Tribological behaviour of powder metallurgy-processed aluminium hybrid composites with the addition of graphite solid lubricant

The tribological behaviour of powder metallurgy-processed Al 2024–5 wt% SiC–x wt% graphite (x=0, 5, and 10) hybrid composites was investigated using a pin-on-disc equipment. An orthogonal array, the signal-to-noise ratio and analysis of variance were employed to study the optimal testing parameters using Taguchi design of experiments. The analysis showed that the wear loss increased with increasing sliding distance and load but was reduced with increased graphite content. The coefficient of friction increased with increasing applied load and sliding speed. The composites with 5 wt% graphite had the lowest wear loss and coefficients of friction because of the self-lubricating effect of graphite. Conversely, due to the effect of the softness of graphite, there was an increase in wear loss and the coefficient of friction in composites with 10 wt% graphite content. The morphology of the worn-out surfaces and wear debris was examined to understand the wear mechanisms. The wear mechanism is dictated by the formation of both a delamination layer and mechanically mixed layer (MML). The overall results indicated that aluminium ceramic composites can be considered as an outstanding material where high strength and wear-resistant components are of major importance, particularly in the aerospace and automotive engineering sectors.     

Particles in High-Pressure Cylinder Gases

An improved test protocol is presented for the measurement of particle concentrations in high-pressure cylinder gases. With the screening method, particles entrained in a cylinder gas can be collected and chemically analyzed for the isolation of particle sources. Results are presented for argon, helium, and nitrogen cylinder gases. Many fine particles are formed from the trace organic vapors present in the cylinder gas by gas-to-particle conversion occurring downstream of such pressure-reducing devices as an orifice plate. It is demonstrated that these fine particles in the cylinder gas can be significantly reduced by as much as three orders of magnitude by the insertion of an appropriate purifying stage before the pressure-reducing devices.     

NITROGEN REAGENTS IN METAL ION SEPARATION. PART VIII SUBSTITUTED IMIDAZOLES AS EXTRACTANTS FOR Cu3+

ABSTRACT

A number of derivatives of imidazole have been synthesized. Their extraction behaviour towards Cu²⁺ in dilute acid medium have been investigated in both chloride and perchlorate media. The influence of electronic and stereochemical effects are discussed. Two-phase potentiometric titrations were employed to determine the two-phase protonation constants and Cu(II) complex species present in the organic phases. The N-decylimidazole derivative has a higher extraction efficiency than the other C-ring substituted imidazoles in spite of their greater protonation constants.     

New Red- and Green-Emitting Phosphors, AYP2O7.5:RE3+ (A=Ca and Sr; RE=Eu and Tb) under Near-UV Irradiation

New red- and green-emitting phosphors, AY_{1− x} P₂O_7.5: x RE³⁺ (A=Ca and Sr; x =0.01, 0.03, 0.05, 0.10; RE=Eu and Tb) were synthesized by the conventional ceramic route and their photoluminescence properties under near-ultraviolet (UV) irradiation were investigated. It was found that CaYP₂O_7.5: Eu³⁺ phosphor emits strong red light when excited by a radiation of 394-nm wavelength and SrYP₂O_7.5:Eu³⁺ gives intense orange light when excited by a radiation of 396-nm wavelength. Strong green emission for AY_{1− x} P₂O_7.5:Tb³⁺ is also observed under near-UV irradiation (378 nm). When compared with emission intensity from a standard YPO₄:0.05Tb³⁺, the emission from SrYP₂O_7.5:0.05Tb³⁺ showed greater intensity values under the same excitation wavelength (378 nm). X-ray powder diffraction analysis showed that AYP₂O_7.5 has xenotime-type structure.     

A thermal investigation on coals from Assam (India)

A thermal characterization of two coal samples from Ledo and Tikak collieries of Makum coalfield, Assam, India using XRD, FT-IR, and TGA was reported in this paper. The coal samples were heated for 20, 40 and 60 min in a 1000-watt heater (temperature ∼ 250 °C) in presence of air and characterized by XRD and FT-IR spectroscopy. Both the coals contain amorphous and crystalline phases. The raw coals also contain very small peaks due to quartz, calcite, gypsum, pyrite, and chlorite. The XRD patterns were found to change upon heating. In the coals heated for 20 and 40 min, it was observed that both amorphous and crystalline parts are common in them; crystalline part being the major one in the 40 min heated samples. The XRD patterns of the samples heated for 60 min indicate the presence of major quantities of α-quartz, hematite, and chlorite in them. They also show some new peaks, which are assigned to be kaolinite, illite, magnetite and very small in comparison to the amorphous portion in raw coals. α-quartz was found to be most stable crystalline phase of silica in the coals. The crystallinity % (X-ray) of the coals heat-treated for different times was determined and found to be increasing with time of heating. The FT-IR spectra of raw and heat-treated coal samples at 250 °C were also recorded and compared. The spectra were observed to be almost similar and it was observed that few functional groups disappear on heating at 250 °C. The same coal samples were also characterized by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques. On heat treatment in air atmosphere up to 800 °C, 20–27% weight loss occurs due to removal of various volatile materials. DTA results indicate the chemical reactivity of the coal sample initially at 80–110 °C due to loss of water, and two other major reactions at around 420 and 530 °C due to primary and secondary volatization.     

An ultrasonic collision detection system

Robots in manufacturing are increasingly being called on to do complex tasks that require intelligence beyond merely following a preprogrammed path. In robotic assembling of mechanisms, welding, machine tending and other tasks, sensing enables robots to adapt to their environments. In this research, an ultrasonic collision detection system for an industrial robot was designed, constructed and tested. Two ultrasonic transducers and ranging modules were mounted on the robot wrist to detect and prevent collisions with objects placed in the end effector's path. Experiments were conducted to determine objectto-robot distance as a function of robot speed after the robot had stopped. Two robot motions and two loads were studied. Statistical methods of stopping distance vs. robot speed are presented and will be useful in planning robot tool paths. This ultrasonic collision detection system can be used on stationary and mobile robots, automatic-guided vehicles, and other manufacturing applications.     

Single-step growth dynamics of core–shell GaN on Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> freestanding nanoprotruded microbelts

Freestanding wurtzite GaN nanoprotruded microbelts with Ga₂O₃ core, with typical thickness 1–10 μm, and length of few millimeters are synthesized by thermal annealing of Ga metal and subsequent reaction with ammonia at a low flow rate. They are of distinctive rectangular shape with a typical width of 10–100 μm. Thickness of the belt is about 1/10th of the width and length up to a few millimeters. The GaN, Ga₂O₃ layers and the GaN–Ga₂O₃ interface are characterized by high-resolution transmission electron microscopy after focused ion beam sectioning of the belt. Initially, Ga₂O₃ nucleates after reaction with the O₂ available in the environment, and subsequent reaction with NH₃ results in the formation of core–shell structure in the catalyst-free vapor–solid growth process. Having a low-symmetry phase, Ga₂O₃ can grow only in certain preferred directions thus controlling the final morphology of the belt. Nanoscale protrusions ~50–100 nm found on the surface of the belts could be an ideal system for building functional devices.