Improvement in dry sliding wear resistance of Al-17Si-5Cu alloy after an enhanced heat treatment process

To improve the wear resistance of cast Al-17Si-5Cu alloy (AR alloy), isothermal heat treatment is employed to modify the morphology of Si particles (particularly eutectic Si particles). Furthermore, wear behaviour of heat-treated alloy (HT alloy) along with AR alloy is studied using a pin-on-disc tribometer. Worn surfaces are then characterised using scanning electron microscope. The result reveals considerable microstructural modifications after the heat treatment. Accordingly, higher hardness value in HT alloy is obtained compared with AR alloy. The overall wear rate for HT alloy is found to be significantly lower compared with AR alloy at all the applied loads, indicating remarkable improvement in wear resistance. Eutectic Si particles become from acicular/rod-like to spherical/equiaxed morphology (aspect ratio close to 1) on heat treatment, resulting in good bonding with the matrix. Thus, they remain intact during wear and being harder, providing resistance to wear. Moreover, the increased hardness on heat treatment causes further resistance to wear. Therefore, the combined effect of intact harder Si particles on the wearing surface and higher hardness results in superior wear behavior in HT alloy at all loads compared with AR alloy.     

Microwave assisted polymer stabilized synthesis of silver nanoparticles and its application in the degradation of environmental pollutants

Graft copolymers of polyacrylamide (PAM) and dextran (Dx) are synthesized by grafting PAM chains onto a Dx backbone (Dx-g-PAM) with ceric ion induced solution polymerization technique. Partial hydrolysis of Dx-g-PAM is carried out with sodium hydroxide solution to obtain HDx-g-PAM. To synthesize silver nanoparticles dispersed copolymer nano-composite (Ag-HDx-g-PAM), reduction of silver ions with HDx-g-PAM is carried out using microwave heating. The environmentally benign and biodegradable copolymer, HDx-g-PAM acts as both stabilizer and reducing agent. The copolymer nano-composite, Ag-HDx-g-PAM is characterized by FT-IR, transmission electron microscopy, scanning electron microscopy and optical spectroscopy. Further, the catalytic activity of Ag-HDx-g-PAM nano-composite towards the reduction of environmental pollutants like phenosafranine dye and aromatic nitro compounds are studied.     

High-Temperature Corrosion Behavior of Different Regions of Weldment of 2.25Cr-1Mo Steel in SO<Subscript>2</Subscript> + O<Subscript>2</Subscript> Atmosphere

This paper investigates the corrosion behavior of different regions of weldment of 2.25Cr-1Mo steel exposed in mixed oxidation and sulfidation (SO₂ + O₂) environment up to 500 h at 773 K. Microstructural investigation and characterization of oxide scales are done using SEM, TEM, and XRD. The obtained results infer that heat-affected zone corrodes faster than both base and weld metal. The reaction kinetics follows a parabolic growth rate for all regions. The higher corrosion rate of heat-affected zone is attributed to the formation of Cr₂₃C₆ secondary precipitates leading to depletion of protective inner scale of the Cr-rich oxide during welding.     

Assessment of structural behavior of transmission line tower using strain gauging method

Design of latticed steel transmission towers is a challenging task which involves lengthy modeling and detailing of significant amount of steel members and connections. After that full scale testing of towers validates the modeling and detailing and ensures that the towers are designed to withstand design loads without premature failures. In present work, a 132 kilovolt double circuit suspension tower has been considered for study. The tower was designed using Staad.pro software and the member forces were calculated at design loads. After design, the full scale testing of the tower was carried out. During testing, the strains in some of the critical members were measured using strain gauges. Using these strain values, the actual load in selected members are calculated. The paper provides the comparison between actual load in members during full scale testing and computed loads from software. The paper also discusses the possible reasons behind the difference between actual and computed loads. Loads on the tower at different points for different conditions are presented. The paper also provides a discussion about the possible reasons of premature failure of tower during full scale testing or at site and the remedial measures are presented to avoid the failure.     

Stereoselective Synthesis of Donor-Acceptor Cyclopropapyranone by Intramolecular Cyclopropanation of Vinylogous Carbonates: Application to the Total Synthesis of (±)-Diospongin B

An intramolecular, stereoselective cyclopropanation of vinylogous carbonates with carbenes using copper catalyst is developed for the synthesis of donor-acceptor substituted cyclopropapyranones. Completely regioselective ring cleavage of each of the cyclopropane bonds was achieved under suitable reaction conditions, leading to a diverse array of cyclic ethers. The developed method is utilized in the total synthesis of (±)-diospongin B.