Structure and properties of plasmochemical powders of aluminum oxide

Using modern methods of analysis, investigations of the phase composition, structure, and properties of powders of aluminum oxide synthesized by the plasmochemical method are carried out. The possibility of plasmochemical technology of treatment of dispersed raw materials for obtaining submicrometer and nanodimensional particles of aluminum oxide is shown.     

Effect of surface oxide films on the properties of pulse electric-current sintered metal powders

Metallic powders with various thermodynamic stability oxide films (Ag, Cu, and Al powders) were sintered using a pulse electric-current sintering (PECS) process. Behavior of oxide films at powder surfaces and their effect on the sintering properties were investigated. The results showed that the sintering properties of metallic powders in the PECS process were subject to the thermodynamic stability of oxide films at particles surfaces. The oxide films at Ag powder surfaces are decomposed during sintering with the contact region between the particles being metal/metal bond. The oxide films at Cu powder surfaces are mainly broken via loading pressure at a low sintering temperature. At a high sintering temperature, they are mainly dissolved in the parent metal, and the contact regions turn into the direct metal/metal bonding. Excellent sintering properties can be received. The oxide films at Al powder surfaces are very stable, and cannot be decomposed and dissolved, but broken by plastic deformation of particles under loading pressure at experimental temperatures. The interface between particles is partially bonded via the direct metal/metal bonding making it difficult to achieve good sintered properties.     

Effect of the granulometric composition of aluminum powder on the properties of semi-finished sintered aluminum powders

Powder Metallurgy and Metal Ceramics -     

Laser synthesis of ultradisperse powders of aluminum oxide

We have studied laser synthesis and the structure and properties of ultradisperse aluminum oxide powders. We show that the laser radiation intensity affects the phase composition. We find that the following conditions are optimal for production of these powders: power 500 W, pressure 0.1 atm (1–10 kPa), helium as the synthesis atmosphere.Scientific-Research Institute of Problems in Powder Technology and Coatings, Republic Engineering and Technical Center of Powder Metallurgy, Perm. Translated from Poroshkovaya Metallurgiya, Nos. 1/2(377), pp. 1–4, January–February 1995.     

铝粉对Al2O3–MgO复合材料抗氧化性的影响

以烧结刚玉、α-Al₂O₃微粉、高纯镁砂、金属铝粉为原料, 酚醛树脂为结合剂, 制备Mg O–Al₂O₃和Al–MgO–Al₂O₃系复合材料, 样品成型后经过200℃烘干, 于1500℃氧化气氛烧成。利用X射线衍射仪, 扫描电子显微镜和能谱仪研究了金属铝粉对MgO–Al₂O₃复合材料抗氧化性的影响。结果表明: 未添加金属铝粉的样品烧后主晶相为α-Al₂O₃及镁铝尖晶石, 微观结构较为疏松; 引入金属铝粉后, 样品烧后主晶相为α-Al₂O₃及镁铝尖晶石, 新生相包括Al₄O₄C、Al₄C₃、(Al₂OC)_x(AlN)_1-x等, 微观结构较为致密, 样品性能得到改善。添加金属铝粉样品的内外组成呈梯度变化, Al₄O₄C相主要出现在样品内部, 并有金属铝残留; 金属铝粉引入使样品氧分压从表面到内部依次降低, 金属铝粉氧化后与Mg O原位合成尖晶石, 使结构致密化, 阻隔了氧气的进一步渗入, 样品内部形成的Al₂O与C反应得到晶须状Al₄O₄C。     

Synthesis of nanostructured spherical aluminum oxide powders by plasma engineering

Irregularly shaped aluminum oxide particles were plasma atomized resulting in narrow size range distribution of spherical nanostructured powders. Cooling rates, on the order of 10⁶ to 10⁸ K/s, were obtained from the different quenching medias, viz. air, water, and liquid nitrogen. Plasma-engineered powder particles developed nanosize crystallites, while solidification provided insight into the morphological feasibility in refinement of grain size. X-ray diffraction (XRD) methods have been used to quantify the crystallite size obtained with different quenching media. Raman peak shift validated the X-ray analysis in anticipating the grain refinement with increasing cooling rates. Salient structural morphology characteristics and a detailed understanding of spheroidized plasma-sprayed alumina powders were analyzed through scanning electron microscopy (SEM) studies. Formation of nanograins, novel metastable phases, and amorphous structure were endorsed by transmission electron microscopy (TEM) investigations.     

尿素对前驱物及氮化铝粉末粒度形貌的影响

以硝酸铝、葡萄糖为原料,用碳热还原法制备氮化铝粉末,研究尿素对前驱物及其氮化反应产物的组成和显微形貌的影响,发现尿素不仅可以影响前驱物的组成和显微形貌,还对氮化反应产物的显微形貌有重要影响。在溶液里添加尿素后,它与硝酸铝发生了低温燃烧合成反应,生成了比表面积高的泡沫状前驱物,该过程中碳由于燃烧损失较大,在没有添加尿素的溶液中,没有燃烧反应发生,碳的损失小,生成的前驱物团聚现象严重,比表面积低,两种前驱物保留了前驱物的形貌特征,对于不添加尿素合成的前驱物,在其氮化反应后所生成的氮化铝粉末板结严重;而添加尿素合成的前驱物的氮化反应产物是由球形颗粒组成的软团聚体。利用XRD,SEM等分析方法对粉末进行了表征。     

Influence of the method of production of aluminum oxide-titanium oxide composite powders on structure formation

Institute of General and Inorganic Chemistry of the Academy of Sciences of the Ukraine. Translated from Poroshkovaya Metallurgiya, No. 4(364), pp. 44–49, April, 1993.     

In situ observations of crystalline oxide formation during aluminum and aluminum alloy oxidation

Anin situ morphological study of the oxidation of electron transparent specimens of aluminum and aluminum alloys containing zinc and magnesium has been carried out in the temperature range 400 to 520°C using the hot stage of a 1 MeV transmission electron microscope. The structure and morphology of the crystalline oxide produced in each alloy has been carefully examined by selected area electron diffraction and stereomicroscopy. In pure aluminum, oxidation takes place after a temperature dependent induction period, by the nucleation of crystalline γ-Al₂O₃ at the amorphous oxide/metal interface. This process is delayed by additions of zinc which modify the structure of the oxide. In alloys containing magnesium, oxidation takes place by the rapid nucleation and growth of MgAl₂O₄ or MgO, with a secondary form of magnesia developing from the reduction of the amorphous γ-Al₂O₃ surface layer.

     

Composition and thickness of surface oxide films on aluminum alloy granules

Conclusions The composition of oxide layers on granules is affected most by magnesium, the magnesium content of the layers being strongly dependent on the conditions of casting of granules. The thickness of surface oxide films on aluminum alloy granules produced by vibratory casting in water does not exceed 5–6 nm. In the casting of granules in water it is necessary to control the latter's impurity content. This applies particularly to closed water circulation systems, in which the degree of contamination of water increases with time.Translated from Poroshkovaya Metallurgiya, No. 8(260), pp. 4–9, August, 1984.