Microstructural developments in TLP bonds using thin interlayers based on Ni–B coatings

Oxide dispersion strengthened alloy MA 758 was transient liquid phase (TLP) bonded using thin interlayers based on Ni–B electrodeposited coatings and the microstructural developments across the joint region were studied. The bonding surfaces were electrodeposited with a coat thickness of 2–9 μm and microstructural features were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The homogeneity of the joint was assessed performing micro-hardness test. The results showed that the coating thickness as well as the amount of melting point depressants (boron) in the coatings had a significant effect on the microstructural developments within the joint region. TLP bonds made using a 2 μm thick coating interlayer produced a joint with no visible precipitate formation and parent metal dissolution, and the absence of precipitates was attributed to the lower volume concentration of boron in the 2 μm thick coating interlayer.     

Experimental investigation and empirical modeling of the dry electric discharge machining process

Dry electric discharge machining (EDM) is an environment-friendly modification of the oil EDM process in which liquid dielectric is replaced by a gaseous medium. In the current work, parametric analysis of the process has been performed with tubular copper tool electrode and mild steel workpiece. Experiments have been conducted using air as the dielectric medium to study the effect of gap voltage, discharge current, pulse-on time, duty factor, air pressure and spindle speed on material removal rate (MRR), surface roughness (R_a) and tool wear rate (TWR). First, a set of exploratory experiments has been performed to identify the optimum tool design and to select input parameters and their levels for later stage experiments. Empirical models for MRR, R_a and TWR have then been developed by performing a designed experiment based on the central composite design of experiments. Response surface analysis has been done using the developed models. Analysis of variance (ANOVA) tests were performed to identify the significant parameters. Current, duty factor, air pressure and spindle speed were found to have significant effects on MRR and R_a. However, TWR was found to be very small and independent of the input parameters.     

Synthesis of nanocrystalline hydroxyapatite using surfactant template systems: Role of templates in controlling morphology

Hydroxyapatite (HA) nanopowder was synthesized by reverse microemulsion technique using calcium nitrate and phosphoric acid as starting materials in aqueous phase. Cyclohexane, hexane, and isooctane were used as organic solvents, and Dioctyl sulfosuccinate sodium salt (AOT), dodecyl phosphate (DP), NP5 (poly(oxyethylene)₅ nonylphenol ether), and NP12 (poly(oxyethylene)₁₂ nonylphenol ether) as surfactants to make the emulsion. Effect of synthesis parameters, such as type of surfactant, aqueous to organic ratio (A/O), pH and temperature on powder characteristics were studied. It was found that the surfactant templates played a significant role in regulating the morphology of the nanoparticle. Hydroxyapatite nanoparticle of different morphologies such as spherical, needle shape or rod-like were obtained by adjusting the conditions of the emulsion system. Synthesized powder was characterized using X-ray diffraction (XRD), BET surface area and transmission electron microscopy (TEM). Phase pure HA nanopowder with highest surface area of 121 m²/g were prepared by this technique using NP5 as a surfactant. Densification studies showed that this nanoparticle can give about 98% of their theoretical density. In vitro bioactivity of the dense HA compacts was confirmed by excellent apatite layer formation after 21 days in SBF solution. Cell material interaction study showed good cell attachment and after 5 days cells were proliferated on HA compacts in OPC1 cell culture medium. The results imply this to be a versatile approach for making hydroxyapatite nanocrystals with controlled morphology and excellent biocompatibility.     

Optimization of bead geometry in electron beam welding using a Genetic Algorithm

Bead-on-plate welds were carried out on austenitic stainless steel plates using an electron beam welding machine. Experimental data were collected as per central composite design and regression analysis was conducted to establish input–output relationships of the process. An attempt was made to minimize the weldment area, after satisfying the condition of maximum bead penetration. Thus, it was posed as a constrained optimization problem and solved utilizing a Genetic Algorithm with a penalty function approach. The Genetic Algorithm was able to determine optimal weld-bead geometry and recommend the necessary process parameters for the same.     

Purification and characterization of thermophilic and alkalophilic tributyrin esterase fromBacillus strain A30-1 (ATCC 53841)

An extracellular esterase (EC 3.1.1.1) from a thermophilicBacillus A30-1 (ATCC 53841) was purified 139-fold to homogeneity by sodium chloride (6 M) treatment, ammonium sulfate fractionation (30–80%) and phenyl-Sepharose CL-6B column chromatography. The native enzyme was a single polypeptide chain with a molecular weight of about 65,000 and an isoelectric point at pH 4.8. The optimum pH for esterase activity was 9.0, and its pH stability range was 5.0–10.5. The optimum temperature for its activity was 60°C. The esterase had a half-life of 28 h at 50°C, 20 h at 60°C and 16 h at 65°C. It showed the highest activity on tributyrin, with little or no activity toward long-chain (12–20 carbon) fatty acid esters. The enzyme displayed K_m and K_cat values of 0.357 mM and 8365/min, respectively, for tributyrin hydrolysis at pH 9.0 and 60°C. Cyclodextrin (α, β, and γ), Ca²⁺, Co²⁺, Mg²⁺ and Mn²⁺ enhanced the esterase activity, and Zn²⁺ and Fe²⁺ acted as inhibitors of the enzyme activity. The enzyme activity was not affected by ethylenediaminetetraacetic acid, p-chloromercuribenzoate andN-bromosuccinimide. This paper was presented in part at the 82nd Annual Meeting and Exposition of the American Oil Chemists’ Society, held May 12–15, 1991, in Chicago, Illinois.     

Functional properties of sonicated and non-sonicated extracted leaf protein concentrate from Diplazium esculentum

Leaf protein concentrate of edible fern Diplazium esculentum was extracted using sonication and non-sonication methods and its functional properties were evaluated. The leaf protein concentrate contained 34.28 and 9.89% protein for sonicated and non-sonicated extractions, respectively. Sonication yielded (36.36%) better emulsion activity over non-sonication (31.10%). Foaming capacity was also found better in sonication (7.27%) over non-sonication (6.99%), and oil absorption capacity also improved in sonication (7.55 g of oil/g) over its counterpart (7.41 g of oil/g). Contact angle experiments with the leaf protein concentrate evidenced the enhancement of more hydrophilicity of the sonicated sample. Thermal properties of the leaf protein concentrate with sonication evidenced more stability (55.58 and 95.95°C) over the non-sonicated (46.75 and 75.60°C). Fourier transform infrared spectral analysis with the leaf protein concentrate of Diplazium esculentum was used to assess the secondary structural data such as α-helix and β-sheets. The various percentages of secondary structures of protein in sonicated and non-sonicated samples were 49.06 and 69.16% for α-helix, 33.59% and 17.02% for β-sheet and 42.02 and 35.68% for turn, respectively. The results of the present investigation showed credible evidence to support that sonication method of extraction of leaf protein concentrate was better in terms of protein yield and functional properties as compared to the non-sonication. The sonicated extracted leaf protein concentrate has the potential for developing value added products.     

On the nature and structure of ‘niobic acid’ and its pyrolytic products: 1H NMR,I.R., conductivity and Ion exchange studies

Niobic acid of composition H₈Nb₆O₁₉ has been prepared by thorough drying of the hydrated oxide at 150°C. The mass was heated in stages up to 1200°C and the intermediate products were subjected to ¹H NMR measurements for determining their proton content. Infra red spectra indicate the presence of protons which are highly delocalised among different oxygen sites. The electrical conductivity of niobic acid has been interpreted as due to proton-hopping. The ion exchange capacity of the material has also been studied. The data have been used to formulate the structure of niobic acid and to obtain the correct procedure for the gravimetric determination of niobium as oxide.     

Strengthening of alumina by cerium-zirconate (Ce2Zr2O7)

Composite powders of Al₂O₃ and 0 to 30 vol% Ce₂Zr₂O₇ are prepared by a hybrid sol-gel method using Al₂O₃ powders and a sol formed from Zr-alkoxide and cerium nitrate. All the Zr from the sol goes to form the cerium zirconate phase when the powders are calcined in N₂. Pressureless sintering in air at 1500°C yields composites with high density (98%). Maximum values of fracture toughness and strength, 6.5 MPa and 620 MPa respectively, (e.g. 3.5 MPa and 350 MPa for pure Al₂O₃) are obtained in 10 vol% Ce₂Zr₂O₇ composite sintered in air. The dominant mechanism for enhancement in K _IC is believed to be crack bridging. Crack bridging activity in the 10 vol% composite is found to be maximum and extends upto 190 m from the crack tip.     

Relative viscosity models and their application to capillary flow data of highly filled hard‐metal carbide powder compounds

The rheological behavior of highly filled polymer systems used in powder injection molding (PIM) technology strongly influences the final properties of the products. In this study, the capillary flow data of multi‐component polymer binders—based on polyethylene, paraffin, ethylene‐based copolymers, and polyethylene glycol—compounded with three various hard‐metal carbide powders were employed. The rheology of such highly filled (up to 50 vol%) multiphase systems is necessarily a complex phenomenon characterized by strain dependent, non‐Newtonian properties complicated by flow instabilities and yield. Over 15 mathematical models proposed for highly filled systems were tested, some of them calculating the maximum filler loading. Due to the complex structure of the filler (irregular shape, particle size distribution) and a multi‐component character of the binder, the applicability of these models varied with the powder‐binder systems studied. However, the particular values of maximum loadings are in good accordance with the predictions based on powder characteristics. Simple modification of Frankel‐Acrivos model to the systems containing unimodal hard‐metal carbide powders with particles of an irregular shape and broad particle size distribution gave precise agreement between experimental data and model prediction. POLYM. COMPOS., 26:29–36, 2005. © 2004 Society of Plastics Engineers.