Search Results
Abstract
The powders of Ni−P alloys containing 13% of phosphorus were obtained by precipitation from the solution. The oxidation of Ni−P alloys in polythermal conditions was studied. It was found that oxidation of Ni−P alloys goes through stages and that intermediate products of the oxidation are: Ni2P and Ni2P2O7. The final products of oxidation process are NiO and Ni3(PO4)2. The sequence of chemical reactions describing the oxidation of Ni−P alloys was proposed.
Abstract
Oxidation of saturated fatty acids ethyl esters: laurate, myristate, palmitate and stearate was investigated by means of DSC techniques under isothermal and non-isothermal conditions. The activation energies of isothermal oxidation were similar to each other (112–123 kJ mol−1) and no influence of carbon length on the rate of oxidative decomposition was observed. Results obtained from non-isothermal experiments were similar only for the first stage of oxidation.
Abstract
The oxidation of Ni100–xPx(7.3 at%<x<25.0 at%) powders in air in the temperature range 350–450C was determined by kinetics and X-ray diffraction. The isothermal kinetics was modeled using theGinstling–Brounstein equations. The oxidation process was found to be thermally activated with activation energy 127.8 kJ mol–1 for x=7.3 at% to 157.7 kJ mol–1 for x=25.0 at%. It was found that the rate constants for x=7.3 at% were approximately 100 times lower than those for x=25.0 at%.
Abstract
Tungsten carbide, WC, has shown dissimilar thermal behavior when it is heated on changeable heating rate and flow of oxidant atmosphere. The oxidation of WC to WO3 tends to be in a single and slow kinetic step on slow heating rate and/or low flux of air. Kinetic parameters, on non-isothermal condition, could be evaluated to the oxidation of WC to heating rate below 15°C min−1 or low flow of air (10 mL min−1). The reaction is governed by nucleation and growth at 5 to 10°C min−1 then the tendency is to be autocatalytic, JMA and SB, respectively.
Abstract
This paper reports on the results attained in the determination of the mechanism of oxidation of molybdenum sulphide under non-isothermal conditions in an air atmosphere. The mechanism of the process was determined by simultaneous DTA-TG-DTG, and the kinetic parameters of the reactions involved were obtained according to the methods of Kissinger and Ozawa.
Abstract
Ethers are widely used as a solvent for synthesis reactions, however, they are known as hazardous chemicals as they have low flash points and form peroxides under oxidative conditions. In this study, the oxidative reactivity of cyclic ethers was evaluated by thermal analysis. The accelerated test was performed in a pressure vessel under a high oxygen pressure (2 MPa), and DSC was used to detect the products of the reaction. Tetrahydrofuran (THF) and 1,3-dioxolane were used as a sample. The result of the DSC measurement of THF without any antioxidant showed that the DSC curve depended on the exposure time. It was found that this method can be used for the oxidation evaluation. The DSC measurement was also used for the detection of ether peroxides, and this method was faster and simpler than the potassium iodine titration.
Abstract
DTA in conjuction with X-ray diffraction analysis with a high-temperature camera and infrared spectroscopy was employed to determine the mechanism of oxidation of Ni-P alloys. Amorphous Ni-P powders were obtained from a nickel(II) sulphate bath as a nickel source and sodium dihydrophosphate(I) as a reducing agent. The crystallization product is composed of two phases: (f.c.c.) Ni and (b.c.t.) Ni3P. The amorphous to crystalline transformation takes place in the temperature range 280–330C. Ni3P samples were heated from room temperature to 1050C in air atmosphere at 5C min−1. It was found that the first stage of oxidation of Ni3P goes through the intermediate phase of Ni12P5 formation to Ni2P. Some exothermic reactions were observed. Heating runs were interrupted after each reaction for crystal structure determination by IR spectrometry. Infrared spectra are reported and it is shown that the structure units present in the amorphous products at about 700C were the oxoanions PO3 − and P2O7 −. The final products of the oxidation process are NiO and Ni3(PO4)2.
Abstract
The aim of the presented work was the investigation of thermal oxidation of ilmenite in static air atmosphere. The investigations were carried out by use of a derivatograph (MOM, Hungary). The changes of crystallographic structure of investigated samples were identified by X-ray diffractometry on Philips PW-1710 diffractometer. In temperature above 500C appears structure of hematite Fe2O3. On the basis of the thermogravimetric measurements, the contracting area and contracting volume models were found as the best fitting experimental data.
Abstract
A theory of the evaluation of kinetic parameters of induction periods for non-isothermal processes is outlined and a method to obtain the parameters from non-isothermal differential scanning calorimetry measurements, based on the dependence of onset temperature of oxidation peak on heating rate, is presented. The applicability of the method is demonstrated on the study of oxidation induction periods of edible oils and polyolefines. In all cases, the parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained. It is shown that the method gives the parameters not affected by oxygen diffusion which are transferable to be used in modelling the non-isothermal induction periods where the effects of diffusion, heat transfer and evolution of reaction heat are explicitly involved. A method of estimating the residual stability after a thermooxidative stress of the material is suggested.
Abstract
Two oxidation stages of electrolytic ultradispersed iron powder at the temperature range of 90–450C have been stated. The contribution of increasing mass and evolving heat at the first oxidation stage due to changing Fe0 into Fe2O3 in the total oxidation effect is predominant. The thermal method of active metal determination in electrolytic iron powders has been developed. The coarse-grained reduced iron powder was not oxidized completely just to 900C because of local sintering of big iron particles as a result of evolving heat at oxidation of high-dispersed iron particles.
