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The chemical plating Prepared nano Co-Al_2O_3 composite powder

Author: MaZhiYong
Tutor: LingGuoPing
School: Zhejiang University
Course: Materials Processing Engineering
Keywords: Nano-Al2O3 Metal - ceramic composite Ultrasonic wave Electroless plating drill Reaction time Plating rate Coating composition Nanocomposite powder morphology
CLC: TQ153
Type: Master's thesis
Year: 2002
Downloads: 307
Quote: 14
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Abstract


In this paper, through the preparation of nano ceramic Fund is a composite material means to solve the brittleness of ceramic materials for the target. The idea is: First preparation of nano metal coated ceramic composite powders. Thus, in the subsequent preparation of the block material during the sintering process, the metal surface layer can inhibit the fusion of the nano ceramic powder to grow, so that the powder after sintering to maintain the nanometer size, and thus play the role of nanometer size on toughness; by introducing at the same time evenly distributed the toughness of the metal phase, and further improve the brittleness of the ceramic. Therefore, the research content is set to use chemical plating the nanoscale Al 2 O 3 ceramic powder coated metal cobalt, preparation of nano-metal package re-type ceramic composite powders. Used in the experiments, Al 2 O 3 powder average particle diameter of 10 ~ 20nm, chemical plating cobalt before the necessary pretreatment, so the Al 2 < / sub> O 3 powder surface catalytic activity. The chemical plating cobalt solution is basic, and sodium hypophosphite as the reductant bath, plating in temperature or low temperature, under the conditions of the ultrasonic wave. Deposition rate by weight gain, bath composition was determined by chemical titration. Observe the morphology of the composite powders with the Philips EM430 type high-resolution transmission electron microscopy (HRTEM); D/3AX 3B-type X-ray diffraction analysis of composite powder material composition; DSC7 with U.S. PE firm DELTA SERIES differential scanning The calorimeter of the composite powder was subjected to DSC analysis in order to determine a phase change occurs during heating of the composite powder. First explored the feasibility of The nanopowder ultrasonic electroless plating. The ultrasonic wave added to make the plating conducted at room temperature, and to accelerate the process of plating, more important is to improve a powder plating uniformity. HRTEM high-resolution transmission electron microscopy showed cobalt composite powders obtained ultrasonic electroless plating, powder particle size from 10 ~ 20nm increased to 50 to 60nm; particles be coated granular become approximate angular spherical; close to the size of the resulting powder, found no plating reunion led to uneven; X-diffraction analysis showed that the chemical plating composite powders obtained surface coated with a layer of Co-P alloy. Nano powder ultrasonic bath composition and plating conditions Plating Co the relationship between the in-depth study. The experiment found that the the nano Al 2 O 3 powder coating start and after a period of time, the reaction will automatically stop. After plating bath composition of the analysis showed that the reaction stopped spontaneously due to the low pH value of the bath, or the plating solution of sodium hypophosphite in the plating process is consumed, so that its concentration falls to a very low due. This time is defined herein as the \conditions of process parameters such as reaction time. The results showed that the PH value of the bath, the plating temperature is increased, due to the speed of the reaction, the reaction time is shortened; cobalt sulfate concentration increased, helps to speed up the reaction rate, so as to shorten the reaction time; the citric satisfied concentration increased, the bath stability increased, the influence of the reaction time is equivalent to decrease in the concentration of cobalt sulfate; sodium hypophosphite concentration was increased, although the speed of reaction, but can be used to restore the amount of increase, so the reaction time increased; loading increased , by an increase in the surface area of ??the plating, so that the reaction time is shortened. Ultrasonic frequency and power, and pretreatment conditions will have an impact on the reaction time. Bath composition and process parameters on the deposition rate, weight gain in the units within the reaction time has a great influence. In this paper, the PH value of the bath, the plating temperature, cobalt sulfate concentration of citric acid is satisfied, the concentration of sodium hypophosphite, boric acid concentration, loading amount and the plating rate. These factors affect the chemical the plating reaction time and powder weight gain and affect the deposition rate. The results showed that the pH value of the bath and plating temperature increased, the deposition rate increased; to improve cobalt sulfate concentration, deposition rate can be increased; increase the concentration of citric satisfied, the increased stability of the bath, deposition rate decreased; With the concentration of sodium hypophosphite improve the plating rate is first increased and then decreased, there is a maximum of 20g / l; borate able to buffer the change of the bath pH value, the plating rate increases with the increase in the concentration of boric When boric acid is able to guarantee electroless plating reaction completely , the plating rate no longer changes. This paper also studied the influence of the bath composition and plating process parameters on the phase structure of the composite powders. Powder X-ray analysis showed that the sodium hypophosphite, the amount of rise, will dry alloy composite powders of Co from crystalline to amorphous; loading amount of the change will cause the metal content in the composite powder major changes. By adjusting these parameters, you can control the content and phase behavior of the composite powder metal. In addition, vacuum heat treatment of the with Amorphous CO dry alloy composite powder C. -P alloy in addition to crystalline transition occurs, precipitation of C. . P. Drilled for electroless plating the resultant composite powders TIM observation results show that the thickness and uniformity of the coating is mainly determined by the reaction time, the longer the reaction time, the thicker the coating, the better the uniformity. Therefore, it is possible by changing the parameters of the bath in the concentration of sodium hypophosphite, pH, and loading to adjust the reaction time, to thereby control the thickness and uniformity of the coating. Among them, the better way to control the thickness of the coating by controlling the concentration of sodium hypophosphite and loading. In addition, the quality of the nanocomposite powder coating is also influenced by the parameters of the bath composition and plating conditions, these factors include the concentration of each component in the pH of the bath, the bath loading. Experiments showed that the pH of the bath is too low or too high not conducive to obtaining the plating quality good composite powders; increase in the concentration of cobalt sulfate or reduce the concentration of citric acid, sodium, and improved quality of the composite powder coating; increase the bath amount of sodium hypophosphite, the resulting composite powder coating quality is greatly improved, but increased with concentration, reaction time is greatly extended: initial boric acid concentration in order to ensure the quality of the composite powder coating; loading lower amount, is conducive to the good quality plating composite powders.

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