包覆型纳米铜-银双金属粉研究

目前,导电胶或者电磁波屏蔽涂料用的导电性填料主要有三类,一是铜粉,二是银粉,三是铜-银双金属粉。铜粉具有来源广、价格低廉、导电性好等优点,但其抗氧化性能弱;银粉导电性与抗氧化性好,但其资源日益匮乏。大量的研究试图通过对铜粉进行表面改性来提高其性能。表面改性有两种方法,一是包膜处理,用SiO2溶胶处理铜粉,铜粉抗氧化性能提高,但其表面导电性能大大降低犤1犦;另一类方法是在铜粉表面覆盖一层导电性能与抗氧化性能均佳的银或金而制成双金属粉末犤2～5犦。制取高性能的铜-银双金属粉是该领域的研究重点。目前获得铜-银双金属粉的方…     

微米级铜-银双金属粉镀层结构及其抗氧化性

微米级铜粉具有许多优良的物理特性与催化活性 ,被广泛用于导电涂料、电极材料、催化剂等领域 但铜粉微细化后 ,由于粒子的比表面很大 ,其化学活性很高［１］,在空气中极易被氧化成氧化亚铜［２］,失去原有的物理化学特性 在铜粉表面镀银形成铜 银双金属粉 ,既能提高铜粉的抗氧化能力 ,又可保持铜粉优良特性［３ ,４］ 我们在铜粉表面镀银的研究中发现 ,当铜粉表面银含量达到一定值后 ,铜 银双金属粉就具备了常温抗氧化能力 ,并不需要铜粉表面完全包覆银 ;而温度升高时 ,表面银含量不同的双金属粉抗氧化温度不同 说明镀银铜粉氧化性与…     

超细核壳铜-银双金属粉末的抗氧化性能研究

本文采用液相化学还原法分别制备了粒径均为50 nm和 1 μm的超细铜粉末，采用置换反应法制备得到了与原铜粉粒径和形貌大致相同的核壳铜-银双金属粉末，用热重仪和XRD衍射仪分别测定了铜－银双金属粉末的热重曲线和XRD图谱，研究了粉末的抗氧化性能。并用透射电子显微镜和X射线荧光光谱仪对粉末的形貌和组成进行了测定。     

油溶性金属Ni纳米微粒的制备与表征

纳米材料的制备、性能与应用已成为近年来的研究热点之一犤１犦。由于在催化、光学和电学材料中的广泛应用，超细单分散的金属微粒的制备与性质已引起人们的广泛兴趣。通常制备金属纳米微粒的方法有两种：一是把固体金属材料分裂为纳米尺寸的颗粒，如机械粉碎、电弧放电及金属原子蒸气沉积犤２犦，用这种方法制备的金属微粒粒径一般都比较大，且粒子尺寸分布宽，另一种是把金属原子制成纳米尺度的颗粒，如乳液聚合法犤３犦、热解犤４犦、γ－射线辐照犤５犦、脉冲电沉积犤６犦和化学还原犤７犦等，这种方法制备的微粒粒径通常分布窄且粒子小…     

柠檬酸溶胶凝胶法制备LiCoO_2电极材料及其表征

目前研究较多的锂离子电池正极材料主要有LiCoO2、LiNiO2和LiMn2O4犤1犦,虽然LiCoO2的成本相对较高,但LiCoO2具有最为优良的电化学性能,如高且平稳的充放电平台、高比容量以及良好的循环性能犤2犦,是目前应用最广泛的商品化电极材料。LiCoO2材料主要采用高温固相法犤3～5犦制备,该方法工艺简单,容易实现大规模生产,但缺点是需要较高的焙烧温度和较长的焙烧时间,且反应原料混合均匀程度有限,易导致非化学计量、非均相以及不规则的颗粒形貌等,因此材料的比容量、循环寿命等电化学性能以及反应的可控性还不甚理想。研究表明犤6犦电极材…     

[Cu(Hsal)2(py)2]n晶体结构和二维堆积网络

０引言水杨酸具有羧基和羟基，是双功能基配体，羧基和羟基可分别脱去氢，因此有多种形式可参与配位（见Scheme１），其中Hsal－１的形式仅见一例报道犤１犦，其可靠性有待更多的研究来确证。对铜／水杨酸／吡啶三元体系的研究已有多篇文献报道犤２～４犦，亦有几种化合物合成，例如Cu（Hsal）２（py）２和Cu（sal）（py）２等。配合物Cu（sal）（py）２的可靠性值得怀疑，原文中无合成和表征犤３犦。铜／水杨酸／吡啶衍生物三元体系已有多个晶体结构报道犤５，６犦，但迄今无铜／水杨酸／吡啶三元体系晶体结构报道。对于配合物Cu（Hsal…     

用银氨溶液对微米级铜粉镀银反应机理的研究

微米级铜粉具有许多优良的物理特性与催化活性,被广泛应用于导电涂料、电极材料、催化剂等领域。但铜粉微细化后,由于粒子的比表面很大,其化学活性很高 [1],在空气中极易被氧化成氧化亚铜,失去原有的物理化学特性。在铜粉表面镀银形成铜银双金属粉,既提高铜粉的抗氧化能力,又可保持铜粉的优良特性 [2,3],此项研究已成为国内外科学工作者注目的课 题 [4,5]。本文对微米级铜粉镀银反应的机理进行了探索研究。 高分散度的微细体系,拥有极大的表面积,具有很高的表面吉布斯自由能,会产生很强的界面吸附作用,该作用将会对化学反应产…     

螯合萃取剂在制备镀银铜粉中的应用

用铜粉自身还原银氨溶液中的Ag+,制备镀银铜粉时使用螯合萃取剂RE608,其与生成的Cu2+形成螯型化合物并进入有机相中,防止[Cu(NH3)4]2+吸附于铜粉表面而阻碍还原反应的继续进行,可一次性制得具有常温抗氧化能力的镀银铜粉.研究了RE608的用量对镀银铜粉抗氧化性的影响.     

以甲醛作还原剂制备超细铜粉

以甲醛作还原剂制备超细铜粉刘志杰，赵斌，张宗涛，胡黎明（华东理工大学化学系，上海２００２３７）（华东理工大学国家超细粉末工程研究中心）超细铜粉已得到广泛应用，不同粒径的铜粉有不同的用途：应用于电学领域的铜粉大部分是微米级铜粉［１］；纳米级铜超微粒子分...     

超声波法制备超细铜粉

在40k Hz超声波作用下,使用以Na BH4作为还原剂的化学还原法制备具有粒径约300 nm~500 nm、产率约为80~90%的超细铜粉,其具有反应温度低反应速率快的优点。最佳制备条件为Cu SO4溶液初始浓度为20 g/L、Na BH4的加入量为1.5 g/L、p H值为11.5、反应温度20~30℃;反应时间20~25 min。通过XPS、XRD、SEM对超细铜粉表面进行检测发现分析表明所制备的超细铜粉呈类球状,其表面有少量Cu2O和Cu(OH)2存在。     

激光气相法研制硅系超微粉

激光气相法是制备超微粉末的新方法之一,目前还存在超微粉末粒径太小难于收集,原料SiH_4价格较昂贵等困难。我们以SiH_4为主要原料,成功地合成出超微Si、Si_3N_4、SiC粉末,研究了反应条件对超微粉性能的影响,探索了用廉价原料代替SiH_4的可能性,并且在超微粉的收集方面做了若干探索,取得了一些有意义的结果。     

非氧化物陶瓷超细粉的制备

非氧化物陶瓷以优异的综合性能,在冶金、化工、机械、电子等领域有着广阔的应用前景.为了制备出适于烧结的非氧化物陶瓷超细粉体,人们进行了大量的研究工作.本文综述了非氧化物陶瓷超细粉的研究进展,其中涉及机械粉碎法、金属元素反应法、金属氧化物碳热还原(氮化)法、聚合物热解法、气相化学反应法及溶剂热合成法等,并对金属氧化物碳热还原(氮化)法的进展进行了较为详细的描述.     

Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic Ag_coreCu_shell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag⁺ and Cu²⁺ ions.     

Evaluation of Dispersant Efficiency for Aqueous Alumina Slurries by Concurrent Techniques

This article reports on results from a comparative study assessing a suitable method for dispersant efficiency evaluation in the case of water‐based suspensions of ultrafine alumina stabilized by a commonly used dispersant, Dolapix CE64. The following measurements were evaluated: zeta potential, specific surface charge, sedimentation behavior, and capillary suction time. The suitability of each of the tested techniques is discussed. A good agreement between the zeta potential and the specific surface charge as a way to determine the optimal dose of dispersant is documented.     

不同晶相草酸钙超细微晶的合成及其与硫酸软骨素A的相互作用

采用配位沉淀法制备了二水草酸钙(COD)和一水草酸钙(COM)超细微晶,其尺寸分别为150nm和320nm。通过扫描电子显微镜(SEM)、X射线衍射(XRD)、红外光谱(FTIR)、纳米粒度仪(Nano-ZS)和紫外-可见吸收光谱(UV-Vis)表征了这两种草酸钙微晶。研究了尿大分子硫酸软骨素A(C4S)对上述COM和COD微晶ξ电位、粒径、聚集程度和紫外吸光度的影响。随着cC4S从0增加到1.0g·L-1,COD微晶的ξ电位从-9.7mV减小到-46.1mV,COM微晶的ξ电位从-15.9mV减小到-49.0mV;微晶表面ξ电位变负后,有利于稳定溶液中悬浮的微晶。在水溶液中,COD和COM微晶均存在显著的聚集现象,而C4S的存在可抑制COD微晶的聚集,并在浓度为0.05g·L-1时抑制效果最好。由于尿液中存在大量草酸钙微晶,本研究有助于阐明草酸钙结石的形成机理和C4S对草酸钙结石形成的抑制作用。     

Effect of quenching conditions on particle formation and growth in thermal plasma synthesis of fine powders

The vapor-phase synthesis of ultrafine powders in reactive thermal plasma systems is studied. A mathematical model is developed to determine the effect of quenching conditions on the size characteristics of powders produced. The particle nucleation is considered to be due to both condensation of product vapor and surface reaction between adsorbed reactant species. The particle growth is considered to be exclusively due to further condensation of product vapor. Numerical predictions on powder formation are explored through a case study for the synthesis of zinc oxide powders from zinc vapor and oxygen carried in argon gas. The results of the present srudy indicate that the size characteristics of plasma-produced powders can be significantly enhanced by gradual, regulated quenching, as opposed to the rapid quenching conventionally used in the past. The results further indicate that distribution of the quench gas along the reactor provides an effective means to accomplish the much desired control over the powder properties.     

A novel method for preparing and characterizing alcoholic EPD suspensions

Ceramic suspensions composed of alumina and mixtures of alumina and zirconia powders in ethyl alcohol were prepared. A solution of citric acid and triethylamine was used as dispersant. The citric acid, which usually is used as dispersant in water alumina suspensions, gave excellent results in ethyl alcohol also if it was used in conjunction with triethylamine. A novel method consisting of combined measurements of grain size, zeta potential, and transmittance was optimized to study the dispersion and stability properties of the ceramic suspensions; by using this method the optimal dispersant amount was determined. The suspensions based on alumina and alumina-zirconia powders were used to coat stainless steel plates by electrophoretic deposition (EPD); the optimal composition of suspensions and the used EPD parameters made it possible to obtain coatings with uniform thickness and composition.     

Dispersion of TiN in aqueous media

The dispersion of TiN powders in aqueous media was studied through XPS, zeta potential, adsorption, sedimentation, and rheology measurements. XPS showed that there are TiO2, TiN, and TiOxNy sites on the TiN particle surface. In the absence of dispersant, the isoelectric point (pH(IEP)) of the TiN particles was at pH 2.2. Based on the surface properties of TiN particles, a cationic polymer, polyethylene imine (PEI), was selected as a dispersant. In the presence of PEI, the pH(IEP) shifted from pH 2.2 to pH 11.10. It was evidenced that TiN slurries could be stabilized around pH 9.50 with 1-2 wt% PEI as dispersant. Subsequently, TiN slurries with solid content as high as 57 vol% were developed and exhibited dilatant rheological behavior at high shear rate. The results showed that PEI is an effective dispersant for TiN in aqueous media.     

Synthesis and characterization of bimetallic Ni-Cu particles

Bimetallic Ni-Cu particles were synthesized from either suspensions of nickel carbonate and copper carbonate, and solutions of nickel nitrate and copper nitrate in ethylene glycol which acts both as solvent and reducing agent. The nature and composition of the powders depend on both the reaction temperature and time, and the reactants. Using the carbonates, bimetallic Ni-Cu powders composed of a nickel-rich and a copper-rich solid solution were obtained after 39 h at 140°C. Increasing the reaction temperature to 190°C gives a Ni-Cu powder composed of a copper-rich solid solution and nickel. Particles obtained under these conditions, however, are polydisperse. The nitrate solution gave bimetallic Ni-Cu particles with a narrow size distribution of about 140 nm after 4 h of reaction at 196°C. These particles are made of a copper core and a nickel shell. The mechanism of bimetallic particle formation is controlled by the solubility of the reactants, the formation of intermediate metal glycolates and Cu₂O, and the required reduction temperature.     

Changes to the physicochemical characteristics of wheat straw by mechanical ultrafine grinding

To investigate changes on the physicochemical characteristics of wheat straw by mechanical ultrafine grinding, wheat straw powders of four different particle sizes and distributions were produced using a sieve-based Retsch ZM100 grind mill and CJM-SY-B ultrafine vibration grind mill. Changes on the microstructure and physicochemical characteristics of the different powders were assessed by scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and relevant standard laboratory analysis methods. Ultrafine grinding reduced the crystallite size and crystallinity of the wheat straw. New surfaces were exposed on the ultrafine powder with high levels of cellulose/hemicelluloses components but there was no apparent change in chemical structure. Wheat straw powders were smaller in size but had a higher bulk density (from 0.19 to 0.54 g/mL) and angle of repose (from 46.02° to 55.61°) and slide (from 37.26° to 41.00°). The hydration properties (water-holding capacity and swelling capacity) decreased with reduction in particle size of the wheat straw. Both the sieve-based and ultrafine powder exhibited a good ability to remove Pb²⁺ and Cd²⁺ and there was marginal improvement when using the ultrafine powder. The thermal stability of the ultrafine powder measured by thermogravimetric analysis decreased significantly because of the low cellulose crystallinity.