Mo2C Carbides Research Articles

Study of molybdenum precipitation in steels using thermoelectric power measurement

Abstract The precipitation of molybdenum in iron has been investigated using thermoelectric power measurement. We found an increase of the thermoelectric power of iron with the molybdenum content and a coefficient of its influence has been determined. A correlation between secondary hardening due to the precipitation of Mo2C carbides and thermoelectric power variations has been established.

Role of alloying elements and carbides in the chlorine-induced corrosion of steels and alloys

The high temperature corrosion of steels and Ni-base alloys in oxidizing and chloridizing environments is of practical interest in relation to problems in waste incineration plants and power plants using Cl containing fuels. The behaviour of the most important alloying elements Fe, Cr, Ni, Mo, Mn, Si, Al upon corrosion in an oxidizing and chloridizing atmosphere was elucidated: the reactions and kinetics can be largely understood on the base of thermodynamic data, i.e. free energy of chloride formation, vapor pressure of the chlorides and oxygen pressure pO2 needed for the conversion chlorides ® oxides. The mechanism is described by 'active oxidation', comprising inward penetration of chlorine into the scale, formation of chlorides at the oxide/metal interface, evaporation of the chlorides and conversion of the evaporating chlorides into oxides, which occurs in more or less distance from the surface (depending on pO2). This process leads to loose, fragile, multilayered oxides which are unprotective (therefore: active oxidation). Fe and Cr are rapidly transferred into such scale, Ni and Mo are relatively resistant. In many cases, the grain boundaries of the materials are strongly attacked, this is due to a susceptibility of chromium carbides to chloridation. In contrast the carbides Mo2C, TiC and NbC are less attacked than the matrix. Alloys on the basis Fe-Cr-Si proved to be rather resistant, and the alloying elements Ni and Mo clearly retard the attack in an oxidizing and chloridizing environment.

Formation of encapsulated molybdenum carbide particles by annealing mechanically activated mixtures of amorphous carbon with molybdenum

The investigation of morphological and structural changes during high-energy ball milling and thermal annealing of mixtures of amorphous carbon and molybdenum demonstrated that the activation leads to the formation of a nano-size carbide Mo2C phase. Morphological characteristics of the annealed, mechanically activated amorphous carbon–molybdenum samples depend on the time of preliminary mechanical activation. Annealing of amorphous carbon–molybdenum samples after preliminary mechanical activation, at a temperature of 860 °C, caused the formation of nano-sized encapsulated particles of molybdenum carbide Mo2C. The surface of the Mo2C nanoparticles was coated with a shell composed of hexagonal polyaromatic carbon 5–20 nm thick. The size of the encapsulated particles varies within a rather broad range from 10 to 20 nm to several hundred nanometers.

Fabrication of molybdenum carbide and hafnium carbide field emitter arrays

We report on a process for the fabrication of Mo2C and HfC refractory metal carbide field emitter arrays using a modified Spindt tip fabrication process. Measurements of the aspect ratios of emitter cones showed that Mo2C tip structures have an aspect ratio similar to Mo field emitter tips. Where as with HfC, tip structures with a higher aspect ratio than either Mo or Mo2C were obtained. The measured aspect ratios for Mo, Mo2C, and HfC tips were 1.09, 1.10, and 1.20, respectively. While the target materials to fabricate the arrays were the appropriate carbides, x-ray photoelectron spectroscopy of the carbide films showed evidence for the presence of significant amount of oxygen throughout the films, mostly in the form of oxycarbides. The primary purpose of this report is to describe materials and processes suitable for large area field emission display applications. However, we also provide preliminary electrical results which demonstrate the feasibility of fabrication of metal carbide field emitters and identify important details to be addressed to achieve successful electrical performance.

Preparation of Molybdenum Carbides Using Butane and Their Catalytic Performance

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...

Carbide precipitation in martensite during the early stages of tempering Cr- andMo-containing low alloy steels

The microstructures of a 2.25% Cr–1% Mo–0.15 wt% C steel, and a steel with identical alloying additions but a higher carbon level, 2.25% Cr–1% Mo–0.4 wt% C, have been examined in the martensitic condition for a variety of tempering heat treatments by transmission electron microscopy and atom probe field ion microscopy. Ultra-thin films which were carbon enriched have been observed at some of the martensite lath boundaries. Brightly imaging clusters of Mo and C atoms, which represent the earliest stages of the precipitation of Mo 2C carbide were observed. In the very early stages of ageing at 350°C, individual molecular ions of MoN 2+ were observed using atom probe selected area analysis. No partitioning of Cr, Mo and Mn, was observed between cementite and martensite after tempering at 350°C for times up to 40 h. The enrichment behaviour and interface concentrations of Cr, Mn and Mo in the cementite after prolonged ageing at 450°C for 187 h were found to be the same in both the low and high carbon alloys, despite the fact that the predicted equilibrium concentrations of the various alloying elements in the cementite were very different. These results demonstrate that cementite, in Cr and Mo containing alloy steels, precipitates from supersaturated ferrite via a paraequilibrium transformation mechanism.

Evolution of Structure, Phase Composition, and X-Ray Reflectivity of Multilayer Mirrors Mo–(B + C) after Annealing at 250–1100°C

Structural, phase, and chemical stabilities of x-ray multilayer mirrors Mo–(B + C) with periods in the range 8–11.5 nm were studied at temperatures of 250–1100°C by small-angle and large-angle x-ray diffraction and electron microscopy methods. Two amorphizations at ∼450 and ∼750°C and two crystallizations at ∼650 and ∼850°C of Mo-based layers were observed, which were due to the formation of the molybdenum carbides MoC (hex), γ-MoC, and Mo2C instead of the metal Mo, and to the formation of the molybdenum borides MoB2and Mo2B5instead of molybdenum carbides, respectively. Both amorphizations of Mo-based layers were accompanied by smoothing of interfaces and by an increase of the multilayer x-ray reflectivity at λ = 0.154 nm. Both crystallizations of Mo-based layers promoted the development of interface roughness and a decrease of multilayer x-ray reflectivity. The destruction of Mo–(B + C) multilayers at ∼1100°C was caused by the recrystallization of Mo2B5layers.

Evolution of Structure, Phase Composition, and X-Ray Reflectivity of Multilayer Mirrors Mo–(B + C) after Annealing at 250–1100°C

Structural, phase, and chemical stabilities of x-ray multilayer mirrors Mo-(B + C) with periods in the range 8-11.5 nm were studied at temperatures of 250-1100°C by small-angle and large-angle x-ray diffraction and electron microscopy methods. Two amorphizations at ~450 and ~750°C and two crystallizations at ~650 and ~850°C of Mo-based layers were observed, which were due to the formation of the molybdenum carbides MoC (hex), γ-MoC, and Mo2C instead of the metal Mo, and to the formation of the molybdenum borides MoB2 and Mo2B5 instead of molybdenum carbides, respectively. Both amorphizations of Mo-based layers were accompanied by smoothing of interfaces and by an increase of the multilayer x-ray reflectivity at λ = 0.154 nm. Both crystallizations of Mo-based layers promoted the development of interface roughness and a decrease of multilayer x-ray reflectivity. The destruction of Mo-(B + C) multilayers at ~ 1100°C was caused by the recrystallization of Mo2B5 layers.

The behaviour of the molybdenum-CVD diamond interface at high temperature

Abstract Molybdenum was deposited onto a H-saturated surface of high quality polycrystalline HF-CVD diamond films in UHV. The interface structure and its composition were studied by XRD and RBS in the temperature range 100 °C–800 °C. Interdiffusion and formation of a hexagonal Mo2C carbide were detected after annealing at T ≥ 550 °C. The solid state reaction leading to the bulk carbide formation is, probably, limited by carbon diffusion through the interface.

Carbon interaction with heated molybdenum surface

High-resolution AES was used to determine the character of the processes that take place during carbon adsorption on the surface of heated (to T ≈ 1600 K) texturized Mo ribbon with a (100) face. The products of this solid-state reaction on the surface and in the bulk of the metal were determined. Carbonization starts with surface carbide (SC) MoC formation. After reaching the solubility limit in the solid-state solution of carbon in molybdenum, the bulk carbide Mo 2C forms under the SC and spreads to the center of the ribbon. The final stage of the carbonization is the formation of a graphite monolayer above the bulk and surface carbides, perhaps after reaching the carbon solubility limit now in the bulk carbide. Carbon in the surface carbide form drastically increases the work function of the Mo(100) face from eϕ = 4.45 to eϕ = 5.25 eV.

Influence of tempering temperature on stability of carbide phases in 2.6cr-0.7mo-0.3v steel with various carbon content

The present work evaluates the influence of the bulk carbon content (0.1, 0.006, and 0.005 wt pct) and tempering temperature (823, 853, and 913 K) on stability, chemical composition, and size of carbide particles in 540 ks tempered states of 2.6Cr-0.7Mo-0.3V steel. The scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDXS) and electron diffraction methods were used to analyze the carbide particles. A characteristic energy-dispersive X-ray (EDX) spectrum can be attributed to each of the identified carbides. The MC carbide is stable in all experimental states. The phase stability of Fe-Cr-rich carbides increased in the order e, Fe3C → M3C → M7C3, with tempering temperature increasing. In steels with higher carbon content tempered at low temperature, M23C6 carbide was also noted. The Mo2C and M6C carbides were not observed. It was shown that the decrease of the bulk carbon content has the same influence on the carbide phases stability as the increase of the bulk vanadium content at the unchanged Cr, Mo, C bulk contents and tempering temperature. Similarly, the decrease of tempering temperature has the same influence on the carbide phases stability as the decrease of the bulk Cr content at the unchanged V, Mo, and C bulk contents.

An APFIM study of the microstructure of a ferrite alloy after high fluence neutron irradiation

The microstructure of a low alloyed ferritic pressure vessel steel irradiated under representative conditions (1.4 x 10 20 neutrons cm -2, E > 1 MeV, 13 years at 265°C) has been investigated using the atom probe technique. Evidence of Si, Ni, Mn and Cu clustering in the irradiated ferritic matrix has been found. Silicon, associated with nickel and manganese appears to play a dominant role in the segregation process. In addition, some M 3C cementite-type (M = Fe + Mn) and Mo 2C carbides have been analyzed.

Ion Implantation of Ti,Mo W,Mo+C and W+C in H13 Steel and Aluminum at Elevated Temperature

ABSTRACTThe chemical change in the surface of H13 steel or aluminum is produced by implanting a reactive elements, such as Ti, Mo and W. The X-ray diffraction pattern shows that implanted Ti at 400 C has reacted with carbon(0.35 in wt.%) forming a second phase TiC. Auger analysis shows that the carbon atoms have been condensed in the Ti implanted region. Carbon peak concentration of 30 At.% is greater than Ti atom peak concentration of 12 At.%.Several second phases are formed during pulsed Mo ion implantation 2 into aluminum with high ion flux of 50˜80µA/cm2 which raises the target temperature from 400°C to 600°C.More second phases are formed by dual Mo+C implantation with high dose of 3˜5×10 17/cm2 and high flux of 50˜75µA/cm2 . And the target temperature is raised from 400 to 600°C. The FeMo Fe3Mo2, Fe2MoC, Mo2C, MoC, MoCx, phases and iron carbides are identified by X-ray diffraction technique.

Synthesis of a diamond and metal mixture by the chemical vapor deposition process

A mixture of diamond and metal film was synthesized by a hybrid process combining plasma-jet chemical vapor deposition and a plasma-spray process. Sprayed molybdenum and tungsten were changed to Mo2C and tungsten carbide, respectively, and the lattice constants of Ni, Fe, and Co were increased by carbon-plasma spraying. Adhesion of film to the substrate was improved using the hybrid process to form a layer 50 to 150 μm thick of mixed metal and diamond between the substrate and pure diamond film.

Molybdenum carbide catalysts 3. Turnover rates for the hydrogenolysis of n-butane

The hydrogenolysis of n-butane was studied on Mo and M0 2C supported on A1 2O 3 as well as on bulk carbides Mo 2C and α-MoC 1-x. Well-reduced molybdenum clusters supported on Al 2O 3 were prepared according to the method of Burwell and co-workers. The clusters were transformed in CH 4H 2 mixtures into M02C as shown by X-ray absorption spectroscopy. Turnover rates, v t, referred to the number of surface metal atoms titrated by irreversible chemisorption of CO were very high both on supported and unsupported catalysts. The value of v t for supported Mo 2C clusters was slightly less than that for Ru and Os, the most active metals known for the hydrogenolysis of alkanes. The reaction was found to be structure-sensitive since v t, values changed with particle size and crystal structure of catalysts. The presence of polymeric carbon on the surface, or possibly oxygen, and the structure sensitivity of the reaction seem responsible for the low vt of unsupported Mo 2C reported previously. Molybdenum surfaces that were initially metallic transformed to carbides under reaction conditions, indicating that the active catalytic phase of metallic Mo was also Mo 2C.

Tungsten-free die steels with increased thermal stability

1. An austenitic dispersion-hardened chromium manganese die steel type 5Kh10G15SM2F2R has been developed whose thermal stability is 160–190°C higher than for the martensitic class steels 4Kh4VMFS and 5Kh2MNF used currently, for similar purposes. 2. Strengthening of steel 5Kh10G15SM2F2R occurs as a result of precipitation of carbide phases type VC, Cr23C6, and Mo2C during aging. 3. Steel type 5Kh10G15SM2F2R is recommended for hot-forming tools for alloys that are difficult to work, liquid forming of copper alloys, and for hot pressing of metal powders whose operating temperature does not exceed 830–850°C at pressures up to 700–800 MPa.

TEM investigation of the tempering behaviour of the maraging PH 17.4 Mo stainless steel

The PH 17-4 Mo steel (Z6 CND 17.04.02), used in the steam generator of nuclear reactors, was investigated in order to determine the structural evolution occurring during tempering carried out under various conditions of duration and temperature. The formation and growth of different types of carbides such as Mo2C, M23C6 and M7C3 and of Fe2Mo intermetallic compound were studied and also of reversed austenite. A small secondary hardening peak was observed for tempering close to 400' C which is related to the Mo2C carbide precipitation; beyond this temperature, softening occurs.

Synthesis of methyl formate from methanol over metal carbide catalysts

Catalytic decomposition of methanol has been studied on the transition metal carbides TiC, TaC, Mo2C, W2C, and WC; on WC methyl formate was produced with high selectivity (>90%), whereas other catalysts produced mainly CO and H2.

Relative stabilities of Mo2C and V4C3carbides in a low-alloy ferritic steel at ∼6OO°C

(1984). Relative stabilities of Mo2C and V4C3 carbides in a low-alloy ferritic steel at ∼6OO°C. Metals Technology: Vol. 11, No. 1, pp. 207-207.

Metallurgical Influences on the Hydrogen Uptake by Steel in H2S Environment

Abstract The hydrogen uptake by steels naturally corroding in an acidic H2S solution, varied significantly with microstructure and chemical composition. It changed in very close association with the secondary precipitation hardening process; i.e., hydrogen entry was enhanced by the precipitation of Mo2C and (Fe,Cr)7C3 carbides, and such enhancement diminished as the overaging process took place. The precipitation of fine carbide particles provides sites of hydrogen trap at the carbide interface and increases the amount of hydrogen absorbed. (Fe,Cr)7C3 carbide appears to have a larger binding energy with hydrogen than Mo2C carbide because Cr-containing steels absorbed hydrogen to a significantly greater extent. Cementite of Cr steels played a peculiar role in hydrogen uptake; i.e., it had only a minimal effect in tempered martensite structure, but absorbed large amounts of hydrogen in upper bainite structure. Because of the effect of (Fe,Cr)7C3, hydrogen uptake increased with Cr content of steel up to 17% ...