| Cu-W composites have been widely used in military, electronic and other fields because of its good comprehensive performance. In recent years, the rapid development of modern material industry has presented other new requirements on the performance of Cu-W composite materials. On the one hand, it's the requirement of the diversity of composition. On the other hand, it's the requirement of high density and structure uniformity. Na2CO3 is introduced into the co-precipitation reaction in this study based on the co-precipitation hydrogen reduction process. A new preparation method of Cu-W composite powders with precise control of composition is proposed.The main content of this paper: Experimental research on the pretreatment of waste materials of brass and scheelite. Experimental investigation on the reaction conditions of Cu- W precursor prepared by in-situ co-precipitation method and characterization of precursor powders. Thermodynamic calculation of two-stage hydrogen reduction and experimental study on phase transition dynamics. The effect of reducing conditions on the alloy particles is also investigated. Finally, the reduction powder is characterized and analyzed. The result of investigation demonstrates as follows.Brass can get best leaching effect after reaction for 2 hours in leaching solution, which includes 1:6 ammonia and 30% H2O2. 15% N910 extraction agent is used in the experiment and the phase ratio(O/A) is 2:1. 3mol/L sulfuric acid solution is used as stripping agent. The phase ratio(O/A) is 1:1 and the reaction time is both 5min. Scheelite reacts for 20 minutes in 30% hydrochloric acid at 70?.Then the filtered tungstenic acid slurry is dissolved by 25% ammonia for 1.5 hour. Ammonium tungsten crystal is obtained by filtering and crystallization.The pale green precursor powders are mainly consisted of CuWO4 and Cu4(OH)6CO3 under the best reaction conditions that pH value of 5,temperature at 75 ?,the(NH4)2WO4/Na2CO3 molar ratio of 1/10.578,the reaction solution volume of 300 mL and feeding way of adding together. The median particle size of the filter powder is about 1.3?m, and the particle size is uniform with no obvious agglomeration. The yield of alloying elements is higher than 95%, and the proportion meets that of the target.The removal of crystal water and thermal decomposition are mainly happened during calcination. Then the mixture of CuWO4 and copper oxide is obtained. The precursor can be completely decomposed at 350?. The weight loss curve of the calcined products shows that the reduction weight loss occurred mainly during low and high temperature stages, but weight lost less during the intermediate heating stage.By accurate thermodynamic calculation of the H2 reduction process,450 ? is determined as the first stage reducing temperature and 720? is determined as the second stage W-O oxides reducing temperature. The particle size of the reduced powder is the smallest and there is no reduced residue inclusion and Cu phase sintering at the reducing temperature of 720?. By the research and analysis on dynamics of reduction process, reduction gas flow rate of 5L/min is the most saving and efficient and the reduction powder specific surface area has a maximum value. High purity Cu-W composite powder is obtained after reduction, which has low oxygen introduction of 0.085%. Copper is semi covered by tungsten and the powder is approximately spherical. Particle size and element distribution are more uniform. Compared with other similar products, the physical properties are more excellent. |
PDF Full Text Request