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.

scholarly journals Characterization of MgSO4 Hydrate for Thermochemical Seasonal Heat Storage

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
V. M. van Essen ◽  
H. A. Zondag ◽  
J. Cot Gores ◽  
L. P. J. Bleijendaal ◽  
M. Bakker ◽  
...  
Keyword(s):  
Water Vapor ◽  
Built Environment ◽  
Vapor Pressure ◽  
Atmospheric Pressure ◽  
Heat Storage ◽  
Storage System ◽  
Water Vapor Pressure ◽  
Salt Hydrates ◽  
Seasonal Heat

Water vapor sorption in salt hydrates is one of the most promising means for compact, low loss, and long-term storage of solar heat in the built environment. One of the most interesting salt hydrates for compact seasonal heat storage is magnesium sulfate heptahydrate (MgSO4⋅7H2O). This paper describes the characterization of MgSO4⋅7H2O to examine its suitability for application in a seasonal heat storage system for the built environment. Both charging (dehydration) and discharging (hydration) behaviors of the material were studied using thermogravimetric differential scanning calorimetry, X-ray diffraction, particle distribution measurements, and scanning electron microscope. The experimental results show that MgSO4⋅7H2O can be dehydrated at temperatures below 150°C, which can be reached by a medium temperature (vacuum tube) collector. Additionally, the material was able to store 2.2 GJ/m3, almost nine times more energy than can be stored in water as sensible heat. On the other hand, the experimental results indicate that the release of the stored heat is more difficult. The amount of water taken up and the energy released by the material turned out to be strongly dependent on the water vapor pressure, temperature, and the total system pressure. The results of this study indicate that the application of MgSO4⋅7H2O at atmospheric pressure is problematic for a heat storage system where heat is released above 40°C using a water vapor pressure of 1.3 kPa. However, first experiments performed in a closed system at low pressure indicate that a small amount of heat can be released at 50°C and a water vapor pressure of 1.3 kPa. If a heat storage system has to operate at atmospheric pressure, then the application of MgSO4⋅7H2O for seasonal heat storage is possible for space heating operating at 25°C and a water vapor pressure of 2.1 kPa.

scholarly journals Characterization of hydroxyapatite laser ablation plumes by fast intensified CCD-imaging

1995 ◽  
Vol 10 (2) ◽  
pp. 473-478 ◽  
Author(s):  
P. Serra ◽  
J. Palau ◽  
M. Varela ◽  
J. Esteve ◽  
J.L. Morenza
Keyword(s):  
Water Vapor ◽  
Laser Ablation ◽  
Vapor Pressure ◽  
Water Vapor Pressure ◽  
Laser Pulses ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Vapor Pressures ◽  
Ccd Imaging ◽  
193 Nm

ArF excimer laser pulses (193 nm, 20 ns, 150 mJ) have been focused on a hydroxyapatite (HA) target in similar conditions to those normally used for thin film deposition. Fast intensified CCD images of HA laser ablation plumes have been taken in vacuum and under different water vapor pressures ranging from 0.01 mbar to 1 mbar. Images of HA ablation in vacuum have shown a plume freely expanding at a constant velocity of 2.3 × 106 cm/s. HA ablation under a water vapor pressure of 0.01 mbar has revealed an expansion behavior very similar to that of ablation in vacuum. Images taken under a water vapor pressure of 0.1 mbar have shown the formation of a shock structure in the plume. Finally, HA ablation under a water vapor pressure of 1 mbar has revealed the development of some irregularities in the shape of the plume.

THE LOW PRESSURE DEHYDRATION OF MAGNESIUM SULPHATE HEPTAHYDRATE AND COBALTOUS CHLORIDE HEXAHYDRATE

1956 ◽  
Vol 34 (5) ◽  
pp. 591-599 ◽  
Author(s):  
R. W. Ford ◽  
G. B. Frost
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Magnesium Sulphate ◽  
Copper Sulphate ◽  
Water Vapor Pressure ◽  
Adsorbed Water ◽  
Vapor Pressures ◽  
Cobaltous Chloride ◽  
Chloride Hexahydrate ◽  
Initial Drop

Rates of dehydration under vacuum, and at a series of controlled water vapor pressures, have been carried out for powdered samples of magnesium sulphate heptahydrate and of cobaltous chloride hexahydrate. It has been found for the magnesium salt that as the pressures are increased, the rate at first drops rapidly, this decrease being followed by a period of acceleration which is followed in turn by a decline. The curves are similar to those previously reported for copper sulphate pentahydrate, but the changes occur over a much wider range of water vapor pressures. In the dehydration of cobaltous chloride hexahydrate the initial drop in rate with increase in water vapor pressure is not observed. The results are interpreted in terms of the crystallization of intermediate products in the presence of adsorbed water.

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO4•2H2O

1964 ◽  
Vol 42 (4) ◽  
pp. 792-801 ◽  
Author(s):  
H. G. McAdie
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Water Vapor Pressure ◽  
Vapor Pressures ◽  
Heat Of Solution ◽  
Temperature Dependent ◽  
Exponential Factor ◽  
Fixed Composition ◽  
Kinetics Of ◽  
Partial Water

Kinetics of the two-stage dehydration of CaSO4•2H2O have been examined under controlled water vapor pressures up to one atmosphere. For both stages water vapor initially accelerated the rate of dehydration and subsequently retarded it. Separate, temperature-dependent water vapor pressures were noted above which each stage could be suppressed.The hemihydrate was clearly defined either as a change in the rate of weight loss during dehydration or, at higher water vapor pressures, as a fixed composition. The heat of solution of the hemihydrate increased linearly with the partial water vapor pressure present during its formation, but was independent of the formation temperature over the range studied. Activation energy and pre-exponential factor for the dihydrate → hemihydrate process also increased linearly with water vapor pressure. Hemihydrates produced at the extremes of water vapor pressure corresponded to the α- and β-modifications, as defined thermodynamically, and the production of a hemihydrate series with properties varying linearly from one extreme to the other is discussed.

Physiologically derived critical evaporative coefficients for protective clothing ensembles

1987 ◽  
Vol 63 (3) ◽  
pp. 1095-1099 ◽  
Author(s):  
W. L. Kenney ◽  
D. A. Lewis ◽  
D. E. Hyde ◽  
T. S. Dyksterhouse ◽  
C. G. Armstrong ◽  
...  
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Protective Clothing ◽  
Water Vapor Pressure ◽  
Radiant Heat ◽  
Ambient Water ◽  
External Work ◽  
Metabolic Heat ◽  
Physiological Approach ◽  
Sweating Efficiency

When work is performed in heavy clothing, evaporation of sweat from the skin to the environment is limited by layers of wet clothing and air. The magnitude of decrement in evaporative cooling is a function of the clothing's resistance to permeation of water vapor. A physiological approach has been used to derive effective evaporative coefficients (he) which define this ability to evaporate sweat. We refined this approach by correcting the critical effective evaporative coefficient (K for sweating efficiency (Ke,eta') since only a portion of the sweat produced under such conditions is evaporated through the clothing. Six acclimated men and women walked at 30% maximal O2 consumption (150–200 W.m-2) at a constant dry bulb temperature as ambient water vapor pressure was systematically increased 1 Torr every 10 min. Critical pressure was defined as the partial pressure of water vapor (Pw) at which thermal balance could no longer be maintained and rectal temperature rose sharply. Each test was performed in various clothing ensembles ranging from cotton shirt and pants to “impermeable” suits. This approach was used to derive he by solving the general heat balance equation, M - W +/- (R + C) = w.he.(Psk - Pw), where M is metabolic heat production, W is external work, R is radiant heat exchange, C is convective heat transfer, w is skin wettedness, and Psk is water vapor pressure of fully wet skin.(ABSTRACT TRUNCATED AT 250 WORDS)

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...

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