Specific Surface Area Of Solids Research Articles

Measuring Air−Water Interfacial Areas with X-ray Microtomography and Interfacial Partitioning Tracer Tests

Air-water interfacial areas as a function of water saturation were measured for a sandy, natural porous medium using two methods, aqueous-phase interfacial partitioning tracer tests and synchrotron X-ray microtomography. In addition, interfacial areas measured in a prior study with the gas-phase interfacial partitioning tracer-test method for the same porous medium were included for comparison. For all three methods, total air-water interfacial areas increased with decreasing water saturation. The interfacial areas measured with the tracer-test methods were generally larger than those obtained from microtomography, and the disparity increased as water saturation decreased. The interfacial areas measured by microtomography extrapolated to a value (147 cm(-1)) very similar to the specific solid surface area (151 cm(-1)) calculated using the smooth-sphere assumption, indicating that the method does not characterize the area associated with microscopic surface heterogeneity (surface roughness, microporosity). This is consistent with the method resolution of approximately 12 microm. In contrast, the interfacial areas measured with the gas-phase tracer tests approached the N2/BET measured specific solid surface area (56000 cm(-1)), indicating that this method does characterize the interfacial area associated with microscopic surface heterogeneity. The largest interfacial area measured with the aqueous-phase tracer tests was 224 cm(-1), while the extrapolated maximum interfacial area was approximately 1100 cm(-1). Both of these values are larger than the smooth-sphere specific solid surface area but much smaller than the N2/BET specific solid surface area, which suggests that the method measures a limited portion of the interfacial area associated with microscopic surface heterogeneity. All three methods provide measures of total (capillary + film) interfacial area, a primary difference being that the film-associated area is a smooth-surface equivalent for the microtomography method. An advantage of the microtomography method is the ability to determine explicitly both total and capillary-associated interfacial areas, which is problematic for the tracer-test methods.

Characterization and re-use potential of by-products generated from the Ohio State Carbonation and Ash Reactivation (OSCAR) process

Two novel sorbents (i.e. “regenerated sorbent” and “supersorbent”) for dry flue gas desulfurization were tested, and by-products characterized, using a pilot-scale version of the Ohio State Carbonation and Ash Reactivation (OSCAR) process. The main elements of the process consisted of sorbent production, a riser reactor, cyclone and baghouse. Trace elements, including As, Se and Hg, were found at higher levels in the OSCAR solid by-products (in both the cyclone and baghouse) compared to traditional lime spray dryer (LSD) ash. Polycyclic aromatic hydrocarbons (PAHs) detected on solid by-products were primarily small molecular weight compounds at low concentration (e.g., μg/kg). Small particulates (⩽3 μm) that escaped from the cyclone and were captured by the baghouse showed higher trace element concentrations, possibly due to the lower operating temperature and greater specific surface area of solids in the baghouse. Operating conditions including flue gas flow rate and sorbent injection rate influenced the levels of trace elements and PAHs in OSCAR by-product material. Capture of PAHs was observed to increase with Ca concentration in experiments using supersorbent injection. However, possible release of PAHs occurred with regenerated sorbent injection. The concentrations of trace elements in leachate for all OSCAR cyclone samples tested were below Resource Conservation and Recovery Act limits. The concentrations of most trace elements in OSCAR by-product were also below the limits regulated in the EPA 503 Rule except As and Se. The similarity in the physical and engineering properties of OSCAR cyclone samples to natural cohesive soils suggests that this material can be utilized in a variety of construction, reclamation, and agricultural applications.

Relationships among air‐water interfacial area, capillary pressure, and water saturation for a sandy porous medium

The relationships among air‐water interfacial area, capillary pressure, and water saturation were investigated for a sandy, natural porous medium. Air‐water interfacial areas as a function of water saturation were measured using two methods, gas phase partitioning tracer tests and synchrotron X‐ray microtomography. The tracer test method provides a measure of effective total (capillary and film) interfacial area, whereas microtomography can be used to determine both capillary‐associated and total areas (the latter is the focus of this study). Air‐water interfacial areas determined with both methods increased continuously with decreasing water saturation. The areas measured with the tracer test method were significantly larger than those obtained from microtomography. The maximum values measured with the tracer test method approached the N2/BET‐measured specific solid surface area, whereas the maximum values measured by microtomography approached the smooth‐sphere‐calculated specific solid surface area. The interfacial area‐saturation data were combined with capillary pressure‐saturation data obtained from water drainage experiments to examine the relationship between total air‐water interfacial area and capillary pressure. Air‐water interfacial area was observed to increase monotonically with increasing capillary pressure and then to plateau at values that correspond to areas associated with residual water saturation. These results are consistent with previously reported theoretically and computationally based analyses of functional relationships between total nonwetting‐wetting interfacial area and capillary pressure.

Surfactants and interfacial phenomena

Surfactants and interfacial phenomena

The influence of lithium on the hydrogen peroxide decomposition activity of manganese–alumina catalysts

Addition of small quantities of Li 2O to Al 2O 3 was studied with respect to its influence on the catalytic decomposition of H 2O 2 over Mn/Al mixed oxide catalysts calcined at 400, 700 and 1000 °C for 6 h. The specific surface areas of pure and doped solids were determined by BET analysis of nitrogen adsorption isotherms. The catalytic activities and the values of S BET of pure and doped mixed oxides were found to decrease by increasing the amount of Li 2O present. The activation energy of sintering, Δ E, of various solids decreased considerably by increasing the amount of Li 2O added. The maximum decrease in Δ E due to the doping with 6 mol% Li 2O attained 50%. In other words, Li 2O doping facilitates the sinterability of the treated solids to an extent proportional to the amount of lithia present. This treatment did not modify the activation energy of the catalyzed reaction, i.e. doping of Mn/Al mixed oxides did not alter the mechanism of the catalytic reaction but changed the concentration of catalytically active sites taking part in the catalytic process without altering their energetic nature.

Effect of gamma-irradiation on surface and catalytic properties of Co3O4 and NiO catalysts

The effects of g-irradiation (0.2-1.6 MGy) on the particle size, specific surface area and catalytic activity of Co3O4 and NiO solids were investigated. The investigated solids were prepared by heat treatment of cobalt carbonate at 500 and 700 °C and basic nickel carbonate at 400 °C. The techniques employed were XRD, nitrogen adsorption at -196 °C and decomposition of H2O2 at 30-50 °C. The results showed that g-irradiation resulted in a small decrease in the particle size of the investigated solids and effected a progressive increase in their specific surface areas. On the other hand, the exposure of Co3O4 and NiO catalysts to a dose of 0.2 MGy resulted in a significant decrease in their catalytic activities, which suffered further progressive decrease upon increasing the doses up to 1.6 MGy. Gamma-irradiation did not modify the activation energy of the catalyzed reaction but decreased the concentration of catalytically active sites without changing their energetic nature. These results were discussed in terms of splitting of the particles of the treated solids and removal of chemisorbed species present in nonstoichiometric cobalt and nickel oxides.

圧縮性ろ過ケークを形成するボディフィード精密ろ過過程の解析

The process of body-feed microfiltration of yeast suspension to which kieselguhr was admixed to reduce the filtration resistance was evaluated using the average porosity and the average specific filtration resistance determined from filtration experiments in which a filter was subjected to a sudden reduction in its filtration area. The dependence of local porosity and effective specific surface area of cake solids on the mixing ratio of filter aids was evaluated by a packing model of binary mixtures. The average porosity and the average specific filtration resistance were calculated from these local values by accounting for the non-homogeneity of the compressible filter cake. On the basis of these values, the filtration rate in body-feed filtration was accurately predicted. The method presented in this paper can be applied for the determination of the optimum dosage of filter aids in body-feed filtration.

Measurement of liquid permeability in the mushy zones of aluminum-copper alloys

Measurements of liquid permeability in the mushy zones of Al-15.42 pct Cu and Al-8.68 pct Cu alloy samples were performed isothermally just above the eutectic temperature, using eutectic liquid as the fluid. A modified method was developed to determine the specific permeability as a function of time (K s) during the test from the data collected on these alloys. Factors affecting permeability measurements are discussed. The permeabilities are observed to vary throughout the experiment. This is attributed to microstructural coarsening and channeling that occur in the sample during the experiment. Coarsening rates are determined for the isothermal coarsening tests without fluid flow, and the results are observed to be less than the rates indicated from permeability tests where fluid flow is present. Careful measurement of the volume fraction of liquid (g L) shows that g L decreases during the test. The permeability is then related to the microstructure of the sample using the Kozeny-Carman equation. The correlation between the measured K S, g L, and specific solid surface area (S V) improves markedly when compared to previous studies, when microstructural parameters at the initial stage of the test are used.

Fly-ash/calcium hydroxide mixtures for SO2 removal: structural properties and maximum yield

Abstract The structural properties and sulfation capacity of mixed solids obtained from pressurized hydration of commercial calcium hydroxide and coal combustion fly-ashes have been analyzed. Hydration experiments were planned according to a 2 5 fractional factorial design, studying the influence of temperature, time, pressure, fly-ash/Ca(OH) 2 weight ratio and water/solid weight ratio, on the BET specific surface area (5) and pore volume ( V p ) of the final solids, as well as on the dissolved calcium concentration [Ca]in the slurries. Whereas a strong dependence of the ratio fly-ash/Ca(OH) 2 on ( S ) and [Ca]functions was observed, with values of these parameters in the ranges 2.5-64.3 m 2 g −1 and 6.0–748.0 mg l −1 , respectively, no dependence was found of the studied variables on the pore volume (determined by Hg intrusion porosimetry), obtaining an average value of 1.077 cm 3 g −1 . Sulfation runs using the hydrated solids were conducted in a packed bed reactor with a pure humidified SO 2 gas phase, leading to a constant sulfation yield of 0.56 ± 0.07 mol SO 2 per mol Ca; this yield was independent of the solids specific surface area, and related only to the sorbents calcium content.

Computer driven apparatus for adsorption measurements

The idea and programs for an automatic microcomputer driven multiple-sample apparatus for measurements of gas adsorption is presented. The Surfamat-5x system is useful for determination of specific surface area and porosity of solids by analysis of adsorption isotherms of nitrogen at the temperature of a liquid nitrogen bath. The system consists of a five-channel measuring unit and a CP/M microcomputer-based control unit with FORTRAN/ASSEMBLER programs for control and interpretation of measurements. The measurement control/optimization and data interpretation programs were intensively developed and the MS-DOS interpretation program was prepared. Raw data stored in disk files by control programs are transferred to an MS-DOS computer for further interpretation. The interpretation program allows us to choose among many models of adsorption/desorption and condensation/evaporation in mesopores as well as adsorption in micropores depending on the kind of solid investigated.

Effect of lithium oxide doping on surface and catalytic properties of [formula omitted] solids

The influence of Li 2O doping (0.75–3.0 mol%) on surface and catalytic properties of NiO Fe 2O 3 , having a molar ratio of 1:2, was investigated. Pure and doped mixed solids were heated in air at 700 and 800 °C. The surface characteristics of various solids were determined from N 2-adsorption isotherms conducted at −196 °C and their catalytic activities were measured by following up the kinetics of CO oxidation by O 2 at 300–400 °C using a static method. The results revealed that the doping process brought about an increase in the specific surface area (S BET) of mixed solids. A maximum increase of about two-fold was observed by treating with 1.5% Li 2O. On the other hand, this treatment resulted in a drastic decrease (about 50%) in the catalytic activities of the doped catalysts. Lithium oxide doping altered the pre-exponential factor of the Arrhenius equation without changing the magnitude of the apparent activation energy of the catalytic reaction which might indicate that Li 2O did not change the mechanism of the catalytic reaction.

Decomposition kinetics of alkaline-earth hydroxides and surface area of their calcines

Thermal decomposition of Mg(OH) 2 and Ca(OH) 2 particles produces highly porous calcines that react rapidly with acidic gaseous pollutants at moderate temperature. Increasing- and constant-temperature gravimetric methods were employed to measure the rates of decomposition of hydroxide particles at temperatures 290–430°C. The measured data wree tested empirically by fitting to the nth-order rate equation of Arrhenius type, and the values of the kinetic parameters were estimated. Differences are explored in the course of the decompo sition of magnesium hydroxide and that of calcium hydroxide. The sintering rate of the nascent, hydroxide-derived oxides was measured in a nitrogen atmosphere at temperatures from 400 to 700°C. An empirical kinetic model has been proposed to correlate the experimental data on the specific surface area of solids. Comparison of the results indicates that particles of MgO exhibit a surface area which is half an order greater than that of CaO sintered under the same conditions.

Estimating the surface area of fluid phase interfaces in porous media

An equation is derived to calculate the specific interfacial area of any two continuous immiscible fluids contained in a porous medium. Use of the equation requires the volume fraction of fluids, a capillary water retention relation and the specific solid surface area of the porous medium of interest. Calculations of the air-water interfacial area as a function of volumetric water content are presented for a hypothetical sand, silt loam and clay soil. These values are compared to those calculated from two other equations that have been proposed in the literature. The method presented here is novel in that it is based on the area of continuous liquid films covering the solid phase matrix and so includes both convex and concave curvatures. It also is developed such that it converges to the correct known areas at total saturation and at monolayer coverage of the solid matrix.

Stepwise isotherms and phase transitions in physisorbed films

The present paper outlines the evolution during the last thirty years of research in the field of physisorption of gases on solids with a homogeneous surface. It relates this evolution as lived by some researchers of a physical chemistry laboratory whose objective was not originally to study physisorption as such, but to use it as a method to determine the specific surface area of solids participating in gas reactions. Consequently, the aim is not to give a complete review even of only those results obtained from adsorption isotherms, but simply to recall the way which led to the discovery of several of the most typical adsorption phenomena, i.e.: “gas-liquid-solid” and “commensurate-incommensurate” 2D transitions, 2D polymorphism, wetting transitions and specific behaviour of mixed films.

The cycling of iron in natural environments: Considerations based on laboratory studies of heterogeneous redox processes

The various pathways for the oxygenation of ferrous iron and for the dissolution of Fe(III) (hydr) oxides, especially by reducing ligands with oxygen donor atoms in thermal and photochemical processes, are assessed on the basis of laboratory experiments for application to natural systems. The typically large specific surface area of Fe-bearing solids in natural systems and the ability of these surfaces to interact chemically (surface complexation, ligand exchange) with reductants and oxidants facilitates electron transfer as well as dissolution and precipitation. Adsorption of Fe(II) to particle surfaces (complexation with surface hydroxyl groups) enhances the oxygenation rate of Fe(II) in a similar way as hydrolysis in solution (complexation with OH − ions). Surface processes (and not transport processes) control the dissolution kinetics. The rate of dissolution is proportional to the surface complexes formed on the surface of Fe(III) (hydr)oxides. Thus, a reductant, such as ascorbate, exchanges electrons with a surface Fe(III) ion subsequent to its inner-sphere coordination to the oxide surface. The Fe(II) thereby formed becomes more easily detached from the surface. Complex formation reactions of Fe(III) and Fe(II) with organic and inorganic ligands to form solute and solid complexes makes it possible that electron cycling of Fe(III)-Fe(II) transformations can occur over the entire E H range within the stability of water ( E H from −0.5 V to +1.1 V). Solid and solute Fe(II) complexes with silicates, with hydrous oxides (e.g., Fe 3O 4), and with sulfides are very efficient reductants from a thermodynamic as well as from a kinetic point of view. Photosynthetic processes occurring on some inorganic Fe-bearing surfaces (semiconductors) and with iron species may be looked at as “primitive” alternatives or precursors to biological photosynthesis. In light-induced reductive dissolution of Fe(III) (hydr)oxides, dissolved Fe(II) (example: reduction of solid Fe(III) phases with an organic ligand such as oxalate) is formed. In the heterogeneous photoredox reaction, the inner-sphere surface coordination of the electron donor to the oxide surface is essential for the efficiency of the electron transfer.

A new method of evaluation of specific surface area of solids using inverse gas chromatography at infinite dilution

A new method is proposed for the determination of specific surface areas of solids using gas solid adsorption inverse chromatography at infinite dilution. It is shown that this method is valuable especially for low surface area solids.

Intra- and inter-estuarine variability of particle microstructure

A systematic study has been made of the particle microstructure and chemical composition of suspended solids from large U.K. estuaries (Humber, Mersey, Tamar) and a German estuary (Elbe). The mean specific surface areas of the suspended solids were in the sequence Elbe (25.6 m 2 g −1) = Humber (24.0 m 2 g −1) > Tamar (14.9 m 2 g −1) > Mersey (9.6 m 2 g −1). In addition, the Elbe, Humber and Tamar estuaries had higher specific surface areas in the very low salinity, turbidity maximum zone. There was no evidence of similar effects in the Mersey Estuary. These differences in specific surface areas (and hence the heterogeneous chemical reactivity of the particles) are interpreted in terms of the relative proportions of carbon to iron and manganese in the samples. Thus, the high specific surface area in the Humber is associated with a C/Fe + Mn ratio of 4, whereas that for the Mersey is about 11. The implication of these results is that the surface chemical composition determines the particle reactivity and where adsorbed ions are ultimately located on the particle (i.e. either on the surface or in the internal pore structure). This finding is discussed in the context of the uptake of dissolved constituents and the potential for irreversible adsorption.

Thermal radiation of gas/solid mixtures

AbstractThermal radiation of gas/solid mixtures in high‐temperature heat exchangers is of considerable importance for the design of heat exchange surfaces. Therefore, an experimental plant was constructed to measure solid particle emissivities, since there is a lack of relevant data in the existing literature. A theoretical equation was derived to describe the solid particle emissivity as a function of layer thickness, specific solid surface area, solid loading and absorption and scatter coefficients. Measurements were carried out for fluidized bed ash and quartz sand. The emissivities of these particle fractions increase with increasing layer thickness, slid loading, specific solid surface area and temperature. The description of these data by the derived model equation is very satisfactory. No dependence on wavelength was observed. The ash components do exert some influence which, for the present, cannot be described exactly.

Determination of the specific surface area of solids by means of adsorption data

An experiment that brings to the students' attention the basic problems connected with the measurement of specific surface areas of solids.

Variability of aquifer sorption properties in a field experiment on groundwater transport of organic solutes: Methods and preliminary results

Methods to characterize the organic solute sorption distribution coefficient, organic carbon content, and specific surface area of aquifer solids from the site of a field experiment on solute transport in groundwater were refined for application to small subsamples of 10-cm depth increments taken from 5-cm diameter cores. Initial results indicate that the average sorption characteristics of the Borden aquifer do not vary appreciably along the trajectory of the solute plumes. However, the sorption distribution coefficient of tetrachloroethylene varied over nearly an order of magnitude among 10-cm depth increments in one core sample. Preliminary evidence suggests that the sorption distribution coefficients for four halogenated organic solutes vary proportionally among core strata. However, the distribution coefficients for sorption of tetrachloroethylene on various depth increments are not well correlated with either organic carbon content or specific surface area, suggesting that as yet unidentified mineral phases may play a significant role in sorption of such solutes by the sandy aquifer solids.