Materials Science Forum Vols. 561-565

Abstract: Thermal decomposition characteristic of waste material from oil extraction of Jatropha (physic nut), including shell and kernel, was investigated using thermogravimetric analysis (TGA) and pyrolysis experiments. Effects of heating rate (5-90°C/min), reaction temperature (500-900°C) and hold time at final temperature (3-15 min) on the feature of thermogram, kinetic parameters as well as product distribution were evaluated. Thermal conversion of this residue composed of cellulose, hemicellulose, and lignin degradation steps with maximum weight losses around 250 to 450°C. The order of reaction increased with temperature from 0.28 at 250°C to 0.81 at 450°C. The activation energies ranging from 105-184 kJ/mol depend on the stage of devolatilization. The amount of gas product increased with temperature with the expense of reducing char and liquid from secondary heterogeneous cracking reactions. More than 14% of hydrogen in residue was converted to H2 during pyrolysis at 900°C. Major hydrocarbon gases are those of C4+ species with measurable amount of CH4 and C2 derivatives. Increase in reaction temperature can lead to a noticeable increase of hydrogen and hydrocarbon gas yields. Addition of catalyst and steam would promote the formation of fuel gas from this waste material.

Abstract: The spherical indentation obeys Hertz contact theory when the applied load is within the elastic limit. Once the applied load is over the elastic limit, the indentation curve starts to deviate from the original purely elastic indentation curve. This deviation point, which indicates the start of the nonlinear deformation, is an important characteristic of a spherical indentation curve. The indentation force corresponding to the deviation point is related to a basic material constant, which is the yield stress for an elastic-plastic material or the transformation stress for a shape memory alloy. This relationship can be applied to measure the yield stress or the transformation stress from a simple spherical indentation curve. Detailed discussion on the relationship and the method is presented in this short paper.

Abstract: The microstructures of high-temperature oxide scales on the Si-terminated surface and C-terminated surface of 6H-SiC were investigated by transmission electron microscopy (TEM). We found that mechanical polishing caused surface strains, about 100 nm in depth, on both sides of specimens. Mechanically polished specimens were oxidized at 1473 K for 20 h in air. Oxide scales of about 250 nm in thickness were formed on the Si-terminated surface and of about 400 nm on the C-terminated surface. Since the strain regions caused by mechanical polishing were oxidized, strains were no longer observed. As a result, this oxidation condition effectively removed the strains. The oxide scales were identified as amorphous silica on the Si-terminated face, while crystalline oxides and amorphous silica were observed on the C-terminated face.

Abstract: Metal injection molding (MIM) process has the advantage of better formability of three dimensional complex shape products with high density and high performance properties compared to the ingot metallurgy (I/M) process. Two kinds of pure titanium specimens, i.e., the first one is prepared by the I/M process and the second one is prepared by MIM process are used in this experiment, and their corrosion behavior under stress has been investigated in several aqueous solutions by Slow Strain Rate Tensile (SSRT) test. Both I/M and MIM specimens showed good corrosion resistance in the aqueous solution composed of 2.5 kmol/m3 H2SO4 and 0.2 kmol/m3 NaCl as well as saline solution. This aqueous solution is noted one in which Type 304 stainless steel showed SCC. In the aqueous solution composed of CH3OH and 0.1 kmol/m3 HCl containing 8.6kg/m3 H2O, the elongation of MIM specimen was slightly higher than that of I/M specimen though both specimens indicated the remarkable decrease in elongation.

Abstract: The extruded AZ31B Mg alloy specimens using powders fabricated by roll compaction processing (RCP) was prepared, and their corrosion behavior has been investigated through the polarization test, electrochemical impedance spectroscopy test, immersion test and SEM observation in comparison to that of the conventional AZ31B Mg alloy, hereafter shortened as I/M specimen. The extruded AZ31B Mg alloys using RCP powder showed little change in Ecorr irrespective of number of pass cycles. Both anodic and cathodic current density suppression of the RCP specimens became larger with an increase in number of pass cycles. It was also confirmed that the corrosion characteristics of the RCP specimens depended strongly on their structural morphology and that the corrosion resistance of the RCP specimens subjected to 50 pass cycles was nearly same as that of the I/M specimen.

Abstract: Three cemented carbide specimens, i.e., WC-Co (Sample A), WC-Cr3C2-Co (Sample B) and WC-βt-Co (Sample C) in which βt indicates (Ti,W,Ta,Nb)C, are prepared by liquid phase sintering, and their corrosion behavior has been investigated by the electrochemical methods. The similar activation, passive state and over passive state regions as SUS304 stainless steel during the polarization test, and the preferential dissolution of Co were observed for all of the three specimens mentioned above. Both Cr3C2 and βt improved the corrosion resistance of WC-Co alloy, in which the effect of the former was better than that of the latter. Sample B also showed the best corrosion resistance in all the samples for the electrochemical impedance spectroscopy (EIS) test.

Abstract: Crack formation by a rolling contact fatigue in a high carbon chromium bearing steel has been discussed. Newly developed method for preparing specimens including pre-existing voids enabled one to observe the early stage of fatigue crack formation. Many fatigue cracks were formed around the voids. The positions of crack formation and the direction of the cracks were consistent with those forecasted by finite element analysis. Fatigue crack formation was followed by formation of the WEAs.

Abstract: The particle size distributions of tin oxide powders produced from the calcining of precipitated tin oxalate were determined by four methods, these being two static and two dynamic light scattering techniques. Although the individual particle sizes were ~ 75 nm, all of the powders were heavily agglomerated as plates. The non-spherical shape resulted in the following interpretational problems: • None of the measurements was in agreement with any others. • There were very significant disagreements between the two light scattering methods. • The particle size distributions were multimodal. • The main peaks in the distribution curves, which were used to calculate the averages and standard deviations, were not Gaussian. The main uncertainty with these data is associated with the non-spherical agglomerates, which result in the multimodal size distributions. These probably were caused by variable-sized but large platy agglomerates.

Abstract: Anodic oxidation has been used to make well adhered and porous (≤1 μm pore diameter) thin films of anatase on titanium using electrolytic solutions with combinations of H2SO4, H3PO4, and H2O2. The crystallinity, film thickness, and pore size and number increase with time and voltage. The voltage is limited to ~180 V by electrolysis and/or breakdown and the film thickness is ≤3 μm.

Abstract: Rutile nano-powders were suspended in a solution of acetylacetone and iodine. The suspensions were electrophoretically deposited on titanium foil at a voltage range of 5-30 V over times of 5-120 s. The dried tapes then were sintered at 800°C for 2 h in flowing argon. Both the green and fired tapes were examined by field emission scanning electron microscopy, optical microscopy, X-ray diffraction, and Raman microspectroscopy. The thickness of the films depended on the voltage and the time of deposition. The sintered microstructures depended significantly on the thickness of the film, which was a function the proximity to the Ti/TiO2 interface. The interface is critical to the microstructure because it acts as the source of defect formation, which enhances sintering, grain growth, and grain facetting.