Modification of the thermal dehydroxylation of antigorite by ultrasound treatment

Summary The differences on the thermal behaviour (DTG-DTA) of antigorite sample measured before and after sonication have been studied. Sonication treatment produces negligible changes in the structure of the material but substantial textural modifications. These modifications produce changes in the thermal behaviour of antigorite sample. Thus, it has been observed a decrease in the dehydroxylation temperature as measured by DTG and DTA effects. For sonication treatments longer than 20 h, two new effects of dehydroxylation are observed, the intensity of these two new effects increases with the sonication time showing a modification in the release of structural OH. It has been also observed that the formation of forsterite takes place simultaneously with the dehydroxylation of the antigorite. The high temperature exothermic effect is due to the recrystallization of forsterite and not to the formation of forsterite as traditionally assumed. Modifications in the thermal dehydroxylation of antigorite observed in this study are related to the pronounced decrease in particle size obtained by sonication.     

A comparative study of the dehydroxylation process in untreated and hydrazine-deintercalated dickite

A dickite from Tarifa (Spain) was used to study the influence of the intercalation and the later deintercalation of hydrazine on the dehydroxylation process. The dehydroxylation of the untreated dickite occurs through three overlapping endothermic stages whose DTA peaks are centred at 586, 657 and 676°C. These endothermic effects correspond, respectively, to the loss of the inner-surface, the inner hydroxyl groups, and the loss of the water molecules, product of dehydroxylation process, which has been trapped in the framework of the dehydroxylated dickite. The intercalation of hydrazine in the interlayer space of dickite and the later deintercalation affect the dehydroxylation process. It occurs through only two endothermic stages which DTA peaks are centred at 575 and 650°C. The first corresponds to the simultaneous loss of both the inner and the inner-surface hydroxyl groups, whereas the second one is analogous to that at 676°C observed in the DTA curve of untreated dickite. These effects appear shifted to lower temperatures compared to those observed in the untreated dickite.     

Application of thermal analysis to study smelting reduction kinetics

A thermal analysis study on the reduction of iron oxide rich slags under different conditions is presented in this paper. The effects of important process variables such as time, temperature, lime-silica ratio, FeO level in slag etc. are discussed. It is shown that the mechanism of reduction by externally added graphite is different from that by a carbon saturated bath although the activation energy values are similar.     

Study of the structure and thermal behaviour of intercalated kaolinites

Intercalation complexes of three different Hungarian kaolinites with hydrazine and potassium acetate were investigated by FT-IR (DRIFT) spectrometry, X-ray diffraction, and thermogravimetry combined with mass spectrometry. Differences were found in the thermal behaviour of the complexes as well as in the rehydration — reexpansion patterns of the heated intercalates. An XRD method is proposed for the distinction of kaolinite and 7.2 Å halloysite present in the same mineral.The authors wish to thank Dr. E. Máttyás for providing the kaolinite samples and for carrying out their chemical analysis. Financial support from the Hungarian Scientific Research Fund under grant No. OTKA-014179 is gratefully acknowledged.     

Kinetic characterization of the reduction of silica supported cobalt catalysts

Abstact  The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

Studies on the kinetics of synthesis of TiC by calciothermic reduction of TiO<Subscript>2</Subscript> in presence of carbon

Reaction kinetics of the formation of TiC by calciothermic reduction of TiO₂ in presence of carbon have been investigated using thermal analysis (TG-DTA) of a powder mixture of TiO₂, Ca, and C in argon atmosphere at different heating rates. Both the reaction initiation and the peak temperatures are found to increase with heating rates. The appearance of exothermic peaks in the DTA plots after Ca melting indicates the reduction of TiO₂ by liquid calcium and formation of TiC by in-situ reaction of Ti with C. The apparent activation energy of the process has been found to be 170.8±0.5 kJ mol^–1.     

Influence of the molecular mass on the segmental relaxation times of polystyrene determined by DSC

Journal of Thermal Analysis and Calorimetry - The segmental dynamics of narrow fractions (áMwñ/áMnñ ≈1.05) of polystyrene with molecular masses ranging from 4000 to 600000...     

High-temperature Study of Phase Equilibria in the Systems CsCl-LnCl3 (Ln=Ce,Nd) by Knudsen Effusion Mass Spectrometry

Pulse thermal analysis (PTA) is based on the injection of a specific amount of gaseous reactant into a carrier gas stream. PTA provides the following advantages compared to conventional TA: (i) quantitative calibration of the mass spectrometric signals allows increasing the sensitivity of TA measurements; (ii) monitoring of gas-solid processes with defined extent of reaction i.e. the reaction can be stopped at any point between pulses, enabling elucidation of the relationship between the composition of the solid and the reaction progress; (iii) simultaneous monitoring of changes in mass, thermal effects, composition and amount of gaseous reactants and products under pulse conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of heat treatment on electromagnetic properties of polyimide/carbon black composites

A kind of absorbing materials was prepared by hot pressing method using polyimide as matrix and carbon black (CB) as filler. The mechanical properties, the electromagnetic properties, and the thermal stability of polyimide/CB composites were studied. The results showed that the complex permittivity increased from 6.82 + 1.38i to 18.69 + 9.47i, whereas the flexural strength decreased from 108 MPa to 77 MPa, respectively, when the CB content increased from 2 wt% to 8 wt%. The reflection loss curves shifted to low frequency with increase of the thickness at the same content. The reflection loss below ?10 dB could be obtained in the X band with 6 wt% CB content and did not display significant difference before and after the heat treatment at 400°C for 5 h. When the content of CB was 8 wt%, the decomposition temperature (at 5% weight loss) increased approximately 42°C compared with pure polyimide matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

先锋褐煤的热处理和水热处理改质

通过先锋褐煤热处理和水热处理,结合处理煤结构与性质表征,研究了热处理和水热处理对先锋褐煤结构、抽提和溶胀性能的影响,探讨了热处理过程水的作用。结果表明,低于热解温度下的热处理以非共价键解缔合及部分弱共价键热解为主,水与煤的水热反应能够抑制水热处理过程中煤的热解和小分子化合物释放。高温热处理以热解和脱氧为主,水热反应可以稳定煤热解活性基团,避免其二次裂解和交联,在一定程度上提高处理煤的混合溶剂抽提率,改善其溶胀性能。     

A convenient electrolytic process for the reduction of aldehydes

We report an efficient electrolytic procedure for the reduction of aldehydes to primary alcohols in the absence of dimeric products. In this promising approach, based on environmentally friendly chemical synthetic methods, a simple electrolytic undivided cell was designed. Two copper plates served as electrodes and recycled water as the medium. A 6-V battery provided the required energy. Although initially the method was intended for the preparation of 2-aryl-3-hydroxymethyl imidazo[1,2-a]azines, it was successfully extended to reduce other aliphatic and aromatic aldehydes. The attractiveness of this procedure includes its operational simplicity, practical viability, inexpensiveness and good yields. In most cases the results were better than those obtained with the standard reduction procedure using sodium borohydride.     

Thermoanalytical Investigations on Intercalated Kaolinites

The thermal behaviour of ordered kaolinites from Hungary and Australia intercalated with potassium acetate, cesium acetate and urea has been investigated by simultaneous TG-DTG-DTA, TG-MS, Raman microscopy and XRD. Remarkable changes in the thermal decomposition pattern of the intercalates were obtained as a function of the nature of the intercalating re-agents. Replacing the potassium cation to cesium leads to a change in the OH environments resulting in a more complicated dehydroxylation pattern. The urea intercalates can be decomposed completely without dehydroxylating the mineral, although further treatments are necessary to restore the original d-spacing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of chromium modification on the properties of MnOx-FeOx catalysts for the low-temperature selective catalytic reduction of NO by NH3

Catalytic properties of MnO_x-FeO_x complex oxide (hereafter denoted as Mn-Fe) catalysts modified with different loadings of chromium oxide were investigated by using the combination of physico-chemical techniques, such as N₂ physisorption, X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), in situ Fourier transform infrared spectroscopy (in situ FT-IR) and temperature-programmed reduction (TPR) and their catalytic activities were evaluated with the selective catalytic reduction (SCR) of NO_x by NH₃. It was found that with the addition of Cr, more NO could be removed in the low-temperature window (below 120 °C). Among the tested catalysts, Mn-Fe-Cr (2 : 2 : 1) catalyst exhibited the best catalytic performance at 80 °C with the NO conversion higher than 90%. The combination of the reaction and characterization results indicated that (1) the strong interaction among tertiary metal oxides existed in the catalysts when Cr was appropriately added, which made the active components better dispersed with less agglomeration and sintering and the largest BET specific surface area could be obtained; (2) Cr improved the low-temperature reducibility of the catalyst and promoted the formation of the active intermediate (–NH⁺₃), which favored the low-temperature SCR reaction.     

Characterization of the Influence of Thermal Sterilization on the Volatiles in Flat Peach Juice

This study characterized the effect of thermal sterilization on the volatiles in flat peach juice. In three independent trials, juice samples prepared with flat peaches from Shihezi, Xinjiang, China were divided into groups sterilized at 65, 75, and 85°C for 30?min. The chemical compositions were identified by gas chromatography–mass spectrometry combined with headspace solid-phase microextraction and analyzed by hierarchical clustering and principal component analysis. Fourteen volatiles (seven esters, four alcohols, two aldehydes, and one ketone) were identified as characteristic in fresh peach juice. Esters of thermally treated samples were significantly decreased by threefold (P?相似文献   

Influence of moisture on transient oxidation and reduction of alumina-supported platinum

The transient surface behavior on oxidation and reduction of a partially oxidized alumina-supported platinum catalyst containing residual water have been observed by AC electrical conductance (G) measurements.     

Investigations on the selectivity of catalytic no reduction by ammonia

The activity and selectivity of V₂O₅/γ-Al₂O₃ catalyst were studied in the catalytic reduction of nitrogen oxide by ammonia. The activity of the catalyst monotonically increases as a function of temperature, however, its selectivity decreases. The DeNOx reaction of nitrogen oxides with ammonia can be described well by a mathematical model, which considers selectivity-decreasing side reactions as well in a wide temperature range (220–420°C).     

Influence of selenium on the catalytic properties of ruthenium-based cluster catalysts for oxygen reduction

The favourable influence of selenium on the catalytic properties of Ru-based catalysts for the oxygen reduction reaction in acid electrolytes has been investigated by rotating disk electrode measurements. Compared to the oxygen reduction of selenium-free Ru-based catalysts, the overpotential at low current densities (ca. 10 μA cm⁻²) is not affected by the presence of selenium whereas selenium-containing catalysts show higher current densities under fuel cell relevant conditions. The kinetically controlled current density at 0.6 V versus SHE increases 4–5 fold with increasing selenium content. A maximum value is obtained at about 15 mol% Se. This effect is tentatively explained by a modification of the catalytic active centre, which is assumed to consist of Ru---C---CO complexes. IR spectroscopic investigations indicate a reaction of selenium with these complexes. This model is also supported by the study of the electrooxidation of CO. In contrast to the selenium-free catalyst, no CO oxidation is observed on the selenium-containing catalyst. Additional effects of selenium are an enhanced stability towards electrochemical oxidation and a lower amount of Ru oxides formed during synthesis, as evidenced from XRD investigations. Direct four electron oxygen reduction to water is efficient and H₂O₂ production of these catalysts is small (about 5% at potentials <0.3 V vs. SHE ).     

Structure Relaxation of n-alkanes Observed by the Simultaneous DSC-FTIR Method

Phase transitions of hexatriacontane (C36) and octacosane (C28), both as the solution grown single crystal (SGC) and polycrystalline aggregates (MCC) prepared by cooling at 1 K min^–1 from the isotropic liquid state, were measured by the simultaneous DSC-FTIR method. MCC of C36 showed the freezing of the high temperature stable phase, which had a slight lower order of the lattice vibration mode comparing with the room temperature stable phase. MCC of C28 demonstrated thermo-reversible phase transition, however, had a binomial distribution of crystal stability of the monoclinic phase.This revised version was published online in November 2005 with corrections to the Cover Date.     

Monitoring of the Gas Phase Composition: A Prerequisite for Unravelling the Mechanism of Decomposition of Solids. Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products. Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Co_met, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Co_met. The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H₂, Co_met oxidation under rich and lean oxygen conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction process

Zircon ore carbothermal reduction with yttria addition has been carried out. The influences of heating temperature and yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction have been investigated in detail. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure and micro-area chemical analysis of the products were characterized by scanning electron microscopy and energy dispersive spectrometer. The chemical states of Zr 3d, Y 3d and O 1s presented in the products of zircon carbothermal reduction with 10 wt% yttria addition were investigated by X-ray photoelectron spectroscopy. The results showed that the optimized heating temperature of zircon carbothermal reduction with no addition was 1600 °C, and the main phase of the products consists of m-ZrO₂, c-ZrO₂, ZrC and β-SiC. Yttria addition could be introduced into zirconia lattice and caused it to form Y₂O₃ stabilized zirconia. Zirconia in the products would be turned into partially stabilized zirconia with yttria addition from 1 wt% to 5 wt% while it would exist in the form of fully stabilized zirconia with over 8 wt% yttria addition.