Carbide

About: Carbide is a research topic. Over the lifetime, 36331 publications have been published within this topic receiving 503586 citations.

Ductile Regime Nanomachining of Single-Crystal Silicon Carbide

Abstract: We have demonstrated the ability to perform a ductile material removal operation, via single-point diamond turning, on single-crystal silicon carbide (6H). To our knowledge, this is the first reported work on the ductile machining of single-crystal silicon carbide (SiC). SiC experiences a ductile-to-brittle transition similar to other nominally brittle materials such as silicon, germanium, and silicon nitride. It is believed that the ductility of SiC during machining is due to the formation of a high-pressure phase at the cutting edge, which encompasses the chip formation zone and its associated material volume. This high-pressure phase transformation mechanism is similar to that found with other semiconductors and ceramics, leading to a plastic response rather than brittle fracture at small size scales.

Carbon fiber reinforced hafnium carbide composite

Abstract: Hafnium carbide is proposed as a structural material for aerospace applications at ultra high temperatures. The chemical vapor deposition technique was used as a method to produce monolithic hafnium carbide (HfC) and tantalum carbide (TaC). The microstructure of HfC and TaC were studied using analytical techniques. The addition of tantalum carbide (TaC) in the HfC matrix was studied to improve the microstructure. The microstructure of HfC, TaC and co-deposited hafnium carbide-tantalum carbide (HfC/TaC) were comparable and consisted of large columnar grains. Two major problems associated with HfC, TaC, and HfC/TaC as a monolithic are lack of damage tolerance (toughness) and insufficient strength at very high temperatures. A carbon fiber reinforced HfC matrix composite has been developed to promote graceful failure using a pyrolytic graphite interface between the reinforcement and the matrix. The advantages of using carbon fiber reinforcement with a pyrolytic graphite interface are reflected in superior strain capability reaching up to 2%. The tensile strength of the composite was 26 MPa and needs further improvement. Heat treatment of the composite showed that HfC did not undergo any phase transformations and that the phases comprising composite were are thermochemically compatible.

Fischer-Tropsch synthesis over iron catalysts

Abstract: Because of the decreased profitability of making synthetic fuels, Sasol intends expanding its production of the higher valued chemicals, in particular waxes and olefins. The advantages and disadvantages of using Fe, Co and Ru catalysts are discussed from the point of view of costs, availability, product selectivity, activity and sensitivity to poisons. The loss of activity and selectivity of iron based catalysts in both fixed and fluidized bed reactors is discussed. The main contributing factors are sulfur poisoning, oxidation and coke fouling. In fixed bed reactors sulfur poisoning and “coke” laydown deactivates the front end of the bed while hydrothermal sintering/oxidation deactivates the back end. In fluidized beds the deposition of large amounts of Boudouard carbon doesnot markedly lower the activity. The smaller catalyst particles end up consisting of small iron carbide entities embedded in a matrix of carbon. The larger catalyst particles consist of cores of inert magnetite surrounded by the carbide/carbon matrix. FT reactor development at Sasol is briefly reviewed.

Analysis on high-speed face-milling of 7075-T6 aluminum using carbide and diamond cutters

Abstract: This research is concerned with the analytical and experimental study on the high-speed face milling of 7075-T6 aluminum alloys with a single insert fly-cutter. The results are analyzed in terms of cutting forces, chip morphology, and surface integrity of the workpiece machined with carbide and diamond inserts. It is shown that a high cutting speed leads to a high chip flow angle, very low thrust forces and a high shear angle, while producing a thinner chip. Chip morphology studies indicate that shear localization can occur at higher feeds even for 7075-T6, which is known to produce continuous chips. The resultant compressive residual stresses are shown for the variation of cutting parameters and cutting tool material. The analysis of the high-speed cutting process mechanics is presented, based on the calculation results using extended oblique machining theory and finite element simulation.

Preparation of Molybdenum Carbides Using Butane and Their Catalytic Performance

Abstract: The synthesis of high surface area molybdenum carbides from molybdenum oxide and butane has been studied via temperature-programmed reaction (TPRe), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C solid-state NMR, infrared (IR), and Raman spectroscopy (LR) The molybdenum oxygen/carbon system passes through four phase transitions before transforming into the pure Mo2C carbide Carbon exists in two forms within high surface area molybdenum carbide The initially produced molybdenum carbide has a face-centered-cubic (fcc) structure but is gradually converted into the hexagonal-close-packed (hcp) structure with increasing carburization temperature, and eventually at high temperature coke is deposited During the early stages, MoO3 is reduced by H2, but at higher temperatures, butane also takes part in the reduction and, besides being consumed in the formation of carbide, is catalytically converted into methane, ethane, propane, and benzene The high surface area of the molybdenum carbide mat