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1.
Results are presented of a study in air of mixtures in the system CaO-Cr2 O3 -SiO2 . The phase equilibrium diagram shows relations at liquidus temperatures for all but the high-lime part of the system. In this omitted part chromium in the mixtures oxidizes in air to higher valence forms. The compound Ca3 Cr2 Si3 O12 (uvarovite) occurs at subsolidus temperatures, decomposing at 1370°C. to α-CaSiO3 and Cr2 O3 . The inhibiting action of chromium oxide on the inversion of high-temperature forms of Ca2 SiO4 to the low-temperature γ-Ca2 SiO4 is discussed in the light of new data. Evidence is presented for the existence of a pentavalent chromium compound, Ca3 (CrO4 )2 , having solid-solution relations with Ca3 SiO4 . 相似文献
2.
Eugene B. Pretorius R. Snellgrove Arnulf Muan 《Journal of the American Ceramic Society》1992,75(6):1378-1381
Equilibrium ratios Cr2+ /Cr3+ of chromium oxide dissolved in CaO–chromium oxide–Al2 O3 –SiO2 melts have been determined by analysis of samples equilibrated at 1500°C under strongly reducing conditions ( p o2 = 10−9.56 to 10−12.50 atm). 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/SiO2 ratios. In addition, Cr2+ /Cr3+ ratios, at a given CaO/SiO2 ratio, are relatively unaffected by the amount of Al2 O3 present. 相似文献
3.
Antonio H. de Aza Juan E. Iglesias Pilar Pena Salvador De Aza 《Journal of the American Ceramic Society》2000,83(4):919-927
Solid-state compatibility and melting relationships in the subsystem Al2 O3 —MgAl2 O4 —CaAl4 O7 were studied by firing and quenching selected samples located in the isopletal section (CaO·MgO)—Al2 O3 . The samples then were examined using X-ray diffractomtery, optical microscopy, and scanning and transmission electron microscopies with wavelength- and energy-dispersive spectroscopies, respectively. The temperature, composition, and character of the ternary invariant points of the subsystem were established. The existence of two new ternary phases (Ca2 Mg2 Al28 O46 and CaMg2 Al16 O27 ) was confirmed, and the composition, temperature, and peritectic character of their melting points were determined. The isothermal sections at 1650°, 1750°, and 1840°C of this subsystem were plotted, and the solid-solution ranges of CaAl4 O7 , CaAl12 O19 , MgAl2 O4 , Ca2 Mg2 Al28 O46 , and CaMg2 Al16 O27 were determined at various temperatures. The experimental data obtained in this investigation, those reported in Part I of this work, and those found in the literature were used to establish the projection of the liquidus surface of the ternary system Al2 O3 —MgO—CaO. 相似文献
4.
P. L. ROEDER F. P. GLASSER† E. F. OSBORN 《Journal of the American Ceramic Society》1968,51(10):585-593
Liquidus phase equilibrium data are presented for the system Al2 O3 -Cr2 O3 -SiO2 . The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al2 O3 -ICr2 O3 -93SiO2 ) coexists with a mullite solid solution (61Al2 O3 -10Cr2 O3 -29SiO2 ), a corundum solid solution (19Al2 O3 -81Cr2 O3 ), and cristobalite (SO2 ). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases. 相似文献
5.
An isothermal section of the ternary system MgO–Al2 O3 -Cr2 O3 was determined at 1700°± 15°C to delineate the stability field for spinel crystalline solutions (cs). Crystalline solutions were found between the pseudobinary joins MgAl2 O4 –Cr2 O3 and MgCr2 O4 -Al2 O3 , and the binary join MgAl2 O4 -MgO. The first two crystalline solutions exhibit cation vacancy models while the latter can probably be designated as a cation interstitial model. Precipitation from spinel cs may proceed directly to an equilibrium phase, (Al1-x Crx )2 O3 , with the corundum structure or through a metastable phase of the probable composition Mg(Al1-x Cr )26 O40 . The composition and temperature limits were defined where the precipitation occurs via metastable monoclinic phases. The coherency of the metastable monoclinic phase with the spinel cs matrix can be understood by considering volume changes with equivalent numbers of oxygens and known crystallographic orientation relations. Electron probe and metallographic microscope investigations showed no preferential grain boundary precipitation. 相似文献
6.
Keith T. Adendorff Johan P. R. de Villiers Gert J. Kruger 《Journal of the American Ceramic Society》1992,75(6):1416-1422
The crystal structures of Ca5 Cr3 O12 and Ca5 Cr1.8 Si1.2 O12 , the chromium analogues of silicocarnotite, Ca5 P2 SiO12 , 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 group Pnma . 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 also shown. 相似文献
7.
Donald B. Dingwell 《Journal of the American Ceramic Society》1992,75(6):1656-1657
8.
Yangyang Ji Jingkui Liang Zhan Chen Sishen Xie 《Journal of the American Ceramic Society》1991,74(2):444-446
The phase relations at a temperature below "subsolidus" in the system Al2 O3 –B2 O3 –Nd2 O3 are reported. Specimens were prepared from various compositions of Al2 O3 , B2 O3 , and Nd2 O3 of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100°C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl3 (BO3 )4 (NAB), has a phase transition at 950°C ± 15°C. The high-temperature form of NAB has a second harmonic generation (SHG) efficiency of KH2 PO4 (KDP) of the order of magnitude of the form which has been used as a good self-activated laser material, and the low-temperature form of NAB has no SHG efficiency. 相似文献
9.
F. G. BUTTLER L. S. DENT GLASSER H. F. W. TAYLOR 《Journal of the American Ceramic Society》1959,42(3):121-126
Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al2 O3 . 13H2 O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca2 (OH)7 - 3H2 O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12 O3 .13H2 O, from which it is derived by substitution of CO3 2- for 20H- + 3H2 O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2 O3 .Ca Y 2 - xH2 O and 3CaO Al2 O3 Ca Y xH2 O. On dehydration, 4CaO.Al2 O3 .13H2 O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2 O3 .3H2 O are formed and, by 1000°C., CaO and 12CaO.7Al2 O8 . The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2 O3 .3H2 O is formed. 相似文献
10.
Yusuke Kaminaga Hisanori Yamane Takahiro Yamada 《Journal of the American Ceramic Society》2007,90(6):1917-1920
Compounds in a CaO–Y2 O3 –SnO2 system were prepared by a solid-state reaction at 1673 K. The phase relation in this system was investigated by powder X-ray diffraction. Besides the previously reported ternary compounds, CaSnO3 , Ca2 SnO4 , Y2 Sn2 O7 , and a quaternary compound Ca0.4 Y1.2 Sn0.4 O3 , solid-solution series of Ca2− x Y2 x Sn1− x O4 with 0≤ x ≤0.5, and Ca1− y Y2 y Sn1− y O3 with 0≤ y ≤0.2 and 0.95≤ y ≤1.0 were found. The cell parameters of these solid-solution series were refined. The changes of rhombohedral cell parameters in the samples prepared in the range 0.565< y <0.714 of Ca1− y Y2 y Sn1− y O3 suggested the existence of solid solutions of Ca0.4 Y1.2 Sn0.4 O3 , although their single phases could not be prepared, except at y =0.6. 相似文献
11.
Activity–composition relations of FeCr2 O4 –FeAl2 O4 and MnCr2 O4 –MnAl2 O4 solid solutions were derived from activity–composition relations of Cr2 O3 –Al2 O3 solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr2 O3 –Al2 O3 and MnO–Cr2 O3 –Al2 O3 . Moderate positive deviations from ideality were observed. 相似文献
12.
TiO2 above 4 mol% is an effective nucleating agent for CaO–P2 O5 glass which also contains substantial SiO2 and Al2 O3 additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β-Ca2 P2 O7 , whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca-P-Ti-Si-Al oxide phase surrounded by impure AlPO4 dendrites. Metastable calcium phosphate grows on the AlPO4 dendrites and later transforms to β-Ca2 P2 O7 . 相似文献
13.
Koichiro Fukuda Ken-ichi Matsunaga Takahiro Bessho Hideto Yoshida 《Journal of the American Ceramic Society》2005,88(4):954-962
The phase stability in part of the P2 O5 -bearing pseudoquaternary system CaO–SiO2 –Al2 O3 –Fe2 O3 has been studied by electron probe microanalysis, optical microscopy, and powder X-ray diffractometry. At 1973–1653 K, the α-Ca2 SiO4 solid solution [α-C2 S(ss)] and melt coexisted in equilibrium, both chemical variations of which were determined as a function of temperature. The three phases of melt, calcium aluminoferrite solid solution (ferrite), and C2 S(ss) coexisted at 1673–1598 K. On the basis of the chemical compositions of these phases, a melt-differentiation mechanism has been, for the first time, suggested to account for the crystallization behavior of Ca3 Al2 O6 solid solution [C3 A(ss)]. When the α-C2 S(ss) and melt were cooled from high temperatures, the melt would be induced to differentiate by the crystallization of ferrite. Because the local equilibrium would be continually attained between the rims of the precipitating ferrite and coexisting melt during further cooling, the melt would progressively become enriched in Al2 O3 with respect to Fe2 O3 . The resulting ferrite crystals would show the zonal structure, with the Al/(Al+Fe) value steadily increasing up to 0.7 from the cores toward the rims. The C3 A(ss) would eventually crystallize out of the differentiated melt between the zoned ferrite crystals in contact with their rims. 相似文献
14.
Yoshikazu Suzuki Masahiro Tsukatsune Susumu Yoshikawa Peter E. D. Morgan 《Journal of the American Ceramic Society》2005,88(11):3283-3286
Porous Al2 O3 /20 vol% LaPO4 and Al2 O3 /20 vol% CePO4 composites with very narrow pore-size distribution at around 200 nm have been successfully synthesized by reactive sintering at 1100°C for 2 h from RE2 (CO3 )3 · x H2 O (RE = La or Ce), Al(H2 PO4 )3 and Al2 O3 with LiF additive. Similar to the previously reported UPC-3Ds (uniformly porous composites with a three-dimensional network structure, e.g. CaZrO3 /MgO system), decomposed gases in the starting materials formed a homogeneous open porous structure with a porosity of ∼40%. X-ray diffraction, 31 P magic-angle spinning nuclear magnetic resonance, scanning electron microscopy, and mercury porosimetry revealed the structure of the porous composites. 相似文献
15.
The influence of citric acid on paste hydration of 3CaO· Al2 O3 in the presence of CaSO4 ·2H2 O and Ca(OH)2 was studied using X-ray diffraction, scanning electron microscopy, and conduction calorimetry. The time at which the citric acid is added (either prior to or with the mixing water) determines how it affects the reactivity of the aluminate. Immediately after the paste is gaged citric acid promotes a more rapid reaction, but later reactions are retarded. Hexagonal calcium aluminate hydrates, ettringite, and monosulfate were all detected as early hydration products. The influence of citric acid on the hydration of 3CaO·Al2 O3 slabs immersed in saturated CaSO4 ·2H2 O solutions was also studied and a reaction scheme proposed. 相似文献
16.
Bertha Alicia Vázquez Ángel Caballero Pilar Pena 《Journal of the American Ceramic Society》2005,88(7):1949-1957
Solid-state compatibility and melting relations of MgAl2 O4 in the quaternary system Al2 O3 –CaO–MgO–SiO2 were studied by firing and quenching selected samples located in the 65 wt% MgAl2 O4 , plane followed by microstructural and energy dispersive X-ray analysis. A projection of the liquidus surface of the primary crystallization volume of MgAl2 O4 was constructed from CaO, SiO2 and exceeding Al2 O3 , not involved in stoichiometric MgAl2 O4 formation; those three amounts were recalculated to 100 wt%. The temperature and character of six invariant points, where four solids co-exist with a liquid phase, were defined. One maximum point was localized and the positions of the isotherms were tentatively established. The effect of CaO, SiO2 , and Al2 O3 impurities on the high temperature behavior of spinel materials was also discussed. 相似文献
17.
Teresa Durán Sara Serena Pilar Pena Ángel Caballero Salvador De Aza Antonio H. De Aza 《Journal of the American Ceramic Society》2008,91(2):535-543
The isoplethal sections CaAl2 O4 –MgO and CaAl4 O7 –MgO of the Al2 O3 –MgO–CaO ternary system have been experimentally established at 1 bar total pressure and air of normal humidity. The sections obtained provide new data and information that are in disagreement with thermodynamic evaluations and optimizations of the Al2 O3 –MgO–CaO ternary system published to date. These differences arise mainly from the inclusion, or exclusion, of the binary compound Ca12 Al14 O33 , mayenite, as a stable phase in the reported studies of the system. The presence or absence of this compound within the system has an important impact on the solid state and melting relationships of the whole ternary system. The present study confirms the solid-state compatibility CaAl2 O4 –MgO and CaAl2 O4 –MgO–MgAl2 O4 up to 1372°± 2°C, the peritectic melting point of the later mentioned subsystem. 相似文献
18.
The phase relations in the systems MgO-Y2 O3 -ZrO2 and CaO-MgO-ZrO2 were established at 1220° and 1420°C. The system MgO-Y2 O3 -ZrO2 possesses a much-larger cubic ZrO2 solid solution phase field than the system CaO-MgO-ZrO2 at both temperatures. The ordered δ phase (Zr3 Y4 O12 ) was found to be stable in the system ZrO2 -Y2 O3 at 1220°C. Two ordered phases φ1 (CaZr4 O9 ) and φ2 (Ca6 Zr19 O44 ) were stable at 1220°C in the system ZrO2 -CaO. At 1420°C no ordered phase appears in either system, in agreement with the previously determined temperature limits of the stability for the δ, φ1 , and φ2 phases. The existence of the compound Mg3 Yz O6 could not be confirmed. 相似文献
19.
J. P. COUTURES 《Journal of the American Ceramic Society》1985,68(3):105-107
A tentative phase diagram for the system Al2 03 -Nd2 O3 is presented. Three compounds were obtained: a β -A12 O3 -type compound, the perovskite NdAlO3 , and Nd4 Al2 O9 . The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al2 O3 , mp 1900°C; Nd4 Al2 O9 , mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al2 O3 , 1750°C; 23 mol% Al2 O3 ,1800°C. Nd4 Al2 O9 decomposes in the solid state at 1780°C. 相似文献
20.
Results are presented of a study of phase equilibria among crystalline and liquid phases in the quaternary system CaO–MgO-Al2 O3 –SiO2 at Al2 O3 contents greater than 35%. Equilibrium diagrams shown are for the five triangular joins CaAl2 Si2 O3 -Ca2 Al2 SiO7 -MgAl2 O4 , Ca2 Al2 SiO7 -MgAl2 O4 -Al2 O3 , CaAl2 Si2 O8 -MgO-Al2 O3 , CaAl2 Si2 O8 -Mg2 SiO4 -MgAl2 O4 , and CaAl2 Si2 O8 -MgO-Mg2 SiO4 . The composition and nature of the four quaternary peritectic points and the relationships of univariant lines and primary phase volumes are discussed. 相似文献