Dissolution of Si in Al–Si Melts. Effect of Sb on the Crystallization Process and As-cast Structure of Al–Si Alloys

The effect of Sb on the dissolution of Si single crystals (face {111}) in Al–Si melts is studied. The dissolution isotherms at three temperatures and fixed undersaturation are obtained. The experimental data are treated according to the Bliznakov's ratio. Some conclusions are made with reference to the crystal growth process. A probable mechanism of the influence of Sb on the structure of Al–Si alloys is given.     

Kinetics of Structural Coarsening of Microcrystalline Al—Si—Mg Alloys during Thermal Treatment and Compacting

The structures of microcrystalline AlSiMg alloys during heat treatment were studied using optical microscope Reichert MeF₂ equipped with a monochrome TV camera VS-700. The average size of the silicon particles was determined. The significant influence of magnesium on the microstructure at high temperatures was demonstrated. Magnesium accelerates the structure coarsening process and a decrease of the effective activation energy of the silicon particles growth was found.     

Comparative modelling of mono- and dinitrophenols sorption on yellow bentonite from aqueous solutions

Equilibrium removal of three substituted nitrophenols, namely 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP), by adsorption on yellow bentonite was tested. The batch kinetic data are described by the pseudo-first order, pseudo-second order, and intraparticle diffusion models. Results show that chemisorption processes could be rate limiting in the sorption step. The adsorption equilibrium was modelled by the Langmuir and Freundlich equations. The Langmuir model better represents the equilibrium isotherm data for 2-NP, 4-NP, and 2,4-DNP uptake on yellow bentonite. 4-NP is adsorbed in larger amounts than the disubstituted nitrophenol. Uptake of nitrophenols increases in the order 2-NP < 2,4-DNP < 4-NP.     

Eutectic crystallization of aluminium copper alloys (II). Influence of impurity elements

The directional crystallization of eutectic Al–Cu alloys with Fe additions under molten salts has been studied. According to Tiller's theory the specific interphase boundary energy σ_αβ was estimated for eutectic Al–Cu alloys with three concentrations of additive. Values of σ_αβ depend on Fe-concentration. Small additions of Fe modify the eutectic structure in two directions: a) enlargement of interlamellar spacings. b) formation of rod-like structure.     

Eutectic Crystallization of Aluminium Copper Alloys

The directional freezing of Al-Cu eutectic alloys under molten salts has been studied. The value of the specific interphase boundary energy σ_αβ is found to be smaller than CHADWICK 'S and of the same order as for other eutectics. An attempt has been made to appreciate the influence of the growth rate on the interlamellar spacing and tensile strength of alloys investigated.     

Thermal investigations on phase transformations of Syrian phosphorite: Part I

The phase transformations of Syrian phosphorite upon mechanochemical activation are examined in the present work. The latter is carried out in planetary mill equipped with 20 mm steel milling bodies and duration from 30 to 300 min. The established by means of DTA, DTG, TG analyses transformation of non-activated carbonate fluorine apatite type B into the carbonate hydroxyl fluorine apatite (COHFAp) mixed type A2-B leads to substantial changes in the properties of the activated samples expressed in lowering the degree of crystallinity, strong defectiveness of the structure, and increase of the citric solubility. The thermal analysis gives evidence for the decomposition of the carbonate-containing component within the phosphorite, as from the positions placed in the vicinity of the hexagonal 6₃ axis (type A2), as well as from the positions of the phosphate ion (type B), and from the free carbonates. The data from the thermal analysis, the powder X-ray analysis and the infrared spectroscopy give also evidence for phase transformations of the activated apatite (with admixtures of quartz and calcite) into Ca₁₀FOH(PO₄)₆, β-Ca₃(PO₄)₂, Ca₄P₂O₉, Ca₃(PO₄)₂ · Ca₂SiO₄ and for that one of the quartz—into larnite and wollastonite. The influence of the α-quartz as a concomitant mineral is considered to be positive. The α-quartz forms Si–O–Si–OH bonds retaining humidity in the solid phase thus facilitating the isomorphous substitution OH⁻ → F⁻ with the subsequent formation of partially substituted COHFAp. Calcium silicophosphate and Ca₄P₂O₉ are obtained upon its further heating. The presented here results settle a perspective route for processing of low-grade phosphate raw materials by means of tribothermal treatment aiming at preparation of condensed phosphates suitable for application as slowly acting fertilizer components.     

Phase changes in the syrian phosphorite–ammonium sulphate system

With a complex of physico-chemical methods for analysis it is proved that in the course of mechanochemical treatment of a Syrian phosphorite and ammonium sulphate mixture new phases have been formed. The thermal analysis proves an increase in the reaction properties of the ammonium sulphate and the Syrian phosphorite which is a prerequisite for the increase in the content of P₂O₅^assimilated , in the activated phosphorite mixtures and the possibility to use them in the production of NP complex fertilizers.     

Direct Red 28 Adsorption on Amosil and <Emphasis Type="Italic">Avena sativa </Emphasis> L.: Mass Transfer and Kinetics Modelling on the Solid/Solution Interface

Adsorption kinetics is a key issue for successful sorbent selection and the proper design of batch and fixed-bed adsorption systems. The aim of the present study was to determine the kinetics, mass transfer and diffusion coefficients and to establish the rate-controlling mechanism/s during Direct Red 28 adsorption on Amosil and Avena sativa L. biomass. Five kinetic models (pseudo-second order, Blanchard, Avrami, Ritchie and power function) and and four mass transfer (external diffusion, film diffusion, particle diffusion, intraparticle diffusion) mathematical models were applied to the experimental data. To confirm the best-fitting model(s), error analyses were conducted. The integrative comparative analyses of the values of the predicted model parameters, coefficients and error functions established that the intraparticle diffusion model best represented the experimental results of the dye sorption on dried A. sativa L. biomass, while for the Direct Red 28/Amosil system, the kinetic behavior is the best described by either the pseudo-second or Blanchard’s model. Boyd’s effective intraparticle diffusion coefficient (D _i ), characterizing the dye sorption on Amosil, is significantly lower than that for the system Direct Red 28/A. sativa L. biomass. The low values of the Bi number (Bi < 0.5) suggests that the mass transfer resistance, for both systems, is concentrated at the fluid/solid phase surface.     

Polymer nanodroplets forming liquid bridges in chemically structured slit pores: a computer simulation

Using a coarse-grained bead-spring model of flexible polymer chains, the structure of a polymeric nanodroplet adsorbed on a chemically decorated flat wall is investigated by means of molecular dynamics simulation. We consider sessile drops on a lyophilic (attractive for the monomers) region of circular shape with radius R(D) while the remaining part of the substrate is lyophobic. The variation of the droplet shape, including its contact angle, with R(D) is studied, and the density profiles across these droplets also are obtained. In addition, the interaction of droplets adsorbed on two walls forming a slit pore with two lyophilic circular regions just opposite of one another is investigated, paying attention to the formation of a liquid bridge between both walls. A central result of our study is the measurement of the force between the two substrate walls at varying wall separation as well as the kinetics of droplet merging. Our results are compared to various phenomenological theories developed for liquid droplets of mesoscopic rather than nanoscopic size.     

Preparation of Polyclonal Antibodies with Application for an Organophosphorus Pesticide Immunoassay

Haptens of dichlorvos and paraoxon were conjugated to the carrier proteins of bovine serum albumin. The obtained conjugates were characterized by infrared and ultraviolet–visible spectroscopy. The binding ratios of dichlorvos and paraoxon-to-carrier proteins were also evaluated. The number of hapten molecules per protein molecule of dichlorvos–cationized bovine serum albumin conjugate was higher than for paraoxon–bovine serum albumin conjugate. The sheep polyclonal antibodies were produced against the dichlorvos and paraoxon. New multipolyclonal antibodies were obtained and characterized following the immunization of a 1:1 mixture of the immunogens for the simultaneous determination of dichlorvos and paraoxon by the immunoassay. An indirect enzyme-linked immunosorbent assay was used to characterize the reactivity of the antibodies to hapten conjugates. The multiantibodies showed lower affinities than the separate antibodies, but their affinities were sufficient for an immunoassay for the simultaneous determination of the analytes. The detection limit and linear range for the determination of dichlorvos and paraoxon alone and together were determined. The recovery was characterized to determine dichlorvos and paraoxon fortified in model solutions and milk. These results demonstrate the potential of this immunoassay for the quantitative screening of dichlorvos and paraoxon.