Effect of ball milling process on the microstructure of titanium-nanohydroxyapatite composite powder

Titaninm-nanohydroxyapatite （Ti-nHA） composite powders, composed of titanium with 10 vol.% and 20 vol.% of nano-hydroxyapatite, were milled in a planetary ball mill using alcohol media to avoid excessive heat. XRD and SEM were performed for characterization of the microstructure, and the homogeneity of Ti/HA nanocomposite powder was evaluated by EPMA with prolonged ball milling time. The results show that under the condition of wet milling, the grain size of Ti-nHA composite powders is decreased with the increase in ball milling time and the amount of the addition of nHA. While for milling of 30 h, the nanocomposite powder with free structure, which consists of the nano-hydroxyapatite （nHA） particles and titanium （Ti） phase, is obtained. Three stages of milling can be observed from the dement mapping of Ti, Ca, and P by EPMA; meanwhile, it is found that the nHA would be more homogenously distributed after milling for 30 h.

Microstructure and phase composition of Ti-based biocomposites with different contents of nano-hydroxyapatite

Nano-hydroxyapatite(nHA) and titanium(Ti) powders with different ratios were prepared by mechanical ball milling,and then sintered in vacuum environment. The microstructure and phase composition of Ti-based biocomposites with different contents of nHA(5% and 10%,in volume fraction) were investigated. Meanwhile,the phase composition of pure Ti was studied for contrast. The results show that Ti phase forms a finer continuous network microstructure with few porous after milling and sintering. The higher amount of nHA powders are added,the higher amount of porous are achieved,while the fracture morphology becomes coarser. The specimen with contents of 10% nHA has serious interface reaction after sintering at 1 100 ℃,it varies with the pure Ti specimen. Combined with the XRD and EDS analysis,it can be founded that elements Ca,P,O and Ti diffuse on the interface,and the phases of Ti,Ti2O,Ti5P3,CaTiO3 and TiOx can be ascertained in nHA/Ti composites.

Friction and wear properties of PM cam materials with different boron contents

In this study,effects of B addition on the sintering densification,microstructure,hardness,friction and wear properties of sintered Fe-2.4C-4Cr-1Mo-0.5P-0.7Si-2.5Cu(in wt%)were investigated.In spite of the decreased sintered density,the addition of B changes the phase composition of the materials and their ratio.Moreover,hardness of either the matrix or the liquid solidification structure dramatically increases.These changes in micro structure result in higher friction coefficient and lower wear loss.It is observed that the addition of0.1 wt%B offers the optimum friction and wear properties with a running-in period of only 30 s and wear volume loss of 0.006 mm^(3) under the testing conditions.Such friction and wear properties are superior to those of the other two widely used cam materials,cast iron and 45 steel.

Optimization of electrocatalytic properties of NiMoCo foam electrode for water electrolysis by post-treatment processing

Hydrogen is a potential alternative to fossil fuels in coping with the increased global energy demand,and water electrolysis is an attractive approach for H2production. Nickel–molybdenum–cobalt（Ni Mo Co） foam electrodes used for water electrolysis were prepared by the electrodeposition method, and the influence of heat treatments on the surface structure of Ni Mo Co foam electrodes,mechanical properties, and electrochemical performance of the synthesized electrodes was investigated in order to optimize the post-treatment processes. The residual carbon in the surface of the electrode was removed by decarbonization in the atmospheric condition. The carbon content decreases to lower than 200 ×10-6when the temperature exceeds 500 °C. Next, the material is reduced in hydrogen atmosphere from 500 to 1100 °C to remove the surface oxides. As the temperature increases, the surface molybdenum content increases significantly between 500 and 800 °C, the surface grains become coarser, and the tensile strength and elongation increase as well. The lowest polarization overpotential is obtained at 800 °C. Below 800 °C, the electrode is only partially reduced and some black oxide zones are observed on the electrode surface,which leads to the higher polarization overpotential. Thesamples heat-treated at the temperatures of higher than 800 °C show better strength and toughness as well as brighter appearance. However, the surface particle coarsening leads to a decrease in the specific surface area and a higher overpotential.

Microstructure and graphitization behavior of diamond/SiC composites fabricated by vacuum vapor reactive infiltration

To inhibit the graphitization of diamond under high temperature and low pressure, diamond/SiC composites were firstly fabricated by a rapid gaseous Si vacuum reactive infiltration process. The microstructure and graphitization behavior of diamond in the composites under various infiltration temperatures and holding time were investigated. The thermal conductivity of the resul- tant materials was discussed. The results show that the diamond-to-graphite transition is effectively inhibited at temperature of as high as 1600 ℃ under vacuum, and the substantial graphitization starts at 1700 ℃. The microstructure of those ungraphitized samples is uniform and fully densified. The inhibition mechanisms of graphitization include the isolation of the catalysts from diamond by a series of protective layers, high pressure stress applied on diamond by the reaction-bonded SiC, and the moderate gas-solid reaction. For the graphitized samples, the boundary between diamond and SiC is coarse and loose. The graphitization mechanism is considered to be an initial detachment of the bilayers from the diamond surfaces, and subsequently flattening to form graphite. The ungraphitized samples present higher thermal conductivity of about 410 W.m-1.K-1 due to the fine interfacial structure. For the graphitized samples, the thermal conductivity decreases significantly to 285 W.m-1.K-1 as a result of high interfacial thermal resistance.

Electrocatalytic characterization of Ni-Fe-TiO_(2) overlayers for hydrogen evolution reaction in alkaline solution

The Ni-Fe-TiO_(2) overlayers on mild steel strips were prepared by electrochemical deposition.The layers were characterized morphologically by confocal laser scanning microscopy and scanning electron microscopy(SEM) coupled with energy-dispersive spectroscopy(EDS)analysis.The layers exhibit a quasi-three-dimensional(3D)morphology in which the crystalline,TiO_(2),is embedded.Electrocatalytic activity of the Ni-Fe-TiO_(2) layers for the hydrogen evolution reaction(HER) was assessed by using pseudo-steady-state polarization curves and electrochemical impedance spectroscopy(EIS) in alkaline solution.The results were compared with the properties of Ni-Fe electrodes and used for determining the mechanism and kinetics of HER.In comparison with Ni-Fe electrodes,the synthesized Ni-Fe-TiO_(2) electrodes present higher catalytic activity for HER due to the increase in the real surface area and high intrinsic elec trocatalytic activity of titanium dioxide.The present study provides valuable insight for exploring practical applications of Ni-based alloys as hydrogen evolution electrodes.

Engineering oxygen vacancies and localized amorphous regions in CuO-ZnO separately boost catalytic reactivity and selectivity

Generating different types of defects in heterogeneous catalysts for synergetic promotion of the reactivity and selectivity in catalytic reactions is highly challenging due to the lack of effective theoretical guidance.Herein,we demonstrate a facile strategy to introduce two types of defects into the CuO-ZnO model catalyst,namely oxygen vacancies(OVs)induced by H2 partial reduction and localized amorphous regions(LARs)generated via the ball milling process.Using industrially important Rochow–Müller reaction as a representative,we found OVs predominantly improved the target product selectivity of dimethyldichlorosilane,while LARs significantly increased the conversion of reactant Si.The CuO-ZnO catalyst with optimized OVs and LARs contents achieved the best catalytic property.Theoretical calculation further revealed that LARs promote the generation of the Cu3Si active phase,and OVs impact the electronic structure of the Cu3Si active phase.This work provides a new understanding of the roles of different catalyst defects and a feasible way of engineering the catalyst structure for better catalytic performances.