Advanced Materials Research Vol. 815

Abstract: Known from the gas dynamic model of cold spraying, the properties of process gas including gas temperature, gas pressure and gas source have great influence on the critical velocity of powder. The influences of the three kinds of gas properties on the quality of the NiCoCrAlY coating on the magnesium substrate by the experiments of the cold gas dynamic spraying were discussed in this study. The results of the experiments show that, when the pressure value of process gas is 3.5MPa, the density of the coating is perfect, and there are obvious layered structures. The porosity is only 0.45%. The influence of gas temperature on the coating quality is the influence of that on the oxygen content. When the temperature of the process gas is confined to 600°C~700°C, the oxygen content is low and the coating comprehensive quality is best. On the premise that other parameters are kept constant, when nitrogen and helium gas are used together, the coating quality is better.

Abstract: The weld seam and weld toe surface were treated by ultrasonic impact method. The contrast corrosion tests were performed in 3.5% NaCl aqueous solution both for the un-treated and treated joint. The experimental results indicate that the severe plastic deformation on the surface of weld seam and weld toe were formed by ultrasonic impact for different time, the maximum depth of the plastic deformation layer is about 300μm. Residual tensile stress in the surface of weld seam and weld toe can be changed to residual compressive stress by impact treatment, and the grain in the surface of welded joint could be refined. Compared to the un-treated joint, when the impact current is 1.2A and 1.5A, respectively, the corrosion rate of treated joint was reduced by 22.67%, 54.59%, 43.99% and 33.92%, 56.54%, 49.29%, respectively for 10, 20 and 30 min. treating. The corrosion resistance of welded joint has a certain relationship with the residual stress on the surface of welded joint. The ultrasonic impact treatment has distinct effect on the corrosion resistance of 16MnR welded joint.

Abstract: The weld toe surface and its nearby area of welded cruciform joints were treated by ultrasonic impact. Under the same stress concentration and after heat treatment to eliminate residual stress, the effect of residual stress on the fatigue life of joint was researched. The fatigue tests are performed on the joints of 16MnR both for the un-treated and treated joints by using EHF-EM200K2-070-1A type fatigue tester when the load ratio is 0.1, frequency is 10Hz. The experimental results indicate that the severe plastic deformation in the vicinity of weld toe surface was formed by impact treating for 2 minutes, the thickness of the plastic deformation layer is about 60μm. Residual tensile stress in the weld toe surface can be changed to residual compressive stress by impact treatment. The fatigue life of welded joint is 0.260×10⁶ cycle, and the fatigue life of treated joint is 0.499×10⁶ cycle. Compared to the un-treated joint, the fatigue life of treated joint has been increased by 91.92%. The residual stress contributed to fatigue life is about 16%. Residual stress has great effect on the fatigue life of welded cruciform joint.

Abstract: In order to obtain the tensile strength of the C40 concrete accurately, the comparative study between Brazilian disc splitting experiment and the direct tensile experiment is conducted with a self-modified tensile loading device. The study shows that the tensile strength observed from the direct tensile experiments (3.64MPa) is lower than that from the experiments (5.44MPa). A comprehensive analysis of experimental results is conducted focusing on the perspectives of the specimen failure forms, energy dissipation, the correlation of strength and hydrostatic pressure etc. The study suggests that the main reasons for the differences between Brazilian tensile experimental strength and direct tensile experimental strength include the surface energy required by the specimen destruction, the bond strength between the aggregate, the hydrostatic pressure in the process of loading and other factors.

Abstract: Jet milling is an innovative method to prepare micropowder with high efficiency and pureness, while the particles obtained through this way exhibit a prominent agglomeration due to the electrostatic attraction caused by friction of particles during jet milling progress. Recently, we have developed a new method to prepare micropowder by combination of jet milling and electrostatic dispersion. In this paper, both fine powders of calcium carbonate and talc were produced by J/E method, the particle size and its distribution were evaluated by SEM and LPSA as well. The results of our research reveal that the dispersion state of the micropowder thus prepared is influenced by its properties and the combined process is effectiveness in powder pulverization and dispersion.

Abstract: Surface potential of TC11 titanium alloy handled by beta phase (1150°C) solid solution for one hour and then taking water cooling, air cooling and furnace cooling as cold method were investigated using scanning Kelvin probe technique. The corrosion resistance difference of samples was analyzed through their surface potential. At the same time, corrosion experiments were adopted to verify it. The results show that the result of the samples corrosion resistance analyzed by scanning Kelvin probe technique is reliable and the method is feasible. Compared with water cooling sample, the corrosion resistance of furnace cooling and air cooling samples is worse and their surface potential present cathode and anode area obviously. The corrosion of furnace cooling sample is slight serious to that of air cooling sample in the early corrosion, but their corrosion resistances are almost equal. Passivation layer formed by alloy elements in the water cooling sample avails to prevent alloy from corrosion.

Abstract: The research reported in this paper aimed at exploring the advantages of using supercritical carbon dioxide (scCO₂) as an environmentally benign solvent and swelling agent for carrying out the grafting process of acrylonitrile (AN) onto polypropylene (PP) in the solid state by using benzoyl peroxide (BPO) as initiator in the reaction. In order to get a well graft ratio, the effects of various factors in this grafting reaction are investigated. Those factors included the reaction time, reaction temperature, monomer and initiator concentrations and the CO₂ pressure. IR was used to characterize the constituent of the graft polymer. Then anti-aging of the PP-g-AN was studied by UV-vis. Results showed that the scCO₂-assisted solid-state grafting process of AN onto PP did have some scientifically interesting and industrially relevant advantages over the melt process. Compare with virgin PP, the graft polymer have a better performance in anti-aging.

Abstract: The nitrogen in raw natural rubber is mainly derived from crude protein of latex. In this study, the nitrogen content of six kinds of raw natural rubber was analyzed for evaluating Kjeldahl and elemental analysis methods. The nitrogen content ranged from 0.43% to 0.66% for Kjeldahl methods and from 0.45% to 0.75% for elemental analysis method. There was no significant difference between the two methods. The coefficient of variation was below 1%. The data of nitrogen content showed a simple linear correlation (r=0.9937) between the two methods. It was concluded that the elemental analysis method could replace Kjeldahl method in nitrogen analysis of raw natural rubber.

Abstract: Due to the low-meting characteristics of the BaO-B₂O₃ binary composition, the dense ceramics with peculiar properties, so called low-temperature sintering ceramics, were prepared by the introduction of other oxides, e.g., SiO₂, Al₂O₃, ZnO, CaO to the BaO-B₂O₃ binary compositions at a sintering below 1000°C. The low-temperature preparation of the ceramics are achieved by milling the aqueous suspension mixtures of Ba (OH)₂·8H₂O, H₃BO₃ ,H₂SiO₃, Al (OH)₃, ZnO. By the aqueous suspension process, some compounds with a low-melting point such as hydrated barium borate, and the precursor compounds of the functional mineral phases, e.g., BaSiO₃, ZnSiO₃, BaAl₂Si₂O₈, etc. can be formed easily from a suspension solution, which consequently supply more possibilities to fabricate the low-temperature sintering ceramics with peculiar physical properties.

Abstract: An innovating slag system, Fe (OH)₃-SiO₂-CaF₂ system, was introduced in the metallurgical methods to purify silicon for photovoltaic application. The partition ratio of boron (L_B) between slag and silicon was studied under different mass ratio of slag to silicon and varying mass ratio of Fe (OH)₃ to SiO₂ under argon condition at 1873K. The distribution of impurity elements in silicon after slag refining was detected by scanning electron scope and electron probe micro analysis. Experimental results illustrated that the Fe-Si binary system could promote the L_B. Silicon was surrounded by amorphous slag. Impurity elements are concentrated in slag.