Heat Of Immersion Research Articles

Catechol derivatives and anion adsorption onto alumina surfaces in aqueous media: influence on the electrokinetic properties

Abstract A high state of dispersion of alumina particles can be achieved by using molecules derived from Catechol 1,2(OH)2C6H4, such as Tiron (OH)2C6H2(SO3Na)2 which allows to obtain stable alumina suspensions. In the field of understanding the dispersion mechanism of Tiron and the contribution of each functional group grafted onto the benzene ring of the Tiron molecule, adsorption experiments and surface charge measurements were conducted by using several compounds, containing a benzene ring, and by varying the nature and the number of substituents. The influence of the size and of the charge of the counter ion, electrostatically attracted by a positive charged alumina surface, onto the suspension stability was also studied. Electrokinetic properties of the suspensions versus pH appear to be very useful to characterize the ion adsorption sequence for an oxide surface. With a high immersion heat, an alumina surface better adsorbs ions with a high structuring power for water molecules. This influences the charge developed onto the oxide surface.

Liquid phase microcalorimetry applied to evaluate surface polarity of MCM-41 type aluminosilicates

Three calorimetric methods have been used to evaluate the surface polarity of three MCM-41 materials characterised by different Si:Al ratios (referred to as SiAl xC14, where x is the moles of Si:Al ratio, and 14 the chain length of the surfactant template). In the liquid phase, the heats of adsorption of 1-butanol from n-heptane and the heats of immersion in water, n-heptane and formamide were compared with the corresponding heat values obtained for two reference solids, viz. silica XOB015 and alumina. Surface (internal) energy of all MCM-41 samples appeared to be smaller than that of any reference solid, the differences being more marked in the case of alumina. In the gas phase, the combination of ammonia gas adsorption and mirocalorimetry measurements was used to evaluate the number and strength of acidic surface sites. With the exception of SiAl8C14, which contains 46% of strongly acidic sites, SiC14 and SiAl32C14 have low surface acidity. The broad distribution of adsorption energy values indicates the energetic heterogeneity of the acidic sites. Incorporating Al into the silicate matrix caused the surface polarity of the materials to increase.

The effect of hot‐water immersions on the appearance and microbiological quality of skin‐on chicken‐breast pieces

Summary Immersion in hot water is one of many potential methods for reducing levels of pathogenic bacteria on the surface of poultry meat. However, if the meat is to be sold in the raw state reductions in microbiological numbers need to be achieved without changing the appearance of the meat. Samples of vacuum‐packed skin‐on chicken breast were immersed in hot water for a range of temperatures and times. Samples were then water cooled to arrest further heating. The final appearance of the samples was assessed visually and instrumentally with a chroma meter. Surface and internal temperatures were also measured. From this series of initial experiments a range of maximum temperature–time treatments were identified that would not cause unacceptable changes to surface appearance. Microbiological tests were then conducted on samples inoculated with a nalidixic acid resistant strain of Escherichia coli serotype O80 subjected to these treatments. The results showed that determining changes to the appearance of skin from samples by using a chroma meter was difficult. The changes caused to the samples by heat treatment were initially textural rather than colourimetric and thus could be identified visually but not instrumentally with a chroma meter. Visual changes were found for immersion times greater than 120 s at 50 °C, 60 s at 60 °C, 9 s at 70 °C, 6 s at 80 °C, 2 s at 90 °C and 1 s at 100 °C. The average temperatures measured on the surface after 2 s immersion at 90 °C and after 60 s at 60 °C were 20.5 °C and 54.8 °C, respectively. No reductions in counts of E. coli serotype O80 were measured on samples treated under these conditions. The results indicate that there is no immersion heat treatment (below 90 °C) capable of reducing contamination with E. coli, or similar thermotolerant microorganisms, on poultry without causing adverse changes in the product.

Comparison of the techniques used to modify amorphous hydrated silicas

Two techniques were used to modify the surface of a hydrated silica. The new, `wet' technique of silica surface modification involved a direct reaction of the modifying agent with the surface groups of the just-forming hydrated silica. Commercial silane coupling agents of Y(CH 2) n Si(OR) 3 type were used as modifying substances. For comparison, the classical `dry' modification of the silica, earlier precipitated from sodium metasilicate solution, was conducted in parallel. In order to compare effects of modification performed using either of the techniques, basic physicochemical analysis of products was conducted, supplemented by near infrared (NIR) spectroscopy, calorimetric analysis to estimate heats of immersion of silica surface, transmission electron microscopy (TEM) to evaluate surface morphology of the products and DLS technique to evaluate the presence of agglomerate and aggregate structures. The studies demonstrated that the newly developed `wet' modification technique was useful in production of modified precipitated silicas with hydrophobic surfaces.

Precipitated silicas modified with 3-aminopropyltriethoxysilane

A comparison was made of the methods used to modify the surface of hydrated silicas employing aminosilane coupling agent. The so-called dry technique of modification and the newly elaborated technique of modification in the course of precipitation were applied. The extent of modification of precipitated silicas was determined on the basis of heats of immersion of silica surface and of spectrophotometric analysis. Morphology of silica particle surface and size distribution of silica particles were determined by transmission electron microscopy (TEM) and by ZetaPlus instrument using dynamic light scattering.

DETERMINATION OF THE IMMERSION ENTHALPY OF ACTIVATED CARBON BY MICROCALORIMETRY OF THE HEAT CONDUCTION

By means of a heat conduction microcalorimetric technique, the immersion heat in CCl4 is determined for five samples of activated carbon, with results between −32.45 and −179.3 Jg−1, presenting a precision for all cases less than 0.8%. With the results of the immersion heat, the total surface area is calculated; the obtained values are between 280 m2g−1 and 1500 m2g−1 indicating the difference in the superficial characteristics of the samples.

シリカ粉体表面に加熱生成されたシロキサンの水およびアルコールに対する反応性

Reactivities of siloxane bridge formed by thermal treatment of fine silica powder surfaces for water and several aicohols were studied quantitatively. Aerosil 200 as a fine silica powder was thermally treated in vacuum, in the temperature range from 25 to 500°C for 4hrs. The heats of immersion in water of heated silica have a broad maximum at about 300°C. The results of immersional heat suggested that rehydroxylation of siloxane on surface of thermally treated silica dose not completely restore the surface to its original condition. The interesting result obtained by Grignard's reagent test was that the siloxanes, in the all of heat-treated silica, were rehydroxylated by exposure to saturated water vapor for 12hrs. This result was also substantiated by change in the spectra of FT-IR and 29Si CP/MAS NMR. In conclusion, rehydroxylation of siloxane was observed by the heat-treatment ranging from 200 to 500°C. However, for the surfaces treated above 300°C, the reaction rate of rehydroxylation decreased. On the other hand, significant reactions were not observed on a few alcohols.

Adsorption of nonelectrolytes from dilute aqueous solutions in carbon micropores: a condensation approximation approach

The Dubinin model of micropore volume filling for gas/solid adsorption is extended to describe the adsorption of nonelectrolytes from dilute aqueous solutions. Adsorption of poorly soluble organic compounds leads to the complete displacement of water from micropores and to formation of an interface between an adsorbed phase and the solution. The maximum molar work supplied by the field of the adsorption forces is considered to be made up of the work of adsorbate compression, Ac, the work of water desorption, Ad, the work associated with the interface formation, Ai, and the work required for overcoming solute–solvent interactions, Aa. The work of the adsorption forces is found from the relationship between the adsorption energy and slit-like micropore sizes; Ad is determined using the affinity coefficient of water desorption derived from immersion heats; Ai is taken to be the product of the interface tension and the interface area; and Aa is approximated by the interchange energy. The expression for a micropore filling concentration as a function of micropore sizes (a local isotherm) is derived from the condition of thermodynamic equilibrium on the basis of a condensation approximation approach. The generalization of the local isotherm to encompass a heterogeneous adsorbent with a Normal distribution of micropore sizes leads to a liquid/solid isotherm equation. It is emphasized that there is an urgent need for the independent experimental verification of the present approach.

Wettability of fine silica powder surfaces modified with several normal alcohols

The chain length effects of chemical modification with various normal alcohols on the wettability of silica have been studied. The modifications were carried out by chemical reaction of alcohol molecules with surface silanols. The amount of silanols on sample surface was obtained by the Grignard method, and the amount of modifiers was determined by thermal analysis. As a result, surfaces were designed to have various concentrations of normal alkoxyl groups. The wettability of these well-defined samples for water were investigated by water vapor adsorption, heat of immersion and various preferential dispersion tests. The results are summarized as follows: (1) the wettability of samples with modifiers of carbon number above eight markedly changes at the modification ratio of about 20%; (2) the samples chemisorbed alcohol with less than eight carbon atoms, the modification ratios of above 20% are required to give hydrophilic surfaces. Because the bulkiness effect of modifiers on wettability decreases with reduction of chain length; (3) in the cases of hydrophobic samples, cooperative water adsorption takes place at the first stage of adsorption. With the occurrence of multilayer adsorption, a continuous two dimensional water layer is formed at the latter stage of adsorption. In the cases of the hydrophobic samples, the adsorbed amount was less than theoretical monolayer capacity in spite of high relative pressure at about P/ P 0=1. Therefore, such a continuous two dimensional water layer is not formed as a result of the steric hindrance of the modifiers. In this case, multilayer adsorption dose not occur. The surface property is estimated to be hydrophobic; (4) the results of preferential dispersion tests as the evalution of macroscopic wettability are in agreement with the results of water vapor affinity and heat of immersion as the nanoscopic wettability.

A Study on the Surface Silanol Groups Developed by Hydrothermal and Acid Treatment of Faujasite Type Zeolites

The surface silanol groups on faujasite type zeolites, which were formed by hydrothermal and acid treatments and considered to be lattice defect, were characterized. IR measurements of silanol groups were madein situand thermogravimetic analysis was conducted under vacuum so as to quantify their content. It was thus possible to quantify separately the concentration of silanol groups forming hydroxy nests and the concentration of terminal silanol groups present on the secondary pores and crystal external surfaces. As the evacuation temperature increased, silanol groups forming hydroxy nests were found to decrease as a result of dehydroxylation condensation. The number of terminal silanol groups on the secondary pores and external surface remained virtually unchanged. The concentration of terminal silanol groups agreed well with the value calculated according to the proposed destruction model of the zeolite framework. This justified the model that there remained the double 6-ring structure on the secondary pore surfaces after the sodalite cage was collapsed as a result of the treatments. The effect of silanol groups forming hydroxy nests on the zeolite surface polarity was examined by measuring immersional heats in various solvents. It turned out that the extremely localized silanol groups forming hydroxy nests in the framework were linked via hydrogen bond to each other and showed nonpolar behavior.

Hydrated silicas modified by nonsilane pro-adhesion compounds

The surface modification of hydrated silicas, precipitated from a solution of sodium metasilicate and gaseous carbon dioxide, was carried out. The modification was conducted in three ways (modification with evaporation of the solvent, heating of the silica-modifying compound solution system in a reflux condenser, and surface modification in a vacuum evaporator), using various amounts of pro-adhesion compounds, dissolved in organic solvents or in water. The extent of modification was established on the basis of heats of immersion of silica in water and benzene, by estimating a loss of silica surface silanol groups in reaction with functional groups of pro-adhesion compounds, and by testing the agglomerability of primary silica particles by electron microscopy. The modified silicas were used as fillers in rubber mixtures based on SBR rubber. The effects of modifying agents were studied by measuring the physicomechanical properties of vulcanizates filled with the modified silicas. Silica surface modification with oxyethylene compounds leads to an evident hydrophobization of the surface. Following modification with oxyethylene compounds [in particular, following modification with 5(1-piperidyl)-3-oxapentanol and 4-aza-3-oxaoctanol], silicas exhibit a clearly elevated condensation of surface silanol groups. When applied for silica surface modification, amine derivatives of oxyethylene compounds clearly improved the tensile strength and modulus of the filled SBR vulcanizates.

Origin of Differences in Heats of Immersion of Silicas in Water

The origin of differences in immersional heats of various silicas in water has been investigated by measurements of water vapor adsorption isotherms, strength of electrostatic fields of surfaces, and concentration and infrared spectra of hydroxyl groups. The contribution of interaction energy between dipole moments of water molecules and the electrostatic fields of silica surfaces to immersional heat was 30–40% of the total heat of immersion. The differences in immersional heats of silicas in water significantly depend on the interaction of hydrogen bonds between water molecules and surface hydroxyl groups rather than on the interaction between dipole moments of water molecules and surface polarity. The hydrogen-bonded hydroxyl groups strongly interact with water molecules rather than the free hydroxyl groups and cause an increase in heat of immersion.

Effect of Surface Geometric Structure on the Adhesion Force between Silica Particles

The adhesion force between nonporous and porous silica particles was measured by AFM as a function of relative humidity. Various porous samples were prepared by hydrothermal treatments in different conditions. Geometric structure was evaluated by gas adsorption, and the mechanism of rehydroxylation that occurred in hydrothermal treatments was investigated by silanol density, IR spectra, and immersional heat. The adhesion force was measured by AFM, and the result was compared with the geometric structure and the rehydroxylation process. As a result, we proved that capillary condensation occurred in small spaces between two particles contacting each other after water filled the pores and capillary force appeared to contribute to a steep increase of adhesion force. The adhesion force under low relative pressure was attributed to hydrogen bonding force and reflected both the contact area and hydrophilicity of the surface.

Adsorption and Heats of Immersion of n-Alkanes on Model Silica Gel

Grand canonical ensemble Monte Carlo simulations are performed with configurational bias to investigate the adsorption behavior of n-alkanes on a model microporous silica gel. The qualitative shape of the adsorption isotherm is seen to change with increasing alkane chain length. A transition from continuous pore filling to layering of molecules at the surface is observed between n-octane and n-dodecane. In addition, heats of immersion are calculated for the model adsorbents in alkanes via computer simulation. This quantity, which to our knowledge has not been calculated in this manner previously, provides a convenient point of contact between simulation and experiment. Agreement between experimental and calculated heats is quite good, provided careful accounting is made of the accessible pore volume and surface area.

Adsorption-energetic and IR spectroscopic studies of NH4 natrolite

The ammonium form of natural zeolite, natrolite, obtained by vapor phase ion exchange is similar to calcium-containing zeolites of the natrolite group in its de- and rehydration characteristics and the heats of immersion in water. The adsorption capacity and the heat of immersion in water are maximum after evacuation of the zeolite at 200 °C. The irreversible sintering of NH4 natrolite occurs above 200 °C (up to 45% at 500 °C), accompanied by the formation of hydroxyl groups.

Heat of immersion of amorphous and crystalline silicas in water: effect of crystallinity

The origin of the difference in the heat of immersion in water between amorphous and crystalline silicas has been studied. We have investigated the effect of crystallinity of silicas on the heat of immersion. The degree of crystallinity was controlled by heating a amorphous silica with sodium chloride appropriate time. The heat of immersion closely depended on the crystallinity. The IR spectra of surface hydroxyl groups revealed that the increase in the heat of immersion with the crystallinity was attributed to the increase in hydrogen-bounded hydroxyl groups. It is concluded that a regular arrangement of the hydrogen-bounded hydroxyl groups on the crystalline silica surfaces stabilizes adsorbed water layer extensively and causes the increase in the heat of immersion compared to that of amorphous silicas.

Synthesis and characterizations of hydroxy-aluminum cross-linked montmorillonite

Cross-linked montmorillonite was prepared by reacting homoionic sodium form of bentonite (Na-M) from Istenmezeje (Hungary) with high molecular weight polyhydroxy-aluminum complex. The complex was prepared by controlled hydrolysis of alumina macrocation. The intercalated clay (Na-Al-M) was thermally treated to convert the hydroxy cations to oxide pillars. The pillared products were characterized by X-ray powder diffraction (XRD), Fourie transform infrared spectroscopy (FTIR), (thermogravimetry (TG), differential thermal analysis (DTA) and thermal analysis-mass spectrometry (TA-MS) methods. The specific surface area as well as pore size and pore structure distribution of samples were measured by nitrogen, water and carbon tetrachloride adsorption, and the heat of immersion was also determined. The pillared products were characterized by d(001) reflections of 19 A, which is stable even at 500°C. The interaction of polymer alumina caused several changes in the obtained FTIR spectra due to the formation of different new bonds. The rate of dehydroxylation of the pillared product is very moderate, the water release occurred in different temperature ranges according to TA-MS results. Dehydration starts at interfaces and at the wall of pores, occurring nearly with uniform rate at 250-500°C. DTA curve indicates the formation of a new phase at 950°C. The obtained surface area of the pillared product by nitrogen adsorption becomes larger (208 m2 g-1) with respect to the non pillared clay, which decreases less than 10% upto 700°C. The pillared sample has a definite pore structure, the quantity of micropores (0-40 A) decreased with increasing of macropores (>1000 A). The obtained domestic pillared montmorillonite possesses a high degree of thermal stability and may be used as adsorbent.

水熱処理による多孔性シリカ粉体の表面性状変化

Various hydrothermal treatments have been carried out for mesoporous silica particles. The hydrothermal treatments are classified into two categories according to the phase in which reactions progresses. In liquid phase, reactions were initiated by immesrsing silica particles in various solutions, whereas in gas phase, silica particles were exposed to water vapor under high pressure by means of autoclave. By measuring increases in immersional heat and H-bond type silanol density, progress of the rehydration of surface siloxane is quantified in both methods. Particulary in liquid phase, rehydroxylation was significantly promoted by the addition of basic substances and also at high temperature. On the other hand, in gas phase, nitrogen and water adsorptions change geometric structure of silica particles in addition to rehydroxylation. This is because dissolution of silica surface, redeposition of the solute and consequently the rehydration occurred in the process of hydrothermal treatments in gas phase. The dissolution progressed significantly with temperature higher than 160°C

Calorimetric Measurement of the Enthalpy of Hydration of Clinoptilolite

AbstractThe enthalpy of hydration of natural clinoptilolite was determined by isothermal immersion calorimetry on Ca-, Na- and K-exchanged clinoptilolite (Fish Creek Mountains, Nevada). Heats of immersion of clinoptilolite were determined at initial H2O contents ranging from θ = 0.02 to 0.85 (where θ is the ratio [H2O content]/[maximum H2O content]). The heat of immersion (liquid H2O reference state) of Ca-clinoptilolite ranged from -7.5 (θ = 0.87) to -25.7 kJ/mol-H2O (θ = 0.19); values for Na-clinoptilolite ranged from -6.3 (θ = 0.85) to -21.8 kJ/mol-H2O (θ = 0.11); and values for K-clinoptilolite ranged from -7.7 (θ = 0.80) to -24.6 kJ/mol-H2O (θ = 0.02). Linear regression of the calorimetric data provided the following values for the complete heat of immersion (from θ = 0): Ca-clinoptilolite, -30.3 ± 2.0; Na-clinoptilolite, -23.4 ± 0.6; and K-clinoptilolite, -22.4 ± 0.8 kJ/mol-H2O.The heat of immersion measurements were compared with the enthalpy of hydration results of Carey and Bish (1996) determined in a thermogravimetric study of the same samples. The heat of immersion data are similar but of smaller magnitude than the values of enthalpy of hydration and are believed to be more accurate because they represent direct measurements of this thermodynamic property.The effect of dehydration of clinoptilolite on the thermal evolution of the potential high-level radioactive waste repository at Yucca Mountain was considered by comparing the amount of energy consumed by clinoptilolite dehydration with the amount of energy necessary to heat rocks lacking hydrous minerals. The extra energy consumed on heating clinoptilolite from 25 to 200 °C ranges between 70 and 80% in excess of that required for nondehydrating materials (that is, clinoptilolite acts as a heat sink). These results indicate that accurate thermohydrologic modeling of rock units at Yucca Mountain should consider the thermal effect of dehydration/hydration processes in clinoptilolite and other hydrous minerals, in addition to the water produced/adsorbed during heating/cooling.

Determination of the Carbon Black Surface Free Energy Components from the Heat of Immersion Measurements

A carbonaceous material (Black Pearls 2000) was used for measurements of heat of immersion in water, formamide, n-dodecane, benzene, bromoform, and diiodomethane. Using the values obtained and the adsorption data from the literature, the Lifshitz−van der Waals component and the electron-acceptor and electron-donor parameters of the acid−base component of the surface free energy of the carbon black have been determined. The surface free energy of carbon black was found to result mainly from Lifshitz−van der Waals intermolecular interactions; however, it can interact with an adherent medium also by acid−base forces. The electron-acceptor parameter of the carbon black surface free energy is higher than zero, but the electron-donor parameter is close to zero. It was also found that the surface free energy of carbon black has a high value close to that for graphite.