Papers by Keyword: Calcite

Abstract: Calcium carbonate (CaCO₃) has been known as one of the components of carbonate apatite (CO₃Ap) cement. Calcite is one of the polymorph of CaCO₃ with big particle size and excellent stability. In contrast, vaterite has small particle size and a metastable phase. To discover the effect of particle size on the properties of CO₃Ap cement, this study investigated the different particle size of vaterite; calcite from vaterite, which has almost similar particle size and shape with vaterite; grounded calcite and ungrounded calcite. The powder phase of calcite or vaterite combined with dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of Na₂HPO₄ solution in 0.45 liquid to powder ratio. The paste was packed into a split stainless steel mold, covered with glass slide and kept at 37°C and 100% relative humidity for a period of time. XRD and FT-IR analysis revealed that CO₃Ap cement consisted of vaterite and DCPA transformed to pure B-type CO₃Ap in 72 hours while CO₃Ap cement that consisted of calcite with different particle size was not completely transformed to CO₃Ap even until 240 hours. We concluded that CO₃Ap cement consisted of vaterite with small particle size and metastable phase properties is more effective as starting material due to its fast transformation to CO₃Ap.

Abstract: In this study the structural and chemical properties of barnacle shell based bioceramic materials (i.e. hydroxyapatite, whitlockite, monetite and other phases) were produced by using mechano-chemical (hot-plate) conversion method. Cleaned barnacle shells were ball milled down to <75µm in diameter. Differential thermal and gravimetric analyses (DTA/TGA) were performed to determine the exact CaCO₃ content. Sample batches of 2g were prepared from the fine powders produced. For each batch, the required volume of an aqueous H₃PO₄ solution was calculated in order to set the stoichiometric molar ratio of Ca/P equal to 1.5 for ß-tricalcium phosphate (ß-TCP) or to 1.667 for hydroxyapatite (HA). The temperature was set to 80°C for 15 minutes to complete the process. After the titration of the equivalent amount of H₃PO₄ into the prepared solution, agitation was carried out on a hot-plate (i.e. mechano-chemical processing) for 8 hours. The sediments formed were dried and the resulting TCP and HA powders were calcined at 400°C and 800°C respectively. For complete characterization of the bioceramics produced, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) analyses were carried out. The current study proposes a simple, economic and time efficient method for nano-bioceramic production.

Abstract: The scale-inhibition effect of electromagnetic field was tested on circulating cooling water of power plant, and then the scale sample was analyzed by SEM and XRD. The results showed that, under optimum scale-inhibition conditions, aragonite content increased and calcite content decreased, and scale-inhibition rate was up to 78.2%; under the poorest conditions, both aragonite and calcite crystals existed, and the scale-inhibition rate was-201.0%; after treating with electromagnetic field, size of both calcite and aragonite particles decreased, making them more easily flown away and thus showing better overall scale-inhibition effect; when energy provided by the electromagnetic field was more than the decrease in free energy of the system, extra energy turns the calcite CaCO₃ into other forms of metastable crystalline phases, then content of different crystalline phases is changed in favor of scale inhibition.

Abstract: The largest gold district in China is the Jiaodong Peninsula. This study is based on chemical composition characteristics of calcite from gold deposits in Jiaodong. In this paper, a new formula was proposed to character the chemical composition characteristics of calcite in gold and silver deposits. The results showed that the chemical composition characteristics of calcite between gold and silver deposits were of great difference. And each data focused in each area. The spots of gold deposits located in the area of riched CO₂ areas. But the spots of silver deposits located in the area of riched CaO areas. The reason of these differences was mainly resulted from each different ore-forming condition.

Abstract: According to the characteristics that purple red of nixing pottery contains an amount of calcite; different samples were fired with different content of calcite in the mud and varying temperature under oxidizing conditions. The phase composition and microstructure were analyzed. The results show that number and size of pores in the sintered samples increased and pore morphology changed from irregular closed hole to round closed then converted to irregular inter-connected one along with the increase of calcite content. As calcite content in the mud increases the viscosity of liquid phase decreases while the crystalline phase gradually increased as sintering, thus wollastonite phase transformed into eutectic phase of aluminum scapolite and wollastonite, and quartz content gradually reduced. Higher sintering temperatures and content of calcite were helpful to the reduction in viscosity, as calcite content increased gradually, the amount of liquid phase increased at first then decreased.

Abstract: The effects of hygienization and moisture content on pyrolysis of sewage sludge obtained from wastewater treatment plants were examined in this study. The sewage sludge samples with CaO, without CaO, dry and wet (70 wt.% moisture) were used. The pyrolysis experiments were conducted in two reactor setups at 750 °C and 850 °C. The effect of pyrolysis temperature, heating rate on the gaseous pyrolysis products as well as thermal behavior of sewage sludge were investigated. The CaO addition increased the total yield of pyrolysis gaseous products, whereas moisture significantly increased CO₂ production as well as CO and CH₄.

Abstract: Based on analyzing of chemical composition, mineral composition and thermal stability of red mud, preparation of ceramisite, using anthracite added as foaming agent, was investigated. Internal structure was observed by scanning electron microscopy (SEM). The results showed the bulk density of ceramisite was obviously reduced by anthracite added. The ceramisite with bulk density of 1.30g/cm³, water absorption rate£ ̈WAR£©of 2.98% and cylinder compressive strength £ ̈CCS£©of 9.48 MPa was obtained when weight ratio of red mud/waste glass/bentonites/anthracite was at 73:15:11:1. Majority of porosity in ceramisite was closed based on SEM. The porosity of ceramisite was much higher when anthracite was added as foaming agent than only calcite in red mud was used as foaming agent. The bulk density of the former was lower than that of the latter.

Abstract: We use quantum-mechanical calculations to study single-crystalline elastic properties of (Ca,Mg)CO₃ crystals with concentrations ranging from calcite CaCO₃ to magnesite MgCO₃. By analyzing results for a dense set of distributions of Ca and Mg atoms within 30-atom supercells, our theoretical study shows that those atomic configurations, that minimize the total energy for a given concentration, are characterized by elastic constants that either increase with the Mg content or remain nearly constants. Employing these ab initio calculated single-crystalline elastic parameters, the polycrystalline elastic properties of (Ca,Mg)CO₃ aggregates are determined using a mean-field self-consistent homogenization method. The computed integral elastic moduli (bulk and shear) show a significant stiffening impact of Mg atoms on calcite crystals. Our analysis also demonstrates that it is not advantageous to use a granular two-phase composite of stoichiometric calcite and magnesite instead of substituting individual Ca and Mg atoms. Such two-phase aggregates are not significantly thermodynamically favorable and do not offer any strong additional stiffening effect.

Abstract: In the present work, high density polyethylene based composites filled with glass spheres, talc and calcite particles were prepared. Fillers contents in the HDPE were 5, 10, 15, and 20 wt%. The mechanical, morphological and tribological properties of the polymer composites were investigated. Substantial improvements in the some mechanical properties were obtained by the addition of filler. For example, the results showed that the elasticity modulus of composites improved with increasing the filler content. The addition of fillers to the HDPE changed significantly the friction coefficient and wear rate of the composites. HDPE filled with a high level content of fillers showed higher wear rate than pure HDPE under dry sliding. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM).

Abstract: Pulp pH value plays a significant role in the froth flotation. Especially in the flotation of fluorite, the performance of flotation will be affected greatly by pulp pH. MO, a new kind of modified fatty acid was used as collector, and H2SO4 and Na2CO3 were used to regulate pulp pH in the experiment. The mechanism of influence of pulp pH on flotation of fluorite and calcite was investigated by such parameters as fluorite recovery, zeta potentials and the infrared spectroscopy about minerals at different pulp pH values. As is shown in the results, the point of zero charge(PZC) of fluorite is pH=9.5 and the PZC of calcite is pH=8.5. The optimum pulp pH of the flotation of fluorite and calcite is determined as 9.5~10 and 8~9 respectively. pH value should be controlled above 9 to depress calcite. Finally, 9.5~10 was determined as the optimum pH to float the fluorite from the calcium-containing fluorite ores.