Differential Thermal Analysis Results Research Articles

Mineralogical and thermal characteristics of low-grade Jinlong bauxite sourced from Guangxi Province, China

Characteristic samples from the No. 1 ore body of the Jinlong bauxite deposit in Guangxi Province, China, were assessed to determine their chemical composition using whole-rock geochemical analysis, their mineral components using X-ray diffraction, their thermal characteristics via differential thermal analysis, thermogravimetry and differential thermogravimetry, and their dissemination characteristics by scanning electron microscopy/energy-dispersive spectrometry. The results show that the average Al2O3 content in the Jinlong bauxite deposit is 41 % and that the Al2O3/SiO2 ratio is approximately 2.17, and thus, the ore may be defined as low-grade bauxite. The main minerals found in the ore were diaspore (20.3–43 %), gibbsite, clays and hematite. In differential thermal analysis results, the bauxite samples exhibit two distinct endothermic peaks, with the dehydration of gibbsite occurring in the 200–260 °C range and the dehydration of diaspore occurring in the 524–550 °C range. Thermogravimetry and differential thermogravimetry indicate four decomposition stages: evaporation of adsorbed water (50–160 °C), gibbsite decomposition (190–280 °C), goethite decomposition (190–280 °C) and diaspore dehydroxylation (460–580 °C). The diaspore belongs to the orthorhombic dipyramidal class and exists primarily in three dissemination forms—euhedral and subhedral grain, bean and oolitic shaped, and aphanitic and microcrystalline aggregates, and is always accompanied by kaolinite and pyrophyllite.

Performance of magnesium phosphate cement at elevated temperatures

This research studied effect of elevated temperature on properties of magnesium phosphate cement (MPC). Properties, including strength, colour, mass loss, and microstructure, of MPC specimens before and after exposure different high temperature were measured or observed in this paper. Seven sample mixtures contained varying amounts of fly ash and sand are considered in the experimental program. The mechanical properties of MPC were measured by heating 40×40×160mm sample to 130, 500 and 1000°C at a rate of 10°C/min. The obtained results demonstrate that strength of MPC decreased significantly when the temperature passed 130°C. After 130°C, the amplitude of strength decreased of MPC became less with the increasing of temperature. The results of Differential thermal analysis (DTA) and thermo-gravimetric analysis (TG) indicate that the crystal water in MKP·6H2O were lost at the temperature of 125°C. The loss of crystal water in MKP·6H2O was the main reason of strength decreasing and mass loss of MPC after exposure to high temperature. The results also show that the presence of fly ash and sand decrease residual strength of MPC.

Synthesis and physicochemical characterization of LaCr1−xCuxO3

Different citrate precursor powders of lanthanum chromite doped with copper LaCr1−xCuxO3 (0 ≤ x ≤ 0.4) have been synthesized by sol–gel method. After calcination, its structural and surface characteristics have been examined by X-ray diffraction to confirm the formation of the pure perovskite phase. Fourier transform infrared, differential thermal analysis and thermogravimetric analysis results indicate that the pure orthorhombic phase was obtained at temperature above 800 °C. The structure and morphology of the samples are characterized by SEM measurements indicating that the particles have nearly spherical shapes and are agglomerated. The study of electrochemical behavior shows that the electrode with large copper content has a better electrocatalytical activity.

Solid fraction evolution characteristics of semi-solid A356 alloy and in-situ A356-TiB2 composites investigated by differential thermal analysis

The key factor in semi-solid metal processing is the solid fraction at the forming temperature because it affects the microstructure and mechanical properties of the thixoformed components. Though an enormous amount of data exists on the solid fraction-temperature relationship in A356 alloy, information regarding the solid fraction evolution characteristics of A356-TiB2 composites is scarce. The present article establishes the temperature-solid fraction correlation in A356 alloy and A356-xTiB2 (x = 2.5wt% and 5wt%) composites using differential thermal analysis (DTA). The DTA results indicate that the solidification characteristics of the composites exhibited a variation of 2°C and 3°C in liquidus temperatures and a variation of 3°C and 5°C in solidus temperatures with respect to the base alloy. Moreover, the eutectic growth temperature and the solid fraction (f s) vs. temperature characteristics of the composites were found to be higher than those of the base alloy. The investigation revealed that in-situ formed TiB2 particles in the molten metal introduced more nucleation sites and reduced undercooling.

Low-temperature solid state synthesis of TiC from Ti/C elemental powder mixture induced by polytetrafluoroethylene

In order to significantly reduce the synthesis temperature, polytetrafluoroethylene was employed to induce the solid state synthesis of titanium carbide from elemental reactants. According to differential thermal analysis and X-ray diffraction results, titanium carbide can be synthesised successfully at the temperature as low as 825 K from Ti/C mixture with 3 wt-% polytetrafluoroethylene addition. The field emission scanning electron microscopy image showed that the size of the as-prepared titanium carbide particle was smaller than 150 nm.

Molecular Study of Cs and CO 2 Adsorption Sites in Smectite Nanoparticles

The Cs adsorption sites were specifically studied by means of positronium annihilation spectroscopy. Beside the interlayer Cs+ cations, a population of Cs is able to adsorb on the surfaces of open nanospaces A and B with their sizes of ~ 0.3 nm and ~ 0.9 nm, which are formed by inserting one- and two-clay nanosheets into the interlayer spaces. The chemical form for Cs in the open nanospace A is the Cs+ cation, whereas the CsOH compound followed by the Cs2O compound and its corresponding hydrate exists at the two-nanosheet edge site in addition to the Cs+ cations on the surfaces in the open space B. Cs adsorbed on the surfaces of both the open nanospaces A and B is so adhesive that it cannot be removed even by the hydrochloric acid solution of pH 1.0, the open nanospaces A and B thus acting as the specific Cs adsorption site. The characteristic local molecular sites as a clay-nanosheet edge and a wedge-shaped frayed part available in the open spaces A and B are responsible for the specific Cs adsorption. Preliminary results of thermogravimetry and differential thermal analysis (TG-DTA) after CO2 gas flow implied that above-mentioned adsorption sites play an important role in capturing CO2.

Role of gadolinium(III) complex in improving thermal stability of polythiophene composite

AbstractThis paper involves the preparation of polythiophene (PTP) and its composite by the oxidative polymerisation method by using ferric chloride as an oxidant and thiophene monomer. The gadolinium( III) complex obtained by the refluxing technique was used as dopant in the PTP matrix. On the basis of the spectroscopic characterisation, seven-coordinate geometry is proposed for the complex. Conductance measurement confirms the non-selectrolyte nature of complex. The PTP and its composite were subjected to FTIR, X-ray diffraction and scanning electron microscope techniques. The powder X-ray diffraction pattern showed the high crystalline nature of the complex which in turn developed a good degree of crystallinity in the PTP composite. The average particle size was calculated as 4.655 ˚A and 3.737 ˚A for the dopant and PTP composite, respectively, by using Debye Scherrer’s equation. Thermal analysis was performed by thermogravimetric (TG) analysis, differential thermal analysis (DTA) and differential scanning calorimetry (DSC) techniques. The TG, DTA and DSC results were well-correlated. The thermal analysis revealed the high thermal stability of the dopant which in turn improved the thermal stability of the PTP composite, revealing the potential of the composite for high temperature applications.

Thermal behavior of Fe40Co8Cr15Mo13Y2C16B6 bulk metallic glass with reference to irreversible structural relaxation

Reversible and irreversible structural relaxation in the Fe40Co8Cr15Mo13Y2C16B6 bulk metallic glass (BMG) were studied and characterized via dilatometry. Glass transition and crystallization temperatures defined by dilatometry found to be in a good agreement with the results of Differential Thermal Analysis (DTA). Besides, the effect of irreversible structural relaxation on the free volume and the glass transition temperature was investigated. Results showed that the glass transition temperature for the as-cast samples in their dilation curves is more distinct compare to DTA, and temperatures at which structural relaxations occur can be well determined. It is also suggested that the difference in the dilatation of as-cast and relaxed sample can be a reliable method to measure the density of free volume in this BMG.

A new ball milling method to produce organo-montmorillonite from anionic and nonionic surfactants

BackgroundOrgano-montmorillonite (OMt) is widely used in oil well drilling fluids, paint, grease, cosmetics, and personal care products. Nanocomposites which are prepared using organoclays and polymers. Generally, organo-montmorillonite can be prepared using ion-exchange reactions with cationic surfactants. However, cationic-organo-montmorillonite (COMt) has poorer thermal stability. In addition, the preparation process of traditional OMt uses a large amount of water. The process would emit a large amount of effluent and increase cost. ObjectiveThe aim of this work is to prepare nonionic-organo-montmorillonite (NOMt) and anionic-nonionic-organo-montmorillonite (ANOMt) using ball milling method. And NOMt and ANOMt are of better thermal stability than COMt. MethodOrgano-montmorillonite was prepared using ball milling method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), Thermogravimetric (TG) analysis, differential thermal analysis (DTA) and contact angle test. ResultsXRD analysis indicated that the interlayer spacing of Ca2+-montmorillonite (Ca-Mt) was expanded. ANOMt showed a large d-spacing above 5.0nm. SEM analysis demonstrated that the ANOMt was flaky in substance. FT-IR spectra proved that the chemical environment of the surfactants changed. TG and DTA results showed that the thermal stabilities of NOMt and ANOMt were better than that of COMt. FT-IR and thermal analysis indicated that the interlayer water was replaced. The contact angle tests of the samples indicated that NOMt and ANOMt were of oleophilic property. ConclusionCa-Mt was modified with nonionic surfactant and anionic surfactant by ball milling method, without any added water. NOMt and ANOMt were prepared. The thermal stabilities of NOMt and ANOMt are better than COMt. Dual mechanisms of intercalation and stacking were proposed.

Polythermal section Ge-SnAs of the Sn-As-Ge system

The T-x diagram of the polythermal section Ge-SnAs of the Sn-As-Ge system was constructed using the results of X-ray powder diffraction and differential thermal analyses. It was found that the Ge-SnAs section is not quasi-binary. In the ternary system, two four-phase peritectic transformations occur: L + GeAs ↔ Sn4As3 + Ge at 821 K and SnAs ↔ Sn4As3 + GeAs at 834 K.

Effect of cooling methods on residual compressive strength and cracking behavior of fly ash concretes exposed at elevated temperatures

SummaryThis paper presents the effects of cooling methods on residual compressive strength and cracking behavior of concretes containing four different class F fly ash contents of 10%, 20%, 30% and 40% as partial replacement of cement at various elevated temperatures. The residual compressive strength of the aforementioned fly ash concretes is measured after being exposed to 200, 400, 600 and 800 °C temperatures and two different cooling methods, for example, slow cooling and rapid water cooling. Results show that the residual compressive strengths of all fly ash concretes decrease with increase in temperatures irrespective of cooling regimes, which is similar to that of ordinary concrete. Generally, control ordinary concrete and all fly ash concretes exhibited between 10% and 35% more reduction in residual compressive strength because of rapid cooling than slow cooling except few cases. Cracks are observed over concrete specimens after being exposed to temperatures ranging from 400 to 800 °C. Samples that are slowly cooled developed smaller cracks than those rapidly cooled. At 800 °C, all fly ash concretes that are exposed to rapid cooling showed the most severe cracking. X‐ray diffraction analysis shows reduction of Ca(OH)2 peak and formation of new calcium silicate peak in concretes containing 20% and 40% fly ash when subjected to 800 °C in both cooling methods. Thermo gravimetric analysis and differential thermal analysis results show increase in thermal stability of concrete with increase in fly ash contents. The existing Eurocode also predicted the compressive strength of fly ash concretes with reasonable accuracy when subjected to the aforementioned elevated temperatures and cooling methods. Copyright © 2014 John Wiley & Sons, Ltd.

Spin-crossover thermal hysteresis and light-induced effect on iron(II) complexes with tripodal tris(2-pyridyl)methanol

The X-ray crystal structure of Me4N[Fe(py3COH)(NCS)3](1-PrOH)0.5(H2O)2 [1; py3COH stands for tris(2-pyridyl)methanol] was successfully determined, clarifying that the complex has a pseudo-trigonal molecular arrangement, though the space group was P1¯. Possible π–π interaction is operative between the pyridine rings from neighboring [Fe(py3COH)(NCS)3]− ions. After annealing of 1 at 400K, the resultant compound was characterized to be Me4N[Fe(py3COH)(NCS)3](H2O) (1′), which showed a relatively abrupt spin-crossover (SCO) with thermal hysteresis. Combining the differential thermal analysis results, the SCO temperatures were determined as T1/2↓=224K and T1/2↑=246K. Compound 1′ also showed light-induced excited spin-state trapping (LIESST), as indicated with the χmT increased to a 32% level of the high-spin moment upon Xe-lamp irradiation at 5K. The LIESST effect disappeared at around 26K on heating. The complex ion [Fe(py3COH)(NCS)3]− is a rare anionic SCO and LIESST building block.

Formation of liquid crystals in the KCl-TaCl5 system

The data on the formation of liquid crystals in inorganic substances, in particular, in the chloride system KCl-TaCl5, were presented for the first time. The obtained experimental results of differential thermal and visual polythermal analyses and electrical conductivity measurements indicated the presence of liquid crystals in this system. Important factors of the formation of liquid crystals are the existence of a congruently melting substance in the system and the existence of polymorphic modifications of this substance.

Sealed-tube synthesis and phase diagram of LixTiS2 (0 ≤ x ≤1)

We reported a new method to prepare LixTiS2 (0≤x≤1) at 600°C in sealed tube using Li2S as lithium source. The LixTiS2 samples were characterized by powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and differential thermal analysis. The variations of the lattice parameters with lithium content x in LixTiS2 were determined by X-ray powder diffraction analysis for both 1T and 3R phases. The phase transition between low-temperature 1T phase and high-temperature 3R phase was confirmed by the powder X-ray diffraction analysis. Based on the differential thermal analysis and X-ray diffraction results, a schematic phase diagram of the LixTiS2 system has been constructed, providing a guideline to synthesize LixTiS2 in 1T structure or 3R structure.

Formation of less-known structurally complex ζb and orthorhombic quasicrystalline approximant εn on solidification of selected Al–Pd–Cr alloys

The evolution of phases was investigated on cooling of Al71Pd24Cr5, Al73Pd20Cr7, and Al73Pd23Cr4 alloys from 1350°C down to ambient temperature with the rate of 10°C·min−1. To perform the investigation, differential thermal analysis, synchrotron X-ray powder diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used. In all the investigated alloys structurally complex phases εn (ε6+ε28) and ζb, as well as the δ-phase were identified. Based on the results of differential thermal analysis, sequences of phase transformations were determined. The Al71Pd24Cr5 alloy started to solidify at 1031.4°C through β. Primary dendrites of ζb were observed in Al73Pd20Cr7 and Al73Pd23Cr4 alloys. In the second step of solidification δ and/or ζb were formed. The peritectic reaction, liquid+ζb+δ→εn+ζb+δ, leading to the formation of the quasicrystalline approximant εn (ε6+ε28) took place in the final step of solidification at approximately 792°C.

Spectroscopic Investigation of Tungsten Ions in Lead Scandium Phosphate Glass System

ABSTRACT Lead scandium phosphate glasses (PbO-Sc2O3-P2O5) containing different concentrations of tungsten oxide (WO3) ranging from 0 to 5 mol% were prepared. A number of studies, viz. differential thermal analysis (DTA), infrared spectra, optical absorption, and electron spin resonance (ESR) spectra, have been carried out. The results of DTA indicated the highest glass forming ability for the glass containing 5 mol% of WO3. The results of spectroscopic studies have been analyzed in light of different oxidation states of tungsten ions.

Reaction chemistry in the Mg–B2O3–MoO3 system reactive mixtures

Fundamental aspects of reaction path in the MoO3+B2O3+Mg system to synthesize molybdenum boride have been investigated. The phase transformation and structural evaluation were studied by means of differential thermal analysis (DTA) techniques, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Thermodynamic evaluations indicated that the reaction was highly exothermic and should be a mechanically induced self-sustaining reaction (MSR). According to DTA results, for unmilled sample, the reaction's sequence includes the following reactions: MoO3 reduction→B2O3 reduction→molybdenum boride formation. For 3h-milled sample, the temperature of exothermic reaction decreased significantly and all the reactions occurred, simultaneously. Based on XRD results, the mechanochemical products including MgO and mix of molybdenum boride phases were achieved after 4h of high energy ball milling. SEM and TEM observations confirmed that the range of particle size was within 100nm.

Characteristics of nanoparticles emitted from burning of biomass fuels

The characteristics of the particles of the smoke that is emitted from the burning of biomass fuels were experimentally investigated using a laboratory-scale tube furnace and different types of biomass fuels: rubber wood, whole wood pellets and rice husks. Emitted amounts of particles, particle-bound polycyclic aromatic hydrocarbons (PAHs) and water-soluble organic carbon (WSOC) are discussed relative to the size of the emitted particles, ranging to as small as nano-size (<70nm), and to the rate of heating rate during combustion. differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques were used to examine the effect of heating rate and biomass type on combustion behaviors relative to the characteristics of particle emissions. In the present study, more than 30% of the smoke particles from the burning of biomass fuel had a mass that fell within a range of <100nm. Particles smaller than 0.43μm contributed greatly to the total levels of toxic PAHs and WSOC. The properties of these particles were influenced by the fuel component, the combustion conditions, and the particle size. Although TG–DTA results indicated that the heating rate in a range of 10–20°C did not show a significant effect on the combustion properties, there was a slight increase in the decomposition temperature as heating rate was increased. The nano-size particles had the smallest fraction of particle mass and particle-bound PAHs, but nonetheless these particles registered the largest fraction of particle-bound WSOC.

Formation mechanism of B4C–TiB2–TiC ceramic composite produced by mechanical alloying of Ti–B4C powders

In this study, the B4C–TiB2–TiC composite powder was synthesized by mechanical alloying (MA) of Ti–B4C powder mixture. For this purpose, four powder mixtures of Ti and B4C powders with different molar ratios were milled. In order to study the mechanism of Ti–B4C reaction during milling, structural changes and thermal analysis of powder particles were studied by X-ray diffractometry (XRD) and differential thermal analysis (DTA). Morphology and microstructure of powder particles during milling were studied by scanning electron microscopy (SEM). It was found that during MA, after decomposition of the outer layers of B4C particles, first, C reacted with Ti and after that, B was diffused in Ti structure and TiC and TiB2 phases were formed in gradual reaction mode. Also, the results of DTA and thermodynamic analysis confirmed the suggested mechanism for Ti–B4C reaction.

The influence of valence states of tungsten ions on PbO–Y2O3–P2O5 glass network

Lead yttrium phosphate glasses mixed with different concentrations of WO3 (ranging from 0 to 5.0mol%) were synthesized. Differential thermal analysis (DTA), optical absorption, ESR and IR spectral studies have been carried out. The results of DTA have indicated that there is a gradual decrease in the resistance of the glass against devitrification with increase in the concentration of WO3 up to 3.0mol%. The optical absorption spectra of these glasses exhibited a relatively broad band peaking at about 850nm identified due to dxy−dx2–y2 transition of W5+ ions; this band is observed to be more intense in the spectrum of glass containing 3.0mol% of WO3. The ESR spectra of these glasses recorded at room temperature exhibited an asymmetric signal at g⊥∼1.71 and g||∼1.62. The intensity of the signal is observed to be maximal for the spectrum of the glass PYPW3. The optical absorption and ESR spectral studies have indicated that there is a maximum reduction of tungsten ions from W6+ state to W5+ state in the glass containing 3.0mol% of WO3. The IR spectral studies have indicated that there is an increasing degree of disorder in the glass network with increase in the concentration of WO3 up to 3.0mol%.