Correlation of Electrochemical Noise Parameters with Degree of Sensitization in AISI Type 316LN Stainless Steel

Degree of sensitization in 316LN stainless steel (SS) specimens sensitized at 898, 923 and 948 K for 500 h was obtained using double loop electrochemical potentiokinetic reactivation (DLEPR) technique as 7.4, 14.5 and 9.3% respectively. The sensitized specimens were pulsed polarized so that only Cr-depleted regions of the sensitized grain boundaries contributed to the electrochemical noise (EN) study. The DOS values evaluated from DLEPR technique were correlated with the EN parameters viz. standard deviation of current, σ_I and characteristic charge, q and characteristic frequency, f _n , obtained from shot noise analysis in order to assess the extent of intergranular corrosion (IGC) attack in 316LN SS. The plot of σ_I versus time showed highest σ_I values for the specimen sensitized at 923 K for 500 h, indicating high grain boundary dissolution and hence, severe IGC attack, whereas the specimen sensitized at 898 K for 500 h showed the least σ_I values indicating lower dissolution and least IGC attack. 316LN SS specimen heat-treated at 948 K for 500 h showed intermediate grain boundary dissolution rate. The charge q, determined from σ_I versus time plot showed a good correlation (>99%) with the DOS values obtained from DLEPR experiments. The power spectral density values of the current signal in the frequency independent region were found to have excellent correlation with these observations. The above findings were further supported by scanning electron microscopic examination which showed an increase in grain boundary width in the sensitized specimens when the heat-treatment temperature was raised from 898 to 923 K and on further increasing the temperature to 948 K, a marginal decrease in the grain boundary width was observed.     

Co-pyrolysis of waste polypropylene and rice bran wax‒ production of biofuel and its characterization

The present study aims to investigate the interaction during co-pyrolysis of Polypropylene (PP) and Rice bran wax (RBW). Initial characterization of feedstock was found to be suitable to carry out further experimental sets. Further, the pyrolysis experiments of PP, RBW and different blends (1:1, 1:2, 1:3, 2:1 and 3:1) were carried out in a semi-batch reactor. As per TGA analysis the temperature range between 400 °C and 650 °C at a constant heating rate of 25 °C/min was determined. The maximum liquid yield of PP, RBW was approximately 76%, 86% at the temperature of 500 °C and 600 °C respectively. Whereas maximum liquid yield from co?pyrolysis was obtained at 1:3 blend i.e. 81% at 550 °C.GC?MS results inferred the highest percentage of hydrocarbon whereas 1:3 blends has lower oxygen containing groups than RBW in liquid products. FTIR data of all blends indicates higher range of alkyl and aromatic compounds. H1 NMR results also confirmed the higher compounds into aliphatic region than aromatics or heteroaromatics groups. Further, most of the fuel properties of 1:3 blend falls within the range of gasoline and diesel properties. Study was extended to know crystallization behaviour of fuel by DSC analysis from two consecutive heating and cooling cycles of ?50 to 60 °C and reversed till ?50 °C at 10 °C min ?1. Two peaks at ?24 °C and 26 °C were observed during heating cycle whereas single peak at 23 °C during cooling cycle. 1:3 blend residual char characterization was also included in the work. Unfortunately, the SEM and BET results inferred that the char was not highly porous.     

Study of electrical and optical properties of Mn doped ZnS clusters

A simple, easy approach to the synthesis of manganese Mn doped zinc sulphide (ZnS) clusters is reported. The synthesis of Mn–ZnS clusters involved mixing and drying of zinc acetate, sodium sulphide and acrylic acid in appropriate ratio and adding Mn at proper conditions. These clusters were trapped in polyacrylic acid (PAA) to form PAA capping to provide stability. The clusters were characterized using high resolution SEM for morphological investigation; XRD for its crystalline nature; photoluminescence (PL) for optical characterization and electrical conductivity measurement. Clusters of Mn–ZnS were formed of the size ~ 10 nm.     

Characterization of surface charge and mechanical properties of chitosan/alginate based biomaterials

This study aims to examine mechanical properties and surface charge characteristics of chitosan/alginate-based films for biomedical applications. By varying the concentrations of chitosan and alginate, we have developed films with varying surface charge densities and mechanical characteristics. The surface charge densities of these films were determined by applying an analytical model on force curves derived from an atomic force microscope (AFM). The average surface charge densities of films containing 60% chitosan and 80% chitosan were found to be ? 0.46 mC/m² and ? 0.32 mC/m², respectively. The surface charge density of 90% chitosan containing films was found to be neutral. The elastic moduli and the water content were found to be decreasing with increasing chitosan concentration. The films with 60%, 80% and 90% chitosan gained 93.5 ± 6.6%, 217.1 ± 22.1% and 396.8 ± 67.5% of their initial weight, respectively. Their elastic moduli were found to be 2.6 ± 0.14 MPa, 1.9 ± 0.27 MPa and 0.93 ± 0.12 MPa, respectively. The trend observed in the mechanical response of these films has been attributed to the combined effect of the concentration of polyelectrolyte complexes (PEC) and the amount of water absorbed. The Fourier transform infrared spectroscopy experiments indicate the presence of higher alginate on the surface of the films compared to the bulk in all films. The presence of higher alginate on surface is consistent with negative surface charge densities of these films, determined from AFM experiments.     

Few layered graphene oxide thin films: A potential matrix for immunosensors

ABSTRACT

We have synthesized highly exfoliated graphene oxide (GO) and used it for the fabrication of electrochemical immunosensor. The thin films of GO were spin coated onto ITO/glass substrate and thereafter Bovine Serum Albumin (BSA) antibodies (Ab) were immobilized using EDC-NHS binding chemistry to design immunobioelectrode. The graphene oxide films were characterized using different spectroscopic techniques viz FT-IR, UV-Vis spectroscopy and HRTEM. The electrochemical activity of designed immunoelectrodes was studied by cyclic voltammetry (CV) that revealed a quasi reversible behaviour of graphene oxide films. The differential pulse voltammetry (DPV) measurements of the fabricated immunoelectrodes showed successful detection of analyte at very low concentration ranges (50 fg/mL–100 ng/mL). The present study entails the potential of GO for the development of various immunosensors for different diseases.     

Pitting Corrosion Behaviour of Boron Added Modified 9Cr–1Mo Steel: Combined Effects of Alkali and Chloride Ions

Pitting corrosion behaviour of modified 9Cr–1Mo ferritic steel containing 100 ppm of boron was studied in deaerated 0.1, 0.2 and 0.5 M sodium hydroxide solutions containing 0.1, 0.2 and 0.5 M sodium chloride. The chemical compositions of the passive film developed at applied potentials were studied using XPS. E_pit values decreased with increase in chloride concentrations for the given concentration of alkali. The effect (of Cl^?) was less pronounced in higher alkali concentrations. Pit diameters were observed to be significantly higher in 0.1 M sodium hydroxide containing 0.1 M sodium chloride; with increase in alkali concentration pit diameters were found to be restricted to lower values even at higher chloride concentrations. Energy dispersive spectroscopic (EDS) studies showed that pits had nucleated at Al₂O₃ inclusions/matrix interface. XPS analysis revealed the presence of Fe₃O₄, Fe(OH)₃ at lower potentials (150 and 209 mV(SCE)) whereas Fe₂O₃, Fe(OH)₃ and FeO₂ ^2? at higher potentials (400 and 650 mV(SCE)).     

Additive Change Detection in Nonlinear Systems With Unknown Change Parameters

We study the change detection problem in partially observed, nonlinear systems [which satisfy the hidden Markov model (HMM) property]. The change parameters are assumed unknown, and the changes can be slow or sudden. A partially observed system needs to be tracked first before changes can be detected. Sudden changes result in significant loss of track. These can be detected easily using the increase in tracking error (TE) or observation likelihood (OL) or using a CUSUM-type method applied to either of these. However, slow changes (which result in small loss of track) often get missed. We propose here a statistic that uses the tracked component of the change to detect it and, hence, detects slow changes faster than TE or OL. We show, both analytically and through simulations, that this statistic complements OL and TE for change detection     

Room-temperature H2S gas sensing at ppb level by single crystal In2O3 whiskers

In₂O₃ whiskers and bipyramidal nano-crystals were prepared by a carbothermal method. These were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), photoluminescence and Raman spectroscopy. These were studied for application to sensing of H₂S gas. The single crystal whiskers were found to be sensitive to as low as 200 ppb of H₂S gas at room temperature and showed saturation in response at 10 ppm. On the other hand, the films made of bipyramids were less sensitive to H₂S gas and the response was found to be a nearly linear function of concentration in a concentration range of 10–80 ppm.