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Study On A New Method For Preparing Special Nickel Powder

Posted on:2004-05-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:J H WuFull Text:PDF
GTID:1101360125958081Subject:Non-ferrous metallurgy
Abstract/Summary:PDF Full Text Request
Ultrafine nickel powder with high surface activity , fine electrical and heat conductivity has broadly been used for chemical catalyst , sintering activate , slurry of conduct electricity , battery , hard metal etc. In our country, the demand for the products only in battery profession has already risen from more than 200 tons to 6000 tons since several years ago, however the quantity or quality of the nickel powder at home, can't satisfy with the market's need. According to this, a new method of "Precipitation Converting-Thermal Decomposition" has been adopted to prepare the special nickel powder in Ni2+-NH3-NH4+-C2O42--H2O system in this paper, and series of theories and actual problems were systematically studied in the whole process, nanocrystalline fibrous special nickel powder is also obtained. The main innovation contents in this dissertation are as follows:For the first time, membrane electrolytic method was used to prepare high-purity nickel chloride solution for producing special nickel powder in a membrane electrobath designed ourselves, and with choosing anion membrane.According to the law of conservation of mass and the law of Nsimultaneous equilibrium, the mathematics model of Ni -NH3-NH4 -C2O42-H2O thermodynamic equilibrium system was first built, and the corresponding logarithms concentration -pH diagrams of the system were also drawn.The effect of ligands and pH value on the system was investigated.Nickel complexes were firstly prepared by Precipitation Converting method, the influences of technological conditions on the morphology , grain degree and dispersion were systematically studied by using SEM and XRD. The results show that morphology is obviously dependent of operation conditions in the preparation of mono-dispersed fibrous nickel complexes, and the grain degree and dispersion are also affected by the condition, such as the temperature , concentration , pH value etc.Abstractmorphology of nickel complexes is of fiber, the ratio of long and short diameter is big ,the dispersion is good. The optimum conditions are as follows , the concentration of Ni2+ 0.6 0.8mol/l, pH 8.2 8.8, temperature 6070 etc.The mechanism on nickel complexes formation was studied through analytical methods of IR XRD, which is identified as a precipitation conversion process, i.e.,Firstly, Ni reacts with C2O4 to form the precipitation equation is expressed asAnd then, excessive NHs in the solution reacts with NiC2C>4 to form the precipitation of nickel complexes, as the following equation,Based on the analytical results of IR, XRD TGA/DTA of the products, the mechanism on the nickel complexes thermal decomposition was also studied, it is considered that the thermal decomposition process includes three stages, i.e.,First stage (removal of ammonia ):.NiC2O4-x(NH3)yH2ONiC2O4yH2O+xNH3t Second stage (dehydration ): NiC2O4yH2ONiC2O4+yH2Ot The third stage (thermal decomposition ): NiC2O4-Ni+2CO2t Effects of the thermal decomposition conditions of nickel complexes on nickel powder performance, and surface treatment were studied, the thermal decomposition and surface treatment are carried out in the same furnace. The results show that the fibrous nickel powder with a good degree of crystallinity can be obtained from the nickel complexes with a lower crystallinity by thermal decomposition. Nickel powder inherits the morphology from nickel complexes, in thermal decomposition stage, the atmosphere , temperature and time of decomposition have dominant effects on dispersion of nickel powder. The nanocrystalline fibrous nickel powder with goodIVAbstractdispersion was obtained at the proper decomposition conditions, such as the fibrous nickel complexes of the good dispersion, weak reducing atmosphere, temperature 400~440, time 30 minutes. The oxidation of nickel powder was avoided in the process of storage and use by using nitrogen mixed with a little air and inert gases to passivate the surface.The pilot experiment with the capacity of lOOt/y special nickel powder was first ca...
Keywords/Search Tags:fibrous, nickel complexes, nickel powder, precipitation converting, thermal decomposition
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