Papers by Author: Zhi Hong Li

Abstract: A kind of vitrified bond was selected to be sintered with diamond powders to prepare diamond abrasive. The effect of the additive of CeO2 and sintering parameters on the performance of vitrified bond diamond abrasive was investigated. The mechanical properties of diamond abrasives were tested on ZMC-Ⅱ type diamond static strength tester and the interfacial bonding states between diamond powders and vitrified bonds were studied by Scanning Electron Microscopy (SEM). The results indicated that CeO2 improved the performance of diamond abrasive by means of strengthening the bonding between diamond grits and vitrified bond. The admirable diamond abrasive was achieved when the sample was sintered at 800°C holding for 120min.

Abstract: Eight kinds of materials with diverse pore-forming mechanism were added into the ceramic ingredient of superfinish grinding tool with the same amount, and the specimens were prepared and sintered in the same condition. Their pore-forming abilities in the sintered bodies were compared through several performance tests. By measuring the porosity, bulk density, water absorption and flexural strength of these sintered bodies, and observing the SEM images, pore-forming agents with the best working mechanism was identified. It is proved that those pore-forming agents which have pore structures in themselves process the best pore-forming ability, and they can maintain relatively high porosity and high mechanical strength, which is good for the superfinish grinding tools.

Abstract: Cubic boron nitride (cBN) grains treated with hydrochloric acid, nitric acid and sulphuric acid were investigated, respectively. The results indicated that the surface treatment technique with hydrochloric acid was an excellent method for improving the properties of cBN grains. After hydrochloric acid treating, cBN grains with clean surface and satisfied strength were obtained. Moreover, the bonding strength between cBN grains and vitrified bond was increased significantly for application in vitrified bond grinding tools.

Abstract: Preparation of high wear-resistant ceramic parts was studied in this paper. The mechanical property was measured by the three-point bending tester, and the microstructures were analyzed with the scanning electronic microscope (SEM). The experimental results showed that vitrified bond CM2 was suitable for the preparation of high wear-resistant ceramic parts because of its lower refractoriness, and higher bonding strength sintering at 850oC. Moreover, containing 8- 12μm CBN abrasive grains, the ceramic parts reached higher strength and higher wear resistance than other samples.

Abstract: FePt nanoparticles (NPS), ~2nm in diameter, were synthesized and then coated with silica (SiO2) shells ~1.5nm-thick using reverse micelles as nanoreactors. The silica-coated FePt core–shell (FePt @silica) NPS were characterized by direct techniques of transmission electron microscopy (TEM). The results showed that the silica shells prevented the aggregation in liquid comparing to their bare counterparts. The as-synthesized FePt@SiO2 NPS exhibited essential characteristics of superparamagnetic behavior, as investigated by a vibrating sample magnetometer (VSM). X-ray diffraction (XRD) studies proved that the annealing at 700 °C for 30min under argon atmosphere caused the crystal structure of FePt core to transform from disordered face centered cubic (fcc) to the chemically ordered L10 FePt with face-centered tetragonal (fct) structure. This phase transition caused the change of magnetic properties of the FePt@SiO2 particles from superparamagnetism to ferromagnetism.

Abstract: Fe-Pt binary alloy thin films were fabricated through a pluse electrodeposition in a novel bath with a simple composition on copper substrates. Composition, morphology and structure of electrodeposited Fe-Pt films were investigated in dependence on deposition potential. In a broad potential range from 2.0 to 6.0V, oxygen was detected in the films. Continuous Fe-Pt alloy films with controllable compositions in 16-58 atom% Fe were achieved on copper substrates. In particular, the films with a composition close to 1:1 Fe/Pt was obtained at -4.7V. All Fe-Pt films as-synthesized exhibited essential characteristics of soft magnetic and isotropic behavior, as investigated by a vibrating sample magnetometer (VSM).

Abstract: Diamond polycrystalline composites with some different elements were prepared by HPHT (high pressure and high temperature). The dependence between emission energy and excitation energy was characterized by PL technique. The results showed that the photoluminescence of diamond polycrystalline composites was not affected by additives, only related to the excitation. The emission wavelengths of composites decreased with excitation, at the same time, emission peaks shifted to high energy region and the peak width at half-height decreased relatively. The energy of emission had a linear relationship with that of excitation. The emission band peak location shifted from 1.57 (790nm) to 1.97eV (628nm) as the excitation wavelength changed from 2.34 (530nm) to 2.95eV (420nm). Emission intensity decreased linearly with the decrease of excitation energy intensity. However, this linear dependence disappeared as excitation wavelength was below 400nm.

Abstract: Zn and Cu were separately incorporated to the diamond powder and then the compacts were prepared under 5GPa, 1273K. The results showed that Zn was a good additive to prepare polycrystalline diamond by high-pressure and high-temperature (HPHT) because it could inhibit the graphitization of diamond. The element Zn left in the polycrystalline was in the form of ZnO. The photoluminescence spectroscopy showed that there were a series of sharp bands between 310 and 390nm when the excitation was above 200nm. However, the full width at half maximum of the diamond peaks mostly was below 0.5nm. The intensity of sharp band decreased with the decrease of excitation energy and then disappeared at last.

Abstract: Alkaline-earth metal oxides (MgO, CaO, SrO and BaO) were introduced to Na2O-B2O3-Al2O3- SiO2 vitrified bond, and their effects on the properties of the vitrified bond were investigated through the measurements of refractoriness, fluidity and bending strength. The results showed the refractoriness of the vitrified bond was reduced and the fluidity of the bond increased with the addition of alkaline earth metal oxides in the order of CaO>SrO>BaO>MgO. When 2-10wt% MgO, CaO and BaO was added into the bond respectively, the vitrified bond was relatively dense due to high viscosity, and the strength was all improved to some extent. However, when more than 4wt% SrO was added, the strength decreased sharply because of the deterioration of microstructure. It was concluded that the bending strength of the bond was affected by alkaline-earth metal oxides in the order of CaO>MgO>BaO>SrO.

Abstract: Synthesis processes of nano alumina abrasive precursor using precipitation method and sol-gel method were investigated in this study. Using pressureless sintering, the nano alumina abrasive was prepared. Mechanical properties of the samples were measured by using single particle compressive strength tester. The microstructures of them were examined by using field emission scanning electron microscopy (FESEM). The results indicated that the performance and microstructure of the samples are greatly relative to the synthesis processes. Compared with samples prepared by precipitation method, the samples prepared by sol-gel method have higher compressive strength, smaller grain size and more uniform microstructure. The average grain size of the alumina abrasive was below 100nm.