The effect of reaction condition on composition and properties of ultrafine amorphous powders in (Fe, Co, Ni)-b systems
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I.
INTRODUCTION
AMORPHOUS alloys have usually been prepared by three techniques: liquid quenching, vapor deposition, and solid-state reaction. However, a chemical reduction method to prepare ultrafine amorphous alloy powders has recently attracted increasing attention probably because of the unique preparation process and the fine morphology of the resulting powder. [1-4] The amorphous powders prepared by this method have spherical shapes and their particle sizes are in the range of 5 to 50 nm. These ultrafine amorphous powders have been expected to be used in various new application fields by taking advantage of the unique physical and chemical properties resulting from their fine powder size. In particular, their magnetic properties have intensively been investigated. [s-u~ However, little has been known about the effect of the reduction condition on the chemical and physical properties, including magnetic properties of the ultrafine amorphous powders, though the reduction condition is thought to exert a significant effect on their properties, t12] This paper is intended to clarify the effect of the reduction conditions (the ratio of KBH4 to metal ions and reduction temperature) on the structure, morphology, concentration, thermal stability, and magnetic properties of the Fe-B, Co-B, and Ni-B alloy powders prepared by the chemical reduction method. II.
EXPERIMENTAL PROCEDURE
A KBH4 was used as a reduction agent. A KBH4 aqueous solution was added into metallic salt solutions in air, and the mixed volume ratio of their solutions was fixed to be 1.0. Metallic salts used were Fe, Co, and Ni sulfates. The molar ratio of KBH4 to metal ions, MR ( M R : MKBH4/MMetal, where MKBH4 is the mol concentration of KBH4 and MMetaI is the mol concentration of JUNJI SAIDA, Visiting Researcher, Institute for Materials Research, Tohoku University, is on leave from Steel Research and Development Laboratories, Nisshin Steel Co., Ltd., Sakai 592, Japan. AKIHISA INOUE and TSUYOSHI MASUMOTO, Professors, are with the Institute for Materials Research, Tohoku University, Sendal 980, Japan. Manuscript submitted March 12, 1990. METALLURGICAL TRANSACTIONS A
metal ions) was changed in the range of 1.0 to 20. The powders were prepared in the temperature range of 275 to 333 K. After stirring for 10 minutes, the black product was immediately collected on a filter and washed with distilled water followed by acetone rinse and dried in air. Alloy composition of the product and B concentration in the residual aqueous solution were determined within an accuracy of 0.01 wt pct by inductively coupled plasma spectrometry, and the product's structure and morphology were examined by X-ray diffractometry with Cu K a radiation, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The generation of hydrogen during the reduction reaction was examined by hydrogen gas detector using semiconductor sensor. Crystallization temperature and heat of crystallization were measured by differential scanning calorimetry (DSC) with a heating ra
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