Interfacial Precipitate Research Articles

Growth and mechanical properties of a MoC precipitate at a Mo grain boundary: Anab initiodensity functional theory study

Atomic-scale stages of the growth of an interfacial precipitate film of tetragonal molybdenum carbide at a $\ensuremath{\Sigma}5$ (310) [001] symmetrical tilt grain boundary in body-centered cubic molybdenum were investigated by means of atomistic supercell calculations on the basis of ab initio density functional theory. The structural development of the precipitate with increasing carbon concentration is analyzed qualitatively and quantitatively. The structurally optimized atomistic model for the fully developed precipitate is compared to experimental high-resolution images from transmission electron microscopy. Characteristic interface energies are calculated to evaluate the influence of the precipitate on the mechanical stability of the material. Finally, an atomic-scale twinning mechanism in the MoC precipitate is proposed.

Enhancement of Lipase Enzyme Activity in Non-Aqueous Media through a Rapid Three Phase Partitioning and Microwave Irradiation

Three phase partitioning is fast developing as a novel bio-separation strategy with a wide range of applications including enzyme stability and enhancement of its catalytic activity. pH tuning of enzyme is now well known for use in non-aqueous systems. Tuned enzyme was prepared using a rapid drying technique of microwave dehydration (time required around 15 minutes). Further enhancement was achieved by three phase partitioning (TPP) method. With optimal condition of ammonium sulphate andt-butanol, the protein appeared as an interfacial precipitate between uppert-butanol and lower aqueous phases. In this study we report the results on the lipase which has been subjected to pH tuning and TPP, which clearly indicate the remarkable increase in the initial rate of transesterification by 3.8 times. Microwave irradiation was found to increase the initial reaction rates by further 1.6 times, hence giving a combined increase in activity of about 5.4 times. Hence it is shown that microwave irradiation can be used in conjunction with other strategies (like pH tuning and TPP) for enhancing initial reaction rates.

Aging Behaviors in AZ91D/Al<SUB>18</SUB>B<SUB>4</SUB>O<SUB>33w</SUB> Composite Fabricated by Squeeze Casting

Aluminum borate whisker (Al18B4O33w, denoted by ABOw) reinforced AZ91D (Mg-9.1 mass%Al-0.7 mass%Zn) magnesium alloy composite was fabricated by squeeze casting. AZ91D/ABOw composite and AZ91D alloy were aged at 443 K in oil-bath. The composite exhibited an accelerated age-hardening response comparing with AZ91D alloy. Age-hardening efficiency of composite was better than that of AZ91D alloy. It was attributed to the interfacial reaction between AZ91D alloy matrix and ABOw. The interfacial reaction increased aluminum elements in the matrix and MgO interfacial reaction layer restrained the formation of interfacial precipitate, resulting in more amounts of continuous precipitates and smaller inter-precipitates spacing within the composite matrix.

Refolding of a denatured α-chymotrypsin and its smart bioconjugate by three-phase partitioning

α-Chymotrypsin inactivated with 8 M urea and 100 mM dithiothreitol could be completely reactivated by subjecting it to three-phase partitioning (TPP). TPP consisted of adding 30% w/v ammonium sulfate and t-butanol (volume equivalent to aqueous solution of denatured α-chymotrypsin) at 25°C. The activated α-chymotrypsin was recovered as an interfacial precipitate between the upper organic and lower aqueous phase. It was found that this could be extended to a thermally inactivated smart bioconjugate of α-chymotrypsin with Eudragit S-100 (a reversibly soluble–insoluble methmethacrylate). The thermally inactivated bioconjugate had to be further subjected to urea and dithiothreitol before refolding by three-phase partitioning. Ninety per cent of the activity of the bioconjugate could be recovered. The free enzyme and its bioconjugate which lost activity in the presence of 90% dioxane recovered 94 and 90% of their activities, respectively, by employing TPP. The refolded free enzyme and its bioconjugate were evaluated in terms of Vmax/Km and their fluorescence emission spectra.

A novel process for extraction of edible oils: Enzyme assisted three phase partitioning (EATPP)

Three phase partitioning (TPP), a technique used in protein purification has been evaluated, for extraction of oil from three different plant sources viz: mango kernel, soybean and rice bran. The process consists of simultaneous addition of t-butanol (1:1, v/v) and ammonium sulphate (w/v) to a crude preparation/slurry. Under optimized condition, the protein appears as an interfacial precipitate between upper t-butanol containing oil and lower aqueous phase. Pretreatment of the slurries with a commercial enzyme preparation of proteases, Protizyme™, followed by three phase partitioning resulted in 98%, 86% and 79% (w/w) oil yields in case of soybean, rice bran and mango kernel, respectively. The efficiency of the present technique is comparable to solvent extraction with an added advantage of being less time consuming and using t-butanol which is a safer solvent as compared to n-hexane used in conventional oil extraction process.

Recovery of biological activity in reversibly inactivated proteins by three phase partitioning

Three phase partitioning (TPP) is carried out by adding ammonium sulphate and t-butanol to an aqueous solution of proteins. Under optimized conditions, the protein appears as an interfacial precipitate between upper t-butanol and lower aqueous phases. It is shown that TPP can be used to recover biological activities of cellulase, cellobiase and β-glucosidase from their urea-denatured forms. The activities were originally present in a commercial preparation and TPP led to simultaneous purification as well. The best results were 94% regain of activity with 73-fold purification for cellulase, 98% regain of activity with 65-fold purification for cellobiase and 90% regain of activity with 101-fold purification for β-glucosidase. Working with more concentrated protein solutions was possible but poor results were obtained beyond 10 mg ml −1 of the starting protein concentration.

Affinity precipitation and macroaffinity ligand facilitated three-phase partitioning for refolding and simultaneous purification of urea-denatured pectinase.

Protein refolding is an integral step in the recovery of protein activity from inclusion bodies. It is shown that affinity precipitation and macroaffinity ligand facilitated three-phase partitioning (MLFTPP) led to refolding of urea-denatured pectinase present in a commercial preparation, with simultaneous purification. Affinity precipitation consists of precipitation of the desired enzyme by complexing it with a suitable stimulus-sensitive macroaffinity ligand. This ligand in this case was alginate/esterified alginate. The complex of the polymer-pectinase could be precipitated by adding calcium ions. In MLFTPP (carried out by adding tertiary butanol and ammonium sulfate to the aqueous solution of crude enzyme and the polymer), the polymer or its complex with the enzyme form an interfacial precipitate between tert-butyl alcohol phase and aqueous phase. It is believed that in both processes, while molecular recognition of alginate/esterified alginate to pectinase facilitates their selective binding to the enzyme, the correct refolding is facilitated by preventing molecular aggregation of unfolded enzyme molecules. Three-phase partitioning with esterified alginate as the macroaffinity ligand gave 100% recovery with 4-fold purification. Affinity precipitation with 1% alginate gave 52% yield with 18-fold purification. On the other hand, use of 0.5% esterified alginate gave only 7-fold purification but with 75% recovery of activity.

Three-phase partitioning for simultaneous renaturation and partial purification of Aspergillus niger xylanase

Three-phase partitioning (TPP) is carried out by mixing ammonium sulfate and t-butanol to obtain organic phase, interfacial precipitate and aqueous phase. It is shown that TPP of an 8 M urea/100 mM dithiothreitol-denatured xylanase preparation resulted in simultaneous renaturation and purification. This integrated novel approach gave recovery of 93% enzyme activity with 21-fold purification. The implications of this in the context of recovering activity from inclusion bodies are discussed.

Separation of enzymes by sequential macroaffinity ligand-facilitated three-phase partitioning

Pectinase and cellulase were separated from a commercial enzyme preparation called Pectinex Ultra SP-L. This was carried out using a process called macroaffinity ligand-facilitated three-phase partitioning (MLFTPP). In this method, a water-soluble polymer is floated as an interfacial precipitate by adding ammonium sulfate and tert.-butanol. The polymer (appropriately chosen) in the presence of an enzyme for which it shows affinity, selectively binds to the enzyme and floats as a polymer–enzyme complex. In the first step, pectinase was purified (with alginate as the polymer) 13-fold with 96% activity recovery. In the second MLFTPP step, using chitosan, cellulase was purified 16-fold with 92% activity recovery. Both preparations showed a single band on sodium dodecylsulfate–polyacrylamide gel electrophoresis. This illustrative example shows that the strategy of sequential MLFTPP can be used to separate important biological activities from a crude broth.

Macroaffinity ligand-facilitated three-phase partitioning for purification of glucoamylase and pullulanase using alginate

Starch-degrading enzymes glucoamylase (from Aspergillus niger), and pullulanase (from Bacillus acidopullulyticus) were purified using alginates (polysaccharides consisting of mannuronic acids and guluronic acids) by a recently developed technique called macroaffinity ligand-facilitated three-phase partitioning (MLFTPP). In this process, a crude preparation of the enzyme was mixed with alginate. On addition of appropriate amounts of ammonium sulfate and t-butanol, the alginate bound enzyme appeared as an interfacial precipitate between the lower aqueous and the upper t-butanol phase. Enzyme activity from this interfacial precipitate was recovered using 1 M maltose. Glucoamylase and pullulanase were purified 20- and 38-fold with 83% and 89% activity recovery, respectively. Both the purified preparations showed a single band on SDS–PAGE.

Some studies on characterization of three phase partitioned chitosan

Three phase partitioning (TPP) is generally carried out by adding ammonium sulfate and t-butanol to a solution of a macromolecule. Chitosan could be obtained as an interfacial precipitate with 88% yield by subjecting 0.2% (w/v) chitosan solution to TPP with 45% (w/v) ammonium sulfate, with an equal volume of t-butanol at 40 °C. TPP resulted in structural changes which could be seen in its UV spectra, FT-IR spectra and solubility characteristics. TPP-treated chitosan also showed decreased susceptibility towards hydrolysis by chitinase. Thus, TPP can be used as a useful way of altering the properties of chitosan.

Aging behavior of squeeze cast SiCw/AZ91 magnesium matrix composite

The aging behavior of SiC whisker reinforced AZ91 magnesium matrix composites was investigated with Vickers hardness measurement, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The precipitation process observed in the monolithic alloy was not altered by the addition of SiC whiskers. The composite exhibited an accelerated hardening response compared with the unreinforced matrix alloy. However, the addition of SiC whiskers altered the distribution of the Mg 17Al 12 precipitates. Mg 17Al 12 precipitated preferentially at the SiCw–AZ91 interface, with a definite orientation relationship with SiC whisker: (1̄10) Mg17Al12//(111) SiCw, [111] Mg17Al12//[01 1 ̄ ] SiCw. The preferential interfacial precipitate decreased the Al content in the matrix, resulting in a decrease in the amount of continuous precipitates. As a consequence, the age-hardening efficiency in the composite was lower.

Macroaffinity ligand-facilitated three-phase partitioning (MLFTPP) for purification of xylanase.

It is shown that eudragit S-100, a copolymer of methylacrylic acid and methylmethacrylate, undergoes three-phase partitioning. It was found that 95% eudragit S-100 could be recovered as the interfacial precipitate by using 30% (w/v) ammonium sulfate, 1:1 ratio of t-butanol to polymer solution at 40 degrees C. Three-phase partitioning of proteins uses simultaneous addition of ammonium sulfate and t-butanol to precipitate proteins in an interfacial layer separating the aqueous phase and organic solvent. Exploiting the affinity of xylanases towards eudragit S-100, it was possible to purify xylanase from Aspergillus niger; 60% recovery of activity with 95-fold purification could be obtained by this process. The purified enzyme showed A single band on SDS-PAGE. The technique shows promise to develop into a general method that could be termed "macroaffinity ligand-facilitated three-phase partitioning (MLFTPP).

Three phase partitioning of carbohydrate polymers: separation and purification of alginates

Three phase partitioning, a technique described for protein purification, has been employed for precipitation and purification of three different commercial preparations of alginates. Three phase partitioning works by the addition of t-butanol to aqueous solution of the polymer containing 20–30% ammonium sulphate (w/v). Three phases formed are: upper t-butanol layer, interfacial polymer precipitate and lower aqueous phase. In all the three cases, the process optimization was carried out by varying ammonium sulphate concentration, volume of t-butanol, alginate concentration and temperature. Fluorescence spectroscopy was used to show that repeated cycles of TPP also resulted in considerable reduction in polyphenol content of a crude alginate preparation.

Interface structure in graphite‐fiber‐reinforced metal–matrix composites

AbstractFiber/matrix interfaces in continuous fiber‐reinforced composites are the regions of imperfections, high dislocation densities and residual stresses that affect the material's properties. The interfacial bond integrity, dislocation substructure and precipitate morphology in the interfiber matrix region in diffusion‐bonded graphite–aluminum (Gr–Al), graphite–magnesium (Gr–Mg) and cast Gr–Mg composites has been examined by transmission electron microscopy. This paper discusses the observations of the typical interface structure in Gr–Al and Gr–Mg composites. The Gr–Al composites exhibit different precipitate morphologies (blocky, lath‐shaped and fine cuboidal of similar chemical composition) and Gr–Mg composites show both spherical and lamellar Mg17Al12 precipitates. A typical interface structure in diffusion‐bonded composites exhibits no voids and reaction compounds, whereas in cast Gr–Mg composites patches of microvoids are observed sporadically near the interface, along with Mg2Si and MgO phases formed due to the chemical interaction between the matrix and SiO2 fiber coating. Adjacent to the interface, both Gr–Al and Gr–Mg exhibit a high density of dislocations that can be attributed to the residual stress state generated because of differential contraction between the fiber and matrix during the fabrication process. Copyright © 2001 John Wiley & Sons, Ltd.

Extraction of lysozyme and ribonuclease‐a using reverse micelles: Limits to protein solubilization

Experiments are reported here on the equilibrium partitioning of lysozyme and ribonuclease-a between aqueous and reversed micellar phases comprised of an anionic surfactant, sodium di-2-ethylhexyl sulfosuccinate (AOT), in isooctane. A distinct maximum, [P](rm,max) was found for the quantity of a given protein that can be solubilized in the reverse micelle phase by the phase-transfer method. This upper limit depended upon the size of the protein, the surfactant concentration, and the aqueous phase ionic strength, and was determined by complex formation between protein and surfactant molecules to form an insoluble interfacial precipitate at high values of [P](rm). In this work, it was found to be possible to dissociate the protein-surfactant complex and recover the precipitated protein. The kinetics of protein-surfactant complex formation depended upon the nature and concentration of the solubilized protein and on the surfactant concentration. Calculations of micellar occupancy and the relative surface areas of protein molecules and surfactant head-groups suggested that it was the exposure of the solubilized protein to the bulk organic solvent which promoted protein-surfactant complex formation as [P](rm) --> [P](rm,max). In the light of the experimental results and calculations described above, a mechanistic model is proposed to account for the observed phenomena. This is based upon the competing effects of increasing the solubilized protein concentration and the corresponding increase in the rate of protein-surfactant complex formation. The dynamic nature of the reverse micelles is inherent in the model, explaining the formation of the interfacial precipitate with time and its dependence on the internal phase volume of the micellar phase. Experiments on the co-partitioning of water and measurement ofthe AOT concentration in both phases verified the loss of protein, water, and surfactant from the organic phase at high values of [P](rm). (c) 1995 John Wiley & Sons Inc.

Elaboration and TEM structural study of interfaces in composites produced by precipitation

Model ceramic matrix composites have been manufactured in a wide range of materials using the precipitation of a metal (Cu, Ni, Cr) in a ceramic matrix (nitride AlN or oxides MgO, Al 2 O 3 ) providing, in each case, low energy configurations at the heterophase interfaces. In connection to microelectronic applications, copper metallic particles precipitate in AlN after implantation by copper ions and anneal of the ceramic matrix. Faceted particles are imaged by HRTEM an are associated to a low energy structural and chemical configuration. Internal reduction experiments have been carried out on (Mg,Ni)O, (Mg,Cu)O and (Al,Cr)203 mixed oxides; the morphology, chemical composition and orientation relationship of the different precipitates are obtained through TEM observations and discussed in terms of interfacial energy and precipitate growth mechanism and kinetics. Conventional and high resolution TEM in conjonction to structural models have allowed a comprehensive description of the interface

The electrograining of aluminium in hydrochloric acid—II. Formation of ETCH products

During a.c. electrograining of aluminium in HCl electrolyte, a non-uniform etch film is developed over the aluminium surface. The film is deposited as colloidal material, containing fine, amorphous Al(OH) 3 particles, together with appreciable quantities of water (about 90%); additionally, metallic aluminium particles, resulting from undermining of the substrate during pit propagation, are resident within the film. By examination of etch film development as a function of a.c. waveform frequency, it is evident that the film develops during negative half cycles when sufficient boundary layer alkalinity occurs. Thus, for a.c. waveform frequencies below about 250 Hz, hydrogen evolution causes a significant local increase of pH allowing the formation of aluminate ions. The aluminate ions are soluble only in the high pH interfacial region and precipitate as Al(OH) 3 upon contact with the bulk acid electrolyte.

Atom probe and transmission electron microscopy study of aging of cast duplex stainless steels

The microstructural evolution of Mo bearing and Mo free cast duplex stainless steels, induced by long term aging in the range 350–4507deg;C has been studied using atom probe and field ion microscopy and transmission electron microscopy. The salient features of this evolution at 350 and 400°C are spinodal decomposition and G phase precipitation in the ferrite. The nucleation of the G phase is enhanced by spinodal decomposition. Other intermetallic phases observed at higher temperatures may also be formed at 400°C. In the ferrite/ austenite interface, an intermetallic film, possibly an icosahedral phase, is formed after aging for 30 000 h at 400 and 450°C in Mo bearing steels, whereas interfacial M23C6 carbides precipitate in the Mo free materials. The observed evolution of the spatial and compositional parameters of the spinodal decomposition in Mo bearing steels is described and its relationship with the evolution of mechanical properties is outlined.MST/1185

The Gibbs-thomson equation for a spherical coherent precipitate with applications to nucleation

The conditions for interfacial thermodynamic equilibrium form the basis for the derivation of a number of basic equations in materials science, including the various forms of the Gibbs-Thomson equation. The equilibrium conditions pertaining to a curved interface in a two-phase fluid system are well-known. In contrast, the conditions for thermodynamic equilibrium at a curved interface in nonhydrostatically stressed solids have only recently been examined. These conditions can be much different from those at a fluid interface and, as a result, the Gibbs-Thomson equation appropriate to coherent solids is likely to be considerably different from that for fluids. In this paper, the authors first derive the conditions necessary for thermodynamic equilibrium at the precipitate-matrix interface of a coherent spherical precipitate. The authors' derivation of these equilibrium conditions includes a correction to the equilibrium conditions of Johnson and Alexander for a spherical precipitate in an isotropic matrix. They then use these conditions to derive the dependence of the interfacial precipitate and matrix concentrations on precipitate radius (Gibbs-Thomson equation) for a such a precipitate. In addition, these relationships are then used to calculate the critical radius for the nucleation of a coherent misfitting precipitate.