氧化铟纳米棒的气敏特性

以非离子表面活性剂烷基苯酚聚氧乙烯醚OP-10为形貌控制剂合成In2O3纳米棒.用热重-差示扫描量热法、X射线衍射和透射电镜对In2O3纳米棒的热分解过程、晶体结构和微观形貌进行表征.对纳米棒制得的气敏元件进行气敏性能测试,同时用扫描电子显微镜及比表面积和孔隙度分析仪对元件的表面形貌和材料的介孔结构进行了分析.结果表明:制得的In2O3为立方晶型的纳米棒,直径约20 nm,长度约120 nm.与In2O3纳米颗粒气敏性能相比,In2O3 纳米棒对三甲胺具有更高的灵敏度和选择性.用In2O3纳米棒制的气敏元件对三甲胺在一定的浓度范围内的灵敏度与浓度呈现良好的双对数线性关系.棒状材料中形成的大量介孔对气敏性能的提高有着重要的作用.     

SnO2基CO/CH4气敏元件的研究

以溶胶凝胶法合成的SnO2纳米粉体为基料,制备了平面厚膜CO/CH4气敏元件。实验研究了配方中添加有机硅化合物和稀土材料、加热器阻值对元件性能的影响。结果表明：通过控制合适的条件,可使元件对CO和CH4气体都有很好的灵敏度,且CO和CH4气体之间不存在相互干扰现象。     

碳纳米管掺杂纳米ZnO气敏元件敏感特性

采用溶胶–凝胶法合成纳米ZnO,以碳纳米管(carbonnanotube,CNT)为掺杂剂制备CNT–ZnO旁热式气敏元件样品。用X射线衍射和透射电镜分析了ZnO的结构,用扫描电镜观察CNT–ZnO气敏元件样品表面的显微形貌,研究了CNT–ZnO元件对甲醛和丙酮等气体的气敏性能。结果表明:CNT存在于平均粒径为20～30nm的ZnO晶粒间,增加了CNT–ZnO材料的气孔率。CNT–ZnO气敏元件对丙酮的灵敏度高于纯ZnO元件,掺0.6%(质量分数)CNT的ZnO气敏元件(0.6%CNT–ZnO)气敏元件对质量分数为40×10–6甲醛有最高灵敏度(15.11)。而且具有能检测低浓度甲醛气体、选择性好,响应速度快(响应时间约为15s)的优点。     

聚噻吩/WO_3纳米复合材料的制备及气敏性能研究

采用化学氧化聚合法制备出了不同聚噻吩(PTh)掺杂量的PTh/WO3纳米复合材料进行制备,利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)对PTh/WO3纳米复合材料的晶体结构和形貌进行了表征;并研究了PTh/WO3纳米复合材料制备的气敏元件对H2S气体气敏性能。结果表明:PTh/WO3纳米复合材料对H2S气体具有较高的灵敏度,用PTh质量分数为50%的复合材料制成的气敏元件在工作温度为60℃时,对500×10-6的H2S灵敏度达到98,且具有较快的响应与恢复时间。     

WO_3粉体的溶胶-凝胶合成法与气敏性能

以有机溶剂为诱导剂,采用溶胶-凝胶法制备了纳米WO3粉体,使用XRD进行了结构表征。结果表明,合成的WO3粉体为正交相。用该粉体制成厚膜型旁热式气敏元件,测试结果发现：在工作电压为5V时,气敏元件对甲醇、乙醇等还原性气体具有较高的灵敏度,可以检测体积分数低至5×10-4%的甲醇、乙醇。可望用于制备对甲醇气体的体积分数进行测定的价廉的气敏元件。     

EuFeO_3纳米材料的制备及其气敏特性研究

以Eu_2O_3和Fe(OH)_3为反应前驱体,以NaCl为介质,采用固相反应法合成了稀土复合氧化物EuFeO_3纳米粉体。分别用XRD和TEM对粉体的物相和形貌进行了表征,并测试了其气敏性能。结果表明:反应物料于1000℃煅烧4 h可获得纯相EuFeO_3纳米粒子;在工作温度320℃时,以该纯相纳米EuFeO_3材料为基的元件对丙酮的响应强且选择性好,其灵敏度与丙酮气体的浓度的对数之间有良好的线性关系,元件对浓度为50 ppm(10~(-6))丙酮气体的灵敏度达26.2,响应-恢复时间为14 s和23 s。     

WO3基H2S气敏材料的研究

采用正交试验法和单水平试验法研究了热处理温度及掺杂元素对ＷＯ３基Ｈ２Ｓ气敏元件灵敏度、选择性、稳定性,响应恢复特性及元件阻值的影响,得到了较为理想的Ｈ２Ｓ气敏元件。根据提出的气敏机理模型较好地解释了热处理温度、掺杂氧化物酸碱性及催化活性等对Ｈ２Ｓ气体灵敏度的影响。     

α-Fe_2O_3纳米微球的合成及气敏性能研究

采用溶剂热法制备了球状结构的氧化铁前驱体,再经400℃热处理后得到α-Fe_2O_3纳米微球。通过TG、IR、XRD和SEM等手段对产物结构和形貌进行了表征。结果表明,合成的α-Fe_2O_3纳米微球直径约为500 nm。此外,我们将α-Fe_2O_3纳米微球制备成厚膜型气敏元件并进行气敏性能测试,在工作温度为150℃时,α-Fe_2O_3纳米微球对苯胺(AN)有良好的选择性和较高的灵敏度,最低检出限可达到1.9 mg/m3,对38 mg/m3苯胺的响应值为10.4。测试结果表明,α-Fe_2O_3纳米微球可用于制备苯胺气体传感器。     

Cu掺杂SnO_2纳米粉体的制备及气敏特性

控制不同n(Cu2+)/n(Sn4+),用均匀共沉淀法制备了平均粒径约80 nm的金红石型结构Cu掺杂SnO2纳米粉体;并以白云母为基片制备出Cu掺杂SnO2气敏元件。用TG-DSC、XRD、SEM对样品的相变、结构、形貌进行了分析,并测试了气敏元件的阻温特性和75℃氢气敏感性能。结果表明,Cu掺杂抑制了SnO2晶核的生长,使SnO2结晶度由约75%减小到50%,晶粒尺寸由约18 nm减小到6 nm;Cu掺杂使n型半导体SnO2的空气电阻值由1~8 kΩ提高到9×105~3×107MΩ,并使元件在75℃对体积分数为2 000×10-6氢气的灵敏度提高约20倍;n(Cu2+)/n(Sn4+)≈0.01时,元件对体积分数为4 000×10-6氢气的灵敏度高达约42。     

分等级结构ZnSnO_3气敏材料的合成及其气敏性能研究

ZnSnO_3用传统工艺制备的气敏元件就能表现出良好的敏感特性,是当前研究热点之一。采用沉淀法制备了ZnSnO_3的前驱体,之后再将制得前驱体进行高温焙烧,最后得到我们所需的钙钛矿型复合氧化物。制备是通过锌离子与柠檬酸钠以及四氯化锌反应制得制得六羟基合锡酸锌,控制两组变量形成能对照,这两组变量分别为锌离子的来源以及柠檬酸钠的用用我们通过高温焙烧得到ZnSnO_3制成气敏器件,然后对其进行气敏测试,得到使ZnSnO_3气敏性达到最佳的气体条件。     

Application of Compositionally Diphasic Xerogels for Enhanced Densification: The System Al2O3-SiO2

Stoichiometric mullite (71.38 wt% Al₂O₃-28.17 wt% SiO₂) and 80 wt% Al₂O₃-20 wt% SiO₂ gels were prepared by the single-phase and/or diphasic routes. Dense sintered bodies were prepared from both sets of gels in the Al₂O₃-SiO₂ system. Apparent densities of 96% and 97% of theoretical density were measured for the diphasic (using two sols) mullite samples sintered at 1200° and 1300°C for 100 min, respectively; this compared with 85% and 94% for the single-phase xerogels under the same conditions, and to much lower values for mullite prepared from conventional mixed powders. The microstructure of the mullite pellets from diphasic xerogel precursors is also considerably finer.     

Preparation of KTaO3 and KNbO3 Solid Solutions through Sol–Gel Processing

Potassium tantalate–niobate solid-solution (KTN) powders and thin films were prepared from metallo–organic compounds through sol–gel processing. The KTN precursors were chemically modified and then prehydrolyzed with various concentrations of water. The stability of the modified solutions and the effects of prehydrolysis on the crystallization are discussed. Powder gels were obtained by exposing the solution to the atmospheric water, hydrolyzing the solutions. Alternatively, thin films were deposited on fused silica, silicon, sapphire, MgO, and SrTiO₃, using the spinning technique. The pyrolysis and crystallization of KTN powders and films were investigated by differential thermal analysis, theromogravimetric analysis, and X-ray diffraction. The effects of substrate and other processing parameteres on the crystal structure of the KTN phases were also investigated. KTN powders crystallized into a perovskite phase regardless of the processing conditions. The crystal structure of the KTN thin films had a strong dependency on the crystal structure of the substrates, while other processing parameters played smaller roles. Pyrochlore KTN was the major phase that crystallized on fused silica and silicon, whereas oriented perovskite KTN was obtained on single-crystal MgO and SrTiO₃.     

Synthesis of LaAlO3 powder using triethanolamine

LaAlO₃ powders were successfully synthesized by pyrolysis of complex compounds of lanthanum and aluminum with triethanolamine (TEA). The precursors and the derived powders were characterized by simultaneous thermogravimetry analysis (TG) and differential scanning calorimetry analysis (DSC), X-ray diffractometry (XRD), specific surface area measurements, and transmission electron microscopy (TEM). Pure LaAlO₃ phase was obtained at 775 °C for 2 h or 750 °C for 4 h, without formation of any intermediate phase. Pores were found from TEM images of LaAlO₃ powders prepared at 800 °C for 2 h.     

Microwave-assisted preparation of submicron-sized FeTiO3 powders

FeTiO₃ powders were prepared from (Fe+Ti) mixed carbonate precursor by the microwave-assisted calcination method. The thermal analysis of the precursor was conducted by TG/DSC. It is demonstrated that the calcination process can be divided into three different stages: the removal of water, the decomposition of precursor and the formation of FeTiO₃. A variety of techniques, such as XRD, FT-IR, SEM and EDS were utilized to characterize the samples. The results indicated that FeTiO₃ powders can be prepared by microwave-assisted calcination for 20 min at 450 °C, while those cannot be obtained by conventional one until reaction time exceeds 120 min at 600 °C. The FeTiO₃ powders prepared by microwave-assisted calcination are nearly spherical with limited aggregation and have a mean particle size of 400–500 nm.     

Sm掺杂BaTiO3纳米粉体的制备与表征

以钛酸四丁酯与醋酸钡为钛酸钡前驱体,PEG为分散剂,硝酸钐为掺杂物种给体,采用溶胶-凝胶法制备改性的Sm掺杂BaTiO3纳米粉体。样品经X射线衍射(XRD)与差热-热重联用(DSC-TGA)的方法对其进行了表征。研究了煅烧温度与分散剂对BaTiO3粉体粒径与相的影响。结果表明:立方相在700～850℃生成,前驱体经950℃热处理制得后呈四方相BaTiO3。分散剂PEG可抑制BaTiO3晶粒增长;随煅烧温度升高,粉体粒径增大。适量Sm掺杂可以抑制杂质BaCO3相的形成。     

Effect of propellant on the combustion synthesized Sr-doped LaMnO3 powders

Lanthanum strontium manganite (LSM) powders of composition La_0.7Sr_0.3MnO₃ are good candidates for cathode application in solid oxide fuel cells. This paper reports the synthesis of LSM powders from nitrate precursors by the combustion method, using two different propellants (urea and glycine) and varying the propellant/nitrate ratio. Thermogravimetric analysis (TGA) revealed two or three decomposition stages of the as-synthesized samples, with complete burn out of organics at about 850–900 °C. X-ray diffraction (XRD) patterns showed formation of only LSM phase for the sample synthesized with excess of urea, whereas SrCO₃ and MnCO₃ phases were also found for the samples prepared from glycine. The powder is better crystallized when a homogeneous gel is formed before burning. The crystallite size calculated using the Scherrer equation is in the range of 15–20 nm. Scanning electron microscopy (SEM) revealed the presence of agglomerates, formed by fine particles of different shapes.     

Synthesis and characterization of Y2O3-ZrO2 and Y2O3-CeO2-ZrO2 precursor powders

Thixotropic gels of the precursor powders of the titled compounds have been prepared by the addition of oxalic acid to the mixed solutions of metal salts at room temperature (≈ 27 °C). The clear sols of yttrium-zirconyl oxalate (YZO) and yttrium-cerium-zirconyl oxalate (YCZO) gelled within a few hours and were oven-dried at 40 °C. The various stages of gelation behaviour of the sols are explained on the basis of DLVO theory. By repeptizing the dried gel powders with water, concentrated sols were prepared. The gelation time as a function of chloride ion concentration is discussed for both sols. The nature of the temperature dependence of the dried gel powders was studied by means of thermogravimetric analysis and differential thermal analysis. Powder X-ray diffraction was used to study the crystallization behaviour of the dried amorphous gel powders. It is found that these powders crystallize in tetragonal phase when calcined at 850 °C for 1 h. Estimation of surface area and infra-red characterization have also been carried out for the prepared powders.     

Synthesis and characterization of Al2O3 nanopowders by a simple chitosan-polymer complex solution route

Al₂O₃ nanopowders were synthesized by a simple chitosan-polymer complex solution route. The precursors were calcined at 800–1200 °C for 2 h in air. The prepared samples were characterized by XRD, FTIR and TEM. The results showed that for the precursors prepared with pH 3–9 γ-Al₂O₃ and δ-Al₂O₃ are the two main phases formed after calcination at 800–1000 °C. Interestingly, when the precursor prepared with pH 2 was used, α-Al₂O₃ was formed after calcination at 1000 °C, and pure α-Al₂O₃ was obtained after calcination at 1200 °C. The crystallite sizes of the prepared powders were found to be in the range of 4–49 nm, as evaluated by the XRD line broadening method. TEM investigation revealed that the Al₂O₃ nanopowders consisted of rod-like shaped particles and nanospheres with particle sizes in the range of 10–300 nm. The corresponding selected-area electron diffraction (SAED) analysis confirmed the formation of γ- and α-Al₂O₃ phases in the samples.     

Structure and Properties of (Ba,Ca) TiO3 Ceramics Prepared Using (Ba,Ca)TiO3 Ceramics I, Crystallographic and Microstructural Studies

Ba_1–xCa_xTiO₃ powders have been prepared using a novel route involving solid-state reaction in a mixture of Ba_1–xCa_xCO₃ and TiO₂. The Ba_1–xCa_xCO₃ precursors used in this method were prepared by a chemical coprecipitation route to ensure a uniform supply of Ba and Ca ions during thermochemical reaction with TiO₂. The compositional homogeneity of Ba_1–xCa_xTiO₃ powder prepared by such a semiwet route is compared with those prepared by the conventional dry route, involving thermochemical reaction in a mixture of BaCO₃, CaCO₃, and TiO₂, using principles of X-ray line broadening. It is shown that the powders obtained by the semiwet route possess better compositional homogeneity, over a length scale of 1800 Å corresponding to the coherently scattering domain size, than those prepared by the conventional dry route. Microstructural studies have revealed grain sizes of the order of 1 μm and several micrometers, respectively, for ceramics prepared by the semiwet and conventional dry routes. The solid solubility limit of Ca in Ba_1–xCa_xTiO₃ ceramics fired at 1300°C is 16 mol% for samples prepared by the semiwet route while conventionally processed ceramics had a Ca solid Solubility limit of 12 mol% at the same temperature.     

Preparation of BaTiO3 by the hydrothermal method

The results of hydrothermal preparation of BaTiO₃ fine powders are reported. The effects of the reaction temperature, the molar ratio of Ba/Ti in the precursors, the chemical form of the precursors on the phase composition, the size and the morphology of the products are presented. The higher the temperature, the higher the basicity and the greater the molar ratio of Ba/Ti in the precursor, the easier the formation of the perovskite type BaTiO₃ crystallite will be. It was found that BaTiO₃ microcrystals(150–300 nm) could be synthesized through the hydrothermal reaction of commercial TiO₂ with Ba(OH)₂ aqueous solution, while the hydrothermal reaction of the newly prepared Ti(OH)₄ gel with the Ba(OH)₂ solution produced highly crystallized, well dispersed perovskite type BaTiO₃ crystallites with very fine (< 100 nm) particles. The newly prepared Ti(OH)₄ gel proved to be suitable precursor for the hydrothermal preparation of BaTiO₃ fine powders. X-ray diffraction (XRD) of the hydrothermal BaTiO₃ powders reveals a simple cubic perovskite structure. Above that, the lattice constant decreased with the increase of the reaction temperature. These abnormal crystallographic features are assumed to result from lattice defects, due to OH⁻ incorporation in the perovskite lattice.