A study of transition from n-to p-type based on hexagonal WO3 nanorods sensor

Hexagonal WO3 nanorods are fabricated by a facile hydrothermal process at 180 ℃ using sodium tungstate and sodium chloride as starting materials. The morphology, structure, and composition of the prepared nanorods are studied by scanning electron microscopy, X-ray diffraction spectroscopy, and energy dispersive spectroscopy. It is found that the agglomeration of the nanorods is strongly dependent on the PH value of the reaction solution. Uniform and isolated WO3 nanorods with diameters ranging from 100 nm-150 nm and lengths up to several micrometers are obtained at PH = 2.5 and the nanorods are identified as being hexagonal in phase structure. The sensing characteristics of the WO3 nanorod sensor are obtained by measuring the dynamic response to NO2 with concentrations in the range 0.5 ppm-5 ppm and at working temperatures in the range 25 ℃-250 ℃. The obtained WO3 nanorods sensors are found to exhibit opposite sensing behaviors, depending on the working temperature. When being exposed to oxidizing NO2 gas, the WO3 nanorod sensor behaves as an n-type semiconductor as expected when the working temperature is higher than 50 ℃, whereas, it behaves as a p-type semiconductor below 50 ℃. The origin of the n- to p-type transition is correlated with the formation of an inversion layer at the surface of the WO3 nanorod at room temperature. This finding is useful for making new room temperature NO2 sensors based on hexagonal WO3 nanorods.     

二氧化锰添加剂对莫来石相发育及性能影响

以氧化铝和二氧化硅作为原料,二氧化锰作为添加剂,在烧结温度1300℃时,研究了不同二氧化锰添加量制备所得试样的结构和性能,通过对试样物相组成、显微结构、体积密度、显气孔率和抗折强度五方面的分析,研究了二氧化锰作为添加剂对莫来石相的形成、发育和性能的影响,并分析了莫来石相形成和发育过程中二氧化锰的作用机理.结果表明:MnO2的添加能促进固相烧结反应,降低烧结温度,抑制石英相的生长,促进莫来石相的形核和发育.同时在烧结过程中Mn4+能够加快晶粒生长.     

氧化钙对陶粒支撑剂结构和破碎率的影响

以铝矾土和煤矸石为主要原料,添加不同含量的碳酸钙,在1350℃制备了低成本的陶粒支撑剂,通过X射线衍射(XRD)和扫描电子显微镜(SEM)对陶粒支撑剂的物相组成和微观形貌进行表征.结果表明,添加了碳酸钙的陶粒支撑剂形成新的物相钙长石,随着氧化钙含量的增加,莫来石的晶粒逐渐细化,细化的晶粒提高了陶粒的强度和抗破碎能力.添加量为5wt;碳酸钙的陶粒支撑剂在35 MPa、52 MPa闭合压力下的破碎率均最低,符合石油天然气行业标准SY/T5108-2014.     

保温时间对添加废陶粒砂制备支撑剂结构和性能的影响

为了缓解高品位铝矾土资源日益匮乏的现状,同时降低支撑剂的生产成本,本研究以二级铝矾土和固废陶粒砂为主要原料,通过添加锰矿粉和白云石作为烧结助剂,最终经1260℃烧结制备得到刚玉-莫来石基陶粒支撑剂.在烧结过程中,讨论了保温时间对支撑剂物相结构和性能的影响.结果表明:随着保温时间的延长,支撑剂物相开始析出针状莫来石,而且晶粒尺寸逐渐变大,随之转变为棒状莫来石并与颗粒状的刚玉相互交叉分布于支撑剂内部,从而形成致密的交联结构.当保温时间为2 h时,支撑剂的性能最佳:体积密度为1.65 g/cm3,52 MPa闭合压力下的破碎率达到8.5;,符合石油天然气行业标准要求,说明固废陶粒砂可以被循环利用制备支撑剂.     

H3BO3添加对MgAl2O4-CaAl4O7-CaAl12O19复合陶瓷的相演变和力学性能的影响

用固相烧结工艺在1300～1600℃温度下制备了MgAl2O4-CaAl4O7-CaAl12O19(MA-CA2-CA6)耐高温复合陶瓷,研究了H3BO3添加对该陶瓷的主相含量、显微结构和力学性能的影响.结果 表明,H3BO3在MA-CA2-CA6复合材料中产生少量的富硼液相,加速了基体中物质互相扩散和转移,促使CA2相通过溶解沉淀机制生成了片状的CA6和硼酸钙液相,并使CA6晶粒由长板片状向短片等轴状演变,提高了材料的力学性能,有效促进了MA-CA2-CA6复合材料显微结构致密化.经1600℃下烧结的样品,当添加H3BO3含量为5wt;时,样品中CA2相含量由58.63;降为7;,而CA6相含量由31.22;增为75.2;,同时样品的显气孔率减少至9.7;,其体积密度增大到3.18 g/cm3,此时MA-CA2-CA6耐高温复合陶瓷显微结构致密,力学性能最佳.     

Room temperature NO_2-sensing properties of hexagonal tungsten oxide nanorods

Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope(SEM), transmission electron microscope(TEM), energy dispersive spectroscopy(EDS), and x-ray diffraction(XRD). The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor(400-℃-annealed WO_3 nanorods) showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.     

烧结温度对添加复合助剂制备莫来石-刚玉基陶粒支撑剂性能的影响

为了降低陶粒支撑剂的烧结温度,本文以低品位铝矾土和粘土为主要原料,通过添加复合助剂锰矿粉及白云石制备陶粒支撑剂,并研究烧结温度对陶粒支撑剂结构、性能的影响.在烧结过程中发现,引入一定量的锰矿粉和白云石后,在陶粒内部会形成适量液相,可以填充孔隙,包覆于莫来石和刚玉晶粒间促进晶体的生长发育,从而形成致密结构.当烧成温度为1310℃时,制备得到的支撑剂体积密度与视密度分别为1.65 g/cm3和2.99 g/cm3,52 MPa闭合压力下破碎率为8.97;,符合石油天然气行业标准对低密、高强陶粒支撑剂的要求,说明复合助剂在降低烧结温度的前提下还能够提高支撑剂抗破碎能力.     

多孔硅基WO3气敏传感器的制备与性能研究

以钨酸钠和氯化钠为原料,采用水热法在硅基多孔硅上原位生长WO3纳米棒薄膜,制成p型多孔硅基-n型WO3复合结构气敏传感器.为了获得最大比表面积的复合形貌,详细研究了水热反应时间和温度对多孔硅基WO3复合结构显微组织表面形貌的影响.利用扫描电镜、粉末衍射等表征手段测试并分析了多孔硅基表面WO3纳米棒薄膜的形貌以及晶体结构,并测试了复合结构传感器在不同工作温度下的气敏响应特性,结果表明:该气敏传感器在室温下便对有毒气体NO2具有高灵敏度以及稳定的重复性.