| ITO gas-sensing material is a composite that composed of indium oxide and tin oxide. It has many advantages as:high sensitivity,simple structure, small size, light weight, durable, high impedance of the toxic gas and output signal, low cost. In order to make it more suitable for actual production, people always use various means to improve its gas sensing performance.Nowadays, the improve methods of gas-sensing properties of ITO gas sensor chiefly were noble metal-doped and increase the specific surface area. In this paper, we tested the sensitivity of porous ITO gas sensing materials and porous ITO material that loaded with noble metals. Simulated the change process of grain size, porosity, sintering neck and the diffusion process of noble metal atoms using molecular dynamics simulation. We obtained good experimental and simulation results.Mapped the oxygen potential diagram of SnO2and In2O3through thermodynamic calculation.According to the definition of oxygen potential diagram we decided the solid-phase sintering process as:1h heating from room temperatureâ†'873K(supply oxygen, maintain the temperature for1h)1.5h heatingâ†'1573K(supply oxygen, maintain the temperature for3h)â†'furnace colling(supply oxygen)â†'800K(stop supplying oxygen)Prepared porous ITO material using the above process. The microstructure and phase analysis results showed that the porous ITO matrix had a good structure of porous material: the pore was evenly distributed, the particle size and the pore size was similar.Calculated the respective thermal decomposition temperatures of AgN03, Pd(NO3)2and PtC14. Than decided the thermal decomposition process as:the thermal decomposition temperatures were719.1K,1101.3K and858.3K. The analysis of the result of experiment showed that the noble metal was loaded on the porous ITO material and all of them were elemental. But the surface micro-structure was unsatisfied after loading.The sensitivity test results showed that, the porous ITO sample which did not be loaded with noble metal showed a best sensitivity as1.76to3000ppm ethanol vapor at room temperature. The sensitivity of porous ITO was improved by Pd loading. But overall, the sensitivity of noble metal loaded porous ITO was unsatisfied because of the surface damage by impregnating solution and the noble metal covered on the ITO grain. It showed that, the microstructure of the surface of porous ITO and noble metal was the important factor which affected the sensitivity.Simulation of the sintering process using Materials Explorer5.0showed that, the simulation result was corresponded with the experimental result. Through the analysis of simulation result, we found that Sn atoms dissolved in the In atoms and formed reunions..The In atoms was the main role in promoting the sintering process.The sintering neck and grain growth,and stomatal narrowing was caused by the diffusion of In atoms.Through the simulation of the high-temperature-diffusion process of the precious metal atoms on porous ITO, we found that, at the different simulation temperature the diffusion motion of the noble metal atoms on the ITO material was varies. Ag and Pt atoms always gathered in the vicinity of the sintering neck, small part of the atoms on the aggregation toward the pore direction. Small portion of Pd atoms gathered in the vicinity of the sintering neck, most of them gathered around the pore or in the pore. Analyzed the reason of the different load position between noble metal atoms at atomic level... |
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