Gibbs free energies of formation of molybdenum carbide and tungsten carbide from 1173 to 1573 K

The gas equilibrium method of CH₄/H₂ has been widely used for measuring carbon potential. However, it has been reported that this method is not applicable at high temperatures since the equilibrium between CH₄ and H₂ is disturbed by the reaction of CH₄ with moisture in the system. Nevertheless, this method should be applicable theoretically at high temperatures below which CH₄ decomposition can be neglected because the equilibrium between CH₄ and H₂ reaches constant ratio in spite of the reaction. Since the role of moisture is to oxidize the sample during the measurements under the oxygen potential determined byPh ₂ o/ph ₂ ratio, the Gibbs free energies of formation of Mo₂C and WC were successfully measured from 1173 to 1573 K by keeping the moisture level in the system low enough not to oxidize the sample. The experimental results are expressed by the following equations which were derived by least squares treatments of the data: Mo₂C:ΔG = -68270 + 8.23T J mol^-1 WC:ΔG = -52330 + 14.06T J mol^-1 These values were in good agreement with those measured by M. Gleiseret al. for narrow tempareture ranges using the CO/CO₂ gas equilibrium method.     

Magnesium-thermic synthesis of molybdenum carbide in ion melts

The physicochemical aspects of the synthesis of the powders of molybdenum carbide by the magnesium-thermic reduction of its oxide in melts of lithium, sodium, and potassium carbonates are considered. The thermodynamic evaluation of reactions based on the synthesis is given. The influence of the melt temperature on the granulometric characteristics of the carbides is revealed. It is shown that the powders with the largest specific surface are formed in the melt of lithium carbonate (Mo₂C of 7.96 m²/g) at 750°C.     

电感耦合等离子体原子发射光谱法测定碳化钼催化剂中钼

研究了电感耦合等离子原子发射光谱法测定碳化钼催化剂中钼的测定条件包括溶样酸、仪器参数、分析线和干扰的消除等,在此基础上建立了碳化钼催化剂中钼的测定方法。样品用 HNO₃、HF、HClO₄的混酸溶解处理后,在体积分数为2.5%的硝酸和1%氢氟酸混酸介质中,以Mo 202.030{166} nm 作为分析谱线,采用电感耦合等离子原子发射光谱法测定。通过筛选分析谱线、合理设置背景扣除位置,避免了光谱干扰。方法应用于碳化钼催化剂样品中钼的测定,结果与重量法(GB 50591-85)一致,相对标准偏差(n=6)小于1.5%,回收率在99%～100%之间。     

氮掺杂碳负载超细碳化钼析氢电催化剂

近年来，碳化钼（Mo₂C）因其良好的稳定性及类Pt催化特性而广泛应用于电解水析氢领域，但Mo₂C在高温制备条件下易过度生长导致其催化活性降低。为解决上述问题，以多糖瓜尔豆胶为碳源，利用其分子结构中丰富的羟基与钼酸根的强烈配位作用，抑制钼原子在高温处理过程中的团聚；同时，氮元素的引入能够进一步提高碳基底的电子转移速率及催化特性。结果表明，在800 ℃高温下可获得超细Mo₂C@氮掺杂碳纳米片复合结构，该产物在碱性介质中，在10 mA/cm2的电流密度的过电位为163 mV，塔菲尔斜率为64.8 mV/（°）。同时材料体系表现出良好的稳定性，经过12 h的耐久性测试，电极材料电流密度无明显衰减。该制备方法的提出有望为其他超细金属碳化物体系的合成提供新的思路。      

Determination of thermodynamic activity of carbon in alloyed molybdenum carbide

Conclusions It is demonstrated that the thermodynamic properties of carbon in the carbide {ie736-01}. and {ie736-02}, vary greatly under the action of alloying, and that the effect shows up at concentrations of alloying elements less than 1%.The complex nature of the concentration dependence of carbon bond energy in alloyed carbides is due to the simultaneous effect of a variety of factors. The contribution of a particular factor to the overall bond energy differs with different concentrations.Translated from Poroshkovaya Metallurgiya, No. 9, pp. 64–70, September, 1967.     

The composition of eta carbide phase in 2 1/4 Cr-1 Mo Steel

The metal-to-carbon ratio in the eta phase in 2 1/4 Cr-1 Mo steel exposed to sodium at 566°C for 26,500 h, and probably under a variety of service conditions, approaches four, rather than six, a fact which may be influenced by the presence of Si, O, and perhaps Cr. Silicon is present in the eta phase, probably on a metal sublattice, while oxygen is probably present on the metalloid sublattice. The observation is supported by both structural and compositional data from the literature.     

The composition of eta carbide phase in 2 1/4 Cr-1 Mo Steel

The metal-to-carbon ratio in the eta phase in 2 1/4 Cr-1 Mo steel exposed to sodium at 566°C for 26,500 h, and probably under a variety of service conditions, approaches four, rather than six, a fact which may be influenced by the presence of Si, O, and perhaps Cr. Silicon is present in the eta phase, probably on a metal sublattice, while oxygen is probably present on the metalloid sublattice. The observation is supported by both structural and compositional data from the literature.     

Study on leaching of molybdenum and nickel from Ni–Mo ore using sodium chlorate

Abstract

The leaching of molybdenum and nickel from a Ni–Mo ore was investigated by acidic oxidative leaching with sodium chlorate followed by caustic leaching of the acid leach residue. The results indicated that the sulphides of nickel and molybdenum in the Ni–Mo ore were oxidised and dissolved in the solution. The molybdenum remaining in the residue was further recovered by direct caustic leaching. The leaching of nickel and molybdenum reached 92 and 60% respectively, with sodium chlorate consumption of 60 g per 100 g ore and hydrochloric acid consumption of 0·52 mol per 100 g ore at a L/S ratio of 3∶1 and 90°C for 2 h. After caustic leaching of the acid leach residue with sodium hydroxide consumption of 45 g per 100 g dried residue at a L/S ratio of 3∶1 and 40°C for 15 min, the total leaching of molybdenum increased to 96%. A conceptual process flowsheet for the leaching of the Ni–Mo ore has been developed.

On a examiné le lessivage du molybdène et du nickel à partir d’un minerai de Ni-Mo, par lessivage acide oxydant avec du chlorate de sodium suivi par lessivage caustique du résidu d’attaque acide. Les résultats indiquaient que les sulfures de nickel et de molybdène du minerai de Ni–Mo étaient oxydés et dissous dans la solution. Le molybdène du résidu était davantage récupéré par lessivage caustique direct. Le lessivage du nickel et du molybdène atteignait 92 et 60%, respectivement, avec une consommation de chlorate de sodium de 60 g par 100 g de minerai et une consommation d’acide chlorhydrique de 0·52 mol par 100 g de minerai avec un rapport de L/S de 3∶1 à 90°C pendant 2 h. Après le lessivage caustique du résidu d’attaque acide avec une consommation d’hydroxyde de sodium de 45 g par 100 g de résidu séché avec un rapport de L/S de 3∶1 à 40°C pendant 15 min, le lessivage total du molybdène augmentait à 96%. On a développé un schéma de procédé conceptuel pour le lessivage du minerai de Ni–Mo.     

Carbon diffusion in Mo2C as determined from carburization of Mo

A diffusion coefficient of C in nonstoichiometric α-Mo2C has been determined from the growth kinetics of the carbide layer. The results conform to the relationship:Dc (in cm²/s) = 68.86 ± 1.51 exp [(-294.77 ± 4.98)/RT] for the temperature range of 1273 to 1673 K, with the activation energy in kJ/mole. The growth rate,Kp, of the carbide thickness can be expressed as:Kp (in cm²/s) = 32.63 ± 1.52 exp [(-319.06 ± 5.12)/RT].     

Free energy of formation of Mo2C and the thermodynamic properties of carbon in solid molybdenum

The activity of C in the two-phase region Mo+Mo₂C has been obtained from the C content of iron rods equilibrated with metal+carbide powder mixtures. From this activity data the free energy of formation of α-Mo₂C has been determined as ΔG _f ^o (α-Mo₂C) (1270 to 1573 K)=−47,530−9.46T±920 J/mol. This is in good agreement with the expression obtained from gas-equilibration studies by Gleiser and Chipman, ΔG _f ^o (α-Mo₂C) (1200 to 1340 K)=−48,770−7.57 J/mol, but both our and Gleiser and Chipman's values are about 10 pct lower than those of Pankratz, Weller and King calculated from ΔH _f,298 ^o andC _p vs T data. With the aid of available data for the solid solubility of C in Mo, the thermodynamic properties of C in the terminal solid solution have been calculated as J/mol, J/mol and , the excess entropy ofC in the solid solution assumingC is in the octahedral interstices =43.4±8.2 J/deg.-mol.