High-temperature DTA Research Articles

TG—DTA studies on the pyrolysis of limestone—laterite mixtures

TG and DTA studies conducted on 15 Indian laterite samples, limestone as well as three limestone—laterite mixes revealed the influence of minerals in laterite on the pyrolysis of limestone. Stanton Redcroft high temperature thermobalance HTSF and DTA model 674 were used. The 15 laterites could be classified broadly into three groups based on DTA peaks up to 1000°C. The minerals identified by DTA were confirmed by X-ray diffraction study on one selected sample from each group. Their approximate quantification was possible from the chemical composition and TG studies done up to 950°C. While gibbsite present in laterite showed no significant influence on the calcination of limestone, goethite retarded the rate of decomposition, particularly in the temperature range 700–840°C. From burnability experiments up to 1400°C, it was found that the sintering of limestone—laterite mixes is favourably influenced by goethite present in the laterite.

The structural behaviour of the nepheline family: (1) Sr and Ba aluminates (MAl2O4)

AbstractThe structural relations of solid solutions in the series (Sr1−xBax)Al2O4 were studied using room- and high-temperature X-ray methods, infra-red spectroscopy, and DTA. At room temperature, SrAl2O4 and solid solutions with x up to 0.31 are monoclinic, between x = 0.31 and 0.43 monoclinic and hexagonal forms coexist, and between x = 0.43 and 1.0 only hexagonal forms occur. On heating, a member of the monoclinic series of solid solutions transforms to hexagonal symmetry over a range of temperature within which both monoclinic and hexagonal forms coexist. The proportion of the hexagonal form increases instantaneously as the temperature is raised. The transformation temperature decreases with increasing BaAl2O4 in solid solution and, in addition, the temperature width of the region of coexistence is markedly enlarged. SrAl2O4 transforms over the range 665–705 °C and (Sr0.7Ba0.3)Al2O4 over 170–405 °C. The DTA trace for SrAl2O4 shows a peak at 677 °C. On cooling, the transformations show hysteresis of 15 to 25 °C.The coexisting monoclinic and hexagonal forms are believed to be isochemical, and discontinuities in cell parameters occur within the region of coexistence both in the compositional series at room temperature and in the elevated temperature transformation experiments. The low-to-high transformation is accompanied by a volume change of −0.2 to −0.3 %, and is believed to be first-order displacive with additional characteristics similar to those of martensitic transformations.The thermal expansion behaviour of structures in the (Sr,Ba)Al2O4, series indicates that two tilt systems are operative: co-operative rotation of tetrahedra about the c-axis, and tilting of tetrahedra relative to the 0001 plane.The results for the (Sr,Ba)Al2O4 series are shown to be invaluable in reinterpreting the structural behaviour of members of the nepheline and leucite groups of minerals.

Phase diagram and order-disorder transition of vacancies in Fe xVS 2 (0.20 < x < 1.00)

The system Fe XVS 2 has been investigated by X-ray and DTA measurements. In this system, iron atoms are located in the alternative metal layers, and vacancy-ordered structures appear at low temperatures. The order-disorder transition of metal vacancies was confirmed by high temperature X-ray and DTA measurements. The nature of the order-disorder transition can be interpreted by the theory proposed by the present authors (1).

Phase Transformation of Iron Vanadium Sulfides at High Temperatures

Abstract The phase relations of iron vanadium sulfides with the atomic Fe: V ratios 3 : 2 and 71 : 29 were examined by the high-temperature DTA and X-ray measurements. It was found that the structure of iron vanadium sulfide changes gradually from a less symmetric form to a highly symmetric form with the increase in temperature. Two types of phase transformations by vacancy order-disorder were observed at temperatures above 800 °C. One was due to the intralayer disordering of metal vacancies: V3S4-type→Cd(OH)2-type (type Ia) or V3S4-type+NiAs-type→Cd(OH)2-type (type Ib) at T1. The other was due to the entirely interlayer disordering of metal vacancies: Cd(OH)2-type→NiAs-type (type II) at T2 (T2&amp;gt;T1). The tentative phase diagram of iron vanadium sulfides with the atomic Fe: V ratio 3 : 2 was constructed on the basis of the DTA results.

Order-disorder transition of the metal vacancies in the vanadium-sulfur system. I. An experimental study

The phase diagram of the VS-VS 2 system was studied by high-temperature DTA and X-ray measurements. As a result, it has been confirmed that the vacancy-ordered V 3S 4-type structure transforms into the CdI 2-type structure at T c 1 while the vacancy-ordered V 5S 8-type structure shows successive transformations on heating; V 5S 8 type → T c2 V 3 S 4 type → T c1 Cdl 2 type. The mechanisms of the phase transitions are discussed from the viewpoint of structural relationships. The phase diagram of the VS-VS 2 system is constructed in the temperature range up to 1200°C. In the VSe system similar results to those in the VS system have been obtained. The VSSe system has also been studied and the result supports the above-mentioned results on the VS and VSe systems.

An X-ray diffraction and DTA study of the ferroelectric transition in barium sodium niobate

The structural behaviour of barium sodium niobate has been studied in the region of the ferroelectric Curie point (∼ 580°C) by means of high-temperature X-ray diffraction and DTA. No significant changes in the diffraction pattern are observed until temperatures in the vicinity ofTc are reached; the patterns are then consistent with the structure retaining tetragonal symmetry through the transition but assuming a significantly lowerc/a ratio. The results are compared with thermal expansion measurements made on single crystals. The thermal effect associated with the transition has been used to determine the order of the transition and the results suggest that the reaction is first order.

Thermal decomposition of Ca 2SiO 4·CaCl 2

High-temperature microscopy, high-temperature X-ray diffraction, DTA and TGA indicated that synthetic Ca 2SiO 4·CaCl 2 decomposes according to the reaction ▪ The direct development of ga′-Ca 2SiO 4 from structural relics of decomposed Ca 2SiO 4·CaCl 2 is proposed.

Preparation and Characterization of Submicron Hafnium Oxide

Submicron hafnium oxide powder prepared by hydrolytic decomposition of alkoxides was studied. The particle size range of this powder was 10 to 50 Å. Emission spectrographic analysis of the powder after it was calcined at 250°C for 0.5 h indicated a purity of &gt;99.995%. Up to 320°C, the powder showed no crystallinity by X‐ray analysis. The amorphous HfO2 was isothermally aged at 5° to 10°C intervals between 200° and 500°C. X‐ray diffraction patterns indicate a sharp transition from an amorphous state to the monoclinic phase at 325°C. High‐temperature X‐ray studies and DTA suggest nucleation and growth of small crystallites at 420°C leading to conversion to monoclinic HfO2 at 480°C. BET surface area measurements and TGA of the powders were also conducted. A powder which transformed at 325°C to the monoclinic phase was isothermally aged below 325°C for 150 h without change.

Heterogenite from Naganobori Mine, Yamaguchi Prefecture, Japan

The first occurrence of heterogenite in Japan is descrived. The mineral occurs as irregular masses, 0.1 to 3cm in diameter, in the oxidation zone of the Naganobori metasomatic cobalt-copper deposit, Yamaguchi Prefecture, associated with goethite, montmorillonite, quartz, malachite and etc. Color steely black, luster dull to submetallic, streak iron gray. Cleavage none. D 3.1-3.4, Vickers hardness 217 (weight 100 gr.). Chemical analysis data coresponds closely to the formula of (Co, Cu) (O, OH)•OH. X-ray study shows the mineral to be rhombohedral with a0 4.72_??_;, α 35°14'. The high-temperature x-ray diffraction and DTA indicate the mineral with some impurities changes to the mixture of CoO, Co3O4, CoFe2O4 and Co2SiO4 at about 1, 000°C.

Kôzulite, a new alkali amphibole, from Tanohata Mine, Iwate Prefecture, Japan

New mineral kozulite belongs to the alkali amphibole group in which manganese (II) is the predominant cation of the Y-position. The mineral occurs as banded aggregate of short prismatic crystala with the faces of b, m and r up to 3.5×2.0×1.5mm in size, in the bedded magnanese deposit of Tanohata Mine, Iwate Prefecture, Japan, in the highly metamorphosed Jurassic chert-hornfels by the intrusion of granodiorite. Associated minerals are braunite, rhodonite, manganiferou alkali pyroxene, manganiferou alkali amphibole and quartz. Color reddish black to black, streak light purplish brown, luter vitreous, H. 5, G. measured 3.30, calculated 3.36. Cleavage (110) perfect. Optically biaxial negative, ns α=1.685, β=1.717(mean), γ=1.720, 2Vα=34-36°, cΛX=25°. Strongly pleochroic with X yellow-brown, Y reddish brown, Z dark brown, absorption Z〉Y〉X, dispersion very weak, probably r〉v. Chemical analysis gave SiO2 51.38, TiO2 none, Al2O3 1.69, Fe2O3 2.85, FeO none, MnO 27.96, ZnO 0.03, MgO 2.71, CaO 1.12, BaO none, Na2O 8.41, K2O 1.36, H2O (-) 0.06, F 0.08, sum 99.75-O (=F2) 0.03=99.72%, corresponding to (Na2.54 K0.27 Ca0.19)3.00 [(Mn3.69 Mg0.63)4.32 (Fe+30.33Al0.31)0.64]4.96Si8.00O21.78[(OH)2.18F0.04]2.22, as O+OH+F=24. The x-ray powder data showed the mineral to be monoclinic with a0=9.91, b0=18.13, c0=5.28A, β=104.5° and precession photographs of the same specimens by N. Morimoto, Osaka University, showed it to be monoclinic, space group C2/m, a=9.91±0.02, b=18.11±0.04, c=5.30±0.02A, β=104.6°±0.1°, Z=2. The strongest x-ray lines are 8.51 (100) (110), (4.52) (10) (040), 3.40 (10) (131), 3.29 (17) (240), 3.15 (67) (310), 2.96 (6) (221), 2.827 (31) (330), 2.748 (8) (331), 2.722 (10) (151), 2.602 (6) (061), 2.545 (6) (202), 2.349 (7) (351), 2.174 (9) (261), 1.908 (7) (510), 1.447 (7) (661). The high-temperature x-ray study and DTA indicate that the mineral breaks down to braunit plus glas at about 950°C. The name is for late Dr. Shukusuke Kozu (1880-1955), formerly Professor in Tohoku University, Japan who made many contributions to the study of rock forming minerals. Type material is preserved at Tohoku University. The mineral and name were approved before publication by the Commission on New Minerals and Mineral Names, IMA.

Some Observations in High Temperature DTA for Some Indian Clays

Some Observations in High Temperature DTA for Some Indian Clays

Kinetics of phase changes during the heating of specimens of zirconia and copper oxides

Equipment for simultaneous high-temperature x-ray studies, DTA curves, and resistivity curves was used to observe the changes and reactions taking place in a specimen of zirconium dioxide and copper oxides. It was found that the solid phases of this mixture of oxides form no new compounds whose crystal lattice parameters differ from the crystal parameters of ZrO2, CuO, and Cu2O.

Alkaline-Earth Tungstates: Equilibrium and Stability in the M-W-O Systems

Phase relations in the systems alkaline earth oxide-tungsten trioxide and their stability with metallic tungsten were investigated by the quenching technique using sealed capsules. In the system BeO-WO2, no intermediate compounds were formed. Binary mixtures resulted in a eutectic at 1185°C and 37 mole % BeO. In the system MgO-WO3, the 1:1 compound was stable and melted congruently at 1358°C. There are two crystalline modifications of this compound. The well-known wolframite-type form is stable below 1165°C. Two eutectics were found: 1120°C and 28.5 mole % MgO and 1318°C and 55.0 mole % MgO. In the systems CaO-WO3, SrO-WO3, and BaO-WO3, two binary compounds are stable. The 1:1 compounds with the scheelite-type structure melt, respectively, at 1580°, 1535°, and 1475°C, and form eutectics with WO3 at 1135°, 1073°, and 935°C, all with a eutectic composition near 75 mole % WO3. The 3:1 compounds having the distorted (NH,)3FeF6-type structure melt at ∼2250°, 2225°, and 1795°C. The eutectics between these two compounds are at 1490°C and 56.5 mole % CaO, 1410°C and 57.0 mole % SrO, and 1320°C and 58.2 mole % BaO. Phase transformations to an ideal (NH4)3FeF6-type structure in Sr3WO6 and Ba3WO6, were observed at 1100° and 805° C, respectively, by application of both high-temperature X-ray diffraction and DTA. At 1700°C, metallic tungsten exists in equilibrium with liquid, the alkaline earth oxides, W18O49, the 3:1 ternary oxides, and with combinations thereof.