| The property of its gas sensor is directly affected by the preparation technology and gas sensitivity of metal oxide semiconductor materials. Gas sensor manufactured by metal oxide semiconductor materials gas sensitive materials of single SnO2 or In2O3 has the disadvantages of bad stability,low selectivity, and low sensitivity and so on. Whereas in recent years,people discovered that metallic oxide composite material has a good gas property,and it has better selectivity and sensitivity than single metallic oxide. Consequently,the study of the preparation technology and gas sensitivity of SnO2-In2O3 composite material is of critical direction significance to the improvement of gas sensor property.In this thesis,it carries out the thermodynamic study of sintering process of solid-phrase preparation of porous SnO2-In2O3 composite materials based on the subjects of porous SnO2-In2O3 composite materials. It controls the technological conditions of the SnO2 contents,sintering temperature and ssing pressure to improve the pore structure and gas sensing property of porous SnO2-In2O3 composite materials; it analyzes carefully the microcosmic microstructure and performance of the porous SnO2-In2O3 composite materials after sintering by modern analysis and test methods of X-ray diffraction,scanning electron microscope and gas sensing testing system;it also calculates and simulates the SnO2 low index surfaces and the CO adsorption mechanism by using the first principle. And the final results are as follows:To prepare the thermodynamic study of porous SnO2-In2O3 composite materials we find that,SnO2 and In2O3 will decompose at 102O.685K and 1262.584K. In order to prevent it,SnO2 and In2O3 should be preserved heat for sometime. By analyzing CO gas sensing properties of porous SnO2-In2O3 composite materials with different sintering temperatures,ssing pressures and SnO2 contents and get the final olid-phrase method: ITO and SnO2 mixde powder with 30% SnO2 93MPa(ssing pressures)â†'873k(oxygen free and heat preservation for lh)â†'1573k(oxygen free and heat preservation for 3h)â†'furnace cooling(keep on providing oxygen)â†'reducing temperature to 800k(cut off the oxygen)By analyzing microscopic constitutions and gas sensing properties of porous composite materials with different SnO2 contents,sintering temperatures and ssing pressures,we get to learn that the SnO2 finally solutes into In2O3,the grain size enlarges and the pore structure and gas sensing property improve with the rising of the sintering temperature; and that the pore structure and CO gas sensing property of porous SnO2-In2O3 composite materials can be improved with the increase of SnO2 contents;but the pore structure of porous SnO2-In2O3 composite materials changes a little with the increasing of ssing pressure.The results of calculation and simulation of density functional first-principal present that the two low indexes in the family of crystal planes-{110},{100} among the rutile type of SnO2(110) surface has the lowest surface energy and the most stable structure compared with other low index surfaces.By contrasting and analyzing the electronic density of states of SnO2 oxidized (110) surface and the reductive (110) surface,we know that the reductive (110) surface has better electric conductivity and is selected as the research surface of the CO adsorption mechanism;calculating and simulating the adsorption of CO by the reductive (110) surface,and the analysis results of adsorption energy,density of energy state and electron population show that the best adsorption site of CO on the reductive (110) surface is Sn4C;CO adsorption not only influences the electronic density of state at the adsorption site of Sn4c,but also the distribution of electronic density of state of Sn5C and the inner atoms and as a result,it changes the electric conductivity of the whole reductive (110) surface;and since the CO adsorption leads to the deviation of Fermi energy,the Fermi energy lifts and this is an important reason affecting the electric conductivity of the SnO2 surface.By calculating and simulating the density functional first-principal,we find out that the rutile type of SnO2 is a kind of semiconductor surface-controlled gas sensor,and it has good adsorption towards CO and belongs to self-adsorption. The research of the adsorption of rutile type of SnO2 towards CO provides a theoretical foundation for the argument of the gas sensitivity of porous SnO2-In2O3 composite materials towards CO with the increasing of SnO2 contents. |
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