Preparation of the powders of ferromagnetic alloys by hydrogen dispersion in ultrasonic fields
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PREPARATION OF THE POWDERS OF FERROMAGNETIC ALLOYS BY HYDROGEN DISPERSION IN ULTRASONIC FIELDS Yu. B. Basaraba,1 T. M. Zasadnyi,2 and Т. I. Lutsyshyn1
UDC 621.785.36+66.084.8
We study the granulometric composition of powder particles of a ferromagnetic alloy obtained as a result of ultrasonic dispersion under elevated static pressure in a working chamber. It is shown that the use of hydrogen increases the efficiency of ultrasonic dispersion. The results of analysis of the powders obtained by using ultrasound and by milling in a planetary ball mill in ethanol are compared. Keywords: ferromagnetic alloys, ultrasonic dispersion, hydrogen.
The necessity of production of highly dispersed powders of ferromagnetic alloys is connected with their extensive application both for the production of sintered high-energy rare-earth permanent magnets and plastomagnets [1–4] and for the preparation of magnetic foams [5] used to clean water surfaces polluted by petroleum products due to their good radiation-absorption properties in broad frequency ranges. In this case, the spectrum of absorption can be changed by choosing the optimal compositions and sizes of particles. At present, there are different methods used for the preparation of highly dispersed powders based on the mechanical, thermal, and electrochemical procedures of milling. For ferromagnetic alloys on the basis of rare-earth metals, it is also customary to apply hydride dispersion [6–8] with subsequent milling in vibratory mills, planetary ball mills, and jet mills in the flow of argon. The ultrasonic method of getting highly dispersed materials under elevated static pressure in a working chamber proves to be fairly efficient [9, 10]. It is also used for the production of materials with particle sizes within the range 10–40 nm [11]. The highest values of the coercive force (1600 kA/m) and magnetic energy (360–460 kG/m 3 ) [12] are attained in magnetically hard materials based on Nd 2 Fe14 B . Thus, the theoretical limit of magnetic energy for the Nd 2 Fe14 B ferromagnetic phase is 509 kG/m 3 , whereas the theoretical limit of residual induction is 1.6 Т [13]. These alloys are structurally very sensitive and, according to the theoretical computations, the magnetic energy of permanent magnets made of these alloys in the nanocrystalline state may attain 1000 kG/m 3 [14]. The cost of permanent magnets made of the Nd 2 Fe14 B alloy depends mainly on the cost of separation of neodymium from the mixture of rare-earth metals and varies within the range 70–150 USD per kilogram in the world market [15]. To reduce the costs, it is possible to use mixtures of rare-earth metals enriched with neodymium. The magnetic characteristics of these sintered magnets in the intact state ( Br = 0.96 Т, H c = 824 kA/m, and (BH )max = 183 kG/m 3 [15]) are lower than the corresponding characteristics of magnets of the Nd 2 Fe14 B system. However, their relatively lower cost (40–45 USD per kilogram) and the prospects of improving their 1
Ivano-Fankivs’k National Technical University of Oil and Ga
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