Papers by Author: Long Hao Qi

Abstract: Slurry pumps are used to transport the liquid fluids with solid particles in the industries. The materials of flow passage in a slurry pump are subjected to severe damage due to abrasive erosion. This paper compares the abrasive erosion for an engineering ceramics i.e. hot pressed Si3N4 ceramics and a high chrome cast iron i.e. Cr26 by laboratory test and industrial operation. The results indicate that the erosion rate of Cr26 is much larger than that of hot pressed Si3N4 ceramics under the same test conditions. That indicates that the engineering ceramics is a promising alternation of the expensive material such as Cr26 in the application of slurry pumps. It is noted that the erosion pattern such as scale ripple has the similar features for both materials, even the hardness of hot pressed Si3N4 ceramics is much higher than Cr26. Further, the scale ripple is suspected to be originated from the relatively weak grain boundary and enhanced by cavitation.

Abstract: Aluminum nitride (AlN) powder was synthesized by gas reduction–nitridation of γ-Al2O3, using NH3 as the reactant gas. The results showed that AlN can be fabricated by this process at 1100°C for over 480 min in the flowing NH3 atmosphere. However, no AlN was found in the products synthesized at 1300°C and 1400°C, which was different from the former reports. A series of experiments with different parameters were carried out, and the effects of reacting temperature and time on the synthesis of AlN were investigated. The reaction mechanism was also studied.

Abstract: In this paper, the TiCN-based cermets were fabricated with ultrafine TiCN, metal binders and carbide additives. Different content of C and Al were separately added to eliminate the oxygen contamination. The composition of the mixture was TiCN-10Mo-20WC- 20Ni-xC/Al. Effect of the C and Al addition on microstructure and mechanical properties was investigated. Results indicated that cermets with carbon addition had higher relative density and more homogenous microstructure while the Al addition had the opposite effect. Proper addition of carbon improved the mechanical properties.

Abstract: The chemical composition and solid state reaction of the nano-Ti(CN) base cermets in different sintering temperature were studied. The total carbon and oxygen content in compact were declined gradually with the increasing of sintering temperature, the nitrogen content in compact began to decline above 1100°C, the peak of de-gassing of N2 was formed before the emergence of liquid phase, the decomposition of N2 was arisen acutely above 1500°C. Mo2C and TaC diffused and took part in solid state reaction with Ti(CN) above 900°C, the solid state reaction was finished below 1200°C. WC diffused and took part in solid state reaction with Ti(CN) above 1100°C, it was dissolved below 1250°C, there were only two phases, Ti(CN) and Ni(Ni+Co), in the alloy.

Abstract: Erosion wearing regulation with different erosion angel for Si3N4 ceramics were systematically studied by liquid-solid dual phase erosion wearing test with rotation disk through comparing with Cr15Mo3 high chromium cast iron for pumps in industry. Besides the micro failure mechanism and the relationship between mechanical behavior and anti erosion wearing have been analyzed for the experimental materials. The experimental results were concluded as following: the erosion resistance of Si3N4 ceramic is about 20 times better than that of Cr15Mo3 high-Cr cast ion in erosion test angle, and the effect of erosion angel on the erosion wearing volume lose features as N-shaped curve with the biggest volume lose at 45° erosion angle while most erosion wearing volume at 90° angle, which indicates that it should avoid 45° or 90° erosion angle during materials designing. Obvious direction and erosion trace are revealed and volume lose mainly featured with tiny cutting, pear ditch and erosion hole, and micro crack and grain falling off at high angle erosion on the surface of Cr15Mo3 materials, besides smooth surface, high ductile, compact structure, fine grain and fine cylinder grain explaining main reason for excellent anti erosion wearing for Si3N4 ceramic.

Abstract: A slurry pot tester was used to evaluate the erosion behavior of alumina (Al2O3), zirconia toughened alumina (ZTA), and silicon nitride ceramics. The eroded surface of sample was studied by scanning electronic microscope and the primary erosion wear mechanisms for ceramic materials were analyzed. On the same experimental condition, erosion wear resistance of materials follows this rule: Si3N4>ZTA>Al2O3. The key factor affecting erosive wear performance of ceramics is their microstructure. The primary erosive wear mechanisms for Al2O3, ZTA and Si3N4 ceramics are lateral crack propagation, whole grains pulled out and plastic deformation. The erosive wear performance of Si3N4 ceramic is the best in this experiment, due to their microstructure morphology with elongated grains.

Abstract: Sm1.9Ca0.1Zr2O6.95 ceramic was sintered at 1600°C for 10 h in air by solid-state reaction method. The phase structure and thermal expansion coefficient were measured by XRD and a high-temperature dilatometry, respectively. The results show that the crystal structure of Sm1.9Ca0.1Zr2O6.95 ceramic is still pyrochlore. The doping with calcium cation leads to a shift of the X-ray spectrum of Sm1.9Ca0.1Zr2O6.95 ceramic to lower 2θ values. The experiments also show that the thermal expansion coefficients of Sm1.9Ca0.1Zr2O6.95 ceramic are higher than those of Sm2Zr2O7 ceramic. These results are related to the vacancy induced by doped calcium cation in the samarium lattice.

Abstract: Three rare earth zirconates (Sm2Zr2O7, Gd2Zr2O7 and Er2Zr2O7) were prepared by solid state reaction. The crystal structure and ionic conductivity of these zirconates were characterized by X-ray diffraction (XRD) and complex impedance spectroscopy. The results show that Sm2Zr2O7 exhibits single-phase pyrochlore structure and Er2Zr2O7 exhibits single-phase fluorite structure, while Gd2Zr2O7 has pyrochlore and fluorite structure. Among three zirconates, the ionic conductivity of Sm2Zr2O7 is highest, while that of Er2Zr2O7 is lowest.

Abstract: In this paper, the Ti(CN)-based cermets were fabricated with ultrafine Ti(CN) powders, additives WC, Cr2C3 and Mo, metal binder Ni by vacuum sintering and HIP treatment. The composition of the mixture was Ti(CN)-10Mo-20WC-xCr2C3-20Ni. Effect of Cr2C3 addition on microstructure and mechanical properties was investigated. Results indicated that with increasing Cr2C3 content, the relative densities after vacuum sintering decreased and the grain sizes of cermets increased. Cr2C3 addition to the cermets improved the hardness but had some negative effect on the performance of bending strength.

Abstract: Silicon carbide whiskers (SiCw) as a kind of high strength fibrous material are widely used in the reinforcement of metal, ceramic and polymer. In this paper preparation of Silicon carbide whiskers by carbon thermal reduction reaction from the mixture of Silica and carbon was investigated with an emphasis on the study of the effect of catalyst. Fe, Co, Ni and their compounds were used as catalyst in this study. Since vapor–liquid–solid (VLS) mechanism was found to be responsible for the growth of whiskers, the formation of catalyst and its subsequent evolution on whisker nucleation, growth and appearance was a subject of extensive research. The catalyst that has the best effect among iron, nickel, cobalt and their compounds was made certain by comparing the products.