Thermal transitions in metastable Cu – 68.5 at. % Co alloy.

Arc melted and drop tube processed Cu – 68.5 at. % Co alloy has been subjected to differential thermal analysis (DTA). The liquidus temperature determined from the DTA curves in the arc melt sample (1664 K) was found to be close to phase diagram estimate of 1662 K. In contrast as a result of liquid phase separation in the drop tube samples, the values obtained in the powders were much lower mainly because the compositions of the demixed phases vary from that of the parent melt. The liquidus temperature of the 850 + μm powders was 1632 K while that of the < 38 μm sieve size powder was 1616 K. This variance is due to the asymmetric nature of the metastable phase diagram of the system.

Modeling of thermal studies on melt quenched Ge18Bi4Se78 chalcogenide

The crystallization characteristics for Ge18Bi4Se78 glass are studied in this work by means of DTA under the non-isothermal conditions. One stage endothermic glass transition and one exothermic crystallization are observed in the DTA curves. The results of topological constraints for Ge18Bi4Se78 glass show that the calculated value of glass transition temperature (Tg) is very close to that of the experimental results. The as-prepared as well as the annealed samples are examined using XRD, EDX, SEM techniques. Avrami exponent reveals the complicated stage of growth. Many models are used to estimate the activation energies for glass transition (Eg) and crystallization (Ec). The crystallization process found to be described by the Sestak- Berggren SB(M,N) model.

Investigating the Effect of α-Fe2O3 Oxides on the BaFe2O4 Pyrosynthesis Temperature - The Digital Processing of TG and DTA Curves

In the research activities on the barium monoferrite pyrosynthesis, an important place is occupied by TG and DTA analysis. The effects of different hematite (α-Fe2O3) granulations on the BaFe2O4 pyrosynthesis temperature were followed. Four types of commercial hematite powders were used, the difference between them being the fineness of the powder granules and the purity. Only one type of commercial barium carbonate (BaCO3) powder was also used as a barium additive in the BaFe2O4 pyrosynthesis. Each of the 4 types of α-Fe2O3 with BaCO3 were subjected to the homogenization process in a planetary mill for a more intimate mixing of the powders in order to obtain error-free results regarding the pyrosynthesis reaction. To determine BaFe2O4 pyrosynthesis temperature, a derivatograph device was used. All the data obtained with this thermal device were digitally processed in order to extract the two TG and DTA curves. The protective atmosphere in the furnace was nitrogen. BaFe2O4 pyrosynthesis temperatures recorded different values for the four mixtures, depending on the particle size of the α-Fe2O3 powders, protective atmosphere from furnace and the mixing conditions. The effects of Fe2O3 oxides on the BaFe2O4 pyrosynthesis temperature is observed when are used very fine hematite powders in mixtures, obtaining a reduction of pyrosynthesis temperature up to 16% compared to the mixture where the size of the hematite is coarser.

Thermal degradation of açaí seeds and potential application in thermochemical processes

Purpose: Thermal and Physicochemical evaluation of açaí seeds for its use in thermochemical conversion processes for clean energy generation. Methodology: Experimental and qualitative research, using analyzes such as: Thermal analysis (TG/DTG and DTA curves) and Calorimetry, Ultimate and Proximate analyzes, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-Ray Diffraction, Fourier Transform Infrared Spectroscopy and Optical Emission Spectroscopy - Inductively Coupled Plasma. Findings: It was noted that the açaí seeds presented carbon, hydrogen, and oxygen contents as majority elements and a Higher Heating Value (HHV) of 19.8 MJ kg-1. Nitrogen and lead elements were found as trace elements. However, highly polluting elements, e.g., sulfur, cadmium and arsenic were not detected in the samples. Originality: The utilization of açaí seeds by means of thermoconversion processes for bioenergetic purposes can be an attractive socioenvironmental, reducing disposal in inappropriate places, adding considerable value to waste and still protecting the environment.

Growth and study of 4-sulfobenzenaminium potassium dihydrogenphosphate for mechanical, dielectric and photonics applications

This article describes the growth and characterization of 4-sulfobenzenaminium potassium hydrogen phosphate (SPH) sulphanilic acid with potassium dihydrogen phosphate (KDP) doped semi-organic single crystals. The crystal was grown by the slow evaporation method. Examination of the crystalline nature of the sample was carried out by single crystal X-ray diffraction and it confirmed that the sample crystallizes in orthorhombic structure in the centrosymmetric space group P212121. The optical transmittance behavior was tested by UV-Vis spectral analysis. FT-IR spectral investigations have been carried out to indicate the presence of functional groups. The chemical structure of the compound was established by 1H and 13C NMR spectra. The SHG efficiency of the powdered SPH crystal is around 1.7 times that of pure KDP. The grown crystal was stable up to 270 °C as observed from TGA and DTA curves. The microhardness test was carried out to study the load dependency of hardness. The result of this study indicates that SPH crystal is a malleable material. From the hardness values, the stiffness constant and yield strength were calculated. The dielectric response of the novel crystal was studied in the frequency range of 50 Hz to 5 MHz at various temperatures. By employing FE-SEM, the surface morphology and the particle size of the crystal were assessed.

The Influence of Initiator Concentration on Selected Properties of Thermosensitive Poly(Acrylamide-co-2-Acrylamido-2-Methyl-1-Propanesulfonic Acid) Microparticles

Thermosensitive polymers PS1–PS5 were synthesized via the surfactant free precipitation polymerization (SFPP) using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA), and potassium persulfate (KPS) at 70 °C in aqueous environment. The effect of KPS concentrations on particle size and lower critical temperature solution (LCST) was examined by dynamic light scattering (DLS). The conductivity in the course of the synthesis and during cooling were investigated. The structural studies were performed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), H nuclear magnetic resonance (1H NMR), thermogravimetric analysis (TGA/DTA) and powder X-ray diffraction (PXRD). ATR-FTIR, 1H NMR and PXRD data confirmed the polymeric nature of the material. TGA/DTA curves demonstrated thermal stability up to approx. 160 °C. The effect of temperature on the hydrodynamic diameter (HD) and zeta potential (ZP) were evaluated by dynamic light scattering (DLS) and electrophoretic mobility (EM) in 18–45 °C range. The LCST values were between 30 and 34 °C. HD and polydispersity index (PDI) of aqueous dispersions of the synthesized polymers PS1–PS5 at 18 °C were found to be 226 ± 35 nm (PDI = 0.42 ± 0.04), 299 ± 145 nm (PDI = 0.49 ± 0.29), 389 ± 39 nm (PDI = 0.28 ± 0.07), 584 ± 75 nm (PDI = 0.44 ± 0.06), and 271 ± 50.00 nm (PDI = 0.26 ± 0.14), respectively. At 18 °C the ZPs of synthesized polymers suspensions were −13.14 ± 2.85 mV, −19.52 ± 2.86 mV, −7.73 ± 2.76 mV, −7.99 ± 1.70 mV, and −9.05 ± 2.60 mV for PS1–PS5, respectively. We found that the initiator concentration influences the physicochemical properties of products including the size of polymeric particles and the LCST.

The effect of calcium fluoride on extracting magnesium from magnesite and calcium carbonate by silicothermal reduction in flowing argon

At present, the production of magnesium is mainly carried out semi-continuously with ferrosilicon as reducing agent under high temperature and high vacuum. In order to continuously produce magnesium, anew method of extracting magnesium from low-grade magnesite and calcium carbonate by silicothermal method in flowing inert gas was proposed. The effects of calcium fluoride(CaF2)on decomposition rate, decomposition kinetics, reduction rate of magnesia and crystal type of dicalcium silicate in reduction slag were investigated in the paper. The experimental results showed that calcium fluoride could accelerate the decomposition of carbonate, and had no side effect on the calcined products. In addition, the analysis results of DTA curves showed that calcium fluoridecould reduce the decomposition reaction activation energy and the reaction temperature of carbonatein the prefabricated pellets. The results of reduction experiments showed that proper calcium fluoridecould promote the reduction rate of magnesia, and in the temperature range of 1250? ~ 1350?, with same timeframe, the corresponding calcium fluoride contents were5%, 3% and 1% respectively when the reduction rate reached the maximum. Excessive calcium fluoride could reduce the reduction rate of magnesia, but it couldpromote the transformation of dicalcium silicate to ? phase in the reduction slag.

Influence of Variant Temperatures in Optical, Magnetic Properties of NiO Nanoparticles and its Supercapacitor Applications via Precipitation Method

In this study, nickel oxide nanoparticles have been synthesized via precipitation method and calcinated at 500, 600, 700 and 800 ºC, respectively. TG/DTA curves expose the thermal stability of the prepared/asprepared product. The XRD results revealed that NiO nanoparticles have cubic structure. Crystallite sizes increase with increasing calcination temperatures by using two different methods via Scherer′s method and W-H method. The SEM and TEM images confirmed that the NiO nanoparticles have a spherical morphology with high agglomeration. The photoluminescence (PL) and FT-IR spectra give details of the crystal defects and functional groups present in the prepared samples. The energy bandgap of the prepared products was observed to be decreasing (3.59 to 3.01 eV), respectively. The VSM study confirms the occurrence of weak ferromagnetic behaviour. The highest specific capacitance of 555.62 F g-1 at 10 mV/s was obtained for NiO (800 ºC) nanoparticles.

Determination of the Order of Kinetics of a DTA Curve by Using the Concept of Skewness

In the present paper, a novel way of finding out the order of kinetics of differential thermal analysis (DTA) curves by using the concept of skewness (Sk) has been investigated. It is found that for a particular DTA peak, skewness is a function of both the order of kinetics and the quantity, First order DTA peaks are characterized by negative skewness whereas those for the second order are characterized by positive skewness. Therefore, skewness can be used as an indicator of the order of kinetics of a DTA peak. We have evaluated and compared the orders of kinetics of some reported DTA peaks using the concept of skewness and found that the resulting values of the orders of kinetics are in fair agreement with those reported in literature.

Synthesis, characterization, and thermal behavior of amidosulfonates of transition metals in air and nitrogen atmosphere

The amidosulfonates of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ were prepared by the direct reaction between the metal carbonate and the amidosulfonic acid with heating and stirring. The compounds were characterized by infrared absorption spectroscopy (IRFT), elemental analysis, thermal analysis (TG and DTA) and X-ray diffraction by the powder method. The absorptions observed in IR spectra are associated with N-H and O-H stretching, as well as symmetrical and asymmetric S-O stretching in the sulfonic group. The compounds present X-ray diffraction pattern with well-defined reflections, showing no evidence of isomorphism. The TG-DTA curves allowed to establish the stoichiometry of compounds as M(NH2SO3)2.xH2O, where M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ and x ranging from 1 to 4. Dehydration leads to the formation of stable anhydrous. In all cases the respective sulfates are formed as an intermediate. After consecutive steps of decomposition, the respective oxides were obtained: Mn3O4, CoO, NiO, CuO and ZnO. The TG-DTA curves are characteristic for each sample, with thermal events related to dehydration and ligand decomposition.