性能热稳定性研究

以TiO₂、ZrO₂为形核剂制备了透明低膨胀锂铝硅系微晶玻璃, 通过测定其等温转变动力学曲线,讨论锂铝硅玻璃析晶及相变与热处理温度和时间的关系, 并采用DTA、XRD和SEM等方法研究锂铝硅微晶玻璃结构和性能的热稳定性. 结果表明, 以β-石英固溶体为主晶相的透明微晶玻璃能在750~900℃较宽的温度范围和较长的时间内保持主晶相和结构的稳定, 850℃保温5h仍具有较高的透光率和极低的热膨胀系数, 性能具有很好的高温稳定性. 材料结构和性能的稳定性均源自钛锆复合形核剂较高的形核效率.     

IT-SOFC硼酸盐玻璃体系封接材料的制备与性能研究

基于B2O3-CaO-BaO-Al2O3-SiO2-La2O3体系制备了BCAS微晶玻璃封接材料,利用X射线衍射定性分析、差热分析、热膨胀仪分析等手段对其进行了表征.热膨胀系数(TEC)为10.41×10-6K-1,与电解质YSZ的热膨胀系数(10.2～10.8)×10-6K-1相接近.玻璃转变温度T8值为638℃,在768～852℃之间有一个强的放热峰.700℃时其主晶相为BaAl2 Si2 O8,800℃时以钡长石为析出的主晶相,900℃时析出单一的BaAl2Si2O8相及少量的BaSiO3相.封接材料的电阻随温度升高而减小,在650～800℃之间,阻抗值均在104～105Ω·cm2范围内,离子跃迁活化能为101.38 kJ/mol.其高温浸润性研究表明BCAS1微品玻璃封接材料可用于IT-SOFC对电解质YSZ的封接.     

B203-Li20玻璃的制备与性能的研究

采用高温熔融法制备了不同配比的硼锂二元体系玻璃，并利用UVPC、NMR和DSC等手段研究了不同锂含量对玻璃透过率、结构和热稳定性的影响。结果表明：在硼酸盐玻璃中引入少量Li2O，[B03]三面体会向[B04]四面体转变，使玻璃的网络结构有所加强，热稳定性提高，且玻璃中非桥氧数量降低，紫外透过率升高；当加入过量Li2O时...     

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     

B2O3对氟化物乳浊玻璃微结构和性能的影响

以钠钙硅系统玻璃为基体,以氟硅酸钠作为乳浊剂,利用传统熔融法制备乳浊玻璃。采用SEM、XRD和透过率测试分别对其微结构、析晶及乳浊性能进行表征,分析讨论了B2O3对乳浊玻璃微结构和性能的影响。研究结果表明:添加适量的B2O3可有效控制玻璃的析晶尺寸和析晶密度,有利于制备出微结构均匀、乳浊程度可控的乳浊玻璃,其主晶相为CaF2。B2O3的引入可降低玻璃的析晶倾向,且随着B2O3引入量的增加乳浊玻璃的晶粒密度、尺寸相应减小,乳浊程度下降。     

SiO2-MgO-Al2 O3-F系玻璃陶瓷的析晶

本文应用TEM,XRD和EDAX等技术,系统研究了SiO2-MgO-Al2O3-F系玻璃陶瓷的析晶过程.结果表明:在玻璃熔体的冷却过程中,由于弛豫作用而形成晶核,在随后的热处理过程中,中间相Mg2FB3和KAlSiO4以此核为中心析出;氟的存在促进了晶体的整体析出,而主晶相氟金云母在中间相的晶界处形核长大.     

复合形核剂对CaO-MgO-Al2O3-SiO2系玻璃陶瓷微观结构与力学性质的影响

以CaO、MgO、Al2O3和SiO2为主要原材料,采用熔融法制备添加复合形核剂Cr2O3和CaF2的CaO-MgO-Al2O3-SiO2 (CMAS)系玻璃陶瓷,借助X射线衍射(XRD)、扫描电子显微镜(SEM)和电子万能试验机等测试手段研究了复合形核剂对CMAS系玻璃陶瓷微观结构与力学性质的影响.结果表明:当试样中复合形核剂的组成变化时,其析出的主晶相类型不变,均为透辉石,主晶相的结构和含量发生变化,引起玻璃陶瓷力学性质的改变.     

烧结法制备煤矸石微晶玻璃及其烧结性能研究

以淮南矿区煤矸石为主要原料,采用烧结法制备了微晶玻璃,并研究了Na_2O含量对基础玻璃熔制温度、微晶玻璃晶化温度、物相组成和微观结构的影响及其对微晶玻璃体积密度、耐酸碱等物化性能的影响。结果表明,以淮南矿区煤矸石为主要原料可以制备出性能优良的微晶玻璃;并且随Na_2O含量从10%增至25%,玻璃熔制和晶化温度分别从1450℃降低到1300℃,950℃降低到700℃;微晶玻璃的主晶相由含铁镁橄榄石相转变为霞石相,最终转变为硅铝酸钠相,且微晶玻璃的结构均匀性不断提高;微晶玻璃的致密性先增加后降低,耐酸碱性良好,但Na_2O含量过多对微晶玻璃耐酸性不利。     

SiO2—MgO—Al2O3—F系玻璃陶瓷的析晶

本文应用TEM,XRD和EDAX等技术,系统研究了SiO2-MgO-Al2O3-F系玻璃陶瓷的析晶过程。结果表明：在玻璃熔体的冷却过程中,由于驰豫作用而形成晶核,在随后的热处理过程中,中间相Mg2FBO3和KAlSiO4以此核为中心析出,氟的存在促进了晶体的整体析出,而主晶相氟金云相在中间相的晶界处形核长大。     

凝胶玻璃网络稳定性与析晶分析

利用溶胶-凝胶方法制备了：BaO-TiO2-Al2O3-SiO2体系的凝胶玻璃，以及其不同晶相的玻璃陶瓷。利用X-衍射分析确定凝胶玻璃析出的晶相。利用晶格能对凝胶玻璃的稳定性与析晶特性进行了定性分析。在凝胶玻璃的析晶过程中，品格能大者优先析晶。BaO-TiO-Al2O3-SiO2体系凝胶玻璃析出离子晶体的晶格能由大到小依次为BaTiO3、Ba2TiSi2O8、BaAl2Si2O8，这与实验结果的析晶次序一致。     

Characterization of fluorine-doped silica glasses

Fluorine-doped silica glasses containing up to 2 wt% were prepared by the vapour-phaseaxial-deposition (VAD) sintering process. The characteristics of these glasses were investigated by Raman spectroscopy, vacuum-ultraviolet-ultraviolet (v.u.v-u.v.) spectroscopy, and viscosity measurements. From the Raman spectroscopic investigation, it has been shown that the Si-F bond structure in the fibres is the same as that in bulk glass and is not affected by codoped additives such as B₂O₃. From the u.v.-v.u.v, spectroscopic investigation, it has been shown that the absorption band at 7.6 eV in high-purity silica glass is removed with the addition of fluorine. This addition produces a silica glass with most excellent transparency in u.v. and v.u.v. regions. Also it was observed that the optimum addition is around 1 wt%. This fact proves that fluorine incorporation in glass prevents the generation of defects related to optical loss in fibres. From the viscosity study, it was found that the viscosity decreases with an increase of the fluorine content in glass and the activation energy also decreases with increasing fluorine content.     

Ab initio study of phase stability in doped TiO2

Ab initio density functional theory calculations of the relative stability of the anatase and rutile polymorphs of TiO₂ were carried out using all-electron atomic orbitals methods with local density approximation. The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F^? doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F?>?Si?>?Fe?>?Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies.     

Viscosity properties of sodium borophosphate glasses

The viscosity behavior of (1 − x)NaPO₃−xNa₂B₄O₇ glasses (x = 0.05-0.20) have been measured as a function of temperature using beam-bending and parallel-plate viscometry. The viscosity was found to shift to higher temperatures with increasing sodium borate content. The kinetic fragility parameter, m, estimated from the viscosity curve, decreases from 52 to 33 when x increases from 0.05 to 0.20 indicating that the glass network transforms from fragile to strong with the addition of Na₂B₄O₇. The decrease in fragility with increasing x is due to the progressive depolymerization of the phosphate network by the preferred four-coordinated boron atoms present in the low alkali borate glasses. As confirmed by Raman spectroscopy increasing alkali borate leads to enhanced B-O-P linkages realized with the accompanying transition from solely four-coordinated boron (in BO₄ units) to mixed BO₄/BO₃ structures. The glass viscosity characteristics of the investigated glasses were compared to those of P-SF67 and N-FK5 commercial glasses from SCHOTT. We showed that the dependence of the viscosity of P-SF67 was similar to the investigated glasses due to similar phosphate network organization confirmed by Raman spectroscopy, whereas N-FK5 exhibited a very different viscosity curve and fragility parameter due to its highly coordinated silicate network.     

Synthesis of SiC/Al Co-Continuous Composite by Spontaneous Melt Infiltration

1. IntroductionBecause of the adVantages such as ease of fabrication, low cost and near net shape forming capability,liquid metal infiltration has become a popular technique to fabricate metal matriX composites(MMCs)with high contellt reinforcements. In the process ofmelt infiltration, liquid metal penetrates into the continuous porosity of a packed ceramic filler or preform either by aPPlied positive or negative pressuresuch as in vacuum infiltration[1], pressurized liquldmetal infiltration…     

Influence of Cerium on Microstructure and Solidification of Eutectic Al–Si Piston Alloy

Thermal analysis has become very important in foundry because it aids in studying the effect of additives on eutectic growth temperature and assessing the quality of modifications. This research was performed to investigate the influence of the addition of Ce (0.1–1.0 wt.%) on the eutectic Al–Si–Cu–Mg alloy characteristics of solidification. Field emission scanning electron microscopy (FESEM) and optical microscopy were employed to characterize the alloy microstructure. The main phases studied were the Al–Cu (Al₂Cu) and Al–Si phases. The addition of Ce decreased the nucleation and growth temperatures and acted as a refiner for the alloy. The larger amounts of Ce significantly impacted the Si structure: the average Si particle size decreased as the Ce concentration was increased, which led to a finer grain structure. The Ce formed intermetallic compounds with the alloyed elements that had plate- or needle-like structures and that interrupted the modification of Si. The solidification parameters, including the growth and nucleation temperatures, increased with increasing change in the morphology of the Al–Cu phase that were caused by Ce addition.     

Si对SiC－Al系统浸润行为的影响

用液滴技术（Ｔｈｅ　Ｓｅｓｓｉｌｅ　Ｄｒｏｐ　Ｔｅｃｈｎｉｑｕｅ）、ＳＥＭ、ＥＤＳ等研究了Ｓｉ对ＳｉＣ－Ａｌ系统浸润行为的影响，结果表明，在较低温度下，Ｓｉ在熔融Ａｌ合金中的含量不明显影响Ａｌ对ＳｉＣ的浸润行为，然而，在高温下ＳｉＣ和Ａｌ的接触角θ值随时间而减小的速率随Ｓｉ含量的增加而增大；ＳｉＣ－Ａｌ系统从非浸润到浸润的转变温度随Ｓｉ含量的增加而降低；Ｓｉ的添加引起Ａｌ合金在ＳｉＣ表面扩展和向ＳｉＣ基体渗透，而且扩展和渗透的程度随Ｓｉ含量增加而增大。说明在Ａｌ合金中添加Ｓｉ可促进对ＳｉＣ的浸润。本研究还证实了基体参加反应可增强金属Ａｌ对ＳｉＣ陶瓷的浸润能力。     

Microstructures and properties of high-fraction Sip–6061Al composites fabricated by pressureless sintering

Pre-treated Si powder (Sip) and 6061Al powder were used to fabricate high-fraction Sip/6061Al composites via pressureless sintering, and the effects of the Sip content and the sintering temperature on the microstructures and properties of the composites were studied. The results show that in the composites, there exist MgAl₂O₄ nanocrystalline particles, and the Si phase varied from a discontinuous particulate state to a semi-continuous skeleton state as the Si content increased from 30 to 50?wt-%. Densities, bending strengths, hardness, and thermal conductivities of the composites all increased initially and then decreased with the sintering temperature. The 680°C sintered 30?wt-% Sip/6061Al composites and the 700°C sintered 50?wt-% Sip/6061Al composites have the optimal mechanical and thermophysical properties.     

Preliminary study on calcium aluminosilicate glass as a potential host matrix for radioactive 90Sr--an approach based on natural analogue study

Given the environmental-, safety- and security risks associated with sealed radioactive sources it is important to identify suitable host matrices for (90)Sr that is used for various peaceful applications. As SrO promotes phase separation within borosilicate melt, aluminosilicate bulk compositions belonging to anorthite-wollastonite-gehlenite stability field are studied in this work. Tests for their homogeneity, microstructural characteristics and resistance to phase separation narrowed the choice down to the composition CAS11 (CaO=35 wt%, Al(2)O(3)=20 wt%, SiO(2)=45 wt%). We find that up to 30 wt% SrO can be loaded in this glass without phase separation (into Ca, Sr-rich and Sr-poor, Si-rich domains). Leaching behaviour of the glasses differs depending on the content and distribution of Sr. In general, the elemental leach rates determined from conventional PCT experimental procedure yield values better than 10(-7)gcm(-2)day(-1) for both CAS11 base glass as well as SrO doped glass. It was noted that leach rates calculated on the basis of Ca(2+) and Sr(2+) were of the same order and bit higher compared to those calculated on the basis of Si(4+) and Al(3+). During accelerated leaching tests, zeolite and zeolite+epidote were found to have developed on CAS11 base glass and SrO doped glasses respectively. The Sr bulk diffusion coefficients is found to vary from ～ 10(-15) to 10(-13)cm(2)/s at temperature intervals as high as 725-850°C. Based on the experimental observations, it is suggested that CAS11 glass can be used as host matrix of (90)Sr for various applications of radioactive Sr-pencils.     

Effects of MO (M = Mg, Ca, Ba) on crystallization and flexural strength of semi-transparent lithium disilicate glass-ceramics

In this study, semitransparent lithium disilicate glass-ceramics in the Li₂O-K₂O-Al₂O₃-Y₂O₃-La₂O₃-SiO₂ system was investigated by incorporation of P₂O₅ as nucleation agent and alkaline earth oxides as additive. The influence of alkaline earth oxides on the structure of glasses network, crystalline phases, microstructure and mechanical properties were investigated by means of Raman spectra, differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The mechanical strength was measured corresponding to norm ISO 6872. The Raman spectra predominantly showed that small additions of alkaline earth oxides not only form asymmetrical vibrations of the M-Si-O bonds, but also enhance the intensities of symmetrical vibrations of the P-O bonds, making the glass network more stable. And the small additions of CaO or BaO has more influence on the crystallization behaviour, crystalline phase, microstructure and mechanical properties of the glass-ceramics than the addition of MgO. The additions of alkaline earth oxides enhanced the first exothermic peak temperature but decreased the flexural strength of lithium disilicate glass-ceramics.     

Raman microprobe analysis of preforms and optical fibers

The concentration profile of various dopants (germanium, phosphorus, and fluorine) in preforms and optical fibers has been obtained with a Raman microprobe. A 2-microm spatial resolution was achieved. In the case of germanium and phosphorus, the results agree quite well with those obtained with an electron microprobe. Raman spectroscopy easily detects fluorine. From measurements of various F-doped samples, diffusion of fluorine in undoped and doped silica is suggested.