摘要:

The thermal‐imaging floating zone technique can be used to grow crystals of yttrium iron garnet (Y3Fe5O12), aluminum‐doped yttrium orthoferrite (YFe0.88Al0.12O12), and magnetite (Fe3O4), which represent peritectic compounds, solid‐solution crystals, and atmosphere‐sensitive materials, respectively. The reactions involved in floating zone crystal growth are explained on the basis of phase diagrams. A review of crystal growth reports, including unpublished findings by the present authors, demonstrates how the crystallization processes, the reaction with the ambient atmosphere, and the composition variation in the obtained crystals can be explained or controlled on the basis of phase equilibrium. The floating zone technique is applicable to a variety of materials and remains a handy tool for materials research; however, its industrial application may be

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04207.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Phase equilibria in the Ta‐Co‐O and Nb‐Co‐O systems have been studied at 1200°C at oxygen partial pressures from 10−0.68to 10−13.50atm for the former and from 10−0.68to 10−13.30atm for the latter. In both systems, M2CoO6and M2Co4O9are stable ternary compounds under the experimental conditions, and a new phase, Nb5Co2O14, has been identified. The Ta‐Co‐O system is simple, whereas the Nb‐Co‐O system is somewhat more complicated because of the extra phase. The lattice constants of the ternary compounds have been determined and compared with previous values. The standard Gibbs energies of reactions have been determined using oxygen partial pressures in equilibrium

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04208.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The equilibrium reaction 3‘(Fe, Co)O’(ss) +1/2O2(g) ⇄ (Fe, Co)3O4(ss) was studied in the temperature range 970 to 1370 K for seven different total compositions of molar ratios 0.5

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04209.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A complete solid‐solution series exists between diopside (CaMgSi2O6) and its nickel analogue, “niopside”(CaNiSi2O6). Activity–composition relations within this solid solution, and the stability of the end member CaNiSi2O6, have been determined by equilibrating CaNiSi2O6with SiO2, CaSiO3, and metallic Ni in atmospheres of known oxygen pressures. Within limits of accuracy of the experiments, the solution is ideal at 1350°C. From the experimental data obtained in the present investigation, the standard free energy (ΔG°) of formation of CaNiSi2O6according to the equation CaO + NiO + 2SiO2= CaNiSi2O6is calculated to be ΔG°=−165862 + 42.40TJ. Experiments in the system CaO–NiO–SiO2have shown that the nickel analogue of the phase pseudo‐enstatite (MgSiO3) is unstable with respect to SiO2and nickel olivine (Ni2SiO4), and the nickel analogues of the phases akermanite (Ca2MgSi2O7) and monticellite (CaMgSiO4) are unstable relative to the phase assemblage pseudo‐wollastonite (CaSiO3) plus NiO. In the system CaO–MgO–NiO–SiO2, however, substitution of Ni for Mg in these phases was observed. The percentage substitution of Ni for Mg in the phases is given in parentheses: diopside (100%), olivine (100%), enstatite (18%), akermanite (

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04210.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states>3+ (Ca5Cr3O12, Ca3(CrO4)2, and Ca5(CrO4)3) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite,δ‐CaCr2O4, is observed. In the CaO‐rich section of the CaO–Al2O3–Cr2O3system a ternary intermediate phase, chrome‐haüyne, Ca4[(Al,Cr3+)6O12](Cr6+O4), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca6Al4Cr2O15, coexists with CaO, CaCr2O4, chrome‐haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al2O3syste

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04211.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Activity–composition relations in CaO–MnO and MgO–MnO solid solutions were determined by equilibrating oxide solid solutions with platinum–manganese alloys under controlled oxygen partial pressures at 1500° and 1600°C. Both systems show considerable positive deviation from

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04212.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Pure fayalite liquid was reduced at 1300°C in variable C/H ratio gas mixtures, all with constantfO2both with and without various cation additives that included Cr2O3, MnO, CaO, TiO2, Al2O3, Na2O, and K2O. Similar studies were also performed on Carol Lake iron ore pellets without these cation additives. The role of cation additives in reduction with CO‐rich gases is minimally important. In hydrogen‐rich reduction studies, the reduction per hour was increased 50% by a 2.5 wt% addition of CaO, increased by about 75% by a 2.5 wt% addition of Cr2O3, and increased by about 50% for a 2.5 wt% addition of MnO as compared to the reduction rate of pure fayalite liquid. Much more dramatic than any cation additive effect is the role of the hydrogen content of the gas mixture. At 1300°C and a fixed –logfO2= 13, the reduction per hour of pure fayalite liquid triples with the replacement of the CO by hydrogen even with just the first 10 vol% of hydrogen. Theoretical discussions of the role of cation additives and gas speciation on fayalite melt structure are pr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04213.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

An isothermal section of the Al–Li–O system has been constructed at 1000 K using available thermodynamic data. Oxide stability is shown as a function of alloy composition and oxygen partial pressurepO2). Rigorous experimental verification of the calculated phase relations is precluded by the extremely low values ofpO2) at equilibrium. The validity of the computed phase relations is considered from the results of laboratory studies of refractory compatibility and observations of interfacial phases in aluminum alloy matrix composi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04214.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Activity–composition relations of NiO have been determined at 1435°C in melts of the system CaO–NiO–SiO2and at 1400°C in melts of the systems CaO–MgO–NiO–SiO2, CaO–MgO–NiO–Al2O3–SiO2, and CaO–MgO–NiO–K2O–SiO2. In the CaO–NiO–SiO2and CaO–MgO–NiO–SiO2systems the activity coefficient of NiO (γNiO) decreases as the polymerization of the melt increases (basicity decrease). γNiOstays contant up to several weight percent NiO for melts with similar basicity, an indication of Henry's law behavior. Minima in the NiO activity coefficient are observed in melts of the CaO–MgO–NiO–Al2O3–SiO2and CaO–MgO–NiO–K2O–SiO2systems at NBO/Si ratios between 1.0 and 1.5; i.e., γNiOdecreases with decreasing basicity for NBO/Si ratios>1.5 and increases with decreasing basicity for melts with NBO/Si ratios<1.0 (NBO/Si; nonbridging oxygens per silicon). The addition of Al2O3and K2O to the CaO–MgO–NiO–SiO2

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04215.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The system MgO–Al2O3was assessed with the CALPHAD technique using a computerized optimization procedure called PARROT. Two of the solid phases, MgO and spinel, showed extensive solid solubility at high temperature and were modeled with the compound energy model. The third solid phase,α‐Al2O3, was modeled as a stoichiometric phase. For the liquid phase, an ionic two‐sublattice model was used. In total, 13 adjustable parameters were optimized: 3 for the MgO, 8 for the spinel, and 2 for the liquid. This resulted in a consistent thermodynamic description for most of the available experimental data points on the phase diagram as well of the thermodynamic prop

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04216.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY