Effects of Impurities and Manufacturing Methods on the Devitrification of Silica Fibers

Devitrification resistance is one of the most important properties of silica fibers. The devitrification behavior of silica fibers made by the acid leaching method, the sol-gel method, and the high-purity silica fusing method, and the effects of small amounts of Al₂O₃ and B₂O₃, were studied by using X-ray diffraction. The results indicated that the devitrification tendency of silica fibers made by the high-purity silica fusing method is apparently greater than that of the fibers made by the other two methods. A small amount of B₂O₃ has the effect of retarding devitrification, while Al₂O₃ promotes devitrification of the fibers. The combined effect of Al₂O₃ and B₂O₃ is to strongly enhance the devitrification of silica fibers. The results are discussed in the context of structural analysis.     

Thermal, Dielectric, and Optical Properties of Neodymium Borosilicate Glasses for Thick Films

Because of their thermal, dielectric, and optical properties, new glass compositions and thick-filmed transparent dielectrics containing neodymium oxide (Nd₂O₃) were studied as a source of purer images in plasma display panels. In the present study, PbO–B₂O₃–SiO₂ and PbO–B₂O₃–SiO₂–ZnO–Al₂O₃ were used as starting glass compositions, to which up to 25 wt% of Nd₂O₃ then was added. Increased amounts of Nd₂O₃ increased the glass transition temperature and dielectric constant of the bulk glasses and decreased the coefficient of thermal expansion. The fired thick films (around 30 μm) allowed selectively visible light to penetrate and showed deep absorption properties at 585 nm that were related to an extraneous gas from neon discharge.     

Water Absorption and Mechanical Properties of Silica Porous Glasses

We have estimated the mechanical properties of silica porous glasses (SPG) using special two-layered structures consisting of a SPG layer on a solid glass substrate. These structures turned curved after keeping them in moist atmosphere. The linear dimensions of dry free-standing SPG wafers with the same pore size distribution increased significantly (up to 1.5%) after water vapour soaking. Bending angles of two-layered structures and the values of linear expansions were used to estimate SPG elastic constants and the mechanical stresses arising in porous glasses as the result of water absorption.     

Effect of Nitriding on Electrolysis and Devitrification of High-Silica Glasses

Devitrification occurs near the cathode when reconstructed high-silica glasses and fused quartz undergo electrolysis at 900°C. The crystalline phase is cristobalite and results from a concentration of alkali ions. Subsequent and more superficial crystallization around the alkali-rich spot is caused by interaction of the glass with alkali vapors coming from the central spot. The degree of devitrification increases with the alkali content of the glass. Devitrification at constant alkali level can be reduced in reconstructed glasses by nitriding the porous glass with ammonia at a high temperature before consolidation. Devitrification decreases and viscosity and electrical resistivity increase as the nitriding temperature increases 500° to 1000°C. Nitrided glasses are more resistant to electrolytically induced devitrification than is fused quartz.     

Al2O3对电子玻璃高温黏度及析晶性能的影响

研究了不同含量的Al2O3对电子玻璃高温黏度和析晶性能的影响。结果表明,随着氧化铝含量的增加,电子玻璃的高温黏度、成型温度均降低,但析晶黏度减小,与成型的砖尖黏度差值减小,不利于溢流下拉成型。     

Effect of Trace Impurities on Devitrification of Vitreous Silica

Devitrification rates were measured for a series of vitreous silica glasses doped with trace levels of alkali metal oxide (1.6 to 57.8 molar ppm) and aluminum oxide (22 to 73.3 molar ppm). The devitrification rate varies inversely with the molar ratio of aluminum oxide to alkali metal oxide, a direct consequence of the effect of these trace impurities on viscosity .     

共沉淀法合成掺钕钇铝石榴石纳米粉体的研究

掺钕钇铝石榴石(Nd:YAG)多晶透明陶瓷具有良好的化学稳定性、光学性能和耐高温性能,是一种很有前途的激光工作物质.以Al(NO3)·9H2O,Y2O3,Nd2O3,(NH4)2SO4和NH4HCO3为原料,正硅酸乙酯为添加剂,采用共沉淀法制备出分散均匀、团聚程度轻、YAG立方晶相的Nd:YAG纳米前驱体粉末,采用TG/DTA,XRD,FT-IR和TEM等测试手段对Nd:YAG陶瓷材料进行表征.研究结果表明:前驱体粉末在800℃时为无定型态,当温度达到900℃时析出大量的晶体YAlO3(YAP)和少量的YAlO3(YAP),当温度达到1100℃时就全部转化为立方晶相;前驱体纳米粉末中存在轻微的团聚,主要是在1100℃高温时晶粒发生了生长,连接在一起,但是作为团聚整体而言,颗粒分布比较均匀.     

高门尼稀土顺丁橡胶在白炭黑体系中的性能研究

研究高门尼稀土顺丁橡胶(NdBR)/天然橡胶(NR)并用胶在白炭黑体系中的混炼工艺及性能。结果表明,两种高门尼NdBR/NR并用后均有较高的耐磨性能、较好的滚动阻力性能和较佳的动态力学性能。其中NdBR-1_#的动态力学性能更佳,NdBR-2_#的优势在于能进一步提高耐裂口增长性能。为了改善NdBR在白炭黑体系中的工艺性能,有必要在配方和混炼工艺上进行优化调整。     

Effect of Magnesium Oxide on Faceted Vicinal (0001) Surface of Aluminum Oxide

Atomic force microscopy has been used to observe the vicinal (0001) surface of Al₂O₃. The surface develops a hill-and-valley structure when heat-treated in air and becomes defaceted and therefore atomically rough when heat-treated in an MgO atmosphere at 1600°C. The results are consistent with the previously observed polyhedral equilibrium shape of Al₂O₃ crystal and the surface roughening effect of MgO.     

Zno对E-CR玻璃析晶及Redox平衡的影响

通过向CaO-MgO-Al203-SiO2四元系统玻璃中引入ZnO,采用梯温炉测定了玻璃的析晶上限温度,在偏光显微镜下观察了析出晶体的形态,同时测定了玻璃中Fe2 /Fe3 比值.结果发现,ZnO的引入可以降低玻璃液相温度,降低玻璃析晶倾向,所析出晶体种类由透辉石和硅灰石共存变为以硅灰石为主,没有钙长石出现.由于ZnO的引入增大了玻璃的碱度,从而使铁更倾向于以高价的形式存在.     

含钐稀土硼硅酸盐玻璃形成能力

通过玻璃形成区实验探索了含钐稀土硼硅酸盐玻璃的形成区范围,研究了Sm2O3含量对稀土玻璃形成区的影响和相应的玻璃形成区图,以及Al2O3含量对含钐稀土硼硅酸盐玻璃形成区的影响. 结果表明,当Sm2O3含量从10%增加到30%时,玻璃形成区有所增大,但当Sm2O3含量大于30%时玻璃形成区减小,当Al2O3含量为20%~25%时有较大的稀土玻璃形成区. 同时利用热分析结果所得到的玻璃析晶倾向参数b值,讨论了含钐稀土硼硅酸盐玻璃的形成能力,其中当Sm2O3含量为20%, Al2O3含量为25%时,b=0.8~0.85,这时玻璃形成能力较大.     

Effect of Nd2O3 Doping on the Densification and Abnormal Grain Growth Behavior of High-Purity Alumina

The densification behavior and microstructural development of high-purity Al₂O₃ doped with different levels of Nd₂O₃ were investigated. Dopant levels ranged from 100–1000 ppm (Nd/Al atomic ratio). The densification behavior of the doped powders was studied using constant heating rate dilatometry. It was found that neodymium additions inhibited densification, with a corresponding increase in the apparent activation energy. The level of grain-boundary segregation was studied using high-resolution analytical electron microscopy. At dilute concentrations, the degree of neodymium grain-boundary excess was found to be consistent with a simple geometrical model relating this quantity to the overall dopant concentration and average grain size. For certain combinations of dopant level and heat treatment, supersaturation of the grain boundaries was observed, which was found to correlate with the onset of abnormal grain growth. Possible explanations for this behavior are discussed.     

稀土钕在釉中的变色机理

稀土钕的电子结构为[Xo]4f^3,其中3个4f电子可在7个4f轨道上任意分布,并产生多种光谱项和能级。本文根据稀土钕独特多变的光谱特征及物理化学特征,阐述了其在釉中的变色原因及机理,希望能对变色釉的开发和理论研究有所帮助。     

Effect of Silica Nanoparticle Size on the Stability of Alumina/Silica Suspensions

The influence of the addition of silica particles (5, 15, 25, and 300 nm) on the zeta potential and viscosity of aqueous alumina slurries (250 nm particles) was investigated in a pH range where the surface charge was positive for alumina and negative for silica. For slurries formulated with the smaller silica particles, the isoelectric point shifted from pH 9.0 to pH ∼3 (depending on the particle size of the silica) with increasing volume fraction of silica particles. At pH 9, the original isoelectric point for the alumina alone, these mixed slurries had a shear-rate-independent, low viscosity (Newtonian behavior). Both of these results show that the smaller (≤25 nm) silica particles adsorb to the surface of alumina. The fraction of silica adsorbed to the alumina surface was dependent on the size of the silica particles, and was consistent with surface coverage calculations based on the effect of surface curvature on the limits of dense random parking. The larger silica particles (300 nm) could not physically cover the surface of the alumina particles, and simply formed a mixed, attractive particle network that exhibited a much higher viscosity with non-Newtonian (viz., shear rate thinning) behavior.     

添加剂对铅硅酸盐低熔点玻璃热性能的影响

采用常规玻璃熔融退火工艺制备了两组铅硅酸盐玻璃试样,玻璃组成为(物质的量含量,下同):(55-x)PbO-(10+x)B2O3-30SiO2-5ZnO(x=0,5,10,15)和(55-x)PbO-10B2O3-30SiO2-5ZnO-xSB2O3(x=5,10,15),以及与两组参照的传统铅硅酸盐玻璃55PbO-5Al2O3-10B2O3-30SiO2.利用热膨胀仪观察氧化物添加剂对玻璃转变温度范围△T(T1-Tg)的影响.实验结果表明,随着氧化硼加入量的不断提高,玻璃的转变温度(Tg)与软化温度(Tf)随之提高,而△T先减小后增大,即出现所谓的硼反常现象.当添加的氧化锑量在5%～10%(物质的量含量,下同)范围时,与参照样品相比,玻璃的软化温度(Tf)基本保持不变而转变温度(Tg)则提高10℃以上.当添加的氧化锑量达到15%时,玻璃的转变温度(Tg)与软化温度(Tf)均显著下降,但△T基本保持不变.     

Influences of Zirconia and Silicon Nucleating Agents on the Devitrification of Li2O · Al2O3· 6SiO2 Glasses

The effects of Si and ZrO₂ dopants on the crystallization and phase transformation process in Li₂O · Al₂O₃· 6SiO₂ glasses were investigated using differential thermal analysis, X-ray powder diffractometry (XRD), and high-resolution transmission electron microscopy (TEM) interactively. Phase separation was observed in the studied glasses prior to substantial crystallization. Elemental Si (1 mol%) significantly aided in glass devitrification. Dropletlike phase-separated regions in the as-quenched or heat-treated glass devitrified at ∼760°C, which in turn provided sites for the heterogeneous nucleation and growth of β-quartz(ss) (solid solution), which transformed to β-spodumene(ss) at higher temperature. Low-temperature surface crystallization in these glasses occurred as low as 760°C. ZrO₂ has limited solubility in this glass system. Small ZrO₂ crystallites (·5 nm) in the as-quenched glass acted as sites for the heterogeneous nucleation and subsequent growth of large (<5 μm) β-quartz(ss) crystals in glasses containing 1.0 mol% or more ZrO₂. The transformation from β-quartz(ss) to β-spodumene(ss) was increasingly inhibited with ZrO₂ additions. The nucleating efficiency of Si was significantly greater than that of ZrO₂ in this glass system.     

Physical Properties and Structure of Silica-Alumina-Europium Oxide Glasses

SiO₂–Al₂O3–Eu₂O₃ glasses were prepared for the composition 50siO₂·(50 – x )Al₂O_3·xEu₂O₃, and their density, sound velocity, and elastic modulus were measured. The chemical shift of the AIK a band emission spectra and the isomer shift of ¹⁵¹Eu by Mössbauer effect were obtained to determine the coordination states of Al³⁺ and Eu³⁺ ions in these glasses. It was found that the coordination number of Eu³⁺ ions was 12 and that the average coordination number of A1³⁺ ions was almost 5 in these glasses. By introducing Eu₂O₃, the packing of constituent ions was strongly enhanced and the elastic modulus increased in this system. The compositional dependence of the molar volume and elastic modulus were explained by these states of high coordination number for Eu³⁺ and low coordination number for Al³⁺ ions compared with those in the corresponding M₂O₃ crystals.     

硅硼比对镁铝硼硅酸盐玻璃结构、化学稳定性和介电性能的影响

采用熔融冷却的方法制备了镁铝硼硅玻璃。研究了SiO_2取代B_2O_3对玻璃结构、化学稳定性和介电性能的影响。傅里叶变换红外光谱(FTIR)结果表明,随着SiO_2/B_2O_3比的增大,玻璃网络结构中桥氧增多,非桥氧减少。镁铝硼硅酸盐玻璃的耐酸侵蚀能力随SiO_2/B_2O_3比的增大而增强,而耐碱侵蚀的能力则变差。随SiO_2/B_2O_3比的增大介电常数逐渐增大。当SiO_2/B_2O_3摩尔比为2.08时,玻璃具有最小的介电常数值4.9。SiO_2/B_2O_3比为3.11时,玻璃的介电损耗出现最小值。     

钕及其配合物对重金属铅污染植物的缓解作用

以盆栽法研究了 Pb2 +对绿豆、小白菜和菠菜的伤害以及 Nd3+的配合物 (钕 -苯氧乙酸 - 8-羟基喹啉 )对Pb2 + 伤害的缓解效应。结果表明 ,5 0 0 mg· L的 Pb Ac2 严重抑制绿豆、小白菜和菠菜的生长与代谢 ,叶面喷施 Nd3+及其配合物一次 ,能缓解 Pb2 +造成的伤害     

从粉煤灰中提取氧化铝工艺的研究进展

就目前国内外由粉煤灰制备氧化铝(Al2O3)的方法分别从各制备工艺的特点、优点及其存在的问题等方面进行评述,并对其研究热点及其发展趋势进行了阐述.