Heat Of Immersion In Water Research Articles

Heats of immersion related to the extent of water loss and specific surface areas: SrCl 2- and BaCl 2-loaded aluminas as desiccant materials

SrCl 2- and BaCl 2-loaded aluminas were thermally dehydrated in vacuo at various temperatures in the range 20–500 °C. The water loss, specific surface area for nitrogen adsorption and the integral heat of water immersion were determined for thermally treated samples. Possible changes in the porosity of the samples investigated were studied using the V 1- t method. The model-less method was used to determine the surface locations and the area fraction located in the mesopores was calculated. This fraction indicates the surface accessibility of various samples to nitrogen adsorbate molecules and to the smaller water molecules. The integral heats of water immersion normalized to nitrogen Brunauer-Emmett-Teller surface areas were studied over the entire temperature range. The samples with the highest surface accessibility to water molecules together with relatively high heats of immersion in water were assumed to be effective dehydrating materials. It was found that SrCl 2- and BaCl 2-loaded aluminas required heat treatment at 400 °C and 300 °C respectively to optimize their use as desiccant materials. Further detailed discussion is presented.

Related surface and heat of immersion characterization of some alumina samples part III. Magnesium chloride- and calcium chloride-loaded aluminas

MgCl 2− and CaCl 2-loaded aluminas were thermally dehydrated in vacuo at different temperatures in the range of 20–500°C. Thermally treated samples were subjected to an accurate estimation of water loss and specific surface area using nitrogen as adsorbate at −195.6°C. The integral heats of water immersion were also determined. The samples under investigation were analysed using several methods: Possible changes in porosity were determined using the V a versus t method; the corrected modelless method was applied to determine surface locations and the area fraction located in wide (meso) pores was also determined. The latter denotes the surface accessibility of different samples for nitrogen adsorbate molecules (as well as for smaller water molecules). Based on integral heats of immersion in water and by normalizing these heat values to a nitrogen BET surface area basis, the heat changes along the entire temperature range could be studied. Samples having the highest surface accessibility for water molecules, which are characterized by relatively high heat of immersion, could be assumed as effective dehydrating materials. MgCl 2-loaded aluminas can be treated thermally in the temperature range of 300–400°C in order to obtain their appropriate use as a desiccant material; CaCl 2-loaded alumina has to be treated to temperatures as low as 200°C. Further discussions are given later.

Heat of immersion of silica in water

The heats of immersion of thermally treated silicas and metal modified silicas, obtained from colloidal silica, were studied in water at 298 K. Silica was heat-treated in the range 383–1273 K in air. The thermal treatment effects on the water contents, specific surface areas, and the change of crystal structure were investigated and discussed. The values of the heat of immersion in water are independent of the specific surface areas of silicas in the range 125–240 m 2 g −1. The results indicate that there is no maximum of the function: heat of immersion vs. thermal treatment temperature. Owing to the purity of the SiO 2 obtained, the change of the amorphous into the crystal structure (α-cristobalite) takes place at 1573–1673 K.

Interaction of hydrogen chloride and water with oxide surfaces: III. Titanium dioxide

Adsorption of hydrogen chloride and water vapors on five TiO 2 powders in both the anatase and rutile crystalline forms have been investigated as a function of temperature, pressure, and outgas conditions. Characterization of the adsorbents was performed using X-ray powder diffraction, scanning electron microscopy (SEM/EDAX), surface area analysis, indicator method, microelectrophoresis, XPS, and infrared spectroscopy. Water vapor adsorption isotherms at 30, 40, and 50°C and heats of immersion in water were measured on TiO 2 after outgassing at 100, 200, 300, and 400°C. Both outgas temperature and adsorption temperature influenced the adsorption of water vapor on TiO 2. Water vapor adsorption on TiO 2 was completely reversible. Differences in the adsorption capacity of water on the different titanium dioxides were explained on the basis of the number of hydroxyl groups present on the surface. Isosteric heats of adsorption of water on TiO 2 were determined as a function of surface coverage. Heats of immersion in water were affected significantly by outgas temperature. Hydrogen chloride adsorption isotherms at 30°C were measured on TiO 2 after outgassing at 100–400°C. A part of the total HCl adsorbed was irreversibly adsorbed. Anatase showed the highest HCl adsorption capacity per unit area while pure rutile showed the lowest adsorption capacity. XPS, indicator analysis, and infrared analysis after HCl adsorption further confirmed the conclusions based on adsorption. Heats of immersion of TiO 2 were higher in 0.1 N HCl (aq) than in water and the difference was greater for the alumina-coated rutiles.

Surface Characterization of Ti and Ti (6% AI-4%, V) Metal Powders and Interaction with Primer Solutions

Abstract The surfaces of Ti and Ti (6% Al-4% V) powders were characterized by several techniques. BET surface areas as a function of temperature were measured using nitrogen adsorption. Heats of immersion (δwH) of these metal powders in water were measured after evacuation over the temperature range 100°–400°C. The δwH in water increased with increasing evacuation temperature and an anomalous increase was observed between 300° and 400°C. This was attributed to exposure of water to elemental titanium by cracking of the oxide layer at 400°C. XPS analysis did not support the possibility of metal migration through the oxide layer. Higher heats of immersion in water were determined for chemically pretreated compared to untreated Ti 6–4 powders. Water vapor adsorption isotherms were measured after evacuation of the metal powders at 100°C. Partial irreversibility of the water adsorption was observed on both powders. Water adsorption on Ti was temperature dependent. Heats of immersion measurements were used to study the interaction of primer solutions with these metal powders. Polyimide (LARC-13) and polyphenylquinoxaline (PPQ) interacted preferentially compared to the solvents with both powders. This polymer-metal interaction improved significantly after pretreatment of the Ti 6–4 powder by the Turco® 5578 and phosphate-fluoride processes. Again, an anomalous increase in the heat of immersion of Ti 6–4 evacuated at 400°C in the primer solution/solvents was observed. Anatase and rutile TiO2 powders are not satisfactory models for the surface oxide layer on either Ti or Ti 6–4 powders.

Related surface and heat of immersion characterization of some alumina samples II: Water-soaked activated alumina

Soaked alumina was prepared by leaving Rhône Poulenc activated alumina in doubly distilled water for 24 h. The activated alumina was then air dried. Both processes were carried out at room temperature. The soaked alumina was thermally dehydrated in vacuo at various temperatures in the range 20–500 °C. Water losses (in grams of water per 100 g of the sample) for all the heat-treated samples were determined; it was shown that the soaked alumina samples exhibit higher water losses than those determined for the parent activated alumina samples. This was considered to be ample evidence for chemisorption and/or strong uptake of water molecules at the surface and in the pore system of the bulk alumina. Nitrogen adsorption measurements were carried out at liquid nitrogen temperature for all the samples. All the isotherms were of type II according to the classification of Emmett and Brunauer and were characterized by the occurrence of hysteresis loops. The areas of the hysteresis loops initially increased up to 200 °C; decreases in the areas of the hysteresis loops were then noted up to 400 °C. The increase in area of the hysteresis loops below 200 °C is attributed to the increased loss of physisorbed water. The decreased rate of water loss (water loss from the surface and/or structural water loss) corresponds to the observed decrease in area of the hysteresis loops up to 400 °C. Analysis suggested that the surface areas are mostly located in wide pores. The presence of some narrow pores (or micropores) was detected mainly at temperatures above 300 °C. Heat of immersion measurements were carried out using water as the immersion liquid for all the samples investigated. Despite the observed increase in water loss and nitrogen surface area for the soaked samples, the parent activated and soaked alumina samples exhibit almost the same integral heats of immersion up to 300 °C. At higher temperatures, the soaked alumina exhibited higher heats of immersion in water, which is directly related to the high extent of dehydration (or to the dehydroxylation of the surface hydroxyl groups) and the exposure of both aluminium ions (Al 3+) and oxygen anions (O 2-) to the surface, which enhance the formation of excess hydrous alumina and/or aluminium hydroxide. On calculation of the heats of immersion in water per unit area, it is found that activated alumina has higher heats of immersion up to 300 °C, whereas the soaked alumina preheated above 300 °C has higher heats of immersion because of the higher concentration of surface hydroxyl groups as well as the increased Al 3+ and O 2- ion content of these soaked samples.

Related surface and heat of immersion characterization of some alumina samples I: Rhône poulenc activated alumina

Activated alumina was thermally dehydrated in vacuo at different temperatures in the range 20 – 500 °C. Nitrogen adsorption measurements, heats of immersion in water, methanol and carbon tetrachloride, and water losses (in grams of water per 100 g of the sample) of the different heat-treated samples were estimated and correlated. Nitrogen adsorption measurements show the occurrence of type II adsorption isotherms which are characterized by hysteresis phenomena. The area of the hydteresis loop increases up to 200 °C; thereafter, it decreases with further increase temperature until 500 °C is reached. An initial increase in the area of the hysteresis loop (below 200 °C) is interpreted on the basis of the increased physisorbed water loss up to 200 °C. The decreased area of the hysteresis loop at higher temperatures (above 200 °C) is attributed to the decreased rate of water loss at these high temperatures. Water losses were found to increase abruptly between 200 and 300 °C and to increase gradually in the lower and higher temperatures range until 500 °C is reached. These changes in water loss are consistent with the changes in the heats of immersion in water, to a lesser extent with the changes in the heats of immersion in methanol and to a limited extent with the changes in the heats of immersion in carbon tetrachloride. Generally, the heats of immersion follow the order water > methanol > carbon tetrachloride; this has been related to changes in the chemistry of the alumina surface and is also discussed in relation to the porosity characteristics. From pore structure studies it was found that these samples contain both mesopores (or wide pores) and narrow pores (or micropores). After an analysis for the surface areas located in wide pores, the heats of immersion in water were found to follow the fraction of the area located in wide pores (or mesopores); this has been interpreted on the basis of a reduction in the mutual repulsions encountered between water molecules inside these mesopores or wide pores.

Heats of immersion of titania powders in primer solutions

The oxide layer present on titanium alloys can play an important role in determining the strength and durability of adhesive bonds. Here, three titania powders in different crystalline phases, rutile-R1, anatase-A1, and anatase-A2, are characterized by several techniques. These include microelectrophoresis, X-ray diffractometry, surface area pore volume analysis, X-ray photoelectron spectroscopy, and measurements of the heats of immersion. Of the three powders, R1 has the highest heat of immersion in water, while the interaction between water and A1 powder is low. Experimental data also suggest a specific preferential interaction of polyphenylquinoxaline with anatase.

Heat of immersion of iron(III) oxides in water at 25°C

The heat of immersion in water was measured at 25°C for three iron(III) oxides using a twin-type microcalorimeter. One of the samples was commercial α-Fe 2O 3 (sample C) and the other two (samples M and F) were prepared by calcining magnetite and iron(III) hydroxide in air at various temperatures, T p, from 300 to 700°C. The samples were evacuated at outgassing temperature, T o, between room temperature and 500°C at a pressure of 1 × 10 −2−2.7 × 10 −2N m −2 for 6 h. The heat of immersion, h i (J m −2), of samples C and M increased with an increase in T o and showed the maximum h i at T o =400°C, while sample F did not show the maximum up to T o =500°C. The systematic correlation was not observed between h i and T p of sample F. The heat of reproduction of the surface hydroxyl group on sample F was approximately estimated as 6.6 × 10 4 J mole −1 H 2O.

Heats of immersion of manganese nodule, manganese dioxide, and manganese-iron oxide

The heats of immersion in water and thermal desorption spectra of manganese nodule, manganese dioxide, and manganese-iron mixed oxide were measured in order to clarify the surface properties of the nodule. The heat of immersion of manganese dioxide increased with increasing pretreatment temperature from 393 to 623 K and then decreased up to 723 K, accompanied by a structure change to sesquioxide; the heat of immersion of the nodule had a maximum value at 423 K. The results of TDS showed that chemisorbed water on the nodule was evolved at lower temperature and the surface was easily stabilized compared with manganese dioxide. For the mixed oxides, the heat of immersion had a minimum value at 26% of the iron content and the temperature at which water was evolved became higher with the iron content. On the basis of these results the surface of the nodule will be discussed.

Thermal treatment of aerosil 200 silica: Induced surface porosity and surface chemistry relative to the heat of immersion in water

Silica Aerosil 200 was thermally dehydrated in vacuo in the temperature range 20 – 900 °C. The nitrogen Brunauer-Emmett-Teller (BET) surface areas and the heats of immersion in water are estimated and discussed. The changes in the surface area and the heat of immersion are related to the water content, the number of surface silanols and the average pore radius. All these changes are dependent on the pretreatment temperature. The adsorption studies show that the BET surface area and the reciprocal of the average pore radius are harmonic functions of the pretreatment temperature. The increase in the area of the hysteresis loops in the adsorption isotherms in the temperature range 110 – 480 °C indicates that there is a successive loss of water from the surface and/or the pore system which affects the heats of immersion in water. The heats of immersion in water show two maxima, one at 200 – 300 °C and the other at 480 °C. The number of surface silanols decreases over the temperature range studied. The changes in the heats of immersion are related to the surface chemistry and to the porosity induced by the thermal treatment.

Heats of immersion in relation to water losses of copper- and manganese-exchanged mordenites

Copper- and manganese-exchanged mordenites were prepared from synthetic sodium mordenite by cation-exchange technique. The samples were subjected to different heat treatments in vacuo. The accompanying changes in parameters of water loss and heat of immersion in water were determined. Generally, the integral heat of immersion changes in widely different fashions. In copper-exchanged mordenite, the decrease in integral heats above 300°C is interpreted based on an increased role of the structural collapse taking place at high dehydration temperatures, while in manganese-exchanged mordenite, the hydration effects of vacated small pockets is responsible for the increase in heats of immersion above 300°C, exceeding a less significant effect from the structural collapse.

Heats of immersion in relation to water losses of cobalt- and nickel-exchanged mordenites

Cobalt- and nickel-exchanged mordenites were prepared from synthetic sodium mordenite by cation-exchange technique. The samples were thermally dehydrated in vacuo in the temperature range 100–480°C. The effects of thermal treatment on water losses and heats of immersion in water are discussed. For both mordenites, the integral heats of immersion change in similar fashion, with some limited variation in values of the water loss and heat of immersion. Cobalt-exchanged mordenite samples show greater water losses and consequently have higher immersional heats. Based on the changes of the heat of immersion per molecule, the occurrence of some specific interactions in the system water + sample NiNa-M at low dehydration temperature (100°C) is evident. At higher dehydration temperatures, the two mordenite samples were significantly comparable in the rates of water loss, and consequently less significant changes in average heats of immersion were observed. This is taken as evidence for some reversible dehydration/hydration phenomena at high-temperature treatments.

Surface areas, pore structures, and heats of immersion of titania gel in correlation to thermal treatment

The surface properties of titanium(IV) hydroxide gel and its thermal dehydration products between 110 and 600°C were investigated by nitrogen and water adsorption. Structural and phase changes were studied by X-ray diffractometry and differential thermal analysis. Up to 250°C samples were X-ray amorphous and formed anatase at 350, 450, and 600°C. The glow phenomenon is attributed to the conversion to anatase at 380°C. Standard adsorption data on titanium(IV) hydroxide gel thermally treated at 600°C provide a basis for the analysis of the isotherms by the application of the α s method. Between 110 and 350°C micropores disappeared and widened due to the development of mesopores at 450°C. At 600°C an open surface was obtained. Heats of immersion in water depend on the hydrophilic centers on the surface, whereas surface and pores in the gel control the heats of immersion in cyclohexane.

The surface structure of ethoxylated silica gel

The surface and pore structures of ethoxylated silica gel were studied by means of infrared spectroscopy and heat of immersion in water and n-hexane. The ethoxylation of this sample was carried out at about 240°C in liquid phase for various periods of time. The infrared study of ethoxylation shows that all silanol groups on the outer surface (free silanol groups) can be ethoxylated, but most of the hydrogen-bonded silanol groups around the points of contact between primary particles, and the inner OH groups cannot be substituted. The number of ethoxy groups per unit area of fully ethoxylated silica gel is approximately 3 nm −2, and this value is equal to the number of free silanol groups on the outer surface of silica gel. The number of silanol groups thus obtained is in good agreement with values estimated by different methods reported previously. The values of the heat of immersion of ethoxylated silica gels in water decrease in proportion to the number of ethoxy groups per unit surface area, or are proportional to the number of remaining silanol groups. The heat of immersion in n-hexane is constant and independent of the surface concentration of these groups.

Effect of thermal dehydration on surface characteristics of titania gel

The surface properties of titania gel and its thermal dehydration products were investigated by nitrogen and water vapour sorption between 110 and 600°C. Structural and phase changes were studied by X-ray diffractometry and differential thermal analysis. Up to 200°C, samples were X-ray amorphous and formed anatase at 300, 450 and 600°C. The glow phenomenon is attributed to the conversion to anatase at 350°C. Thermal dehydration of the gel between 110 and 300°C and 600°C led to the widening of the pore radii of the gel. At 450°C, marked steps appeared on the nitrogen isotherm, and was accompanied by a sharp increase in nitrogen uptake. The stepwise character is attributed to the presence of a certain porosity characteristic of the gel. Heats of immersion in water depend mainly on the hydrophilic centres on the surface, whereas heats of immersion in cyclohexane are controlled by the micropore fraction of the gel.

Heats of immersion in relation to water losses of chromium exchanged mordenite

Chromium-exchanged mordenite samples were thermally dehydrated in vacuo over the temperature range 100–480°C. The effects of thermal treatment on water losses and heats of immersion in water, methanol, and cyclohexane are discussed. From the results obtained, it is concluded that the chromium ions reflect smaller heats of ion hydration compared with the sodium ions in sodium mordenite 1. The displaying parameters are, the hydration of metal cations, filling of the vacated pore structure, and the structural collapse at the high temperature studied. It was found that the heats of immersion decrease with increasing molecular size of the wetting liquid.

ChemInform Abstract: HEAT OF IMMERSION OF THERMALLY TREATED SILICA GEL

AbstractSilicagelproben mit bekanntem Gehalt an Na+‐Ionen als Verunreinigungen werden in Gasen wie Luft, He, O2 und H2O sowie im Vakuum (≈︁0.1 N m‐2) einer Wärmebehandlung zwischen ≈︁450 K und der Temp., oberhalb der durch Sintern starke Eigenschaftsänderungen auftreten, unterworfen.

Water Vapor Isotherms and Heat of Immersion of Na/Ca-Montmorillonite Systems—II: Mixed Systems

AbstractAdsorption isotherms for water vapor, c-spacing and heat of immersion in water of mixed Na/Ca-montmorillonite were measured at 25°C at various RH. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. It was concluded that the electrostatic forces between the adsorbed cations and the water molecules are the dominant forces in the hydration of the clay. Thus, at low moisture content, only the adsorbed Ca-ions are hydrated. The heat released when Na-platelets condense to form Ca-packets was measured, and it was suggested that this energy term is the driving force for the demixing phenomena.

Heat of immersion of thermally treated silica gel

The heat of immersion of thermally treated silica gel in water, aliphatic alcohols and other organic compounds was studied. Silica gel was heathyphen;treated in the range from ≈ 450 K to the temperature above which a vigorous change in properties occurred by sintering. Heat treatment was performed in gases such as helium, oxygen, air and water, and a vacuum of ≈ 0.1 N m–2; a known amount of Na+ ion impurity was present in silica gel to be treated. The values of heat of immersion in water, aliphatic alcohols, aromatic compounds and compounds with dipole moments were proportional to the number of OH groups per unit surface area in the range 0 to ≈ 4 OH groups per nm2. This relation is discussed with respect to the surface and pore structures of silica gel.