Influence of additives of Al2O3 on properties of aluminum nitride-based ceramic

The properties of AlN-based materials with additives of 5–50 mass% Al₂O₃ are investigated. It is established that addition of Al₂O₃ to AlN increases the oxidation resistance of the materials as well as their mechanical strength and thermal resistance while preserving their electroinsulating properties and corrosion resistance to molten metals. AlN-Al₂O₃ composites may be used in high-temperature technology as refractory materials, electrical insulators, as well as radio-transparent materials.     

Al2O3对烧结矿RDI的影响规律

采用断裂韧性的方法并结合电子显微分析技术,研究了Ａｌ２Ｏ３对烧结矿的低温还原粉化率（ＲＤＩ）的影响规律。研究结果表明：Ａｌ２Ｏ３主要分布在烧结矿的玻璃相中,并以硅铝酸铁和硅铝酸钙的形式存在;烧结矿中Ａｌ２Ｏ３的增加导致玻璃相的断裂韧性降低。作认为,玻璃相断裂韧性的降低是引起烧结矿的ＲＤＩ增大的主要原因,并确定了烧结矿综合断裂韧性与ＲＤＩ良好的对应关系。     

Dissolution of alumina in molten cryolite

Alumina powder dissolves rapidly in molten cryolite,i.e. in 4 to 8 seconds, provided that the particles are effectively dispersed in the melt. At alumina contents well below saturation the time of dissolution is independent of the alumina concentration, and it is not appreciably affected by additions of NaF, A1F₃, or CaF₂. Coarse grains dissolve more slowly than fine grains and α-Al₂O₃ (floury) dissolves more slowly than γ-Al₂O₃ (sandy). The rate-controlling step appears to be a slow chemical reaction. Bottom sludge in industrial cells contains about 40 pct A1₂O₃. This material has a higher α/γ-ratio than the alumina being fed to the cells, while the grain size is smaller due to disintegration of aggregates. The time of dissolution is identical to that of any other alumina with the same α/γ-ratio.     

Influence of MgO addition on the properties of porous Al2O3 refractory containing TiO2 and Al2O3 in the matrix

The properties of porous Al₂O₃ refractory containing TiO₂/Al₂O₃ with a molar ratio of 0.96 in the matrix were studied with different amounts of MgO additives. Bright glossy areas were observed around and inside the Al₂O₃ particles. These were determined as Al₂O₃ · TiO₂ from the results of X-ray diffraction and EPMA analyses. The addition of MgO generated the dark glossy areas the compound of which was Na₂O · 4 MgO · 15 Al₂O₃. But for high MgO contents, Al₂O₃ · TiO₂, MgO · Al₂O₃ and Na₂O · 4 MgO · 15 Al₂O₃ coexisted in the dark glossy areas. These products prevented TiO₂ from invading the grain boundary, consequently grain-boundary cracks in the particles decreased and the physical properties, especially compressive and bending strength, were extremely improved. Thermal shock resistance was also improved by the rise of strength and fracture energy due to the addition of MgO. Corrosion resistance increased as the content of MgO increased. This was considered to be generated by the occlusion of FeO into MgO. Particularly, the fact that the penetration thickness decreased by the addition of MgO will contribute not only to the stable operation in actual use but also eliminating the procedure during which the porous plugs are cleaned by O₂ after every usage.     

The reduction of Al2O3 to aluminum in a plasma

The reduction of aluminum oxide to aluminum in radio frequency generated plasmas was studied experimentally. Argon with hydrogen, carbon dioxide, and methane were used as plasma gases. Product was collected from the reactor walls and/or cold-finger collectors. Gaseous quenching was also investigated, using hydrogen, methane, and carbon dioxide. Conversions up to 50 pct were determined using wet chemistry. Optical and X-ray methods confirmed the species present during and after reaction. The effects of particle size, flow rates, and power input were determined. Solutions of energy, momentum, and mass balances yield a qualitative explanation of the process. Vaporization rate controls. Formerly at the University of Michigan, Ann Arbor, Mich. Arbor, Mich.     

Solutions of iron oxides in molten cryolite

All the iron oxides (FeO, Fe₃O₄, Fe₂O₃, and FeAl₂O₄) dissolve in cryolite-alumina melts to give solutions containing both Fe(II) and Fe(III). The factor controlling the Fe(II)/Fe(III) ratio is the oxygen pressure, and experimental results are interpreted on that basis. Predictions are made of the variation of solubility with oxygen pressure, and the standard potential of the Fe²⁺/Fe³⁺ redox couple is calculated. The anode and anode gas of an industrial Hall-Heroult cell appear to be insufficiently oxidizing to cause significant conversion of Fe(II) to Fe(III). An anomaly in the liquidus diagrams for FeF₂ – Na₃AlF₆ and FeO – Na₃AlF₆ is accounted for in terms of solid solution of FeF₂ in cryolite. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee.     

Na3AlF6-Al2O3熔盐中铝溶解度的测定

研究了铝在Na3AlF6-Al2O3熔盐中溶解度的测定方法。采用氟化钠与试样在高温下熔融,熔融物溶解水后加入硼酸-氢氧化钠溶液,过滤沉淀将氧化 铝除去,取其中一部分溶液在pH5.5～6.0 的条件下,加入过量的EDTA标准溶液,加热煮沸使之与铝完全络合,以二甲酚橙作指示剂,用锌标准溶液 滴定过量的EDTA ,从而得到Na3AlF6-Al2O3熔盐中铝离子的含量,再采用氟离子选择电极测定另一部分溶液中氟含量,计算得到冰晶石中铝离子含量 ,采用减氟法得到铝在Na3AlF6-Al2O33体系中溶解量。这个值是用来表征铝在电解质熔体中的溶解损失能力的大小,对生产工艺很重要。     

Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis

Temperatures for primary crystallization of Na₃AlF₆ in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na₃AlF₆ was derived: $$\begin{gathered} t/(^\circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - \frac{{3.45[CaF_2 ]}}{{1 + 0.0173[CaF_2 ]}} \hfill \\ + 0.124[CaF_2 ] \cdot [AlF_3 ] - 0.00542([CaF_2 ] \cdot [AlF_3 ])^{1.5} \hfill \\ - \frac{{7.93[Al_2 O_3 ]}}{{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \cdot [Al_2 O_3 ]}} \hfill \\ - \frac{{8.90[LiF]}}{{1 + 0.0047[LiF] + 0.0010[AlF3]^2 }} - 3.95[MgF_2 ] - 3.95 \hfill \\ \end{gathered} $$ wheret is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na₃AlF₆-AlF₃-CaF₂-Al₂O₃-LiF-MgF₂-KF. The composition limitations are [AlF₃] ≈ [CaF₂] ≈ [LiF] < 20 wt pct, [MgF₂] ≈ [KF] < 5 wt pct, and [A1₂O₃] up to saturation.     

Interactions in the Al2O3-ZrO2-Y2O3 system

The phase diagram of the Al₂O₃-ZrO₂ system was replotted over a broad range of concentrations (0–100 mole %) and temperatures (1150–2800°C). The polymorphic transformation of zirconium F ? T occurs via the metatectic reaction F ? T + L at 2260°C. Phase triangulation was employed to plot the diagrams of the partially quasibinary sections in the Al₂O₃-ZrO₂-Y₂O₃ system. Since there is a wide solubility range based on ZrO₂ in the binary ZrO₂-Y₂O₃ system, the triangulation conodes are displaced in the F-solid solution corners. The two-phase regions Y₃A₅-F are quite broad. The reactions in all three are of the eutectic type. The ternary solid solution fields in the Al₂O₃-ZrO₂-Y₂O₃ system had no observable width.     

Influence of Al2O3 Level in CaO-SiO2-MgO-Al2O3 Refining Slags on Slag/Magnesia-Doloma Refractory Interactions

Metallurgical and Materials Transactions B - The influence of the Al2O3 level in CaO-SiO2-MgO-Al2O3 (CSMA) stainless steel refining slags on the degradation of magnesia-doloma refractories was...     

Al2O3含量对Al2O3弥散强化铜基复合材料性能的影响

探索了在不同浓度的Al（NO3）3溶液中加入铜粉,搅拌至糊状,在80℃干燥后,在H2保护气氛下加热至500℃使得Al（NO3）3分解成Al2O3,所得粉末在真空烧结机中加热到800℃,制备出Al2O3弥散强化铜基复合材料的新型工艺．研究了Al2O3含量对该复合材料各种性能的影响规律,结果表明：随着Al2O3含量的增加,材料的导电率下降;当Al2O3含量达1．0％时,材料的硬度达到最大值,而密度随Al2O3含量的增加而下降。     

Influence of the Ratio of Ethanol to Water on the Agglomeration of Al2O3/Y2O3-ZrO2 Nanoparticles

A method of heating ethanol-aqueous salt solution combined with co-precipitation was used to synthesize Al2O3/ZrO2 nanoparticles. The analysis of DSC and XRD revealed that the transformation temperature from amorphous to crystal phase was about 850℃. The grain size was increased with the raising of calcine temperature. The alcohol-water ratio did not affect the formation of main crystal phases, but affected the agglomeration of nanoparticles based on the results of TEM. When alcohol-water ratio was 51, the dispersion of nanoparticles was good. When there was not alcohol, the dispersion of nanoparticles was poor because there was only pure co-precipitation reaction and the speed of co-precipitation reaction was too high to have enough time of PEG. dispersing particles.     

高炉炼铁工艺中Al2O3的影响及适宜w(MgO)/w(Al2O3)的探讨

 高Al2O3铁矿石使用量的增加导致高炉炉渣Al2O3含量大幅度攀升。针对高Al2O3铁矿的高炉冶炼,定量综述了Al2O3对烧结工艺、烧结矿冶金性能、高炉冶炼产生的负面影响,分析了中国高Al2O3的高炉冶炼现状以及高Al2O3渣高炉冶炼应采取的措施,重点探讨了高炉炉渣适宜的w(MgO)/w( Al2O3)比。     

碱度和Al2O3含量对高炉渣性能的影响

以鞍钢高炉渣为基础,在实验室条件下研究碱度、Al2O3和MgO含量对炉渣粘度和熔化性温度的影响,确定了鞍钢高炉合理的炉渣成分范围为：碱度R2 1．05—1．10,Al2O3含量小于14％,MgO含量8％-10％。     

稀土对Al2O3陶瓷涂层组织及性能的影响

采用等离子喷涂方法制备Ａｌ２Ｏ３陶瓷涂层,研究了稀土对涂层组织及耐蚀性的影响。结果表明,在喷涂粉末中添加适当的稀土硅铁合金不仅可以改变涂层显微组织、减少和消除层状结构,而且显著提高了涂层的耐蚀性。     

Interfacial tension of aluminum in cryolite melts

The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured based on a combination of the sessile drop and X-ray radiographie technique. A computer program was used to calculate the interfacial tension from approximately twenty randomly measured coordinate points of the drop profile. Aluminum and salt mixtures containing different amounts of Na₃AlF₆, A1F₃, NaF, A1₂O₃, CaF₂, KF, LiF, and NaCl were melted in a graphite or alumina crucible in a graphite resistor furnace under an argon atmosphere. The interfacial tension was found to be strongly dependent on the NaF/AlF₃ ratio. At the cryolite composition the interfacial tension was 481 mN/m at 1304 K, while it was 650 mN/m when the NaF/AlF₃ ratio was equal to 1.5. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. Additions of A1₂O₃ increased the interfacial tension for a given NaF/AlF₃ ratio. KF was found to be surface active, while CaF₂, LiF, and NaCl slightly increased the interfacial tension by decreasing the sodium activity.     

Influence of an electric field on the plastic deformation of fine-grained Al2O3

The influence of an electric field E = 300 V/cm on the plastic deformation at 1450 °C to 1600 °C of fine-grained alumina with ∼300 ppm MgO and d _o=1.4 to 2.5 μm was investigated. After removal of the effect of Joule heating, the field reduced the flow stress by ∼4 MPa relatively independent of temperature, representing a 25 to 70 pct reduction in the flow stress. The field had no effect on the stress exponent n=2.2, nor on the grain size exponent p=1.9. It did however have an appreciable effect on the combined constant AD _o of the Weertman-Dorn equation and the activation energy Q. The latter increased from 492 kJ/mole without the field (typically that for Al³⁺ ion lattice diffusion) to 880 to 1070 kJ/mole with the field, which is more typical of sub-boundary or grain boundary diffusion of either Al³⁺ or O²⁻-ions in alumina. It therefore appears that the field changed the rate-controlling, grain boundary sliding accommodation mechanism from the lattice diffusion of Al³⁺ ions to either sub-boundary or grain boundary diffusion of Al³⁺ or O²⁻-ions. The electric field caused isotropic swelling of the specimen when applied for an extended period of time without application of stress. Pores responsible for the swelling occurred along the grain boundaries. They may have resulted from electrotransport of Al³⁺ ions, leaving behind an Al-deficient layer from which free oxygen bubbles formed along the grain boundaries. Electric field-enhanced gas reactions at the pores may have also contributed to the swelling. It is proposed that swelling due to electrotransport may possibly be avoided by the addition of solutes, which increase the electronic or oxygen ion conductivity transference numbers compared to the aluminum ions.     

Wettability of silicon carbide ceramic by Al2O3/Dy2O3 and Al2O3/Yb2O3 systems

Wettability is an important phenomenon in the liquid phase sintering of silicon carbide (SiC) ceramics. This work involved a study of the wetting of SiC ceramics by two oxide systems, Al₂O₃ /Dy₂O₃ and Al₂O₃ /Yb₂O₃, which have so far not been studied for application in the sintering of SiC ceramics. Five mixtures of each system were prepared, with different compositions close to their respective eutectic ones. Samples of the mixtures were pressed into cylindrical specimens, which were placed on a SiC plate and subjected to temperatures above their melting points using a graphite resistance furnace. The behavior of the melted mixtures on the SiC plate was observed by means of an imaging system using a CCD camera and the sessile drop method was employed to determine the contact angle, the parameter that measures the degree of wettability. The results of variation in the contact angle as a function of temperature were plotted in graphic form which showed that the curves displayed a fast decline and good spreading. All the samples of the two systems presented final contact angles of 40° to 10° indicating their good wetting on SiC in the argon atmosphere. The melted/solidified area and interface between SiC and melted/solidified phase were evaluated by scanning electron microscopy (SEM) and their crystalline phases were identified by X-ray diffraction (DRX). The DRX analysis showed that Al₂O₃ and RE₂O₃ reacted and formed the Dy₃Al₅O₁₂ (DyAg) and Yb₃Al₅O₁₂ (YbAg) phases. The results indicated that the two systems had a promising potential as additives for the sintering of SiC ceramics.