Advanced Materials Research Vols. 146-147

Abstract: New salt core technique for using in the high duty internal combustion engine piston under high pressure cast was developed.With special additional ceramic, the salt core’s compressive strength and the density performance were improved. Granulation technique could refine the grain microstructure. Orthogonal experiments were adopted for getting the process parameters, in this way, oil cooling gallery can be formed completely by the new technology. The new progress has been widely used by the high duty pistons.

Abstract: A Zr55Cu30Ni5Al10 bulk amorphous alloy was prepared by using copper mold suction casting and the X-ray diffractometer (XRD) was utilized to determine its structure. The non-isothermal crystallization behavior of the amorphous alloy was studied via a differential scanning calorimeter (DSC) by Kissinger and Ozawa methods. The results showed that all the thermodynamic parameters move to higher temperatures with increasing heating rates. The activation energies for crystallization calculated by Kissinger and Ozawa method are 291.27 and 288.53 kJ/mol, respectively. With the increase of heating rate, the rate of x vs. T descends. The crystallization mechanism is typical nucleation and growth of crystalline grains, among which the latter dominates the total crystallization process.

Abstract: Rock tunnel boring machine is one of the main machineries and equipments for underground engineering ,and the failure of tool systems is the main failure form of this machinery. Rock hob test-bed is the only testing equipment for tool failure and wear. In this paper, the hydraulic-driven system of the rock hob test bench is designed and simulated, and the effect of load and flow rate of hydraulic oil in this hydraulic system on characteristics of this test-bad is analyzed. The results show that the horizontal movement speed of test bench is directly proportional to the flow rate, but the effect of the load on this speed can be ignored; the delay of the movement of the test bench are proportional to the load. These results are very helpful to the structure optimization of tool system and the improvement of working efficiency.

Abstract: This paper described the application of neural networks in predicting the rate of producing magnesium by silicon-thermo-reduction. Fir st of all, a mathematical model between the process parameters and the the rate of producing magnesium was set up with neural network. When the model was satisfied, it could be used for predicting the rate of producing magnesium. Through doing a great number of productive tests in the winca(hebi) magnesium company with limited liability according to the satisfied model, the rate of the producing magnesium is increasing obviously. So it is a kind of effective means for increasing producing magnesium by silicon-thermo-reduction.

Abstract: A kind of graphitized carbon black 40B2 was incorporated in natural rubber matrix and vulcanizates were prepared. The content of carbon black varied from 4 to 100phr for 100phr of natural rubber. Thermal conductivity of the CB/rubber composites was studied as a function of CB loadings and temperature. TEM and SEM were employed to explore the morphology of the carbon black and the composites. It was found that percolation phenomenon existed in thermal conductivity of CB/rubber composites at different filler loadings, which was much similar with percolation behavior in electrical conductivity properties of many composites, and the percolation threshold was about 13.63%. The influence of temperature on thermal conductivity was more obviously within the region from the percolation threshold to the volume fraction of 26.2%.However, no great effect could be found on the percolation behavior of the composites in thermal conductivity. The result of TEM indicated that the mean size of CB particles was about 25nm, the maximum size of CB aggregates was about 125nm, and the CB aggregates were multichain in shape. The results of SEM showed that the distribution of CB differed at different filler loadings. Before the percolation threshold, the CB aggregates existed isolatedly, nevertheless at the percolation threshold, some long chains made up of CB aggregates ran through the rubber matrix, which resulted in the rapid increase in thermal conductivity value, and then with the addition of CB loadings, the number of chains increased. When the volume fraction was up to 26.2%, some three dimensional networks formed.

Abstract: Cementitious composites reinforced with multi-wall carbon nanotube (MWNT) (MWFRC) were prepared with surfactant dispersion, ultrasonication, and subsequently high-speed mixing process. Fracture mechanical performance of the cured MWFRC was characterized according to three-point bending method (ASTM 399). It is found that the addition of nanotubes significantly improve the flexural strength, the stress-intensity factor of the nanocomosites with dispersed MWNT fiber, the maximal enhancement amplitude is near to 45%, 80% with respect to the baseline, respectively. The superior fiber bridging capability of the dispersed MWNTs upon the micro-cracks contributes to the reinforcement to cement matrix.

Abstract: Mg-7.3Al magnesium alloys were investigated in the paper. The paper presents microstructural characterization of Mg-7.3Al alloy after casting and heat treatment. The casting temperature was 740°C and heat treatment was performed at 420 °C for 24 h with aging at 180 °C for 8h,16h,24h. The microstructure of the casting alloy consists of α-Mg phase matrix with a primary β phase (Mg17Al12) at grain boundaries. After solution treatment β phases were soluted in α-Mg phase matrix . Aging treatment caused β phases precipitation. The corrosion resistance of magnesium alloy was determined in 3.5 % NaCl by immersion tests and polarization curves. The results shows that the corrosion resistance of magnesium alloy after solution treat is the best than that of the others heat treatment in polarization curve tests and the samples with aging for 16h and 24h presents higher corrosion resistance than those with solution and aging for 8h in immersion tests. Solution treatment plays a main role for corrosion resistance of Mg-7.3Al magnesium alloy in short term corrosion, but more continuous β phases in Mg-7.3Al alloy after ageing act as a barrier and play a main role in long term corrosion.

Abstract: The galactomannan from endosperm of G. sinensis seeds was used as sustained release material in the matrix tablets prepared at different concentration of 5, 10 and 15 % corresponding to formulations of G5, G10 and G15, for the release of theophylline. The drug release behaviors of the systems were investigated, including the swelling and morphological studies and texture analysis. The dissolution tests were conducted in 0.1 M hydrochloric acid and pH 6.8 phosphate buffered saline. The results of release studies demonstrated that G10 with 10 % galactomannan concentration showed a better control of the drug release profiles. The percents of cumulative drug released in 24 h were 98.8, 90.2 and 83.4 % for G5, G10 and G15, respectively. All the systems exhibited the typical morphological behavior of a swellable matrix. Results of texture analysis on the swollen tablets confirmed that diffusion drug release mechanism played the major role in G10 and G15 systems while the drug delivery kinetic towards an erosion/relaxation mechanism for G5 matrix tablets.

Abstract: The shell distribution in the slab continuous casting mold has been simulated coupling a 3-D flow, temperature and volume fraction equations of the molten steel in FLUENT. The simulated results show that the flow velocity around the upper vortex center is decrease and the location of lower vortex center move down as the nozzle port angle increases. The simulated shell thickness in the center on the narrow face become thicker at meniscus and the shell thickness in the center on wide face decreases but the basic distributions of the shell tend to consistency as the nozzle port angle increases. The simulated results also show that the effects of solidified shell on flow field in mold is slight but the velocity of molten steel near the solidified shell. There are remelting near the impact regoins implicit our attentions in order to avoid breaking out.

Abstract: The influence of grain size on the lattice constant in some nanocrystallites was studied by in experiment. It is found that the lattice constant of NaCl, CsCl structure ionic crystallites decreases with the reduction of the grain size. The lattice constant of ultrafine iron and nickel particles increases with the reduction of the grain size. As to the experiment result of g-Fe2O3 nanocrystallites, the lattice constant increases with the decreasing of the grain size. It is opposite to the theoretical result of ionic crystallites, which reason is that the combination of most of atoms in g-Fe2O3 is by the covalent bond other than electrovalent bond.