A method for directly preparing samarium-iron alloy powder by spray pyrolysis reduction method

Abstract

The invention discloses a method for directly preparing samarium-iron alloy powder by a spray thermal decomposition reduction method. Using the mixed aqueous solution of samarium salt and iron salt as the spray precursor solution, the spherical samarium-iron composite oxide is prepared by ultrasonic spray pyrolysis, and then the samarium-iron alloy is obtained by hydrogen pre-reduction followed by calcium reduction or direct calcium reduction. The raw material cost of the method is low, the molar ratio of samarium and iron in the samarium-iron alloy is easily obtained by adjusting the ratio of samarium salt and iron salt in the precursor solution, good dispersion of samarium and iron during reduction diffusion, low reduction temperature and short reaction time, can effectively Reduce the volatilization of samarium and inhibit the agglomeration of samarium-iron alloy powder. This method does not require the subsequent ball milling process, and can directly prepare pure-phase samarium-iron alloy powder with a size of 0.5-10 microns and nearly spherical particles, so that the grains of the samarium-iron alloy are complete, which is conducive to the subsequent improvement of the performance of samarium-iron-nitrogen, and is compatible with polymers It has good flow processability when compounding.

Description

technical field [0001] The invention belongs to the technical field of metal magnetic material preparation, and relates to a method for directly preparing samarium-iron alloy powder by a spray pyrolysis reduction method, specifically a method for synthesizing spherical samarium-iron composite oxides by spray pyrolysis first, and then obtaining a nearly spherical, Pure phase samarium-iron alloy with a size of 0.5-10 microns. Background technique [0002] In 1990, Coey et al. introduced N atoms into Sm through a gas-solid reaction. 2 Fe 17 alloys, obtained Sm with excellent intrinsic magnetic properties 2 Fe 17 N x (x≈3), its saturation magnetization μ 0 m s =1.54T, anisotropy field H a =17.5MA / m (about 3 times that of Nd-Fe-B) and Curie temperature T c =475°C (about 160°C higher than Nd-Fe-B), and Sm 2 Fe 17 N x The rare earth content contained in NdFeB is lower than that of NdFeB, which is conducive to the protection of precious rare earth resources in our country...

AI Technical Summary

Problems solved by technology

Both the alloy smelting method and the melt rapid quenching method are prepared by smelting metal samarium Sm and iron Fe first, because the melting point of iron (1538°C) is obviously higher than that of samarium (1072°C), and the saturated vapor pressure of samarium is very low. Volatilization, so when the two are co-melted, the volatilization of samarium will be extremely large, and the volatilization of samarium will cover the smelting observation window, making the operation difficult; at the same time, these two methods have high requirements for equipment, especially the rapid quenching of the melt The pure-phase samarium-iron alloy must be obtained under a very high degree of subcooling and precise samarium content, so the process is difficult to control; in addition, the alloy powder obtained by the melt rapid quenching method is in the shape of scales, which cannot reach the level of samarium-iron-nitrogen and high Fluidity requirements for composite processing of molecular materials

The mechanical alloying method is to mix iron powder and samarium powder and then perform ball milling in a planetary high-energy ball mill. Through the ball milling process, a solid phase reaction occurs to prepare samarium-iron alloy. The mechanical alloying method has a long cycle and high energy consumption, which limits its application in industrial production. application, and the powder cannot be completely oxidized during the long-term ball milling process, and the high stress of the powder obtained by ball milling will also reduce the magnetic properties

The reduction diffusion method mixes samarium oxide with iron powder and calcium particles, uses Ca to reduce samarium oxide into samarium metal and then alloys it with iron to obtain a samarium-iron alloy. Reduce the cost of raw materials, but the traditional reduction and diffusion method is to directly mix the samarium oxide powder with the iron powder. Since the size of the iron powder in the market is relatively large, and the samarium oxide powder is relatively fine, such mechanical mixing cannot realize the full separation of samarium oxide and iron powder. Uniform dispersion, which affects the alloying process; in addition, the traditional reduction and diffusion temperature range is 1010-1280 ° C, generally around 1100 ° C to form Sm 2 Fe 17 alloy, and the saturated vapor pressure of Sm at this temperature still exceeds 1000Pa, and the reduction diffusion needs to last for several hours to obtain a single-phase product, so the volatilization of Sm is still controlled by the synthesis of Sm 2 Fe 17 One of the difficulties of alloy

In addition, long-term reaction cannot avoid particle agglomeration caused by excessive sintering

The direct co-precipitation reduction method is to mix the iron salt and samarium salt and then add a precipitant to form a samarium-iron composite hydroxide, and then reduce it to form a samarium-iron alloy. Since the pH value of iron salt and samarium salt precipitation is different, it is necessary to To obtain the required molar ratio of samarium-iron composite hydroxide, it is difficult to control the ratio of iron salt and samarium salt, and the addition of nitrogen-containing or carbon-containing precipitants will affect the purity of samarium-iron alloy

The smaller the size of the SmFeN powder, the higher the magnetic properties, especially the coercive force. Therefore, except the mechanical alloy method, the SmFe alloy prepared by other methods must be refined by ball milling to make it close to 0.5-10 microns before nitriding. , while the ball milling process not only increases the possibility of magnetic powder being oxidized, but also destroys the complete crystal form of samarium-iron alloy, which also leads to a decrease in magnetic properties

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