The Research On Preparation And Properties Of Cobalt-Based Amorphous Alloys Powder

In this paper, The Co-B and Co-Zr-B Nano-amorphous alloy powders were obtained by that the aqueous solution of NaBH₄ was added in the solution CoCl₂·6H₂O or the mixing aqueous solution CoCl₂·6H₂O and Zr (SO₄)₂·4H₂O. The compositions , constructions and magnetic properties of the powders were analyzed by Inductively coupled plasma-atomic emission spectroscopy (ICP) , X-ray diffraction (XRD) , selective area electronic diffraction (SAED), transmission electron microscope (TEM), differential scanning calorimetry (DSC) , and vibrating sample magnetometer (VSM) .In the Co-B binary system , the effect of the prepared conditions , which contained the addition rate , the reaction temperature , the concentration of NaBH₄ solution and the feeding order . for the boron content and structure of the Co-B amorphous alloy powders have been investigated . It is found that the as-prepared powders had a nearly spherical morphology with diameters of 20-60 nm and the boron content of the samples increased along with the addition rate and concentration of NaBH₄ solution and reaction temperature. When the feeding order was reversed, a lot of CoO crystals were appeared in the samples.It is found that the crystallization of amorphous Co_74.4B_25.6 powder occurs through a single exothermic peak, and it is confirmed by X-ray diffraction that the structure after crystallization consists of face-centered cubic Co, body-centered tetragonal Co₂B and orthorhombic Co₃B phases.The activation energy E for the crystallization of the Co_74.67 B_{25. 33} amorphous powder is determined as (422.76 ±4.89) kJ / mol by means of the Kissinger analysis. This value is greater than the activation energy of the resemble component Co₇₅B₂₅ amorphous thin cingulum . It shows the thermal stability of Co-B amorphous powders prepared by the chemical reduction is higher than the liquid rapid cold .In the Co-Zr-B ternary system, The two group samples was preparated by altering the ratio of Co²⁺/Zr⁴⁺ and the adding rate of NaBH₄ .XRD, SAED and DSC studies showed that the resultant were partially amorphous together with a tiny volume fraction of crystalline phases, and the main amorphous phase consisted of the Zr-based amorphous particles and theCo-based Zr-containing amorphous particles. It is found that the Co/Zr ratio in the powders was indistinguishably equal to the Co²⁺/Zr⁴⁺ ratio in the original mixed solution and the boron content of the samples increased along with the addition rate of NaBH₄ solution. The crystallization temperatures of the resultant powders were in the range of 765.1-771.3 K. The thermal stability of amorphous Co-Zr-B powder increased with increasing the zirconium content. When the Co/Zr ratio in the samples increased from 1.94 to 5.14, the saturation magnetization increased monotonously from 4.76 to 8.87 emu/g, but the coercivity increased irregularly from 15.98 to 26.81 Oe.