Wettability of two-phase composites by molten metals

Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 40–44, June, 1992.     

Interfacial reaction wetting in the boron nitride/molten aluminum system

An improved sessile drop technique which prevented the oxidation of aluminum was used to measure the changes in contact angle between boron nitride and molten aluminum in a purified He-3% H₂ between 1173 and 1373 K. The contact angle progressed through the four wetting phases similar to other ceramics when the results were plotted on a logarithmic time scale. However, at and above 1273 K the equilibrium contact angle was 0° which is much less than those of typical ceramics. Using the value in phase II, the original contact angle between boron nitride and aluminum (contact angle between non-reacted boron nitride and aluminum) was estimated to be 133° at 1373 K. The wetting progressed by producing another non-wetting material, AIN, in this non-wetting system. The detailed mechanism of the solid/liquid/vapor interfacial advance during wetting in such a system was also explained using Cassie's equation.     

Wetting of boron carbonitride by molten metals

Translated from Poroshkovaya Metallurgiya, No. 12(324), pp. 61–66, December, 1989.     

Reaction of a molten mixture of titanium,aluminum, and silicon oxides with hot-pressed silicon nitride

The formation temperature of a liquid phase and the solidification temperature of a molten mixture of Al₂O₃-TiO₂-SiO₂ oxides on a silicon nitride substrate are determined. Data are obtained for the change in kinetics. It is established that the intensity of interaction of molten Al₂O₃-TiO₂-SiO₂ with silicon nitride depends on the oxide mixture composition. With heating there are two possibilities: improvement and worsening of Si₃N₄ crystallite wetting with a liquid phase as well as solidification of the melt. The temperature range where a liquid phase exists for actual materials is about 15°C, which markedly worsens the process of structure formation with Si₃N₄ during sintering.Translated from Poroshkovaya M etallurgiya, No. 5, pp. 39–44, May, 1993.     

溶胶-凝胶工艺制备氮化铝陶瓷超细粉末

采用硝酸盐-有机物低温燃烧反应溶胶-凝胶工艺,以硝酸铝(Al(NO_3)_3·9H_2O)、葡萄糖(C_6H_(12)O_6·H_2O)、尿素(CO(NH_2)_2)为原料,制备出粒度细小、混合均匀的铝源和碳源的混合前驱物,然后以该前驱物为原料进行碳热还原反应制备氮化铝粉末。研究表明,氮化铝的生成温度降低,在1350℃时即有大量氮化铝生成,1550℃时仅用90 min即可实现完全转化。SEM分析结果表明合成粉末为粒度分布均匀的纳米级(～100 nm)粉末。     

The oscillatory spectra of aluminum nitride

Translated from Poroshkovaya Metallurgiya, No. 2(326), pp. 80–82, February, 1990.     

Intermetallic compound layer growth at the interface of solid refractory metals molybdenum and niobium with molten aluminum

The growth mechanisms and growth kinetics of intermetallic phases formed between the solid refractory metals Mo and Nb and molten aluminum have been studied for contact times ranging from 1 to 180 minutes at various temperatures in the range from 700 to 1100°C. The growth of the layers of the resulting intermetallic phases has been investigated under static conditions in a saturated melt and under dynamic conditions using forced convection in unsatured aluminum melts. The Nb/Al interfacial microstructure consisted of a single intermetallic phase layer, Al₃Nb, whereas two to four different phase layers were observed in the Mo/Al interface region, depending upon the operating temperature. It was found that, in a satured melt, the intermetallic phase growth process was diffusion-controlled. The parabolic growth constants of the first and second kind and integral values of the chemical diffusion coefficients over the widths of the phases were calculated for both Mo/Al and Nb/Al systems. It also was found that the AlNb₂ phase grew between the Nb and Al₃Nb phases after consumption of the saturated Al phase. Similarly, the AlMo₃ phase grew between the Mo and Al₈Mo₃ phases with diminishing of all the other existing compound phases. In an unsaturated melt, the intermetallic phase layer grows at the solid surface while, simultaneously, dissolution occurs at the solid/liquid interface. This behavior is compared to the growth mechanisms proposed in existing theories, taking into consideration that interaction occurs between neighboring phases. It was found that the intermetallic phase, Al₈Mo₃, adjoining the base metal, was not bonded strongly to the base metal Mo and was brittle; its hardness also was larger than that of the layer near the adhering aluminum and the adjacent phases.     

物理富集—熔盐电解法从二次铝灰回收金属铝

二次铝灰是铝工业生产过程中产生的固体废弃物,含有金属铝、氧化铝和氮化铝等。通过球磨—筛分富集铝灰中的金属铝,研究球磨过程铝灰的粒度分布和金属铝的分离规律。结果表明,球磨后铝灰中的金属铝粒径变大,而其他盐类组分变细。较优条件是球磨3 h并筛分,粒度范围97～150μm的铝灰中金属铝的质量分数为24.51%,金属铝的质量占原料中金属铝总质量的41.40%。在冰晶石熔盐中电解最优条件下球磨—筛分后的铝灰,XRF分析表明：电解产物中Al和Si的质量分数分别为97.3%和1.6%,铝回收率为45.89%,电流效率为46.06%。     

Oxide skin strength on molten aluminum

The oxide skin strength on molten aluminum has been measured as a function of temperature for pure aluminum and some aluminum alloys. The measured values fit well to previous published data of surface tension of liquid aluminum, σ _lg , combined with the wetting angle, ϑ, and the mechanical strength of the oxide. It is assumed that the work per area needed to stretch and rupture the oxide skin is a sum of the interfacial tensions and tensile strength of oxide, times oxide thickness:

Atomizing molten metals — a review

Abstract

Data from the literature were used to construct activity diagrams for the systems Mn–Fe–C, MnO–CaO–SiO₂ and CaO–Al₂O₃–SiO₂ with 10% MnO. Assuming that the reduction temperature is close to slag melting point, the MnO content required to obtain a 75% Mn alloy can be found. One can also calculate the Si content corresponding to the slag composition. Fixing the allowable %Si it is found that the slag will contain more than 25% MnO in the MnO–CaO–SiO₂ system. The effect of CO pressure is minor. If it is practical to add Al₂O₃ to the slag, its melting point can be lowered sufficiently to obtain slags with 10% MnO in the CaO–Al₂O₃–SiO₂ system while keeping Si in the metal low.

Résumé

Des données de la littérature ont été employées pour construire les diagrammes d'activité des systèmes Mn–Fe–C, MnO–CaO–SiO₂, et CaO–Al₂O₃–SiO₂ it 10% de MnO. En admettant que la température de la zone de réduction est proche de celle de fusion du laitier, on trouve la teneur en MnO nécessaire pour obtenir l'alliage à 75% de Mn. La quantité de Si réduit a également été déterminée. Le calcul montre qu'en fixant la teneur finale silicium à moins de 0.5% la teneur en MnO doit être supérieure à 25% . dans les laitiers MnO–CaO–SiO₂. La pression de CO n'a guere d'effet. S'il est pratique d'ajouter du Al₂O₃ au laitier pour en abaisser le point de fusion on peut obtenir avec un laiter it 10 % de MnO un alliage pour lequelle Si ne dépasse pas les bornes permises.     

Sintering aluminum nitride at high pressure

Sintering kinetics have been examined for finely divided aluminum nitride powder at 5 GPa pressure and at 1920, 2020, 2120, and 2220 K. Sintering this material at high pressures is based on the mechanism of plastic strain combined with postdeformation annealing.Institute of Solid State Physics and Semiconductors, Belarus Academy of Sciences, Minsk. Institute of Problems in Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 8(368), pp. 62–65, August, 1993.     

Self-reinforced materials based on aluminum nitride

Powder Metallurgy and Metal Ceramics -