Effect of the solidification time on the median particle size of powders produced by water atomisation

Present empirical correlations to predict the median particle size of water atomised powders have a validity restricted to a particular atomiser and alloy family. This work proposes a mathematical function that takes into account the influence of the heat transfer coefficient and, therefore, of the solidification time on the median particle size. This equation is applied in combination with previously proposed empirical correlations to extend their validity to a broader range of alloys. Experiments were conducted with alloys of different melting point (Fe base, Cu base and Sn). Quantitative measurements of the median particle size, tap density and several shape factors, and qualitative observations of the particle shape confirmed the importance of the heat transfer rate. It is shown that the inclusion of the solidification time effect results in a better agreement between calculated and experimental data when both low and high melting temperature alloys are taken together.     

Effect of current source characteristics on powder particle size in electric-pulse atomization

Conclusions Tests of a high-power current pulse source with a capacitive energy accumulator for the atomization of metal jets have shown it to be suitable for the production of very fine powders. Depending on the diameter of the jet being disrupted, there exists some limiting value of capacitor battery capacitance above which the particle size analysis of the powder undergoes no marked changes. Increasing the initial battery voltage at an unchanged battery energy is accompanied by a substantial increase in the yield of fine powder fractions.Translated from Poroshkovaya Metallurgiya, No. 1(265), pp. 5–10, January, 1985.     

Characteristics of powders produced by the electroerosion disintegration of aluminum in water

Conclusions Fine (from 50 to 100m) aluminum powders of predominantly spherical particle shape can be produced by electroerosion disintegration in cooled water. They contain not more than 0.5% oxygen and are free from aluminum hydroxide. The degree of oxidation of such powders depends on the water temperature, decreasing with fall in the latter. The excellent corrosion resistance of aluminum powders is attributable to the highly homogeneous structure of the material of their particles, attained as a result of drastic quenching from the liquid state, which leads to rapid formation of uniform passivating-Al₂O₃ films on their surface.The authors wish to express their gratitude to A. V. Popov, M. V. Levchuk, A. S. Myuller, and V. P. Tarabrina for assistance with experiments.Translated from Poroshkovaya Metallurgiya, No. 10(262), pp. 7–11, October, 1984.     

Effect of particle size on the magnetic properties of powders and finished pieces

Conclusions The properties of individual particles can be used as factors in predicting finished piece properties.Particle size and active surface retain their effect on finished piece properties for different sample treatment regimes.Translated from Poroshkovaya Metallurgiya, No. 1(253), pp. 73–76, January, 1984.     

Effect of high-voltage discharge on the particle size of hard alloy powders

Powder Metallurgy and Metal Ceramics - The effect of high-voltage discharge treatment of Fe–20% TiC and VK6–1% ASUD75 diamond powder mixtures on their particle size and morphology is...     

Centrifugal hydraulic method of melt disintegratio. II. Effect of the physicochemical properties of metallic melts on the particle size of powders

Conclusions Lowering the surface tension of the melt leads to a decrease in the mean powder particle size. By adding a small amount (0.5%) of a surface-active agent to the melt, it is possible to substantially increase the yield of fine powder fractions. Lowering the viscosity of the melt, e.g., by superheating it by 10–20% above its melting point, enables the mean powder particle size to be decreased by a factor of 1.5–2. Powders of smaller particle size can be produced by using atomization injectors made of materials exhibiting lower adhesional activity toward melts. CHA of melts of lower density results, other things being equal, in the formation of finer powders.Translated from Poroshkovaya Metallurgiya, No. 9(321), pp. 10–14, September, 1989.     

球磨时间对钨粉粒度分布及形貌影响

通过改变球磨时间,获得不同粒度分布的钨粉颗粒,分析球磨时间对钨粉粒度分布和形貌特征的影响,提高粒度分布在目标区间（5～11 μm）的钨粉颗粒体积分数。结果表明,球磨的前2 h对原料中大颗粒钨粉的影响较大,钨粉颗粒最大粒径由134 μm迅速下降到20 μm左右。随着球磨时间的增加,钨粉粒度分布指标减缓下降,除粒径变小外,颗粒形貌基本无变化,但是在球磨10 h后开始出现团聚现象。综合分析可知,球磨时间的改变对钨粉粒度分布指标影响较大,球磨时间为8 h时,可获得粒度分布最窄的钨粉颗粒,在目标区间的钨粉颗粒体积分数达到75%。     

Effect of chemistry and particle size of cryochemical powders on the properties of humidity sensors

A comparative analysis of various sintered materials based on cryochemical powders was carried out. The electrical resistance of compacts of pure aluminum oxide and its mixtures with CoO, MgO, ZrO₂, and Y₂O₃ were compared with data on the specific surface area, phase composition, and pore size distribution in the sintered ceramics. Conclusions were drawn about the suitability of the materials as humidity sensors. Highest sensitivity was found in sensors based on aluminum—cobalt spinel, and aluminum—magnesium spinel mixed with zirconium oxide. Deceased. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(400), pp. 39–43, March–April, 1998.     

Control over the particle size of stainless-steel powders

Conclusions Replacing some of the metallic iron by ferric oxide, Fe₂O₃, in the charge for the preparation of Kh18N15 and Kh23N28 stainless-steel powders by the calcium-hydride reduction process increases (two- to threefold) the yield of the fine fraction (-0.063 mm) without affecting the apparent density of the powders (1.4–1.85 g/cm³) or the sponge shape of their particles. At the present time, stainless-steel powders are being manufactured using a charge in which 20–30% of metallic iron has been replaced by the oxide Fe₂O₃.Translated from Poroshkovaya Metallurgiya, No. 2 (134), pp. 1–8, February, 1974.     

Effect of particle size on the amount of residual austenite in atomized high-speed steel powders

Conclusions The presence of -phase and decomposition of martensite in fine particles as a result of heating by large particles alter the relative intensities of the austenite and martensite lines. Because of this, determination of the amount of residual austenite in a fine fraction by the existing x-ray methods gives low results. A more accurate estimate of the amounts of residual austenite in fine and coarse particles is obtained by measuring the areas of corresponding austenite lines.Translated from Poroshkovaya Metallurgiya, No. 11(275), pp. 6–8, November, 1985.