氧化钇稳定立方晶型氧化锆增强钨基合金制备工艺及性能北大核心CSCD

采用共沸蒸馏法结合粉末冶金法制备了氧化钇稳定立方晶型氧化锆增强钨基合金（W-3.0 mass%YSCZ）。利用XRD、SEM、EDS、TEM等检测手段对合金制备过程中不同阶段材料组织、形貌及微观结构进行了分析与表征,测定了复合钨粉的粒度、钨合金的密度、显微硬度、磨损性能及动态压缩性能。结果表明：p H值对前驱体粉体的粒度有显著影响,p H=2的初始溶液制得的前驱体粉体粒径细小,随着初始溶液的p H值增大,复合粉末粒径逐渐增加;p H=2的初始溶液制得的前驱体粉经550℃×4 h煅烧后得到粒径为40～60 nm煅烧粉体,再经750℃×2 h＋900℃×4 h氢气还原后得到尺寸为35～50 nm的钨与ZrO_2-Y2O3构成的近球形纳米级复合粉末;制得的钨合金中的ZrO_2为立方晶型,表明常温下Y2O3对ZrO_2晶型起到了稳定作用;ZrO_2-Y_2O_3颗粒对钨晶粒具有明显的细化作用,获得的钨晶粒粒径为3～6μm;钨基合金相对密度达90.9%,抗压强度达到1009 MPa,耐磨性较纯钨提高了约18.7%。     

氧化钇稳定立方晶型氧化锆增强钨基合金制备工艺及性能

采用共沸蒸馏法结合粉末冶金法制备了氧化钇稳定立方晶型氧化锆增强钨基合金(W-3.0 mass%YSCZ)。利用XRD、SEM、EDS、TEM等检测手段对合金制备过程中不同阶段材料组织、形貌及微观结构进行了分析与表征,测定了复合钨粉的粒度、钨合金的密度、显微硬度、磨损性能及动态压缩性能。结果表明:p H值对前驱体粉体的粒度有显著影响,p H=2的初始溶液制得的前驱体粉体粒径细小,随着初始溶液的p H值增大,复合粉末粒径逐渐增加;p H=2的初始溶液制得的前驱体粉经550℃×4 h煅烧后得到粒径为40~60 nm煅烧粉体,再经750℃×2 h+900℃×4 h氢气还原后得到尺寸为35~50 nm的钨与ZrO_2-Y2O3构成的近球形纳米级复合粉末;制得的钨合金中的ZrO_2为立方晶型,表明常温下Y2O3对ZrO_2晶型起到了稳定作用;ZrO_2-Y_2O_3颗粒对钨晶粒具有明显的细化作用,获得的钨晶粒粒径为3~6μm;钨基合金相对密度达90.9%,抗压强度达到1009 MPa,耐磨性较纯钨提高了约18.7%。     

纳米银的制备及其表征

采用液相化学还原法以抗坏血酸为还原剂,十二烷基硫酸钠为表面活性剂,在不同温度磁力搅拌的作用下,还原硝酸银溶液,制备成球形的纳米银粒子。利用紫外分光光度计考察反应温度、AgNO3浓度以及还原剂浓度对纳米银粒径的影响,利用XRD来观察纳米银粒子的晶型,用SEM观察纳米银粒子的表面结构以及粒径大小的分布范围。在AgNO3浓度为0.08mol/L、抗坏血酸浓度为0.1mol/L、温度为20℃时,制备的纳米银粉末纯净而均匀,平均粒径为30nm。     

球形纳米银粉的制备研究

在较高浓度的硝酸银溶液中，采用水合肼为还原剂，PVP为保护剂的化学还原法制备了纳米银粉。通过对还原剂、保护剂用量和硝酸银浓度、温度、还原剂的加入方式、pH值等因素对纳米银粉粒度和形貌影响的考察，获得了制备纳米银粉的工艺。在AgNO3浓度为0．6mol／L，PVP／Ag摩尔比为1．5，水合肼浓度为0．6mol／L，pH值为5～6，温度为60℃的条件下，制备出了粒度均匀且粒度在50nm左右的纳米银粉。     

配位共沉淀-直接还原法制备超细纤维状铁镍合金粉(英文)

采用配位共沉淀制备了铁镍合金前驱体,用氢气直接还原前驱体得到了超细纤维状铁镍合金粉。系统研究了反应物浓度、pH值、反应温度及添加剂等参数对前驱体制备过程的影响。分别采用XRD、TG-DTA和SEM对前驱体的结构、热分解过程和形貌进行了表征。结果表明,采用质量分数2%的PVP作为添加剂,当Fe2+和Ni2+(1:1)总浓度为0.8mol/L,pH值为6.2,反应温度为60°C时,可以制得分散良好、形貌均匀的纤维状前驱体。前驱体在420°C的氮气和氢气混合气氛下直接还原可以得到纯度高、分散性好的纤维状铁镍合金粉。     

超细晶碳化钨-钴复合粉短流程制备工艺研究

以偏钨酸铵、醋酸钴及葡萄糖为原料,采用短流程工艺,通过喷雾转化法制备出含W、Co等元素的前驱体粉末、煅烧制备W、Co的氧化粉、最后以低温连续还原碳化法制备出WC晶粒尺寸约为260 nm的WC-Co复合粉。研究了短流程工艺3个关键步骤的参数变化对粉末形貌、粒径、氧含量、总碳和化合碳含量等特征的影响。结果表明,当溶液浓度为60%、进料速度为2 000 mL/min、离心转速为12 000 r/min时,制备的前驱体粉末粒度分布均匀,相互粘结的现象较少。温度为550℃、保温时间20 min时煅烧前驱体制备出的氧化物粉末粒度较均匀。当低温连续还原碳化温度为900℃、氢气流量为1.3 m3/h、保温时间为60 min时,可获得WC晶粒细小均匀、总碳和化合碳较为一致且接近于理论碳含量的WC-Co复合粉。     

前驱体碳热还原法制备纳米V8C7粉末

将偏钒酸铵和纳米碳黑溶于去离子水中,通过加热、干燥后制得前驱体粉末,将前驱体粉末还原/碳化后得到纳米V8C7粉末.采用X射线衍射仪(XRD)、扫描电镜(SEM)和透射电镜(TEM)对不同保温时间下的反应产物进行了分析.结果表明保温时间过短或过长,都会造成反应产物的形貌和晶粒尺寸偏大.保温时间过短,反应不完全,正在发生相转变,颗粒形貌和晶粒尺寸偏大;保温时间过长,反应产物呈熔融状,并有游离碳和VC析出.只有当保温时间达到或接近最佳值时,反应才能进行彻底,颗粒的形貌较规则,呈球形或类球形,平均粒径在20 nm左右.     

添加碳对氧化钨氢还原制备纳米钨粉的影响

针对氧化钨氢还原过程中因"挥发-沉积"作用而导致W粉晶粒快速长大和异常长大现象,利用添加碳的方法抑制氧化钨挥发,制备了平均粒径56.4 nm的球形W粉,并研究了添加碳对还原机制的影响。结果表明,W粉的粒度和纯度与前驱体配碳比有关,最佳配碳比为2.6。W粉粒径随还原时间延长不断增加,长大趋势与还原温度密切相关。随着还原温度由680℃升高至760℃,W粉晶粒长大速率变慢,粒径和残余碳含量显著降低,分散性变好;继续升高温度,W粉粒径略有增加。在710℃以上,还原产生的水蒸气与碳反应生成CO和H_2,显著降低体系中水蒸气的分压,抑制挥发性水合物WO_2(OH)_2的产生,W粉的主导长大方式也由挥发-沉积转变为原子扩散机制。     

采用有机还原剂化学还原法制备纳米银粉的研究

采用化学还原法制备纳米银粉,研究了以有机试剂BSG为还原剂,碱性条件下表面活性剂的种类和用量、银离子浓度以及反应温度对所生成银粉粒径的影响.以PVA为表面活性剂,在反应温度为25～50℃、[Ag ]为0.1～0.5mol/L和高速搅拌的条件下,制备出了平均粒径小于100nm的银粉.     

碳氢协同还原-碳化法制备纳米WC粉的工艺及机理

针对传统还原-碳化工艺中WC粉颗粒长大的问题,采用碳氢协同还原-碳化法制备纳米级球形WC粉,研究了前驱体配碳比和反应温度对WC粉性能的影响。结果表明,WC粉的碳含量与前驱体的配碳比密切相关,最佳配碳比(即n(C)/n(W)值)为3.6。W转变为WC具有结构遗传性,WC粉的平均粒径与还原温度和碳化温度密切相关。随着还原温度由680℃升高至800℃,还原水蒸气与碳反应生成CO和H_2,显著降低体系中水蒸气的分压,从而抑制中间产物W颗粒的挥发-沉积长大,WC粉的平均粒径随还原温度升高而减小。碳化过程中的高温促进WC颗粒的晶界迁移和纳米W颗粒之间的烧结合并长大,WC粉的平均粒径随碳化温度的升高而增大。n(C)/n(W)为3.6的前驱体粉末经800℃还原和1100℃碳化后,得到平均粒径为87.3 nm的球形WC粉。     

Generation of nanostructured CuO by electrochemical method and its Zn–Ni–CuO composite thin films for corrosion protection

Nanocrystalline copper oxide (CuO) powder of varying sizes (22, 25, 28 and 36 nm) have been successfully synthesized by hybrid electrochemical method using aqueous sodium nitrate electrolyte with Cu electrodes under galvanostatic mode at room temperature. The as‐synthesized CuO sample was calcined for an hour at temperatures ranging from 60 to 900 °C. The crystallite size, morphology, and chemical state of the synthesized powders were characterized by powder XRD, XPS, SEM/EDAX, TEM, and UV–Vis spectral methods. The effect of calcination temperature on crystallite size and morphology was studied. The TEM result revealed that, the particles are hexagonal and the sizes are in 30–50 nm in diameter and 120–200 nm in length. The band gap values are 5.60 and 5.54 eV. The crystallite size increased with increase of calcination temperature. The CuO nanopowder is used to fabricate Zn–Ni–CuO composite thin films and its corrosion behaviour was analysed by Tafel extrapolation and electrochemical impedance spectroscopy. The results indicate that the Zn–Ni–CuO composite thin films provided good corrosion protection.     

Effects of different functional group-containing organics on morphology-controlled synthesis of silver nanoparticles at room temperature

Silver nanoparticles with average particles sizes ranging from 2 to 131nm were manipulatively synthesized starting from silver nitrate using different functional group-containing organic modifiers at room temperature. The effects of the organic modifiers on the morphology of the resulting silver nanoparticles were strongly dependent on the intrinsic properties of the functional groups and the reducibility of the reductant. Numerous ether bonds （-0-）present in polyethylene glycol and Tween-80 were beneficial to the formation of silver nanoparticles with particle sizes of several nanometers in a narrow size distribution in both weak and strong reducing environments. Cetyltrimethylammonium bromide induced the formation of nanosized silver triangle plates in a weak reducing environment. The crystal growth of the silver nanoparticles with particle sizes of more than lOnm was postulated through an adhesion process of small-sized particles followed by a subsequent coalescence process under the present reaction conditions.     

Preparation of ultrafine silver powders with controllable size and morphology

The ultrafine silver powders were prepared by liquid reduction method using Arabic gum as dispersant. The effects of different dispersants, pH values, and temperature on the morphology and particle size of silver powders were investigated. It is found that Arabic gum can better adsorb on silver particles via chemical adsorption, and it shows the best dispersive effect among all the selected dispersants. The particle size of silver powders can be finely tuned from 0.34 to 4.09 μm by adjusting pH values, while the morphology of silver powders can be tuned by changing the temperature. The silver powders with high tap density higher than 4.0 g/cm³ were successfully prepared in a wide temperature range of 21.8–70 °C. Especially, the tap density is higher than 5.0 g/cm³ when the temperature is optimized to be 50 °C. The facile process and high silver concentration of this method make it a promising way to prepare high quality silver powders for electronic paste.     

Nanocrystalline spherical iron–nickel (Fe–Ni) alloy particles prepared by ultrasonic spray pyrolysis and hydrogen reduction (USP-HR)

FeCl₂ and NiCl₂ were used for synthesis of nanocrystalline spherical Fe–Ni alloy particles by ultrasonic spray pyrolysis and hydrogen reduction (USP-HR). Spherical ultrafine Fe–Ni particles were obtained by USP of aqueous solutions of iron–nickel chloride followed by thermal decomposition of generated aerosols in hydrogen atmosphere. Particle sizes of the produced Fe–Ni particles can be controlled by the change of the concentration of an initial solution. The effect of the precursor solution in the range of 0.05, 0.1, 0.2 and 0.4 M on the morphology and crystallite size of the Fe–Ni alloy particles are investigated under the conditions of 1.5 h running time, 900 °C reduction temperature, and 1.0 L/min H₂ volumetric flow rate. X-ray diffraction (XRD) studies and Scherrer crystallite size calculations show that the crystalline size was nearly 28 nm. Energy dispersive spectroscopy (EDS) was performed to determine the chemical composition of the particles. Transmission electron microscope (TEM) was used to confirm the crystalline size, that was determined using XRD results. Scanning electron microscopy (SEM) observations reveal that the precursor solution strongly influences the particle size of the synthesized Fe–Ni alloy particles. Spherical nanocrystalline Fe–Ni alloy particles in the range of 80 and 878 nm were obtained at 900 °C.     

Sodium alginate mediated route for the synthesis of monodisperse silver nanoparticles using glucose as reducing agents海藻酸钠为保护剂葡萄糖为还原剂合成单分散银纳米粒子

报道了一种在水溶液中的简单绿色法制备纳米银溶胶。硝酸银,海藻酸钠素,葡萄糖分别做为银源,保护剂和还原剂。纳米溶胶的颜色从无色变到黄色,表明生成了纳米银粒子。利用透射型电子显微镜（TEM）,紫外可见光谱（UV-vis）和X-射线衍射（XRD）对样品进行了分析。TEM图像表明,所得到的银纳米颗粒的为粒径较小,分散性较好的球状粒子,分布范围较窄,从3 nm 到12 nm。XRD结果表明所得到的纳米金属粒子为单晶的纳米银颗粒。通过UV光谱对反应时间、反应温度、银离子浓度及还原剂的浓度对粒径的影响进行了研究。由于该方法具有无污染、简单、廉价等优点,因此该方法可以做为一种较好的制备纳米银粒子的方法。该方法可以扩展到其它贵金属的技术应用,例如药用,工业应用等。     

Preparation of ultrafine/nano Mo particles via NaCl-assisted hydrogen reduction of different-sized MoO2 powders

The current study investigated the effects of the amount of NaCl addition, particle size of MoO₂, temperature (under isothermal condition) and heating rate (under non-isothermal condition) on the morphology, particle size and dispersivity of prepared Mo by hydrogen reduction of MoO₂. The formation of sufficient dispersed Mo nuclei and their controllable growth were crucial for transforming the large MoO₂ particles to dispersed ultrafine/nano Mo particles. It was found that in the absence of NaCl, it was hard to control the nucleation and growth of Mo grains, and the morphology and particle size of products still retain those of the raw MoO₂ in the temperature range of 840–1000 °C. However, as the amount of NaCl addition was above 0.05%, it was successful to control the nucleation and growth of Mo. Ultrafine/nano Mo powders with the average particle size from 100 nm to 800 nm were successfully prepared via adjusting the particle size of MoO₂ and temperature under isothermal condition. The use of MoO₂ with small particle sizes can increase the reaction rate and the number of Mo nuclei number, thus improve the particle dispersivity and decrease the particle size. Additionally, after reaction at 900 °C and 1000 °C, the residual Na was reduced to 140 ppm and 33 ppm from the initial value of 380 ppm, respectively. Under non-isothermal condition, the temperatures for the nucleation and growth could be adjusted by changing heating rate and particle size of raw MoO₂ particles. Mo nanoparticles with smaller particle size and better dispersivity were successfully prepared, and the average particle size can decrease to about 80 nm.     

非水溶液体系中晶种法制备球形银纳米颗粒

以丙三醇作溶剂,硝酸银为原料,聚乙烯吡咯烷酮(PVP)为分散剂,硼氢化钠为还原剂制备了银纳米晶种;以此银纳米粒子作为初级晶种,以丙三醇作溶剂和还原剂,通过升温提高丙三醇的还原性制备银纳米颗粒。研究分散剂种类、生长液银浓度、晶种加入量对银粉的影响,采用X射线粉末衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)对制备产物的结构、物相、形貌进行表征。结果表明,通过改变条件可以制备出分散性良好、粒径均匀的70 nm左右的球形银粉。     

Preparation of micro-sized and uniform spherical Ag powders by novel wet-chemical method

A novel wet-chemical method was presented for the preparation of the micro-sized and uniform spherical Ag powders on a mass-production scale. The well-defined particles were synthesized by mixing the iron(II) sulfate heptahydrate solution with silver nitrate solution directly by high-speed stirring at room temperature. It is found that a large number of micro-sized and uniform spherical particles with rough surfaces are obtained. The mass ratio of iron(II) sulfate heptahydrate to silver nitrate greatly affects the shape of particles, and when it is relatively low, spherical particles cannot be obtained. The reaction temperature has a great impact on the particle size. As the reaction temperature increases from 8 to 15 °C, the mean diameter of particles decreases from 3.5 to 1.6 (m. The additive n-methyl-2-pyrrolidone improves the surface smoothness and compactness of the particles while the particle size is kept unchanged. Scanning electron microscopy, X-ray diffractometry and energy dispersive X-ray analysis were used to characterize the particle products.     

用苦瓜提取液还原制备纳米银的研究

分别以中国种和印度种苦瓜的提取液为还原剂、硝酸银为前驱体制备纳米银颗粒,并采用紫外可见光谱(UV-Vis)、红外光谱(FTIR)、X射线衍射(XRD)、和透射电镜(TEM)进行表征。结果表明,当硝酸银浓度为10 mmol/L时,制备得到平均粒径最小为8.72和7.46 nm的球形纳米银颗粒。制备反应机理为类黄酮作为还原剂,通过失去H⁺由烯醇结构变为醌型结构来还原Ag⁺获得Ag⁰,蛋白质及其它三萜类化合物起保护剂作用。苦瓜提取液种类对纳米银的粒径、形貌、分散性及均匀性等总体影响不大。     

纳米银导电墨水的制备及电极性能研究

用硝酸银、己二酸二酰肼和葡萄糖为主要原料,通过化学还原法制备出粒径为30~50 nm的纳米银颗粒;将其分散于特殊配制比例的溶剂中,制备得到纳米银导电墨水。将纳米银导电墨水高精度图案化喷墨打印,分析了纳米银的形貌及其导电性能;研究了烧结温度和烧结时间对打印电极电阻率的影响,结果表明,200℃烧结40 min,电阻率为0.34 m?·cm的较低值。