摘要:

Equilibrium ratios Cr2+/Cr3+of chromium oxide dissolved in CaO–chromium oxide–Al2O3–SiO2melts have been determined by analysis of samples equilibrated at 1500°C under strongly reducing conditions (po2= 10−9.56to 10−12.50atm). The majority of the chromium is divalent (Cr2+) under these conditions and Cr2+/Cr3+ratios at given constant oxygen pressures decrease with increasing basicity of the melts, expressed as CaO/SiO2ratios. In addition, Cr2+/Cr3+ratios, at a given CaO/SiO2ratio, are relatively unaffected by the amount of Al

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04197.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Equilibrium relations in the system NiO–TiO2–SiO2in air have been investigated in the temperature range 1430° to 1660°C. The most conspicuous feature of the phase relations is the existence of a cation‐excess spinel‐type phase, in addition to NiO and NiTiO3, on the liquidus surface and at subsolidus temperatures down to 1430°C. Three invariant points have been located on the liquidus. There is a peritectic at 1540°C characterized by coexisting NiO (ss), spinel(ss), cristobalite, and liquid of composition 47 wt% NiO, 29 wt% TiO2, and 24 wt% SiO2. Two eutectics are present, one at 1480°C, with spinel(ss), NiTiO3, cristobalite, and liquid (42 wt% NiO, 43 wt% TiO2, and 15 wt% SiO2), as the coexisting phases. The other is at 1490°C with NiTiO3, rutile, cristobalite, and liquid (32 wt% NiO, 56 wt% TiO2, and 12 wt% SiO2). A liquid miscibility gap extends across the diagram from the two bounding binary systems NiO–Si

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04198.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

We have investigated the distribution of Mg, Fe, Al, and Cr among olivine, orthopyroxene, spinel, and liquid in the system MgO–FeO–Fe2O3–Al2O3–Cr2O3–SiO2for temperatures from 1309° to 1471°C under an atmosphere of constant CO2/H2= 10/1 at a total pressure of 1 atm. Crystal–liquid and crystal–crystal distribution coefficients defined (with Fe and Mg as examples) in the formKc‐liqD= (Fe2+/Mg)crystal/(Fe2+/Mg)liquid, andKc‐cD= (Fe2+/Mg)crystal 1/ (Fe2+/Mg)crystal 2, were calculated from the experimental data. The crystal‐liquid coefficients for the silicate minerals are relatively constant [Kol‐liqD(Fe2+/Mg) =0.33;Kopx‐liqD(Fe2+/Mg) = 0.29]. However, the crystal‐liquid coefficient for spinel is more variable [Ksp‐liqD(Fe2+/Mg) =1.2 to 1.7]. Chromium is strongly partitioned into spinel relative to coexisting liquid, olivine, and orthopyroxene (Dsp‐liqCr= 80 to 170,Dsp‐olCr= 100 to 230, andDsp‐opxCr= 60 to 120), and Al is enriched in the liquid and the spinel relative to olivine and orthopyroxene. Values of (Al/Cr)opx/(Al/Cr)sprange from 4 to 8. The experimental results also show that the Al/Cr ratio in spinel increases with decr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04199.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al2O3at 1300° and 1400° C with the aim of deriving information on the thermodynamic properties of the spinel phases. Synthetic samples in selected phase assemblages of the system were equilibrated with metallic nickel and a gas phase of known oxygen partial pressures at a total pressure of 1 atm. The data on NiO activities and directions of conjugation lines between coexisting oxide and spinel phases were used to establish the activity–composition relations in spinel solid solutions at 1300° and 1400°C. The MnAl2O4–NiAl2O4solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2O4from its oxide components (MnO + Al2O3) at 1300° and 1400°C is calculated to be −24.97 and −26.56 kJ. mol−1, respectively. The activities determined in the stoichiometric spinel solid solutions are more negative as compared with those predicted from cation

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04200.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Activity–composition relations of FeCr2O4–FeAl2O4and MnCr2O4–MnAl2O4solid solutions were derived from activity–composition relations of Cr2O3–Al2O3solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr2O3–Al2O3and MnO–Cr2O3–Al2O3. Moderate positive deviations from ideal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04201.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Activity–composition relations in Al2O3–Cr2O3solid solutions at 1500° and 1600°C were determined by equilibrating members of this solid‐solution series with Mo–Cr alloys of known activity–composition relations and a gas phase of known oxygen potentials. The oxide solid solution shows considerable positive deviation fr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04202.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The crystal structures of Ca5Cr3O12and Ca5Cr1.8Si1.2O12, the chromium analogues of silicocarnotite, Ca5P2SiO12, have been determined. Both compounds were grown at 1250°C and analyzed by electron microprobe analysis. Diffraction data collection was done on spherically ground crystals which are both orthorhombic with space groupPnma. Charge‐balance requirements as well as siteoccupancy refinement of the Si‐containing compound point strongly to the presence of both tetravalent and hexavalent chromium in tetrahedral sites. The Si is located together with tetravalent Cr in a general position, whereas the hexavalent Cr is situated on a mirror plane. The calcium atoms are located in seven‐, eight‐, and nine‐coordinated sites. The presence of vacant channels of 3.5 Å diameter perpendicular to (100) is a feature of this structural type. Its relation to the apatite and glaserite structures is

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04203.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Compositions along the Ca2SiO4–Ca3(PO4)2join were hydrated at 90°C. Mixtures containing 15, 38, 50, 80, and 100 mol% Ca3(PO4)2were fired at 1500°C, forming nagelschmidtite +a1‐CaSiO4,A‐phase and silicocarnotite anda‐Ca3(PO4)2, respectively. Hydration of these produces hydroxylapatite regardless of composition. Calcium silicate hydrate gel is produced when Ca2SiO4≠ 0 and portlandite when Ca2SiO4is>50%. Relative hydration reactivities area‐Ca3(PO4)2>nagelschmidtite>α1‐Ca2SiO4>A‐phase>silicocarnotite. Hydration in the presence of silica or lime influences the amount of portlandite produced. Hydration in NaOH solution produces 14‐A tobermorite rather than calcium

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04204.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Using high‐temperature solution calorimetry in molten 2PbO. B2O3, the enthalpy of reaction of the formation of zircon, ZrSiO4, from its constituent oxides has been determined: ΔrH977(ZrSiO4) =−27.9 (± 1.9) kJ/mol. With previously reported data for the heat contents of ZrO2, SiO2, and ZrSiO4and standard‐state enthalpies of formation of ZrO2and SiO2, we obtain ΔfH°298· (ZrSiO4) =−2034.2 (±3.1) kJ/mol and ΔfG°298(ZrSiO4) =−1919.8 kJ/ mol. The free energy value is in excellent agreement with a range previously estimated from solid‐state reaction equilibria. At higher temperature also the data are in close agreement with existing data, though the data sets diverge somewhat with increasingT. The limitations of the data for predicting the breakdown temperature of zircon into its constituent o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04205.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The pseudobinary phase diagrams MOx, where M is La4BaCu5, La4SrCu5, Pb2Sr2Y0.5Ca0.5Cu3, and YBa2Cu3, are useful in the preparation of compounds with homogeneous oxygen content, for single‐crystal growth, and in investigations, of physical properties which are dependent on oxygen content. The high mobility of oxygen and the coexistence of metallic and nonmetallic oxides suggest the use of the cuprates in oxygen concentration cells with a nonmetallic O2−electrolyte and metallic cathode or anode materi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04206.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY