Friction and wear characteristics of organic thiophosphoro derivatives — a critical appraisal

The friction- and wear-reducing characteristics of a number of oil soluble sulphurised and phosphosulphurised derivatives for automotive and industrial applications have been reviewed. A critical appraisal of the suggested causes and mechanism of friction reduction and antiwear characteristics has been made. A review of the investigations carried out so far indicates that the creation of in situ films of simple inorganic salts, such as molybdenum disulphide, iron sulphide or phosphates of low shear strength and lamellar structures, does not appear to be the primary cause of low friction and wear. The authors have, therefore, undertaken a programme to synthesise and study the chemistry and tribochemical reactions in relation to friction and wear characteristics of hydrocarbon-soluble thiophosphoro derivatives of alkyl phenol, alcohols and fatty esters, in order to establish relationships between the reactivity, chemical nature and crystal structure of films formed on rubbing surfaces, and antifriction and antiwear characteristics. Molybdenum salts of various phosphorothio derivatives of pentadecylphenol and lauryl oleate of specific structures have been synthesised, and the friction and wear properties of their blends in mineral oil base stock have been studied. It can be clearly inferred from the results that type of bonding between sulphur, phosphorus and molybdenum, and reactivity of these derivatives with rubbing surfaces, determine their friction-reducing and antiwear characteristics. Their reactivity with iron and the nature of films formed are under investigation.     

Comparative analysis of a Sisko nanofluid over a stretching cylinder through a porous medium

The present article examines the Sisko nanofluid flow and heat transfer through a porous medium due to a stretching cylinder using Buongiorno's model for nanofluids. Suitable similarity transformations are used to transform the governing boundary layer equations of fluid flow into nonlinear ordinary differential equations. The finite difference method is used to solve coupled nonlinear differential equations with MATLAB software. The impact of different parameters viz., the Sisko material parameter, porosity parameter, curvature parameter, thermophoresis parameter, and Brownian diffusion parameter on the velocity and temperature distribution are presented graphically. Moreover, the effect of the involved parameters on the heat transfer rate is also studied and presented through table values. It is noticed from the numerical values that the porosity parameter reduces the velocity while enhancing the temperature. The curvature parameter enhances the velocity throughout the fluid regime and reduces the temperature near the surface while enhancing the temperature far away from the surface. The study reveals that the thermophoresis and Brownian diffusion parameters that characterize the nanofluid flow reduce the wall heat transfer rate, while the curvature parameter enhances it. This investigation of wall heating/cooling has essential applications in solar porous water absorber systems, chemical engineering, metallurgy, material processing, and so forth.     

Failure analysis of air pre-heater tubes of a petrochemicals plant

Heat resistant alloy tubes used in the higher temperature range of 1150–1273 K depends on the protective scale integrity for prevention of corrosion induced premature failures in a mixed gas environment with potential corrodents for oxidation, carburization and sulphidation attack. Cast HK40+Nb alloy tubes of an air pre-heater unit of a petrochemical industry failed prematurely after 13,000 h in service. The unit used smoke gas containing gaseous corrodents that could cause oxidation/sulphidation/carburization type of attack. Failed parts showed crack/punctures below the corrosion product filled pits. The crack occurred in the fully carburized zone present at the thinned out centre of the pit. Factors like excessive temperature cycling, overheating, presence of impurities either in the pre-heating gas mixture or that got introduced while in operation were found to be the reasons for breach of protective scale integrity leading to unwarranted corrosion attack resulting in thinning of tube material and internal corrosion penetration which finally led to premature failure.     

Determining the number of layers in graphene films synthesized by filtered cathodic vacuum arc technique

We have synthesized graphene film by the filtered cathodic vacuum arc (FCVA) technique and determined the number of layers in graphene films by various techniques. Amorphous carbon (a-C) films of different thicknesses (1, 2, 3, 6, 10 and 18 nm) were synthesized by the FCVA technique on Si/SiO₂/Ni substrate and then annealed in vacuum at 800°C and cooled down to room temperature naturally to obtain graphene. Prepared graphene films were transferred on different substrates and characterized by the Raman spectroscopy, UV-VIS-NIR spectroscopy, high-resolution transmission electron microscopy (HRTEM), optical microscopy, atomic force microscopy (AFM) and sheet resistance to determine the number of layers present in the graphene films. Raman spectra of the prepared graphene films exhibit that there is red shift in the position of D, G and 2 D peak. The value of I_2D/I_G varied from 0.18 to 0.51, I_D/I_G varied from 0.82 to 1.02 and full width at half maximum of 2 D peak varied from 101.2 to 128.0 cm^?1, for different thicknesses of graphene films, respectively. The value of transmittance decreases from 97 to 63.7% and that of sheet resistance increases from 460 to 1400 Ω/square with the increase in the thickness of the prepared graphene film. The HRTEM and AFM study revealed that the graphene synthesis from 1 nm thick a-C film possesses a single layer structure.     

Effect of functionalized silicon carbide nano-particles as additive in cross-linked PVA based composites for vibration damping application

In this research study, a comprehensive effort has been made to functionalize silicon carbide particles using the acidic oxidation with nitric acid to obtain homogeneous stabilized distribution of activated SiC particles within a polymer matrix, and develop functionalized silicon carbide (f-SiC) particle reinforced polyvinyl alcohol (PVA) based cross-linked composite. After fabrication of functionalized silicon carbide (f-SiC) particle reinforced polyvinyl alcohol based cross-linked composite with varying f-SiC weight percentages of PVA (0%, 1%, 2%, 3%, and 4%) were placed to various investigations. Processed samples are initially examined based by the physical tests (water absorption tests), followed by mechanical test (tensile test) and then micro-structural tests (scanning electron microscopy). Lastly, thermal tests were also concluded which involved the dynamic mechanical, differential thermal and thermo gravimetric analysis. The cross-linked polyvinyl alcohol-based composite with 2 weight % of f-SiC content is observed to be the superlative of all the compositions under this research study that was confirmed by the mechanical and micro-structural tests. This composite material shows high storage modulus with visco-elastic behavior, therefore, the material can be utilized to diminish the transmission of noise, as a shock absorber and vibration isolator.     

Multiple material domain‐based computational tools for ease assessment of modal parameter in photonic crystal fibers

We report here the development of two computational tools PCFPS (Photonic Crystal Fiber Parameter Study) and PCFPA (Photonic Crystal Fiber Parameter Analysis), equipped with graphical user interface (GUI) for modeling of photonic crystal fiber. The tools are based on different structural parameters, and they provide characteristic analysis of the modal parameters from the structural parameters. The main feature of PCFPS is that it enables the user to find out the values of each defining modal parameter that has an immense contribution towards the manufacture of photonic crystal fiber. Additionally, PCFPA allows the user to observe the variation in the modal parameters with respect to the changes in structural parameters (such as d, Λ, d/Λ, and λ/>Λ). Besides their ease of use, these two schemes have high computational precision and adaptability, giving a novel platform to optical engineers to modulate the microstructured fibers according to their requirement.     

Increased thermal tolerance in Cronobacter sakazakii strains in reconstituted milk powder due to cross protection by physiological stresses

Cronobacter sakazakii (C. sakazakii) is an opportunistic, neonatal, and food borne pathogen primarily associated with the contamination of powdered infant formula (PIF). The pathogen is reported to overcome the food safety barriers such as increased acidity, heat treatment, and so on. This study evaluates the thermal tolerance of C. sakazakii strains independently at 52, 55, and 58°C in reconstituted PIF after exposure to physiological stresses: refrigeration (4°C for 24 hr), starvation (37°C for 48 hr), and desiccation (25°C for 4 days). The Log₁₀ CFU/ml and D-values indicated that survival rate of all the strains decreased significantly (p < .05) after desiccation as compared to those of the control condition (without stress exposure). However, cold stress increased the thermal tolerance of all strains at all temperatures (52, 55, and 58°C) as indicated by increased D-values. Among the tested strains, C. sakazakii strain N15 was found to be the most resistant to thermal treatment after each stress exposure as depicted by principal component analysis (PCA). No apparent correlation between thermal tolerance and starvation stress was observed. The findings indicate that prior exposure to stress conditions may induce cross protection to thermal treatment in C. sakazakii.     

Supercritical carbon dioxide–assisted synthesis of stimuli-responsive magnetic poly(N-isopropylacrylamide)–ferrite biocompatible nanocomposites for targeted and controlled drug delivery

Supercritical carbon dioxide–assisted synthesis of poly(N-isopropylacrylamide)–ferrite nanocomposites was carried out by polymerization reaction of N-isopropyl acrylamide monomer in the presence of ferrite nanoparticles. They were characterized by Fourier transform infrared, X-ray diffraction, transmission electron microscopy, atomic force microscopy, and vibrating sample magnetometry analysis. Drug loading and release profiles were studied. Nanomaterials showed pH-dependent drug release profile. Polymer nanocomposites in comparison to ferrite nanoparticles showed impressive drug release activity, with a release percent of 20.98–76.54%, and greater biocompatibility in breast cancer cells, with a cell viability of 81–93%. This pH-dependent drug release activity and magnetic property of polymer nanocomposites can be used for controlled and targeted drug delivery.     

Biomimetic synthesis and patterning of silver nanoparticles

The creation of nanoscale materials for advanced structures has led to a growing interest in the area of biomineralization. Numerous microorganisms are capable of synthesizing inorganic-based structures. For example, diatoms use amorphous silica as a structural material, bacteria synthesize magnetite (Fe3O4) particles and form silver nanoparticles, and yeast cells synthesize cadmium sulphide nanoparticles. The process of biomineralization and assembly of nanostructured inorganic components into hierarchical structures has led to the development of a variety of approaches that mimic the recognition and nucleation capabilities found in biomolecules for inorganic material synthesis. In this report, we describe the in vitro biosynthesis of silver nanoparticles using silver-binding peptides identified from a combinatorial phage display peptide library.     

Chemical composition and antifungal activity of essential oils from three Himalayan Erigeron species

Three Himalayan Erigeron (Asteraceae) species viz Erigeron mucronatus, Erigeron annuus and Erigeron karwinskianus growing in sub-alpine region revealed occurrence of isomeric polyacetylenic constituents viz., matricaria and lachnophyllum esters which accounted for 83.3%, 69.3% and 30.1% of the essential oils from these species, respectively, in addition to mono- and sesquiterpenoids as minor constituents. The antifungal activity tested by poisoned food (PF) techniques against Fusarium oxysporum, Helminthosporium maydis, Rhizoctonia solani, Alternaria solani and Sclerotinia sclerotiorum demonstrated significant inhibition of the mycelial growth of all strains (p < 0.05). The oils (500 μg/mL) showed significant antifungal effect against tested fungi in the growth inhibition range of 37.6–85.5% with respective IC₅₀ values ranging from 88.8 to 660.0 μg/mL as compared to standard fungicides (100% inhibition) with IC₅₀ value in the range of 32.2–129.4 μg/mL. Significant inhibition of spore germination was noticed for F. oxysporum, Curvularia lunata and Albugo candida which were highly susceptible to E. annuus oil with their IC₅₀ values 120.7, 253.5 and 300.4 μg/mL, respectively. Thus, the results obtained in this study demonstrate the potential of essential oils from Himalayan Erigeron species as non-toxic, eco-friendly and biodegradable natural fungicides.