Ab Initio Study on Dopant Relaxation Mechanism in Ti and Ce Cationically Substituted in Wurtzite Gallium Nitride

The changes in properties of materials upon introduction of impurities is well documented but less is known about the location of foreign atoms in different hosts. This study is carried out with the motivation to explore dopant location in hexagonal GaN using density functional theory based calculations. The dopant site location of the individual dopants Ti, Ce, and Ti-Ce codoped wurtzite GaN was investigated by placing the dopants at cationic lattice sites as well as off-cationic sites along the c-axis. The geometry optimization relaxed individual dopants on cationic Ga sites but in the case of codoping Ce settled at site 7.8% away along [0001 ¯] and Ti adjusted itself at site 14% away along [0001] from regular cationic sites. The analysis of the results indicates that optimized geometry is sensitive to the starting position of the dopants. The magnetic exchange interactions between Ti and Ce ions are responsible for their structural relaxation in the matrix

Effect of Carbon Nano-Tubes, Micro and Nano Dispersions of SiC and Al2O3 on the Mechanical and Physical Properties of Pure Copper

 Reviews on Advanced Materials Science 52(1):126-133 · December 2017This paper studies the physical and mechanical properties of pure copper powder with various reinforcement materials at different volume fractions. The used reinforcement materials are carbon nanotubes CNT (0.5-2 wt.%) as nano particles, Al2O3 (1-4 wt.%), and SiC (1-4 wt.%) as micro particles. Various characteristics were evaluated on the composite specimens such as microstructures, density, electrical conductivity, thermal conductivity, hardness, and compression properties to investigate the suitable reinforcement percentage that achieves the best physical and mechanical properties. The micron-sized Al2O3 and SiC and nano sized CNT has shown an enhancement on the mechanical and physical properties of the composite. The electrical and thermal conductivities were evaluated and the results have shown positive enhancements

Physical Survey of Thermally Heated Non-Newtonian Jeffrey Fluid in a Ciliated Conduit Having Heated Compressing and Expanding Walls

An analytical study is reported that highlights the physical aspects for a heated non-Newtonian Jeffrey liquid in a duct possessing sinusoidally moving ciliated walls. A comprehensive and specific convection analysis is conveyed for this ciliated elliptic duct problem by considering the viscous dissipation effects. The dimensional mathematical problem under consideration is transformed into its dimensionless form by means of appropriate and useful transformations. Then, velocity and temperature equations are exactly evaluated with given boundary conditions. The velocity profile is integrated over the elliptic cross-section and exact mathematical solution is obtained for the pressure gradient. Moreover, the distinct physical flow properties combined with the convection heat transfer phenomenon are discussed in detail through graphical outcomes. The illustrative streamline description shows an enhancing closed contour size with increasing Q (dimensionless flow rate)

Rheological, Aging, and Microstructural Properties of Polycarbonate and Polytetrafluoroethylene Modified Bitumen

Deterioration of asphalt pavements due to massive load of vehicles and climatic variation has demanded the use of pavements construction material with an excellent resilience characteristic, resistance to permanent deformation, and most importantly, a much longer service lifespan. The main structural distresses in pavement construction are permanent deformation at high temperatures and fatigue cracking under repetitive traffic loadings. To comprehensively investigate the performance of bitumen penetration grade (PG) 70 against rutting, fatigue, and high temperature cracking in hot mix asphalt (HMA) pavements, polycarbonate (PC) and polytetrafluoroethylene (PTFE) were used. The investigation of the internal structure, rheological, and physical properties of base and modified bitumen (MB) mixes with different percentages of modifiers (0%, 2.5%, and 5%) by weight were performed via scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) analysis, X-ray diffraction (XRD) pattern analysis, rolling thin-film oven test (RTFOT), pressurized aging vessel (PAV), dynamic shear rheometer (DSR), rotational viscosity (RV), and bending beam rheometer (BBR). The results of the RV test indicate that modification of neat bitumen with polycarbonate and polytetrafluoroethylene increased the viscosity for polycarbonate-modified bitumen (PCMB), polytetrafluoroethylene-modified bitumen (PTFEMB), and for a blend of PCMB-PTFEMB by 44%, 50%, and 55.75% at 135 °C and 111.10%, 127.80%, and 138.88% at 165 °C, accordingly. BBR test results revealed that modifiers increased the rigidity of neat bitumen by 74.8%, 75.8%, and 74.5% at −16 °C, −22 °C, and −28 °C, respectively

Tribological Analysis of Molybdenum Disulfide (MOS₂) Additivated in the Castor and Mineral Oil Used in Diesel Engine

The lubrication phenomenon is used to reduce friction and wear between two rubbed surfaces, such as in engine and cutting processes. Different oils such as mineral oil and synthetic lubricant are being used for this purpose. With the passage of time, the demand of energy will get higher and natural resources and mineral lubricants will be diminished. Furthermore, biodegradation of mineral oil is too slow, and it remains on the surface of earth for a long period of time, creating atmospheric pollution. To overcome this problem, bio lubricants are being used to reduce wear and friction due to their high biodegradability. In order to increase the lubrication capacity of castor oil, a 1 wt. % concentration of MoS2 nanoparticles was added to the base oil. Moreover, to stabilize the additives, 2 wt. % gum arabic and 1 wt. % Oleic acid (OA) were also added. Then, multiple tests, such as of physicochemical properties, Fourier transform infrared (FTIR), and atomic absorption spectroscopy (AAS) of synthetic lubricant and conventional lubricant, were carried out before and after the operational running of 100 h on the diesel engine for each lubricant at 75% throttle, 2200 rpm, and 50% of total load. The results show that the behavior of newly prepared MoS2-based synthetic lubricant possessed higher characteristics in some physicochemical properties and was marginally lacking in other properties compared to shell lubricant. The flash point and specific gravity of synthetic lubricant were decreased compared to shell oil, with relative decreases of 0.27% and 1.15%, respectively. Ash and kinematic viscosity of 40 °C had a relative increase of 4.17% and 1.61%, respectively, and at a kinematic viscosity of 100 °C, the pour points and total base number (TBN) were relatively increased at 1.09%, 6.02%, and 1.38%, respectively, with respect to the properties of the shell lubricant. Moreover, this analysis evaluated that the reduction of wear and tear in synthetic lubricant regarding chromium (Cr), copper (Cu), and iron (Fe) was decreased by 21.12%, 3.39%, and 0.96%, respectively, but in the case of aluminum (Al) the wear and tear was marginally increased, at 1.17%, compared to shell lubricant. In the case of calcium (Ca) and zinc (Zn), the concentration was decreased by 3.59% and 17.41%, respectively. The FTIR analysis shows that all the peaks of the synthetic lubricant and shell lubricant were overlapping each other in the first three regions of the mid-IR spectra from 4000 to 1500 cm−1 and had the same functional groups—hydroxyl stretch (O-H), alkanes (C-H), carbonyls (C=O), aromatic amines (C-N), and alkyl halides (C-Br)—which were attached but fluctuating in the fingerprint region. The results show that shell lubricant can be replaced with MoS2-based synthetic lubricant because the latter has superior friction reduction and load-bearing capability and can compete favorably with commercial shell oil in wear protection when additivated with MoS2-based nanoparticles, and hence can be a good alternative for diesel engine oil