Materials Science Forum Vol. 814

Abstract: The TiO₂ reduced graphene oxide (TiO₂/RGO) nanocomposites were synthetized by hydrothermal method. The microstructure and morphologies of them were characterized by XRD and SEM. The photocatalytic activity was investigated by the methyl orange photogradation under UV illumination. The results showed that GO sheets had wrinkles and folds, and anatase-structured TiO₂ covered on graphene surface after hydrothermal reaction. Compared to the TiO₂ nanoparticles, the TiO₂/RGO nanocomposites display the higher photogradation efficiency. In 90 minutes, the gradation percentage of TiO₂/RGO nanocomposites to methyl orange is 80%, higher than TiO₂ nanoparticle (40%). This is attributed to the large surface area of TiO₂/RGO nanocomposites and their improved separation efficiency of electron-hole pair.

Abstract: The effect of particle size of natural graphite on the size and structure of graphene oxide (GO) was investigated by using natural flake graphite (NFG) with different particle size. GO was prepared by modified Hummers method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, laser scattering particle size distribution analyzer and Atom force microscopy (AFM) were used to identify the characteristics of NFG and GO. The results provide evidence of how the graphite particle size affects the oxidation process and sheet size of the GO. Varies size monolayer GO sheets could be produced from the graphite with different particle size. The sheet size of GO is much smaller than that of the graphite, and the sheet size reduced multiple is proportional to the graphite particle size. The smaller particle size graphite is easily to be oxidized for a higher concentration GO suspension, and for more defect in the structure. Thus, this study leads to a better understanding of the preparation process of GO and provides a way to produce GO in different sheet size suitable for different applications.

Abstract: In this study, a novel polymer retarder DRH-200LG was synthesized to solve the problems of retarding failure, strong dispersivity under high temperature and adverse impact on the strength development of cement stone. The composition of the polymer was confirmed by IR, and its thermal stability was proved by DSC, TG analysis and thermal treatment at 200 °C. Furthermore, the stability and strength development of cement slurry was evaluated by the comparative consistency method and ultrasonic method, respectively. The results show that DRH-200LG has good high temperature-resistance and retarding performance, presenting favourable influence on the stability and strength development of cement slurry. DRH-200LG shows a good application prospect in the cementation of deep & ultra-deep wells. And it has some guiding significance in the research and innovation of a novel polymer used as oil well cement retarder.

Abstract: The fibri-form silica was successfully synthesized from the short chrysotile fibers by inorganic acid-leaching. X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), thermogravimetry and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and N₂ adsorption isotherms were used to characterize the products. The results indicate that the fibri-form silica is a kind of noncrystalline material, and the content of SiO₂ in the fibri-form silica is 98.30%. From 50°C to 1200°C, the structure of fibri-form silica is stable. The average diameter of single fiber range from 20 nm to 50nm and the lengths are 50nm to 3μm. The surface area and pore volume of fibri-form silica are 369.22m²/g and 0.43cc/g, respectively. And the size of pore diameters are different, is one of mesopore materials presenting high quality filler and catalyzer carrier.

Abstract: With the analysis of the seawater corrosion effect on low-heat Portland cement concrete under wetting-drying test, the compressive strength and quality change of concrete test specimen were investigated for different test periods. According to the evaluation of seawater corrosion resistance, the low-heat Portland cement showed better corrosion resistance than that of ordinary Portland cement and moderate-heat Portland cement. Moreover, the corrosion mechanism was expounded through XRD and SEM analysis. It was found that lots of C₂S in the low-heat Portland cement play an important role in corrosion resistance of cement concrete.

Abstract: The low-grade ludwigite is one of the complex and refractory ores. Based on the high energy consumption and inefficient in the grinding process and according to the microwave-assisted grinding principle, this paper studied the microwave absorption property of ludwigite and researched the effect of microwave heating on the grinding efficiency of it. The non-microwaved and microwaved samples were characterized with regard to the chemical components, mineral compositions, macroscopic structure and microstructure, grinding efficiency by methods of the chemical analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and grain size analysis, etc. The results indicated that ludwigite, with good microwave absorption property, was suitable for microwave processing. The grindability of microwaved ludwigite was related to the microwave power and microwave heating temperature. By the microwave heating temperature attained 500~650°C, many macro-cracks and micro-cracks were produced by thermal stress between different mineral interfaces, which resulted in the decrease of strength of ludwigite and easy levigation, but the mineral compositions had no obviously changed, which would not affect the subsequent magnetic separation. It was concluded that short, high-power treatments were most effective but over-exposure of the sample led to reductions in efficiency. Under the same conditions, the grinding efficiency of ludwigite was improved 24.54% higher than untreated ore, which significantly improved the grinding efficiency and reduced energy consumption.

Abstract: With an analysis on the structure of water-soluble sodium silicate and its polymerization, it was found that the poor stability of silicate drilling fluids lies in the relevance between the inherent nature and the pH value of sodium silicate. The modification of water-soluble sodium silicate in this paper was to improve its stability and keep the inhibitive property simultaneously. The a-olefin sulfonate (AOS) was employed as the modifer agent acted on the water-soluble sodium silicate monomer and oligomers. Furthermore, the modification mechanism was discussed through FTIR, Laser particle size, Zeta potential and SEM. A stable sodium silicate drilling fluids with better inhibitive property was obtained by the comparison of modified sodium silicate and unmodified ones.

Abstract: Crystalline alumina samples with Al₂O₃ content of 95.23 wt.% were prepared directly from the nepheline ore in Nanjiang county, Sichuan province of China. Four steps were involved in the experiment of alumina preparation, including calcination, dissolution, carbonation and re-calcination. Lime was used in the calcination process with the nepheline concentrates powders to generate soluble aluminates and insoluble silicates. NaOH solution was used as the mother solution in the dissolution process. CO₂ was introduced into the solution to precipitate the Al (OH)₃ precursor, which was then fired to obtain crystalline alumina. Among the crystalline alumina obtained three phases of crystals existed which were detected by XRD and SEM, including δ-Al₂O₃ as the major phase, while θ-Al₂O₃ and κ-Al₂O₃ as the minor phases. Various crystal phases of alumina could be ascribed to the purity and crystal structure of precursor, as well as the re-calcination temperature and time.

Abstract: The average grade of iron ores in China is around 32%, about 10% lower than the world’s average level. In order to alleviate the demand of iron ore for steelmaking industries, it is urgent to develop a highly efficient, energy-saving, low-carbon and environment-friendly technology. The goethite ore from Northern Hainan Island was studied via reduction magnetization by pine, rice chaff, and corn straw biomass fuels. The magnetic properties and magnetic separation were discussed by optimizing the parameters of roasting temperature, roasting time, and the ratio of biomass fuels. The results show that we could obtain concentrated iron ore grade of pine roasting and magnetic separation grade of iron concentrate 61.64% with the recovery of 79.75% via pine fuel roasting, 61.75% with the recovery 80.16% via rice chaff, and 61.47% with the recovery of 81.28% via corn straw roasting. Thereby, we could deduce that biomass fuels for reduction roasting of low goethite ore is promising to substitute the traditional coal and coke fossil fuels.

Abstract: Fluid cylinder as an important fracturing equipment with stable and reliable performance is commonly applied in oil and gas fields, but it fractures frequently and its working life is generally low, which has seriously affected the fracturing process efficiency. In this paper, we used the stereo microscope, scanning electron microscope (SEM), direct reading spectrometer, metallurgical microscope and bending fatigue testing machine to study the fatigue failure mechanism of steel E4330 for fluid cylinder. The fracture analysis, hardness test, metallographic observation, bending fatigue test and pre-corrosion fatigue test were carried out. The result shows that the main cracking form of the fluid cylinder is fatigue cracking, the cleavage crack initiated near the intersection line and extended friable due to the corrosion and impact wear effects from the fracturing fluid and the high stress of the fluid cylinder; the fluid cylinder material E4330 contains a variety of alloy elements, and its organization is the uniform sorbite which can meet the working requirements. It has been observed that the fatigue limit of the material is 607MPa, and at a higher stress, the fatigue life would be nearly halved in the corrosive environment. As the fatigue life would greatly reduce due to the corrosion effects from the fracturing fluid, we should control the working stress and make measures for anti-corrosion.