多相爆轰管的优化设计及其制备纳米氧化钛材料的探索研究

以三种前驱气体(CH4-2O2、H2-0.5O2、C2H2-2.5O2)进行爆轰试验,研究了初始压力对爆轰参数的影响及规律,以测得的预混气爆轰压力、速度、胞格等性能参数表征了预混气爆轰特性。以测得的爆轰参数为依据自主设计了长度2m、内径80mm、壁厚8mm、点火能量为40J的爆轰管道。在自主设计的爆轰管道内采用氢气、氧气和四氯化钛为混合前驱体,通过气液爆轰法合成了纳米二氧化钛,采用TEM对产物进行了表征,结果表明获得的纳米二氧化钛其球形或者类球形颗粒大约为20-150nm。     

气相爆轰压力及环境温度对制备纳米TiO2粉末的影响

采用气相爆轰方法制备出金红石和锐钛矿相混合晶型的纳米二氧化钛粉末,并用X射线衍射(XRD)、透射电镜(TEM)等表征手法,研究了环境温度变化对其晶粒尺寸和晶相结构的影响.结果表明,随着环境温度的升高,所生成的二氧化钛颗粒的尺度变大,产物中金红石相含量增加,锐钛矿相含量减少.通过测定爆轰压力的变化,得出了反应发生爆燃转爆轰的过程中.     

爆轰对纳米晶体微结构的影响

利用X射线衍射对爆轰法制备的纳米晶粒如二氧化钛和纳米发光粉(SrAl2O4Eu2 ,Dy3 )进行了初步研究.通过比较纳米晶粒的XRD微结构参数(晶粒度、晶面指数(hkl)、晶格常数、晶面间距等)和常规粗晶的差异,以及平均畸变度的计算,定量地揭示了爆轰对纳米晶粒微结构的影响.研究表明,爆轰会对合成的纳米氧化物以及复合氧化物的微结构能产生不同的畸变效应.不同的晶粒尺度,不同的前驱体,产生的晶格畸变呈现各向异性晶格膨胀和收缩现象,如液相混合炸药制备的纳米氧化钛产生的平均畸变度是固相炸药制备纳米氧化钛的1.98倍,甚至达到2.72倍,同时随着晶体粒径的增大,平均畸变度减小;而爆轰法制备的SrAl2O4Eu2 ,Dy3 纳米发光粉,在晶粒度变化不大的条件下,经过600～800 ℃的热处理后却产生了先增大后减小的平均畸变度.     

气相爆轰法制备球形铜纳米粒子及其形成机理

本文以氢氧混合气体为爆炸源,乙酰丙酮铜(II)为前驱体,采用操作简单、高效的气相爆轰方式合成了类球形的铜纳米晶颗粒。进一步采用XRD、TEM、SAED和EDX对所获得产物的形貌特征、物相组成和微观结构进行了表征和分析。同时为了预测气相爆轰流场中铜纳米颗粒的生长特性,将Kruis模型引入气体爆轰反应程序中。研究结果表明：实验合成的类球型FCC结构纳米铜晶体分散性良好,平均粒径在24 nm左右且纳米铜晶体外包覆了1nm左右的较薄石墨层。基于Kruis模型对球形铜纳米粒子的生长特性预测结果与实验数据吻合较好,为可控合成铜纳米粒子提供了可靠的理论指导。     

爆轰法制备碳包覆铁镍合金纳米颗粒及其表征

对掺杂硝酸铁和硝酸镍复合炸药前驱体,采用爆轰法合成碳包覆铁镍合金纳米颗粒。通过XRD,TEM,XRF,VSM等方法对合成的碳包覆合金纳米颗粒的形貌特征、结构组成及磁性行为进行了分析表征。结果表明,通过有效调整前驱体中金属源材料比例和碳材料组成,可爆轰合成较为完美的核壳结构碳包覆铁镍纳米颗粒,所得球形的纳米颗粒尺寸主要分布在10～60nm范围内且分散性较好,组成核主要由不同比例的铁镍元素构成,外壳层主要由石墨碳构成;由室温下磁性分析可知,该纳米颗粒表现出良好的超顺磁性。     

含金属铜离子炸药爆轰合成石墨包覆铜纳米颗粒

主要采用硝酸铜、柠檬酸、油酸和RDX成功制作了含有铜离子的溶胶凝胶前驱体炸药,并在密闭容器中氩气保护下炸药爆轰合成了球形、颗粒尺寸均匀、核壳结构的石墨包覆铜纳米颗粒(Cu-Gs)。采用XRD、TEM、Raman等表征了爆轰产物的结构组成、形貌特征及包覆层构成。通过优化设计调整前驱体炸药的元素摩尔组成、密度及氧平衡,从而来寻求控制合成Cu-Gs的途径。最后简要讨论了Cu-Gs的生长机理。     

用溶胶-凝胶法在纳米孔材料VSB-1中制备纳米二氧化钛

采用溶胶-凝胶方法在纳米孔材料VSB-1的孔道中制备了二氧化钛的纳米颗粒.通过XRD,EDX,FTIR,UV-Vis和N2吸附等方法证实了纳米TiO2的确存在于VSB-1的孔道中.但当合成条件不同时,所得到产品的存在状态和性质也不同.主要研究了不同前驱体的浓度、不同的反应时间和不同尺寸的前驱体对产物的影响.     

水溶性聚合物对液相法合成纳米氧化锌的影响

以[Zn(OH)_4]~(2-)为前驱体溶液,利用聚合物和表面活性剂的共同作用来控制纳米晶的生长,化学液相法合成了纳米ZnO 单晶.借助于X-射线衍射仪、透射电镜、紫外可见光谱分析仪等手段表征和探讨了氧化锌纳米晶的物相组成、显微结构和谱学特征.并讨论了反应时间、反应温度、反应物配比等因素对产物形态的影响以及水溶性聚合物和表面活性剂的添加对无机粒子的成核和晶体生长的影响.结果表明,所得产物物相为球形结构的颗粒状纳米氧化锌,直径约为50 nm,粒径分布均匀,样品在200～300 nm可见光区域内有强的紫外吸收峰.     

低温制备纳米尖晶石粉体相变温度的研究

采用沉淀-低温燃烧法合成化学计量的纳米镁铝尖晶石粉体的前驱体 ,通过高温x射线衍射试验研究前驱体完全转变为纳米尖晶石的温度.结果表明相变的温度是1000℃.本研究在1000℃,1 h的条件下获得了纳米尖晶石粉体,通过XRD、TEM、BET等手段对所制各粉体进行了表征,一次颗粒为球形多晶,晶体结构完整,颗粒小,只有软团聚.     

烧结多孔Cu-Zn合金的脱合金行为

采用粉末冶金工艺制备微米多孔Cu-Zn合金前驱体,进而脱合金制备微纳米多孔铜。首先研究了烧结温度对前驱体合金微观结构的影响,然后对比了不同前驱体在不同浓度盐酸溶液中脱合金后的相组成和微观形貌,最后分析了前驱体合金在脱合金过程中的电化学行为。结果表明,以粉末冶金法与脱合金法相结合,可制备出微纳米双级多孔铜。不同烧结温度会造成前驱体合金的物相含量和孔结构发生变化,进而造成其脱合金过程的显著差异。Cu_(30)Zn_(70)前驱体包含Cu_5Zn_8与CuZn_5两相,脱合金时CuZn_5相优先被腐蚀;而Cu_(50)Zn_(50)前驱体仅含CuZn相,腐蚀速率更慢。在0.1mol/L腐蚀液中,试样不能完全脱合金;腐蚀液浓度增大至0.5 mol/L时,前驱体中的Zn完全脱去,微米级韧带由纳米多孔结构构成,其微米孔孔径为3.02～3.68μm,纳米孔孔径为157～183 nm。     

The preparation and characteristics of a rare earth/nano-TiO2 composite coating on aluminum alloy by brush plating

Nano-TiO₂ modified rare earth composite coatings are prepared on 2024 aluminum alloy by brush plating. The composite coating is composed of mainly Ce(OH)₃, Ce(OH)₄, CeO₂ and TiO₂, with less cracks and lower porosity. The addition of nano-TiO₂ enhances the adhesive strength of the rare earth coating to Al substrate, results in refined coating grains and increases the micro-hardness of the coating. The nano-TiO₂ modification obviously improves the corrosion resistance of the rare earth coating. For the composite coating containing 2% TiO₂, both the corrosion current density and the impedance are reduced by more than one order of magnitude in contrast to the values for the pure rare earth coating. The higher barrier ability and increased Ce³⁺ content in the Ce oxides may explain the increase of the corrosion resistance.     

Production of tungsten boride from CaWO4 by self-propagating high-temperature synthesis followed by HCl leaching

In this study, the conditions of producing tungsten boride powder from calcium tungstate (CaWO₄) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques were investigated. In the first stage of the experimental study, the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of CaWO₄, Mg and B₂O₃. It was found that increasing B₂O₃ content in the initial mixture resulted in an increase of W₂B₅/WB ratio along with Mg₃B₂O₆ in the SHS product. In the second step, Mg and Ca containing byproducts (i.e. MgO, Mg₃B₂O₆ and Ca₃B₂O₆) found in the SHS product were leached out by using aqueous HCl solution to obtain a clean tungsten boride product. The effects of particle size, temperature, time, acid concentration and solid/liquid ratio were selected as leaching parameters. The acid leaching experiments of the SHS product synthesized at 1:8:2.5 initial molar ratio of CaWO₄:Mg:B₂O₃ showed that optimum leaching conditions could be achieved by using 2.85 M HCl at 1/10 S/L ratio and the temperature of 80 °C for 60 min.     

Synthesis of LiFePO<Subscript>4</Subscript>/C as cathode material by a novel optimized hydrothermal method

Olivine LiFePO 4 , as a cathode material for lithium ion batteries, was prepared by a novel optimized hydrothermal method; afterwards, the product mixed with glucose was two-step (350℃ and 700℃) calcinated under high-purity N 2 atmosphere to obtain the LiFePO 4 /C composite. The study on the hydrothermal preparation method, which focused on the influences of molar ratios, initial pH value, reaction temperature, and duration, was made to promote the resultant performances and to investigate the relations between the performances and the reaction conditions. The resultant samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests, which include charge-discharge, electrochemical impedance spectroscopy, and cyclic voltammetry. The result shows that the optimal hydrothermal condition is to set the Li:Fe:P molar ratio at 3:1:1 and the reaction temperature at 180℃ for 5 h duration with an initial pH value of 7. The optimized sample, with an average particle size of 100 to 300 nm and a discharge capacity of 118.2 mAh·g-1 at 0.1C, exhibits a stable and narrow-gapped charge-discharge platform and small capacity losses after cycles.     

A study on water absorption in freestanding polyurethane films filled with nano-TiO2 pigments by capacitance measurements

The electrochemical impedance spectroscopy (EIS) was used to evaluate the water transport and dielectric properties of polyurethane films filled with nano-TiO₂ at different pigment/base (P/B) values in 0.5~mol/L NaCl solutions. EIS results were compared with gravimetric measurements on the freestanding films. The amount of water absorption showed great discrepancy between the two methods. The diffusion coefficient in the polyurethane film with P/B=30% was the smallest among those filled with nano-TiO₂ pigments. The dielectric constant  ε of the polyurethane varnish film obtained from the initial capacitance was in the range of typical values of polymers. SEM was used to measure the distribution of nano-TiO₂ particles in the polyurethane films.     

The evaluation of W/ZrC composite fabricated through reaction sintering of two precursors: Conventional ZrO2/WC and novel ZrSiO4/WC

In this study the W-ZrC composites fabricated by in situ reaction sintering of two precursors were compared, 1-The conventional WC and ZrO₂ which are ball milled with established molar ratio of 3–1 for 12 hours, gelcasted to form a green body and then undergo a pressure less sintering cycle, 2-A new and innovative way in which for the first time ZrSiO₄ was used instead of ZrO₂, and by testing different molar ratio between WC and ZrSiO₄ it was understood that the optimum ratio is 3–1 once again. Furthermore the starting ZrO₂ and ZrSiO₄ powder were selected in nano size and it was understood that by using nano powders the amount of unreacted and unwanted phase reduce, the reaction progress and the mechanical proprieties improve. Although the reaction sintered WC/ZrO₂ possess better properties, regarding the cost considerations, reaction sintering of WC/ZrSiO₄ is a much cheaper process.     

Sol-gel assisted preparation and characterization of silver indium diselenide powders

AgInSe₂ powders were successfully prepared via mixing sol-gel derived precursors, followed by a selenization process. To obtain the pure AgInSe₂ compound, excess amounts of In³⁺ ions were added into the starting solution to compensate the loss of In₂O₃ during the selenization process. A figure that depicts the relationship between the resultant compounds and different selenization temperatures was constructed according to the formed phases. The Raman spectrum and Rietveld refinement confirmed that the prepared AgInSe₂ belonged to the chalcopyrite structure. With increasing selenization temperatures, the AgInSe₂ powder particle sizes as well as the crystallinity increased significantly. The AgInSe₂ formation mechanism during the selenization process is proposed as a two-step process. Ag₂Se is formed in the first step and then induces the second-step reaction to produce AgInSe₂. The sol-gel route with a selenization process is introduced as a new approach to fabricate pure AgInSe₂ powders for use in thin-film solar cells.     

Electrolytic production of Ti-Ge intermetallics from oxides in molten CaCl2-NaCl

Titanium germanium intermetallics (Ti_xGe_y) were directly prepared from titanium oxide (TiO₂) and germanium oxide (GeO₂) powders mixture by using an electrodeoxidation process. The electrochemical experiment was carried out in a molten flux CaCl₂-NaCl at 800 °C with a potential of 3.0 V. The results show that monolithic germanide Ti₅Ge₃ intermetallic can be directly produced from TiO₂-GeO₂ or CaTiO₃-GeO₂ precursors (both molar ratios are 5:3), and the obtained Ti₅Ge₃ powders exhibit homogenous particle structure. In addition, the phase composition of the final product can be dramatically affected by the initial molar ratio of TiO₂ to GeO₂. The reaction mechanism of the electrodeoxidation process was discussed based on the experimental results. It is suggested that the electrodeoxidation process is an environmentally friendly method for the preparation of Ti-Ge intermetallics.     

Lanthanum ferrite ferromagnetic nanocrystallites by a polymeric precursor route

Reactive lanthanum orthoferrite nanoparticles were obtained by a polymeric precursor route. Nanoparticle growth and crystallization from amorphous precursor, as well as the formation of a grain boundary network in polycrystalline aggregates at different calcination temperatures were studied by conventional and high-resolution electron microscopy; electron and X-ray diffraction analysis; Raman; IR; and UV-vis spectroscopy. Microstructure measurements were compared to X-ray diffraction and chemical analysis results. Electron diffraction, combined with electron microscopy results were used to determine the content of amorphous phase. The coherent crystalline domain size and the particle size have been monitored by XRD and electron microscopy in order to determine the evolution of both crystal size and the onset temperature for crystallites formation. The results demonstrate that at 550 °C we obtain pure single-phase nanocrystalline LaFeO₃, sized ∼40 nm, without the presence of amorphous phase. The magnetization curves in the 5-350 K range indicate weak ferromagnetism of the LaFeO₃ powders.     

溶胶-凝胶法合成导电SrVO3 粉末

通过溶胶-凝胶法结合热处理合成了导电SrVO₃粉末。在溶胶配制过程,对Sr:V摩尔比进行精确调控,再通过对凝胶热分解行为的表征,确定其煅烧温度和除去残余碳,从而获得前驱体粉末,再将其在H₂中还原以获得最终产物。研究了煅烧温度、Sr:V摩尔比对产物形貌、结构和组成的影响,并采用标准直流四探针技术对样品的电导率进行测试。结果表明,当Sr:V摩尔比为1:1.06,煅烧温度500 ℃,再在850 ℃氢气还原,可以制备没有残余碳或钒的氧化物杂质的单相SrVO₃粉末。SrVO₃粉末的电导率达到714.3 S/cm,比石墨粉末的电导率（500 S/cm）高。     

Synthesis of a NiFe2O4 catalyst for the preferential oxidation of carbon monoxide (PROX)

The aim of this work was to study the NiFe₂O₄ spinel catalyst obtained by combustion reaction in the preferential oxidation of carbon monoxide reaction to conversion reactants H₂, CO and O₂ and to conversion products CH₄, H₂O and CO₂. The powders were prepared according to propellants chemical concept and characterized by XRD, TEM and catalytic tests. The XRD pattern shows the characteristic peaks of the spinel phase. The particle size calculated by TEM was 10.7 nm. The catalyst proved to be more selective to reagents for conversion into O₂ (89.5%) at 350 °C.