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1.
A thermodynamic analysis of chemical composition data for a series of iron alloys containing chromium and carbon has been
completed. These data were obtained from literature compilations for alloys equilibrated for extended times at 700 °C under
neutral atmospheres. The results of this analysis, when supplemented with thermochemical data from the literature, permitted
the calculation of the standard Gibbs energies of formation for the chromium carbides Cr7C3 and Cr23C6 over the range 600 to 1000 °C. These standard Gibbs energies were compared to data for these carbides from other sources.
Available Gibbs energy data for the third pure chromium carbide, Cr3C2, were also evaluated. For each of these three compounds, a separation of the values for the Gibbs energy of formation into
two distinct groups was observed. Each of these groups can be classed according to the nature of the experimental study used,
whether it be a high temperature solid-gas equilibration involving a system of a carbide-chromic oxide-carbon (or chromium)
with carbon monoxide, on one hand, or a series of investigations concerned mainly with electrolytic cell measurements, plus
the work on which the present study is based. It is suggested that the differences in the Gibbs energies of formation for
the respective carbides are associated with 1) the nonstoichiometric nature of these carbides and 2) possible dissolution
of oxygen in the carbides during the equilibration studies. 相似文献
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3.
The thermodynamic properties of CrC6/23, CrC3/7, CrC2/3, and MoC1/2 reported in the literature have been correlated with the relative stabilities of these carbide phases derived from ternary
phase diagrams. On the basis of the free energy of formation for one of the carbides and the free energy changes for the various
equilibria occurring in ternary Mo-Cr-C system at 1300°C, free energies of formation for the stable and unstable carbide phases
have been obtained. Using this free energy data, a calculated ternary Mo-Cr-C phase diagram is presented which agrees well
with the experimentally determined one. 相似文献
4.
超音速火焰喷涂Cr_7C_3-NiCr、Cr_(23)C_6-Ni涂层性能研究 总被引:1,自引:0,他引:1
采用超音速火焰喷涂工艺分别制备了新型的Cr7C3-Ni Cr和Cr23C6-Ni金属陶瓷涂层,并与Cr3C2-Ni Cr涂层进行了对比。利用扫描电镜观察了涂层组织,利用显微硬度仪测量了涂层显微硬度,并对涂层的热震性能进行了测试。结果表明,Cr7C3-Ni Cr涂层硬质相晶粒尺寸0.5~2μm之间,涂层的显微硬度Hv0.3为8.53 GPa,950℃水淬循环次数大于113次,性能优于Cr3C2-Ni Cr和Cr23C6-Ni涂层。 相似文献
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6.
The values of the activity of Cr2O3 in the slags based on the CaF2−CaO−Cr2O3 and the CaF2−Al2O3−Cr2O3 systems which may be used in the electroslag remelting (E.S.R.) process have been determined at 1450, 1500 and 1550°C by
equilibrating the slags with Pt−Cr alloys of known chromium activity under known oxygen partial pressure and studying the
equilibrium 2[Cr] alloy+3/2 O2(g)=(Cr2O3)slag. It was found that activity of Cr2O3 decreases with the addition of CaO and Al2O3 in the respective systems. In slags containing less than about 20 wt pct CaO and in the Al2O3 bearing slags, solutions of Cr2O3 showed a positive deviation from ideality and in slags containing more than 20 wt pct CaO, they showed a negative deviation.
Both the authors were formerly with the Department of Metallurgy, University of Sheffield, England 相似文献
7.
应用热压技术制备了添加不同含量Cr3C2和(W,Ti)C的Al2O3/Cr3C2/(W,Ti)C复合陶瓷材料。利用光学显微镜、环境扫描电镜、透射电镜和能谱分析仪等对~203/30%Cr3C2、Al2O3/30%(W,Ti)C、Al2O3/20%Cr3C2/10%(W,Ti)C三种复合陶瓷材料的显微组织结构进行了观察分析。研究表明:同其它两种材料相比,Al2O3/20%Cr3C2/10%(W,Ti)C陶瓷复合材料组织细化均匀,有连续骨架结构生成。Cr3G和(W,Ti)C颗粒的共同加入有利于晶粒生长的制约,裂纹分枝与偏转、晶粒拔出、以及纳米相等等,有效提高了氧化铝陶瓷材料的力学性能。 相似文献
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9.
《Canadian Metallurgical Quarterly》2013,52(4):370-379
AbstractExtremely dense zirconia–mullite composites were developed by reaction sintering of microcalcined fine alumina powder and zircon flour taken in different ratios with Cr2O3 as an additive. The powder mixes were isostatically pressed and sintered at 1550°C. The sintered compacts were characterised by different physicomechanical properties, microstructure developed and phase compositions. Cr2O3 exhibited positive influence up to certain level of addition on the thermomechanical properties of reaction sintered zirconia–mullite composites including corrosion resistance and microstructure.On a développé des composites extrêmement denses de zircone et mullite par frittage réactif de poudre fine d’alumine micro calcinée et de farine de zircone en différentes proportions, avec du Cr2O3 comme adjuvant. On a pressé les mélanges de poudres au moyen d’une presse isostatique et on les a frittés à 1550°C. On a caractérisé les différentes propriétés physico mécaniques, la microstructure développée et la composition de phases des compacts frittés. Le Cr2O3 exhibait une influence positive jusqu’à un certain niveau d’addition sur les propriétés thermomécaniques des composites de zircone et mullite à frittage réactif, incluant la résistance à la corrosion et la microstructure. 相似文献
10.
The rate of nitrogen dissolution in CaO-Al2O3, CaO-SiO2, and CaO-CaF2 melts was measured by 14N-15N isotope exchange reaction. The rate constant of nitrogen dissolution in CaO-based oxide melts, which is defined as first
order with respect to nitrogen partial pressure, was found to be much smaller than that in molten iron-based alloys investigated
in our previous work. The activation energies for nitrogen dissolution in 40 mass pct CaO-60 Al2O3 and 50 CaO-50 SiO2 melts are 224 and 581 kJ/mol, respectively. For CaO-Al2O3 and CaO-SiO2, dependence of the rate constant on composition is very similar to that of nitride capacities. Moreover, it was confirmed
that the rate constant was not affected by oxygen or nitrogen partial pressure. 相似文献
11.
Measurements of the rates of reduction of iron oxide from molten CaO-SiO2-Al2O3-Fe
x
O slags by Ar-CO mixtures have been made using a thermogravimetric method. The apparent first-order rate constant, with respect
to the partial pressure of CO, of the gas/slag interfacial reaction was deduced from the measured rates, where the effects
of the mass transfer in the gas and slag phases were minimized. It was found that the apparent first-order rate constant decreased
with the concentration of ‘FeO’ from 100 to 20 wt pct, whereas it remained essentially constant in the range from 5 to 20
wt pct ‘FeO’. At a given iron oxide concentration, the reduction-rate constant increased significantly with an increase in
the CaO/SiO2 ratio. For fixed slag compositions, the reduction rate increased slightly with the oxidation state of the slags. When the
rate constant is expressed in the form of k=k′(Fe3+/2+)α, the values of α range from 0.15 to 0.25. The effect of temperature in the range from 1673 to 1873 K on the reduction rate of iron oxide in
a 40.4CaO-40.4SiO2-14.2Al2O3-5‘FeO’ (wt pct) slag was studied. The calculated activation energy, based on these results, is 165 kJ/mol. 相似文献
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Gregory J. Yurek Robert A. Rapp John P. Hirth 《Metallurgical and Materials Transactions A》1979,10(10):1473-1480
The products of the displacement reaction between solid iron and Cu2O in the temperature range of 800 to 1050°C are solid copper, wustite and magnetite. The product oxide in contact with the
iron phase is in the form of rods embedded in a matrix of copper. A thin layer of copper separates the oxide rods from the
Cu2O phase. The rates of growth of the product phases are controlled by solid-state counterdiffusion of oxygen and iron through
the product phases, except for the initial stage of the reaction. A previously developed kinetic model for the diffusion-controlled
growth of the product phases is employed to calculate the rates of growth of each of the product phases. Theoretical values
of growth rates are in excellent agreement with experimental values for temperatures above 950°C. Below 950°C, the mechanism
for the growth of the magnetite phase changes, which yields marked differences between the experimental and theoretical rates
of growth. The mechanism for the displacement reaction below 950°C has not been determined. 相似文献
14.
Li Qiuhan Gao Jintao Zhang Yanling An Zhuoqing Guo Zhancheng 《Metallurgical and Materials Transactions B》2017,48(1):346-356
Metallurgical and Materials Transactions B - In this study, the effects of different Cr2O3 contents and optical basicity (denoted by Λ) on the viscosity and structure of the Cr2O3-bearing... 相似文献
15.
Yoshinao Kobayashi Kazuki Morita Nobuo Sano 《Metallurgical and Materials Transactions B》1995,26(3):557-561
The standard Gibbs energy of formation of 3BaO · Cr2O3 has been measured by a chemical equilibrium technique and is expressed as follows: 3BaO (s) + 2Cr (s) + 3/2 O2 (g) = 3BaO · Cr2O3 (s) ΔGo = -1,260,000 (±3000) + 282 (±24)r(J/mol)
The activity coefficient of chromium in copper, which was needed for the foregoing measurement, may be expressed by the following
equation: 5790 log γ
Cr
o =5790/T-2.10
The value of standard Gibbs energy at 1573 K was found to be close to that of reaction of formation of CaO · Cr2O3 expressed in the similar form. The BaO saturated BaF2 flux is shown to be far more promising in the oxidative dephosphorization of chromium-containing hot metal in comparison
with the CaO-SiO2-CaF2 flux doubly saturated with CaO and 3CaO-Cr2O3. 相似文献
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Gregory J. Yurek Robert A. Rapp John P. Hirth 《Metallurgical and Materials Transactions B》1973,4(5):1293-1300
The displacement reaction between iron and Cu2O at 1000°C results in the lamellar modifi-cation of the aggregate product morphology. According to a model presented for
the growth kinetics, the reaction rate depends on two parameters: the oxygen activity at the growth front of the product-oxide
lamellae and the volume fraction of oxide in the product zone. Two mathematical expressions for the condition of steady-state
growth are necessary to solve the kinetic expressions. One condition is that the fluxes of the reactants at the growth front
are equal at steady state. As a second condition, it is postulated that the two param-eters adjust such that these fluxes
are maximized. Based on these conditions, a numerical solution of the flux equations for the reaction between iron and Cu2O at 1000°C yields an oxygen activity of 10-8.4 atm at the growth front. Thus, the product-oxide lamellae should comprise wüstite and magnetite. This prediction is confirmed.
Calculated reaction rates and product-layer thicknesses are in reasonable agreement with experimental results.
This paper is based upon a thesis submitted by GREGORY J. YUREK in partial fulfillment of the re-quirements for the degree
of Doctor of Philosophy at The Ohio State University. 相似文献
18.
Die vorliegende Arbeit stellt eine neue Hypothese zur Karbidausscheidung in rostfreien, austenitischen Stählen auf. Diese Karbidbildung verursacht die Anfälligkeit für interkristalline Korrosion. Im Gegensatz zu der verbreiteten Vorstellung, daß die Chromdiffusion der bestimmende Vorgang für die Kinetik ist, wird hier von der Annahme ausgegangen, daß es die Kohlenstoffdiffusion sei. Da die Chromatome substitutionell eingelagert sind, läuft die Chromdiffusion sehr langsam ab; die Diffusion der interstitiell eingelagerten Kohlenstoffatome erfolgt über die Gitterlücken und ist damit um 5 Größenordnungen schneller. Die Hypothese wird gestützt durch die Tatsachen, daß die Kohlenstoffkonzentration in der Legierung viel kleiner als die des Chroms ist, daß die Diffusionswege für Kohlenstoff viel größer sind, der Kohlenstoffübersättigungsgrad jedoch viel kleiner ist und schließlich, daß die Chromdiffusion entlang der Korngrenzen abläuft, wo sie 106 mal schneller abläuft als im Korninneren. Ein Stahl mit 0,08% C wird unterschiedlich lang bei 3 Sensibilisierungstemperaturen angelassen. Der bei der Temperatur flüssiger Luft gemessene elektrische Widerstand der Proben ist – nach einer Oxalsäure-Behandlung – ein Maß für die ausgeschiedene Karbidmenge. Unter Voraussetzung des bekannten Mechanismus’ der Zementitbildung erhält man theoretische Vorstellungen, die auch bei der Chromkarbidbildung Voraussagen ermöglichen, die sich in guter Übereinstimmung mit den experimentell ermittelten Daten befinden. 相似文献
19.
用柠檬酸溶胶-凝胶法制备了分别掺Fe2O3和Cr2O3的4YSZ前驱体凝胶,凝胶在500℃预烧,压制成圆片状后在1 300℃煅烧2 h得到所需试样;分别研究Fe2O3、Cr2O3的不同掺量对试样的烧结性能、电导率的影响。结果表明掺Fe2O3可提高试样的电导率和烧结性能;掺Cr2O3可提高试样的低温电导率,但使试样的烧结性能下降。 相似文献