Study On Preparation Of Ultrafine And High Pure NiO

The ultrafine and high pure NiO powder, with green or black green color and high quality, is widely used in the fields of catalysts, electromagnetic cells, magnetic materials, colorants of ceramics, and so on. The preparation and research on NiO and other compounds of Ni are full of scientific and actual significance due to abundant resource of Ni in our country.Using nickel chloride as raw material, sodium carbonate or ammonium bicarbonate as precipitant, ultrafine and high pure nickel monoxide was prepared via aqueous-precipitation and thermal decomposition process route. The influences of the precipitant reacting conditions on producing basic nickel carbonate were investigated, such as precipitant, ultrasonic irradiation, temperature of reaction, feeding mode and washing mode. And the effect of heat treatment on purity, shape, crystal form and particle size of NiO was also investigated. On the foundation of the research above, the process of producing NiO via aqueous- precipitation and thermal decomposition route under ultrasonic irradiation was optimized. The detail results of the experiments were as following:(1) According to the calculation and analysis of thermodynamics, the log[Ni]_T～pH plots of the two precipitants system were drawn, then the basic conditions of the precipitating reactions were ascertained, such as the pH of the reaction, the temperature, and the dosage of the precipitants.(2) The experimental results of producing basic nickel carbonate showed: that the dosage of sodium carbonate as precipitant was less than ammonium bicarbonate, the conversion percent of Ni could be above 95%, but the agglomeration of the basic nickel carbonate was obvious, the particle size distribution was broad, the content of Na was more, which could be cut down by a new washing method of washing-drying-washing; When ammonium bicarbonate was used as precipitant, the average particle size of basic nickel carbonate was smaller, the particle size distribution was narrower,but the dosage of ammonium bicarbonate was more and the conversion percent of Ni was lower, so the recovery of Ni from the filtrate was needed. On the whole, ammonium bicarbonate was better than sodium carbonate as a precipitant.(3) The method of producing basic nickel carbonate under ultrasonic irradiation solved the problem of precipitate agglomeration. The basic nickel carbonate, with average particle size of 2～3μm, narrow particle size distribution, regular shape and less agglomeration, could be obtained when parallel feeding mode was selected, the precipitating and ageing stages were carried out in a ultrasonic field at 80℃, then washed at 80℃.(4)The temperature and time of calcination can influence the shape, crystal size and particle size. The as-prepared nickel carbonate under the optimized conditions above was calcined at 400℃for an hour, then NiO was obtained with an average particle size of 1μm and Na<0.0028%, Cl < 0.0031%(wt%), according with the standard of NiO powder used in electronic industry.(5)The thesis discussed the causations of process conditions effects on the particle size and purity of the product from the chemical principle of precipitation, the principle of nucleation and the growth of crystal in the stage of precipitation and crystallization. It also explained that washing method of washing-drying-washing can remove the impurity deeply from the theory of electric double layer.Using the route of aqueous-precipitation under ultrasonic irradiation and thermal decomposition to prepare ultrafine and high pure NiO, the raw material is facile, the process is simple, the cost is low, and production in commercial scale is easy to be realized. The calculation and analysis of thermodynamics for carbonate precipitation reaction is important to guide the process, and the washing method of washing-drying-washing to remove impurity in precipitate from electrolity solution has reference application.