Thermal Decomposition and Kinetics of Pentlandite-Bearing Ore Oxidation in the Air Atmosphere

The roasting of sulfide ores and concentrates is one of the most important steps in pyrometallurgical metal production from primary raw materials, due to the necessity of excess sulfur removal, present in the virgin material. Pentlandite is one of the main sources for nickel pyrometallurgical production. The knowledge of its reaction mechanism, products distribution during oxidation and reaction kinetics is important for optimizing the production process. Raw pentlandite-bearing ore from the Levack mine (Ontario, Canada) was subjected to oxidative roasting in the air atmosphere. A chemical analysis of the initial sample was conducted according to EDXRF (Energy-Dispersive X-Ray Fluorescence) and AAS (Atomic Adsorption Spectrometry) results. The characterization of the initial sample and oxidation products was conducted by an XRD (X-ray Diffraction) and SEM/EDS (Scanning Electron Microscopy with Energy Dispersive Spectrometry) analysis. Thermodynamic calculations, a phase analysis and construction of Kellogg diagrams for Ni-S-O and Fe-S-O systems at 298 K, 773 K, 923 K and 1073 K were used for proposing the theoretical reaction mechanism. A thermal analysis (TG/DTA—Thermogravimetric and Differential Thermal Analyses) was conducted in temperature range 298–1273 K, under a heating rate of 15° min−1. A kinetic analysis was conducted according to the non-isothermal method of Daniels and Borchardt, under a heating rate of 15° min−1. Calculated activation energies of 113 kJ mol−1, 146 kJ mol−1 and 356 kJ mol−1 for three oxidation stages imply that in every examined stage of the oxidation process, temperature is a dominant factor determining the reaction rate.

Electrochemical Investigation of Under-Deposit Corrosion Behavior for Aluminum Brass in Artificial Seawater

The under-deposit corrosion behavior and mechanism of aluminum brass (HAl77-2) were investigated in artificial seawater with a custom double electrolytic cell. The experiments included linear polarization, electrochemical impedance spectroscopy, and multielectrode arrays analysis. The electrochemical results revealed a pronounced effect of temperature on the under-deposit corrosion behavior of HAl77-2. The corrosion of HAl77-2 inside the CaCO3 scale is aggravated with increasing temperature. However, the increasing frequency of the corrosion rate of HAl77-2 gradually decreased after 333 K. Moreover, in the desalination of artificial seawater, the corrosion rate of HAl77-2 in the occulated area initially increased and subsequently decreased with increasing Cl− concentration. The scanning electron microscopy and energy dispersive spectrometry analysis showed a remarkable appearance of selective localized corrosion on the surface of HAl77-2.

Microstructure, hardness, and tribology properties of the (Cu/MoS2)/graphene nanocomposite via the electroless deposition and powder metallurgy technique

To increase the strength and to reduce the wear rate of the copper composite that used as a solid self-lubricant materials, Cu/10MoS2/ (0, 0.2, 0.4, 0.6, 0.8, and 1 wt.% graphene nanosheets) hybrid matrix nanocomposites were fabricated using the electroless copper precipitation process followed by the cold pressing and sintering in a hydrogen atmosphere furnace with a double-heating rate cycle. The microstructure of the as-received powders, as well as the produced samples, was examined using the scanning electron microscope. The chemical composition of the fabricated composites was evaluated by the energy dispersive spectrometry analysis. The effect of the graphene nanosheets (wt.%) addition on the densification, the hardness, the adhesive wear rate, the wear mechanism, and the coefficient of friction was investigated. The low heating rate of 5℃/min was the best for the fabrication process. The microstructure of the composites reveals the good distribution of the (graphene nanosheets and MoS2) in the copper matrix and good adhesion between graphene nanosheets and the (Cu-10MoS2) matrix as well. The 0.4 wt.% graphene nanosheets composite exhibits the highest hardness, the lowest wear rate, and the lowest coefficient of friction. The adhesive regions were dissipated by increasing the graphene nanosheets up to 0.6 wt.% then increased.

Diffusion welding of stainless steel 304L/Monel K-500 composite materials produced with different methods

The stainless steel 304L (commercially supplied) and Monel K-500 that was prepared through cold pressing of metal matrix composite materials powder mixtures were joined by diffusion welding. Welding was performed under uniaxial compression using the 50 µm-thick nickel (Ni) and aluminum (Al) 2024 interlayers under 3 MPa at 950–980°C for 60 min in an argon gas atmosphere. After welding, the diffusion and intermediate zones of the samples were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive spectrometry analysis. As evaluating the diffusion zone with interlayer, it was determined that different interlayers expanded due to increasing temperature of the diffusion area. Interlayers expanded more on the K-500 side and relatively less on the 304L side. On the other hand, when samples with Ni interlayers were examined, high amount of Ni contained by both base material (304L) and interlayer led to the formation of rich Ni phases in the diffusion side. The brittle FeNi, Fe3Ni2, CuNi, Cu9Si, Cu0,81Ni0,19, Fe0,64Ni0,36, CrNi, Cr2Ni3, FeNi3, FeCu4, and Al0.71Cr0.3Fe17.65, which were identified to form irregularity in the diffusion zone. These intermetallic phases increased the hardness and significantly decreased the ductility of different material couples joined by diffusion welding. As a result, the microhardness and lap shear tests were applied to specimens to characterize the mechanical properties of the joint zones. The maximum hardness and maximum lap shear values were obtained at joint that made with the Al interlayer at 980°C as 432.8 HV and 165 MPa.

Physiological response to silver toxicity in the extremely halophilic archaeon Halomicrobium mukohataei

ABSTRACT Adaptive strategies responsible for heavy metal tolerance were explored in the extremely halophilic archaeon Halomicrobium mukohataei DSM 12286. The tested strain was seemingly able to overcome silver-induced oxidative stress (assessed by malondialdehyde quantification, catalase assay and total antioxidant capacity measurement) mainly through non-enzymatic antioxidants. Energy dispersive spectrometry analysis illustrated the presence of colloidal silver in Hmc. mukohataei cultures exposed to AgNO3. Bright-field and transmission electron microscopy images, as well as dynamic light scattering analysis, demonstrated the presence of intracellular nanoparticles, mostly spherical, within a size range of 20–100 nm. As determined by the zeta potential measurement, the biosynthesized nanoparticles were highly stable, with a negative surface charge. Our research is a first attempt in the systematic study of the oxidative stress and intracellular silver nanoparticle accumulation, generated by exposure to silver ions, in members of Halobacteria class, thus broadening our knowledge on mechanisms supporting heavy metal tolerance of microbial cells living under saline conditions.

Solder Joint Reliability on 3-D MID LCP Substrates

This paper presents the results from an experimental reliability study. Two different kinds of SMD (surface mount device) components were assembled with Sn/Ag/Cu solder paste onto injection molded, thermoplastic LCP (liquid crystal polymer) substrates patterned with MID/LDS technology. Two different LCP grades were chosen for the experiments. The assembly was also realized on FR-4 PCBs (printed circuit boards), which served as control samples. The assemblies were exposed to a thermal cycling test followed by failure analysis. As predicted, failures in solder joints occurred earlier on the LCP thermoplastic substrates than on the FR-4 PCB laminates. It was noticed that with one of the LCP grades, the CTE was not the major factor determining the lifetime of the solder joints. A more prominent factor was the dimensional changes that had occurred in the substrates. An SEM/EDS (scanning electron microscope/energy dispersive spectrometry) analysis on the microstructure of the LCP substrates was performed to explain the findings. The analysis showed that there were differences in the detailed microstructure between the two LCP grades. These differences seemed to be related to the different filler particles.