Thermodynamics of surfaces and adsorption in the Fe-S, Fe-N, and Fe-S-N systems at 1823 K

The present investigation calculates the surface tension and adsorption functions of the Fe-S, Fe-N, and Fe-S-N melts at 1823 K using the modified form of Butler's equations and the derived values of the surface interaction parameters of the systems. The calculated values are found to be in good agreement with those of the experimental data of the systems. The present analysis indicates similar adsorption behavior of sulfur for the Fe-S and Fe-S-N systems at 1823 K. Although a linear adsorption behavior is observed in the Fe-N system, an inverse relationship in the adsorption behavior exists between sulur and nitrogen in the Fe-S-N system.

Effect of packing density and adsorption parameters on the throughput of a thermal compressor

Vapour adsorption refrigeration systems (VAdS) have the advantage of scalability over a wide range of capacities ranging from a few watts to several kilowatts. In the first instance, the design of a system requires the characteristics of the adsorbate-adsorbent pair. Invariably, the void volume in the adsorbent reduces the throughput of the thermal compressor in a manner similar to the clearance volume in a reciprocating compressor. This paper presents a study of the activated carbon +HFC-134a (1,1,1,2-tetrafluoroethane) system as a possible pair for a typical refrigeration application. The aim of this study is to unfold the nexus between the adsorption parameters, achievable packing densities of charcoal and throughput of a thermal compressor. It is shown that for a thermal compressor, the adsorbent should not only have a high surface area, but should also be able to provide a high packing density. Given the adsorption characteristics of an adsorbent-adsorbate pair and the operating conditions, this paper discloses a method for the calculation of the minimum packing density necessary for an effective throughput of a thermal compressor. (C) 2002 Elsevier Science Ltd. All rights reserved.

A method for the calculation of the adsorbed phase volume and pseudo-saturation pressure from adsorption isotherm data on activated carbon

We propose a new method for evaluating the adsorbed phase volume during physisorption of several gases on activated carbon specimens. We treat the adsorbed phase as another equilibrium phase which satisfies the Gibbs equation and hence assume that the law of rectilinear diameters is applicable. Since invariably the bulk gas phase densities are known along measured isotherms, the constants of the adsorbed phase volume can be regressed from the experimental data. We take the Dubinin-Astakhov isotherm as the model for verifying our hypothesis since it is one of the few equations that accounts for adsorbed phase volume changes. In addition, the pseudo-saturation pressure in the supercritical region is calculated by letting the index of the temperature term in Dubinin's equation to be temperature dependent. Based on over 50 combinations of activated carbons and adsorbates (nitrogen, oxygen, argon, carbon dioxide, hydrocarbons and halocarbon refrigerants) it is observed that the proposed changes fit experimental data quite well.

Adsorption of 1,1,1,2-Tetrafluoroethane on Activated Charcoal

This paper presents adsorption isotherms for HFC-134a on activated charcoal, in the temperature range of 273-353 K and for pressures up to 0.65 MPa, measured using the volumetric method. Three samples of charcoals with widely varying surface areas were chosen. The shapes of the isotherms,obtained from the experimental data were similar in all cases and comparable to those reported in the literature. Adsorption parameters were evaluated from the isotherms using the Dubinin-Astakhov (DA) equation. The concentration dependence of the isosteric enthalpies of adsorption is extracted from the data.

Removal of As(V) by adsorption onto mixed rare earth oxides

Arsenic pollution of water is a major problem faced worldwide. Arsenic is a suspected carcinogen in human beings and is harmful to other living beings. In the present study, a novel adsorbent was used to remove arsenate [As(V)] from synthetic solutions. The adsorbent, which is a mixture of rare earth oxides, was found to adsorb As(V) rapidly and effectively. The effect of various parameters such as contact time, initial concentration, pH, and adsorbent dose on adsorption efficiency was investigated. More than 90% of the adsorption occurred within the first 10 min and the kinetic rate constant was found to be about 3.5 mg min(-1). Adsorption efficiency was found to be dependent on the initial As(V) concentration, and the adsorption behavior followed the Langmuir adsorption model. The optimum pH was found to be 6.5. The presence of other ions such as nitrate, phosphate, sulphate, and silicate decreased the adsorption of As(V) by about 20-30%. The adsorbed As(V) could be desorbed easily by washing the adsorbent with pH 12 solution. This study demonstrates the applicability of naturally occurring rare earth oxides as selective adsorbents for As(V) from solutions.

CO adsorption on ionic Pt, Pd and Cu sites in Ce(1-x)M(x)O(2-delta) (M = Pt(2+), Pd(2+), Cu(2+))

Noble metal ion substituted CeO(2) in the form of Ce(0.98)M(0.02)O(2-delta) solid solution (where M = Pt, Pd, Cu) are the new generation catalysts with applications in three-way exhaust catalysis. While adsorption of CO on noble metals ions is well-known, adsorption of CO on noble metal ions has not been studied because creating exclusive ionic sites has been difficult. Using first-principles density functional theory (DFT) we have shown that CO gets adsorbed on the noble metal Pt(2+), Pd(2+), Cu(2+) ionic sites in the respective compounds, and the net energy of the overall system decreases. Adsorption of CO on metal ions is also confirmed by Fourier transform infrared spectroscopy (FTIR).

Microscopic modelling of adsorption and the generalised surface layer hypothesis

Two- and three-state models for the adsorption of organic compounds at the electrode/electrolyte interface are proposed. Different size requirements, if any, for the neutral molecule and the adsorbing solvent are also considered. It is shown how the empirical, generalised surface layer (GSL) relationship (between the potential difference and the electrode charge) formulated by Damaskin et al. can be understood at the molecular level.

Some adsorption-nucleation-based models for electrochemical phase formation

A new class of models which are based on adsorption, nucleation growth and their coupling is discussed. In particular, the potentiostatic response of a model that involves nucleative phase growth via direct incorporation and adsorptive discharge of metal ions on the free area is analysed for both instantaneous and progressive nucleation. This model is able to predict certain experimental features in the potentiostatic transient, like the initial fall, shoulder or maximum (as well as minimum) which have not been predicted by models analysed hitherto.Limiting behaviour for short and long times as well as a description of the above-mentioned features in terms of model parameters are given.A special case of the above model, viz. a reversible adsorption–nucleation model, wherein the adsorption is very fast, is shown to give rise to transients which can be distinguished from the pure nucleation-growth transients only by its parametric dependence, but not by the form.

Injection-molded high-density polyethylene-hydroxyapatite-aluminum oxide hybrid composites for hard-tissue replacement: Mechanical, biological, and protein adsorption behavior

In this article, we report the mechanical and biocompatibility properties of injection-molded high-density polyethylene (HDPE) composites reinforced with 40 wt % ceramic filler [hydroxyapatite (HA) and/or Al2O3] and 2 wt % titanate as a coupling agent. The mechanical property measurements revealed that a combination of a maximum tensile strength of 18.7 MPa and a maximum tensile modulus of about 855 MPa could be achieved with the injection-molded HDPE20 wt % HA20 wt % Al2O3 composites. For the same composite composition, the maximum compression strength was determined to be 71.6 MPa and the compression modulus was about 660 MPa. The fractrography study revealed the uniform distribution of ceramic fillers in the semicrystalline HDPE matrix. The cytocompatibility study with osteoblast-like SaOS2 cells confirmed extensive cell adhesion and proliferation on the injection-molded HDPE20 wt % HA20 wt % Al2O3 composites. The cell viability analysis with the 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay revealed a statistically significant difference between the injection-molded HDPE20 wt % HA20 wt % Al2O3 composites and sintered HA for various culture durations of upto 7 days. The difference in cytocompatibility properties among the biocomposites is explained in terms of the difference in the protein absorption behavior. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

(Dimethylamino)borylene and Related Complexes of Electron-Rich Metal Fragments: Generation of Nucleophile-Resistant Cations by Spontaneous Halide Ejection

Spontaneous halide ejection from a three-coordinate Lewis acid has been shown to offer a remarkable new route to cationic metal complexes featuring a linear, multiply bonded boron-donor Ligand. The exploitation of electron-rich [CpM(PR3)(2)] fragments within boryl systems of the type LnMB(hal)NR2 leads to the spontaneous formation in polar solvents of chemically robust borylene complexes, [LnM(BNR2)](+), with exceptionally low electrophilicity and short M-B bonds. This is reflected by M-B distances (ca. 1.80 angstrom for FeB systems) which are more akin to alkyl-/aryl-substituted borylene complexes and, perhaps most strikingly, by the very low exothermicity associated with the binding of pyridine to the two-coordinate boron center (Delta H = -7.4 kcal mol(-1), cf. -40.7 kcal mol(-1) for BCl3). Despite the strong pi electron release from the metal fragment implied by this suppressed reactivity and by such short M-B bonds, the barrier to rotation about the Fe=B bond in the unsymmetrical variant [CpFe(dmpe)(BN{C6H4OMe-4}Me)](+) is found to be very small (ca. 2.9 kcal mol(-1)). This apparent contradiction is rationalized by the orthogonal orientations of the HOMO and HOMO-2 orbitals of the [CpML2](+) fragment, which mean that the M-B pi interaction does not fall to zero even in the highest energy conformation.

Surface chemical and adsorption studies using Thiobacillus ferrooxidans with reference to bacterial adhesion to sulfide minerals

Adhesion of Thiobacillus ferrooxidans to pyrite and chalcopyrite in relation to its importance in bioleaching and bioflotation has been studied. Electrokinetic studies as well as FT-IR spectra suggest that the surface chemistry of Thiobacillus ferrooxidans depends on bacterial growth conditions. Sulfur-,Pyrite- and chalcopyrite-grown Thiobacillus ferrooxidans were found to be relatively more hydrophobic. The altered surface chemistry of Thiobacillus ferrooxidans was due to secretion of newer and specific proteinaceous compounds. The adsorption density corresponds to a monolayer coverage in a horizontal orientation of the cells. The xanthate flotation of pyrite in presence of Thiobacillus ferrooxidans is strongly depressed where as the cells have insignificant effect on chalcopyrite flotation. This study demonstrate that: (a)Thiobacillus ferrooxidans cells can be used for selective flotation of chalcopyrite from pyrite and importantly at natural pH values. (b)Sulfur-grown cells exhibits higher leaching kinetics than ferrous ion-grown cells.

Adsorption of cationic dyes on poly(acrylic acid-co-sodium acrylate-co-acrylamide) superabsorbents

Inverse suspension polymerization was carried out to synthesize poly(acrylic acid-co-sodium acrylate-co-acrylamide) superabsorbent polymers (SAPs) crosslinked with ethylene glycol dimethacrylate (EGDMA). The equilibrium swelling capacities of the SAPs, determined by swelling them in DI water, were found to vary with the acrylamide (AM) content. The SAPs were used to adsorb four cationic dyes (Acriflavine, Auramine-O, Azure-I and Pyronin-Y). The effect of AM content in the SAPs on the adsorption of the cationic dyes was investigated. Different initial concentrations of Azure-I were used with the same amount of the SAP to explore the effect of initial dye concentration on the adsorption. The effect of the adsorbent amount was investigated by taking different amounts of SAP with a fixed initial concentration of Acriflavine. The kinetics of the dye adsorption was modeled by a first order model and the equilibrium amount of the dye adsorbed, adsorption rate coefficients, removal efficiency and partition coefficients were determined. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012