Tensile testing and fracture mechanism analysis of polyvinyl alcohol nanofibrous webs

A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.     

Performance of energy-efficient rice mills

ABSTRACT

This study reports the energy-efficient performance of three different brands of rice polisher machines operating at different rice mills. The observations of feed screws, sieves and cams have been recorded and we have analysed the chemical composition, microstructure, hardness of cams of different rice mills and given solutions for the performance enhancement of cams. Our objective is to enhance the production of rice variety with quality characteristics and general appearance as required by the consumers.     

Effect of ecofriendly sealing coat against corrosion protection of steel rebars in concrete

Phosphating is one of the most important chemical conversion treatments for steel, mainly to improve corrosion resistance and paint adhesion and as an absorbing layer for waxes, oils, lacquers, etc. However, phosphate coating are crystalline and porous and need a sealing treatment after phosphating. Chromate sealing is a well known practice, and due to its toxicity, development of an ecofriendly sealing treatment is very essential. This paper focuses on the effect of zinc phosphate chemical conversion coating with the addition of nano-SiO₂ to protect the mild steel rebars against corrosion in chloride contaminated concrete. The coated surfaces were characterised by scanning electron microscopy and X-ray diffraction. Corrosion resistances of coated and uncoated rebars were evaluated by anodic polarisation, linear polarisation resistance, Tafel and alternating current impedance spectroscopy and cyclic polarisation technique. The results indicated that the coated rebars have considerably reduced the corrosion rate even in the presence of 3% chloride environments.     

Some Thermodynamic Aspects of the Oxides of Chromium

To understand Cr emissions from slag melts to a vapor phase, an assessment of the stabilities of the chromium oxides at high temperatures has been carried out. The objective of the present study is to present a set of consistent data corresponding to the thermodynamic properties of the oxides of chromium, with special reference to the emission of hexavalent chromium from slags. In the current work, critical analysis of the experimental data available and a third analysis in the case of Cr₂O₃ have been carried out. Commercial databases, Fact Sage and ThermoCalc along with NIST-JANAF Thermochemical Tables, have been used for the analysis and comparisons of the results that are presented. The significant discrepancies in the available data have been pointed out. The data from NIST-JANAF Thermochemical Tables have been found to provide a set of consistent data for the various chromium oxides. An Ellingham diagram and the equations for the ΔG° (standard Gibbs free energy change) of formation of CrO _x have been proposed. The present analysis shows that CrO₃(g) is likely to be emitted from slag melts at high oxygen partial pressures.     

Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite

Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.     

Defect-sealing synthesis of vertically oriented ordered mesoporous silica membranes

Vertically oriented ordered mesoporous silica membranes have been successfully synthesized in our laboratory in the form of silica plugs filling the macron-sized straight pores of hydrophobic track-etched polycarbonate membrane support. However, these membranes have shown gaps between the plugs and support pore wall which make the membranes unfeasible for use. This paper reports on techniques of synthesis of defect-free ordered mesoporous silica membranes by filling the gaps with microporous silica. Here, the elimination of defects is achieved by filling the membrane gaps with an alkoxysilane followed by exposure to humid air to allow controlled hydrolysis and condensation resulting in the formation of microporous silica within the gaps. Molecular probing gas permeation and helium/nitrogen (or oxygen) binary separation tests, coupled with surface characterization methods, show that the final membranes contain ordered mesopores of about 2.7 nm pore diameter, running through the membrane, with gaps sealed by microporous silica having a pore size <0.55 nm.     

Optimization of testing parameters for tensile property evaluation of poly(vinyl alcohol) nanofibers webs

An optimization study was conducted to understand the influence of thickness, speed of testing, and gauge length (specimen test length) on important mechanical properties of poly(vinyl alcohol) nanofiber webs. Using orthogonal experimental design, experimental trials were optimized for the three testing parameters, which enabled to undertake 25 experiments involving the three variables at five different levels. Polynomial regression equations show that the three variables have interactive influence on the mechanical properties tested. Of the three variables, thickness of nanofiber webs seems to have maximum influence on tensile properties. This study showed that the optimal values for tensile testing of nanowebs are gauge length at 0.50 cm, thickness of nanowebs at 0.10 mm, and speed of testing at 25 mm·min⁻¹. This study will provide an opportunity to establish a standard method for the tensile evaluation of nanowebs involving gauge length, thickness, and speed of testing. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47159.     

Screening efficiency of the Hardy–Rand–Rittler (HRR) colour test (4th edn)

This study evaluates the screening efficiency of the Hardy–Rand–Rittler (HRR) 4th edition colour test. This test was also compared with results from the Ishihara test. Thirty-nine subjects with congenital red–green deficiency and 120 colour normal subjects participated in the study. The subjects were shown the Ishihara (concise version, 2001) and the HRR (4th edn) pseudoisochromatic plates. Each plate was viewed for 3?s. A Macbeth Easel lamp was used for illumination (70?foot-candle). The HRR test had 100% sensitivity and the specificity was 63%. The overall efficiency of the HRR test was less than that of the Ishihara. The results also indicated that plate seven of HRR (4th edn) has poor screening efficiency. Thus the HRR is good for identifying colour deficient subjects but a caveat is that it fails too many normals.     

CuBr2‐induced charge screening on photoactive nanocolloidal polypyrrole:poly(styrene sulfonate) composite multilayer thin‐film counter electrodes for high‐efficiency dye‐sensitized solar cells

Nanocolloidal polypyrrole (PPy):poly(styrene sulfonate) (PSS) particles were synthesized by chemical oxidative polymerization using 15 wt% of PSS. The highly processable polymer composite (PPy:PSS) was spin‐coated at 4000 rpm on fluorine‐doped tin oxide glass and subsequently employed as a counter electrode (CE) for dye‐sensitized solar cells (DSCs). PPy:PSS multilayer (one, three, five) CEs were treated with CuBr₂ salt, which enhances the efficiency of the DSCs. Optical studies reveal that a bulkier counterion hinders interchain interactions of PPy which on salt treatment shows a moderate redshift in absorption maxima. Salt‐treated PPy:PSS films exhibit lower charge transfer resistance, higher surface roughness and better catalytic performance for the reduction of I₃^?, when compared with untreated films. The improved catalytic performance of salt‐treated PPy:PSS multilayer films is attributed to charge screening and conformational change of PPy, along with the removal of excess PSS. Under standard AM 1.5 sunlight illumination, salt treatment is shown to boost the efficiency of multilayer PPy:PSS composite film‐based DSCs, leading to enhanced power conversion efficiency of 6.18, 6.33 and 6.37% for one, three and five layers, respectively. These values are significantly higher (ca 50%) than those for corresponding devices without CuBr₂ salt treatment (3.48, 2.90 and 2.01%, respectively). © 2016 Society of Chemical Industry