R Curves and Crack-Stability Map: Application to Ce-TZP/Al2O3

The concept of a crack-stability map is developed by considering the interaction between the crack-driving force and the rising crack-growth resistance of a toughened ceramic. The map plots normalized transition crack length as function of the ratio of the crack-initiation fracture toughness and the plateau toughness to delineate regimes of stable and unstable crack growth. The plot is used to analyze R curves and fracture stresses of a transformation-toughened Ce-TZP/Al₂O₃. It is shown that the fracture stress and the small scatter measured for this ceramic are consistent with its R- curve behavior, which enables stable growth of surface cracks from flaws (pores and second-phase particles), leading to a flaw-insensitive ceramic.     

Characterization of Thermal-Sprayed HAP and HAP/TiO<Subscript>2</Subscript> Coatings for Biomedical Applications

In the present study, hydroxyapatite (HAP) coating along with HAP/TiO₂ coating has been deposited by high-velocity flame spray (HVFS) technique onto 316LSS. Titania was used as a bond coat and HAP as top coat in HAP/TiO₂ coating. The main aim of the study is to investigate the corrosion behavior of thermal spray coating of HAP and HAP/TiO₂ on steel. Electrochemical corrosion testing was carried out using potentiodynamic polarization test. The corrosion behavior of bare and as-sprayed specimens was analyzed in simulated body fluid known as Hank’s solution. As-sprayed specimens along with corroded specimens were further characterized by XRD, SEM/EDS, and x-ray mapping analysis. It was observed that the HAP/TiO₂ coating possessed higher microhardness (280 Hv) as compared to HAP coating (254 Hv). Surface roughness also got enhanced in case of HAP/TiO₂ coating (9.35 μm) as compared to pure HAP coating (7.37 μm). The porosity of the HAP coating was found to be higher than the bond coating. It was observed that the Ca/P ratio almost resembled that of the natural bone composition. The corrosion resistance of steel increased after the deposition of HAP and HAP/TiO₂ coatings. The maximum corrosion resistance was exhibited by HAP/TiO₂ coating.     

CO2 reduction in a solid oxide electrolysis cell with a ceramic composite cathode: Effect of load and thermal cycling

A solid oxide electrolysis cell (SOEC) powered by a renewable source can convert CO₂ into carbon monoxide, which is a valuable feedstock for a range of fuels and chemical processes. The cathode material of the SOEC is required to possess sufficient catalytic activity for CO₂ reduction, and also sustain the thermal and electrical load cycling to which the SOEC would be subjected when coupled with an intermittent renewable source without an auxiliary electricity or thermal storage system. The operating conditions can become even more challenging if solar or waste heat from exothermic downstream industrial processes is to be embedded in the process. In this study, we evaluated a mixed ionic–electronic conducting composite (La_0·80Sr_0.20Sc_0.05Mn_0·95O_3-δ–Gd_0.20Ce_0·80O_1.95) material as an SOEC cathode. Along with initial electrochemical performance, we investigated the cell's response to accelerated ageing tests, including electrical load cycling and extreme thermal cycling. Factors leading to performance degradation were studied by electrochemical impedance spectroscopy and structural characterisation of the cathode before and after the test. Thermal cycling resulted in more pronounced effect on the cell degradation rate as compared to electrical load cycling.     

Effect of Additives on the Activation Energy for Sintering of Silicon Carbide

The combined-stage sintering model was used to determine the activation energy, Q , of sintering for selected SiC-based materials. SiC densified with a liquid (1.65 wt% Al) had an activation energy of 842±79 kJ/mol, a value between those for a silicon carbide densified with 1 wt% C and 0.25 wt% B₄C ( Q =643±37 kJ/mol) and one densified with 2.5 wt% AlN ( Q =1022±122 kJ/mol), compositions which have no liquid phase below 1850°C. The SiC with Al additive began densification by 1500°C and the densification curve was offset by approximately 100°C compared with the other two materials below 1850°C. The choice and amount of additives not only affect densification and activation energy, but also influence microstructure and fracture mode, allowing engineering of mechanical properties.     

Study of fluid flow in tundishes due to different types of inlet streams

Flow pattern and residence time distribution induced by different methods of pouring of molten steel into a tundish are studied by means of a water model with and without flow modifiers (FM). It was found that the submerged stream without FMs produces short circuiting and argon shrouded stream leads to excessive surface directed flow of liquid in a tundish. Open stream pouring generates surface turbulence and does not produce short circuiting. The effect of FM is found to be different for different methods of pouring, e.g. dam eliminates short circuiting and produces surface directed flow for submerged stream, whereas weir limits the surface turbulence within the inlet region for open stream pouring. Dam is found to reduce the dead volume for argon shrouded pouring.     

Role of iron species as mediator in a PEM based carbon-water co-electrolysis for cost-effective hydrogen production

Renewable sources of energy are becoming more favorable due to the falling prices and the worldwide push for cleaner sources of electricity. However, coal will continue to play a dominant role in global energy mix for at least several more decades. It will be thus imperative to find technologies for efficient utilization of coal with reduced CO₂ emissions and facilitate the goal of limiting climate change. In this study, the role of carbon, which can be sourced from coal or biomass has been investigated in the carbon assisted water electrolysis (CAWE) process for hydrogen generation. CAWE process was studied in a PEM-based zero-gap electrolysis cell with continuous circulation of carbon slurry at 70 °C by using linear-sweep voltammetry and chronoamperometry techniques. The effect of the addition of electrocatalytic mediators Fe²⁺ and Fe³⁺ ions to the carbon slurry was systematically studied on the sustainable current densities. The current densities of up to 52 mA cm^?2 at 1 V have been achieved by the CAWE process in the presence of 100 mM Fe²⁺ ion additives, and carbon has been demonstrated to contribute to over 30% of the total coulombic charges for the hydrogen production.     

Multiphase adhesive coacervates inspired by the Sandcastle worm

Water-borne, underwater adhesives were created by complex coacervation of synthetic copolyelectrolytes that mimic the proteins of the natural underwater adhesive of the sandcastle worm. To increase bond strengths, we created a second polymer network within cross-linked coacervate network by entrapping polyethylene glycol diacrylate (PEG-dA) monomers in the coacervate phase. Simultaneous polymerization of PEG-dA and cross-linking of the coacervate network resulted in maximum shear bond strengths of ～1.2 MPa. Approximately 40% of the entrapped PEG-dA polymerized based on attenuated total reflectance-Fourier transform infrared spectroscopy. The monomer-filled coacervate had complex flow behavior, thickening at low shear rates and then thinning suddenly with a 16-fold drop in viscosity at shear rates near 6 s(-1). The microscale structure of the complex coacervates resembled a three-dimensional porous network of interconnected tubules. The sharp shear thinning behavior is conceptualized as a structural reorganization between the interspersed phases of the complex coacervate. The bond strength and complex fluid behavior of the monomer-filled coacervates have important implications for medical applications of the adhesives.     

Monoazo disperse dyes. Part 3; Synthesis and fastness properties of some novel 4,5-disubstituted thiazolyl-2-azo disperse dyes

Novel blue disperse dyes bearing a 5-nitro substituent on various C-4 substituted thiazolyl-2-azo dyes have been prepared using m -aminoacetanilide derived coupling components. These dyes have been characterised using a range of spectroscopic techniques and exhibit interesting fastness behaviour on dyed polyester. For Parts 1 and 2 in this series, see references 9 and 10, respectively.     

X-ray crystal structure of 2-{2-acetylamino-4-[bis-(2-methoxycarbonylethyl)amino]-phenylazo}-4-methylthiazole-5-carboxylic acid ethyl ester

Crystals of the title novel red disperse dye were grown by slow evaporation from a chloroform solution and the crystal structure was determined by single crystal X-ray diffraction analysis. The dye molecule crystallises in the triclinic space group P 1 with the unit cell dimensions a = 7.561(2), b = 11.628(10) and c = 15.607(3) Å. The diffraction analysis showed that the hetarylazo skeleton of the dye is nearly planar, with the ester groups oriented up and down the plane of the molecule thus imparting it a 'Y' shape structure. The intramolecular hydrogen bonds, together with van der Waals interactions, stabilise the molecular conformation and crystal packing.     

Effect of modified drill point geometry on drilling quality characteristics of metal matrix composite (MMCs)

The abrasive reinforcement present in ‘Metal matrix composites’ (MMCs) is responsible for numerous machining challenges for the research fraternity. The increase in tool wear, burr formation, surface roughness, and increase in cutting forces are few of such machining challenges during the drilling of MMCs. The present research investigation explores the effect of change in drill point geometry on the drilling Quality characteristics (QCs) of the drilled hole wall. The drilling QCs under investigation are, Specific cutting pressure (SCP) and Surface roughness (SR) of the drilled hole wall. The levels of the input process parameters for optimum values of the output responses were established by Taguchi’s methodology. SEM images and contour plots of drilled hole wall have been used to qualitatively explain the drilling behavior of MMCs. The chip formation mechanism observed during drilling establishes the cutting behavior of the different cutting edges of the modified drill point geometry. It has been observed that the single conical chips were produced by primary cutting edge and single ring type chips were produced by secondary cutting edge. The step diameter is the main factor which influences the SCP followed by the feed and point angle. The surface roughness of the drilled hole wall has been governed by the cutting speed, feed and step diameter. Burnishing and honing effect were observed on the drilled hole wall surface because of entrapped free SiC particles using SEM.