Study On The Preparation Of Ultrafine Sm₂Fe₁₇N₃ Magnetic Powder By Reduction Diffusion Method

In recent years,the miniaturization and weight reduction of electronic equipment and the rapid development of new energy vehicles require permanent magnets to have higher working temperatures and magnetic properties.At present,sintered Nd₂Fe₁₄B magnets are widely used in permanent magnets.However,due to the low Curie temperature,heavy rare earths Dy and Tb need to be added to meet the temperature requirements of the working environment.However,the addition of heavy rare earths led to a sharp increase in costs and unbalanced utilization of rare earth resources.Therefore,the development of permanent magnet materials without heavy rare earth is a hot research topic in the industry.Sm₂Fe₁₇N₃ is widely concerned for its excellent intrinsic magnetic properties.However,the properties of Sm₂Fe₁₇N₃ powder have a great relationship with the particle size,and the intrinsic coercive force reaches the maximum near the critical single domain size?0.35?m?.At present,most of the Sm₂Fe₁₇N₃ magnetic powder preparation processes require ball milling or airflow milling to achieve magnetic particle refinement.However,the crushing process will form defects and local demagnetization fields,which affect the comprehensive magnetic performance.Therefore,a method for obtaining submicron-level high-performance anisotropic Sm₂Fe₁₇N₃ magnetic powder without crushing is needed.Based on the above problems,this paper mainly studies the preparation of ultrafine Sm₂Fe₁₇ alloy powder and Sm₂Fe₁₇N₃ magnetic powder by using different precursor preparation methods combined with reduction diffusion method without crushing;the main research results are as follows:?1?Based on the reduction-diffusion method,co-precipitation is used to prepare the reduction-diffusion precursor,and then Sm₂Fe₁₇ alloy powder is obtained by hydrogen reduction and Ca reduction diffusion.The effects of different precipitants,different hydrogen reduction temperature and time,Ca reduction diffusion temperature and different samarium compensation amount on the preparation of Sm₂Fe₁₇ alloy powder by co-precipitation-reduction diffusion method were investigated,among which the influence of hydrogen reduction and Ca reduction diffusion temperature is the most obvious,and the particle size increases obviously with the increase of temperature.The results show that the particle size of the Sm₂Fe₁₇ alloy powder prepared by the coprecipitation-reduction diffusion method can be reduced to submicron by adjusting the hydrogen reduction and the calcium reduction diffusion temperature of the samarium-iron composite oxide.And when the temperature of hydrogen reduction or Ca reduction diffusion is too high,the multi-nuclear growth of?-Fe is the key reason for the growth of Sm₂Fe₁₇ alloy particle.The best process is as follows:NH₄HCO₃ as the precipitant,the samarium compensation is 20%,the hydrogen reduction condition is 600?1 h,and the Ca reduction diffusion temperature is 850?1 h.?2?Attempt to prepare ultrafine Sm₂Fe₁₇ alloy powder by ultrasonic spray pyrolysis-reduction diffusion method.First,the effect of precursor solution concentration and urea addition on the precursor was studied.It was found that the obtained precursors were submicron samarium iron composite oxide spherical particles,In addition,the concentration of the precursor solution has little effect on the phase,particle size and morphology of the product.Urea will decompose at high temperature to release reducing gas,which can reduce the iron oxide in the product,and the amount of urea added will affect the degree of iron oxide reduction.When the amount of urea added is small,the ultrasonic spray pyrolysis product is reduced to Fe₃O₄,increasing the amount of urea added,the ultrasonic spray pyrolysis product is reduced to Fe_0.925O,but the particle size and shape of the product micromorphology has little effect.The effects of different hydrogen reduction temperatures on the precursor particles and subsequent Sm₂Fe₁₇ alloys were studied.The high hydrogen reduction temperature will cause the microspheres of the precursor to have a smooth surface to break,but it has little effect on the subsequent Sm₂Fe₁₇ alloy.?3?Sm₂Fe₁₇N₃ ultrafine magnetic powder successfully prepared by direct hydrogen assisted ultrasonic spray pyrolysis-reduction diffusion method.XRD results show that the prepared sample is single-phase Sm₂Fe₁₇N₃ magnetic powder;SEM results and particle size statistics show that the obtained Sm₂Fe₁₇N₃ magnetic powder is sub-micron nearly equiaxed particles;The PPMS-VSM results showed that the intrinsic coercive force of submicron Sm₂Fe₁₇N₃ particles without oxidation protection measures and dehydrogenation treatment reached 14.7 k Oe.