Preparation Of Cu-Zn Ultrafine Powders By The Method Of Thermal Spray And Ball Milling & Study On Dispersing Of The Powders

The methods of thermal spray and mechanical ball milling are combined in this paper and a new method of preparation of Cu-Zn ultrafine powders is brought forward. On the basis of preparing powders with usual technological parameters of thermal spray, the influences on powders properties of ball milling time, assistant reagents of ball milling and conditions of heat treatments are discussed, and then it comes to the optimal preparation project. The Cu-Zn ultrafine powders of 200~500nm can be prepared by this technic. In allusion to agglomerates of Cu-Zn ultrafine powders in liquid media, dispersing effects of the powders under the action of different dispersants are studied by the methods of sedimentation and spectrophotometery. By the method of orthogonal experiment, this paper optimizes the formulae of dispersants and analyzed kinds of factors that affect dispersing properties. The action mechanism of different dispersants is discussed and the best action conditions of these dispersants are presented. This improves the dispersing stability of Cu-Zn ultrafine powders and provides with effective methods for the preparation of ultrafine powders with steady properties.Powders properties of different phases such as the granularity, theshape and the component have been analyzed by the methods of sieving, gravity sedimentation, spectrophotometry, scan electronic microscope (SEM), transmission electronic microscope (TEM) and X-Ray diffraction (XRD). The results show that technic of ball milling and parameters of heat treatments are important influencing factors to properties of Cu-Zn powders. At the first stage of ball milling, the granularity of powders increases with prolonging the time. But if ball milling continues, the granularity will minish. When minishing to a certain extent, the granularity of powders don' t change greatly along with prolonging the time of ball milling. Assistant reagents can improve efficiency and ameliorated effects of ball milling. The dispersing of powders changes for the better obviously. After heat treatments, the granularity of powders increases and ultraf ine grains decreases. Cracks appear on the surface of powders. So the rigidity of powders descends. At the same time agglomeration of powders weakens. Consequently, adopting the alternation technic of ball milling and heat treatments, Cu~Zn powders of 200?00nm can be available.Through preparative experiments and optimized experiments on Cu~Zn ultrafine powders that are prepared by the method of thermal spray and ball milling, the author finds that dispersants concentration, dispersing time, pH, temperature and adscititious ions have significant influences on dispersing effects. Among single dispersant, there are better action effects for surfactant. Among compound dispersants, there are favorable dispersing effects for the admixture of different kinds of dispersants. This results from cooperation function of different kinds of dispersants. So only with the best combination of dispersants concentration, dispersing time, pH, temperature and adscititious ions, steady dispersing system can be obtained. Two optimum formulae of compound dispersants for Cu-Zn ultrafinepowders are obtained on the basis of multitude experiments. They are as follows: (1) Stearic Acid (0.75%), Sodium Silicate (2.5%), Sodium Chloride (1%), Dispersing Time (5h), pH(9), Temperature (70C), (2) Tween-80 (4%), Sodium Laurate (2.5%), Sodium Chloride (1%), Dispersing Time (2h), pH (5), Temperature (25癈). These two dispersants can ameliorate dispersing state of Cu-Zn powders and solve the problem of agglomeration reasonably in the process of preparation. This provides with foundation for application of Cu-Zn ultrafine powders and study on dispersant for ultrafine powders.