SiC和Si_3N_4纳米陶瓷粉体制备技术

纳米材料科学是近年来兴起的新的科学领域，纳米粉体的制备则是纳米材料研究的主要方面。本文比较详细地介绍了制备碳化物、氮化物纳米陶瓷粉体的四种主要工艺：热化学气相反应法、激光诱导化学气相沉积法、等离子气相合成法和溶胶凝胶法。对于目前碳化物、氮化物纳米陶瓷粉体的制备工艺和目前水平作了一个总体概括     

氨解法制备纳米Ti0.4Cr0.6OxNy粉体

以共沉淀法制备的钛和铬的摩尔比为4：6的TiO2／Cr2O3纳米复合粉体为前驱体,氨气为氮化剂,制备了钛铬双金属氧氮化物纳米粉体。采用Auger电子能谱、X射线衍射、透射电子显微镜、BET比表面积、电子探针等技术对氧化物复合粉体和合成氧氮化物粉体进行了表征。结果表明：前驱体组成均匀、比表面积大、反应活性高,800℃氮化8h可以合成X射线衍射纯立方相钛铬双金属氧氮化物纳米粉体e粉体呈球形,晶粒尺寸在20～35nm,比表面积达35．62m^2／g,基本无团聚。氮化前后粉体的氧含量和氮含量发生了明显变化,粉体的组成可以用Ti0.4Cr0.6OxNy表示。     

表面活性剂含量对微乳液法合成纳米氧化锆粉体结构与性能的影响

采用水/环己烷/TritonX-100/正己醇四元油包水体系,通过微乳液法制备了纳米ZrO2粉体.用X射线衍射、透射电镜等表征所制备的纳米粉体,重点研究表面活性剂含量对ZrO2纳米粒子结构与性能的影响,分析产生团聚的原因,并提出改进措施.结果表明:所制备的纳米单斜相ZrO2粉体的晶粒尺寸可控制在15nm左右;随表面活性剂含量的增加,晶粒的尺寸有所减小,团聚现象亦有所减少.     

超声机械法制备纳米二氧化硅及影响因素分析

引言 20世纪,人们发现了纳米粒子具有传统常规颗粒材料所不具备的优良的理化性质和特殊的光、电、磁等特性,从而开始了对纳米粒子的研究,其中包括对纳米粉体粒子基本制备方法的探索[1].纳米粉体粒子的制备方法可以归结为两大类:一类是粉碎法,即将宏观物体逐步细化得到纳米颗粒;另一类是构筑法,即从原子、离子或分子出发,通过成核和长大两个阶段来构筑纳米粒子[2].构筑法制备纳米粉体粒子所用的能量主要为热能和化学能,需要较高的温度,消耗较高能量,后续的除杂工艺较为繁杂,生产过程中还有可能造成环境污染等.而粉碎法制备纳米粉体粒子,设备投资少、能耗低、效率高、生产能力大、生产过程和产品性能易于控制.     

脉冲喷射电沉积纳米晶镍工艺优化研究

采用脉冲喷射电沉积方法在钢基体表面制备了纳米晶镍镀层,研究了占空比、频率、平均电流密度对镀层硬度的影响,并通过正交试验对工艺参数进行优化,用扫描电镜和X-射线衍射仪对镀层表面形貌和晶粒尺寸进行分析。结果表明,制备纳米晶镍镀层的优化工艺参数为:平均电流密度39.8 A/dm2、频率1 000 Hz和占空比20%,此时镀层最致密,硬度最高(530.6 HV),纳米晶镍平均晶粒尺寸最小(13.7 nm)。     

晶粒细化对金属Cr在含Cl-介质中腐蚀电化学行为的影响

采用机械合金化通过热压烧结工艺制备了纳米晶金属Cr,利用动电位扫描法和交流阻抗技术,与常规尺寸金属Cr对比研究了它们在含Cl-介质中的腐蚀性能以及晶粒细化对其腐蚀电化学行为的影响。结果表明：随着Cl-浓度的增加,不同晶粒尺寸金属Cr的腐蚀电流密度增大,腐蚀速度加快。晶粒尺寸降低后,在相同条件下,腐蚀电流密度变大,其抗腐蚀性能降低。两种尺寸金属Cr的极化曲线均出现了钝化由强到弱交替变化的趋势,反映了Cl-对钝化膜的破坏与修复作用。两种尺寸金属Cr的交流阻抗谱均呈单容抗弧特征,表明腐蚀过程受电化学反应控制。     

占空比对Ni-WC纳米复合镀层耐蚀性及硬度的影响

采用脉冲电沉积法在304不锈钢基体上制备出Ni-WC纳米复合镀层,并研究了占空比对Ni-WC纳米复合镀层耐蚀性及硬度的影响。结果表明:随着占空比的增大,Ni-WC纳米复合镀层的平均晶粒尺寸先减小后增大,硬度先增大后减小;当占空比为50%时,Ni-WC纳米复合镀层的平均晶粒尺寸最小,耐蚀性最好,硬度最大。     

纳米SnO_2粉体的水热法制备及其气敏性研究

以SnCl_4·5H_2O为前驱体,氨水为沉淀剂,利用水热法制备了超细纳米SnO_2粉体。研究了溶液pH值和水热温度对SnO_2粉体粒径的影响。XRD结果表明SnO_2晶粒尺寸范围为3.8~8.8 nm。制备纳米SnO_2的最佳工艺条件为:水热温度180℃,溶液pH值为8,反应时间6 h。纳米粉体对乙醇的气敏性检测表明,制备的纳米SnO_2材料对微量、低浓度的乙醇气体有较好的灵敏度。     

纳米ZrO2的性能及其气敏性的研究

本文用沉淀法制备出平均晶粒尺寸在１８ｎｍ的单斜相ＺｒＯ２纳米粉末。并对其的开头和大小进行了透射电镜及激光散射分析,确认ＺｒＯ２粒子为球形,分散性较好,平均粒径为７０￣８０ｎｍ。本文着重了纳米级ＺｒＯ２细粉对乙醇的乞敏性能,结果表明,用纳米级ＺｒＯ２粒子制备的气敏元件对乙醇气体有好的敏感性,并且随着纳米粒子尺寸降低,对气体敏感性增强。     

柠檬酸络合法制备NiTiO_3纳米粉体

以无机镍盐和钛酸四丁酯为起始原料,柠檬酸为络合剂,采用溶胶–凝胶法制备了NiTiO3纳米粉体。通过X射线衍射、扫描电镜和红外光谱研究了柠檬酸加入量对钛酸镍纳米粉体相组成、显微结构以及晶粒生长活化能的影响。结果表明:在制备过程中加入柠檬酸能明显降低其晶粒生长活化能;随柠檬酸加入量从0g增加至柠檬酸与溶液中阳离子(Ni2++Ti4+)的摩尔比为1:1时,纳米NiTiO3的晶粒生长活化能由60.19kJ/mol降低到43.07kJ/mol;制备的粉体为纯净的NiTiO3物相,结晶性较好。700℃煅烧后NiTiO3粉体颗粒形状为六方形片状结构,粉体的粒子尺寸分布均匀,粒径约为20～30nm。     

Nanosize Powders of Aluminum Nitride Synthesized by Pulsed Wire Discharge

Nanosize particles of aluminum nitride have been successfully synthesized by a pulsed wire discharge (PWD). Intense pulsed current through an aluminum wire evaporated the wire to produce a high-density plasma. The plasma was then cooled by an ambient gas mixture of NH₃/N₂, resulting in nitridation. As a result, nanosize particles of aluminum nitride were formed. The average particle diameter was found to be ∼28 nm with a geometric standard deviation of 1.29. The maximum AlN content of 97% in the powders was achieved by optimizing various parameters: the gas pressure, the ratio of NH₃ and N₂, the wire diameter, the pulse width, and the input electrical energy. The ratio of the AlN powder production to the electrical energy consumption was evaluated as ∼40 g/(kW·h). Thus, PWD is a very efficient and promising method to synthesize nanosize powders of AlN.     

Synthesis of nanosized alumina powders by pulsed wire discharge in air flow atmosphere

Pulsed wire discharge (PWD) is a method to form nanosized powders which is based on evaporation of thin metal wires by applied large electric current. Nanosized oxide powders can be synthesized by PWD in oxygen atmosphere. Since only small amount of powders can be synthesized by single discharge to a piece of wire, the number of discharges has to be increased for mass production of nanosized powders. Then, PWD equipments with wire feeding and gas flow atmosphere systems were developed for mass production. However, effects of gas flow on formed powders have never been investigated. In this study, PWD in air flow atmospheres were tried to synthesize alumina powders from industrial viewpoints. The effects of air flow rate on the oxidation phenomena and the synthesized powders have been investigated. PWD of pure Al wires with diameters of ? 0.3–0.5 mm were examined in air flow rates of 15 L/min and 33 L/min as well as 0 L/min (closed atmosphere condition). The synthesized powders at all experimental conditions were dominantly composed of γ-Al₂O₃ and δ-Al₂O₃ phases. The δ/γ ratios of the Al₂O₃ phases increased with increasing air flow rate and wire diameter. Besides them, small amount of metallic Al phase was remained in the powders synthesized by PWD in the air flow atmosphere of 33 L/min. It is concluded that appropriate air flow rate should be adopted for mass production of alumina powders in order to achieve enough collection of particles and avoid mingling of metallic Al phase.     

NUCLEATION AND GROWTH OF OXIDE NANOPARTICLES PREPARED BY INDUCTION THERMAL PLASMAS

The reactive evaporation method of injected metal powders was investigated for preparing oxide nanoparticles. The method has advantages such as evaporation is enhancement of the injected powder owing to exothermic reaction heat of the metal powder oxidation in induction thermal plasmas. Tangential gas flow injection to the plasma tail flame controls the diameter and the yield of the oxide nanoparticles. The purpose of this research is to investigate the effect of the injection gas flow on the preparation mechanism of oxide nanoparticles in thermal plasmas by experimental work and numerical analysis. An increase in the flow rate of the injection gas leads to an increase in the diameter as well as the yield of the prepared nanoparticles. Numerical analysis for nucleation and growth provides the preparation mechanism of the oxide nanoparticles; however, a more sophisticated model should be developed.     

Single-walled carbon nanotube growth using cobalt nanoparticles prepared by vacuum deposition on a surface-active liquid

We demonstrate that the Co nanoparticles prepared by vacuum deposition on a surface-active liquid can be used as catalysts of single-walled carbon nanotube (SWCNT) growth using alcohol catalytic chemical vapor deposition method. These Co nanoparticles are embedded in the y-type zeolite powder. The Co nanoparticles used in this study is the highly efficient catalysts for CNT growth, which is comparable to the commonly-used Co-Fe binary metal catalysts embedded in the y-type zeolite. The preparation method of the metal nanoparticles used in this study is very simple. Thus, such metal nanoparticles might be promising as catalysts of CNT growth.     

Low-temperature aerosol flow reactor method for preparation of surface stabilized pharmaceutical nanocarriers

Nanoparticles can be used to improve the delivery of many drugs, especially peptides and proteins. Although several methods are available for polymeric nanoparticle preparation, there are few single-stage processes that produce dry, solid nanoparticles that can be easily re-dispersed in pharmaceutical vehicles. The aerosol flow reactor method is a single-stage process that has been used for the preparation of multicomponent, coated nanoparticles under uniform temperature and gas flow field. However, it is traditionally used with high synthesis temperatures. In the present study, the aerosol flow reactor method was further optimized for processing and surface stabilization of pharmaceutical nanoparticles containing temperature sensitive biomolecules. In the developed method, drug-loaded carrier nanoparticles consisting of a biodegradable polymer (Eudragit L100) and a drug (phenylephrine hydrochloride) were first produced by aerosol droplet drying and subsequently coated in the gas phase. The carrier particles were coated with l-leucine in order to inhibit agglomeration of the nanoparticles in solutions before administration. In the coating process, a side stream of l-leucine vapor was directed into the main aerosol flow containing the drug-loaded carriers. The mixing with the main flow at ambient temperature induced a supersaturation of l-leucine vapor and condensation on the carrier particles. The results demonstrate that solid, hydrodynamically stable drug-loaded polymeric nanoparticles can be produced with a thin l-leucine coating. The low process temperature enables the surface engineering of particles loaded with temperature sensitive drugs or bioactive materials to be utilized for drug delivery purposes.     

纳米二氧化钛粉的水热合成与光催化性能研究

以钛酸四丁酯(TBOT)为钛源,NH4Cl为分散剂,不经高温煅烧,直接低温水热合成纳米TiO2粉。采用FT-IR,XRD,TEM等方法研究了低温高压水热条件和NH4Cl浓度对TiO2粉的相组成、组织形貌的影响,并研究了其对甲基橙光催化降解的性能。结果表明,纳米TiO2具有锐钛矿相结构且无有机物残留。晶粒尺寸随着水热合成温度增高(120~180℃)而增大,随着NH4Cl/TBOT的摩尔比(0.1~0.5)增加而减小,但纳米粉逐渐出现团聚现象。水热温度为160℃以及NH4Cl/TBOT=0.25条件下合成的锐钛矿相纳米TiO2具有良好的分散性,其颗粒尺寸约为14 nm,且有高的光催化降解甲基橙的能力。     

Synthesis of Nanocrystalline Cubic Tantalum(III) Nitride Powders by Nitridation–Thermal Decomposition

Tantalum(V) nitride, prepared by nitridation of nanosized Ta₂O₅ at 800°C for 8 h under ammonia flow, was thermally decomposed to cubic nanocrystalline TaN at a temperature of 1000°C for 3 h under argon atmosphere. The resulting powders have been characterized using X-ray diffraction (XRD) and transmission electron microscopy. XRD-pure cubic TaN nanoparticles with a diameter of 50–100 nm can be obtained by the process. The decomposition process was found to depend on the temperature. Mechanisms that account for the decomposition of Tantalum(V) nitride are discussed. The results indicate that the method can permit formation of cubic-phase Tantalum(III) nitride under ambient pressure and moderate temperatures.     

Production of nanosized graphite powders from natural graphite by detonation

A detonation method for preparing nanosized graphite powders from natural graphite is described. The process initiated by a detonator in an explosion vessel features quick release of energy, decomposition of HNO₃ graphite intercalation compounds and the smashing action due to the detonation. The products were soot-like deposits on the inner walls of the vessel, and were studied by XRD, SEM, TEM, BET, energy dispersive X-ray spectroscopy, and Raman spectroscopy. The results show that the as-made graphite powders have a perfect sheet-like structure, and vary in the two-dimensional plane at the micron scale and in thickness at the nanoscale. The specific surface area of the nanosized graphite is six times higher than that of the raw graphite. This technique may offer a low-cost, energy saving and efficient approach to the preparation of nanosized graphite powders.     

Formation of nanosized bimetallic particles based on noble metals

Methods for the preparation of nanosized alloys from noble metals by decomposition of monomolecular precursors are described, and the results of these studies are reported. Other aspects of the synthesis procedure and properties of bimetallic nanostructures are also considered. Thermolysis of noble metal compounds led to the formation of an ultradisperse powder of their alloys. This method affords catalysts with a uniform distribution of active particles. Nanosized particles of a number of alloys in hydrogen and inert media were prepared. The optimum parameters of the reduction of complex compounds (gas medium, thermolysis temperature, heating rate, and annealing time) were determined to obtain ultradisperse powders with the required particle size, phase composition, and structure. For Co-Pt and Pt-Pd systems, bimetallic catalysts deposited on γ-Al₂O₃ and Sibunit can be obtained; these catalysts show higher activity in selective oxidation of CO compared with monometallic catalysts.     

纳米α-Al_2O_3的湿化学法制备

以硝酸铝和碳酸氢铵为主要原料,采用湿化学法,在1 135℃煅烧2 h,制备了平均晶粒尺寸为31.6 nm的α-Al2O3纳米粉末。研究了表面活性剂及水与乙醇的体积比的溶剂以及前驱体的煅烧温度和时间对合成粉末的相组成及晶粒大小的影响。结果表明,制备前驱体的最佳滴定速度为将Al(NO3)3溶液一次性全部加入NH4HCO3溶液中,水和无水乙醇的最佳体积比为1∶1,分散效果最好的分散剂是PEG6000;前驱体的最佳煅烧温度为1 135℃,时间为2 h。