Nanocrystalline Pentaerythritoltetranitrate using Sol-Gel Process

The secondary explosives developed with reduced particle size tend to be more insensitive for mechanical stimuli and may release energy with faster rate and gaining more importance nowadays. Therefore, aiming to reduce the particle size of one of the popular explosives, viz., pentaerythritoltetranitrate (PETN) to the nanometer range, a method for preparation of nanocrystalline PETN in the silica (SiO2) gel matrix using sol-gel process has been demonstrated. The PETN-SiO2 xerogels were prepared containing PETN content ranging from 50 per cent to 90 per cent (w/w) and the xerogels were characterised using different techniques. An exothermic peak at around 185 oC preceded by an endotherm in thermal analysis accompanied with weight loss in the temperature range from 150 oC to 200 oC   for the xerogel confirmed the presence of PETN in xerogel. Infrared spectra of xerogels showed peaks at around 1285 cm-1 and 1700 cm-1 assigned to O-NO2 and C-O bond representing PETN. Small angle x-ray scattering measurements on xerogels indicated that PETN entered in the pores of silica matrix. Transmission electron microscopy revealed that cystalline PETN    with particle size of around 15 nm dispersed in silica xerogel. The specific surface area for the PETN-SiO2 (90:10) xerogels was found to be 75 m2/g.Defence Science Journal, 2011, 61(6), pp.534-539, DOI:http://dx.doi.org/10.14429/dsj.61.59

Development of a simple electroless method for depositing metallic Pt-Pd nanoparticles over wire gauge support for removal of hydrogen in a nuclear reactor

Electroless noble metal deposition on the conducting substrate is widely used to obtain the desired film or coating on the substrate of interest. Wire-gauge-based Pt/Pd/Pt-Pd (individually, sequentially, and simultaneously deposited) catalysts have been developed using formaldehyde and sodium formate as reducing agents. Various surface pretreatment methods like SnCl2 + PdCl2 seeding, oxalic acid etching, and HCl activation (etching) have been employed to obtain the desired noble metal coating. Minimum time duration was observed for simultaneously deposited catalysts using formaldehyde as a reducing agent. Prepared catalysts were characterized for noble metal deposition, coating kinetics, surface morphology, and binding energy. The catalyst was found to be active for H2 and O2 recombination reactions for hydrogen mitigation applications in nuclear reactors

Abrasive water jet drilling of advanced sustainable bio-fibre-reinforced polymer/hybrid composites : a comprehensive analysis of machining-induced damage responses

This paper aims at investigating the effects of variable traverse speeds on machining-induced damage of fibre-reinforced composites, using the abrasive water jet (AWJ) drilling. Three different types of epoxy-based composites laminates fabricated by vacuum bagging technique containing unidirectional (UD) flax, hybrid carbon-flax and carbon fibre-reinforced composite were used. The drilling parameters used were traverse speeds of 20, 40, 60 and 80 mm/min, constant water jet pressure of 300 MPa and a hole diameter of 10 mm. The results obtained depict that the traverse speed had a significant effect with respect to both surface roughness and delamination drilling-induced damage responses. Evidently, an increase in water jet traverse speed caused an increase in both damage responses of the three samples. Significantly, the CFRP composite sample recorded the lowest surface roughness damage response, followed by C-FFRP, while FFRP exhibited the highest. However, samples of FFRP and hybrid C-FFRP recorded lowest and highest delamination damage responses, respectively. The discrepancy in both damage responses, as further validated with micrographs of colour video microscopy (CVM), scanning electron microscopy (SEM) and X-ray micro-computed tomography (X-ray μCT), is attributed to the different mechanical properties of the reinforced fibres, fibre orientation/ply stacking and hybridisation of the samples.Peer reviewe

Nickel-Catalyzed Carbon–Carbon Bond-Forming Reactions of Unactivated Tertiary Alkyl Halides: Suzuki Arylations

The first Suzuki cross-couplings of unactivated tertiary alkyl electrophiles are described. The method employs a readily accessible catalyst (NiBr[subscript 2]·diglyme/4,4′-di-tert-butyl-2,2′-bipyridine, both commercially available) and represents the initial example of the use of a group 10 catalyst to cross-couple unactivated tertiary electrophiles to form C–C bonds. This approach to the synthesis of all-carbon quaternary carbon centers does not suffer from isomerization of the alkyl group, in contrast with the umpolung strategy for this bond construction (cross-coupling of a tertiary alkylmetal with an aryl electrophile). Preliminary mechanistic studies are consistent with the generation of a radical intermediate along the reaction pathway.National Institute of General Medical Sciences (U.S.) (R01-GM62871)Merck Research Laboratories (Summer Fellowship

Identification of herbal teas and their compounds eliciting antiviral activity against SARS-CoV-2 in vitro

Background: The SARS-CoV-2/COVID-19 pandemic has inflicted medical and socioeconomic havoc, and despite the current availability of vaccines and broad implementation of vaccination programs, more easily accessible and cost-effective acute treatment options preventing morbidity and mortality are urgently needed. Herbal teas have historically and recurrently been applied as self-medication for prophylaxis, therapy, and symptom alleviation in diverse diseases, including those caused by respiratory viruses, and have provided sources of natural products as basis for the development of therapeutic agents. To identify affordable, ubiquitously available, and effective treatments, we tested herbs consumed worldwide as herbal teas regarding their antiviral activity against SARS-CoV-2. Results: Aqueous infusions prepared by boiling leaves of the Lamiaceae perilla and sage elicit potent and sustained antiviral activity against SARS-CoV-2 when applied after infection as well as prior to infection of cells. The herbal infusions exerted in vitro antiviral effects comparable to interferon-β and remdesivir but outperformed convalescent sera and interferon-α2 upon short-term treatment early after infection. Based on protein fractionation analyses, we identified caffeic acid, perilla aldehyde, and perillyl alcohol as antiviral compounds. Global mass spectrometry (MS) analyses performed comparatively in two different cell culture infection models revealed changes of the proteome upon treatment with herbal infusions and provided insights into the mode of action. As inferred by the MS data, induction of heme oxygenase 1 (HMOX-1) was confirmed as effector mechanism by the antiviral activity of the HMOX-1-inducing compounds sulforaphane and fraxetin. Conclusions: In conclusion, herbal teas based on perilla and sage exhibit antiviral activity against SARS-CoV-2 including variants of concern such as Alpha, Beta, Delta, and Omicron, and we identified HMOX-1 as potential therapeutic target. Given that perilla and sage have been suggested as treatment options for various diseases, our dataset may constitute a valuable resource also for future research beyond virology

Catalytic Enantioselective Cross-Couplings of Secondary Alkyl Electrophiles with Secondary Alkylmetal Nucleophiles: Negishi Reactions of Racemic Benzylic Bromides with Achiral Alkylzinc Reagents

We have developed a nickel-catalyzed method for the asymmetric cross-coupling of secondary electrophiles with secondary nucleophiles, specifically, stereoconvergent Negishi reactions of racemic benzylic bromides with achiral cycloalkylzinc reagents. In contrast to most previous studies of enantioselective Negishi cross-couplings, tridentate pybox ligands are ineffective in this process; however, a new, readily available bidentate isoquinoline–oxazoline ligand furnishes excellent ee’s and good yields. The use of acyclic alkylzinc reagents as coupling partners led to the discovery of a highly unusual isomerization that generates a significant quantity of a branched cross-coupling product from an unbranched nucleophile

Experimental characterization and finite element modeling of critical thrust force in cfrp drilling

Composite laminates are used in many applications in ae-rospace/defense industries due to their high strength-to-weight ratio and corrosion resistance properties. In general, composite materials are hard-to-machine materials which exhibit low drilling efficiency and drilling-induced delamination damage at exit. Hence, it is important to understand the drilling processes for composite materials. This article presents a comprehensive study involving experimental characterization of drilling process to understand the cutting mechanism and relative effect of cutting parameters on delamination during drilling of carbon fiber reinforced plastic (CFRP). Thrust force and torque data are acquired for analyzing the cutting mechanism, initiation and propagation of delamination, and identification of critical thrust force below which no damage occurs. An FE model for prediction of critical thrust force has been developed and validated with experimental results. A [0/90] composite laminate is modeled simulating the last two plies in exit condition and a thin interface layer is inserted in between the plies to capture delamination extent. The tool geometry is modeled as rigid body with geometric features of twist drill used in experiments. The tool is indented on the workpiece to simulated tool feeding action into the workpiece. The FE model predicts the critical thrust force within 5% of the experimentally determined mean value

High temperature crystallographic and thermodynamic investigations on synthetic calzirtite (Ca<SUB>2</SUB>Zr<SUB>5</SUB>Ti<SUB>2</SUB>O<SUB>16</SUB>)

In the context of formation and stability of synthetic rock (SYNROC), studies on crystal structure and thermodynamic parameters of a mineral analogous material, namely calzirtite has been undertaken. The ambient temperature structural studies revealed a tetragonal (I41/acd) fluorite related super-structure with about 5% intermixing of Ti and Zr sites for calzirtite. High temperature structural studies indicated the retention of tetragonal structure of calzirtite up to 1673 K. The average axial thermal expansion coefficient of calzirtite between 297 and 1473 K is found to be 12.7 × 10−6/K for a-axis and 9.2 × 10−6/K along the c-axis. The thermodynamic parameters of calzirtite have been determined employing high temperature solution calorimetry. The standard molar enthalpy of formation of Ca2Zr5Ti2O16(s) at 298 K is found to be −8964.16 ± 12.59 kJ mol−1. The isobaric heat capacity of the compound has been derived from the enthalpy increment (HT-H298) data measured by drop calorimetric technique. Based on the experimental results thermodynamic functions like C0p,m, S0m, H0, G0, (G0T-H0298)/T, &#916;fH0298 and &#916;fG0T for calzirtite (Ca2Zr5Ti2O16,s) has been generated

Sequential evolution of different phases in metastable Gd<SUB>2–x</SUB>Ce<SUB>x</SUB>Zr<SUB>2–x</SUB>Al<SUB>x</SUB>O<SUB>7</SUB>(0.0 ≤x≤ 2.0) system: crucial role of reaction conditions

The Gd<SUB>2–x</SUB>Ce<SUB>x</SUB>Zr<SUB>2–x</SUB>Al<SUB>x</SUB>O<SUB>7</SUB> (0.0 ≤ x ≤ 2.0) series was synthesized by the gel combustion method. This system exhibited the presence of a fluorite-type phase, along with a narrow biphasic region, depending upon the Ce/Gd content in the sample. Thermal stability of these new compounds under oxidizing and reducing conditions has been investigated. The products obtained on decomposition of Gd<SUB>2–x</SUB>Ce<SUB>x</SUB>Zr<SUB>2–x</SUB>Al<SUB>x</SUB>O<SUB>7</SUB> in oxidizing and reducing conditions were found to be entirely different. It was observed that in air the fluorite-type solid solutions of Gd<SUB>2–x</SUB>Ce<SUB>x</SUB>Zr<SUB>2–x</SUB>Al<SUB>x</SUB>O<SUB>7</SUB> composition undergo phase separation into perovskite GdAlO<SUB>3</SUB> and fluorite-type solid solutions of Gd–Ce–Zr–O or Ce–Zr–Al–O depending upon the extent of Ce and Al substitution. On the other hand, Gd<SUB>2–x</SUB>Ce<SUB>x</SUB>Zr<SUB>2–x</SUB>Al<SUB>x</SUB>O<SUB>7</SUB> samples on heating under reducing conditions show a phase separation to CeAlO<SUB>3</SUB> perovskite and a defect-fluorite of Gd<SUB>2</SUB>Zr<SUB>2</SUB>O<SUB>7</SUB>. The extent of metastability for a typical composition of Gd<SUB>1.2</SUB>Ce<SUB>0.8</SUB>Zr<SUB>1.2</SUB>Al<SUB>0.8</SUB>O<SUB>7</SUB> (nano), Gd<SUB>1.2</SUB>Ce<SUB>0.8</SUB>Zr<SUB>1.2</SUB>Al<SUB>0.8</SUB>O<SUB>6.6</SUB> (heated under reduced conditions), Gd<SUB>1.2</SUB>Ce<SUB>0.8</SUB>Zr<SUB>1.2</SUB>Al<SUB>0.8</SUB>O<SUB>7</SUB> (heated in air at 1200 °C) has been experimentally determined employing a high temperature Calvet calorimeter. On the basis of thermodynamic stability data, it could be inferred that the formation of a more stable compound in the presence of two competing cations (i.e., Gd<SUP>3+</SUP> and Ce<SUP>3+</SUP>) is guided by the crystallographic stability