scholarly journals Kinetics of carbothermic reduction of synthetic chromite

2014 ◽  
Vol 50 (1) ◽  
pp. 15-21 ◽  
Author(s):  
Y. Wang ◽  
L. Wang ◽  
J. Yu ◽  
K.C. Chou
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Reduction Process ◽  
X Ray Diffraction ◽  
X Ray ◽  
Chromite Ore ◽  
Current Reduction ◽  
Increasing Temperature ◽  
Isothermal Mode ◽  
Kinetics Of

In order to optimize the current reduction process of chromite, a good knowledge of reduction mechanism involved is required. The basic component in chromite ore is FeCr2O4, thus, kinetic investigation of synthetic FeCr2O4 with different amount of carbon were carried out in the temperature range of 1473K to 1673K under both isothermal and non-isothermal mode. The iron can be easily reduced compared with chromium. And higher reduction degree of chromite can be achieved by increasing temperature and carbon content. With the supporting of X-ray Diffraction and Scanning Electron Microscope methods, the formation of metallic products followed the sequence: Fe-C alloy, (Fe,Cr)7C3and Fe-Cr-C alloy. Kinetics analysis showed that the first stage was controlled by nucleation with an apparent activation energy of 120kJ/mol, while the chromium reduction was controlled by crystallochemical transformation with an apparent activation energy of 288kJ/mol.

Apparent Activation Energy in Low Temperature Aging of Y-TZP Ceramics

2010 ◽  
Vol 105-106 ◽  
pp. 100-103
Author(s):  
Qi Fei Xie ◽  
Cheng Wang ◽  
Qing Feng Zan ◽  
Li Min Dong
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Apparent Activation Energy ◽  
Coordinate Systems ◽  
X Ray Diffraction ◽  
X Ray ◽  
Low Temperature Aging ◽  
Diffraction Patterns ◽  
Straight Lines ◽  
Temperature Aging

Apparent activation energy in low temperature aging of two kinds of Y-TZP ceramic was studied in this paper. The ceramics were processed into small pieces, and aging in 100°C, 110°C, 120°C, 130°C and 140°C respectively. The content of monoclinic phase was calculated by X-ray diffraction patterns and the microstructure was scanned by SEM. According to MAJ law and Arrhenius formation, straight lines were fitted in coordinate systems of ln (ln (1/(1 − f )))-ln t and ln b-1/T, and the kinetic parameters of low temperature aging of Y-TZP ceramic were calculated according to these lines. The results revealed that grain size significantly affected apparent activation energy of Y-TZP ceramics.

Enhancement of Aurivillius Phase Formation Kinetics in SBT Thin Films using Nanoparticle Seeding

2003 ◽  
Vol 784 ◽  
Author(s):  
Yun-Mo Sung ◽  
Woo-Chul Kwak ◽  
Se-Yon Jung ◽  
Seung-Joon Hwang
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Phase Transformation ◽  
Phase Formation ◽  
X Ray Diffraction ◽  
Aurivillius Phase ◽  
X Ray ◽  
Si Substrates ◽  
Formation Kinetics ◽  
Kinetics Of

ABSTRACTPt/Ti/SiO2/Si substrates seeded by SBT nanoparticles (∼60–80 nm) were used to enhance the phase formation kinetics of Sr0.7Bi2.4Ta2O9 (SBT) thin films. The volume fractions of Aurivillius phase formation obtained through quantitative x-ray diffraction (Q-XRD) analyses showed highly enhanced kinetics in seeded SBT thin films. The Avrami exponents were determined as ∼1.4 and ∼0.9 for unseeded and seeded SBT films, respectively, which reveals different nucleation modes. By using Arrhenius–type plots the activation energy values for the phase transformation of unseeded and seeded SBT thin films were determined to be ∼264 and ∼168 kJ/mol, respectively. This gives a key reason to the enhanced kinetics in seeded films. Microstructural analyses on unseeded SBT thin films showed formation of randomly oriented needle-like crystals, while those on seeded ones showed formation of domains comprised of directionally grown worm-like crystals.

THERMAL BEHAVIOR OF THE METACAOLINE-BASED MIXTURE FOR THE SYNTHESIS OF LEA ZEOLITE: THE INFLUENCE OF ULTRASONIC TREATMENT

1970 ◽  
Author(s):  
A.P. Khramtsova ◽  
V. Yu. Prokofev ◽  
N.E. Gordina ◽  
D.S. Cherednikova ◽  
E.M. Konstantinova
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Ultrasonic Treatment ◽  
Solid Phase ◽  
X Ray ◽  
Sodium Aluminosilicate ◽  
Temperature Ranges ◽  
Pre Treatment ◽  
Increasing Temperature ◽  
Ray Patterns

A study of the influence of ultrasonic treatment on the kinetics of solid-phase interaction of metakaolin with the sodium hydroxide was performed.Reflections corresponding to the zeolite LTA were observed on X-ray patterns according to phase analysis before calcination at 500°C for the sample without pre-treatment.The appearance of a new phase of sodium alumosilicate (Na6Al4Si4O17) was observed with increasing temperature to 700°C.The reflections of sodium aluminosilicate (Na8Al4Si4O18) and nepheline were detected on the X-ray pattern when the temperature calcination 800°C besides to the characteristic reflections of the zeolite.Aluminosilicates were obtained by recrystallization of the zeolitepart.Also the process was accompanied by metakaolin decomposition in silica and mullite. Reflections corresponding to the zeolite was not discovered at 900°C.According to the X-ray analysis, it was found that ultrasonic treatment has no effect on the phase composition of the samples.Based on these data, it was determined the temperature range (500-800°C).There was recrystallization of zeolite in aluminosilicates for this temperature range.According to the thermal analysis, especially the data of mass loss in a given temperature interval, the exact temperature ranges were established for each heating rate of the samples without pre-treatment and the samples after ultrasonic treatment. The Ozawa-Flynn-Wall method was selected as an isoconversional analysis.The monotonous growth of apparent activation energy was found in all range of conversion extents after ultrasonic treatment. It smoothes the change of the transition regime (up to 200 kJ/mol) to kinetic one.The apparent activation energy for the sample without ultrasonic treatment gone approximately at one level (350 kJ/mol) upon reaching the conversion extent of 0.5-0.6.The apparent activation energy increases after ultrasonic treatment from 350 to 450 kJ/mol upon reaching the conversion extent above 0.9.

The Effects of Stress on the Interdiffusion in Si1-xGex/Si Superlattices

1991 ◽  
Vol 226 ◽  
Author(s):  
S.M. Prokes
Keyword(s):  
Activation Energy ◽  
Tensile Stress ◽  
Defect Formation ◽  
External Stress ◽  
X Ray Diffraction ◽  
Strained Si ◽  
X Ray ◽  
Barrier Layers ◽  
Long Period ◽  
Kinetics Of

AbstractThe effects of grown-in stress and applied external stress on the interdiffusion behavior in long-period Si0.7Ge0.3/Si is examined using x-ray diffraction and Raman Spectroscopy. Both symmetrically and asymmetrically–strained superlattices have been examined, and an activation energy for interdiffusion of 3.9 eV and 4.6eV have been obtained, respectively. In addition, an enhanced interdiffusion has also been measured when the asymmetrically–strained superlattice was subjected to an external tensile stress during annealing. In both cases, enhanced interdiffusion has been measured whenever the Si barrier layers experience tensile stress during annealing. The Raman results indicate that enhanced Ge diffusion into the Si barriers occur when these barriers are put under tensile stress. This result will be discussed in terms of the kinetics of defect formation and motion in the strained Si barriers.

scholarly journals Crystallization kinetics of K2O·TiO2·3GeO2 glass studied by DTA

2008 ◽  
Vol 40 (3) ◽  
pp. 333-338 ◽  
Author(s):  
S. Grujic ◽  
N. Blagojevic ◽  
M. Tosic ◽  
V. Zivanovic ◽  
J. Nikolic
Keyword(s):  
Activation Energy ◽  
Thermal Analysis ◽  
Particle Size ◽  
Differential Thermal Analysis ◽  
Crystallization Kinetics ◽  
Crystallization Process ◽  
X Ray Diffraction ◽  
X Ray ◽  
Powder Samples ◽  
Kinetics Of

Crystallization kinetics of K2O?TiO2?3GeO2 glass was investigated by differential thermal analysis (DTA). Experiments were performed on powder samples with a particle size < 0.037 mm. The glass samples were heated at different rates in the temperature range 20-750?C. The kinetic parameters, activation energy for the crystallization process, Ec and Avrami exponent, n were calculated. Powder X-ray diffraction analysis (XRD) of crystallized glass reveals the presence of crystalline K2O?TiO2?3GeO2 indicating polymorphic crystallization with interface controlled crystal growth.

Kinetic mechanisms for mullite formation from sol-gel precursors

1990 ◽  
Vol 5 (9) ◽  
pp. 1963-1969 ◽  
Author(s):  
Dong X. Li ◽  
William J. Thomson
Keyword(s):  
Activation Energy ◽  
Reaction Kinetics ◽  
Single Phase ◽  
Sol Gel ◽  
Mullite Formation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffusion Controlled ◽  
Kinetic Mechanisms ◽  
Kinetics Of

The reaction kinetics for the formation of mullite (3Al2O3 · 2SiO2) from sol-gel derived precursors were studied using dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA). The reaction kinetics of diphasic and single phase gels are compared and different reaction mechanisms are found for each gel. Mullite formation in the diphasic gel exhibits an Avrami type, diffusion-controlled growth mechanism with initial mullite formation temperatures of about 1250 °C and an activation energy on the order 103 kJ/mole. On the other hand, mullite formation from the single phase gel is a nucleation-controlled process with an initial formation temperature of 940 °C and a much lower activation energy of about 300 kJ/mole.

Preparation and Properties of Rectorite/Epoxy Nanocomposites

2014 ◽  
Vol 875-877 ◽  
pp. 145-149
Author(s):  
Ting Ting Zeng ◽  
Lai Chen ◽  
Da Peng Li ◽  
Jin Liang Sun ◽  
Ze Zhou ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Organic Cation ◽  
Epoxy Composites ◽  
X Ray Diffraction ◽  
Epoxy Nanocomposites ◽  
X Ray ◽  
Working Temperature ◽  
Curing Agents ◽  
Exchange Agent

The Org-rectorite, which was used as a filler in the Rectorite/Epoxy nanocomposites, was prepared by the intercalation and exfoliation of rectorite with dodecyl-bis (2-hydroxyethyl)-methylazanium chloride as the organic cation exchange agent. The two curing agents methyl hexahydrophthalic anhydride (MHHPA) and m-phenylenediamine were employed at working temperature ranging from 70 °C to 190 °C. The samples were characterized by Fourier Transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and differential scanning calorimeter (DSC) analysis. The results show that the d001 (55.9 Å) of Rectorite/Epoxy composites cured with MHHPA at 70 °C was larger than the Org-rectorite (28.7 Å), and the Org-rectorite was exfoliated at 90 °C working temperature. While the d001 of Rectorite/Epoxy composites cured with m-phenylenediamine at 70 °C and 90 °C were 40.9 Å and 42.1 Å , and were exfoliated at 140 °C. The apparent activation energy (Ea) of Rectorite/Epoxy composites cured with MHHPA and m-phenylenediamine were obtained to be 74.85 and 59.15 KJ/mol, respectively. The higher apparent activation energy (Ea) of MHHPA systems may be responsible for the lower exfoliation temperature.

Synthesis and nucleation studies onL-leucine hydrobromide: a promising nonlinear optical material

2014 ◽  
Vol 47 (6) ◽  
pp. 1966-1974 ◽  
Author(s):  
Radha Rani ◽  
Kanika Thukral ◽  
Anuj Krishna ◽  
Geetanjali Sharma ◽  
Narayanasamy Vijayan ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Nucleation Theory ◽  
X Ray Diffraction ◽  
Nucleation Kinetics ◽  
Slow Cooling ◽  
X Ray ◽  
Nucleation Parameters ◽  
Water As Solvent ◽  
Increasing Temperature ◽  
Kinetics Of

To achieve good quality bulk size crystal growth, an assessment of the nucleation kinetics of a semi-organic L-leucine hydrobromide (L-LHBr) crystal was carried out using double-distilled water as solvent medium. The effect on metastable zone width (MSZW) with increasing temperature and on induction period with varied supersaturation level was determined experimentally and was found to be very well in accordance with the nucleation theory prospects. Thereafter, various other nucleation parameters, such as Gibbs free energy and interfacial energy, were also determined. The knowledge of these nucleation parameters indicated the requisite temperature domain and the appropriate growth technique, leading to the successful single-crystal growth of L-LHBr by slow cooling in the temperature range 298–291 K. The cooling rate of 0.25 K per day was optimized after repeated trials. X-ray diffraction and Raman analysis were performed on grown crystals for the verification of the material. High-resolution X-ray diffraction analysis was used to assess the crystalline perfection of the grown crystals. To further explore the properties of the grown crystals, photoluminescence and time decay studies, etching analysis, andZ-scan measurements were performed.

Crystallization Kinetics of Sol-gel-derived (1x)SrBi2Ta2O9–xBi3TiTaO9 Ferroelectric Thin Films

2002 ◽  
Vol 17 (6) ◽  
pp. 1463-1468 ◽  
Author(s):  
Woo-Chul Kwak ◽  
Yun-Mo Sung
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Crystallization Kinetics ◽  
Sol Gel ◽  
Avrami Exponent ◽  
X Ray Diffraction ◽  
X Ray ◽  
Isothermal Kinetic Analysis ◽  
Isothermal Kinetic ◽  
Kinetics Of

The crystallization kinetics of Sr0.7Bi2.3Ta2O9 (SBT) and 0.7SrBi2Ta2O9–0.3Bi3TiTaO9 (SBT-BTT) thin films formed by the sol-gel and spin coating techniques were studied. Phase formation and crystal growth are greatly affected by the film composition and crystallization temperature. Isothermal kinetic analysis was performed on the x-ray diffraction results of the thin films heated in the range of 730 to 760 °C at 10 °C intervals. Activation energy and Avrami exponent values were determined for the fluorite-to-Aurivillus phase transformation. A reduction of approximately 51 kJ/mol in activation energy was observed for the SBT-BTT thin films, and an Avrami exponent value of approximately 1.0 was obtained for both the SBT and SBT-BTT. A comparison is made, and the possible crystallization mechanism is discussed.

Crystallization Kinetics of MgO–Al2O3–SiO2 Transparent Glass–Ceramics

2012 ◽  
Vol 509 ◽  
pp. 230-234 ◽  
Author(s):  
Jin Shu Cheng ◽  
Jing Wang ◽  
Li Ying Tang ◽  
Zhen Lu Deng
Keyword(s):  
Activation Energy ◽  
Crystallization Kinetics ◽  
Glass Ceramics ◽  
Crystal Phase ◽  
Spinel Crystal ◽  
X Ray Diffraction ◽  
Isothermal Crystallization Kinetics ◽  
X Ray ◽  
Spinel Mgal2o4 ◽  
Kinetics Of

The non-isothermal crystallization kinetics of the MgO–Al2O3–SiO2 (MAS) glasses were analyzed with the Kissinger equation and the Augis-Bennett equation by differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that two crystal phases of spinel (MgAl2O4) and SiO2 were generated sequentially in the heat treatment process. When the spinel was the only crystal phase, the MAS glass-ceramic was transparent. For glass A (containing one type alkali metal Na2O), the corresponding activation energy was Ep1(A)=325.27kJ/mol, Ep2(A)=364.99kJ/mol; for glass B (containing Na2O and K2O) , the activation energy is Ep1(B)=233.79kJ/mol, Ep2(B)=273.85kJ /mol. The average crystallization index for spinel crystal phase was nA1=1.99, nB1=2.58, By adding K+, which suggested that the spinel crystal phase precipitation have the trend to change from two-dimensional pattern to bulk crystallization.

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