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Carbon nanostructured materials, including nanosheets, are being produced from a variety of natural waste materials. The process involves activation and carbonization. Potassium hydroxide (KOH) is a well-known chemical agent used to generate pore structure and to prepare the micro/nanostructure of carbon. This study compares the effect of the state of KOH (solid or solute) on carbon formation in peanut shells. Carbon nanosheets were formed from peanut shell by activation with KOH and heat treatment. The surface microstructure and individual carbon nanosheets of peanut shell were found to be more distinct after treatment with solute KOH compared to treatment with solid KOH. This suggests that solute KOH treatment is a simple, cheap, and effective method for producing carbon nanosheets from peanut shells.

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Abstract  

Pt/SDBC catalysts, which are used for the hydrogen-water isotopic exchange reaction, were prepared. TGA experiments showed that the treatment temperature of Pt/SDBC catalysts in inert gas is limited to 400 °C and the maximum allowable heat treatment temperature in oxygen is 200 °C. From nitrogen adsorption and hydrogen chemisorption measurements, it was shown that the dispersion of platinum particles depended on the physical properties, i.e., specific surface area and pore structure of SDBC. It was found that the heat treatment could not impact the structure of SDBC and the oxygen treatment at 150 °C improved the platinum dispersion. It was shown by XPS analysis that the oxygen treatment of impregnated Pt/SDBC increased the fraction of platinum metal state and platinum dispersion. As the supported platinum area increases, the catalytic activity of Pt/SDBC for the hydrogen-water vapor isotopic exchange reaction increases. It indicates that the hydrogen chemisorption measurement can be used to estimate the catalytic activities of Pt/SDBC catalysts. It was not observed that the particle size of supported platinum affected the specific reaction rate at 60 °C. It implies that this reaction is structure insensitive.

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A kinetic model for the reaction sintering of oxide ceramics in the system Al2O3–SiO2–ZrO2 using mixtures of intermetallic compounds is presented. A 2D finite-difference model is developed to describe the exothermic gas-solid reactions taking place during the firing of ZrAl3/ZrSi2 powder compacts. The model accounts for the oxidation kinetics of the powder particles, as well as the consumption and diffusion of gaseous oxygen through the porous matrix. Additionally, possible changes in the pore structure of the green body due to the oxidation reactions and sintering effects are incorporated in the model. The resulting differential equations are coupled with a two-dimensional Fourier heat balance equation leading to a system of nonlinear partial differential equations, which is solved by the numerical method of lines. The influence of different processing parameters like sample composition and heating cycle on the reaction sintering process is investigated and the model-predicted reaction behaviour is compared to experimental results.

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Thermal conductivity, specific heat capacity, thermal diffusivity and linear thermal expansion coefficient of two types of carbon fiber reinforced cement composites are measured in the temperature range up to 800�C. Thermal conductivity and thermal diffusivity are also determined for the specimens exposed to thermal load up to 800�C before the measurement. Differential thermal analysis (DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) are utilized for the assessment of thermal decomposition processes taking place in the high temperature range under consideration. The high temperature thermal properties of the studied materials are found to be positively affected by the application of the high alumina cement and in the case of the Portland cement based composite also by using the autoclaving procedure in the production process. Also, the randomly distributed carbon fibers that can reduce the damage of the pore structure by the thermal decomposition processes are identified as a positive factor in this respect. A comparison of thermal conductivity vs. temperature curves obtained for the specimens pre-heated to different temperatures is found to be a useful tool in the identification of major dynamic effects in the specimens due to the thermal decomposition reactions. The results are in a good agreement with the DTA, MIP, SEM and XRD analyses. The character of the thermal conductivity measurements that in fact includes the effects of convection and radiation into the thermal conductivity coefficient can be beneficial for a simple assessment of the influence of the fire on a dividing structure.

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Rice husk ash fired at different temperatures, 450, 700 and 1000°C, was mixed with different concentrations of lime (molar lime/silica ash ratio of 0.2, 0.5 and 1.0). Each dry mixture was first ground and hydrated in the suspension form (water/solid ratio = 10) for various time intervals within the range of 1 to 365 days. The surface properties of the unhydrated and hydrated samples were studied by means of nitrogen adsorption measurements. The results indicated that the surface areas and total pore volumes of unhydrated solid mixtures and hydrated lime-rice husk ash samples, prepared with lime/silica ash ratio of 1.0, decrease with increasing firing temperature of rice husk ash. The effect of varying the lime/silica ash ratio of the solid mixture on the surface area and pore structure was fully discussed. The results of surface area and pore volume measurements could also be related to the crystal structure of silica produced from rice husk ash.

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The thermochemical decomposition of agricultural by-product corn cob impregnated with ZnCl2, as a precursor material for producing the activated carbons, was investigated by thermogravimetric (TG) analysis at the heating rate of 5 and 10°C min–1 under a controlled atmosphere of nitrogen (60 ml min–1). The appearance of a peak in the differential thermogravimetric plot (DTG) in the temperature range of 400–600°C is significantly related to the extent of impregnation. The DTG curve of the sample impregnated with the optimal impregnation ratio of 175% (i.e., the ratio of ZnCl2 mass of 87.5 g in the 200 cm3 of water to corn cobmass of 50 g), which yields an optimal BET surface area of the activated carbon and displays a DTG peak at about 500°C. This may be partially due to the intense chemical activation and results in the formation of a porous structure in the activated solid residue. This observation is also in close agreement with previous results at optimal pyrolysis temperatures of 500°C and with similar experimental conditions. In order to support the results in the TG-DTG analysis, the development of pore structure of the resulting activated carbons thus obtained by previous studies was also examined and explained using the scanning electron microscopy (SEM).

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Simultaneous DSC-TG and DTA-TG were used to investigate the calatytic effect of the metal on the thermal decomposition of a cellulose matrix containing small copper particles. The techniques were also used to demonstrate the effect of the metal particles on the subsequent activation of the carbon matrix, a process which develops the pore structure necessary to expose the metal particles to the gas phase. Temperature programmed desorption was used to study the initial mass loss found on activation. To quantify the catalytic effect of the copper particles on the activation process an estimate was made of the activation energy of the catalysed and uncatalysed reactions. The work gives valuable information on the processes involved in the preparation of a new range of metal-carbon catalysts.

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Properties of limestone related to SO2/SO3 reactivity were investigated. Limestone calcined under different conditions (temperature, time and with/without additives) yield calcines of distinctly different physical structures. The amount of pores and the size of the pores formed during calcination is important. The main purpose of the present work was to gain a better understanding and more reliable explanation of the temperature regime for gas desulphurization using Ca-based sorbents in atmospheric fluidized-bed combustors. Pore size, surface area and pore volume of each calcine were determined by mercury porosimetry and BET methods. At higher calcination temperature and during longer time, sintering became significant and the obtained calcine had a smaller internal surface area and thereby the average pore radius increased. The additives such as NaCl also accelerated sintering thus increasing the pore size. The measurements of porosity were supplemented by scanning electron microscopic observations employed for qualitative description of the pore structure. SEM micrographs are presented.

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the enhancement of strength are limited to 14 days. Khatib and Wild [ 30 ] determined the pore structure and the intruded pore volume by conducting mercury intrusion porosimetry. Metakaolin in cement paste further refines the pore structure; the

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. C.D.L. Cuevas 1997 Pore structure characterization in rock salt Engineering Geology 47 17 30

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