Influence of Experimental Parameters on Friction and Wear Mechanisms of PA66/PTFE Blend Reinforced with Glass Fiber

Polymer blend of composition 80 wt% polyamide 66/20 wt% polytetraflurotheylene (PA66/PTFE) was selected as a matrix and reinforced with different weight percentage of short glass fibers (SGF). These composites were prepared by melt mix method using twin screw extruder followed by injection molding. The tribological behaviors were tested by using pin on disc machine by varying the different experimental parameters. The friction and wear mechanisms were studied as a function of sliding velocity, sliding load, and distance. The effect of fiber loading lowered the wear volume loss of SGF filled PA66/PTFE blend. The least frictional coefficient of 0.24 was obtained for 20 wt% of SGF in the blend. However, the wear resistance was not apparently improved by SGF loading in the experimental range for comparison with unfilled PA66/PTFE blend. The worn surfaces of specimen were examined by scanning electron microscopy photographs. The observations revealed that the frictional behavior was a function of development and formation of transfer film. Matrix wear and fiber wear were the result of frictional mechanism. The critical wear volume of PA66/PTFE/SGF composites was the contribution of both matrix and fiber wear. The abrasive nature of SGF was also one of the important factor for frictional behavior.     

Performance and emission characteristics of diesel engine operated on plastic pyrolysis oil with exhaust gas recirculation

The objective of this research was to study the performance and emission characteristics of using waste plastic pyrolysis oil in diesel engine without any engine modification. The engine used in this study is a four-stroke single-cylinder naturally aspirated diesel engine (compression ignition). In the present work, the engine fuelled with blends of diesel fuel (DF) with plastic oil in the ratio of 90:10 (blend10%), 80:20 (blend20%), 70:30 (blend30%), and 50:50 (blend50%) are experimentally measured the efficiencies and emissions, analysed the performance, and compared results with that of DF.     

Role of SiC on Mechanical,Tribological and Thermal Expansion Characteristics of B4C/Talc-Reinforced Al-6061 Hybrid Composite

Silicon - A hybrid SiC/B4C/Talc reinforced Al-6061 metal matrix composite with improved machinability, wear resistance and low thermal expansion is prepared and evaluated. The primary aim of this...     

Evidence for the improvement of thermostability of the maltogenic α‐amylase of Aspergillus niger by negative pressure

Thermostability of the enzymes is influenced by the different parameters and pressure also influences the biological activity of the enzymes. Recently reported maltogenic α‐amylase from Aspergillus niger acts optimally on starch at 40°C and it was unstable above 40°C at atmospheric pressure. Calcium could stabilize the maltogenic α‐amylase activity up to 50°C at atmospheric pressure. But, at negative pressure (−200 mbar) enzyme was stable at temperatures higher than 50°C either in the presence or absence of the substrate, starch making it adoptable for starch processing. Enzyme showed higher affinity to the starch at negative pressure compared to the atmospheric pressure and change in the surface roughness of the enzyme is almost similar to the native state at 70°C and negative pressure. These results suggest that thermolabile enzymes can be used at negative pressures for industrial applications.     

Reaction Kinetics of Ozone Gas in Green Gram (Vigna radiate)

This study was carried out to evaluate the reaction kinetics of ozone gas in different height (5 and 10 cm), moisture content (10.6 and 13.4% (d.b.)) and gas flow rate (2 and 4 L/min). The decomposition kinetics obtained was first-order model. As far as the half-life of ozone is considered, the highest value obtained was equivalent to 8.72 min for grains ozonated at 5 cm height, 10.6% (d.b.) moisture content and 2 L/min gas flow rate. In the process of ozone reaction rate in green gram grains, height (p < 0.01) and moisture content (p < 0.01) were found to be the key factor for the effectiveness of ozone fumigation.     

Decay Rate Kinetics of Ozone Gas in Rice Grains

The present study was carried out to evaluate the effects of ozone on rice grains for the following three conditions: saturation time, decay rate, and half-life of ozone. Experiments were performed in different bed thicknesses (5 and 10 cm) and moisture content (11.4 and 14.2% wb) at atmospheric conditions. The lowest saturation time of ozone was 119 min, with the concentration of 516 ppm for rice grains ozonated at 5-cm bed thickness with 11.4% (wb) moisture content. The decay rate kinetics of ozone obtained were consistent with a first-order model. Regarding the half-life of ozone, the lowest value obtained was 6.78 min for rice grains ozonated at 10-cm bed thickness with 14.2% (wb) moisture content.     

Pd2(dba)3-catalyzed amination of C5-bromo-imidazo[2,1-b][1,3,4] thiadiazole with substituted anilines at conventional heating in Schlenk tube

ABSTRACT

An efficient Pd₂(dba)₃-catalyzed amination of C5-bromo-imidazo[2,1-b][1,3,4]thiadiazole using conventional heating is reported. The C5-bromoimidazo[2,1-b][1,3,4]thiadiazole was synthesized using a multistep approach which started by cyclization of thiosemicarbazide with a carboxylic acid to give 2-amino[1,3,4]thiadiazoles which were further treated with 2-haloketones to give imidazo[2,1-b][1,3,4]thiadiazoles. Then, the bromination of imidazothiadiazole was done using N-bromosuccinimide to give the C5-bromo-imidazo[2,1-b][1,3,4]thiadiazole. Afterward, various C-N bond-forming approaches were attempted such as S_NAr, Cu(I), Cu(II), Pd(OAc)_2, Pd₂(dba)₃ catalyst with different ligand, additive, base, solvent and temperature conditions. Out of various approaches used, only Buchwald Hartwig amination, performed with conventional heating, gave N-arylamine-5-imidazothiadiazoles. Then, 10 different anilines with different electron-withdrawing and donating groups at different positions were employed to examine the scope and limitations of the method. Salient features of this method include conventional heating in a Schlenk tube as the reaction condition, the absence of the use of toxic isocyanides, the wide nature of substituent tolerance with anilines, and moderately good product yields.     

ADSORPTION EQUILIBRIUM OF CARBON TETRACHLORIDE ON DRY SOILS

Vapor phase adsorption equilibrium of carbon tetrachloride, a priority pollutant, on dry soils was studied at 288, 293, and 298 K. Using a gravimetric adsorption apparatus, adsorption /desorption isotherms of carbon tetrachloride were generated on two different soil samples. The effects of temperature and soil characteristics were examined. Isosteric heals of adsorption were calculated and heat curves were constructed.

Adsorption isotherms of carbon tetrachloride on dry soil samples were Type II, indicating formation of multilayers of adsorbate on the soil particle surface. Considerable hysteresis effects, associated with capillary condensation, were observed upon desorption. Thermal data confirmed that the adsorption of carbon tetrachloride vapor on soil was primarily physical adsorption. Heat curves showed that the soil samples had energetically heterogeneous surfaces. A positive correlation between The soil's specific surface area and its sorption capacity was observed. Clay content and pore size were also dominating factors.

The experimental data were correlated by the Polanyi Potential, the BET, and the GAB models in order to provide input lo fate and transport models predicting the degradation or movement of volatile organic pollutants in soil. The BET equation gave accurate data fit, within a deviation range of 2·63-5·40%, for up to 40% of the saturation pressure. The GAB equation provided superior fit of the data for the entire relative pressure range. Absolute error percentages from the GAB model ranged from 1·77 to 5·38%. Results followed the Potential Theory satisfactorily and led to a single temperature-independent characteristic curve.     

Effect of processing and thickness on the structure in a polyimide film of poly(pyromellitic dianhydride-oxydianiline)

It is well known that poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA), orders at curing temperature well below its Tg with chains oriented parallel to the film plane. Structure analysis using X-ray scattering reveals two structural features: (a) The ordered structure range from biaxial-nematic-like to crystalline; (b) the symmetry of orientation of the ordered regions change from a fiber, to planar to isotropic as a function of depth. Both of these structural features are attributed to surface effects and solvent retention during curing. The solvent profile is estimated during the imidization process using a theoretical model. The model considers the change in temperature, imidization rate, diffusivity, and film thickness with time during the curing. The model indicates that solvent content after most of the imidization is complete is crucial in determining the order and texture in the film. At the air/film interface, a thin skin formation due to solvent depletion and surface ordering is suggested from the model. Depending on the process condition the overall structure of the film can vary from crystalline to mesomorphic. The biaxial nematic and smectic like structure are probably not equilibrium structures but are frustrated order due to limited solvent-induced mobility. The process condition affect the quality and quantity of order, and the texture due to chain's anisotropic cross-section is affected primarily by film thickness. By replacing a single component precursor with a blend of precursors of the same polyimide, both higher isotropy and order can be obtained in thin PMDA-ODA films. The order and extended chain conformation is better than that observed in the top 10 nm nearsurface-structure.     

Synthesis and phase stability of precursor derived HfO2/Si-C-N-O nanocomposites

Hafnium alkoxide modified polysilazane was synthesized by the drop-wise addition of hafnium tetra(n-butoxide) to polysilazane. The solid state thermolysis (SST) temperature and the ceramic yield for both the polysilazane and modified polysilazane were determined by performing thermogravimetry. Fourier transform infrared spectroscopy was performed to understand the polymer to ceramic conversion as well as the bonding characteristics of the ceramics. The modified polymer after crosslinking was subjected to SST at 800 °C at a constant heating rate of 5 °C/min for a dwell time of 2 h in atmospheric ambience. From the X-ray diffractograms, the as-thermolysed ceramics were observed to remain X-ray amorphous and on heat-treatment resulted in the crystallization of tetragonal hafnia. However, on heat-treatment at 1500 °C, reverse phase transformation from tetragonal to monoclinic hafnia was observed. Raman spectroscopy and transmission electron microscopy were employed to further understand the phase evolution. The thermal stability and the influence of amorphous matrix on the coarsening of HfO₂ were also evaluated.