Ductile-phase toughening and Fatigue-Crack Growth in Nb-Reinforced Molybdenum Disilicide Intermetallic Composites

A study has been made of the role of ductile-phase toughening on the ambient temperature fracture toughness and fatigue-crack propagation behavior of a molybdenum disilicide intermetallicmatrix composite reinforced with 20 vol pct niobium spheres. Using disk-shaped compact DC(T) samples, only moderate improvements (∼24 pct) in fracture toughnessK _lcvalues were found for the composite compared to the unreinforced MoSi₂ matrix material. Moreover, (cyclic) fatigue- crack propagation was seen at stress intensities as low as 75 to 90 pct ofK _Ic, with growth rates displaying a high dependency (∼14) on the applied stress-intensity range. The lack of significant toughening due to the incorporation of ductile Nb particles is associated with an absence of crack/particle interactions. This is attributed to the formation of a weak reaction-layer interface and elastic mismatch stresses at the crack tip between the Nb and MoSi₂, both factors which favor interfacial debonding; moreover, the spherical morphology of Nb phase stabilizes cracking around the particle. Results suggest that increasing the aspect ratio of the distributed Nb rein- forcement phase with attendant interfacial debonding and eliminating possible Nb-phase em- brittlement due to interstitial impurity contamination are critical factors for the successful development of tougher Nb/MoSi₂ structural composites. Formerly with McDonnell Formerly with McDonnell     

Synthesis and Characterization of Hydrophobic TMES/TEOS Based Silica Aerogels

The experimental results on the effect of adding trimethylethoxysilane (TMES) as a co-precursor on the hydrophobicity and physical properties of tetraethoxysilane (TEOS) based silica aerogels, are reported. The molar ratio of TEOS, ethanol (EtOH), water (0.001 M oxalic acid catalyst) was kept constant at 1:5:7 respectively, while the molar ratio of TMES/TEOS (A) was varied from 0 to 0.6. It has been observed that as the A value increases, the gelation time increases. The hydrophobicity was tested by measuring the contact angle, and the surface chemical modification was confirmed by the FTIR spectroscopy studies. The thermal stability of the hydrophobic aerogels was studied in the temperature range from 25 to 800°C. The hydrophobic nature of the aerogel could be maintained up to a temperature of 287°C and above this temperature the aerogels become hydrophilic. The bulk density and the optical transmittance of the aerogels have been found to decrease with increase in A value. The aerogels have been characterized by Fourier transform infrared spectroscopy (FTIR), Optical transmittance, Scanning electron microscopy (SEM), Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA), and Contact angle measurements.     

The pitting corrosion of sputtered Fe base alloy films

Predominantly single phase Fe base alloy films were prepared by a DC sputtering method. The compositions of the alloy films, as determined by Auger electron spectroscopy (AES) were Fe-7 at% Cr and Fe-18 at% Cr, Fe-11 at% W and Fe-19 at% W, Fe-9, −13 and −27 at% Ta. The pitting potential of the sputtered alloys determined in chloride solutions was found to be strongly dependent on the nature and the concentration of the alloying element. The pitting potential of sputtered Fe-18 at% Cr and Fe-27 at% Ta alloy films were approximately 0.9 V higher than that of bulk Fe and 0.6 V higher than that of Fe-19 at% W alloy film. A very good correlation was found between the pitting potential of Fe alloy films and the solubility of an alloying element oxide in acidic solutions with a pH corresponding to that within the stable pits of pure Fe (pH = 2). The pitting potential of the Fe alloy was found to increase with a decrease in the solubility of the alloying element oxide in acidic solutions. The pitting potentials of the sputtered Fe-7 at% Cr and Fe-18 at% Cr alloy films were were significantly higher than those of the bulk materials with the same composition. The higher pitting potentials of these alloy films are tentatively attributed to the presence of very fine particles of the oxide phase that are homogeneously distributed in the sputtered alloys.     

Characterization and evaluating the mechanical performance of halloysite nanotubes reinforced acrylonitrile butadiene styrene/polycarbonate composites exposed to aggressive environmental conditions

Developing light weight polymer based composites dispersed with novel reinforcements which can function well in the presence of aggressive environments is an active research field in the materials engineering. Hence, in the current work, halloysite nanotubes (1 %, 2 %, 4 %, 6 %, 8 % and 10 % by weight) were reinforced into acrylonitrile butadiene styrene/polycarbonate blend and the role of reinforcing phases on the mechanical performance under aggressive environmental conditions has been evaluated. Hardness was measured as gradually increased in the composites with the increased content of the reinforcements. Impact strength of the composites was observed as increased in the composites up to 4 % reinforcement and further decreased. Increased strength was measured for the composite up to 2 % reinforcement. Ductility of the composites was decreased as reflected form the decreased % of elongation with the higher fraction of reinforcements due to induced brittleness. The composites were exposed to diluted sulfuric acid for 3 h and 6 h at 60 °C and then subjected to tensile loading. With the increased time of exposure, composites with 1 % and 2 % reinforcement exhibited relatively better performance.     

Post-buckling behaviour of moderately thick cylindrically orthotropic annular plates

A finite element formulation including the effects of shear deformation and cylindrically orthotropic material properties is described for studying the post-buckling behaviour of annular plates. Numerical results for the buckling load parameter and ratios of nonlinear load parameter to buckling load parameter for various values of orthotropic properties, thicknesses and radii ratios of the plates are presented.     

Comparative studies on the physical properties of TEOS,TMOS and Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> based silica aerogels by ambient pressure drying method

In order to compare the various precursors of silica aerogels, three different precursors namely TMOS, TEOS and Na₂SiO₃ were studied in this paper. The property differences of the aerogels caused by the three precursors were discussed in terms of reaction process, gelation time, pore size distributions, thermal conductivity, SEM, hydrophobicity and thermal stability. It has been found that the gelation time of the silica gel is strongly dependent on the type of precursor used. During the surface modification process, organic groups were attached to the wet gel skeletons transforming the hydrophilic to the hydrophobic which were characterized by Fourier Transform Infrared spectroscopy (FTIR). It has been found that the contact angle of the Na₂SiO₃ and TMOS precursor based aerogels with water have the higher contact angle of 149° and whereas Na₂SiO₃ precursor based aerogel has the lower contact angle of 130°. The thermal conductivities of the Na₂SiO₃ and TMOS based aerogels have been found to be lower (0.025 and 0.030 W m^?1 K^?1, respectively) compared to the TEOS based (0.050 W m^?1 K^?1) aerogels. The pore sizes obtained from the N₂ adsorption measurements varied from 40 to 180, 70 to 190, and 90 to 200 nm for the TEOS, TMOS and Na₂SiO₃ precursor based aerogels, respectively. The scanning electron microscopy studies of the aerogels indicated that the Na₂SiO₃ and TMOS based aerogels show narrow and uniform pores while the particles of SiO₂ network are very small. On the other hand, TEOS aerogel show non-uniform pores such that the numbers of smaller size pores are less compared to the pores of larger size while the SiO₂ particles of the network are larger as compared to both Na₂SiO₃ and TMOS aerogels. Hence, the surface are of the aerogels prepared using TEOS precursor has been found to be the lowest (~620 m² g^?1) compared to the Na₂SiO₃ (~868 m² g^?1) and TMOS (~764 m² g^?1) aerogels.     

SYNERGISTIC EFFECT OF N,N-BIS(PHOSPHONOMETHYL) GLYCINE AND ZINC IONS IN CORROSION CONTROL OF CARBON STEEL IN COOLING WATER SYSTEMS

A protective film has been developed on the surface of carbon steel in low chloride aqueous environment using a synergistic mixture of an environmentally friendly phosphonic acid, N,N-bis(phosphonomethyl) glycine (BPMG), and zinc ions. Impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the chosen environment. Potentiodynamic polarization studies showed that the inhibitor is a mixed inhibitor. X-ray photoelectron spectroscopic analysis (XPS) of the film showed the presence of the elements iron, phosphorus, nitrogen, oxygen, carbon, and zinc. Deconvolution spectra of these elements in the surface film showed the presence of oxides/hydroxides of iron(III), Zn(OH)₂, and [Zn(II)-BPMG] complex. This inference is further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. Analysis by SEM is presented for both the corroded and protected metal surfaces. Based on all these results, a plausible mechanism of corrosion inhibition is proposed.     

Monohydroxylation of unsaturated oils: III. Use of halogen intermediates

Hydroxylation of safflower and linseed oils by routes involving halogen compounds is described. A product containing 20.5% Br was obtained by treatment of safflower oil in CCl₄ solution with N-bromosuccinimide (NBS) in presence of benzoyl peroxide and UV illumination. Bromine was totally removed using Ag₂O in 50% dioxan; the resulting hydroxyl value (HV) was only 100, against an expected HV of 180, perhaps because of dehydration and ether formation. Using other silver salts, bromine replacement with hydroxyl was always incomplete. Such residual bromine was totally replaced by hydrogen, without altering other characteristics, by treatment of the product with zinc amalgam in acetic acid. Linseed oil by similar NBS bromination (Br 22.2%) and Ag₂O treatment gave a product with Br 2.9%, HV 74, conj. diene 15% and conj. triene 4%. Halogenreplacement difficulties also attended the hydrobromination of these oils at the double bonds, followed by hydroxylation. Addition of hypochlorous or hypobromous acid to safflower oil, followed by total replacement of halogen with hydrogen using zinc amalgam, yielded products of HV 75 and 83 respectively. The degree of hydroxylation was only half of that expected from the loss of unsaturation.     

Conformal Band Notched Circular Monopole Antenna Loaded with Split Ring Resonator

This article presents the design and analysis of conformal circular monopole antenna with split ring resonator to get frequency notch characteristics in the wideband. Split ring resonators placed on one side of the substrate and complementary split ring resonators placed on the other side of the substrate at defected ground structure, which yields the frequency notch characteristics with respect to the microstrip feeding. Dual notch band characteristics are obtained between 4–4.3 and 7.3–8.1 GHz. The analyzed conformal characteristic of the antenna supports excellent constant reflection coefficient characteristics over the band at different angles. The impedance and radiation characteristics of the antenna model is analysed in simulation along with unit cell analysis of the SRR and the measured results are providing good agreement with them.     

Cooking characteristics,chemical composition and protein quality of newly developed genotypes of pigeonpea (Cajanus cajan L)

Eight newly developed pigeonpea genotypes (ICPL 87, ICPL 151, ICPL 270, ICPL 366, ICPL 87051, ICPL 87063, ICPL 87067, and ICPV 1), and the two controls (BDN 2 and C 11) were analysed for cooking quality parameters and chemical composition, including amino acids and minerals. Protein quality was evaluated by determining the true protein digestibility, biological value, net protein utilisation (NPU), and utilisable protein. These genotypes differed significantly (P < 0–01) in the dhal cooking time. Sensory properties of dhal of these genotypes were found to be within the acceptable range, even though there were considerable differences among genotypes. Dhal protein, calcium, magnesium, zinc, and iron contents of these genotypes showed noticeable differences. Calcium content of ICPL 87067 was the highest (85-6 mg per 100 g) and of ICPL 87 the lowest (54-4 mg per 100 g) indicating large differences among the newly developed genotypes. No noticeable differences in sulphur-containing amino acids of these genotypes were observed. NPU was the highest (65–4%) for ICPL 366 and the lowest (56–6%) for ICPL 270 and ICPL 87067 indicating significant (P < 0–01) differences among genotypes studied.