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1.
Most of the known oxides of lead including the intermediate oxides Pb12 O19 and Pb2 O3 have been prepared under equilibrium conditions. Precise X-ray powder data have been obtained for the intermediate oxide phases. Solid-vapor equilibrium data have been obtained for reactions in the system lead-oxygen over the range 200° to 900° C and 3 to 1400 bars Po2 . Pressure-temperature univariant equilibrium curves are presented for the reactions PbO2 ⇋ Pb12 O19 + oxygen, Pb12 O19 ⇋ Pb3 O4 + oxygen, and Pb3 O4 ⇋ PbO + oxygen. The enthalpies of reaction are, respectively, 26.8, 34.6, and 33.7 kcal per mole. Eutectic melting between PbO and Pb3 O4 occurs at 875° C and 124 bars. A stability field for Pb2 O3 exists above 1000 bars PO2 at 600° C. Approximate resistivity data are presented. 相似文献
2.
The common oxides of lead, PbO, PbO2 , and Pb3 O4 , were examined at pressures of 0 to 60,000 atmospheres and temperatures of 100° to 600° C. The pressure-temperature curve for the litharge-massicot transition was measured, giving a ΔH of transition of 57 cal. per mole. Unusual meta-stability and inversion characteristics of the massicot phase were examined in detail. PbO2 (rutile) transformed at pressures in excess of 13,000 atmospheres at 300°C. to an ortho-rhombic form. The univariant equilibrium curve for the transition gave a Δ H of 11 cal. per mole. Pb3 O4 underwent a disproportionation reaction yielding PbO and "Pb2 O3 ." The equilibrium curve for this reaction was measured, and Δ H was determined to be 4500 cal. per mole. 相似文献
3.
TAKI NEGAS 《Journal of the American Ceramic Society》1968,51(12):716-719
Phase relations in the system PbO-chromium oxide were determined in air at high temperatures and are considered in terms of the PbO-Cr2 O3 −O2 ternary because of reactions with atmospheric oxygen. Although not necessarily binary at all temperatures, four established subsystems characterize the air equilibria and indicate oxidation-reduction of chromium. The PbO-PbCrO4 join contains the compounds Pb5 CrO3 and Pb5 CrO8 and consists of two portions, PbO-Pb2 CrO6 and Pb2 CrO5 −PbCrO4 The former is binary at all temperatures studied, while the latter exists only below 753° C because of the decomposition of PbCrO4 at 753°C to Pb2 CrO5 and Cr2 O3 with oxygen evolution. Similarly, the join PbCrO4 −Cr2 O3 exists only below 753°C yielding to Pb2 CrO3 −Cr2 O3 equilibria above this temperature. 相似文献
4.
Vincenzo Esposito Debora Marani Eric D. Wachsman Enrico Traversa 《Journal of the American Ceramic Society》2008,91(2):437-443
A new chemical route to synthesize nanostructured lead ruthenium pyrochlore (Pb2 Ru2 O6.5 ) powders was developed. The synthesis was performed starting from a metal nitrate aqueous solution and N , N , N ', N ' tetramethylethylendiamine (TMEDA). The amine, which is a mild basic chelating agent, was able to control the simultaneous precipitation of lead and ruthenium oxo/hydroxides. For the sake of comparison, Pb2 Ru2 O6.5 powders were prepared using the more conventional polymeric precursor method. The new method was effective for the synthesis of nanostructured Pb2 Ru2 O6.5 powders already stable at 400°C and up to 1000°C. 相似文献
5.
Twenty hours of mechanical activation of mixed oxides at room temperature led to the formation of Pb(Mg1/3 Nb2/3 )O3 (PMN) in excess PbO. The crystallinity of the activation-derived perovskite PMN phase was further established when the activated PMN–PbO phase mixture was subjected to calcination at 800°C. Pyrochlores, such as Pb3 Nb4 O13 and Pb2 Nb2 O7 , were not observed as transitional phases on mechanical activation and subsequent calcination, although 50% excess PbO was deliberately added. The perovskite PMN phase was recovered by washing off excess PbO using acetic acid solution at room temperature. It was sintered to a relative density of 98.9% of theoretical at 1200°C for 1 h and the sintered PMN exhibited a dielectric constant of ∼14 000 at 100 Hz and a Curie temperature of −11°C. 相似文献
6.
Hisanori Yamane Kazuhiro Ogawara Mamoru Omori Toshio Hirai 《Journal of the American Ceramic Society》1995,78(9):2385-2390
Lattice parameters of RE4 Al2 O9 (RE = Y, Sin, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) prepared at 1600–1800°C and those of RE4 Ga2 O9 (RE = La, Pr, Nd, Sm, Eu, and Gd) prepared at 1400–1600°C were refined by Rietveld analysis for the X-ray powder diffraction patterns. The parameters increased linearly with the ionic radius of the trivalent rare-earth elements ( r RE ). High-temperature differential calorimetry and dilatometry revealed that both RE4 Al2 O, and RE4 Ga2 O, have reversible phase transitions with volume shrinkages of 0.5–0.7% on heating and thermal hystereses. The transition temperatures (7tr ) decreased from 1300°C (Yb) to 1044°C (Sm) for RE4 A12 O9 , except for Y4 Al2 O9 ( Ttr = 1377°C), and from 1417°C (Gd) to 1271°C (La) for RE4 Ga2 O, with increasing ionic radius of the rare-earth elements. These transition temperatures were plotted on a curve against the ionic radius ratio of Al3+ or Gd3+ and RE3+ ( r A1 Ga /rRE ) except for Y4 Al2 O9 . 相似文献
7.
Yoshihide Senzaki Mark J. Hampden-Smith Toivo T. Kodas† John W. Hussler‡ 《Journal of the American Ceramic Society》1995,78(11):2977-2983
Submicrometer crystalline metal ruthenate powders with perovskite structure, MRuO3 (M = Sr, La), and pyrochlore structure, M2 Ru2 O7- x (0.5 < x < 1; M = Bi, Pb, Y, Eu, Gd, Tb, Dy, Ho, Er, Tm), were prepared by spray pyrolysis using metal nitrates and glycolates under an oxygen-gas atmosphere at temperatures up to 1100°C. Submicrometer-sized solid single crystals (SrRuO3 ), submicrometer-sized hollow spheres consisting of nanocrystallites (pyrochlore rare-earth ruthenates, Bi2 Ru2 O7 , and Pb2 Ru2 O6.5 below 1000°C), and nanometer-sized particles (Pb2.31 Ru1.69 O6.5 and Bi-Pb-O above 1000°C) were observed. Particle formation proceeded by intraparticle reaction and intraparticle reaction followed by evaporation of volatile metal oxides to form metal oxide vapors followed by condensation and reaction to form particles. The former was observed for systems where no volatile metal oxides were formed, whereas the latter occurred for the Pb-Ru-O and Bi-Ru-O systems, where volatile metal oxides, such as Bi2 O, PbO, and RuO x could occur. Particle morphology depended strongly on precursor properties. Submicrometer-sized single-crystal SrRuO3 particles could be formed from the metal nitrates but not from Sr(NO3 )2 and ruthenium glycolate, which gave hollow polycrystalline particles. In general, crystallite size could be controlled by varying precursor properties and reactor temperature, with higher temperatures giving larger crystallite sizes. 相似文献
8.
Michael K. Cinibulk Gareth Thomas Sylvia M. Johnson 《Journal of the American Ceramic Society》1992,75(8):2050-2055
The flexural strength and creep behavior of RE2 Si2 O7 –Si3 N4 materials were examined. The retention in room-temperature strengths displayed by these ceramics at 1300°C was 80–91%, with no evidence of inelastic deformation preceding failure. The steady-state creep rates, at 1400°C in flexural mode, displayed by the most refractory materials are among the lowest reported for sintered Si3 N4 . The creep behavior was found to be strongly dependent on residual amorphous phase viscosity as well as on the oxidation behavior of these materials. All of the rare-earth oxide sintered materials, with the exception of Sm2 Si2 O7 –Si3 N4 , had lower creep strains than the Y2 Si2 O7 –Si3 N4 material. 相似文献
9.
B. D. ROITER 《Journal of the American Ceramic Society》1964,47(10):509-511
Phase relations in the spinel region of the system FeO-Fe2 O3 -Al2 O3 were determined in CO2 at 1300°, 1400°, and 15000°C and for partial oxygen pressures of 4 × 10−7 and 7 × 10−10 atmospheres at 15OO°C. The spinel field extends continuously from Fe3 O4-x to FeAl2 O4+z . 相似文献
10.
Samarium oxide forms a ceramic of medium strength and density (6.0) when it is fired at 1300°C. When it is fired at 1500°C., its density is increased to 7.4 but it loses its stability toward boiling water. X-ray data are given concerning the structure of the oxide as received and at 1300°C. and of the reaction product of Sm203 with water. Gadolinium oxide forms a ceramic of somewhat higher density (7.0) at 1300° than does Sm2 O3 ; at 1500°C. its density is slightly higher (7.6) whereas its stability toward water is unchanged. Data concerning both oxides include density, shrinkage, moduli of elasticity and of rupture, linear thermal expansion, differential thermal analysis, and specific heat as well as X-ray data. Results are given of a brief survey of the reaction products obtained when Sm2 O3 and Gd2 O3 are heated at 1500°C. in equimolecular quantities with Al2 O3 , BaO, CaO, CdO, Fe2 O3 , HfO2 , MgO, SO2 , SrO, ThO2 , and ZrO2 . X-ray data for the following rare-earth oxides as received and after calcination at 1400°C. are given: ceria, praseodymia, neodymia, europia, dysprosia, holmia, erbia, thulia, and ytterbia. 相似文献
11.
Formation of lead niobate pyrochlores by the reaction of PbO with Nb2 O5 in various molar ratios and at various temperatures has been investigated. It has been shown that for a PbO/Nb2 O5 molar ratio between 1.5 and 3.0, a pyrochlore solid solution having cubic symmetry is formed at low temperatures (∼500-600°C). X-ray diffraction data show evidence for the existence of compositional inhomogeneity for this phase which contains part of the Pb in the Nb site leading to the formula Pb1.5+ x (Nb2- y Pb y )O7-delta (0.0 < x < 0.5; 0.0 < y < 0.5). A phase-pure Pb-deficient pyrochlore (Pb1.5 Nb2 O6.5 ) and Pb-excess pyrochlores (Pb2.5 Nb2 -O8 , Pb3 Nb2 O8 ) are formed by the decomposition of this cubic solid solution and subsequent reaction at high temperatures. These results indicate that the mechanism of the structural transformation from the low-temperature (LT) cubic solid solution to the corresponding high-temperature (HT) phases is reconstructive. 相似文献
12.
G. Bhattacharya S. Zhang D. D. Jayaseelan W. E. Lee 《Journal of the American Ceramic Society》2007,90(1):97-106
Lithium borate (Li2 B4 O7 ) and sodium borate (Na2 B4 O7 ) mineralize spinel formation from stoichiometric MgO and Al2 O3 between 1000° and 1100°C. Mineralization with both compounds is shown to be mediated by B-containing liquids which form glass on cooling. However, the liquid compositions depend on the type of mineralizer and temperature, suggesting that templated grain growth or dissolution–precipitation mechanisms are operating, one dominating over the other under certain conditions. Na2 B4 O7 -mineralized compositions show predominantly templated grain growth at 1000°C, which changes to dissolution–precipitation at 1100°C, whereas Li2 B4 O7 -mineralized compositions show dissolution–precipitation from 1000°C. Li2 B4 O7 is a stronger mineralizer as spinel formation is complete with 3 wt% Li2 B4 O7 at 1000°C and with ≥1.5 wt% addition at 1100°C, whereas Na2 B4 O7 -mineralized compositions are found to retain some unreacted corundum even at 1100°C. 相似文献
13.
W. A. SCHULZE T. G. MILLER J. V. BIGGERS 《Journal of the American Ceramic Society》1975,58(1-2):21-23
The disappearing-phase method was used to determine the extent of the solid-solution region of the PLZT system for conventionally sintered ceramics prepared at 1100° and 1300°C in a PbO atmosphere provided by pbZrO3 . A decrease in the firing temperature from 1300° to 1100°C lowers the solubility limit by 5 to 8 at.% La. Beyond the limits of solubility, additional La forms La2 Zr2 O7 and/or La2 Ti2 O7 . The limit determined by the disappearing-phase method (1300°C firing) is compared to values determined by the parametric method. The Curie temperature is stabilized at 5 at.% La for modified PbZrO3 (1300°C firing). 相似文献
14.
The effect of rare-earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N2 at 1800° to 2000°C was studied. When a single-component oxide, such as CeO2 , Nd2 O3 , La2 O3 , Sm2 O3 , or Y2 O3 , was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y2 O3 –Ln2 O3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare-earth oxides is discussed in relation to the additive compositions. 相似文献
15.
Marin Cernea Elena Chirtop Dana Neacsu Iuliana Pasuk Sergiu Iordanescu 《Journal of the American Ceramic Society》2002,85(2):499-503
A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC2 O4 ·0.5H2 O and TiO(OH)2 ·1.5H2 O in a molar ratio of 1:4. Crystallized BaTi4 O9 was obtained by the thermal decomposition of a precipitate precursor at 1300°C for 2 h in air. The dimensions of the powder calcined at 1000°C are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300°C are of the order of 10 to 30 μm. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE011 mode. Excellent microwave characteristics for BaTi4 O9 —ɛ= 38 ± 0.5, Q = 3800–4000 at 6–7 GHz and τ f = 11 ± 0.7 ppm/°C—were found. 相似文献
16.
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
17.
Zirconia-Stabilized Cubic Europia 总被引:1,自引:1,他引:0
The system Eu2 O3 -ZrO2 was studied, concentrating attention on the region 0 to 33 mol% ZrO2 , which is of interest for fast-reactor neutron absorber applications. The addition of ∼20% ZrO2 to Eu2 O3 resulted in stable cubic phases. Results are compared for coprecipitated powders and pellets prepared from mechanically mixed powders fired at 1300°C and 1S50°C. The thermal stability of cubic structures at 600°C and 800°C for 8000 h was also demonstrated. 相似文献
18.
Sample disks prepared from Al2 O3 (61 wt%), SiO2 (28 wt%), and Fe2 O3 (II wt%) powders were sintered at 1270° and 1440°C and then annealed between 1300° and 1670°C. The annealed samples consisted of mullite as the main compound with minor amounts of glass and sometimes magnetite. The iron content of the mullites decreases strongly from ∼ 10.5 wt% Fe2 O3 at 1300°C to ∼ 2.5 wt% Fe2 O3 at 1670°C. A complex temperature-controlled exsolution mechanism of iron from mullite is considered. 相似文献
19.
Compound formation in the system PbO-SiO2 was studied; the results are contrasted with those previously reported. Fifteen binary phases, 4 of which had not been reported, were prepared in the present study. The new phases include Pb5 Si8 O21 , an orthorhombic polymorph of PbSiO3 , Pb3 SiO5 , and a high-SiO2 phase containing ∼ 60 mol% SiO2 . It was shown that Pb3 SiO5 is thermodynamically stable relative to Pb2 SiO4 and 4PbO.SiO2 below 640±5°C. A revised phase equilibrium diagram is presented. 相似文献
20.
Atsumi Nitta Hideyuki Nakamura Takayuki Komatsu Kazumasa Matusita 《Journal of the American Ceramic Society》1989,72(8):1351-1354
The interface reations between SiO2 –PbO melt and Mn-Zn ferrite were studied using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Intermediate layers were formed at the interface between the glass and the Mn-Zn ferrite which were heated at 800° and 900°C, although those layers were not found in specimens heated at 1000°C. Using EPMA and XRD, the intermediate layers were found to be Pb2 (Mn, Fe)2 Si2 O9 and Pb8 (Mn, Fe)Si6 O21 . The mechanisms of interface reactions are discussed, related to glassforming regions. It was concluded that the interface reaactions between SiO2 –PbO melt and Mn-Zn ferrite are controlled by the dissolution of Zn ions and Mn ions from the Mn-Zn ferrite. 相似文献