• Volume 30, Issue 5

October 2007,   pages  427-540

• Influence of melt treatments and polished CVD diamond coated insert on cutting force and surface integrity in turning of Al–7Si and Al–7Si–2.5Cu cast alloys

The microstructures, machinability and surface characteristics of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed 𝛼-Al grains, eutectic Al-silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (uncoated and polished CVD diamond coated) were evaluated in machining Al–7Si and Al–7Si–2.5Cu cast alloys under dry environment using a lathe. The polished CVD diamond coated insert outperformed the uncoated cutting insert which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys and their machinability and surface finish when different turning inserts are used.

• Effect of melt treatment on microstructure and impact properties of Al–7Si and Al–7Si–2.5Cu cast alloys

The microstructures and impact toughness of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al–7Si–2.5Cu alloys have microstructures consisting of uniformly distributed 𝛼-Al grains, interdendritic network of fine eutectic silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited improved impact toughness in as cast condition when compared to those treated by individual addition of grain refiner or modifier. The improved impact toughness of Al–7Si–2.5Cu alloys are related to breakage of the large aluminum grains and uniform distribution of eutectic silicon and fine CuAl2 particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification and combined action of both on the impact toughness.

Present study considers microstructural characterization of vanadium-based palladium (V–Pd) alloys, which are widely used in marine environment due to their high corrosion resistance. The X-ray diffraction line profile analysis (XRDLPA) have been used to assess the microstructure in body centred cubic (bcc) V–Pd alloys having four different nominal compositions in wt.%. X-ray diffraction line broadening analysis on V–Pd alloys has been performed by using different methods like the Warren–Averbach, double-Voigt and Rietveld methods. Finally microstructural defect parameters such as domain size (𝐷), r.m.s. microstrain 〈 𝜀21/2, twin fault (𝛽'), spacing fault (𝛼𝜀) and deformation stacking fault (𝛼) were evaluated in these alloys by Fourier line shape analysis using Rietveld method in which the X-ray diffraction profiles of these alloys were described by the pseudo-Voigt function to fit the experimental data. From analysis it has been observed that twin fault, 𝛽', and the spacing fault, 𝛼𝜀, are totally absent in these bcc alloy systems because the twin fault, 𝛽', has been observed to be either negative or very small (within experimental error limit) for these alloy systems and the spacing fault, 𝛼𝜀, appears to be negative. This analysis also revealed that the deformation stacking fault, 𝛼, is significantly present in this alloy system and increases with Pd content.

• Influence of additives on electrodeposition of bright Zn–Ni alloy on mild steel from acid sulphate bath

The influence of a condensation product (CP) of veratraldehyde (VRTD) and 𝑝-amino benzoic acid (PABA) on Zn–Ni alloy electrodeposited onto mild steel was studied in acidic sulphate solutions. Ethylenediaminetetraaceticacid (EDTA) and cetyltrimethylammoniumbromide (CTAB) were used as complexing and wetting agents, respectively. The effect of bath constituents, pH, current density and temperature on nature of deposit were studied through Hull cell experiments. The bath constituents and operating parameters were optimized. Deposit properties and corrosion resistance were discussed. Throwing power, current efficiency and polarization studies were carried out. SEM photomicrographs of the deposit obtained from optimum bath revealed fine-grained deposit of the alloy in the presence of condensation product and hence modified the morphology of zinc–nickel alloy deposit. IR spectrum of the scrapped deposit showed inclusion of addition agent.

• Effect of condensation product on electrodeposition of zinc on mild steel

Electrodeposition of zinc on steel was obtained from acid chloride bath containing condensation products (CP) of 3,4,5-trimethoxy benzaldehyde (TMB) and chitosan (CTN). The effect of bath constituents, pH, current density and temperature on the nature of deposit was studied by Hull cell experiments. The bath composition and operating parameters were optimized. The adhesion, ductility and corrosion resistance of the deposits were discussed. Throwing power and current efficiency values under different plating conditions were measured. SEM photomicrographs of the deposit were taken to study the surface morphology. The inclusion of addition agent in the deposit was investigated from IR spectrum of the scrapped deposit. The consumption of brightener in the lab scale is 10 mLL-1 for 1000 amp-h.

• X-ray study of weak interactions in two flavonoids

X-ray diffraction studies were carried out on single crystals of two flavonoids, viz. 5-hydroxy-6,7,4′-trimethoxyflavone, C18H16O6, (I) and 5-hydroxy-3,7,4′-trimethoxyflavone, C18H16O6, (II). Crystal structures of both the flavonoids were solved by direct methods and refined by full-matrix least-squares procedures. In both the molecules, the benzopyran moiety is planar. The dihedral angle between the phenyl ring and the benzopyran portion is 5.50(4)° in (I) and 29.11(5)° in (II). In (I), the crystal packing is influenced by O–H…O hydrogen bonds, and weak C–H…O and $\pi \ldots \pi$ interactions whereas in (II) the crystal structure is stabilized by the presence of four intermolecular short contacts of the type C–H…O. There is also one C–H$\ldots \pi$ hydrogen bond with H… centroid distance of &lt; 2.7 Å. The molecules are further stabilized by 𝜋–𝜋 interactions.

• Study of microhardness and electrical properties of proton irradiated polyethersulfone (PES)

Polyethersulfone (PES) films were irradiated with 3 MeV proton beams in the fluence range 1013–1015 ions/cm2. The radiation induced changes in microhardness was investigated by a Vickers’ microhardness tester in the load range 100–1000 mN and electrical properties in the frequency range 100 Hz–1 MHz by an LCR meter. It is observed that microhardness of the film increases significantly as fluence increases up to 1014 ions/cm2. The bulk hardness of the films is obtained at a load of 400 mN. The increase in hardness may be attributed to the cross linking effect. There is an exponential increase in conductivity with log frequency and the effect of irradiation is significant at higher fluences. The dielectric constant/loss is observed to change significantly due to irradiation. It has been found that dielectric response in both pristine and irradiated samples obey the Universal law and is given by 𝜀 ∝ 𝑓n–1. These results were corroborated with structural changes observed in FTIR spectra of irradiated samples.

• Spectral analysis of Cu2+ and Mn2+ ions doped borofluorophosphate glasses

We report here on the development and spectral analysis of Cu2+ (0.5 mol%) and Mn2+ (0.5 mol%) ions doped in two new series of glasses. The visible absorption spectra of Cu2+ and Mn2+ glasses have shown broad absorption bands at 820 nm and 495 nm, respectively. For Cu2+ BFP glasses, excitation at 380 nm, a blue emission at 441 nm and also a weak emission at 418 nm ions have been observed. For Mn2+ ions doped BFP glasses, excitation at 410 nm and a red shift at 605 nm emission have been observed.

• Redox ratio and optical absorption of polyvalent ions in industrial glasses

The changes in glass structure and redox ratio, 𝑅 (reduced ion to oxidized ion) of Mn2+–Mn3+, Cu+–Cu2+, Cr3+–Cr6+, Ni2+–Ni3+ and Co2+–Co3+ couples and optical absorption due to Mn3+, Cu2+, Cr3+, Ni2+ and Co2+ ions in industrial soda–lime–silica glass were investigated as a function of Na2O concentration in the range 11–19 mol%. With increasing Na2O concentration in the experimental glasses, the basicity, expressed as calculated basicity, 𝛬cal, increased. 29Si NMR and X-ray diffraction were used to investigate the structural change in glasses. The NMR spectra showed high non-bridging oxygens (NBOs) when the basicity of glass was increased. The results were interpreted to be due to the tetrahedral networks; 𝑄4 species were depolymerized by replacing the bridging oxygens (BOs) with NBOs to 𝑄3 species. These results confirmed the shift of broadening peaks of XRD patterns. The redox reactions of the Mn2+–Mn3+, Cu+–Cu2+ and Cr3+–Cr6+ couples shifted more toward their oxidized ions due to the oxygen partial pressure, 𝑝(𝑂2), during melting and the oxide ion activity, 𝑎O2–, increased with increasing glass basicity. These changes caused the redox ratio of these ion couples to decrease. The Ni2+–Ni3+ and Co2+–Co3+ couples were assumed to be present only in the Ni2+ and Co2+ ions in these glasses, respectively. The optical absorption bands due to Mn3+, Cu2+, Cr3+, Ni2+ and Co2+ ions were also investigated. Their spectra occurred at constant wavelengths with different optical densities or intensities as a function of glass basicity. The increase in the intensities of the absorption bands of these absorbing ions, except for Cr3+ ion, at the maximum wavelength, depends not only on the ion concentration but also on the increase of polarizability of oxide (–II) species, 𝛼oxide(–II), surrounding the ions. This value affected directly the extinction coefficients of the ions, 𝜀ion. The increase of 𝜀ion caused the colour of glasses appearing in high intensity. In the case of Cr3+ ion, the results were reversed such that the lower the concentration, the higher the intensities of colour.

• Conductivity studies of lithium zinc silicate glasses with varying lithium contents

The electrical conductivity of lithium zinc silicate (LZS) glasses with composition, (SiO2)0.527 (Na2O)0.054(B2O3)0.05(P2O5)0.029(ZnO)0.34–𝑥(Li2O)𝑥 (𝑥 = 0.05, 0.08, 0.11, 0.18, 0.21, 0.24 and 0.27), was studied as a function of frequency in the range 100 Hz–15 MHz, over a temperature range from 546–637 K. The a.c. conductivity is found to obey Jonscher’s relation. The d.c. conductivity ($\sigma_{d.c.}$) and the hopping frequency($\omega_{h}$), inferred from the a.c. conductivity data, exhibit Arrhenius-type behaviour with temperature. The electrical modulus spectra show a single peak, indicating a single electrical relaxation time, 𝜏, which also exhibits Arrhenius-type behaviour. Values of activation energy derived from $\sigma_{d.c.}, \omega_{h}$ and 𝜏 are almost equal within the experimental error. It is seen that $\sigma_{d.c.}$ and $\omega_{h}$ increase systematically with Li2O content up to 21 mol% and then decrease for higher Li2O content, indicating a mixed alkali effect caused by mobile Li+ and Na+ ions. The scaling behaviour of the modulus suggests that the relaxation process is independent of temperature but depends upon Li+ concentration.

• Crystal structure and elastic constants of Dharwar cotton fibre using WAXS data

Wide-angle X-ray scattering (WAXS) recordings were carried out on raw Dharwar cotton fibres available in Karnataka. Using this data and employing linked atom least squares (LALS) method, we report here the molecular and crystal structure of these cotton fibres. Employing structural data, we have computed elastic moduli tensor components of these fibres. From these investigations, it turns out that the intrinsic strains present in the fibre arise due to hydrogen bonds and not covalent bonds, which is a significant result.

• Thermochemical behaviour of Ru(II) complex–SiO2 microcomposites

The results from DSC and thermogravimetric analysis of gels produced from a mixture of tetraethoxysilane (TEOS) and octyltriethoxysilane (OtEOS) both with and without immobilized Ru(II) tris(4,7-diphenyl-1,10-phenanthroline) dichloride as well as DSC and TG data for films deposited by deep- or spincoating from the same gels, are reported. The initial products are characterized by elemental analysis, IR, solid state NMR and mass spectroscopy. Elemental analysis and IR spectroscopy are applied for identification of some of the intermediates obtained after heating at different temperatures. The final products are characterized by X-ray diffractometry. A hypothesis for the thermodecomposition processes taking place is proposed. The results reported contribute to elucidation of the properties as well as the temperature intervals in which the studied microcomposites could be used as sensing components of oxygen sensors.

• A study on leaching behaviour of cement blocks used as matrix for fixation of Cs activity along with ferric

Study on the cementation of the regenerated activity (from spent resin using ferric as regenerant) containing ferric in cement matrix showed that compressive strength and leaching behaviour are better when the ferric strength was &lt; 5 N. The diffusion coefficient of Cs from the cement matrix was found to be in the range 2.4 × 10-5 cm2/day and 5.9 × 10-5 cm2/day with ferric solutions of strength in the range 0.5–3 N. When bentonite and vermiculite were included in the cement matrix, the diffusion coefficient of Cs was found to be in the range 6.2 × 10-7 cm2/day to 1.26 × 10-5 cm2/day with ferric strength in the same range.

• Photoluminescence and thermoluminescence properties of tricalcium phosphate phosphors doped with dysprosium and europium

The suitability of calcium phosphate crystals for thermoluminescence dosimetry (TLD) applications is investigated, owing to their equivalence to bone mineral. The 𝛼 and 𝛽 phases of tricalcium phosphate (TCP) were synthesized through wet precipitation and high temperature solid state routes and doped with Dy and Eu. The photoluminescence and thermoluminescence studies of the phosphors have been carried out.

The TL properties were found to be highly dependent on the method of preparation of the material. Eu doping gave good PL emission, whereas Dy doping was more efficient in TL emission. 𝛽-TCP was found to be less TL sensitive than 𝛼-TCP, yet it was identified as a better phosphor material owing to its better fading characteristics.

The dependence of TL of 𝛽-TCP : Dy on the energy and dose of radiation, and on the doping concentration were studied. The TL intensity was observed to fade exponentially during a storage period of 20 days, but it stabilized at 70% of the initial value after 30 days. The optimum doping concentration was found to be 0.5 mol%.

• Effect of size of copper nanoparticles on its catalytic behaviour in Ullman reaction

The condensation of iodobenzene to biphenyl is an industrially important reaction due to its significant role in organic synthesis as drug intermediates. The reaction takes place in the presence of copper powder as catalyst. We have shown in this paper that the size of the copper nanoparticles as well as its exposed surface area is responsible for the yield of chemical reaction. The uncapped copper powder showed a 43% conversion of iodobenzene to biphenyl in 5 h under our experimental conditions. Same amount of copper nanoparticles (size, ∼ 66 nm diameter) prepared by citrate capping showed 88% conversion of iodobenzene to biphenyl, which increased to about 95% when 8 nm diameter capped copper nanoparticles are used. Surprisingly, 5 nm size copper nanoparticles showed no change in the yield of about 95%.

• Bulletin of Materials Science

Volume 43, 2020
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Continuous Article Publishing mode

• Editorial Note on Continuous Article Publication

Posted on July 25, 2019