Papers by Keyword: Precipitation

Abstract: Cerium oxide has been widely used in many application. One of the most important applications is for chemical mechanical application/planarization (CMP). In the current work, ceria nanoparticles have been prepared via precipitation method using ethanol/water mixture as the solvent, while cerium nitrate hexahydrate as cerium source and ammonium solution as precipitant. The effects of two different temperatures (i.e. 30 and 50°C) and two different apparatus setup (i.e. Setup A and Setup B) on the morphology and crystallite size of the ceria nanoparticles were studied. The morphology and crystallite size of the ceria were analyzed using X-Ray Diffractometer (XRD) and Tranmission Electron Microscopy (TEM). The XRD analysis results showed that the peak intensity of the ceria nanoparticles prepared by using setup B was much higher than the ones prepared by using Setup A. The XRD results revealed that the crystallinity growth and mean crystallite size of the ceria was better or higher when using Setup B. The crystallite size of the calcined ceria nanoparticles were found to be 9.8; 10.5; 14.5 nm for Ceria-1, Ceria-2, and Ceria-3 samples, respectively. In addition, the TEM images showed that Ceria-3 sample exhibited better morphology and less agglomerated compared to that of Ceria-1 and Ceria-2 samples. Futhermore, Ceria-3 sample also had better dispersion stability compared to that of Ceria-1 and Ceria-2 samples due to its better morphology.

Abstract: This paper describes a metallographic preparation of the heat-exchanger austenitic stainless steels, i.e., SUPER 304H, HR3C and Sanicro 25. The as-received materials delivered after the solution annealing are very resistant to the chemical etchants. Therefore, it is more efficient to optimize the parameters of the electrolytic etching in the acidic or basic electrolytes. After the materials’ operation under elevated temperatures (600–750 °C), the microstructure is easier to etch due to the reduction of corrosion resistance. For the following analyses, it is necessary to think of the etching purpose in advance. For the grain size determination, it is sufficient to use electrolytic etching in the oxalic acid solution or chemical swabbing in the combination of 15 ml HCl, 10 ml acetic acid and 5 ml HNO₃. For the image analysis of the intermetallics, the previous methods can be too invasive and give skewed results. In many cases, this leads to the overetching and thus removal of the observed particles (intermetallics, carbides, etc.). It is suitable to use selective etching methods or only polishing for a more precise evaluation, e.g., electron microscopy.

Abstract: This research investigated the effect of reactant concentrations, reaction medium, urease enzyme source, and calcium source on the precipitation rate of calcium carbonate (CaCO₃). This project is aiming to develop a biochemical reaction by using Enzyme Induced Calcite Precipitation (EICP) technique. This new technique would help in replacing the traditional cementation for the dune sand stabilization and promise an environmentally friendly and sustainable approach in the field of construction materials. Jack beans and soybeans were employed as a substrate to catalyze the urea hydrolysis in the study. The sources of calcium used in the experiments were calcium chloride (CaCl₂), eggshell and sesame. In addition, both seawater and distilled water were used as a reaction medium to distinguish the effect on calcium carbonate precipitation. The experiments showed that using sesame at a concentration of 4.5 g, 5 g of urea and 6 g of jack bean at 60 mL of distilled water, is the best reaction conditions to precipitate 100.288 g of calcium carbonate. Further, the results indicated that the calcium carbonate precipitation enhanced by using 5 g of urea, 5 g of CaCl₂ and 5 g of soybean at 50 mL of seawater. The precipitation amount was 25.593 g. These results provide a useful way for the bio cementation by following the EICP technique to address the issues of environment friendly practice of ground improvement.

Abstract: Grain-oriented electric steel is hot rolled at different hot rolling temperature, and subsequent thermal maintained. Precipitation features of MnS and Cu₂S were observed under different process conditions using thermal field emission scanning electron microscopy. The results show that Cu is precipitate out in the form of a composite precipitate with MnS during hot rolling, The hot rolling temperature and the postrolling maintain time had no obvious effect on the precipitation of MnS, The lower the hot rolling temperature, the faster the Cu₂S precipitation. And the insulation process after high temperature hot rolling can make a large number of the Cu₂S diffusion precipitation, There was no significant effect on the precipitation of Cu₂S after low temperature hot rolling, still remain in the precipitate state after hot rolling.

Abstract: The effects of Mg/Si ratio on precipitation behaviour and properties of Al-Mg-Si alloys were studied by using electrochemical test, corrosion test and transmission electron microscope (TEM). The results show that with the increases of Mg/Si ratio from 0.9 to 1.1, the density of the β" decreases, and the mechanical properties decrease. When the ratio of Mg/Si increases from 1.0 to 1.1, the density y of β" does not increase significantly, but the continuous degree of the MgSi phase decreases significantly. The source of cracks originate from MgSi phase, which reduces the mechanical properties. When the Mg/Si ratio is 0.9, the alloy is in an over-Si state, which results in serious intergranular corrosion (IGC).

Abstract: The influences of Mg/Si and heat-treatment on the corrosion performance of Al-Mg-Si-Ag alloy were studied. The results show that when the Mg/Si<1, apart from the precipitation of β phase, there is a small amount of elemental silicon. In the corrosion process, the Si element acts as a cathode, which on the one hand leads to the decrease of the corrosion potential, and on the other hand, it increases the corrosion rate. When Si is excessive, the βʺ density increases significantly, and the continuity of the grain boundary phase becomes higher, which promotes electrochemical corrosion, resulting in severe intergranular corrosion (IGC). In under-aging state, the alloy exhibits the best corrosion resistance. The corrosion current density in the slightly over-aged state is slightly lower than that in the peak-aged state. The slightly over-aging treatment can effectively improve corrosion resistance of the alloy. After the alloy treated by severely over-ageing, the grain boundary coarsened and result in the increase of corrosion current density.

Abstract: The effect of high temperature annealing on microstructure evolution of Ni-24Fe-14Cr-8Mo alloy was investigated through Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Rockwell Hardness Testing Machine. Three kinds of grain growth patterns were found at different annealing temperatures due to carbides precipitation and dissolution. After a combination of high temperature annealing and aging treatment, the hardness versus time curves performed a parabolic pattern. The highest hardness was achieved under 1070°C/60 minutes treatment, and the desirable annealing time should be 60 minutes to 90 minutes.

Abstract: Purification on kappa (ƙ) carrageenan was performed by dissolving ƙ-carrageenan powder in distilled water and re-precipitated with ethanol and n-hexane separately during re-precipitation process. The purified kappa carrageenan was analyzed by using Fourier transform infrared (FTIR) spectroscopy and carbon, hydrogen, nitrogen, and sulfur (CHNS) elemental analysis. The outcomes from FTIR showed there are physical changes due to intermolecular interactions which lead to decrease and lower intensity of hydroxyl band at 3345 cm^-1 after re-precipitated with n-hexane, compared to re-precipitation with ethanol and unpurified ƙ-carrageenan. There were variations observed in the percentages of C, H and S in the CHNS analysis between unpurified and purified ƙ-carrageenan. The successfully purified ƙ-carrageenan are suitable to be used for further application.

Abstract: In this work a simple process for the production of high purity biogenic amorphous SiO₂ derived from rice husk ash have been studied. Rice husk ash obtained from heat treatment of rice husk and citric acid leaching of rice husk at 700 ^o C for 6 h. Improvement of purity SiO₂ from rice husk ash conducted by precipitation technique. The precipitated SiO₂ particles obtained were characterized by x-ray fluorescence (XRF) analysis, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction analysis (XRD). The XRF result shows that the high purity of biogenic amorphous SiO₂ obtained is 99.258 %. The XRD result shows the silica have amorphous phase and for the FTIR results shows bending and stretching vibration of Si-O and Si-O-Si.

Abstract: The 7000 series aluminum alloys suffer from intergranular fracture (IGF) that limits the use of the alloys, although they have highest strength among aluminum alloys. The types of IGF can be classified into two categories: (i) with smooth fracture surface showing practically no plastic deformation that takes place in hydrogen embrittlement and stress corrosion cracking, and (ii) with shallow and fine dimples on the fracture surface showing localized plastic deformation inside precipitate free zones. In this study, attempts have been made to suppress the IGF of both types by (a) controlling precipitate microstructure on grain boundaries by quench control and (b) controlling grain boundary morphology by strain induced boundary migration. The IGF of type (i) (hydrogen embrittlement) was successfully suppressed both by the two controlling processes.