Preparation of ZrB2-MoSi2 high oxygen resistant coating using nonequilibrium state powders by self-propagating high-temperature synthesis

To achieve high oxygen blocking structure of the ZrB2-MoSi2 coating applied on carbon structural material, ZrB2-MoSi2 coating was prepared by spark plasma sintering (SPS) method utilizing ZrB2-MoSi2 composite powders synthesized by self-propagating high-temperature synthesis (SHS) technique as raw materials. The oxygen blocking mechanism of the ZrB2-MoSi2 coatings at 1973 K was investigated. Compared with commercial powders, the coatings prepared by SHS powders exhibited superior density and inferior oxidation activity, which significantly heightened the structural oxygen blocking ability of the coatings in the active oxidation stage, thus characterizing higher oxidation protection efficiency. The rise of MoSi2 content facilitated the dispersion of transition metal oxide nanocrystals (5–20 nm) in the SiO2 glass layer and conduced to the increasing viscosity, thus strengthening the inerting impact of the compound glass layer in the inert oxidation stage. Nevertheless, the ZrB2-40 vol%MoSi2 coating sample prepared by SHS powders presented the lowest oxygen permeability of 0.3% and carbon loss rate of 0.29×10−6 g·cm−2·s−1. Owing to the gradient oxygen partial pressure inside the coatings, the Si-depleted layer was developed under the compound glass layer, which brought about acute oxygen erosion.

Development of Scientific Fundamentals for the Conversion of a Virtual Binary Lead Selenide Ferroelectric into a Real Ferroelectric of Lead Selenite for Physico-Chemical Sensors

The scientific basis for the production of a new composite material (1-x)PbSexPbSeO3, where x=0-1, by oxidation with oxygen at temperatures of 500-550 °C and oxidation times of 0.5-4 h from the initial phase of PbSe in the form of powder, film or compact material, having a ferroelectric phase transition in disordered crystals is developed. On the X-ray spectra of the original PbSe samples oxidized at 500°C (oxidation time of 0.5 h) it has been found that the PbSe phase reflexes are predominately present, including the X-ray spectra of the original PbSe samples oxidized at 500 °C (oxidation time of 4 h) - PbSeO3 monoclinic phase reflexes. For all other PbSe oxygen-oxidized samples at temperatures of 500-550 °C and within the time range of 0.5-4 h, X-ray spectra show the simultaneous presence of X-ray reflexes of both phases with the trend of increasing the PbSeO3 phase as the oxidation time increases. Temperature measurements of the DC resistance of the PbSe samples revealed an abnormal change in electrical resistance at the initial oxidation stage for both the film and the compact material, and further oxidation contributed to the capsulation of PbSe grains by the dielectric casing PbSeO3 and the gradual increase in the resistance of the material.

The xanthine oxidase and its associated activities of the ovine milk and liver: distinctive in impact of in vivo molybdenum

Xanthine oxidase is molybdenum and iron-containing flavoprotein, catalyzing the final oxidation stage of purines and oxidative transformation of pterins and some aliphatic and aromatic aldehydes. Despite the importance of this enzyme, the distribution of xanthine oxidase in traditional household animal’s milk and tissues is unknown. Formerly, we have found most of the xanthine oxidase molecules in animal milk are inactive because of a lack of molybdenum. Ovine milk was processed by inserting in vivo molybdenum (tungsten) into drinking water. We gave opposite dates in the presence of tungsten too. Heating the milk of animals at 80 °C for 5 minutes in the presence of molybdenum and cysteine led to a sharp increase of xanthine oxidase and its associated – nitrate reductase and nitrite reductase activities. The change of xanthine oxidase and its associated activities were examined by spectrophotometry after treatment. It was established that metal ions added in drinking water for animals have an impact on enzyme activities. The activity is formed in the ovine liver even in the absence of exogenous molybdenum in drinking water. The associated activities of liver enzymes in the presence of molybdenum in drinking water had slightly increased. Tungsten-containing water led to the loss of all activities of liver xanthine oxidase. It is proposed that the liver contains a special protein involving in the incorporation of molybdenum (or tungsten) into xanthine oxidase molecule, however, the milk or mammary gland compounds lack this protein.

Effect of Al2O3 and SiO2 Inert-Fillers on the Microstructural Evolution and High Temperature Oxidation Resistance of B Modified Silicides Coatings Prepared by Pack Cementation Technology

In this study, B modified silicide coatings were prepared on Nb-Si based alloy with Al2O3 or SiO2 inert-filler by pack cementation technology. Both coatings primarily consisted of a (Nb,X)Si2 with a (Nb,X)B2 + (Nb,X)Si2 outer layer. After oxidation at 1250 °C for 100 h, the coatings showed good oxidation resistance due to the formation of a dense silica. The oxidation products of the coating prepared with Al2O3 inert-filler consisted of SiO2, TiO2 and Cr2O3, while that of the coating prepared with SiO2 inert-filler consisted of SiO2, TiO2, Cr2O3, and HfO2. The different oxidation products may be due to the different oxidation process of these two sample at initial oxidation stage.

PENGARUH UMUR DAUN TEH DAN WAKTU OKSIDASI ENZIMATIS TERHADAP KANDUNGAN TOTAL FLAVONOID PADA TEH HITAM (Camellia sinesis)

Flavonoid compound is an important compound of tea products. However, the flavonoid level content in black tea is lowest than other teas. This is due to the processing of black tea which has an enzymatic oxidation stage and the tea age leaves when picking. Young tea leaves contain higher total flavonoids than old tea leaves. With an average level of total flavonoids, the young tea leaves is 27.76% qe w / w, while for the old tea leaves 18.61% qe w / w. However, the enzymatic oxidation time treatment did not affect the total flavonoids because the process only affected the quality of black tea steeping, on it’s colour, aroma, and taste. Keywords: age of tea leaves, black tea, enzymatic oxidation, total flavonoids

The Role of the Oxidation and Reduction Parameters on the Properties of the Reduced Graphene Oxide

One of the methods of obtaining reduced graphene oxide (rGO) involves the oxidation of graphite to graphene oxide, which is then exfoliated and reduced. Each of these stages has a decisive influence on the properties of the produced nanoadditive, which determines its subsequent application. The process conditions which are examined during the oxidation stage are related to: The mixing time of the reactants before oxidation, sonication of the reaction mixture, and its composition. During reduction optimization, in turn, the form of the GO sample and the method of its purification, as well as the temperature at which this process took place, are examined. At each stage, the determined structural parameters of the produced materials (GO and rGO) are related to their morphology (SEM—scanning electron microscope), oxidation state (FTIR—Fourier transform infrared spectroscopy, EDS—energy-dispersive spectrometer), structure defect (Raman spectroscopy), as well as the number of layers and crystalline structure (WAXS—wide-angle X-ray scattering). The obtained results show that the shorter mixing time of the reactants determines the formation of more oxygen functional groups. On the basis of the obtained results, the process conditions that enable the production of multilayer, well-exfoliated reduced graphene oxide, with only a slightly defected structure, are established.

Reaction model and thermodynamic properties between sulfur-containing active groups and oxygen during coal self-heating

To further study the mechanism of coal self-heating, the reaction sequences and thermodynamic properties between sulfur-containing groups and oxygen during coal self-heating were analyzed. The benzyl mercaptan and diphenyl sulfide were selected as typical sulfur-containing structures existing in coal. Their structural parameters, frontier orbital characteristics, and thermodynamic parameters were analyzed through quantum chemistry calculation and their detailed reaction sequences with oxygen were proposed. The results indicate that the thiol structure in coal can easily react with oxygen at low temperatures and release large amounts of heat (146.70 kJ/mol) during coal self-heating, providing active free radicals and energy for subsequent chain reactions of coal spontaneous combustion. The oxidation reaction between the thioether structure and oxygen cannot occur at room temperature. With the accumulation of heat, thioether gradually becomes active and reacts with oxygen to form sulfoxide and release an enormous amount of heat (248.09 kJ/mol), which can be further oxidized to sulfone with an increase in temperature. The reaction models of thiol and thioether groups during coal self-heating were proposed, which involves eight main reaction sequences (R1∼R8). It indicates that the reactions of thiol and thioether groups play crucial roles during the evolution of coal self-heating, with a slow oxidation stage at low temperatures and an accelerated oxidation stage at high temperatures.

Coal/biomass co-combustion investigation by thermogravimetric analysis

In this study, the thermal characteristics and kinetic parameters of coal/biomass blended fuels (75:25, 50:50 and 25:75 wt.%/wt.%) were investigated by using the thermogravimetric technique under atmospheric air. Three types of agricultural waste biomass including cassava root, palm kernel shell and rice husk were used as raw materials. The experiments were performed under different temperatures, ranging from 313-973 K with the heating rate of 5, 10, 20 and 40 K/min. The results show that the thermal decomposition of biomass exhibit three-four stages including moisture and some light volatile removal stage (up to 463 K), volatile oxidation stage (423-663 K), char combustion stage (663-823 K) and inorganic oxidation stage (803-953 K). Lignite on the other hand exhibits only two main peaks during the entire combustion process, corresponding to the moisture removal (up to 433 K) and the decomposition/oxidation (433-833 K), respectively. In addition, it was also found that the blending of biomass residues improved the ignition temperature of the blended fuels, indicating an improvement of devolatilization of coal. Kinetic studies show that the average apparent activation energies of the co-combustion of coal/cassava root, coal/palm kernel shell and coal/rice husk calculated from the Kissinger-Akahira-Sunose method are reported at ca. 105.25, 179.66 and 121.84 kJ/mol, respectively.