Abstract: The microstructure, hardness, and sliding wear properties of high-pressure torsion (HPT)-processed pure Fe and S45C carbon steel were comprehensively investigated. The grains of Fe and S45C were significantly refined to the submicron size range using the HPT process, and the grain sizes were found to decrease with an increased number of turns (N). The Vickers hardness of HPT-processed specimens increased with increasing N or with distance from the center (i.e., with an increase in the strain), which is attributed to grain refinement. In addition, the hardness of HPT-processed Fe was saturated with a further increase in the number of turns owing to the saturation of grain refinement. However, saturation with hardening was not observed in the case of S45C and the hardness values of S45C were much higher than those of Fe. The wear amount was considerably reduced by HPT processing for both Fe and S45C. A linear correlation was determined between the specific wear rate and the inverse of hardness, which agrees with the Archard wear equation. The experimental results show that the reduction in the wear of Fe and S45C is considered to be due to hardening by the HPT process.
Abstract: Calcium methoxide obtained from quick lime is used as a solid catalyst in the transesterification reaction between palm stearin with methanol using tetrahydrofuran (THF) as co-solvent for biodiesel production. In this work, quick lime was used to prepare calcium oxide by heat treatment at the different temperatures, after that calcium oxide was further reacted with methanol to produce calcium methoxide catalyst. The properties of Calcium methoxide (Ca(OCH3)2) was characterized by XRD, SEM, BET, TGA, EDX and FTIR. The optimum conditions of biodiesel production were studied through response surface methodology and central composite design. The conversion of fatty acid methyl ester (FAME) was determined by proton nuclear magnetic resonance spectroscopy (1H-NMR). The results depicted that calcined quick lime at 800 °C for 3 h contained high calcium oxide content. The Ca(OCH3)2 catalyst prepared at 65 °C for 3 h gave high surface area and catalytic activity. The optimum conditions for biodiesel production were 2.33% w/w of catalyst, 1 : 9.39 of palm stearin to methanol molar ratio, 102 min of reaction time and 9.07% v/v based on methanol of THF co-solvent, the same condition gave 98.23% of FAME conversion.
Abstract: The meso-porous TiO2 and Sm-doped meso-porous TiO2 were synthesized by a sol-gel method. Polyethylene glycol, with different added content, was added as a structure-directing agent. The prepared meso-porous TiO2 was characterized by nitrogen adsorption, X-ray diffraction and ultraviolet-visible diffuse reflectance spectroscopy, and the photocatalytic performance was evaluated by the decomposition of methyl orange. The results revealed that PEG plays a key role in creating porous structure during the heat-treatment. The photocatalytic performance of TiO2 is improved by adding proper content PEG, and Sm-doping can further promote the photocatalytic performance.
Abstract: A copper wire was welded to low-alloy rail steel by exothermic welding. There were pre-heating and post-heating processes before and after welding, respectively. Unfortunately, the cooling rate of temperature could be controlled in the post-heating process. The cooling rate of temperature was too fast because the ambient temperature was very low (-5 °C). After that, the large value of thermal residual stresses remained in the welding joint and led to failure. In the present study, a welded joint between copper and low-alloy rail steel was analyzed using finite element analysis (FEA). The singularity of thermal residual stresses in the welding joint was observed after post-heating processes. The intensity of stress singularity (Kqq) was estimated around a singular point of the welded joint by least-square method. The possibility of crack initiation was determined. Then, a shot-peening process was applied on the surface of the low-alloy rail steel near the singular point of the welded joint. A small particle of 3 mm diameter was shot to make it plastically deform on the low-alloy rail steel surface. The effect of the shot-peening on the singularity of thermal residual stresses around the singular point of the welding joint was determined and found that the value of singularities for the stress sqq profile were reduced and became steady.
Abstract: It is known that the quality of metal-ceramic restorations mainly depends on the interface strength. The aim of the study was to evaluate metal–ceramic interfaces of heat pressed ceramic on Co-Cr frameworks obtained with different technologies: melting-casting (CST), computerized milling (MIL), selective laser sintering (SLS) and selective laser melting (SLM). The microstructure of metal–ceramic interfaces and framework topography were characterized by scanning electron microscope (SEM). Sandblasted, polished surfaces and the cross section on the interfaces were observed. Sandblasted surfaces presented a uniform rough aspect and pronounced porous surface compared to that of polished surfaces and were better visible in SLS and SLM samples. The thickness of the veneer layer had a noticeable effect on the interface, because in the case of thicker veneers, cracks at the interfaces were visible for CST and MIL specimens. Considering the findings reported herein, some suggestions can be considered in practice, such as adaptation of the restorations morphology to the characteristics of the processed materials.
Abstract: Using of supplement based on calcium hydrosilicates as structuring supplement in dry mixes lime is proposed. It shows the impact of supplement synthesis mode on the structure formation of calcareous compositions. The efficiency of the using of modifying supplements of amorphous silica, such as diatomite, in the synthesis is shown. It has been established that in supplement of calcium hydrosilicates synthesized with diatomite a greater amount of calcium hydrosilicates, belonging to low-basic ones, are contained. X-ray analysis of samples based on synthesized supplements is presented. A high activity of synthesized calcium hydrosilicates had been established. It has been established that the injection of supplements of hydrosilicates accelerates the gain of mechanical strength. It is shown that the injection of supplements of hydrosilicates accelerates the increase of water resistance and frost resistance of coatings. The operational properties of coatings based on the developed dry mix with the addition of calcium hydrosilicates synthesized with diatomite are presented.
Abstract: Heat treatment of T-Joint’s steel arc welded are performed are investigated in this research. The heat treatment process that used were annealing and quenching. The microstructure was investigated by optical microscope. The mechanical behavior of the samples was investigated using universal tensile testing machine for tensile test and Microvickers hardness method for hardness testing. The microstructure of welding zone of welding metals with various heat treatments is grain boundary ferrite, Widmanstatten ferrite and acicular ferrite. The weld metal with quenching treatment has a highest tensile strength with tensile strength 197.97 Mpa. The quenching process increases the tensile strength by 49.58 %. The distortion value in weld metal without heat treatment, quenching and annealing is 0.11mm; 0.04 mm and 0.08 mm respectively. The hardness number of weld metals with quenching process have a highest number base metal, HAZ and weld metals. Results showed that the mechanical properties of T-joints steel arc welded can be improved by various heat treatments.
Abstract: The densification kinetics of copper powder during sintering has been investigated using scanning electron microscopy analysis and density measurements. A constitutive model was proposed to predict the densification kinetics as a function of sintering condition by considering the densification parameter to obtain more accurately predicted results. The activation energy for copper densification kinetics was calculated from experimental data and compared with activation energies associated with different densification mechanisms. We found that the lattice diffusion mechanism acted as the primary densification mechanism for copper powder during sintering.
Abstract: We investigated the use of durian shell-derived activated carbon (DSAC) for the removal of Cu2+. To determine the optimal condition for Cu2+ removal, the response surface methodology (RSM) was used to establish a second-order polynomial model with variables such as Cu2+ concentration (Ci), adsorbent dosage (dDSAC) and pH. With R2 = 0.9847 and P-value < 0.0001, the model was proved to be statistically significant. The RSM based confirmation test revealed that the removal of Cu2+ was maximum (99.6%) at optimal conditions: Ci = 61.6 mg/L, dDSAC = 5.0 g/L and pH = 5.2. Based on calculated R2, data fitness for adsorption isotherms were positioned as follows: Langmuir > Tempkin > Freundlich. In other words, monolayer adsorption was the most favorable behavior with maximum capacity of 76.92 mg/g from Langmuir model. Interestingly, DSAC was reused at least five times without a considerable decrease of Cu2+ removal efficiency. Therefore, durian shell can be used as a highly effective, reusable and promising raw material to fabricate the activated carbon.