Materials Science Forum Vol. 814

Abstract: The addition of the rare earth elements into the Ag-based filler alloy, which is typical and important, can control and eliminate the negative effect of impurity elements, and furthermore, it improves the spreading property of the Ag-based filler alloy. Phase diagram provides an important direction for materials design of the Ag-based filler alloy. Thus it is necessary to investigate the phase diagrams and construct the thermodynamic database. On the basis of this background, thermodynamic assessments of the Au-Gd, Tb binary systems were carried out by using the CALPHAD (Calculation of Phase Diagrams) method based on the experimental data including thermodynamic properties and phase equilibrium. The Gibbs free energies of the solution phases were described by sub-regular solution models with the Redlich-Kister equation, while all of the intermetallic compounds were described by sub-lattice models. A consistent set of thermodynamic parameters was derived from describing the Gibbs free energies of each solution phase and intermetallic compound. The calculated phase diagram achieved consistency with the available experiments. Then combined with the assessed relevant binary systems, the Ag-Au-Gd, Tb ternary systems have been predicted. The thermodynamic database of these ternary systems has been developed to present the significant information for the design of Ag-based filler alloys.

Abstract: Among the factors to cause the corrosion in oil and gas fields, H₂S is the most common and harmful corrosive medium. During oil field exploitation, enhancing the ability of the sucker rods to resist corrosion is the key measure of prolonging the service life of sucker rods and guarantee of safe operation of petroleum equipment. This paper focuses on the corrosion of sucker rod steel 20Ni2Mo in different concentrations or temperatures of H₂S. The appearance of corrosive surface scanned by scanning electron microscope was analyzed and theoretic basis for anti-corrosion and material-selecting of sucker rods used in the oil fields was provided. The result shows that the concentration and temperature of H₂S have interaction on the corrosion of 20Ni2Mo, i.e., with the increase of concentration under same temperature or with the rise of temperature under same concentration, the corrosion rate of 20Ni2Mo accelerates.

Abstract: In order to study the effect of welding process on the microstructure and properties of weld joint of X100 pipeline steel, GMAW was used to prepare the weld joint with low-carbon high manganese-molybdenum-nickel flux cored welding wire. SEM and XRD were used to analyze the microstructure and phase morphology of HAZ and weld metal. Hydraulic tensile testing machine and impact test machine were used to test the mechanical properties. The experimental results showed that the weld metal and HAZ were composed of bainite, ferrite and M/A, the microstructure was fine and uniform with columnar crystal morphology, and HAZ was quite coarse. Hardness of weld metal was 248HV, which is higher than that of base metal, however, HAZ was softening. The tensile strength of weld joint was 832Mpa, which is about 96% of the base metal. The impact absorbed energy at-20°C of the base metal and weld metal were 291J and 121J respectively, exhibiting excellent strength and toughness.

Abstract: The chelation adsorption behavior of a salicylic acid-type composite ASA-PGMA/SiO₂ for rare earth ions of the rare earth ore mud leaching solution in Mianning was studied in the present work. The effect of the reaction temperature and medium pH on adsorption properties of the ASA-PGMA/SiO₂ particle was examined. The concentrations of REEs were determined by ICP-MS. The results showed that the ASA-PGMA/SiO₂ possessed strong chelation adsorption ability for rare earth ions. The reaction temperature was 50°C, the adsorption properties of the composite were the best and the adsorption rate of rare earth ions reached above 90%. In the pH range where the hydrolysis of rare earth ions was inhibited, an increase in the pH value of the medium strengthened the chelation adsorption ability of the ASA-PGMA/SiO₂ particle for rare earth ions. The rare earth ions desorption from the ASA-PGMA/SiO₂ particle is effective when using 0.2mol/L of hydrochloric acid solution as the eluent.

Abstract: High-density oil-based drilling fluid already was considered as one of the most effective technologies during the HTHP Ultra-deep well drilling process. The weighting materials sag such as barite sag, however, always occurred because of the density contrast between the base oil and the weighting material, and hence sag can result in excessive torque, lost circulation and many other problems. This study applied three kinds of ultra-fine powder (particle size≤4μm), which are new weighting materials, to replace the common API barite (particle size10~70μm). The different kinds of high-density oil-based drilling fluids, which weighted with micronized barite, micronized ilmenite, manganese tetraoxide and API barite, were prepared and evaluated separately in lab. The performance data showed that compared with conventional weighting materials, the application of ultrafine powder technology could greatly optimize the rheology of high-density oil-based drilling fluids (ρ ≥ 2.3 g/cm³), reduce the amount of emulsifiers about 50% and dramatically enhance the dynamic suspension-stability of the system, Furthermore, OBM drilling fluids weighted with ultrafine weighting materials almost presented lower viscosity, shear force and sedimentation rate, which will meet more severe requirements of ultra-deep complex well drilling.

Abstract: Directional solidification is a main method of mc-Si production for solar cells. The main impurities in MS-Si are oxygen and carbon. In this paper, an improved furnace was designed to reduce the carbon and oxygen impurity in MS-Si at unidirectional solidification process. Simulation results showed that the flow pattern of impurity gas at the top of the silicon melt significantly improved under the small cover conditions and the impurity gas eddy currents was also avoided. Experimental results show that the carbon and oxygen content inside the ingot were both significantly reduced when the eddy currents inside the crucible was suppressed and the average minority carrier’s lifetime of silicon block was significantly increased under the conditions of small cover plate. Meantime, the average cell efficiency of ingot was more than 17% under small cover condition which is significantly higher than that of the ordinary ingot.

Abstract: In this paper, LiNi_1/3Co_1/3Mn_1/3O₂ was prepared via a facile rheological phase reaction method. The effect of synthesis temperature and holding time on its electrochemical performance has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) tests and galvanostatic charge–discharge tests. The results suggest that the synthesis temperature and holding time greatly affect the electrochemical performance of the LiNi_1/3Co_1/3Mn_1/3O₂ and the optimized synthesis condition for the synthesis of LiNi_1/3Co_1/3Mn_1/3O₂ via rheological phase reaction method is 900 °C for 8 h. The obtained sample possesses a highly ordered layered structure and low cation mixing. It delivers an initial discharge capacity of 198 mAh g^-1 at 0.2 C and 140 mAh g^-1 at 1.0 C between 2.5 and 4.6 V, respectively.

Abstract: Graphitized-Carbon coated Li₄Ti₅O₁₂/C (Li₄Ti₅O₁₂/GC) composites were prepared from Li₂CO₃, TiO₂ and aromatic resorcinol via a facile rheological phase method. The microstructure and morphology of the samples were determined by XRD and SEM. The electrochemical performances of the samples were characterized by galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). The results reveal that the coating of graphitized carbon could effectively enhance the charge/transfer kinetics of the Li₄Ti₅O₁₂ electrode. The Li₄Ti₅O₁₂/GC could deliver a discharge specific capacity of 166 mAh/g at 0.2 C, 148 mAh/g at 1.0 C, 142 mAh/g at 3.0 C, 138 mAh/g at 5.0 C and 127 mAh/g at 10.0 C, respectively, and it still could remain at 132 mAh/g after cycled at 5.0 C for 100 cycles. The excellent rate capability of the Li₄Ti₅O₁₂/C makes it a promising anode material for high rate lithium ion batteries.

Abstract: Lithium air batteries have aroused a considerable concern all over the world owing to their outstanding performances. Especially, catalysts of the air electrode, as one of the most core components of lithium air batteries, have been most extensively studied in recent years. In this paper the nanometer manganese dioxide catalysts and their compounds with Super P, TNRGO and OMC were prepared successfully via hydrothermal synthetic method. Characterized by XRD, SEM and BET, most of them have regular shape, perfect dispersion and high specific surface area, especially S_BET of MnO₂/TNRGO/OMC of the three-component catalysts was up to 126.70m²/g. The air electrodes with nanoMn0₂/carbons catalysts have lower resistance, and better reversibility.

Abstract: The nickel ions in industrial wastewater derive from electroplating and chemical plating industry. Heavy metal ions can result in water pollution, and do harm to people’s health. Maifanite is a kind of nontoxic and harmless silicate rock mineral materials which have a certain biological activity. Maifanite porthole effect and surface effect can apply to removal of heavy metal ions from wastewater, for example, nickel ion, etc. However, natural Maifanite porous structure could be jammed by humus and sediment gradually; in order to play better adsorption performance of Ni (II) and other heavy metal ions in water, we need to adopt necessary modification treatment processes. H₂SO₄ was used to modify Maifanite, which prepared a high efficient adsorbent. At the same time, the removal effect of Ni (II) in water at different acid concentration, dosage, temperature, time and etc. was studied. The results showed that the Maifanite obtain better adsorption of 90% when the acid concentration was 2.5 mol/L, dosage of 50 mL, contact time and temperature of Ni (II) were 0.5 h and 30°C respectively. The above treatment has certain effect and meaning to reduce harm extent of industrial wastewater on environment and human health.