Kinetics of hexagonal–cubic phase transformation of zinc sulfide in vacuo, in zinc vapor, and in sulfur vapor

1968 ◽  
Vol 46 (18) ◽  
pp. 2881-2886 ◽  
Author(s):  
Tamas Bansagi ◽  
E. A. Secco ◽  
O. K. Srivastava ◽  
Ronald R. Martin
Keyword(s):  
Phase Transformation ◽  
Zinc Sulfide ◽  
Solid Phase ◽  
Cubic Phase ◽  
Transformation Rate ◽  
Zinc Vapor ◽  
Sulfur Vapor ◽  
Diffusion Controlled ◽  
Transformation Reaction ◽  
Kinetics Of

The kinetics of the hexagonal–cubic phase transformation of zinc sulfide have been studied in vacuo, in zinc vapor, and in sulfur vapor in the temperature range 800–900 °C by a powder X-ray diffraction technique. The transformation rate is enhanced in the presence of sulfur and zinc vapor. In vacuo and in sulfur vapor the reaction is nucleation-controlled with activation energies of 95.0 and 98.5 ± 5 kcal, respectively. In zinc vapor the reaction is diffusion-controlled with the diffusion coefficient expressed as[Formula: see text]The modes of catalytic action by sulfur and zinc vapor on the solid phase transformation reaction are discussed.

scholarly journals Phase Transformation Kinetics of a FCC Al0.25CoCrFeNi High-Entropy Alloy during Isochronal Heating

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1015
Author(s):  
Jun Wang ◽  
Chen Wei ◽  
Haoxue Yang ◽  
Tong Guo ◽  
Tingting Xu ◽  
...  
Keyword(s):  
Phase Transition ◽  
Activation Energy ◽  
Phase Transformation ◽  
High Entropy Alloy ◽  
Transformation Kinetics ◽  
High Entropy ◽  
Phase Transformation Kinetics ◽  
Diffusion Controlled ◽  
Thermal Dilation ◽  
Kinetics Of

The phase transformation kinetics of a face-centered-cubic (FCC) Al0.25CoCrFeNi high-entropy alloy during isochronal heating is investigated by thermal dilation experiment. The phase transformed volume fraction is determined from the thermal expansion curve, and results show that the phase transition is controlled by diffusion controlled nucleation-growth mechanism. The kinetic parameters, activation energy and kinetic exponent are determined based on Kissinger–Akahira–Sunose (KAS) and Johnson–Mehl–Avrami (JMA) method, respectively. The activation energy and kinetic exponent determined are almost constant, indicating a stable and slow speed of phase transition in the FCC Al0.25CoCrFeNi high-entropy alloy. During the main transformation process, the kinetic exponent shows that the phase transition is diffusion controlled process without nucleation during the transformation.

GAS–SOLID EXCHANGE REACTIONS: ZINC VAPOR AND POLYCRYSTALLINE ZINC SULPHIDE

1964 ◽  
Vol 42 (6) ◽  
pp. 1396-1400 ◽  
Author(s):  
E. A. Secco
Keyword(s):  
Zinc Sulphide ◽  
Static System ◽  
Zinc Vapor ◽  
Exchange Reactions ◽  
Polycrystalline Zinc ◽  
Diffusion Controlled ◽  
Fraction Versus ◽  
Exchange Kinetics ◽  
Kinetics Of ◽  
Initial Process

The exchange kinetics of zinc vapor with polycrystalline zinc sulphide, wurtzite structure, have been studied in a static system in the temperature range 720–960 °C.Plots of log10(1−α*), i.e. exchange fraction, versus time reveal two processes. The initial process is a rapid simple exchange, for which the data fit a first-order rate law and which persists to a depth of 15–18 molecular thicknesses. At this depth the second, slower process, which appears to be diffusion-controlled, sets in. Kinetic and structural interpretations of these results along with the existing data on Zn–ZnO exchange are discussed.

scholarly journals Study on the Phase Transformation Kinetics of Sol-Gel DrivedTiO2Nanoparticles

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
H. Mehranpour ◽  
M. Askari ◽  
M. Sasani Ghamsari ◽  
H. Farzalibeik
Keyword(s):  
Activation Energy ◽  
Phase Transformation ◽  
Sol Gel ◽  
Rutile Phase ◽  
Transformation Kinetics ◽  
X Ray ◽  
Prepared Nanoparticles ◽  
Phase Transformation Kinetics ◽  
Diffusion Controlled ◽  
Kinetics Of

Titanium dioxide nanopowders were synthesized by the diffusion controlled sol-gel process (LaMer model) and characterized by DTA-TG, XRD, and SEM. The preparedTiO2nanoparticles have uniform size and morphology, and the phase transformation kinetics of obtained material was studied by interpretation of the X-ray diffraction patterns peaks on the base of Avrami equation. The stating point of anatase-rutile phase transformation temperature in the prepared nanoparticles was found between 100 and200°C. A decreasing trend on the intensity of X-ray peaks of anatase phase was observed up to600°Cwhen the presence of the rutile phase became predominant. Results indicated that the transition kinetics of the diffusion controlled prepared nanoparticles was begun at low temperature, and it can be concluded that the nucleation and growth sites in these particles were more than other. However, it has been found that the nucleation activation energy of rutile phase was 20 kj/mol, and it is the lowest reported activation energy.

Gas–solid exchange reactions: Zinc vapor and polycrystalline zinc selenide

1968 ◽  
Vol 46 (10) ◽  
pp. 1621-1624 ◽  
Author(s):  
E. A. Secco ◽  
Chien-Huo Su
Keyword(s):  
Zinc Selenide ◽  
Static System ◽  
Zinc Vapor ◽  
Exchange Reactions ◽  
Polycrystalline Zinc ◽  
Diffusion Controlled ◽  
Initial Stage ◽  
Exchange Kinetics ◽  
Kinetics Of ◽  
Exchange Data

The exchange kinetics of zinc vapor with polycrystalline zinc selenide have been studied in a static system in the temperature range 720–800 °C.The kinetic data are consistent with a diffusion-controlled process from the initial stage, in contrast with existing exchange data on ZnO and ZnS powders. The diffusion equation is given as:[Formula: see text]

scholarly journals Quench Sensitivity and Phase Transformation Kinetics of AlSi7MnMg High Pressure Vacuum Die Casting

2020 ◽  
Vol 326 ◽  
pp. 02001
Author(s):  
Mengyun Liu ◽  
Zhan Zhang ◽  
Francis Breton ◽  
X.-Grant Chen
Keyword(s):  
High Pressure ◽  
Phase Transformation ◽  
Mechanical Strength ◽  
Isothermal Treatment ◽  
Transformation Rate ◽  
Temperature Property ◽  
Quench Sensitivity ◽  
Transformation Diagrams ◽  
Nose Temperature ◽  
Kinetics Of

The quench sensitivity of an AlSi7MnMg alloy in high-pressure vacuum die (HPVD) casting was investigated by time-temperature-transformation and time-temperature-property diagrams with an interrupted quench technique. The quench sensitive temperature range of the alloy is from 260 to 430 °C and its nose temperature is 350 °C. The mechanical strength versus cooling rates of the HPVD casting was predicted using quench factor analysis method and verified by experimental results. The critical cooling rate is 6 °C/s to remain 95% of the maximal mechanical strength. The coefficients k2 - k5, related to the nucleation and precipitation kinetics of TTP curves, and phase transformation diagrams were determined. The precipitation of Mg2Si phase in the castings was observed during isothermal treatment using transmission electron microscope. Moreover, the quench sensitivity and kinetics of the phase transformation of AlSi7MnMg alloy and AlSi10MnMg alloys were compared. It reveals that the quench sensitivity and phase transformation rate of the former are lower than that of the latter.

NUCLEATION AND GROWTH OF A SOLID PHASE IN A GAS EXPANDING INTO VACUUM

2007 ◽  
Vol 18 (04) ◽  
pp. 676-684 ◽  
Author(s):  
NIKOLAI V. BRILLIANTOV ◽  
JÜRGEN SCHMIDT ◽  
FRANK SPAHN
Keyword(s):  
Growth Rate ◽  
Phase Transformation ◽  
Homogeneous Nucleation ◽  
Solid Phase ◽  
Saturated Vapor ◽  
Nucleation And Growth ◽  
Gas Kinetic Theory ◽  
Long Channel ◽  
Kinetics Of ◽  
New Phase

We study kinetics of homogeneous nucleation in over-saturated vapor expanding from a reservoir through a long channel into vacuum. Assuming adiabatic conditions for the gas, we derive an equation of state which accounts for the phase transformation of vapor into the condensed phase. To describe the growth rate of particles of the new phase gas kinetic theory is employed. We find the size-distribution of these particles, the temperature and flux velocity along the channel. Calculations are performed for the particular case of water vapor expanding to vacuum from its equilibrium state at the triple point. These conditions correspond presumably to the formation of the gas-dust plume, recently detected at Enceladus – the icy moon of Saturn. Our results, therefore, shed some light on this interesting astrophysical phenomenon.

In situ TEM studies of the effect of misfit strain on the kinetics of sil-xgex solid phase epitaxy: temperature calibration & surface effects

1992 ◽  
Vol 50 (2) ◽  
pp. 1344-1345
Author(s):  
David C. Paine ◽  
David J. Howard ◽  
N.D. Evans
Keyword(s):  
Solid Phase ◽  
Misfit Strain ◽  
Alloy Layer ◽  
In Situ Tem ◽  
Transformation Rate ◽  
Solid Phase Epitaxy ◽  
Si Substrates ◽  
Kinetics Of ◽  
Annealing Experiments

While in situ TEM studies have proven useful for the direct observation of solid-state reaction mechanisms, such studies rarely provide quantitative kinetic data. This limitation is due to problems associated with the accurate measurement of local sample temperature, assessment of beam heating and damage, and minimization of thin-film effects. Sinclair et al. have proposed a technique for establishing the temperature of a sample during in situ TEM annealing experiments in which the wellcharacterized Si <001> solid phase epitaxy amorphous-crystalline (a/c) transformation rate is used to estimate the temperature in an adjacent (but not contiguous) region of the specimen. We have used this in situ technique to determine the activation energy for strained solid phase epitaxy of Sil-xGex (x=5.4, 11.6, and 17 at.%). The alloys were grown by CVD on <001> Si substrates to a thickness of approximately 200 nm. The entire alloy layer, and 180 nm of the underlying substrate, were amorphized with 100, followed by 200 keV 29Si implantation.

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