جستجوی مقالات مرتبط با کلیدواژه « calcium carbonate » در نشریات گروه « مواد و متالورژی »

In this paper, the structural , electronic and optical  properties of calcium carbonate in hexagonal (calcite) ,orthorhombic (aragonite)  and orthorhombic( waterite)phases are investigated.The calculations have been performed with pseudopotential methodin the framework of the density functional theory with different approximations and using Quantum Espresso package.The band structure results for the calcium carbonate compound in the hexagonal phase indicate an indirect band gap in the  direction and the orthorhombic phase has a direct band gap.The refractive index obtained for the hexagonal phase in the and  directions are 1.45 and 1.27, respectively. The obtained refractive index for orthorhombic phase in and  directions are 1.48, 1.45 and 1.36, respectively. Also, the value of the optical gap for orthorhombic and hexagonal phases in and directions have been calculated. The obtained results are in good agreement with other available data.

Plastisol is a suspension of small poly(vinyl chloride) particles, plasticizer, stabilizer, pigment and filler and can be used as a coating for the underbody insulator of cars. In this study, the influence of additives and fillers on the rheological and mechanical properties of plastisol were evaluated by Taguchi experimental design method, taking into account that the type and amount of PVC resin and plasticizer remained unchanged. The type of calcium carbonate and the amounts of nano-silica, solvent and liquid additive were investigated as the factors at three levels and the L9 array was used in the Taguchi design of experiment. Low and high-speed viscosities, the Bingham viscosity and the yield strength of the samples, as well as their shear resistance (shear strength) were measured. Nano-calcium carbonate increases the yield strength, Bingham viscosity and improves the flow of plastisol. The influence of liquid additive is better than that of nano-silica powder in improving the properties of plastisol. The solvent decreases the Bingham viscosity while having little effect on the yield strength of the plastisol. Nano-silica and nano-calcium carbonate have a great effect on the shear strength of plastisol and increase the shear strength.

Plastisols are the liquid suspension compositions containing polyvinyl chloride resin (PVC), plasticizers and extenders, with various applications such as automobile coatings as seam sealers, which converts to the flexible material using heat. Rheological and mechanical properties of these compositions are related to the type of reinforcing materials. Reinforcing materials like nano silica has been used for improvement of different properties of these compositions. In this research, using Taguchi method and optimized model calculated from experimental design, effect of PVC type, particle size of calcium carbonate, type of plasticizer and silica particle size on mechanical and rheological properties like viscosity, strength, hardness and morphology were investigated. Particle size was evaluated using scanning electron microscopy and the results were analyzed. Based on variance analysis, it was found that for reaching to the optimum process conditions and highest strength of plastisol coatings, K-value for PVC resin must be about 70, mesh size of calcium carbonate about 1000, type of plasticizer was dibutyl phthalate (DBP) and nano silica particle size was about 200 nm.

In this study, aluminium composite foams reinforced by different volume fractions of SiC particles as reinforcement and stabilizing agent were fabricated with the direct foaming route of melt using different contents of CaCO3 as foaming agent. The density of produced foams were measured to be from 0.38 to 0.68 g/cm3. The microstructural features and compressive properties of the AA356/SiCp composite foams were investigated. The relation between plateau stress, density and, weight percentage of CaCO3 and SiCp volume fraction with a given particle size was also investigated. The results showed that compressive stress-strain curves of the products were not smooth and exhibit some serrations. Also, it was shown that in the same density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiC particles and decreasing weight percentage of CaCO3.

Two batches has been prepared involve calcium carbonate- zirconia and dolomite- zirconia with mole ratio 1:1. After mixing in water and drying, samples were preesed in cylinder form and then fired at four temperatures for three hours. The phase evaluation was studied by XRD technique. Calcium zirconate were established at all samples. At 1300 ˚c monoclinic zirconia phase was observed that its intensity is more in dolomite samples. With increasing temperature the intensity of ZrO2 phase is decreased and stabilized zirconia with calcia (Ca0.15Zr0.85O1.85 ) is observed.

Attempt to significant decreasing of permeability of polymeric material in versus liquid and gases for production of inert polymeric products in engineering applications have special situation in research. The purpose of this research is to study the permeability behavior of Acrylonitril-Butadiene copolymerre inforced by calcium carbonate nanoparticles in the temperature range 25–45°Cand using the solvent permeability tests to microstructure evaluation of the polymer nanocomposites. Results show the concentration of nano particle plays an important role in the diffusion, sorption and permeation coefficients and by increasing the amount ofnano-CaCO3up to optimum content (10-15%) decrease in the secoefficients (22% decrease in diffusion coefficient)is observed, whereas for higher concentrations, especially at higher temperature increasing trend were obtained for the secoefficients. By increase temperature, diffusion mechanism is more close to Ficki an mechanism. Increase of nano particle concentration in nanocomposite decrease ultimate swelling and diffusion rate of solvent and also activation energy (up to two fold).The micro structure and the dispersion of nano-CaCO3in the polymer matrix was evaluated using SEM micrographs and an appropriate relationship was established between the micro structure and the experimental results(permeability and mechanical properties).In general, swelling test and mechanical analysis an delectron micro scope images were presented similar behavior for prepared nanocomposites and can be recommended that swelling and permeability test scan be used as an inexpensive and simple method to characterization and evaluation of the properties of polymer nanocomposites.

In this article, the role of nano-size calcium carbonate in penetration resistance of medium- density polyethylene (PE) was investigated through experiments. In order to study the penetration resistance of PE and its nanocomposites,perforation test was carried out. The results of tests showed that penetration resistance depends strongly on calcium carbonate amount. As a matter of fact, addition of CaCO3 to PE increases resistance against penetration as CaCO3 amount reaches to 5 percent of weight. Stereomicroscope was used to evaluate the damage and plastic zone around the perforated area in all the samples including neat polyethylene and its nanocomposites. The plastic zone was measured using an image analysis as an effective technique. The results of image analysis techniques proved that the addition of calcium carbonate to PE makes a damaged zone around the perforated area. The results of microscopic evaluations showed that the area of plastic zone rises as the amount of calcium carbonate increases up to 7.5 percent of weight. By increasing the amount of CaCO3, resistance against penetration decreases more and some micro cracks appear around the perforated area. For further clarification of the fracture mechanism of MDPE nanocomposites, scanning electron microscopy was employed. Fracture surface images showed that when calcium carbonate is higher than 5 percent of weight, agglomeration of nanoparticles occurs, resulting in lower resistance against penetration to the samples.