Preet M. Singh

Effects of heat treatment and reinforcement size

The effects of heat-treatment, matrix microstructure, and reinforcement size on the evolution of damage, in the form of SiCp cracking, during uniaxial tension testing of an aluminum-alloy based composite have been determined. A powder metallurgy Al-Zn-Mg-Cu alloy reinforced with 15 vol pct of either 5 or 13 μm average size SiCp was heat treated to solution annealed (SA), underaged (UA), and overaged (OA) conditions. The SA treatment exhibited lower yield strength and higher ductility for both particulate sizes compared to the UA and OA conditions. The evolution of damage, in the form of SiCp fracture, was monitored quantitatively using metallography and changes in modulus on sequentially strained specimens. It is shown that the evolution of SiCp fracture is very dependent on particulate size, matrix aging condition, and the details of the matrix-reinforcement interfacial regions. SiCp fracture was exhibited by the UA and OA treatment over a range of strains, while a preference for failure near the SiCp/matrix interfaces and in the matrix was exhibited in the OA material. While thepercentage of cracked SiCp at each global strain typically was equal or somewhat lower in the material reinforced with 5 μm average size SiCp, theabsolute number of cracked SiCp was always higher at each global stress and strain in the material containing 5 μm average size SiCp, for each heat treatment. Damage(e.g., voids) in the matrix and near the SiCp/matrix interfaces was additionally observed, although its extent was highly matrix and particle-size dependent. It was always observed that increases in stress (and strain) produced a larger amount of fractured SiCp. However, neither a global stress-based nor a global strain-based model was sufficient in converging the amount of SiCp fractured for all heat treatments and particle sizes tested.

Stress Corrosion Crack Coalescence

Abstract The stress corrosion cracking of a pipeline steel exposed to a carbonate—bicarbonate solution has been studied under various loading conditions, particularly those involving a relatively s...

Effect of Ethanol Chemistry on Stress Corrosion Cracking of Carbon Steel in Fuel-Grade Ethanol

Abstract A systematic study was carried out to understand the effect of ethanol chemistry (chloride, water, pHe, and oxygen level) as well as other controlling parameters on the stress corrosion cr...

Characterization of Milled Wood Lignin (MWL) in Loblolly Pine Stem Wood, Residue, and Bark

Milled wood lignin samples from Loblolly pine stem wood, forest residue, and bark were isolated and characterized by quantitative (13)C and (31)P nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC) for molecular weight determination. Results from (13)C NMR show the stem wood and forest residue samples have similar functional group contents. However, the bark has fewer methoxyl groups, β-O-4 structures, dibenzodioxocin, and side chains than the other two lignins. The bark lignin has the highest amounts of p-hydroxyphenyl (h) and C-5 condensed lignin, stem wood has the lowest, and the residue lies between. (31)P NMR analysis indicates that bark lignin contains more C-5 substituted phenolics and fewer aliphatic hydroxyl groups than the lignin isolated from stem wood or residue. The molecular weight distribution analysis indicates the bark lignin has higher weight-average molecular weight (M(w)) and polydispersity index than the lignin recovered from stem wood or residue.

Film Breakdown and Anodic Dissolution during Stress Corrosion Cracking of Carbon Steel in Bioethanol

The stress corrosion cracking (SCC) behavior of X-65 carbon steel was investigated in simulated fuel-grade ethanol (SFGE) using the slow strain rate test method, potentiodynamic polarization, electrochemical impedance spectroscopy, open-circuit potential, and potentiostatic current monitoring. Results indicate that crack initiation on carbon steel in the SFGE environment is associated with plastic deformation in the material, which leads to a surface film breakdown. The competition between active anodic dissolution and repassivation ahead of the crack tip controlled the propagation of these cracks in SFGE. Within the anodic dissolution range, both crack density and crack growth rate in the through-thickness direction increased as the potential increased. The applied cathodic potential eliminated the SCC in this system. The mode of SCC for the carbon steel in aerated SFGE was predominately transgranular.

Chloride-Induced Corrosion of Prestressing Steels Considering Crevice Effects and Surface Imperfections

Abstract Cyclic potentiodynamic polarization (CPP) techniques were used to evaluate the influence of crevices present in stranded prestressing steels on the resistance to chloride-induced corrosion. Prestressing wire and strand specimens were exposed to simulated concrete pore solutions with chlorides added as sodium chloride (NaCl) up to 1.0 M. Stranding resulted in a 67% reduction in measured Cl−-induced corrosion resistance when compared with CPP experiments conducted on single prestressing wires. Forensic investigation of tested specimens showed that imperfections in as-received zinc phosphate (ZnPO4) surface coatings also played a role in corrosion initiation. Based on these data, a model has been developed to describe the influence of crevice corrosion mechanisms and surface imperfections on corrosion initiation in prestressing strand. When these reductions in corrosion resistance were applied to service life estimates of model concrete systems, reductions in time-to-corrosion were 28 to 36%.

Investigating a Mechanism for Transgranular Stress Corrosion Cracking on Buried Pipelines in Near-Neutral pH Environments

Abstract Buried carbon steel fuel transmission pipelines, protected by external coatings and cathodic protection, are known to experience transgranular stress corrosion cracking (TGSCC). Failure an...

A Novel Method for Enhanced Recovery of Lignin from Aqueous Process Streams

Abstract This study demonstrates that acid precipitation of lignin in the presence of magnetite followed by an applied magnetic field provides a simple method for enhanced lignin recovery from an aqueous stream. The extraction procedure was shown to be sensitive to the relative charge of magnetite and solution pH. Under optimized conditions, 93 wt.% of the softwood lignin from a kraft cooking liquor could be recovered employing this novel separation approach.

Stress Corrosion Cracking of Type 304L Stainless Steel in Sodium Sulfide-Containing Caustic Solutions

Abstract Austenitic stainless steels (SS) are known to be susceptible to caustic stress corrosion cracking (SCC) at temperatures higher than ∼121°C. However, when sulfides are present in caustic so...

Preparation, structure and adsorption properties of synthesized multiwall carbon nanotubes for highly effective removal of maxilon blue dye

Multiwall carbon nanotubes (MWCNTs) have been hydrothermally prepared using polyethylene glycol as the carbon source. Herein, new MWCNTs composites with high adsorption capacity were prepared and applied as efficient adsorbents for adsorption of maxilon blue dye (GRL) from aqueous solution. The morphologies of the MWCNTs were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform-infrared (FT-IR) spectroscopy. The adsorption property of maxilon blue (GRL) from aqueous solution onto MWCNTs was studied as a function of mass dosage, pH of solution, initial dye concentration and temperature. The adsorption of GRL depends on the initial pH of the solution with maximum uptake occurring at about pH 10. The maximum adsorption capacity of prepared MWCNTs was 260.7mg/g. Langmuir, Freundlich and Temkin isotherms were applied to fit the experimental data. The Freundlich equilibrium isotherm fitted well the experimental data indicating the homogeneity of the adsorbent surface sites. Thermodynamics parameters were studied the changes in free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) during adsorption. It is noticeable that the adsorption of GRL dye onto MWCNTs was a spontaneous and endothermic process and indicates that the adsorption is favored at high temperature.