Microbially induced separation of quartz from calcite using Saccharomyces cerevisiae

Cells of Saccharomyces cerevisiae and their metabolites were successfully utilized to achieve selective separation of quartz and calcite through microbially induced flotation and flocculation. S. cerevisiae was adapted to calcite and quartz minerals. Adsorption studies and electrokinetic investigations were carried out to understand the changes in the surface chemistry of yeast cells and the minerals after mutual interaction. Possible mechanisms in microbially induced flotation and flocculation are outlined. (C) 2011 Elsevier B.V. All rights reserved.

Ultra fine scale phase separated microstructure for Ag-Fe nanoparticle

We report the formation of Ag-Fe nanoparticles with an ultrafine scale phase separated microstructure consisting of Ag and Fe(3)O(4) phases. Ag-Fe particles were synthesised by the co-reduction of Ag and Fe salts in water medium. The co-existing Ag and Fe(3)O(4) phase volumes were around similar to 1 nm in one of the dimensions. (C) 2011 Elsevier B. V. All rights reserved.

Mechanistic overview of the curing behavior of hydride terminated polydimethylsiloxane with allyl functionalized alumina by calorimetry and rheometry

The study of the curing behavior of an encapsulation material is very important and critical in terms of understanding the properties of the material. Differential scanning calorimetry and rheometry are two important tools that have been utilized to study curing reactions in polymeric systems. The present work deals with the curing of a mixture of hydride terminated polydimethylsiloxane, allyl functionalized alumina nanoparticles and Karstedt's catalyst. The real time curing behavior of the typical system was monitored non-isothermally by differential scanning calorimetry and rheometry. The results obtained from the respective techniques reveal that there is a good correlation between these two techniques. A mechanism is proposed for the curing reaction of the polymer system based on the curing curves obtained by the above two studies. In addition, the swelling study and contact angle measurement of the two composites was performed to evaluate the extent of cross-linking and hydrophobicity. (C) 2011 Elsevier B.V. All rights reserved.

Total synthesis of (-)-ent-pachastrissamine (ent-Jaspine B)

The total synthesis of the enantiomer of the tetrahydrofuran containing natural product Jaspine B is reported. The key reactions in the synthesis include formation of the tetrahydrofuran unit by an acid mediated Williamson etherification and a subsequent elaboration with an olefin cross metathesis reaction. (C) 2011 Elsevier Ltd. All rights reserved.

Control of Molecular Weight and Polydispersity of Hyperbranched Polymers Using a Reactive B(3) Core: A Single-Step Route to Orthogonally Functionalizable Hyperbranched Polymers

Molecular weight and polydispersity are two structural features of hyperbranched polymers that are difficult to control because of the statistical nature of the step-growth polycondensation of AB(2) type monomers; the statistical growth also causes the polydispersity index to increase with percent conversion (or molecular weight). We demonstrate that using controlled amounts of a specifically designed B(3) core, containing B-type functionality that are more reactive than those present in the AB(2) monomer, both the molecular weight and the polydispersity can be readily controlled; the PDI was shown to improve with increasing mole-fraction of the B(3) core while the polymer molecular weight showed an expected decrease. Incorporation of a ``clickable'' propargyl group in the B(3) core unit permitted the generation of a core-functionalizable hyperbranched polymer. Importantly, this clickable core, in combination with a recently developed AB(2) monomer, wherein the B-type groups are allyl ethers and A is an hydroxyl group, led to the generation of a hyperbranched polymer carrying orthogonally functionalizable core and peripheral groups, via a single-step melt polycondensation. Selective functionalization of the core and periphery using two different types of chromophores was achieved, and the occurrence of fluorescence resonance energy transfer (FRET) between the donor and acceptor chromophores was demonstrated.

Control of Molecular Weight and Polydispersity of Hyperbranched Polymers Using a Reactive B(3) Core: A Single-Step Route to Orthogonally Functionalizable Hyperbranched Polymers

Molecular weight and polydispersity are two structural features of hyperbranched polymers that are difficult to control because of the statistical nature of the step-growth polycondensation of AB(2) type monomers; the statistical growth also causes the polydispersity index to increase with percent conversion (or molecular weight). We demonstrate that using controlled amounts of a specifically designed B(3) core, containing B-type functionality that are more reactive than those present in the AB(2) monomer, both the molecular weight and the polydispersity can be readily controlled; the PDI was shown to improve with increasing mole-fraction of the B(3) core while the polymer molecular weight showed an expected decrease. Incorporation of a ``clickable'' propargyl group in the B(3) core unit permitted the generation of a core-functionalizable hyperbranched polymer. Importantly, this clickable core, in combination with a recently developed AB(2) monomer, wherein the B-type groups are allyl ethers and A is an hydroxyl group, led to the generation of a hyperbranched polymer carrying orthogonally functionalizable core and peripheral groups, via a single-step melt polycondensation. Selective functionalization of the core and periphery using two different types of chromophores was achieved, and the occurrence of fluorescence resonance energy transfer (FRET) between the donor and acceptor chromophores was demonstrated.

The role of surface texture on friction and transfer layer formation during repeated sliding of Al-4Mg against steel

In the present investigation, various kinds of textures, namely, unidirectional, 8-ground, and random were attained on the die surfaces. Roughness of the textures was varied using different grits of emery papers or polishing powders. Then pins made of Al-4Mg alloys were slid against steel plates at various numbers of cycles, namely, 1, 3, 5, 10 and 20 using pin-on-plate reciprocating sliding tester. Tests were conducted at a sliding velocity of 2 minis in ambient conditions under both dry and lubricated conditions. A constant normal load of 35 N was applied in the tests. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. Surface roughness parameters of the plates were measured using an optical profilometer. In the experiments, it was observed that the coefficient of friction and formation of the transfer layer depend on the die surface textures under both dry and lubricated conditions. More specifically, the coefficient of friction decreases for unidirectional and 8-ground surfaces while for random surfaces it increases with number of cycles. However, the coefficient of friction is highest for the sliding perpendicular to the unidirectional textures and least for the random textures under both dry and lubricated conditions. The difference in friction values between these two surfaces decreases with increasing number of cycles. The variation in the coefficient of friction under both dry and lubrication conditions is attributed to the change in texture of the surfaces during sliding. (C) 2011 Elsevier B.V. All rights reserved.

Tribological characteristics of A356 Al alloy-SiC(P) composite discs

The dry sliding wear and friction behaviour of A356 Al alloy and its composites containing 10 and 20 vol.% SiC(P) have been studied using pin-on-disc set up. In these tests, A356 Al alloy and its composites are used as disc whereas brake pad was used in the form of pins. Wear tests were carried out at a load of 192 N and the sliding speed was varied from 1 to 5 m/s. Tests were done for a sliding distance of 15 km. The effects of sliding velocity on the wear rate, coefficient of friction and nature of tribolayers formed on discs have been studied. Wear rates of composites as calculated by weight loss method, found to be negative at sliding speed of more than 2 m/s. Worn surfaces of pins and discs have been analyzed using scanning electron microscope. SEM and EDAX analysis of worn surfaces of composite discs showed formation of tribolayers, consisting of mixture of oxides of Al, Si, Cu, Ca, Ba, Mg, and Fe. In these layers, copper and barium content found to be increase with sliding speed in the case of composites. (C) 2011 Elsevier B.V. All rights reserved.

Wear behavior of plasma electrolytic oxidation (PEO) and hybrid coatings of PEO and laser on MRI 230D magnesium alloy

Wear resistant coatings were produced on a permanent mould cast MRI 230D Mg alloy by (a) PEO in silicate based electrolyte, (b) PEO in phosphate based electrolyte, (c) hybrid coatings of silicate PEO followed by laser surface alloying (LSA) with Al and Al(2)O(3), and (d) hybrid coatings of phosphate PEO followed by LSA with Al and Al(2)O(3). Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) and X(ray diffraction. The tribological behavior of the coatings was investigated under dry sliding condition using linearly reciprocating ball-on-flat wear test. Both the PEO coatings exhibited a friction coefficient of about 0.8 and hybrid coatings exhibited a value of about 0.5 against the AISI 52100 steel ball as the friction partner, which were slightly reduced with the increase in applied load. The PEO coatings sustained the test without failure at 2 N load but failed at 5 N load due to micro-fracture caused by high contact stresses. The hybrid coatings did not get completely worn off at 2 N load but were completely removed exposing the substrate at 5 N load. The PEO coatings exhibited better wear resistance than the hybrid coatings and silicate PEO coatings exhibited better wear resistance than the phosphate PEO coatings. Both the PEO coatings melted/decomposed on laser irradiation and all the hybrid coatings exhibited similar microstructure and wear behavior irrespective of the nature of the primary PEO coating or laser energies. SEM examination of worn surfaces indicated abrasive wear combined with adhesive wear for all the specimens. The surface of the ball exhibited a discontinuous transfer layer after the wear test. (C) 2011 Elsevier B.V. All rights reserved.

Friction and transfer layer formation in polymer-steel tribo-system: Role of surface texture and roughness parameters

In the present investigation, various kinds of surface textures were attained on the steel plates. Roughness of the textures was varied using various grinding or polishing methods. The surface textures were characterized in terms of roughness parameters using an optical profilometer. Then experiments were conducted using an inclined pin-on-plate sliding apparatus to identify the role of surface texture and its roughness parameters on coefficient of friction and transfer layer formation. In the experiments, a soft polymer (polypropylene) was used for the pin and hardened steel was used for the plate. Experiments were conducted at a sliding velocity of 2 minis in ambient conditions under both dry and lubricated conditions. The normal load was varied from 1 to 120 N during the tests. The morphologies of the worn surfaces of the pins and the formation of a transfer layer on the steel plate surfaces were observed using a scanning electron microscope. Based on the experimental results, it was observed that the transfer layer formation and the coefficient of friction along with its two components, namely adhesion and plowing, were controlled by the surface texture of the harder mating surfaces and were less dependent of surface roughness (R(a)) of the harder mating surfaces. The effect of surface texture on the friction was attributed to the variation of the plowing component of friction for different surfaces. Among the various surface roughness parameters studied, the mean slope of the profile, Delta(a), was found to most accurately characterize variations in the friction and wear behavior. (C) 2011 Elsevier B.V. All rights reserved.

Prediction of activities of oxygen in dilute quaternary solutions using binary data

Equations are developed for predicting the activity coefficients of oxygen dissolved in ternary liquid alloys. These are extensions of earlier treatments, and are based on a model in which each oxygen atom is assumed to make four bonds with neighboring metal atoms. It is also postulated that the strong oxygen-metal bonds distort the electronic configuration around the metal atoms bonded to oxygen, and that the quantitative reduction of the strength of bonds made by these atoms with all of the adjacent metal atoms is equivalent to a factor of approximately two. The predictions of the quasichemical equation which is derived agree satisfactorily with the partial molar free energies of oxygen in Ag-Cu-Sn solutions at 1200°C reported in literature. An extension of this treatment to multicomponent solutions is also indicated.

Solubilities of Pb+2, Bi+3, Sb+3 and Cu+1 sulphides in (NaCl KCl Na2S) melts

Solubilities of common metal sulfides have been determined in the (NaCl+KCl) eutectic melt with and without Na2S. A novel gas-phase equilibrium technique has been used for PbS, Bi2S3, and So2S3, and an improved liquid phase equilibrium technique for Cu2S, which eliminates the errors due to physical entrapment of the sulfide phase and segregation on quenching, enabling precise measurements to be made. Solubilities in the (NaCl+KCl) eutectic melt were determined as a function of temperature in the rante 700° to 950°C, and were found to be small. The partial molar heats of mixing of the sulfides in the eutectic melt have been calculated from the solubility measurements, to be 13.3, 31.4, 37.1, and 49.0 kcal for PbSs), Sb2S2(l), and Cu2S(s), respectively. Sodium sulfide addition was observed to enhance these solubilities, the effect being largest for Cu2S followed by Sb2S3, Bi2S3, and PbS. This effect is explained qualitatively. It was observed that PbS and Sb2S3 obey Henry's law up to saturation in (NaCl+KCl+Na2S) melts.

The oxygen potential of the systems Fe+FeCr2O4+ Cr2O3 and Fe+FeV2O4+ V2O3 in the temperature range 750 1600o C

From electromotive force (emf) measurements using solid oxide galvanic cells incorporating ZrOz-CaO and ThOz-YO~.s electrolytes, the chemical potentials of oxygen over the systems Fe + FeCrzO 4 + Cr20 ~ and Fe + FeV204 + V203 were calculated. The values may be represented by the equations: 2Fe(s, I) + Oz(g) + 2Cr2Oa(s) -- 2FeCr204 (s)Akto2 = - 151,400 + 34.7T (• cal= -633,400 + 145.5T(• J (750 to 1536~ A~tO2 = -158,000 + 38.4T(• cal= -661,000 + 160.5T(*1250) J (1536 to 1700~2Fe (s, I) + O2 (g) + 2V203 (s) -- 2FeV204 (s) A/~Oz = - 138,000 + 29.8T(+300) cal= - 577,500 + 124.7T (• J (750 to 1536~A/IO2 = -144,600 + 33.45T(-300) cal = -605,100 + 140.0T(~-1250) J (1536 to 1700~At the oxygen potentials corresponding to Fe + FeCrzO a + Cr203 equilibria, the electronic contribution to the conductivity of ZrO2-CaO electrolyte was found to affect the measured emf. Application of a small 60 cycle A.C. voltage with an amplitude of 50 mv across the cell terminals reduced the time required to attain equilibrium at temperatures between 750 to 9500C by approximately a factor of two. The second law entropy of iron chromite obtained in this study is in good agreement with that calculated from thermal data. The entropies of formation of these spinel phases from the component oxides can be correlated to cation distribution and crystal field theory.

Solubility and activity of oxygen in liquid germanium and germanium copper alloys

The solubility of oxygen in liquid germanium in the temperature range 1233 to 1397 K, and in liquid germanium-copper alloys at 1373 K, in equilibrium with GeO2 has been measured by the phase equilibration technique. The solubility of oxygen in pure germanium is given by the relation R470 log(at. pct 0)=-6470/T+4.24 (±0.07). The standard free energy of solution of oxygen in liquid germanium is calculated from the saturation solubility, and recently measured values for the free energy of formation of GeO2, assuming that oxygen obeys Sievert’s law up to the saturation limit. For the reaction, 1/2 O2(g)→ OGe ΔG° =-39,000 + 3.21T (±500) cal = -163,200 + 13.43T (±2100) J. where the standard state for dissolved oxygen is that which makes the value of activity equal to the concentration (in at. pct), in the limit, as concentration approaches zero. The effect of copper on the activity of oxygen dissolved in liquid germanium is found to be in good agreement with that predicted by a quasichemical model in which each oxygen was assumed to be bonded to four metal atoms and the nearest neighbor metal atoms to an oxygen atom are assumed to lose approximately half of their metallic bonds.