Thermal annealing

An easy synthesis route for cuprous oxide (Cu2O) anoparticles is reported via thermal annealing improved and controlled by in-situ conductivity measurements. The crystalline structure, phase transition, surface morphology and particle size/shape, were investigated through X-ray diffraction, a conductivity setup and scanning electron microscopy, respectively. X-ray diffraction patterns revealed that initial metallic Cu nanoparticles were transformed to Cu2O nanoparticles with high purity, under specific conditions critically dependent on the temperature and annealing duration. This transformation was also dependent on the film thickness and atmospheric composition in the test chamber during the annealing process.

Annealing of the radiation damage generated in α-decay events is a common phenomenon in natural zircons. We have studied relationships between radiation damage, age and radionuclide content of natural zircons on a micro-scale. The degree of metamictisation was estimated by means of confocal laser–Raman spectroscopic measurements. Raman band broadening in well-ordered to moderately metamict zircons that have not experienced significant healing of the radiation damage since the time of their growth, shows a nearly linear dependence on the α-fluence. This dependence is proposed as a calibration line for examining unknown zircons in order to consider complete or incomplete damage storage, which may contribute to the understanding of the low-T thermal history of their host rocks. Seven examples for the application are presented. Radiation damage may anneal heterogeneously, with preferred re-ordering in more damaged micro-areas. Results suggest that single point defects do not anneal continuously over geologic periods of time but are, in contrast, a comparably stable type of radiation damage. In contrast to recrystallisation processes, structural recovery due to simple thermal annealing is not necessarily connected with loss of radiogenic Pb. The most prominent example for this are concordant zircons from Sri Lanka. Although they are excellent standards for U–Pb dating, Sri Lankan zircons should not be used as standards for structural radiation damage. The experimental work is completed by Monte Carlo simulations of α-decay events in zircon.

Recently, Au/Ni/p-type GaN ohmic contacts annealed in an air ambient have been widely investigated. However, to obtain a low specific-contact resistance, the annealing window is limited. In this study, to understand the oxidation function of metallic Ni, the Au/Ni/p-type GaN structure was annealed in an air ambient for 10 min at various temperatures. Using x-ray photoelectron spectroscopy (XPS) analysis, the metallic Ni was oxidized into NiO and NiO1.3 compositions at annealing temperatures of 500°C and 600°C, respectively. However, metallic Ni still existed on the interface of the Ni/p-type GaN annealed at 400°C. The associated barrier heights of 0.42 eV, 0.21 eV, and 0.31 eV were obtained with p-type GaN for the Ni, NiO, and NiO1.3 contacts, respectively. The hole concentrations of p-type NiO and p-type NiO1.3 were 2.6×1016 cm−3 and 2.0×1018 cm−3, respectively. The lower hole concentration of the p-type NiO would lead to reducing the valence-band bending of the p-type GaN, as well as the barrier height for holes crossing from the p-type NiO to the p-type GaN. The formation of NiO was thus an important issue for lowering the specific-contact resistance of the Au/Ni/p-type GaN ohmic contacts annealed in an air ambient.

Graphene continues to draw considerable research and commercial interest due to its applicability in a variety of industries. There have been various approaches developed to produce high quality graphene in commercial quantities in order to be able to meet the ever-increasing demand from industry. Despite over a decade of research and various examples of lab-scale success in producing highly pure single graphene sheets, there remain considerable challenges in translating them into a commercial success in terms of their large-scale production. To this end, reduction of graphene oxide (GO) is considered the most viable alternative approach to produce highly quality graphene. However, there have been numerous reports documenting a variety of reductants in the literature, making it quite difficult to assess and compare these strategies from the perspective of large-scale commercial production. In this review, we present a critical survey of various reduction methods adopted towards the reduction of GO enabled by chemical, plant extracts, microorganisms and photoreduction with special emphasis on their reduction mechanism and electrical conductivity of the resulting rGO. We also provide a prospective to draw attention to the considerable challenges persisting towards the structural and electronic properties of the synthesised rGO which is limiting the true commercial translation of these materials.

The degree of carbon burnout is an important operating characteristic of full-scale suspension-fired coal combustion systems. Prediction of carbon loss requires special char combustion kinetics valid through the very high conversions targeted in industry (typically >99.5%), and valid for a wide range of particle temperature histories occurring in full-scale furnaces. The present paper presents high-temperature kinetic data for five coal chars in the form of time-resolved burning profiles that include the late stages of combustion. The paper then describes the development and validation of the Carbon Burnout Kinetic Model (CBK), a coal-general kinetics package that is specifically designed to predict the total extent of carbon burnout and ultimate fly ash carbon content for prescribed temperature/oxygen histories typical of pulverized coal combustion systems. The model combines the single-film treatment of char oxidation with quantitative descriptions of thermal annealing, statistical kinetics, statistical densities, and ash inhibition in the late stages of combustion. In agreement with experimental observations, the CBK model predicts (1) low reactivities for unburned carbon residues extracted from commercial ash samples, (2) reactivity loss in the late stages of laboratory combustion, (3) the observed sensitivity of char reactivity to high-temperature heat treatment on second and subsecond time scales, and (4) the global reaction inhibition by mineral matter in the late stages of combustion observed in single-particle imaging studies. The model ascribes these various char deactivation phenomena to the combined effects of thermal annealing, ash inhibition, and the preferential consumption of more reactive particles (statistical kinetics), the relative contributions of which vary greatly with combustion conditions.