Preparation Of Ultrafme Alumina By Ultrasonic Chemical Precipitation Method

Ultrafine alumina has a series physical and chemical properties of optical、electrical、magnetic adsorption.etc, widely used in ceramics, chemicals, electronics and so on, is a kind of important functional ceramic materials. At present, the domestic use of ultrafine alumina mostly by mechanical milling method, the main drawback of this method is the high energy consumption, serious environmental pollution, and the product quality is difficult to meet the requirements. In order to solve this problem, a wide range of domestic and foreign exploration of ultrafine alumina preparation technology, and obtained a lot of valuable conclusions. Based on the detailed data collection and market investigation, according to the characteristics of chemical precipitation method and ultrasonic technology, process technology was adopted to study the preparation of ultrafine alumina by ultrasonic chemistry method, providing a new way to solve the problem.In this paper, using aluminum sulfate(Al2(SO4)3·18H2O), ammonia(NH3·H2O) as raw materials and PEG2000 as dispersing agent, the optimum conditions of preparation of precursor by chemical precipitation method was explored at first. Secondly, the optimum process conditions of preparing precursor by ultrasonic chemical precipitation was studied. On this basis, the product of ultrafine alumina was obtained from precursor calcined. The product have been characterized by XRD, SEM, FTIR, Nano-laser particle size analyzer and TG-DSC.The factors affecting ultrafine alumina precursor by the chemical precipitation through orthogonal experiment were investigated. The conductivity was characterized the differences of chemical precipitation reactions under various conditions. The results showed:(1) Aluminum sulfate(Al2(SO4)3·18H2O)concentration of 0.1mol/L, ammonia(NH3·H2O) at a concentration of 2~4%(mass fraction), PEG2000 concentration of 2~3%( mass fraction), the use of orthogonal experiment prepared the precursor alumina with particle size of 342-380 nm and a certain aggregation.(2)Precursor was amorphous aluminum hydroxide, consistented with IR spectra analysis.(3) During optimal condition for preparing the precursor, the fastest rate of change in conductivity was 65%, before and after titration ammonia, conductivity was 4× 103μS / cm and 6.6× 103μS / cm, respectively.The effect of ultrasound frequency, power and time on the preparation of precursor was studied during the farbrication of precursor by ultrasound chemical precipitation. Conductivity was also characterized the differences of ultrasoinc chemical precipitation reactions. The results showed:(1) Followed by introduction of ultrasonic power 150 W, frequency of 20 KHz and ultrasonic time with 10 minutes of precursor alumina had a average particle size of 190 nm.(2) Compared with the Infrared spectra and XRD of precursor obtained from chemical prepicitation, precursor with the introduction of ultrasonic waves was also the amorphous aluminum hydroxide.(3)It could be seen from TG-DSC, with or without ultrasound, TG pattern was substantially identical, but DCS with ultrasound there had a large exothermic peak around 1000℃.(4) On the basis of chemical precipitation for the prepared precursor, the introduction of ultrasound(20KHz, 100W) for 5min, conductivity was 7.75× 103μS/cm, with respect to changes in the chemical precipitation rate was 93.75%.At last, α-Al2O3 obtained from precursor prepared by chemical precipitation with 1200℃ for 2h, but product fabricated by ultrasound-chemical precipitation only needed 1150 ℃ for 2h. And α-Al2O3 obtained from precursor prepared by ultrasound- chemical precipitation have a better dispersion.Appropriate ultrasonic parameters on chemical prepicitation can be introduced to obtain the precursor with more narrow particle size distribution, and it can also reduce its sintering temperature to obtain ultrafine α-Al2O3 powder.