Key Engineering Materials Vols. 336-338

Abstract: Composite nanoparticles of Ni-TiC and Ni-TiN were prepared by an active plasma-metal reaction method. The structure and morphology were evaluated by X-ray diffraction and transmission electron microscopy observations. The morphology of the composite particles is dice-like or dumbbell-like, where the outer sides are metallic and the inner part of the rod (or dice)-like structure is TiC or TiN. The formation mechanism of the composite particles is considered by analogy to the VSL mechanism. The thermal stability of the nanocomposite particles is vastly superior to that of the metal particle. The excellent catalytic property of the Ni-TiN composite particle was confirmed when compared to the well-known Raney Ni particle and mixed particles of Ni and TiC.

Abstract: WC nanosized powders are synthesized by the plasma arc discharge process and annealing under an inert (Ar) atmosphere. The high temperature used during discharging at local region causes the work-piece and electrode to melt and evaporate. The melted tungsten on the arc discharge electrode and carbon arising from decomposition CH4 gas forms WC1-x nanosized powders. The WC1-x phase is encapsulated in a amorphous carbon shell. The WC1-x nanosized particles are annealed at 1200~1400°C under an Ar atmosphere. The WC1-x nanosized powder is transformed to the W2C phase, and then it becomes WC above at 1400°C.

Abstract: A peptizing-hydrothermal method to prepare nanometer γ-AlOOH crystal powder with industrial Al(OH)3 as raw materials has been proposed in the present paper. The XRD and TEM results show the product is a pure γ type nanometer AlOOH crystal powder with average grain diameter of 70nm. Laser grading analysis indicates the average grain diameters of the product in the solution are 66.52nm in water and 84.33nm in N,N-dimethylformamide, respectively without surface modification and dispersant. The experimental result indicated that polymer/inorganic nano-composite with high content of nanometer AlOOH presents inorganic characteristic of polymer. The wear rate of the alumina ceramic ball sintered at 1465°C from ceramic, which contains 98 % alumina (wt), can be reduced up to 40% with addition of 3.5% nanometer AlOOH.

Abstract: Nano-particle hydroxyapatite (HAp) was directly prepared by a wet chemical precipitation method with the aid of ultrasonic irradiation in solution using Ca(NO3)2, NH4H2PO4 and NH2CONH2 as source materials. The nano-HAp formation rate at different preparation temperatures and under different ultrasonic irradiation powers was measured and the influence of ultrasonic irradiation power on the synthesis kinetics of the nano-hydroxyapatite was investigated. It was found that the nano-HAp content increased with the increase of ultrasonic irradiation power, preparation temperature and reaction time. Under different ultrasonic irradiation power, an Arrhenius relationship was found between the nano-HAp formation rate and preparation temperature. It showed that with the increase of ultrasonic irradiation power from 100W to 200W and 300W, the synthesis activation energy of nano-HAp crystallites decrease from 63.2 KJ/mol to 59.9 KJ/mol and 48.1 kJ/mol respectively by calculation.

Abstract: Hydroxyapatite nanoparticles were synthesized in the presence of two kinds of acidic amino acids in order to investigate the effects of acidic amino acids on the morphology of hydroxyapatite obtained by homogeneous precipitation and hydrothermal treating. The results of X-ray diffraction analysis and microphotographs of transmission electron microscope showed that the morphology of hydroxyapatite nanoparticles changed significantly only with aspartic acid. Hydroxyapatite synthesized with aspartic acid showed smooth flake-like morphology at pH= 11 and flake-like morphology with stripes at pH= 8. However, hydroxyapatite synthesized in the present of glutamic acid showed rod-like morphology at both pH values. Variation in the morphology of nanoparticles could be consistent with the difference in the affinity of amino acids binding at the hydroxyapatite crystal surface. The adsorption process was revealed by computer simulation of molecular mechanics using energy minimizing method.

Abstract: The purpose of the work is to investigate the problems associated with utilization of purified fly ash (PFA) as filler in polymer. The goal is to expand the application field of fly ash. The wet-collected fly ash used in this study was sampled from Huaneng Dezhou Power Plant. Preparation of PFA and composite fly ash (CFA) with nano-structured surface was described in detail. Experimental results show that CFA with rough surface and high whiteness-value had successfully been prepared in Ca(OH)2-H2O-CO2 system. The specific surface area of CFA was thrice or above higher than that of PFA with 2.86 m2·g-1. The whiteness-value of CFA was increased to the range from 63.67 to 73.13 which is more double than that of PFA with 33.54. Filling tests show that the mechanical properties of CFA/PE(polyethylene) composites are superior to these of PFA/PE composites at the same filling ratio of 30/100. This means that change of CFA surface morphology increases contacting opportunities between CFA and polymer matrix and improve the matching state between them when CFA is blended with PE. The results show that CFA as filler appears to have good application, and yet, little serious research has been conducted in the field.

Abstract: Silica xerogels were prepared by sol-gel process and non-supercritical drying. Two kinds of reinforcements, SiC whisker and short carbon fiber (CF), were chosen to control the shrinkage during drying process and improve the mechanical properties of xerogels. Microstructure and mechanical properties of samples were examined. It was found that the addition of SiC whisker could greatly improve the elastic modulus of silica xerogels, while short CF could prominently decrease the volume shrinkage ratio but could not improve the elastic modulus. Analysis showed that the difference between the two reinforcement mechanisms was caused by the interface and the size of the doped fiber and whisker.

Abstract: Monodispersed and nano-sized Ni powders were synthesized from aqueous Ni sulfate hexahydrate (NiSO4· 6H2O) inside sucrose as a nonionic polymer network by using wet chemical reduction process. The influence of a nonionic polymer network on the particle size of the Ni powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). The Ni powders obtained by adding of sucrose were nearly spherical in shape and seemed to be nano-sized, typically in the range of 100 nm with not being agglomerated. As the sucrose content increased, the particle size of Ni powders steeply decreased and reached the minimum value, however, the particle size increased again with a further increase of sucrose content. This is believed to be due to the pore size of the swollen polymer network. As a result, the particle size of the Ni powders prepared by the reduction inside polymer network was strongly dependent of the sucrose content.

Abstract: The nano-size silver particles were prepared in polymer-protecting colloidal dispersion with silver nitride as the raw material, hydrazine hydrate as the reduction reagent and polyvinyl pirrolidone (PVP) as the protective solvent. The optimal conditions for the preparation process were studied experimentally as well. The influences from main factors, such as Ag+ concentration and ratio of hydrazine/AgNO3, on the particle size, appearance shape, particle aggregation condition and size distribution of nano-silver particles were also investigated. The results showed that the size of Ag particles prepared in this polymer-protecting system is less than 50 nm, and PVP can reduce the growing tendency of nano-size silver particles. Meanwhile, the antibacterial dope loaded nano-silver particles were prepared by wetting agent, dispersant, defoamer, etc. The antibacterial and bacteriostatic effects of the dope with or without nano-silver particles were tested with bacilli as the tested bacteria. The experiment results showed that the dope loaded nano-silver particles are of high practicality. Its antibacterial ratio is also up to 91.9% in one hour when the added dosage of nano-silver is 0.02%.