【作者】 甘浩宇；

【导师】 刘天模；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2008， 硕士

【摘要】 传统的陶瓷半导体气敏材料主要有SnO₂、Fe₂O₃、WO₃、ZnO、In₂O₃等过渡金属氧化物,但这些材料大多是广普型的气敏材料,对气体的选择性并不好。虽然通过贵金属掺杂和制膜工艺的改进气敏选择性有所改进,但是又增加了成本。从20世纪80年代起,人们发现ZnSnO₃和LaFeO₃等钙钛矿复合金属氧化物材料用传统工艺制备的气敏元件就能表现出良好的敏感特性。随后就开始了大量的研究,成为近年来研究的热点。本文以ZnSnO₃为研究对象,分别对这种材料的纳米化制备、气敏性能、掺杂改性等方面进行实验研究;对其气敏机理也进行了初步的探索研究。本课题采用共沉淀法制备了ZnSnO₃的前驱体,再通过高温焙烧合成得到了钙钛矿型复合氧化物。XRD图谱分析表明:用超声波振荡分散和低温陈化新工艺制得ZnSnO₃为单相结构,产物中没有杂相出现;而制得的粉末纯度也比传统工艺制得粉末的纯度高。EDS分析表明粉末中都没有别的杂质元素。TEM分析表明新工艺合成的ZnSnO₃材料粒度均匀,粒径小于40nm。将不同工艺制得的ZnSnO₃粉末以及掺杂后的粉末制备成烧结型气敏元件在HW-30A气敏检测仪进行气敏测试。研究结果表明:超声振荡分散后,-15℃陈化10小时,在600℃空气中烧结5小时制得的烧结型ZnSnO₃气敏感传感器对乙醇的灵敏度达15.239,掺入一定量的金属氧化物能不同程度提高传感器对乙醇的灵敏度和选择性。在所有的氧化物掺杂剂中,La₂O₃能显著提高其灵敏度,最佳掺杂量为5%wt。此外,掺La₂O₃的ZnSnO₃传感器的回复-响应时间为10s左右;在有其它气体存在时,这种掺杂ZnSnO₃传感器仍然对乙醇有较高的选择性;稳定性也较好。SEM对敏感层表面分析表明:气敏特性和表面的气孔率、显微裂纹分布和晶粒大小有很大关系。目前对ZnSnO₃的研究主要集中在酒精等有机气体方面,对氢气的气体敏感性能研究还不多见。ZnSnO₃掺杂PdCl2后发现其对H2有较高灵敏度,实验发现最佳掺杂量为5wt%.在1500ppm的气氛下,对H2有较高的灵敏度,是纯的ZnSnO₃对H2的26倍,为63.485。在存在其他气体的干扰下,掺杂5wt%PdCl2制备的ZnSnO₃气体敏感材料仍然对氢气具有较高的选择性,对杂质气体的抗干扰能力强,回复-响应时间足够实际应用。用点缺陷理论和质量作用定律解释了ZnSnO₃的电阻和气体分压成指数关系。其中指数和不同气体在敏感层表面的吸附-脱附反应有很大关系。当两种以上气体存在时,根据气体表面覆盖度的不同,就产生了优先吸附的现象,这是选择性的原因。掺杂剂的作用机理或是对被检测气体有较大的亲和作用,使气体更容易吸附,加速吸脱附和氧化过程;或是能改变表面的酸碱性,促进反应的发生,而提高其选择性和灵敏度;或是抑制晶粒生长,从而充分利用晶粒尺寸效应,提高传感器的灵敏度和稳定性。更多还原

【Abstract】 Traditional semiconductor ceramics gas sensitive materials are mainly some transition metal oxides including SnO₂、Fe₂O₃、WO₃、ZnO、In₂O₃ etc. However, these materials have still some insufficiencies in respects of selectivity, durability, and resistance to environmental influences such as higher temperature, humidity etc. Although much work has been done on the selection of additives and catalysts and on the improvement of production technology etc., things still fall short of the demand for quantitative detection. Consequently, in addition to the continued efforts to improve the existing materials, there is a constant exploration of new material aimed at obtaining gas sensors of better performance and still lower prices. This dissertation aims at an original zinc tin complex oxide （ZnSnO₃） based gas sensitive material. The nano-sized powder preparation, gas sensitive properties, gas-sensitive mechanics and modification of ZnSnO₃ have been researched.Perovskite-type ZnSnO₃ were prepared by the chemical coprecipitation method. Powders prepared by different preparation technology have been analyzed through X-ray diffraction. The results show: With the application of supersonic wave and hypothermia ageing technology to the coprecipitation method, nano-ZnSnO₃ powder prepared was purer than that prepared by the traditional coprecipitation method. Energy spectrum analysis indicated that there have been impurity elements in the powder. TEM analysis indicated that the powder was less than 40 nm and extraordinary mean.Gas sensitive characteristics of all agglomerate type sensors fabricated from the whole samples have been investigated mainly by means of HW-30A gas sensitivity detector. The following results could be highlighted: sensors that is manufactured from powders prepared by the technology of ultrasonic shock, ageing at -15℃for 10 hours and heat treated at 600℃for 5 hours have sensitivity（S=13.239 at the C2H5OH concentration of 1000 ppm）, and some amount of metal oxide additive is helpful for sensitivity and electivity towards ethanol. Among all additives, sensitivity of sensors can be enhanced prominently by La₂O₃ addition and is twice more than sensor from pure ZnSnO₃ as well as the optimal addition amount is 5%wt. Moreover, the response and recovery time is about 10 S, and this sensor with La₂O₃ addition still has a strong selectivity to ethanol when other gases exist at the same time, as well as excellent stability. SEM analysis about sensitive layer indicated that pore and micro crack size distribution and grain size have all significant influences on gas-sensitive characteristic.The point defect theory and the mass action law were applied to explain to the index relationship of the resistance of the sensor and the concentration of the gas in experience. Index value was relation to the adsorption/desorption responses of different gas on the surface of sensitive layer. There being two distinct gases in environment, on the basis of the differentiation coverage of variant gases the phenomenon of priority adsorption come into being, so it appears selectivity to gas. Addition agents either have so biggish appetency for tracer ethanol that it is easy to adsorb and accelerate the course of adsorption/desorption responses, or alter surface pH value to accelerate ethanol decomposed, or restrain grain growth to improve sensitivity and stability of sensor.更多还原