Carbide

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

Electrodeposition of nickel/silicon carbide composite coatings on a rotating disc electrode

Abstract: Composite coatings suitable for protection against wear were prepared by electrodeposition from a nickel Watts solution containing silicon carbide particles maintained in suspension. To obtain a better understanding of hydrodynamic effects on the codeposition process a rotating disc electrode, immersed in a vertical rising flow, was used. The local concentration of embedded SiC along the radius of the disc electrode was studied as a function of suspension concentration, rotation rate and the particle mean diameter. The effect of a rheoactive polymer was also examined. Although it is generally admitted that the particle incorporation rate is governed by a two-step adsorption process, the experimental results show that it is also dependent on the spatial distribution of the wall fluid flow. The normal component of the fluid velocity promotes particle impingement, whereas the parallel component tends to eject the loosely fixed particles. The competition between the forces which tend to maintain particles attached to the surface and the shear force which tends to remove them, depends on several parameters, in particular the surface chemistry and the size of the particles, the flow rate and the current density.

Highly active Au/δ-MoC and Cu/δ-MoC catalysts for the conversion of CO2: The metal/C ratio as a key factor defining activity, selectivity, and stability

Abstract: The ever growing increase of CO2 concentration in the atmosphere is one of the main causes of global warming. Thus, CO2 activation and conversion toward valuable added compounds is a major scientific challenge. A new set of Au/δ-MoC and Cu/δ-MoC catalysts exhibits high activity, selectivity, and stability for the reduction of CO2 to CO with some subsequent selective hydrogenation toward methanol. Sophisticated experiments under controlled conditions and calculations based on density functional theory have been used to study the unique behavior of these systems. A detailed comparison of the behavior of Au/β-Mo2C and Au/δ-MoC catalysts provides evidence of the impact of the metal/carbon ratio in the carbide on the performance of the catalysts. The present results show that this ratio governs the chemical behavior of the carbide and the properties of the admetal, up to the point of being able to switch the rate and mechanism of the process for CO2 conversion. A control of the metal/carbon ratio paves the roa...

Mechanical behavior of zirconium diboride–silicon carbide–boron carbide ceramics up to 2200 °C

Abstract: The mechanical properties of hot pressed zirconium diboride–silicon carbide–boron carbide (ZrB2–SiC–B4C) ceramics were characterized from room temperature up to 2200 °C in an argon atmosphere. The average ZrB2 grain size was 3.0 μm. The SiC particles segregated into clusters, and the largest clusters were >30 μm in diameter. The room temperature flexural strength was 700 MPa, decreasing to 540 MPa at 1800 °C and to 260 MPa at 2200 °C. The strength was controlled by the SiC cluster size up to 1800 °C. At higher temperatures, strength was controlled by formation of liquid phases, and precipitation of large BN and B–O–C–N inclusions. The mechanical behavior of these materials changes at ∼1800 °C, meaning that extrapolation of properties from lower temperatures is not accurate. Mechanical behavior in the ultra-high temperature regime was dominated by impurities and changes in microstructure. Therefore, the use of higher purity materials could lead to significant improvements in ultra-high temperature strength.

Investigation of microstructural changes in a ferritic steel caused by high temperature fatigue

Abstract: The low cycle fatigue behavior of a ferritic steel, Fe9Cr1Mo modified by the addition of small amounts of V and Nb, was studied under total strain control at elevated temperatures. The effects of strain range, temperature, environment, and prior heat treatment were evaluated. The accompanying microstructural changes were observed by conventional and high voltage TEM and carbide coarsening was followed by small angle neutron scattering (SANS). Substantial softening was observed in all fatigue tests. The introduction of hold times at maximum strain decreases cycle life but extends time to failure. The stress relaxes markedly during these hold times. Fatigue life is considerably shorter in air than in vacuum, especially at low strain ranges. The presence of air appears to increase softening. Prior aging or raising the temperature decreases the stress range but, in the case of continuous cycling under vacuum, cycle life is determined primarily by the plastic strain amplitude. Microstructural changes responsible for the observed softening include change from the original lath structure to cells or subgrains; large decrease in the originally high dislocation density; carbide coarsening. Information obtained from SANS measurements is consistent with a rapid coarsening of the fine carbides during high temperature deformation.