Influence Of Water Vapor Pressure Research Articles

Influence of water vapour pressure on the carbonation process of calcium monosulfoaluminate 12-hydrate

Influence of water vapour pressure on the carbonation process of calcium monosulfoaluminate 12-hydrate

Anomalous behavior of mannitol hemihydrate: Implications on sucrose crystallization in colyophilized systems.

When solutions containing mannitol and sucrose are freeze-dried, depending on the processing conditions and the formulation composition, mannitol can crystallize in the anhydrous form, as mannitol hemihydrate (MHH; C6H14O6·0.5H2O) or as a mixture of the two. The retention of MHH in the final lyophile, and its dehydration during product storage could lead to instability of the final drug product. Our aim was to determine the influence of water vapor pressure on the kinetics of MHH dehydration and the implications on the physical stability of sucrose. Therefore, the lyophiles were exposed to a range of relative humidities (RH) and the kinetics of MHH dehydration and sucrose crystallization were monitored by X-ray diffractometry. A second set of vials (rubber stoppers fitted with humidity/temperature sensor) were stored at 40°C, the headspace RH was continually recorded and water content was determined by Karl Fischer titrimetry. The dehydration rate of MHH increased as a function of water vapor pressure, an anomalous behavior explained by the Smith-Topley effect. An increase in headspace RH and decrease in lyophile water content in sealed vials attributed to MHH dehydration, eventually triggered sucrose crystallization. There was also evidence of moisture transfer from the lyophile to the rubber stoppers.

The effect of Fe doping on the electrical conductivities of CaZrO3 and its sensing performance in limiting current oxygen sensor

CaZr1-xFexO3 (x = 0, 0.1, 0.2 and 0.3) solid solutions were synthesized by solid state reaction method. Crystalline structure, microstructure, density, thermal analysis, electronic conductivity and total conductivity were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, thermogravimetric analysis (TG), Hebb-Wagner and DC van der Pauw method, respectively, and the effect of Fe content on the above properties was investigated. Sensing characteristics of a limiting current oxygen sensor with CaZr0.7Fe0.3O3 dense diffusion barrier and YSZ solid electrolyte including recovery time, long-term stability and the influence of water vapor pressure on the limiting current were measured and discussed. CaZr1-xFexO3 series belong to an orthorhombic perovskite structure. The Fe doped CaZrO3 samples have fine density and grains size decreases with increasing Fe content x. Electronic conductivity increases with increasing x and the CaZr0.7Fe0.3O3 sample has the highest electronic conductivity. Total conductivity increases to a maximum for the CaZr0.8Fe0.2O3 sample and then decreases as the increase of x. The recovery time of the sensor is about 100 s and water vapor pressure does not affect the limiting current.

The effect of heat and moisture coupling migration of ground structure without damp-proof course on the indoor floor surface temperature and humidity: Experimental study

The heat and moisture states of building floors without impermeable boundary construction, which affect the indoor thermal and moist environment, are determined by the heat and moisture distribution features and coupled transfer process of the under-soil and groundwater level. Previous studies based mainly on mathematical models only considered heat transfer or simplified the boundary conditions as adiabatic and impermeable, which resulted in limitations in application, specifically greater errors in shallow groundwater areas. In this paper, a scale model experiment that combined the floor, soil and groundwater was conducted to study the affected degree of the thermal and wet conditions of the floor in terms of the combined effect of soil heat and moisture transfer and indoor thermal and moist environment. The results showed that under the influence of the latent heat of vaporization, groundwater increases the floor temperature in the short term, and under the influence of water vapor pressure, groundwater decreases the relative humidity of the floor in the short term. The influence range of underground moisture source, analysis of building energy consumption effected by underground moisture source, process of ground surface hot and humid states reaching equilibrium, were discussed by numerical calculations.

Estimation of Fracture Toughness of Anisotropic Rocks by Semi-Circular Bend (SCB) Tests Under Water Vapor Pressure

In order to investigate the influence of water vapor pressure in the surrounding environment on mode I fracture toughness (K Ic) of rocks, semi-circular bend (SCB) tests under various water vapor pressures were conducted. Water vapor is one of the most effective agents which promote stress corrosion of rocks. The range of water vapor pressure used was 10−2 to 103 Pa, and two anisotropic rock types, African granodiorite and Korean granite, were used in this work. The measurement of elastic wave velocity and observation of thin sections of these rocks were performed to investigate the microstructures of the rocks. It was found that the distribution of inherent microcracks and grains have a preferred orientation. Two types of specimens in different orientations, namely Type-1 and Type-3, were prepared based on the anisotropy identified by the differences in the elastic wave velocity. K Ic of both rock types was dependent on the water vapor pressure in the surrounding environment and decreased with increasing water vapor pressure. It was found that the degree of the dependence is influenced by the orientation and density of inherent microcracks. The experimental results also showed that K Ic depended on the material anisotropy. A fracture process was discussed on the basis of the geometry of fractures within fractured specimens visualized by the X-ray computed tomography (CT) method. It was concluded that the dominant factor causing the anisotropy of K Ic is the distribution of grains rather than inherent microcracks in these rocks.

Influence of water vapor pressure on the induction period during Li 2SO 4·H 2O single crystals dehydration

The dehydration of Li 2SO 4·H 2O single crystals at 80 °C has been studied by means of both isothermal thermogravimetry at 2.6, 3.6 and 4.6 hPa of water vapor and environmental scanning electron microscope. Thermogravimetric experiments allowed the determination of induction periods. Distributions of these isoconversion induction periods for a large number of single crystals showed that increasing the water vapor pressure produced a longer induction period. Moreover, the shape of the distributions of the induction periods over a large number of single crystals changed from one mode at 2.6 hPa to two modes at 3.6 and 4.6 hPa. Using an environmental scanning electron microscope, this result could be attributed to differences in nucleation rates at edges and faces of the single crystals.

Influence of Water Vapor Pressure on Superconducting Properties of YBCO Film by TFA-MOD

We fabricated YBa2Cu3O7−x (YBCO) films on LaAlO3 (LAO) substrates using metal organic deposition of precursor solutions containing metal trifluoroacetates (TFA-MOD). The effect of water vapor pressure on the microstructure, degree of texture, and critical current of prepared YBCO films was evaluated. The firing process was performed in the water vapor pressure range from 7 to 31 kPa. According to the results of the XRD, SEM and X-ray ω scan analyses, the causes of critical properties’ change with the different water pressure were explained. The YBCO film prepared at the lower water pressure showed the low critical current because of the a–b axis grain. The films fired at 20 kPa showed the highest critical current of 3.8 MA/cm2.

Study on reaction mechanism of YBa2Cu3O7–x; film by TFA-MOD process

This paper systematically investigates the intermediate phases of YBa2Cu3O7−x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7−x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40–140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.

ＳＣＢ試験による水蒸気環境下における岩石の破壊じん性の評価

The influence of water vapor pressure of surrounding environment on fracture toughness of rock is clarified, based on the results of a series of semi-circular bend (SCB) test under various water vapor pressures. The rocks used in the test are Kumamoto andesite and Kunnum basalt, and the range of water vapor pressure is from 10-3 to 103 Pa. The results obtained in this paper are summarized as follows: 1) Elastic modulus at 60% of maximum load depends on water vapor pressure, and decreases with increasing water vapor pressure.2) Fracture toughness depends on water vapor pressure, and decreases with increasing water vapor pressure. The tendency of influence of water vapor pressure on fracture toughness is the same as that on uniaxial compressive strength or tensile strength. The relation between fracture toughness and water vapor pressure can be represented as:KIC=βp-mwhere β is a constant and -m is the slope of the approximated line on the logarithmic graph. The value m is 0.013 for Kumamoto andesite and 0.012 for Kunnum basalt, respectively.3) Based on above results for the SCB test, models for load-displacement curve and for relation between crack velocity and stress intensity factor are suggested.4) The time until fracture was calculated under the assumption of the crack velocity V= αKIn and the above equation, where α is a constant and n is stress corrosion index. It is shown that the rock mass of large n and small m should be selected to assure the stability for long term in spite of change in surrounding water vapor environment.

Chemical stability of SrCe 0.95Yb 0.05O 3− α in hydrogen atmosphere at elevated temperatures

The influence of water vapor pressure, P(H 2O), on chemical stability of SrCe 0.95Yb 0.05O 3− α under hydrogen atmosphere was investigated using XRD and Raman spectroscopy. From an XRD study, a second phase assigned to Sr 2CeO 4 was observed under strongly reducing conditions such as dry H 2 with P(H 2O)=4.6×10 Pa [ P(O 2)=3.1×10 −15 Pa] at 1273 K. From Raman spectroscopy, it was found that treated specimens under hydrogen atmosphere exhibited additional Raman bands, which may be assigned to the second phase. The relative intensity of the additional Raman band at 460 cm −1 drastically increased with decreasing P(H 2O) in the region P(H 2O)<7.0×10 2 Pa (2 °C sat.), whereas it was quite low in the region P(H 2O)>7.0×10 2 Pa [ P(O 2)>3.0×10 −14 Pa] at 1273 K. The perovskite phase proved to be stable against hydrogen with an increase in P(H 2O) or a decrease in temperature.

Role of precursor compaction and water vapour pressure during synthesis of corundum insupercritical water

The present paper is devoted to studying the influence of water vapour pressure on theα-Al2O3 phase nucleation process and on the size distribution and doping level of thesynthesized fine crystalline corundum. The effect of preliminary compaction ofprecursors and pressure variation on the corundum synthesis process in watervapour was also investigated. The products of synthesis were studied by variousphysical and chemical methods. It was found that the rise of water vapour pressureduring synthesis leads to diminution of the concentration of nucleation centres andpromotes increase of the corundum crystal size. The higher the pressure the moreperfect the corundum crystals that are formed, having lower concentration ofdefects.

Controlled Rate Thermal Analysis of kaolinite dehydroxylation: effect of water vapour pressure on the mechanism

The present kinetic study is focused on one aspect of kaolinite dehydroxylation, namely the influence of water vapour pressure in the 10 −3 to 5 hPa range and in the presence of crystalline defects. The experimental problem of keeping, throughout the dehydroxylation, the pressure gradients negligible around and within the sample is solved by means of Controlled Rate Evolved Gas Detection (CR-EGD). The dehydroxylation rate selected is as low as 0.014 h −1 (which corresponds to a duration of 70 h for the whole experiment). Moreover, more than 20 independent measurements of the apparent Arrhenius energy of activation are carried out all along the dehydroxylation, with help of the rate–jump method, and therefore, without any assumption about the rate law of the determining step. In these conditions, the apparent Arrhenius energy of activation measured during the dehydroxylation of a poorly crystallised kaolinite is shown to be constant in the range 0.02< α<0.84 (under 10 −3 hPa) and in the range 0.18< α<0.80 (under 5 hPa), indicating that the rate law obeys the Arrhenius law in this range of extent of reaction. The corresponding activation energies obtained are (233±15) kJ/mol under 10 −3 hPa and only (188±10) kJ/mol under 5 hPa. Although this decrease is in contradiction with previously published results, it can be interpreted by considering that, under 10 −3 hPa, diffusion is the limiting step whereas, under 5 hPa, the part of water desorption probably becomes predominant.

Control of the Dehydration Process in Production of Intermediate-Moisture Meat Products: A Review

IM meat products are produced by lowering the aw to 0.90 to 0.60. Such products are stable at ambient temperature and humidity and are produced in nearly every country in the world, especially in developing areas where refrigeration is limited or unavailable. Traditionally IM meats use low cost sources of energy for drying, such as sun drying, addition of salt, or fermentation. Products produced by different processes are of interest since they do not require refrigeration during distribution and storage. Many different IM meat products can be produced by utilizing modern processing equipment and methods. Production can be achieved in a relatively short period of time and their advantages during marketing and distribution can be utilized. Nevertheless, a better understanding of the principles involved in heat transfer and efficiency of production are still needed to increase efficiency of processing. A basic understanding of the influence of water vapor pressure and sorption phenomena on water activity can materially improve the efficiency of drying of IM meats. Predrying treatments, such as fermentation and humidity control, can also be taken advantage of during the dehydration process. Such information can lead to process optimization and reduction of energy costs during production of IM meats. The development of sound science-based methods to assure the production of high-quality and nutritious IM meats is needed. Finally, such products also must be free of pathogenic microorganisms to assure their success in production and marketing.

Surface nucleation and anisotropic growth model for the dehydration of 11-aminoundecanoic acid dihydrate

The experimental results of the title reaction were modeled as a nucleation and growth process. Nucleation is restricted to the lateral faces of the platelets of the parent hydrate (space group Cc), and growth is anisotropic, two rate constants (for lateral and normal growth) being introduced. The results are compared with the empirical description given by Avrami's equation, and shown to rationalize the data adequately. In particular, the influence of water vapor pressure is discussed.

Effect of climate on plant evaporation coefficients for the potato crop

The plant evaporation coefficient, k vm, is defined as the ratio of upper limit plant evaporation to reference crop (short grass surface) evaporation. Variations in k vm for a potato crop were shown to be due to the combined and varying influence of water vapour pressure, ambient temperature, radiation and wind speed. A multiple linear regression model for predicting k vm from these weather elements was developed. The coefficient of determination ( r 2) was 0.81 significant at the 0.1% confidence level, with a standard error of estimate of 0.19. Climatic adjustments to evaporation coefficients for other field crops, were also proposed.

Influence of water vapour on high-temperature oxidation of Al2O3-MgO-doped hot-pressed silicon nitride

Abstract Silicon nitride is particularly sensitive to high-temperature oxidation. The intensity of oxidation is influenced by the chemical composition of the amorphous phases present at the grain boundaries and consequently by the sintering additives responsible for their formation. The presence of water vapour increases Si 3 N 4 oxidation also in intermediate temperature conditions. In this study the influence of water vapour pressure at high temperature (1200°C) on the corrosion of hot-pressed silicon nitride (HPSN) doped with Al 2 O 3 -MgO was evaluated. The water vapour has a great influence on the devitrification of the amorphous oxide upper layer, due to the formation of crystalline oxides (primarily cristobalite and tridymite). This process increases the oxidation rate, consequently increasing the porosity of the exposed surface. The microstructural evolution of HPSN in the presence of water vapour at 1200°C was analysed by SEM and XRD.

Study of thermal dehydration of Co [formula omitted]Mg [formula omitted](H 2PO 4) 2·3H 2O

The dehydration and condensation reactions that take place during calcination of Co 1 2 Mg 1 2 (H 2PO 4) 2·3H 2O have been followed by means of thermal analyses under non-isothermal (dynamic) and quasi-isothermal-isobaric conditions. Isothermal calcination of starting binary dihydrogenphosphate was carried out in an electric oven at various temperatures and water vapour pressures. The reaction intermediates and products obtained were analysed by instrumental analytical methods and extraction experiments with solutions of water, acetone and 0.3 M HCl. Results have been obtained on the influence of water vapour pressure on the course, rate and yield of the condensation reactions and on the formation of the main product considered here, binary cyclo-tetraphosphate (tetrametaphospate) c-CoMgP 4O 12.

Fracture mechanics and surface chemistry studies of subcritical crack growth in AISI 4340 steel

Coordinated fracture mechanics and surface chemistry experiments were carried out to develop further understanding of environment enhanced subcritical crack growth in high strength steels. The kinetics of crack growth were determined for an AISI 4340 steel (tempered at 204°C) in hydrogen and in water, and the kinetics for the reactions of water with the same steel were also determined. A regime of rate limited (Stage II) crack growth was observed in each of the environments. Stage II crack growth was found to be thermally activated, with an apparent activation energy of 14.7 ±2.9 kJ/mole for crack growth in hydrogen, and 33.5 ± 5.0 kJ/mole in water. Fractographic evidence indicated that the fracture path through the microstructure was the same for these environments, and suggested hydrogen to be the embrittling species for environment enhanced crack growth in hydrogen and in water/water vapor. A slow step in the surface reaction of water vapor with steel was identified, and exhibited an activation energy of 36 ± 14 kJ/ mole. This reaction step was identified to be that for the nucleation and growth of oxide. The hydrogen responsible for embrittlement was presumed to be produced during this reaction. On the basis of a comparison of the activation energies, in conjunction with other supporting data, this slow step in the water/metal surface reaction was unambiguously identified as the rate controlling process for crack growth in water/water vapor. The inhibiting effect of oxygen and the influence of water vapor pressure on environment enhanced subcritical crack growth were considered. The influence of segregation of alloying and residual impurity elements on crack growth was also considered.

ChemInform Abstract: EFFECT OF WATER VAPOR ON SODIUM VAPORIZATION FROM TWO SILICA‐BASED GLASSES

AbstractIn einer speziellen Transpirationsapparatur wird der Einfluß des H2O‐Dampfdruckes auf die Gleichgewichts‐Na‐Dampfdichten über gut gerührten Glasschmelzen (25% Na2O + 75% SiO2 und 74 SiO2 + 16 N320 + 10 CaO) untersucht.

Effect of Water Vapor on Sodium Vaporization from Two Silica‐Based Glasses

The influence of water vapor pressure on the equilibrium sodium vapor densities over well‐stirred silica‐based glass melts was investigated. Sodium was assumed to be present in the vapor as Na and NaOH molecules, and the activity of Na.O in the melt was calculated as a function of water vapor pressure above the melt.