Dielectric and impedance spectroscopy of barium orthovanadate ceramics

Barium orthovanadate (Ba₃V₂O₈), a derivative of perovskite family has been prepared using a mixed-oxide technique. The room temperature X-ray diffraction analysis has confirmed the formation of a single phase compound in trigonal crystal structure. The study of microstructure by scanning electron microscopy shows that the compound has well defined grains, distributed uniformly throughout the surface. The studies of dielectric parameters (ε_r and tan δ) of the compound as a function of temperature at three different frequencies (100, 500, 1,000 kHz) exhibit that they are almost temperature independent at low and medium temperature ranges. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature. It shows that the material has negative temperature co-efficient of resistance similar to that of semiconductors. The same behaviour has also been observed in the study of I–V characteristics of the material. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

Enhancement of properties of recycled coarse aggregate concrete using bacteria

Due to rapid construction, necessity for raw materials of concrete, especially coarse aggregate, tends to increase the danger of early exhaustion of the natural resources. An alternative source of raw materials would perhaps delay the advent of this early exhaustion. Recycled coarse aggregate (RCA) plays a great role as an alternative raw material that can replace the natural coarse aggregate (NCA) for concrete. Previous studies show that the properties of RCA concrete are inferior in quality compared to NCA concrete. This article attempts to study the improvement of properties of RCA concrete with the addition of bacteria named as Bacillus subtilis. The experimental investigation was carried out to evaluate the improvement of the compressive strength, capillary water absorption, and drying shrinkage of RCA concrete incorporating bacteria. The compressive strength of RCA concrete is found to be increased by about 20% when the cell concentration of B. subtilis is 10⁶ cells/ml. The capillary water absorption as well as drying shrinkage of RCA are reduced when bacteria is incorporated. The improvement of RCA concrete is confirmed to be due to the calcium carbonate precipitation as observed from the microstructure studies carried out on it such as EDX, SEM, and XRD.     

Nitroarenes as Antitubercular Agents: Stereoelectronic Modulation to Mitigate Mutagenicity

Nitroarenes are less preferred in drug discovery due to their potential to be mutagenic. However, several nitroarenes were shown to be promising antitubercular agents with specific modes of action, namely, nitroimidazoles and benzothiazinones. The nitro group in these compounds is activated through different mechanisms, both enzymatic and non‐enzymatic, in mycobacteria prior to binding to the target of interest. From a whole‐cell screening program, we identified a novel lead nitrobenzothiazole (BT) series that acts by inhibition of decaprenylphosphoryl‐β‐d ‐ribose 2′‐epimerase (DprE1) of Mycobacterium tuberculosis (Mtb). The lead was found to be mutagenic to start with. Our efforts to mitigate mutagenicity resulted in the identification of 6‐methyl‐7‐nitro‐5‐(trifluoromethyl)‐1,3‐benzothiazoles (cBTs), a novel class of antitubercular agents that are non‐mutagenic and exhibit an improved safety profile. The methyl group ortho to the nitro group decreases the electron affinity of the series, and is hence responsible for the non‐mutagenic nature of these compounds. Additionally, the co‐crystal structure of cBT in complex with Mtb DprE1 established the mode of binding. This investigation led to a new non‐mutagenic antitubercular agent and demonstrates that the mutagenic nature of nitroarenes can be solved by modulation of stereoelectronic properties.     

Mechanistic origins of multi-scale reinforcements in segmented polyurethane-clay nanocomposites

The objective of the present work is to get insights into the mechanistic origin of the reinforcement effects of nanoclay on a segmented polybutadiene polyurethane-urea system. To this end, a convergent analysis of the hard domain morphology and conformational state of soft segment in the nanocomposites was carried out by using a combination of complementary characterization techniques, namely, Fourier transform infrared spectroscopy, small angle neutron scattering, transmission electron microscopy, modulated differential scanning calorimetry and dynamic mechanical analysis. Analysis of small angle neutron scattering data by a combination of Percus–Yevick hard sphere and Zernike-Ornstein model coupled with direct visualization of the dispersed hard domain morphology from transmission electron microscopy provided insight on clay induced changes in the hard domain morphology. A monotonic decrease in the domain size as well as the average interdomain distance was observed with increasing nanoclay content in the polymer matrix. Analysis of the carbonyl stretching region from FTIR showed increased degree of hydrogen bonding for the urethane carbonyl groups of the nanocomposites compared to the neat matrix. A combination of calorimetric and dynamic mechanical analysis revealed the existence of a constrained amorphous region; quantified to be ≈ 16% at the highest clay content experimented. The manifestation of these morphological and conformational changes on the nano-, micro- and macro scale reinforcements in the nanocomposites was investigated by mechanical properties at these length scales using nanoindentation, DMA and tensile testing, respectively.     

Composition and Recyclability Analysis of Poly(Vinyl Chloride) Recovered from Computer Power Cables and Commercial Wires

The product‐based recycling of the electrical and electronic devices and their by‐products are limited due to their complex characteristics and dissimilar material characteristics. However, such recycling procedures give clear ideas about the composition and possible recycling options of the materials present in them. Consequently, the present study deals with isolation and recycling of the major polymeric fraction present in the waste computer power supply cables (CPS) and electrical power supply (EPS) wires isolated from the household items. The composition analysis of CPS and EPS indicates that the poly(vinyl chloride) (PVC) is the major polymeric fraction along with minor content of polyethylene (PE) and polycarbonate (PC). Further, this research compares the mechanical recyclability of the PVC recovered from the CPS and EPS. Among the PVC's analyzed, PVC isolated from the EPS has been indicated superior mechanical properties. Similarly, thermal degradation analysis (TGA) indicated higher thermal stability for the PVC isolated from EPS. Besides, the flammability of the PVC specimens was studied and concluded with the possible mechanism occurring during combustion. Moreover, this study points out that PVC recovered from EPS and CPS can be mechanically recycled for the elimination of the waste. J. VINYL ADDIT. TECHNOL., 26:213–223, 2020. © 2019 Society of Plastics Engineers     

Influence of organically modified nanoclay on the performance of pineapple leaf fiber‐reinforced polypropylene nanocomposites

Polypropylene/Pine apple leaf fiber (PP/PALF)‐reinforced nanocomposites were fabricated using melt blending technique in a twin‐screw extruder (Haake Rheocord 9000). Variation in mechanical properties, crystallization behavior, water absorption, and thermal stability with the addition of nanoclay in PP/PALF composites were investigated. It was observed that the tensile, flexural, and impact properties of PP increase with the increase in fiber loading from 10 to 30 wt %. Composites prepared using 30 wt % PALF and 5 wt % MA‐g‐PP exhibited optimum mechanical performance with an increase in tensile strength to 31%, flexural strength to 45% when compared with virgin PP. Addition of nanoclay results in a further increase in tensile and flexural strength of PP/PALF composites to 20 and 24.3%, which shows intercalated morphology. However, addition of nanoclay does not show any substantial increase in impact strength when compared with PP/PALF composites. Dynamic mechanical analysis tests revealed an increase in storage modulus (E′) and damping factor (tan δ), confirming a strong influence between the fiber/nanoclay and MA‐g‐PP. Differential scanning calorimetry, thermogravimetric analysis thermograms also showed improved thermal properties when compared with the virgin matrix. TEM micrographs also showed few layers of agglomerated clay galleries along with mixed nanomorphology in the nanocomposites. Wide angle X‐ray diffraction studies indicated an increase in d‐spacing from 22.4 Å in Cloisite 20A to 40.1 Å in PP/PALF nanocomposite because of improved intercalated morphology. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermodynamic investigations of ThO2-UO2 solid solutions

Heat capacities and enthalpy increments of solid solutions Th_1−yU_yO₂(s) (y = 0.0196, 0.0392, 0.0588, 0.098, 0.1964) and Simfuel (y = 0.0196) were measured by using a differential scanning calorimeter and a high temperature drop calorimeter. The heat capacities were measured in two temperature ranges: 127-305 K and 305-845 K and enthalpy increments were determined in the temperature range 891-1698 K. A heat capacity expression as a function of uranium content y and temperature and a set of self-consistent thermodynamic functions for Th_1−yU_yO₂(s) were computed from present work and the literature data. The oxygen potentials of Th_1−yU_yO_2+x(s) have been calculated and expressed as a polynomial functions of uranium content y, excess oxygen x and temperature T. The phase diagram, oxygen potential diagram of thorium-uranium-oxygen system and major vapour species over urania thoria mixed oxide have been computed using FactSage code.     

Fabrication of nanocrystalline LaFeO3: An efficient sol–gel auto-combustion assisted visible light responsive photocatalyst for water decomposition

Synthesis of nano photocatalysts, LaFeO₃ with orthorhombic perovskite structure by sol–gel auto-combustion method was demonstrated. The samples were characterized by PXRD, SEM, HRTEM, XPS and optical absorption studies. Photocatalytic water decomposition over LaFeO₃ nanoparticles activated at various temperatures without any co-catalyst were investigated under visible light irradiation (λ >> 420 nm). Highest amount of H₂ and O₂ evolved in 180 min over the LaFeO₃ activated at 500 °C was recorded to be 1290 μmol and 640 μmol, respectively having apparent quantum efficiency (AQE) 8.07%. The pronounced activity of nano LaFeO₃ samples towards water decomposition was consistent with BET-surface area and particle size analyses.