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1.
Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al2 O3 at 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 MnAl2 O4 –NiAl2 O4 solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2 O4 from its oxide components (MnO + Al2 O3 ) 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 distribution models. 相似文献
2.
Subsolidus phase relationships in the Ga2 O3 –Al2 O3 –TiO2 system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO2 (rutile), Ga2−2 x Al2 x O3 ( x ≤0.78 β-gallia structure), Al2−2 y Ga2 y O3 ( y ≤0.12 corundum structure), Ga2−2 x Al2 x TiO5 (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga4−4 x Al4 x Ti n −4 O2 n −2 ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work. 相似文献
3.
The preparation of near stoichiometric spinel and alumina-rich spinel composites from Al2 O3 and MgO powders with the addition of Na3 AlF6 up to 4 wt% in the temperature range 700°–1600°C was studied; 98 wt% spinel containing 72 wt% Al2 O3 can be produced from the mixture of 72 wt% (50 at.%) Al2 O3 + 28 wt% (50 at.%) MgO powders with the addition of 1 wt% Na3 AlF6 fired at 1300°C for 1 h. Spinels containing 81–85 wt% Al2 O3 can be produced from either the mixture of 90 wt% (78 at.%) Al2 O3 + 10 wt% (22 at.%) MgO or the mixture of 95 wt% (88 at.%) Al2 O3 + 5 wt% (12 at.%) MgO powders with the addition of 4 wt% Na3 AlF6 in the temperature range 1300°–1600°C by using a torch-flame firing for 3 min, followed by quenching in water, while the same system under slow cooling in a furnace results in spinel containing 74–76 wt% Al2 O3 . Microscopic studies indicate that the alumina-rich spinel composites consist of a continuous majority spinel phase and an isolated minority corundum phase, regardless of slow cooling in a furnace or quenching in water. 相似文献
4.
Hongwu Xu Alexandra Navrotsky Mari Lou Balmer Yali Su Eric R. Bitten 《Journal of the American Ceramic Society》2001,84(3):555-560
Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTi x Al1− x Si2 O6+0.5 x , 0 ≤ x ≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B2 O3 ) at 701°C. As Ti4+ substitutes for Al3+ , the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x = 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short-range order associated with the framework cations Al3+ , Si4+ , and Ti4+ in the structure. Using enthalpies of drop solution of SiO2 , Al2 O3 , TiO2 , and Cs2 O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time. 相似文献
5.
Chang Wei Zheng Shu Ya Wu Xiang Ming Chen Kai Xin Song 《Journal of the American Ceramic Society》2007,90(5):1483-1486
MgAl2 O4 microwave dielectric ceramics were modified by Zn substitution for Mg, and their dielectric characteristics were evaluated, along with their structures. Dense (Mg1− x Zn x )Al2 O4 ceramics were obtained by sintering at 1550°–1650°C in air for 3 h, and the (Mg1− x Zn x )Al2 O4 solid solution was determined in the entire composition range. With Zn substitution for Mg, the dielectric constant ɛ of MgAl2 O4 just varied from 7.90 to 8.56, while the Q × f value had significantly improved up to a maximal value of 106 000 GHz at x =1.0. Moreover, the τf of MgAl2 O4 ceramics had declined from −73 to −63 ppm/°C. 相似文献
6.
Adam J. G. Ellison Paul C. Hess Gerald C. Naski 《Journal of the American Ceramic Society》1998,81(12):3215-3220
The saturation surface of cassiterite, SnO2 , was determined for liquids in the system K2 O–Al2 O3 –SiO2 as a function of bulk composition and temperature. At fixed K2 O/Al2 O3 cassiterite solubility varies weakly with SiO2 concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f O 2 ) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K2 O/Al2 O3 lessthan equal to 1 (peraluminous liquids). As K2 O/Al2 O3 increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K2 O in excess of Al2 O3 . It is proposed that potassium in excess of aluminum combines with Sn4+ to form quasi-molecular complexes with an effective stoichiometry of K4 SnO4 . 相似文献
7.
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
8.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
9.
Takashi Wakasugi Rikuo Ota Jiro Fukunaga 《Journal of the American Ceramic Society》1992,75(11):3129-3132
In order to evaluate the crystallization tendency of glasses, the ratio of the crystallization temperature to the liquidus temperature ( T c / T L ) was obtained by DTA measurement for the Na2 O–B2 O3 and Na2 O–B2 O3 –Al2 O3 systems. The critical cooling rate for glass formation ( Q *) was also measured. The measurements were performed in the composition range of (100 − x )Na2 O–( x )B2 O3 , ( x = 25–35 and 60–100 mol%), and (100 − y )0.5Na2 O·0.5B2 O3 −( y )Al2 O3 , ( y = 6–34 mol%). The relationship between T c / T L and Q * was discussed. A linear relationship between T c / T L and log Q * for these systems was found. Furthermore, the relationship between T c / T L and Q * was verified by computer simulation based on the crystallization kinetics of glass or supercooled liquid. 相似文献
10.
The rate of formation of NiAl2 O4 by reaction between single crystals of NiO and Al2 O3 can be described by k = 1.1 × 104 exp (−108,000 ± 5,000/ RT ) cm2 /s. In NiO the behavior of D as a function of concentration supports the Lidiard theory of diffusion by impurity-vacancy pairs. A good fit of the theory to the experimental results was obtained by assuming that Al3+ ions diffuse as [AlNi · VNi ]'pairs. The diffusion coefficient of pairs, Dp , obeys the equation 6.6 × 10−2 exp (−54,000 ± 3,000/ RT ) cm2 /s. The free energy of association for pairs was calculated to range from 6.5 kcal/mol at 1789°C to 9.0 kcal/mol at 1540°C. The interdiffusion coefficients in the spinel showed a constant small increase with increasing concentration of Al3+ dissolved in the spinel. 相似文献
11.
Mari Lou Balmer Fred F. Lange Carlos G. Levi 《Journal of the American Ceramic Society》1994,77(8):2069-2075
Aqueous solutions of zirconium acetate and aluminum nitrate were spray pyrolyzed at 250°C and upquenched to different temperatures to yield metastable solid solutions of composition Zr(1− x ) Alx O(2− x /2) . An amorphous oxide forms first during pyrolysis which subsequently crystallizes as a single phase for x ≤ 0.57 (≤40 mol% Al2 O3 ). The crystallization temperature increased with Al2 O3 content. Electron diffraction, supported by Raman spectroscopy, indicates that the initial phase is tetragonal. At higher temperatures, the initial solid solation partitions to other metastable phases, viz., t -ZrO2 +γ-Al2 O3 , prior to achieving their equilibrium phase assemblage, m -ZrO2 +α-Al2 O3 . Partitioning yields a nanocomposite microstructure with grain sizes of 20–100 nm, compared to the 3 to 5 nm in the initial, single phase. Compositions containing 45 to 50 mol% Al2 O3 concurrently crystallize and partition. The structure selected during crystallization and the partitioning phenomena are discussed in terms of diffusional constraints during crystallization, which are conceptually similar to those operating during rapid solidification. 相似文献
12.
Tsuyoshi Honma Yasuhiko Benino Takumi Fujiwara Takayuki Komatsu Ryuji Sato 《Journal of the American Ceramic Society》2005,88(4):989-992
The glass formation region, crystalline phases, second harmonic (SH) generation, and Nd:yttrium aluminum garnet (YAG) laser-induced crystallization in the Sm2 O3 –Bi2 O3 –B2 O3 system were clarified. The crystalline phases of Bi4 B2 O9 , Bi3 B5 O12 , BiBO3 , Sm x Bi1− x BO3 , and SmB3 O6 were formed through the usual crystallization in an electric furnace. The crystallized glasses consisting of BiBO3 and Sm x Bi1− x BO3 showed SH generations. The formation of the nonlinear optical BiB3 O6 phase was not confirmed. The formation (writing) region of crystal lines consisting of Sm x Bi1− x BO3 by YAG laser irradiation was determined, in which Sm2 O3 contents were∼10 mol%. The present study demonstrates that Sm2 O3 –Bi2 O3 –B2 O3 glasses are promising materials for optical functional applications. 相似文献
13.
R. R. DAYAL R. E. JOHNSON† ARNULF MUAN‡ 《Journal of the American Ceramic Society》1967,50(10):537-540
The free energy of reaction for the formation of mullite from its oxide components was derived from equilibrium studies in the system CoO-Al2 O3 -SiO2 . Within this system there appears, at solidus temperature in a certain composition area, the phase assemblage mullite + silica + spinel (= cobalt aluminate) + liquid. Determination of the oxygen pressure of a gas phase at which metallic cobalt precipitates from this phase assemblage and from the phase assemblage spinel (= cobalt aluminate) + corundum in the system CoO-Al2 O3 permits calculation of ΔG° for the reaction 3Al2 O3 + 2SiO2 = Al6 Si2 O13 . The value obtained at 1422°C is -5.8 kcal. 相似文献
14.
Microstructure–Dielectric Properties Relationship in Ba0.6 Sr0.4 TiO3 –Mg2 SiO4 –Al2 O3 Composite Ceramics
Ying Chen Yuan-Yuan Zhang Xian-Lin Dong Gen-Shui Wang Fei Cao 《Journal of the American Ceramic Society》2010,93(1):161-166
0.60Ba0.6 Sr0.4 TiO3 (BST)–(0.40− x )Mg2 SiO4 (MS)– x Al2 O3 ( x =0, 0.5, 3, 5wt%) composite ceramics exhibit excellent characteristics suitable for tunable device applications. With increasing amount of Al, the dielectric peak can be quantitatively broadened and suppressed; the "phase transition temperature" T c or ( T m ) shifts to a lower temperature. Meanwhile, the tunability is still high in a wider temperature range. Far from T c , pyroelectric effects are observed by using the Byer and Roundy technology and Slim polarization hysteresis loops are observed under high ac dielectric field at 10Hz. These proved the existence of spontaneous polarization in certain possible orientations in a broad temperature range above T c in the paraelectric medium and reveal why 0.60BST–(0.40− x )MS– x Al2 O3 have such remarkable dielectric nonlinearity. 相似文献
15.
Subsolidus phase relationships in the Ga2 O3 –In2 O3 –SnO2 system were studied by X-ray diffraction over the temperature range 1250–1400°C. At 1250°C, several phases are stable in the ternary system, including Ga2 O3 ( ss ), In2 O3 ( ss ), SnO2 , Ga3− x In5+ x Sn2 O16 , and several intergrowth phases that can be expressed as Ga4−4 x In4 x Sn n −4 O2 n −2 where n is an integer. An In2 O3 –SnO2 phase and Ga4 SnO8 form at 1375°C but are not stable at 1250°C. GaInO3 did not form over the temperature range 1000–1400°C. 相似文献
16.
Debao Zhang Baoyu Chen Zhuping Liu Shunguang Li Lili Hu 《Journal of the American Ceramic Society》2004,87(12):2228-2231
Er3+ -doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO2 ·0.3Al2 O3 )· x Na2 O·8.2La2 O3 · 0.6Er2 O3 ·0.2Yb2 O3 ·1Sb2 O3 (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω t ( t = 2, 4, 6) decreases with increasing Na2 O. Ω2 decreases rapidly with increasing Na2 O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2 O. Fluorescence spectra of the 4 I 13/2 to 4 I 15/2 transition have been measured and the change with Na2 O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2 O. 相似文献
17.
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
18.
Phase relations and lattice constants in the MgO–Al2 O3 –Ga2 O3 system at 1550°C have been determined experimentally. In a large part of this system, only a nonstoichiometric spinel is stable. Compositions as extreme as 12.5 mol% MgO–20.5 mol% Ga2 O3 –67 mol% Al2 O3 for a homogeneous spinel are possible. In the bordering phase diagrams of MgO–Al2 O3 and MgO–Ga2 O3 , the composition of the spinel is as high as 63 mol% Al2 O3 or Ga2 O3 , respectively. The contributions of all simple ionic exchange reactions on the lattice constant of the spinel have been deduced from X-ray diffractometry data. 相似文献
19.
HIROTOSHI OSHIMA 《Journal of the American Ceramic Society》1980,63(9-10):504-508
Phase relations in the quasi-ternary system MgO-V2 O3 -VO2 at 1200°C were studied using the quenching technique under controlled O2 atmospheres. A new phase of a type z VO y Mg2− x V1+ x O4 (0< x <1, y ≥1.5, z >0) was found with a compositional region along the MgV2 O4 -Mg2 VO4 join. Equilibrium P O 2 observed for Mg2− x V1+ x O4 is quite different from that for V n O2 n -1 with an equal ratio of V3+ /V4+ , corresponding to the V3+ stabilities in two types of compounds. Thus, the phase relations in the ternary system were constructed on a conventional triaxial diagram as a function of P O2 . 相似文献
20.
K. Thomas Jacob Kampurath P. Jayadevan Yoshio Waseda 《Journal of the American Ceramic Society》1998,81(1):209-212
The standard Gibbs energy of formation of the spinel MgAl2 O4 from component oxides, MgO and α-Al2 O3 , has been determined in the temperature range 900 to 1250 K using a solid-state cell incorporating single-crystal CaF2 as the solid electrolyte. The cell can be represented as—Pt,O2 ,MgO+MgF2 |CaF2 |MgF2 +MgAl2 O4 +α-Al2 O3 ,O2 ,Pt—The standard Gibbs energy of formation from binary oxides, computed from the reversible emf, can be represented by the expression—capdelta G °f,ox =−23600 − 5.91 T (±150) J/mol—The 'second-law' enthalpy of formation of MgAl2 O4 obtained in this study is in good agreement with high-temperature solution calorimetric studies reported in the literature. 相似文献