Longer Calcination Research Articles

Effect of Calcination Time on the Microstructure and Optical Properties of (Zn<sub>0.5</sub>Cu<sub>0.5</sub>)Al<sub>2</sub>O<sub>4</sub> Spinel Color Pigments

The (Zn0.5Cu0.5)Al2O4 pigments were synthesized by solid state processing with an aim to examine the kinetics of phase formation. The calcining temperature was 1100 °C with firing times of 2, 12, 24, 48 and 96 hours during which intermediate grinding was carried out. All five obtained pigment samples appeared to be single-phase as probed by XRD. However, lattice refinement revealed differences in the lattice constant which kept decreasing and reached constancy after 24 hours of firing. Such reduction in the lattice constant was associated with incorporation of smaller copper cations into the Zn-sites. FTIR spectra also supported this result as the relevant peaks still got broadened and shifted for the calcination times of less than 48 hours. Elemental analysis of the 2-hour sample showed small presence of starting precursor particles, though not detected by XRD, suggesting an incomplete reactivity at a minute scale. These structural changes were resultantly reflected by small but significant alterations in the color parameters. A higher degree of solid solution for the samples fired for longer times, as judged by lowering in the lattice constant, resulted in detectable changes in both a and b parameters. Longer calcination times yielded a brighter (higher L values) brownish tone likely due to both diminution in the averaged particle size from pulverizing and completion of solid solution. The first would be useful for good dispersion in glazes whereas the latter could be directly related to the degree of cationic substitution, confirming the expected “true” color for this specific doping level at a particular calcination temperature.

Influence of calcination time and heating rate on the phase-chemical structure of Pd-doped SiO2 organic-inorganic membrane materials in air

ABSTRACTPd-doped SiO2 organic-inorganic hybrid materials were synthesized using sol-gel technique. The Pd-doped SiO2 samples were calcined at the temperature 350°C for several different time in air atmosphere with two different heating rates. Influence of calcination time and heating rate on the phase-chemical structure of Pd-doped SiO2 membrane materials was discussed by XRD, XPS, FTIR and TG-DTG analysis. The results indicate that the two factors have great influence on the crystal structure of Pd element and minor influence on the chemical structure. A longer calcination time and a slower heating rate can facilitate the oxidation of Pd0 to PdO, and should be conducive to the decomposition of Si-CH3 groups and the dehydration condensation of Si-OH groups. In order to prevent metallic Pd0 in Pd-doped SiO2 organic-inorganic membrane materials from being oxidized in air, the calcination time and heating rate should be chosen carefully.

Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

<p>The present investigation comprises of an attempt to investigate the titania supported chromia catalysts using X-ray diffraction measurements (XRD), evolved gas analysis (EGA), FT infrared spectroscopy (FTIR) and FT-Raman spectroscopic techniques with catalytic evaluation by dehydrogenation of cyclohexane. Evolved Gas Analysis shows a modified decomposition pattern than that of bulk chromia and presence of surface heterogeneity owing to the modified surface anchored chromia species formed as a result of interaction between chromia and titania. Above 773 K, Cr<sup>6+</sup> is not stable over TiO<sub>2</sub> surface and the reduction of the Cr<sup>6+</sup> to intermediate chemical states take place. XRD investigations illustrate the significance of X-ray source in examining supported chromia catalysts to study the morphological modifications of the active phase when crystalline supports are employed. FT Raman spectra reveals that on calcining the sample at 573 K, for 2 hours, the chromia phase assumes a monomerically anchored molecular state. Longer calcination time (6 hours) at the same temperature, leads to the diffusion of <em>in</em><em> </em><em>situ </em>formed Cr<sup>3+</sup> ions into the anatase lattice. On calcination at 973 K for 6 hours, amorphous chromia phase is no more stable on TiO<sub>2</sub> support resulting inagglomeration leading to the germination of microcrystalline α–Cr<sub>2</sub>O<sub>3</sub>. Evaluation of catalytic performance of above catalysts by dehydrogenation of cyclohexane confirms the fact that diffusion of part of Cr<sup>3+</sup> species into the bulk of anatase phase occurs under reaction conditions.</p>

CHARACTERIZATION OF CHEMICAL STRUCTURE FOR BASE ACTIVE METAL (NaOH) ON PALM OIL INDUSTRIAL WASTE

The development of solid catalyst has been investigated by considering the development of the chemical structure. In this study, solid catalyst was produced by using potassium hydroxide (NaOH) as an active metal on three types of support, Magnesium Oxide (MgO), Oil Palm Kernel Shell (OPKS) and Oil Palm Ash (OPA). Catalysts was study at different temperature (300 °C, 400 °C, 500 °C) and time (4 and 5hr) calcination via impregnation process. The catalysts were subjected to the characterization analysis using Chemisorption, Thermogravimetric analysis (TGA) and X-Ray Diffractometer (XRD). Chemisorption results showed weaker active site developed at higher calcination temperature while TGA results showed higher thermal stability at longer calcination time. In addition, the intensity of the XRD peaks also increased with increasing calcination temperature. The result showed that agricultural waste from oil palm industry could be tune as a potential support to produce active catalyst and can be applied in related chemical reaction.

Controlling the size of nanograins in TiO2 nanofibers

The feasibility of controlling the size of nanograins in TiO2 nanofibers by varying the duration of calcination is demonstrated in this study. This result opens up a new dimension in understanding the physical properties of nanomaterials and their applications. Similar to the sintering behavior commonly observed in bulk ceramics, the nanograins in nanofibers grow in size under a longer calcination time.

Early Viridian Pigment Composition CHARACTERIZATION OF A (HYDRATED) CHROMIUM OXIDE BORATE PIGMENT

Pigment analyses on more than 90 paintings dating from between 1885 and 1943 (A. Jawlensky, W. Kandinsky, F. Hodler and C. Amiet) have revealed that the majority of samples with chromium oxide hydrate green contain a spectroscopically conspicuous by-product. With the aim of tracking down the origin of this component, the so-called Guignet green, a variation of viridian produced by calcination, was systematically synthesized under varying conditions. The resulting products were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, energy dispersive spectrometry, electron microprobe microanalysis with wavelength dispersive spectrometry, X-ray diffraction, thermogravimetric analysis, secondary electron and backscattered electron imaging by scanning electron microscopy, polarized light microscopy and colorimetry. The composition of pigment products varies with the calcination conditions. Higher temperatures and/or longer calcination times lead to an insoluble borate matrix incorporating chromium oxide particles. The result is an amorphous chromium oxide borate Cr2O3·(xH2O)–Cr3BO6 polymorph with low water content. Interpreting chromium oxide hydrate green samples within this context, it turns out that calcination conditions in the past were highly variable, leaving behind considerable amounts of borates in the final product. Current data covering more than 60 paintings by Jawlensky suggest that the use of a specific production batch can be resolved in time. Identification of borates in chromium oxide hydrate green samples from paintings may thus provide information about the origin of the paint product used.

Physicochemical and Catalytic Properties of La1 – xCaxFeO3 – 0.5x Perovskites Prepared Using Mechanochemical Activation

The phase composition of La1 – xCaxFeO3 – 0.5x perovskites synthesized from preactivated oxides was studied by powder X-ray diffraction analysis and differential dissolution. The system does not form a continuous series of homogeneous solid solutions. No intermediate samples from this series are monophasic. It was found that the synthesis under nonequilibrium conditions (mechanical activation + calcination at 900°С for 4 h) resulted in nonequilibrium microheterogeneous solid solutions with degrees of calcium substitution for lanthanum of no higher than 0.5. A longer calcination (for 16 h) or an increase in the calcination temperature of solutions up to 1100 °С decreased the calcium content of the samples down to x ∼ 0.2 because of the formation of a brownmillerite phase. The catalytic activity of the test samples in the oxidation of CO changed nonmonotonically with x, and it was maximum at x = 0.5–0.6, which correlates with the maximum density of interphase boundaries in these samples.