Study On Preparation Of Ferroferric Oxide Powders By Impinging Streams Reaction-Precipitation Method

The impinging streams is that two high-speed coaxial fluids flow impinge on each other in opposite directions,resulting in a high turbulence impinging region,which fully meets the high and uniform supersaturation reaction environment required by chemical reaction-precipitation method for preparing ultrafine powders.Thus,it has a significant broad application prospect.In this paper,Fe Cl₂·4H₂O,Fe Cl₃·6H₂O and Na OH were used to prepare Fe₃O₄ powders in a self-designed horizontal opposed impinging streams reactor by impinging streams reactor-precipitation method.The influences of six factors:feed flow rate Q,nozzle spacing L/D,reactant concentration c(Fe³⁺),ratio of iron concentration c(Fe²⁺):c(Fe³⁺),reaction temperature T and impact time t on the preparation of Fe₃O₄ powders were investigated and the experimental conditions were optimized by single factor and orthogonal experiment methods.The influence of ultrasonic enhancement on the mixing process and powders preparation in the horizontal opposed impinging streams reactor were investigated by combining impinging streams technology with ultrasonic enhancement technology.Compared with the traditional stirring process,the effect of Fe₃O₄ powders prepared by impinging streams reactor was obviously better than that by stirring,the particle size was reduced by 79.84%and distribution range was reduced by 74.82%.The results of single factor show that,with the increase of the flow rate,the particle size decreased gradually,and the distribution decreased first and then increased;When the nozzle spacing is 3,the particle size was the smallest and the distribution was the narrowest;The particle size and distribution range first decreased and then increased with the increase of reactant concentration,ratio of iron concentration and reaction temperature.With the increase of cycle time,the particle size decreased but the distribution range became wider.The orthogonal experiment was designed on the basis of single factor experiments to determine the order of the influence of each factor on the size and distribution of Fe₃O₄ particle size and distribution and the optimal working condition combination.The results show that the best working conditions for preparing Fe₃O₄ powders by impinging streams reaction-precipitation method is when Q=800L·h^-1,L=3D,c(Fe³⁺)=0.4mol·L^-1,c(Fe²⁺):c(Fe³⁺)=0.75,T=20?and t=10min.The morphology,size,composition,and pyrolytic properties of the samples prepared under the optimal conditions were analyzed by scanning electron microscopy,X-ray diffractometer,granulometer and thermogravimetric analyzer.It was found that the samples had small particle size,narrow distribution,high purity and good thermal decomposition performance.The mixing process of the impinging streams reactor was studied by planar laser induced fluorescence technology.The results show that the mixing time decreased with the increase of ultrasonic power,and the mixing time was shortest when P=400W,decreased about 19.70%compared with the ultrasound power was 0.In addition,experimental results show that the size and distribution of the powders were significantly affected by ultrasonic enhancement,and the particle size of the powders decreased and the distribution became narrower with the increase of ultrasonic power.The size and distribution of particle size under the combined action of ultrasonic enhancement and cyclic impact were obviously better than that under the conditions of ultrasonic enhancement only and cyclic impact only.