Papers by Keyword: Dehydroxylation

Abstract: The effect of Metakaolinization on the thermal and physicochemical properties of Badau Belitung kaolin is presented. Calcination of Badau Belitung kaolin indicated that kaolin was transformed to metakaolin at temperature above 500°C. The metakaolin was characterized using X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR) and Brunauer-Emmett-Teller (BET). The XRD diffraction pattern of the metakaolin was highly amorphous as a result of calcination effect on the raw kaolin. The FTIR spectra of the metakaolin produced showed that the material was thermally stable at temperature range of 500–700°C, whereas the specific surface area values of the raw kaolin and the metakaolin formed were increased with increasing calcination temperature from 500°C to 700°C.

Abstract: The dehydroxylation of Zn free and 4 mol% Zn CaP powder was investigated using thermogravimetric analysis over the range of room temperature to 1200 °C. The kinetic result of dehydroxylation of Zn free and 4 mol% Zn CaP was calculated by means of the Ozawa–Flynn–Wall method. The XRD result indicated that the amount of Zn incorporated in HA lattice influences the phase stability of HA as it decreases with an increase in Zn concentration. According to calculated activation energy and conversion degree, the kinetics of HA dehydroxylation was identified, which included four successive conversion stages kinetically controlled by different rate-controlling processes. The dehydroxylation analysis of TG/DTG data show that Zn incorporation in HA lattice influences the phase stability of HA.

Abstract: In this paper, the process of the transformation from kaolin to metakaolin was investigated. The kaolin was calcined at different temperatures and analyzed by Xray diffraction (XRD), Fourier transform infrared spectra (FTIR) and solid state nuclear magnetic resonance (NMR). The formation of metakaolin structure was based on the stacking polyhedrons changes, which originated from dehydroxylation of kaolinite. With increasing temperature, kaolin kept structure of kaolinite unchanged in the course of dehydroxylation and then structure of kaolinite transformed to metakaolin when the dehydroxylation was over. It was demonstrated that the essence of pozzolanic activity of metakaolin. The result revealed that the pozzolanic activity of metakaolin increased with increasing temperature at the range of 600~900 °C.

Abstract: Flexural strength (MOR) and Young’s modulus (YM) of Sedlec kaolin were measured using the three point-bending method and modulated force thermomechanical analysis (mf-TMA). Thermal analyses DTA, thermogravimetry and thermodilatometry (TDA). An escape of the physically bound water (20 – 250 °C) strengthens the sample and YM and MOR increase their values significantly. MOR and YM lower their values as dehydroxylation starts at 400 °C. Both quantities, MOR and YM, pass through minimum in the dehydroxylation region (400 – 650 °C). Their next increase is probably caused by the van der Waals forces acting between metakaolinite crystals and by the starting of the solid-state sintering. YM steeply increases above 950 °C as a consequence of the solid-state sintering. A Weibull’s modulus passes through the sharp maximum at the interval 300 – 400 °C.

Abstract: Stability of hydroxyapatite(HA) structure is influenced by preparation conditions and afterwards heat treatment. In this paper, the powders with different Ca/P molar ratio were calcined to investigate the influence of Ca/P and heat treatment on thermal decomposition and reconstitution of HA. The results show that the Ca/P has little change even calcined at a high temperature of 1500°C. The Ca/P molar ratio close to 1.67 is beneficial to form high purity HA. HA gradually releases its OH- ions in the temperature range of 800-1200°C. The decomposition takes place at about 1200°C and will become more and more severe with the increase of temperature. Cooling with slow rate and post-heat treatment in wet atmosphere are beneficial to both the rehydration and the recovery of HA from the decomposition products (TTCP and α-TCP).