Determination Of Characteristic Temperatures Research Articles

Application of Copper Mining Waste in Radionuclide and Heavy Metal Immobilization

AbstractCopper slag flotation tailings (CSFT), as the end waste from copper mining, are evaluated for radionuclide and heavy metal immobilization. Characterization of CSFT based on grain size and mineral composition, surface functional groups, pH and electrical conductivity in aqueous media, thermogravimetric analysis (TGA), determination of characteristic temperatures in sample melting process, leachability, and toxicity tests is conducted. The screening sorption of Mn(II), Co(II), Ni(II), Zn(II), Cd(II), and Pb(II) inactive isotopes from single‐component solutions is performed. The Cd(II) ions show better sorption potential than other ions, with a sorption capacity of 0.08 mmol g−1 at the highest initial concentration. Sorption decreases in the sequence Cd(II) > Pb(II) > Zn(II) > Mn(II) > Ni(II) > Co(II) at all initial concentrations. Although CSFT shows lower sorption capability than synthetic sorbents based on fayalite and magnetite, its inexpensiveness and substantial accessible amount represent great advantages in wider utilization.

Effect of annealing on microstructure, phase composition and mechanical properties of thixo-cast 100Cr6 steel

Abstract Steel is a particularly challenging material to semi-solid process because of the high temperatures involved and the potential for surface oxidation. Hot forged and annealed 100Cr6 steel was used as feedstock for the thixoforming process. Samples were heated in an argon atmosphere up to 1425 °C which corresponded to about 25% of liquid fraction. Specimens after heating were transported into a modified shot sleeve of a high pressure die casting machine and pressed into a die preheated up to 150 °C. After thixoforming the microstructure of thixo-casts consisted of large globular grains (average grain size about 300 μm). Martensitic plates in the form of globules were found inside austenitic matrix. Among large globules, a fine grain structure was identified to appear from the liquid phase (average size 20 μm). A mixture of ferrite and carbides was identified within the region of fine grains. Average hardness of thixoformed samples was 759 HV5, while the compression strength attained 3850 MPa. Dilatometric and calorimetric studies carried out directly after thixoforming allowed the determination of characteristic temperatures of retained austenite decomposition and carbide formation. They were used to choose temperatures of heat treatment conditions: 150 °C, 180 °C, 250 °C, 320 °C and 400 °C. After tempering at 150 °C, precipitates of e carbide in martensite needles were found and at the same time the retained austenite transformed into martensite. X-ray phase analysis showed that thixo-cast contained: 78.7% – α′-Fe, 15.3% – γ-Fe and 6% – e carbides. Hardness increased after annealing at 150 °C up to 808 HV5, while after tempering at 180 °C and 250 °C the hardness decreased to 693 HV5 and 665 HV5, respectively. This effect was connected with the decomposition of austenite into ferrite and transformation of martensite into ferrite. After treatment at 320 °C the hardness decreased to 556 HV5, which, according to quantitative phase analysis was due to the presence of α-Fe and Fe3C. After the treatment at 400 °C for 2 h the microstructure consisted of ferrite and coarse cementite. Its average hardness was 508 HV5. The increase of annealing temperature caused a gradual decrease of compression strength to 2420 MPa at 400 °C with the increase of plastic contraction strain to 22%.

Oxidation of Metal Sulphides and Determination of Characteristic Temperatures by DTA and TG

The oxidation of metal sulphides and sulphide concentrates was studied by means of DTA, TG and DTG curves. The behaviour of ZnS, CdS, GaS, Tl2S, Sb2S3 and Sb2S5 during thermal treatment in an oxidizing medium was investigated. The properties of these sulphides were compared and conclusions were drawn about their probable oxidation reactions and the kind of end-products obtained. The characteristic temperatures of the studied sulphides were determined on the basis of curves (DTA). The values obtained were used to compare the behaviour of the sulphides during the oxidation process in a fluid bed. The results can be used to improve the technological and economic indices in the industrial production of zinc.

Basic Principles of Thermoanalytical Techniques and Their Applications in Preparative Chemistry

AbstractThe investigation of thermodynamic properties and reactivity yields interesting insights into the chemistry of newly synthesized substances. With thermal analysis extensive information can be gained from small samples (often only a few milligrams). In addition, the data obtained by thermal analysis can be used to plan and optimize a synthesis. Among the most important applications are identification and purity analysis, and the determination of characteristic temperatures and enthalpies of phase transitions (melting, vaporization), phase transformations, and reactions. Investigations into the kinetics of consecutive reactions and decomposition reactions are also possible. With the instruments available today such analyses can usually be performed quickly and easily. In this review the fundamentals of thermoanalytical methods are described and illustrated with selected examples of applications to low and high molecular weight compounds.

On the determination of characteristic temperatures in power oil transformers during transient states

Under usual assumptions the equations describing thermal phenomena in a transformer are established. Without neglecting any substantially important factor, algorithms are developed for predicting the temperatures in critical spots in non-stationary states occurring either in practice or in load/time diagrams. This paper suggests the determinaton of conductances dependent on temperature and constant capacitances of equivalent thermal circuits of a transformer. They are based on a small number of experiments (as simple as possible) and on a parameter estimation procedure. In such a way the temperatures of transformer parts in different transient states can be determined by computer simulation established on equivalent circuits, so the operators in power and sub-stations will be able to load their transformers close to the permitted limit. It is felt that this paper may give a stimulation for a possible revision of IEC rules.

Determination of characteristic temperatures with the scanning calorimeter

The uncertainty of the temperature determination by means of scanning calorimeters can be considerably reduced if the heat flow rate to be assigned to the event under discussion is extrapolated up to the abscissa, not up to the interpolated baseline, and the temperature of the intersection point is taken. This reduces, for example, the standard deviation of the measurement of the melting temperature of indium samples of different mass from 109mK to 18mK.

Numerical values of chemical constants and frequencies of the elements

The experimental evidence for the general chemical constant C0 possessing the theoretical value ( - 1.589) is collected. Tables of chemical constants are given and data collected for the determination of characteristic temperatures of the elements. A linear relation between logarithm of mass and characteristic temperature is indicated.