Papers by Keyword: Crystallization

Abstract: Bagasse ash is one of the agricultural wastes and valuable biomass by-products in sugar milling. It was treated hydrothermally with hydrochloric aqueous solution at 100 °C and burned at 600°C for 2 hours under oxygen feeding. The obtained white ash was further used as natural silica source instead of silica sol because of highly silica content from an abundant supply of sugar industries in Thailand. Aluminosilicate precursor gel was prepared from alumina source and silica source via sodium silicate preparation. Different crystallization time was studied for the molar ratio of SiO₂/Al₂O₃ = 2 at 100°C crystallization temperature. The phillipsite zeolite synthesized was characterized using various techniques; X-ray diffraction, Scanning electron microscopy, Fourier Transform Infrared Spectroscopy, and BET-N2 adsorption method. The results can be used as value added for bagasse ash utilization, minimize the environmental impact of disposal problems and further application for heavy metal removal.

Abstract: Undoped amorphous silicon film deposited by PECVD,and annealed by rapid tharmal process,then have been studied by using micro-Raman scattering, X-ray diffraction and scanning electron microscope.It is found that crystallized silicon films is different at different annealing temperatures, there exists a better annealing temperature.

Abstract: Thermotropic liquid-crystalline polymers (TLCPs) have aroused wide public concern which is attributed to their high strength, stiffness, chemical resistance and perfect dimensional stability as high-performance engineering materials. Vectran heat treated after melt spinning is a representative commercial aromatic copolyester fiber. In this study, a novel TLCP melt-polymerized with 4,4’-diphenyloxide dicarboxylic acid (DODA), 4-acetoxybenzoic acid (ABA), hydroquinone diactate (HQA), 2,6-naphthalene dicarboxylic (NDA) and terephthalic acid (TA) were melt spun into fibers and heat treated to enhance the breaking strength and Young’s modulus. Intermolecular mechanical elements slipped between 120-130 °C and crystallization or the conformational rotations occurred along the extended polymer chain. For this new TLCP fiber, the optimal heat treatment temperature was 260 °C and the suitable heat-treatment time was over 48 hours. The breaking strength, Young’s modulus and breaking elongation of the as-spun fiber were improved from 1.58GPa, 45.21GPa and 1.97% to 3.20GPa, 133.44GPa and 2.42% respectively after heat treatment.

Abstract: In most biphasic composite systems consisting of sol-gel derived bioactive glass and a second system that is usually used as a reinforcing agent, thorough stirring is necessary to prevent the precipitation of the grains of the second system. Consequently, the aim of this work is to investigate the impact of various stirring rates on the crystallinity and bioactivity of a bioactive glass in the system 58S. Sol-gel-derived bioactive glass (58S) was produced as described in literature. During the gelation, stirring rates of 0, 200, 400, 600 and 800 rpms were applied producing, respectively, the corresponding glass powders. The in vitro bioactivity of the powders was tested in Simulated Body Fluid (SBF) for various immersion times, while the solution was renewed after 6h, 24h and then every 2 days. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Diffractometry (XRD) were used to characterize all materials before and after immersion in SBF solution. FTIR and XRD measurements of all powders revealed mainly the formation of an amorphous glass, while the main crystalline phase was identified to be Ca2SiO4. After immersion in SBF solution for 12h, SEM microphotographs revealed apatite formation on the surface of all samples, while FTIR and XRD confirmed the aforementioned findings. Furthermore, since EDS analysis proved a mean molar Ca/P ratio of about1.7 after 6 days of immersion of all samples- besides those stirred at 400 and 600rpm- it can be assumed that a thick apatite layer was formed covering the whole surface.

Abstract: The phosphate removal and recovery from lower concentrated phosphate wastewater with the quartz sand, ceramsite, blast furnace slag and steel slag as seed crystals were investigated. The results showed that the steel slag performed a better phosphate removal performance than the other threes. The phosphate crystallization occurred under the reaction conditions of Ca/P 2.0, pH 9.0, phosphate concentration 10 mg/L and reaction time 12h. The steel slag could be employed as an effective seed crystal, of which the phosphate concentration decreased drastically in 12h and almost had been removed completely in 48h. The XRD analysis showed that the main crystallization products were hydroxyapatite (HAP) and the crystallinity increased with the reaction time.

Abstract: Intensified agriculture in response to the growing population has led to excessive nutrient discharges to natural waters causing environmental problems in the form of eutrophication and its associated risks. Treatment options for this adverse effect include removal and recovery of soluble phosphorus by chemical precipitation, biological uptake, and struvite crystallisation. Chemical precipitation is the most common method due to its simplicity, but the chemical requirements can be prohibitive and the removed phosphorus is less reusable. Biological uptake requires less chemicals but the process is complex and prone to seasonal variations. Phosphorus removal and recovery from wastewater by struvite crystallisation is an attractive option since the crystallisation process converts phosphorus into struvite crystals, i.e. phosphate minerals which have proved to be good fertilizer, hence potentially reduces fertilizer production and the subsequent greenhouse gas emissions. Moreover, struvite crystallisation helps prevent scaling of wastewater treatment facilities. A number of struvite crystallisation projects utilising primarily agricultural wastewater is already operational at industrial scale.

Abstract: In this paper, the Urea-SCR system is first introduced; then change of the urea solution concentration under different temperatures with time lapsing is given. Meanwhile, conditions for the urea crystallization are analyzed and SCR converter adaptability is tested under high sulfur environment on engine test bench. As the efficiency of NOx conversion is not significantly reduced after aging and the activity of the catalyst is very little damaged by dense sulfur content in fuel, SCR catalyst is able to adapt to the application of high-sulfur-contained fuel environment in our country.

Abstract: Physics mechanics properties of polymer materials don’t only depend on their chemical constitution, molecular weight and distribution of molecular weight, but also depend on their agglomerate configuration. The effect of vibration on the microstructure and mechanical properties of high-density polyethylene (HDPE) sheets, obtained through vibration plasticating extruder in low temperature, were studied systematically. Crystalline polymer is analyzed by differential scanning calorimetry(DSC), wide angle X ray diffraction(WAXD). The test result which represents parameters of crystalline structure is helped to judge the outside factors for crystalline structure, such as melting point, crystallinity and heat of fusion by DSC and crystallinity, crystal plane distance and grain size by WAXD, and canning electron microcopy (SEM). The results indicate that the vibration extrudate in low temperature has higher crystallinity, perfect crystallite, and strong inter-spherulite ties.

Abstract: At present, the trends for injection molding are higher precision, ultra-thin and light weight, and there are many harsh requirements on injected parts. For the parts manufactured by injection molding, crystallization and orientation of polymer affect the properties of the parts greatly. Crystallization and orientation affect the physical and chemical properties of the injected part, such as strength, stiffness, impact resistance, erosion resistance and so on. According to their formation mechanism, this paper presents the layout and dimensions of the coolant lines, the position, shape and dimensions of the gate, and the injection pressure etc., which play an important role for controlling the degree of crystallization and the direction and degree of orientation.

Abstract: The strength, expansion and amount of scaling of concrete with compound mineral admixture (CMA) from steel slag, granulated blast furnace slag and fly ash were studied. The result shows that damage by crystallization press from sulfate attack when concrete was exposed to sulfate environments under wetting–drying alternation is much larger than that from sulfate chemical attack. Adding CMA to concrete could reduce the damage from expansion of concrete caused by sulfate chemical attack, but the resistance of concrete to damage by crystallization press from sulfate attack was remarkably reduced.