Preparation Of Metal Oxides And Doped Nanocrystallites By Mechanochemical Route

Tin oxide and zinc oxide are important inorganic raw materials, and have been widely used in rubber, coating, ceramics, chemical engineering, military affairs, medicine and electronic industry. Nano-sized particles possess lots of new properties and preparation due to its obvious surface effect, volume effect, quantum size effect, macro quantum tunneling effect, etc.Presently the main preparation techniques are chemical and gas methods, while which have many disadvantages, including high cost, difficult to operate, and with low quantity. Because of the above problems, a new method(called mechanochemistry) was introduced in this paper. This technique has many advantages, such as simple process, short-time operation and suitable for large-scale production. In this paper, mechanochemical principle was used to prepare nanocrystallite oxides SnO2 and ZnO. In this work, tin(zinc) dichlorides and sodium chloride as the main raw materials with sodium chloride as diluent were completely milled to synthesize nanoparticle precursor, whtich was subsequently calcined to decompose.Finally nanocrystallite oxides can be formed after simple washing to remove NaCl and drying. The products show tetragonal crystal SnO2 or hexagonal crystal by TEM,XRD,IR,SEM-EDAX,etc. The minimum crystal size of product was calculated to be several nanometers by XRD calculation. Nanocrystallite oxides prepared under various conditions were different in particle size. Effects of milling time, amount of diluent NaCl, ratio of balls to reacting agent, calcination temperature and time affecting on nanoparticle size were primarily investigated in this paper.The proper process parameters are list in the following: weight ratio of balls to reacting agents is 10:1-15:1, SnCl2(ZnCl2):Na2CO3:NaCl is 1:1:6-1:1:8, milling time 6-8 hours, calcination temperature 500~600癈 and 2 hours heating treatment. At the same time, the SnO2 gas sensing mechanism, the function of NaCl, reaction dynamics thermodynamics and the mechanism of mechanochemical synthesis were also analysized in the paper. Composite nanocrystallites SnO2-ZnO,SnO2-CdO,SnO2-Fe2O3,SnO2-CuO were prepared by the solid-state mechanochemical reaction of SnCl2,ZnCl2(CdCl2,FeCl3,CuCl2) and Na2CO3 with NaCl as diluent, which can prevent nanocrystallite growing during milling and subsequent calcination. This should be applicable for improving the sensing properties of SnO2 matrix chemical gas sensors.