| Cobalt powder is the most excellent cemented carbide binder, which particle sizeand morphology has an important impact on the structure and properties of cementedcarbide. Spherical cobalt powder has the lowest porosity and good liquidity, whenblended with WC hard has good miscibility, effectively reduce the WC-Co carbidegenerated in the cobalt pool and the risk of micro pore. In the WC-Co carbide addingan appropriate amount of rare earth oxide can improve the hardness of cementedcarbide, impact toughness, wear resistance, bending strength, such as service life ofalloy mechanical properties. The composite powders which fully mixed at themolecular scale can be prepared by liquid phase co-precipitation method, and thecomposite powders have the advantages of small size and uniform distribution. In thispaper, Co-Y2O3composite powders can be prepared by liquid phase co-precipitation,and study on the effect of content of YCl3, concentration of CoCl2, surface activeagent and pH of experimental conditions on the Co-Y2O3composite powdersmorphology, particle size, the rate of sedimentation on the base of analyzing thethermodynamic equilibrium of precipitation and calcination reduction process. thispaper obtained the following conclusions:(1) In this paper, we study the thermodynamic equilibrium model of each metal ionin the Co(Π)-Y(Ш)-NH3-C2O42--H2O precipitation system, calculate and draw thesystem lg[Me] T-pH diagram, and comprehensively analyze the influence of solutionpH, the concentration of Oxalic acid root [C]Tand the concentration of ammoniumroot [N]Ton the balance system. Analysis that, Co2+and Y3+ion are precipitation atthe same time in the process of precipitation, and obtain the maximum precipitationrate when pH ranges from1.8to2.(2) From the curve of Gibbs free energy changing with temperature,thedecomposition reaction of cobalt oxalate and oxalic acid yttrium which isendothermic reaction can be carried out at room temperature, and higher temperatureis favorable to the reaction, but the grain grows up easyly in the higher temperature, we choose the reaction temperature is500oC. From the equilibrium constant logarithmchanging along with temperature, the equilibrium constant of the reaction has biggerwhen the temperature is500oC, which indicating the reaction has been completely.(3) Different YCl3content and surfactant have a great influence on the morphologyof composite powders. When the YCl3/CoCl2molar ratio is0.014, the compositepowders morphology is plum blossom-like shape; When it comes to adding surfactantsodium dodecyl sulfate, the composite powders morphology is spherical-like shape,with uniform size and good dispersion.(4) Different concentration of CoCl2has a great effect on the mean particle sizeand dispersibility of composite powders. With the concentration of CoCl2increasingfrom0.2to0.5mol/L, the mean particle size reduce from7μm to4μm, and thedispersibility are improved. When the concentration of CoCl2reaches0.8mol/L, themean particle size increase to10μm, and the dispersibility becomes worse.(5) Different initial pH value of solution has a great effect on the compositepowders morphology, particle size and its precursor precipitation rate. With theincreasing of pH value, composite powders morphology changes from thick stick toglobular clusters, with smaller particle size and better dispersion. From precipitationrate curve, we learn that cobalt has the highest precipitation rate along with the pHvalue changing from2to2.5.(6) From the phase analysis of Co-Y2O3composite powder, we learn that: the Cophase is face centered cubic structure, and adding Y2O3particles it did not cause Cophase diffraction migration peak position; from the DSC curve analysis we can seethat, there is no obvious heat peak curve with the temperature increasing, whichreason is that the face centered cubic Co phase did not has phase transition with thetemperature increasing, this analysis and XRD spectrum are mutual verification. |
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