Abstract: Gypsum building materials can be made from either natural resources or industrial residues. This work introduces the gypsum mixture based on domestic industrial wastes. The waste used as a calcium sulfate source in the mix is FGD gypsum from a power generation plant. Meanwhile, the silica-rich sources, i.e. diatomite, derived from brewery production, and soda-lime glass cullet from automotive safety glass industry are also employed. These wastes were pretreated before mixing and the compositions of the waste-based gypsum were carefully formulated and characterized. Phase presence and microstructural information were determined. Development in strength as well as water resistance was examined. The experimental work suggested that the addition of diatomite can significantly increase both strength and water insolubility.
Abstract: Activated carbons were prepared by chemical activation from scrap tire with two chemical reagents, NaOH and KOH. The activation consisted of different impregnation of a reagent followed by carbonization in nitrogen at 700°C. The resultant activated carbons were characterized in terms of BET surface area, methylene blue adsorption and iodine number. The influence of each parameter of the synthesis on the properties of the activated carbons was discussed, and the action of each hydroxide was methodically compared. It is the first time that preparation parameters and pore texture characteristics are simultaneously considered for two closely related activating agents of the same char precursor. Whatever the preparation conditions, it was shown that KOH led to the most microporous materials, having surface areas and adsorption properties (methylene blue adsorption and iodine number) higher than those obtained with NaOH, which was in agreement with some early works. However, the surface areas, methylene blue adsorption and iodine number obtained in the present study were much higher than in previous studies, up to 951 m2/g, 510 mg/g and 752 mg/g, respectively, using scrap tire waste char:KOH equal to 1:1. The thorough study of the way each preparation parameter influenced the properties of the final materials bought insight into the activation mechanisms. Each time it was possible; the results of scrap tire waste chemically activated with hydroxides were compared with those obtained with anthracites; explanations of similarities and differences were systematically looked for.
Abstract: In this study, silicon nanocrystal (Si-nc) films were synthesized by compositing of Si-nc powder embedded in silicon oxide phase. The Si-nc film produced by the spin-coating methode using Tetraethylorthosilicate, ethanol, phosphoric acid, and Si-nc powder as suspension precursors. The variation in structural and optical properties of Si-nc sol films with the amounts of Si-nc powder have been characterized. Atomic force microscopy (AFM) shows that low density level of Si-nc power can result in the amount of porosity in the Si-nc films. It is found that when the Si-nc films have the higher Si-nc density, the small pores in the SiO2 phase were removed. In addition, optical energy gap (Eg) of Si-nc samples was evaluated by the Tauc plot method. It is a crucial attribute for a promising photonic device. The obtained optical bang gap values were extended from 1.10 eV to 1.40 eV as compared with the typical Si bulk. In addition, density of Si-nc clusters has a considerable effect on the electrical conductance of the Si-nc films measured at room temperature.
Abstract: Due to different heat treatment procedures being required to reduce intergranular corrosion (IGC) of austenitic AISI 304(ASS304) and ferritic AISI 430(FSS430) stainless steels, this work is aimed at achieving proper heat treatment for these metals simultaneously. Heat treatment at a temperature of 900°C for 36 hours followed by water quenching was an applicable heat treatment procedure for this study. This treatment not only prevented the formation of chromium carbides but also promoted the diffusion of chromium back to replenish chromium-depleted zones.
Abstract: Tungsten carbide with nickel (WC-Ni) is generally used in applications in which high wear and corrosion resistance are required. In most cases, WC is mixed with Ni powder through a powder-processing route. In the present study, an electroless deposition technique was employed in order to prepare Ni coated WC particles prior to forming specimens by powder injection moulding method. The starting WC powders were subjected to surface activation followed by electroless Ni coating. The effects of a variety of processing parameters, including coating time and powder to electrolyte content ratio, were examined. The characteristics of the prepared powders were assessed by scanning electron microscopy and laser particle size analysis. It has been found that the fabrication of WC powder coated with Ni can be achieved through the electroless deposition technique. The amount of Ni introduced to the WC particles can be controlled by the powder to electrolyte content ratio and the deposition duration. The use of small particle loadings can ensure relatively large deposition and uniformity of the coatings. It is widely known that powder injection moulding (PIM) is an effective process for fabrication of small and complex shaped components of high performance materials. The PIM process includes 4 main steps: feedstock preparation, injection moulding, debinding and sintering. In this work, the WC-Ni powders were mixed with polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) binder to form feedstock for injection moulding. The injection moulding process was carried out by a laboratory scaled, plunger-type machine. The mouldings were subjected to debinding and sintering. It was found that the PEG could be removed by water leaching. Specimens retained their shapes during and after leaching of the PEG. The remaining binder could be removed through pyrolysis. The mouldings were sintered under vacuum at 1400 °C for 1 hour. The sintered density achieved was at 88% of the theoretical value due to the low powder loading employed in the study.
Abstract: Cryorolling is considered to be the prominent processing method to develop high strength light weight alloys. Even though considerable work is available on mechanical properties of cryorolled materials, no detailed studies are available on corrosion behavior of these cryorolled sheets. Al-Mg-Si alloy is cryorolled to 50% and 75% reduction at -196°C and also at room temperature. Potentiodynamic polarization studies were performed on these rolled sheets in 3.5 wt% NaCl solution and the results were compared with those of the annealed and solutionized samples of Al-Mg-Si alloy. Irrespective of the rolling temperature, all the rolled samples, except for LNR 75%, exhibited inferior corrosion resistance compared with those of the reference samples. This is attributed to the large amount of internal stresses and sub-grain network developed during rolling. The rolled samples evidenced peak shift compared to those of the annealed and solutionized samples and higher peak broadening is observed, which is due to the development of higher grain boundary area and enhanced lattice strains along with large dislocation densities. These grain boundaries and dislocation densities are the root cause for the inferior corrosion properties of the rolled samples.
Abstract: This study investigated the tribological property and wear behavior of pure titanium (Ti) plate coated with un-bundled multi-walled carbon nanotubes (MWCNTs). The network-structured MWCNT films were formed on Ti substrate, and their tribological properties were examined by the ball-on-disk wear test equipment under dry sliding condition. SUS304 stainless steel ball was used as a counterpart material in this test. The mean friction coefficient of the Ti plate coated with MWCNTs was remarkably lower and stable compared to the as-received pure Ti plate without any coating films. SEM-EDS analysis showed the network-structured MWCNT films obviously remained after wear test for 3.6 ks in sliding and no seizure phenomena with the SUS304 ball. The above excellent tribological performance was due to CNTs self-lubricant, their bearing effects and the strong metallurgical bonding between Ti plate and MWCNT films by annealing.
Abstract: Sintered Cu-based frictional materials were developed by using powder metallurgy (PM) method. The materials are aimed for application in a passenger car as a dry friction clutch. Effects of sintering temperature and composition on mechanical and tribological properties were determined. It was found that improper frictional material formulations caused inferior properties, particularly when the sintering temperatures were increased. Admixing of high Sn content (8 wt. %) resulted in decreases of sintered density and hardness with increasing sintering temperature. High Sn contents caused swelling of the sintered materials. Tribological properties (friction coefficient and wear rate) of the sintered specimens of the investigated materials were insensitive to sintering temperatures in the range of 800-950 °C but they were strongly influenced by chemical compositions. Addition of 3 wt. % graphite lowered the friction coefficient, which subsequently lowered the wear rate of the sintered material. To increase friction coefficient, one of the crucial properties of the dry friction clutch, of the sintered Cu-based frictional materials, two approaches were employed. In the first approach, substitution of graphite by SiO2 powders could improve the material friction coefficient. In the second approach, decreases of graphite content from 3 to 1 wt. % and of Sn content from 8 to 2 wt. % were conducted. The latter approach not only improved friction coefficient but also improved sintered density and hardness of the Cu-based frictional materials.
Abstract: Powder injection moulding (PIM) is a process that is suitable for a fabrication of small and complex shape components. It consists of 4 main steps: feedstock preparation by mixing powder and binder, injection moulding of the prepared feedstock into the desired mould, removal of the binder and finally sintering to obtain materials with specific properties. In this study, powder injection moulding of alumina (Al2O3), using polyethylene glycol (PEG) based binder systems, was investigated. PEG is soluble in water; therefore, the use of organic solvents required for debinding of wax-based binder system can be avoided. PEG with a molecular weight of either 1500 or 4000 was used as a major constituent together with polyvinyl butyral (PVB) as a minor component. Stearic acid was also added during feedstock preparation to act as a lubricant. After mixing the powder with the binder, a variety of Al2O3 feedstocks were injected into the moulds. The mouldings were prepared by a laboratory-scaled plunger-typed machine. Debinding was carried out using a combination of solvent extraction and thermal debinding. Water leaching tests were performed at 30 and 50 °C to study PEGs removal rate. The pyrolysis of PVB was completed during ramping up of the mouldings to the sintering temperature. The mouldings were subjected to sintering at 1500 °C in air. It was found from the study that PEG/PVB binder systems can be used for the preparation of alumina powder injection moulding feedstocks. Specimens retained their shapes during and after leaching of the PEGs.
Abstract: Weld metal mechanical properties and weldability of materials are closely related to the microstructure of the weld metal. A significant amount of research has been studied to improve microstructure of weldments such as weld pool stirring by using magnetic arc oscillation and arc pulsation. In this work, the effect of ultrasonic vibration was used to modify weld metal solidification to improve microstructure of the weld metal. Microstructure and mechanical properties of carbon steel weld metal (ER70S-G filler metal) were studied. Filler metal was melted by using Gas Tungsten Arc Welding (GTAW) in a water-cooled copper mold. Ultrasonic vibration with a frequency of 20 kHz was applied during solidification of the weld metal. Microstructure and mechanical properties of weld metal were compared with those of conventional weld metal (no ultrasonic vibration assistance). Scanning Electron Microscopy (SEM) was also used to determine microstructure and phases at high magnification. The results showed that ultrasonic vibration applied during solidification promoted grain refinement in the weld metal. Mechanical properties of weld metal were improved significantly, microstructure analysis correlated well with the mechanical test results.