Papers by Keyword: Dissolution

Abstract: Rare Earth Elements (REE) concentrate from the processing of xenotime minerals still contains a mixture of REE and its impurities, so it requires a further separation process to purify the content of each element. The first step to separating each element of REE is to dissolve the REE concentrate in strong acid as a feed for the liquid-liquid extraction or ion exchange column process. The REE concentrate was dissolved in 3 variations of strong acids, namely hydrochloric acid, nitric acid, and sulfuric acid. XRF and FTIR analyses were done before and after the dissolution process. The results showed that sulfuric acid is the best dissolution reagent for the total rare earth elements (71.75%) but is less selective for separating light REE, heavy REE, and their impurities. Better selectivity for separating light REE and heavy REE is shown by dissolution with nitric acid with dissolution levels of 37.32% and 81.91%, respectively. Meanwhile, hydrochloric acid showed the lowest dissolution results for the total element of REE (63.14%) but had the best selectivity to prevent the dissolving of radioactive elements. The results of the FTIR analysis showed that REE-chloride, REE-nitrate, and REE-sulfate bonds had been formed in each dissolving filtrate.

Abstract: Material choices for liquid lead bismuth spallation target are some of austenitic stainless steel, ferrite martensitic steel and cold-worked austenitic stainless steel. In order to ensure materials resistance to irradiation and corrosion as well as compatibility with lead bismuth, it is appropriate to lower the incident proton current density and the process temperature, in which temperature range engineering design can control to work, especially in ADS (Accelerator-Driven nuclear transmutation System) concept. The lower limit temperature is determined from the physical melting temperature and the engineering efficiency of the steam generator involved in process control. The material related issues for liquid lead bismuth are mass loss by impinging secondary flow, wettability at the device interface for ultrasonic waves application, detachable control of the slag in the flowing system, stabilized electrical resistance between the material and the liquid lead bismuth interface. Electromagnetic fluid analyses show how flow rate relates electrical resistivity of flow channel material.

Abstract: Particle size analysis of synthesized Al₂O₃ by dissolution and alkali fusion-coprecipitation methods has been conducted. The formation of nano- or microparticles can be synthesized by the top-down (physically) and bottom-up (chemically) methods. In this study, the commercial alumina (Merck) with the particle size of 63 µm was synthesized through the bottom-up method. The dissolution method was done by reacting to alumina with ammonium hydroxide (NH₄OH). The alkali fusion method was carried out by reacting alumina with sodium hydroxide (NaOH) and it obtained by coprecipitation of the alkali fusion product with HCl and NH₄OH. The result from both methods were calcined at 600°C. The phase of synthesized Al₂O₃ was identified by using X-ray diffraction (XRD), whereas the morphology observed using a transmission electron microscope (TEM), and the particle sizes measured by particle sizes analyzer (PSA). The XRD pattern shows the γ-Al₂O₃ phases with particle sizes of ~33 nm and ~25 nm from TEM observations, while the PSA results revealed agglomerated particles with particle sizes of 1263 nm and 477 nm for the dissolution and alkali fusion-coprecipitation method, respectively. Therefore, both methods can be used to reduce the particle size of γ-Al₂O₃.

Abstract: Simvastatin is a cholesterol-lowering agent that inhibits the microsomal activity of 3-hydroxy-3-methylglutaril-CoA-reductase (HMG-CoA reductase), enzyme that contributes in biosynthesis cholesterol. Simvastatin has short half-life elimination about 2 hours and low solubility, this condition makes its bioavailability to be quite small. Simvastatin has adverse effect such as myopathy and rhabdomyolysis because of higher dose consumption of simvastatin. Controlled drug delivery system is needed to reduce the adverse effect. One of method that is used in drug delivery system is encapsulation using biodegradable polymer such as poly(L-lactic acid) and poly(ɛ-caprolactone). PLLA and PCL was blended with fix composition PLLA : PCL 60 : 40 (%w/w) by solvent evaporation technique using Tween 80 and Span 80 as emulsifier. Based on the optimization, the best encapsulation efficiency microcapsules were obtained at concentration of Tween 80 0.025% (v/v), Span 80 1% (v/v) with stirring speed at 900 rpm for 1 hour. The encapsulation efficiency was 83.67%. The best microcapsules were dissolved in dissolution media to get drug release profile. The percentage of drug release at pH 1.2 was 0.86% for 3 hours and in the phosphate buffer solution pH 7.4 for 12.22% for 52 hours.

Abstract: Some carbonate reservoirs are known for their high CO₂ content in oil. One possibility to handle this gas without environmental problems is to reinject it into the reservoir. Injection of carbonated water has been drawing attention because it is an advantageous technique when compared to gaseous CO₂ injection, due to its improvement in mobility in the reservoir. The objective of this study is to evaluate the phenomenon of dissolution and precipitation during carbonated water injection in carbonate rocks. These effects are identified by analyzing the porosity variations through X-ray computer tomography images and permeability profile, determined indirectly by pressure transducers that measured the differential pressure by the fluid at the inlet and outlet of the core holders. The Coreflooding test were carried out with two core holders in series to represent a near region at the reservoir by the injection of brine saturated with 25% of CO₂ in reservoir samples, composed of dolomite, calcite and clay. The test were performed using the following reservoir conditions of 8,500 psi at 70°C. Based on the experimental data provided by CT images, it can be seen that the core porosity increases or decrease during carbonated water injection due to coexistence of dissolution (increase of porosity) and precipitation (decrease of porosity) along the samples. These phenomena are observed in regions with high heterogeneity in porosity. In addition, the mineralogy of the cores is composed by three minerals, which influence in the capacity of reaction with carbonated water. For the experiment, the core placed in the core holder one presented a porosity increase and the second one decreased. On the other hand, the permeability showed a significant increase for both cores, it is believed that, the injection promoted a preferential way flow (wormhole) that affected considerably the permeability of the rock. The novelty of the investigation is that the experiments were carried out using Brazilian pre-salt carbonate reservoir rocks with mineralogy composed basically by dolomite, calcite and clay. Also, experimental work was performed at reservoir operational conditions.

Abstract: Carbon dioxide (CO₂) is considered one of the main gases that cause global warming. In this perspective, its injection in aquifers and oil and gas reservoirs has been a possible alternative to reduce its emission in the atmosphere. An alternative strategy in which CO₂ is used efficiently in the Oil Industry is the Carbonated Water Injection (CWI), where the carbon dioxide is injected through the reservoir dissolved in the brine, eliminating problems of gravitational segregation and low sweeping efficiency present in other gas injection methods. Once injected, the fluid may react with the carbonate rock and inducing their dissolution, causing changes in the petrophysical properties of the rock. This work investigated changes in the average porosity of carbonate samples from Brazilian reservoir through a dynamic flow test with enriched brine with 100% CO₂ injection under high pressure and high temperature conditions and simulating a region around the face of the injector well, with an injection pressure of 8,500 psi, a temperature of 70 °C and a flow rate of 2cm3/min. The core-flooding experimental setup includes two coreholders arranged in series with samples confined in its interior, which are swept by X-ray Computed Tomography (CT), taking measurements of average porosity data. The results showed that there was dissolution in the sample assembled in the first coreholder since the porosity had increased, while in the second, no significant alterations of the porosity were observed (around 8.5% of its initial value). This observation can still be confirmed by the analysis of the dissolved moles, which exhibit behavior similar to the porosity, indicating that some minerals actually suffered dissolution from the injection of carbonated brine.

Abstract: The influence of annealing at 1200 °C for 2, 4 and 8 h on the carbide microstructure of AISI M2 type high-speed steel obtained by both the foundry and conventional metallurgy technologies has been studied. The primary focus was on the kinetics of eutectic carbide decomposition and dissolution in both the cast and wrought M2 high-speed steels under the effect of high temperature.

Abstract: Succinic acid is a potential co-former to produce co-crystal, thus an understanding of the dissolution behaviour of succinic acid crystal is crucial for designing the co-crystal. In this works, α-succinic acid was chosen as a model compound for this study regardless its attractive crystal chemistry and its diverse surface properties. The aims of this study are to analyse the morphology of succinic acid crystal (form A) and to analyse the dissolution behaviour of succinic acid crystal (form A) in the ethanol solution using molecular dynamic simulation. Prediction of form A succinic acid morphology were conducted with different combination of charge set and potential function i.e ESP and CVFF which produces hexagonal needle-like shape morphology and shows good agreement with the experimental crystal shape. Dissolution of α-succinic acid in ethanol solvent was investigated using dynamic simulation. Visual observation and mobility assessment shows that the molecules at the edge of the crystal tends to dissolve faster compared to the molecules at other position on the facet.

Abstract: The fast and spontaneous hydrogen diffusion in HCP structures leads to the hydride precipitation. It is often pointed as causing embrittlement and rupture in zirconium alloys for applications in the nuclear industry. In our previous works TEM, DSC, SEM-EBSD and XRD were used to study the hydride stability after many precipitation-dissolution thermal cycles as well as the crystallographic hydride phase nature and the hydride-substrate crystallographic orientation relationships as a function of the hydrogen content. Results showed that the evolution of the dissolution and precipitation energies is correlated to the concentration of hydrogen atoms available to reprecipitate, which is submitted to a diffusion controlled by the misfit dislocation migration. In the present work in-situ TEM thermal cycling was performed in order to locally investigate the crystallographic stability of zirconium hydrides of different structures after many dissolution-reprecipitation cycles.

Abstract: The types of defects occurring during the formation of local zones on the surface of silicon wafers have been established. The dependences of defect formation on the surface from the surface microrelief, thickness of the protective coating of silicon oxide, process temperature, flow rate of the melt, the height of the melt, and the concentration of gallium additives in the aluminum have been determined. The optimum conditions of the process of zones formation have been revealed, and the total relative number of all types of defects has been significantly reduced.