Studies on dissolution kinetics of dolime in electrothermal magnesium slag

The electrothermal process of magnesium metal production is a promising route, where large sized internally heated reactor is used for magnesium production resulting in less energy and labour intensive and high space-time yield process. However, the dissolution behavior of dolime in the electrothermal slag has been found critical for the process optimization. In this paper, the dissolution kinetics of the dolime in the slag was discussed. Quaternary slag (CaO-Al₂O₃-SiO₂-MgO) was prepared having basicity CaO/SiO₂ ≥ 1.8 and Al₂O₃/SiO₂ ≥ 0.26 for dolime dissolution studies by static hot dip method. Prior to the experiments, FactSage calculations were carried out varying temperatures and slag compositions. In the kinetic studies, dolime particles 10–15 mm size was added in slag melted at 1450, 1500 and 1550°C and samples were taken at various time intervals. The chemical analysis of slag sample was carried out to investigate the dissolution kinetics to establish the rate expression. The activation energy for the process was calculated for different models used in study and was found to be in the range of 130–270 kJ/mol. SEM analysis was done for surface analysis of reacted particles. This study would be helpful in optimizing the dolime charging rate during pilot scale trials for electrothermal magnesium production at CSIR-NML, Jamshedpur.     

Nanoencapsulated Lippia origanoides essential oil: physiochemical characterisation and assessment of its bio-efficacy against fungal and aflatoxin contamination as novel green preservative

The study explores in vitro antifungal and aflatoxin B₁ inhibitory potency of chemically characterised Lippia origanoides EO (LOEO) encompassed in chitosan nanoparticle (CS-LOEO-Np). CS-LOEO-Np was physico-chemically characterised through XRD, SEM and FTIR analyses. CS-LOEO-Np exhibited improved antifungal and AFB₁ inhibitory efficacy (0.05 and 0.045 µl mL⁻¹, respectively) in contrast to LOEO (0.30 and 0.25 µl mL⁻¹, respectively). Bioactivity of LOEO loaded nanoparticle was enhanced as reflected by depletion in ergosterol content, rapid cellular ion release and reduced methylglyoxal content. IC₅₀ value equivalent to 4.17 µl mL⁻¹ displayed better antioxidant potency of CS-LOEO-Np as compared to LOEO (IC₅₀ = 6.20 µl mL⁻¹). CS-LOEO-Np preserved sensorial attributes of stored Nigella sativa (model food matrix) samples and have higher lethal toxicity dose, that is LD₅₀ = 8832 mg kg⁻¹. Hence, CS-LOEO-Np could serve as novel green candidate to ensure food security with better nutritional and sensorial features.     

Micromechanics based ply level material degradation model for unidirectional composites

The damaged response of a composite lamina depends on various mechanisms that take place at the microlevel, i.e., at the level of the fiber and matrix. The present work focuses on developing a ply level continuum damage model for point-wise stiffness degradation through simplified representation of the microlevel damage. A three dimensional micromechanical analysis of a single cell representative volume element is carried out for various volume fraction, and levels of damage. The model brings out the coupled effect of damage on the effective point-wise ply level stiffness. Further, the numerical results are employed to develop a functional continuum representation of stiffness degradation as a function of the damage parameters and fiber volume fraction perturbations. The micromechanics model is consistent with experimentally observed stiffness degradation, i.e., a strong influence of fiber breakage and fiber matrix debond, and a weak influence of normal cracking of matrix. The proposed model can be considered as an improved version of the widely accepted diffused (meso) damage models, i.e., DML. The study also gives a generalized and consistent definition for the free energy, which can be used for modeling growth of damage.     

Rhamnolipid–Metal Ions (CrVI and PbII) Complexes: Spectrophotometric,Conductometric, and Surface Tension Measurement Studies

The formation of rhamnolipid complexes with metal ions of chromium (VI) and lead (II) has been studied spectrophotometrically, conductometrically, and by surface tension measurement. The values of the critical micelle concentration (CMC) of rhamnolipid, obtained by spectroscopic, conductometric, and surface tension measurements, were 5.2 × 10⁵ , 5.0 × 10⁵ , and 5.3 × 10⁵ mol.dm⁻³, respectively, which are in close agreement. An increase in CMC on increasing metal ion content in the rhamnolipid solution and a shift in λ_max in the spectra of rhamnolipid indicated the formation of a complex between rhamnolipid and both the metal ions, namely, chromium (VI) and lead (II). The values of stability constants for the {rhamnolipid–chromium (VI)} and {rhamnolipid–lead (II)} complexes have been determined by spectroscopic data and were as 0.58 × 10⁴ and 0.50 × 10⁴ at 308 K, respectively. The thermodynamic parameters for micellization, namely, free energy change (∆G_mic) , entropy change (∆S_mic) , and heat enthalpy change (∆H_mic) , have been determined by conductivity measurements. An increase in the negative value of ∆G_mic and a decrease in the value of ∆S_mic on increasing metal ion content in the surfactant solution indicated lower micellization of rhamnolipid in the presence of metal ions. The electrostatic attractions and entrapment of chromium (VI) in the micelles of the biosurfactants were found to be responsible for {rhamnolipid–lead (II)} and {rhamnolipid–chromium (VI)} complexes, respectively.     

Modelling of a rotor-ball bearings system using Timoshenko beam and effects of rotating shaft on their dynamics

This study has focused on the influence of rotating shaft on the dynamics of rotor-ball bearings system. A mathematical modelling of the system has been carried out by considering shaft as rotating Timoshenko beam model. The radial force of rotor unbalance varied with rotating speed. The contact between balls and races is considered as nonlinear spring, whose stiffness is obtained by using Hertzian contact deformation theory. After the modelling for shaft, the governing equation of bearing are derived. The proposed mathematical model is validated experimentally. Moreover, the proposed model is also validated with previous published studies. The bifurcation diagram and Lyapunov exponent are presented to define the state of the system as a function of rotational speed. Fast Fourier transform (FFT) and phase trajectory are used to investigate the influence of the shaft under dynamics of the system.     

Effect of electron density on the catalysts for copolymerization of propylene oxide and CO<Subscript>2</Subscript>

Copolymerization of propylene oxide and carbon dioxide (CO₂) has been studied using different R-salophenCoOBzF₅ (OBzF₅ = pentaflorobenzoate, R = CH₃, H, Cl, Cl₂) based catalysts. The central moiety of the catalysts R-salophenCoOBzF₅ has been kept the same and effect of the catalyst electron density on the copolymerization reaction has been studied. It has been observed that introduction of an electron withdrawing group (like Cl, Cl₂) on the o-phenylenediamine backbone moiety of the catalyst makes it more selective for poly(propylene carbonate) synthesis. On the other hand, introduction of an electron donating group (like CH₃) makes the catalyst selective for cyclic carbonate conversion. The effect of different type of co-catalysts has also been investigated using tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, [PPN]⁺Cl^? ([PPN]⁺ = bis(triphenylphosphine)iminium), DMAP and tetrabutyl ammonium bromide.     

High-Speed Friction Stir Welding of AA7075-T6 Sheet: Microstructure,Mechanical Properties,Micro-texture,and Thermal History

Friction stir welding (FSW) is a cost-effective and high-quality joining process for aluminum alloys (especially heat-treatable alloys) that is historically operated at lower joining speeds (up to hundreds of millimeters per minute). In this study, we present a microstructural analysis of friction stir welded AA7075-T6 blanks with high welding speeds up to 3 M/min. Textures, microstructures, mechanical properties, and weld quality are analyzed using TEM, EBSD, metallographic imaging, and Vickers hardness. The higher welding speed results in narrower, stronger heat-affected zones (HAZs) and also higher hardness in the nugget zones. The material flow direction in the nugget zone is found to be leaning towards the welding direction as the welding speed increases. Results are coupled with welding parameters and thermal history to aid in the understanding of the complex material flow and texture gradients within the welds in an effort to optimize welding parameters for high-speed processing.     

Material selection for thin-film solar cells using multiple attribute decision making approach

This paper presents a material selection approach for selecting absorbent layer material for thin-film solar cells (TFSCs) using multiple attribute decision making (MADM) approach. In this paper, different possible materials for absorbent layer and their properties like band gap, absorption coefficient, diffusion length, thermodynamic compatibility and recombination velocity is taken into consideration and MADM approach is applied to select the best material for thin-film solar cells. It is observed that Copper Indium Gallium Diselinide (CIGS) is the best material for the absorbent layer in thin-film solar cells out of all possible candidates. It was observed that the proposed result is in accordance with the experimental findings thus justifying the validity of the proposed study.     

Comparative Studies of Pressure Sensitization of Zirconium Carbide and Zirconium Silicate on Burning Rates in a RDX‐AP based Composite Propellant

In a systematic study to compare the effects of the values of burning rate and pressure exponent in RDX‐AP based composite propellant, various compositions with varying percentages of zirconium carbide (ZrC) and zirconium silicate (ZrSiO₄) were formulated to select a suitable candidate. Various rocket parameters of each formulation were theoretically predicted by the NASA CEC‐71 program and the burning rate was evaluated in pressure range of 3–11 MPa. In addition, density, sensitivity, and thermal properties of compositions having maximum effects on pressure exponent’s values were also evaluated. It was concluded that ZrSiO₄ enhances the pressure exponent “n” value substantially, whereas ZrC doesn’t have significant effects on it as compared to base composition and also provides higher density values of composite propellant formulated.