Coordination State of Boron and Aluminum in Low-Alkali Aluminoborosilicate Glasses

The structure of aluminoborosilicate glasses is considered. It is found that the coordination states of boron and aluminum in glasses may vary depending on the composition, which has a perceptible effect on the properties of glaze glasses. Significant discrepancies were found between the experimental and calculated TCLE values of such glasses, which is due to a changed content of four-coordination boron and the emergence of six-coordination aluminum. Considering these data, it is possible to predict the physicochemical properties of glaze glasses.     

Recrystallization of Cerium Oxide in Porcelain Enamels

The effect of cerium oxide incorporated as the principal opacifying agent in the frit batch on the properties of white cover-coat porcelain enamels was studied. The effect of several variables on the opacity of the enamel was investigated as a function of firing temperature. Variables studied included (a) the amount of cerium oxide added, (b) the manner in which cerium oxide was incorporated into the enamel, i.e., mill addition, frit addition, or combination of both, (c) composition of the base glass, (d) weight of application, and (e) type of mill addition. Porcelain enamels were produced which had good acid resistance, high gloss, and a reflectance of 80% or more. Mill-added cerium oxide seemed to be less effective than that which was incorporated in the porcelain enamel as a component of the frit. The spectrophotometric analysis indicated good color stability of cerium oxide enamels.     

Boron Coordination in Rapidly Cooled and in Annealed Aluminum Borosilicate Glass Fibers

The fraction of four-coordinated boron was observed to increase from 10% in a rapidly cooled aluminum borosilicate glass fiber to 16% in the same fiber after it was annealed; the refractive index also increased. The index of the annealed fiber agreed with that of the bulk glass. Crystallization was not observed in the annealed fiber. It is concluded that boron coordination is temperature dependent and associated with structural relaxation.     

Physical Effects of Auxiliary Fluxes in Aluminum Enamels

Auxiliary flux additives to milled enamels for aluminum must serve ( a ) as an inhibitor or alkali "buffer" in enamel-metal reactions and (b) as a flux to aid rapid enamel fusion during the early stages of firing. Raw and fritted mixtures were varied in two milled aluminum enamels. The effects of these mixtures on the physical properties, drying and firing characteristics, and water spalling resistance are tabulated. Results indicate that the proper balance between alkali, B₂O₃, and SiO₂ functions best to meet these requirements.     

硼酐碳热法合成碳化硼的研究

用Ｘ－射线衍射分析方法，研究了温度及反应物中Ｂ２Ｏ３摩尔量对碳热合成Ｂ４Ｃ粉末中残留含量的影响，同时探讨其反应机理，实验表明，碳化硼粉末中的残留碳含量不仅取决于反应而且与Ｂ２Ｏ３的摩尔量有关。在碳管炉内合成Ｂ４Ｃ的反应以液固反应为主，在反应时间一定条件下Ｂ２Ｏ３摩尔量为５－６ｍｏｌ的反应物料，在１６５０℃Ａｒ气氛中反应，其残留碳含量最低，其相对量为１０％左右。     

Effect of Initial Oxide Layer on Ignition and Combustion of Boron Powder

Only few data exist for experimental studies on ignition and combustion of boron particles with initial oxide thickness. The oxidation, ignition and combustion characteristics including the onset temperatures, weight gain, apparent activation energy, emission spectra during combustion, and ignition delay time of crystalline boron powders with different initial oxide thickness (x₀) were studied by a laser ignition and thermogravimetric (TG) analyses. Simulations of the kinetics of oxide layer during boron ignition were conducted using a common model. The results indicated that the onset temperature was approximately 775 °C, independent of x₀. The total weight gain decreased with increasing x_0, whereas the weight gain at 775 °C did not change. The apparent activation energy was found to be insensitive to x₀ and had a constant value of about 210 kJ mol⁻¹. The intensity of the emission spectra gradually decreased while the ignition delay time increased with increasing x₀. Numerical simulation showed that the removal rate of oxide layer enhanced with increasing x₀. The experimental results revealed that the oxidation of boron powder was no diffusion‐controlled process at low temperatures. But the diffusion of oxygen could become important to the oxidation reaction at high temperatures     

葡萄糖对多孔阳极氧化铝模板的影响

选用葡萄糖作为添加剂,高纯铝在10℃,40 V直流电压条件下,利用两步阳极氧化法在0.3 mol/L草酸溶液中加入不同浓度的葡萄糖制备多孔阳极氧化铝模板,并且通过场发射扫描电镜(FESEM)、X射线衍射(XRD)对氧化膜的微观形貌、晶体结构进行表征,从而研究不同浓度的葡萄糖对氧化膜的影响。结果表明:葡萄糖的加入不会改变阳极氧化过程;不同浓度的葡萄糖均能使氧化膜致密,孔径变小,但随着葡萄糖浓度的增加,有序性会遭到破坏,在添加不同葡萄糖浓度时,3 g/L的葡萄糖添加剂会得到孔径更小,一定有序性的氧化铝膜;XRD表明葡萄糖的加入并不会影响氧化铝膜的非晶态结构。     

Grain-Size Effect on Compressive Creep of Silicon-Carbide-Whisker-Reinforced Aluminum Oxide

The steady-state compressive creep of Al₂O₃ with 10 vol% SiC whiskers having grain sizes of 1.2, 2.3, and 4.0 μm has been measured at 1400°C in argon. The creep rate is related to the free volume within the whisker network, not the nominal grain size. The results are consistent with diffusional-controlled creep with different contributions from grain-boundary sliding. Under low stresses, only Liftshitz sliding is possible and the diffusional process controls deformation, while at stresses over a threshold, Rachinger sliding is the mechanism controlling deformation. The evolution between Liftshitz and Rachinger sliding is marked by a significant increase in the value of the stress exponent.     

Effect of Dopants on the Defect Structure of Single-Crystal Aluminum Oxide

Density and lattice parameter changes induced by dopants were studied in Czochralski rubies containing from 0.054 to 0.160 wt% Cr₂O₃, in Czochralski sapphires containing from 0.083 to 0.120 wt% TiO₂, and in verneuil crystals grown from powders containing 250 to 1000 ppm Ca, Mg, Si, and V. Densities were determined within at least ∼0.005% using a hydrostatic weighing technique; lattice parameter shifts were measured within a maximum of 0.25% using a step-scanning goniometer technique. Some crystals which appeared to be clear, transparent, and single-phase contained fine particles of a second phase. It is concluded that Si⁴⁺ and Ti⁴⁺ ions enter solution with the formation of cation vacancies to maintain charge neutrality, that verneuil crystals contain vanadium as V³⁺, that the solid solubility of Ca²⁺ is low (<340 ppm), and that MgO decomposes under verneuil growth conditions, resulting in formation of a second phase.     

Effect Of Grain Boundaries on Diffusion-Controlled Processes in Aluminum Oxide

Oxygen ion diffusion coefficients in single-crystal Al₂O₃ are several orders of magnitude less than alminum ion diffusion coefficients in polycrystalline Al₂O₃. In polycrystalline Al₂O₃, oxygen ion diffusion is enhanced by the presence of grain boundaries as in the chloride ion diffusion in the alkali halides. Creep and sintering of polycrystalline Al₂O₃ occur at a faster rate than is possible through control by lattice diffusion of oxygen; the rates are in fair quantitative agreement with cation diffusion. It is tentatively concluded that enhanced oxygen diffusion in regions adjacent to boundaries allows aluminum ion bulk diffusion to be rate controlling for these processes. The electrical conductivity in Al₂O₃ is too high to be related to either anion or cation diffusion and is predominantly electronic.     

Effect of Yttrium and Lanthanum on the Tensile Creep Behavior of Aluminum Oxide

The tensile creep behavior of two rare-earth dopant systems, lanthanum- and yttrium-doped alumina, are compared and contrasted in order to better understand the role of oversized, isovalent cation dopants in determining creep behavior. It was found that, despite some microstructural differences, these systems displayed qualitatively a similar improvement in creep resistance, supporting the hypothesis that creep is strongly influenced by segregation. Differences in primary creep behavior and activation energy for steady-state creep were, however, observed for these systems. Given these results, it is expected that creep behavior can be further optimized by adjusting the dopant level and by controlling the microstructure.     

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.     

Augmentation of Aluminum and Boron Ignition

Combustion, Explosion, and Shock Waves - Effect of K2CO3 and KCl additives on the process of high-temperature oxidation and ignition of conglomerates of powdered boron and aluminum particles and on...     

Effects of Zirconium Oxide on the Reaction Bonding of Aluminum Oxide

In the reaction-bonded aluminum oxide (RBAO) process, attrition-milled Al/Al₂O₃ powder compacts are reacted in air to form Al₂O₃-based ceramics. Typically, ZrO₂ powder is added to control the final microstructure and properties, resulting in fine-grained, high-strength materials. In this study, the effects of ZrO₂ on the reactivity of RBAO samples were examined using thermogravimetric analysis, X-ray diffractometry, and other techniques. Previously, it was shown that a self-propagating reaction could occur during firing of RBAO in air. This reaction was attributed solely to the fast and highly exothermic oxidation of the aluminum on the surface of the sample, but the results of the current study show that it is related to a reaction between aluminum and ZrO₂, forming Al₂O₃ and Al₃Zr. As a consequence, a new reaction sequence for RBAO consistent with these observations has been proposed.     

釉料组成对骨质瓷热稳定性及抗折强度的影响

骨质瓷作为高级日用细瓷之一,以其高白度、高透光度和高强度等优良性能在国内外市场深受青睐。但骨质瓷的热稳定性远不如传统的K2O-Al2O3-SiO2系统瓷及滑石质日用细瓷。通常日用细瓷对热稳定性要求是制品水中交换温差达到200℃以上;而目前我国实际生产的骨质瓷制品水中交换温差多在140℃以下,即便是优质的骨质瓷水中交换的温差也只是达到160℃。国内外对提高骨质瓷热稳定性进行了大量的研究,笔者在此基础上探讨釉料组成对骨质瓷热稳定性的影响。笔者就釉料的作用与特点进行了简单介绍,阐述了釉料配置应遵循的原则以及各氧化物在釉料中的作用。其着重计算了基础釉料配方以及调整组成后的各组配方的膨胀系数,及其与坯体膨胀系数的差值,介绍了釉浆制备及施釉工艺;着重叙述了各组配方烧成曲线及温度的确定,以及测定各组烧成试样的热稳定性、白度、抗折强度及坯釉适应性等性能的实验过程和实验结果,并进行简要的分析。最后,通过总实验结果的分析与讨论,得出结论,即通过改变釉料组成提高热稳定性是可行的。     

含硼固体推进剂燃烧残渣中三氧化二硼和碳含量测定及燃烧机理研究

为了研究含硼富燃料固体推进剂燃烧机理,对3种配方的不同批次含硼富燃料固体推进剂在不同压强的燃速进行了测试,利用化学分析法对其燃烧残渣中B2O3和C含量也进行了测定。结果表明,硼粒子表面的B2O3延缓了硼粒子的进一步燃烧,因此残渣中B2O3含量较低;随着氮气压强增高,残渣中B2O3含量降低,而C含量、B2O3与C总含量升高;随着推进剂配方中镁含量增高,残渣中B2O3含量降低,C含量先升后降,B2O3和C总含量则降低。