scholarly journals Kinetics and Mechanism of the Dehydration of Calcium Sulfate Dihydrate: A Comprehensive Approach for Studying the Dehydration of Ionic Hydrates under Controlled Temperature and Water Vapor Pressure

2020 ◽  
Vol 124 (48) ◽  
pp. 26352-26367
Author(s):  
João G. D. Preturlan ◽  
Laetitia Vieille ◽  
Sara Quiligotti ◽  
Loïc Favergeon
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Calcium Sulfate ◽  
Water Vapor Pressure ◽  
Kinetics And Mechanism ◽  
Comprehensive Approach ◽  
Calcium Sulfate Dihydrate

EFFECT OF WATER VAPOR ON THE FORMATION OF MODIFICATIONS

1965 ◽  
Vol 43 (9) ◽  
pp. 2522-2529 ◽  
Author(s):  
R. A. Kuntze
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Atmospheric Pressure ◽  
Calcium Sulfate ◽  
Water Vapor Pressure ◽  
Exothermic Peak ◽  
Vapor Pressures ◽  
Ambient Water ◽  
Rate Of Heating ◽  
Calcium Sulfate Hemihydrate

The two recognized forms of calcium sulfate hemihydrate can be identified by the position of a relatively small exothermic peak in their differential thermograms. Hemihydrates prepared at various water vapor pressures up to 760 mm Hg were found to produce this exothermic peak in a position which is characteristic for the β-form. These results indicate that α-hemihydrate cannot be made at atmospheric pressure, as was previously suggested on the basis of heat solution measurements. The typical differential thermogram of α-hemihydrate is only obtained with material made by dehydration in solution or by autoclaving. The effect of ambient water vapor pressure on the position of the three peaks that occur in the differential thermogram of CaSO4•2H2O has also been studied. It was found that the incipient temperature of the second endothermic peak, corresponding to the transition of hemihydrate to soluble anhydrite, is displaced independent of the rate of heating from 145 °C to 187 °C with increasing water vapor pressures up to 760 mm Hg. This indicates that, for each temperature, a threshold water vapor pressure exists, above which soluble anhydrite cannot be formed.

Geometrical Constraints of Thermal Dehydration of β-Calcium Sulfate Hemihydrate Induced by Self-Generated Water Vapor

2021 ◽  
Author(s):  
Shun Iwasaki ◽  
Yuto Zushi ◽  
Nobuyoshi Koga
Keyword(s):  
Water Vapor ◽  
Calcium Sulfate ◽  
Reaction Pathway ◽  
Water Vapor Pressure ◽  
Atmospheric Condition ◽  
Thermal Dehydration ◽  
Reaction Behavior ◽  
Calcium Sulfate Dihydrate ◽  
Geometrical Constraints ◽  
Calcium Sulfate Hemihydrate

The thermal dehydration of calcium sulfate dihydrate exhibits complex reaction behavior, in which the reaction pathway and kinetics vary depending on water vapor pressure (p(H2O)) applied as the atmospheric condition...

scholarly journals Water vapor pressure trends in south and southwest Iran

MAUSAM ◽  
2021 ◽  
Vol 68 (2) ◽  
pp. 335-348
Author(s):  
YOUNES KHOSRAVI ◽  
HASAN LASHKARI ◽  
HOSEIN ASAKEREH
Keyword(s):  
Time Series ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Water Vapor Pressure ◽  
Sen’S Slope Estimator ◽  
Sen’S Slope ◽  
Ground Station ◽  
Mk Test ◽  
Slope Estimator ◽  
The Persian Gulf

Recognitionanddetectionofclimaticparameters inhave animportant role inclimate change monitoring. In this study, the analysis of oneofthe most importantparameters, water vapor pressure (WVP), was investigated. For this purpose, two non-parametric techniques, Mann-Kendall and Sen's Slope Estimator, were used to analyze the WVP trend and to determine the magnitude of the trends, respectively. To analyze these tests, ground station observations [10 stations for period of 44 years (1967-2010)] and gridded data [pixels with the dimension of 9 × 9 km over a 30-year period (1981-2010)] in South and SouthwestofIran were used. By programming in MATLAB software, the monthly, seasonal and annual WVP time series were extracted and MK and Sen's slope estimator tests were done. The results of monthly MK test on ground station observations showed that the significant downward trends are more considerable than significant upward trends. It also showed that the WVP highest frequency was more in warm months, April to September and the highest frequency of significant trends slope was in February and May. The spatial distribution of MK test of monthly gridded WVP time series showed that the upward trends were detected mostly in western zone and near the Persian Gulf in August. On the other hand, the downward trends through months. The maximum and minimum values of positive trends slope occurred in warm months and cold months, respectively. The analysis of the MK test of the annual WVP time series indicated the upward significant trends in the southeast and southwest zones of study area.  

Temperature and Water Vapor Pressure Effects on the Friction Coefficient of Hydrogenated Diamondlike Carbon Films

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Pamela L. Dickrell ◽  
N. Argibay ◽  
Osman L. Eryilmaz ◽  
Ali Erdemir ◽  
W. Gregory Sawyer
Keyword(s):  
Water Vapor ◽  
Friction Coefficient ◽  
Vapor Pressure ◽  
Water Vapor Pressure ◽  
Carbon Film ◽  
Transient Behavior ◽  
Carbon Films ◽  
Pressure Effects ◽  
Diamondlike Carbon ◽  
Gas Surface Interactions

Microtribological measurements of a hydrogenated diamondlike carbon film in controlled gaseous environments show that water vapor plays a significant role in the friction coefficient. These experiments reveal an initial high friction transient behavior that does not reoccur even after extended periods of exposure to low partial pressures of H2O and O2. Experiments varying both water vapor pressure and sample temperature show trends of a decreasing friction coefficient as a function of both the decreasing water vapor pressure and the increasing substrate temperature. Theses trends are examined with regard to first order gas-surface interactions. Model fits give activation energies on the order of 40 kJ/mol, which is consistent with water vapor desorption.

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