Synthesis of MgAl2O4 spinel: seeding effects on formation temperature

1991 ◽  
Vol 26 (14) ◽  
pp. 3797-3802 ◽  
Author(s):  
J. -F. Pasquier ◽  
S. Komarneni ◽  
R. Roy
Keyword(s):  
Formation Temperature ◽  
Mgal2o4 Spinel ◽  
Seeding Effects

scholarly journals Thermodynamics of Mg–Al Order-Disorder Reaction in MgAl2O4-Spinel: Constrained by Prolonged Annealing Experiments at 773–1123 K

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 872
Author(s):  
Yunlu Ma ◽  
Xinjian Bao ◽  
Xi Liu
Keyword(s):  
Spinel Structure ◽  
Structural Model ◽  
Molar Fraction ◽  
Thermodynamic Models ◽  
Mgal2o4 Spinel ◽  
Cation Order ◽  
Prolonged Annealing ◽  
Wide Range ◽  
History Of ◽  
Annealing Experiments

MgAl2O4-spinel has wide industrial and geological applications due to its special structural and physical–chemical features. It is presumably the most important endmember of complex natural spinel solid solutions, and therefore provides a structural model for a large group of minerals with the spinel structure. There exists a well known but still inadequately understood phenomenon in the structure of MgAl2O4-spinel, the Mg–Al cations readily exchanging their positions in response to variations of temperature, pressure, and composition. A large number of experiments were performed to investigate the Mg–Al cation order-disorder process usually quantified by the inversion parameter x (representing either the molar fraction of Al on the tetrahedral T-sites or the molar fraction of Mg on the octahedral M-sites in the spinel structure), and some thermodynamic models were thereby constructed to describe the x-T relation. However, experimental data at some key T were absent, so that the different performance of these thermodynamic models could not be carefully evaluated. This limited the interpolation and extrapolation of the thermodynamic models. By performing some prolonged annealing experiments with some almost pure natural MgAl2O4-spinel plates and quantifying the x values with single-crystal X-ray diffraction technique, we obtained some critical equilibrium x values at T down to 773 K. These new x-T data, along with those relatively reliable x values at relatively high T from early studies, clearly indicate that the CS94 Model (a model constructed by Carpenter and Salje in 1994) better describes the Mg–Al cation order-disorder reaction in MgAl2O4-spinel for a wide range of T. On the basis of the CS94 Model, a geothermometer was established, and its form is T-closure = 21362 × x3 − 12143 × x2 + 6401 × x − 10 (T-closure standing for the closure temperature of the Mg–Al cation exchange reaction). This geothermometer can be used to constrain the thermal history of the geological bodies containing MgAl2O4-spinel.

scholarly journals Carbon Isotope Fractionation during the Formation of CO2 Hydrate and Equilibrium Pressures of 12CO2 and 13CO2 Hydrates

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4215
Author(s):  
Hiromi Kimura ◽  
Go Fuseya ◽  
Satoshi Takeya ◽  
Akihiro Hachikubo
Keyword(s):  
Carbon Isotope ◽  
Isotope Fractionation ◽  
Small Difference ◽  
Hydrate Formation ◽  
Formation Temperature ◽  
Carbon Isotope Fractionation ◽  
Unit Cell Size ◽  
Naturally Occurring ◽  
Three Phase ◽  
The Difference

Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO2 hydrates. We investigated carbon isotope fractionation during CO2 hydrate formation and measured the three-phase equilibria of 12CO2–H2O and 13CO2–H2O systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound 12CO2 and 13CO2 was revealed, although their unit cell size was similar. The δ13C of hydrate-bound CO2 was lower than that of the residual CO2 (1.0–1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in 12CO2 and 13CO2 hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the 12CO2–H2O and 13CO2–H2O systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion.

scholarly journals Dynamic Wetting of CaO-Al2O3-SiO2-MgO Liquid Oxide on MgAl2O4 Spinel

2014 ◽  
Vol 46 (1) ◽  
pp. 208-219 ◽  
Author(s):  
Hamed Abdeyazdan ◽  
Neslihan Dogan ◽  
M. Akbar Rhamdhani ◽  
Michael W. Chapman ◽  
Brian J. Monaghan
Keyword(s):  
Dynamic Wetting ◽  
Mgal2o4 Spinel ◽  
Liquid Oxide

Effect of Ni, Bi and Se on the tetrahedrite formation

RSC Advances ◽  
2016 ◽  
Vol 6 (104) ◽  
pp. 102359-102367 ◽  
Author(s):  
António Pereira Gonçalves ◽  
Elsa Branco Lopes ◽  
Benjamin Villeroy ◽  
Judith Monnier ◽  
Claude Godart ◽  
...  
Keyword(s):  
Formation Temperature

Tetrahedrite formation is influenced positively by selenium and negatively by bismuth and nickel. However, selenium decreases the skinnerite formation temperature.

6H- AND 4H-SiC(0001) Si SURFACE RICHNESS DOSING BY HYDROGEN ETCHING: A WAY TO REDUCE THE FORMATION TEMPERATURE OF RECONSTRUCTIONS

2003 ◽  
Vol 10 (01) ◽  
pp. 55-63 ◽  
Author(s):  
M. DIANI ◽  
J. DIOURI ◽  
L. KUBLER ◽  
L. SIMON ◽  
D. AUBEL ◽  
...  
Keyword(s):  
High Temperature ◽  
Atomic Hydrogen ◽  
Room Temperature ◽  
Binary Systems ◽  
Temperature Treatment ◽  
Heating Time ◽  
High Temperature Treatment ◽  
Formation Temperature ◽  
Hydrogen Etching ◽  
Chemical Surface

In 6H- or 4H-SiC(0001) surface technology, a Si-rich 3 × 3 reconstruction is usually first prepared by heating at 800°C under Si flux, and two other most stable [Formula: see text] or [Formula: see text] reconstructions are obtained by further extensive annealing at higher temperatures ranging between 900 and 1250°C. The 3 × 3 Si excess is thus progressively depleted up to a graphitized C-rich surface. By crystallographic (LEED) and chemical surface characterizations (XPS and UPS), we show that all these reconstructions can be obtained at a unique, low formation temperature of 800°C if the Si richness is controlled before annealing. This control is achieved by exposing the 3 × 3 surface to atomic hydrogen at room temperature. This procedure allows one to etch or partially deplete the (3 × 3)-associated Si excess, and make it more comparable to the final Si coverages, required to form the less Si-rich [Formula: see text] or [Formula: see text] reconstructions. After annealing at 800°C, the latter reconstructions are no longer determined by the heating time or temperature but only by the initial Si coverage set by the H doses inducing the low temperature etching. The high temperature treatment, required to remove by sublimation a significant Si amount associated with the Si-rich 3 × 3 reconstruction, is thus avoided. Such a methodology could be applied to other binary systems in the formation of reconstructions that depends on surface richness.

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