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1.
The quenching technique was used to study subliquidus and subsolidus phase relations in the pseudobinary system Na2 Ti2Si2 O11-Na2 Ti2 Si2 O9. Both narsarukite (Na2TiSi4O11) and lorenzenite (Na2Ti2Si2O9) melt incongruently. Narsarsukite melts at 911°±°C to SiO2+liquid, with the liquidus at 1016°C. Lorenzenite melts at 910°±5°C to Na2 Ti6 O13+liquid; Na2 Ti6 O13 reacts with liquid to form TiO2 and is thus consumed by 985°±5°C. The liquidus occurs at 1252°C.  相似文献   

2.
The system HfO2-TiO2 was studied in the 0 to 50 mol% TiO2 region using X-ray diffraction and thermal analysis. The monoclinic ( M ) ⇌ tetragonal ( T ) phase transition of HfO2 was found at 1750°± 20°C. The definite compound HfTiO4 melts incongruently at 1980°± 10°C, 53 mol% TiO2. A metatectic at 2300°± 20°C, 35 mol% TiO2 was observed. The eutectoid decomposition of HfO2,ss) ( T ) → HfO2,ss ( M ) + HfTiO34,ssss occurred at 1570°± 20°C and 22.5 mol% TiO2. The maximum solubility of TiO2 in HfO2,ss,( M ) is 10 mol% at 1570°± 20°C and in HfO2,ss ( T ) is 30 mol% at 1980°± 10°C. On the HfO2-rich side and in the 10 to 30 mol% TiO2 range a second monoclinic phase M of HfO2( M ) type was observed for samples cooled after a melting or an annealing above 1600°C. The phase relations of the complete phase diagram are given, using the data of Schevchenko et al. for the 50% to 100% TiO2 region, which are based on thermal analysis techniques.  相似文献   

3.
Phase relations in the system Sc2O3-WO3 were characterized. Two stable binary compounds were, found. The 1:3 compound, SC2(WO4)3, melts congruently at 1640°±10°C and forms a simple eutectic with WO3 at ∼90 mol% WO3 and 1309°+10°C. The 3 : 1 compound, Sc6WO12, forms a simple eutectic with the 1:3 compound at -69 mol% WO2, and 1580°+10°C. The melting temperature of SC6WO12 was >1600°C.  相似文献   

4.
Lithium borate (Li2B4O7) and sodium borate (Na2B4O7) mineralize spinel formation from stoichiometric MgO and Al2O3 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. Na2B4O7-mineralized compositions show predominantly templated grain growth at 1000°C, which changes to dissolution–precipitation at 1100°C, whereas Li2B4O7-mineralized compositions show dissolution–precipitation from 1000°C. Li2B4O7 is a stronger mineralizer as spinel formation is complete with 3 wt% Li2B4O7 at 1000°C and with ≥1.5 wt% addition at 1100°C, whereas Na2B4O7-mineralized compositions are found to retain some unreacted corundum even at 1100°C.  相似文献   

5.
New data obtained on the join Ca2SiO4-CaMgSiO4 established a limit of crystalline solubility of Mg in α-Ca2SiO4 corresponding to the composition Ca1.90Mg0.10SiO4 at 1575°C. The α-α'Ca2SiO4 inversion temperature is lowered from 1447° to 1400°C by Mg substitution in the lattice. α'-Ca2SiO4 takes Mg into its lattice up to the composition Ca1.94Mg0.06SiO4 at 1400°C and to Ca1.96Mg0.04SiO4 at 900°C. A new phase (T) reported previously by Gutt, with the approximate composition Ca1.70Mg0.30SiO4, was stable between 979° and 1381°C, and should be stable at liquidus temperatures in multicomponent systems involving CaO–MgO–SiO2.  相似文献   

6.
Alumina reacts with 1 atm of SiF4 below 660°± 7°C to form A1F3 and SiO2. At higher temperatures the product is a mixture of fluorotopaz and AIF3. Mixtures of fluorotopaz and AIF3 decompose in 1 atm of SiF4 at 973°± 8°C and form tabular α-alumina. The equilibrium vapor pressure of SiF4 above mixtures of fluorotopaz and AlF3 is log p (atm) = 9.198 – 11460/ T (K). Fluorotopaz itself decomposes at 1056°± 5°C in 1 atm of SiF4 to give acicular mullite, 2Al2O3.1.07SiO2. Alumina and mullite are stable in the presence of 1 atm of SiF4 above 973° and 1056°C, respectively. The phase diagram of the system SiO2-Al2O3-SiF4 shows only gas-solid equilibria.  相似文献   

7.
Equilibrium partial pressures of SiF4 were measured for the reactions 2SiO2( c )+2BeF2( d )⇋SiF4( g )+Be2SiO4( c ) (log P siF4(mm) = [8.790 - 7620/ T ] ±0.06(500°–640°C)) and Be2SiO4( c ) +2BeF2( d )⇋SiF4( g ) +4BeO( c )(log P siF4(mm) = [9.530–9400/T] ±0.04 (700°–780°C)), wherein BeF2 was present in solution with LiF as molten Li2BeF4. The solubility of SiF4 was low (∼0.04 mol kg-1 atm-1) in the melt. The results for the first equilibrium were combined with available thermochemical data to calculate improved Δ Hf and Δ Gf values for phenacite (–497.57 ±2.2 and –470.22±2.2 kcal, respectively, at 298°K). The few measurements above 700°C for the second equilibrium are consistent with the temperature of the subsolidus decomposition of phenacite to BeO and SiO2 and with the heat of this decomposition as determined by Holm and Kleppa. Below 700°C, the pressures of SiF4 generated showed an increasing positive deviation from the expression given for the equilibrium involving Be2SiO4 and BeO. This deviation might have been caused by the formation of an unidentified phase below 700°C which replaced the BeO; it more likely resulted from a metastable equilibrium involving BeO and SiO2.  相似文献   

8.
Phase relations in the system Bi2O3-WO3 were studied from 500° to 1100°C. Four intermediate phases, 7Bi2O3· WO3, 7Bi2O3· 2WO3, Bi2O3· WO3, and Bi2O3· 2WO3, were found. The 7B2O · WO3 phase is tetragonal with a 0= 5.52 Å and c 0= 17.39 Å and transforms to the fcc structure at 784°C; 7Bi2O3· 2WO3 has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi2O3· WO3 and Bi2O3· 2WO3 are orthorhombic with (in Å) a 0= 5.45, b 0=5.46, c 0= 16.42 and a 0= 5.42, b 0= 5.41, c 0= 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO3, 907°± 3°C and 70 mol% WO3, and 965°± 5°C and 10 mol% WO3.  相似文献   

9.
The phase relations for the system y2o3–Ta2o5 in the composition range 50 to 100 mol% Y2O3 have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C2221), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y2O3 under 17000C and O phase in 70 mol% Y2O3 up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y2O3 and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y2O3, and at about 1990°C, 62 mol% Y2O3. A Phase diagram including the above three phases were not identified with each other.  相似文献   

10.
The solubility of ZnAl2O4 (gahnite spinel) and NZOI (corundum) in their respective molten PbF2 solutions was determined by a sealed-tube quenching method between 900° and 1250°C. Differential thermal analysis was used below 900°C. The solubilities (crystal-constituent/ PbF2 weight ratio) at 1200°C were 0.151 for A12O3 and 0.108 for ZnAl2O4, whereas at 900°C they were 0.093 and 0.048, respectively. These results are compared with those of single-crystal growth experiments and the crystalline products are described.  相似文献   

11.
Lattice parameters of RE4Al2O9 (RE = Y, Sin, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) prepared at 1600–1800°C and those of RE4Ga2O9 (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 RE4Al2O, and RE4Ga2O, 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 RE4A12O9, except for Y4Al2O9 ( Ttr = 1377°C), and from 1417°C (Gd) to 1271°C (La) for RE4Ga2O, 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 A1Ga/rRE) except for Y4Al2O9.  相似文献   

12.
Fresnoite grows at 700° and 800°C, and Ba6Ti7O40 grows at 1200°C with definite orientations, which are determined by X-ray diffraction pole figure analysis. Partially textured fresnoite is formed at higher temperatures. The SiO2 films react with the BaTiO3 crystals, forming the phases Ba2TiSi2O8 (fresnoite) and Ba6Ti17O40. At 700° and 800°C, both phases grow with definite orientations, which are determined by X-ray diffraction pole figure analysis. Partially textured polycrystalline phases are formed at higher temperatures.  相似文献   

13.
The phase relations in the systems MgO-Y2O3-ZrO2 and CaO-MgO-ZrO2 were established at 1220° and 1420°C. The system MgO-Y2O3-ZrO2 possesses a much-larger cubic ZrO2 solid solution phase field than the system CaO-MgO-ZrO2 at both temperatures. The ordered δ phase (Zr3Y4O12) was found to be stable in the system ZrO2-Y2O3 at 1220°C. Two ordered phases φ1 (CaZr4O9) and φ2 (Ca6Zr19O44) 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 Mg3YzO6 could not be confirmed.  相似文献   

14.
Subsolidus phase relationships in the Ga2O3–In2O3 system were studied by X-ray diffraction and electron probe microanalysis (EPMA) for the temperature range of 800°–1400°C. The solubility limit of In2O3 in the β-gallia structure decreases with increasing temperature from 44.1 ± 0.5 mol% at 1000°C to 41.4 ± 0.5 mol% at 1400°C. The solubility limit of Ga2O3 in cubic In2O3 increases with temperature from 4.X ± 0.5 mol% at 1000°C to 10.0 ± 0.5 mol% at 1400°C. The previously reported transparent conducting oxide phase in the Ga-In-O system cannot be GaInO3, which is not stable, but is likely the In-doped β-Ga2O3 solid solution.  相似文献   

15.
The phase relations for the Sc2O3-Ta2O5 system in the composition range of 50-100 mol% Sc2O3 have been studied by using solid-state reactions at 1350°, 1500°, or 1700°C and by using thermal analyses up to the melting temperatures. The Sc5.5Ta1.5O12 phase, defect-fluorite-type cubic phase (F-phase, space group Fm 3 m ), ScTaO4, and Sc2O3 were found in the system. The Sc5.5Ta1.5O12 phase formed in 78 mol% Sc2O3 at <1700°C and seemed to melt incongruently. The F-phase formed in ∼75 mol% Sc2O3 and decomposed to Sc5.5Ta1.5O12 and ScTaO4 at <1700°C. The F-phase melted congruently at 2344°± 2°C in 80 mol% Sc2O3. The eutectic point seemed to exist at ∼2300°C in 90 mol% Sc2O3. A phase diagram that includes the four above-described phases has been proposed, instead of the previous diagram in which those phases were not identified.  相似文献   

16.
A tentative phase diagram for the system Al203-Nd2O3 is presented. Three compounds were obtained: a β -A12O3-type compound, the perovskite NdAlO3, and Nd4Al2O9. The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al2O3, mp 1900°C; Nd4Al2O9, mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al2O3, 1750°C; 23 mol% Al2O3,1800°C. Nd4Al2O9 decomposes in the solid state at 1780°C.  相似文献   

17.
The subsolidus phase relations in the entire system ZrO2-Y2O3 were established using DTA, expansion measurements, and room- and high-temperature X-ray diffraction. Three eutectoid reactions were found in the system: ( a ) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y2O3 and ∼490°C, ( b ) cubic zirconia solid solutiow→δ-phase Y4Zr3O12+hexagonalphase Y6ZrO11 at 45 mol% Y2O3 and ∼1325°±25°C, and ( c ) yttria C -type solid solution→wcubic zirconia solid solution+ hexagonal phase Y6ZrO11 at ∼72 mol% Y2O3 and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y2O3 with ideal formula Y4Zr3O12, and another, a new hexagonal phase, at 75 mol% Y2O3 with formula Y6ZrO11. They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C -type solid solution, respectively. The extent of the cubic zirconia and yttria C -type solid solution fields was also redetermined. By incorporating the known tetragonal-cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO2-Y2O3.  相似文献   

18.
BaCu(B2O5) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B2O5) phase was formed at 700°C and melted above 850°C. The BaCu(B2O5) ceramic sintered at 810°C had a dielectric constant (ɛr) of 7.4, a quality factor ( Q × f ) of 50 000 GHz and a temperature coefficient of resonance frequency (τf) of −32 ppm/°C. As the BaCu(B2O5) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B2O5) was added to the Ba(Zn1/3Nb2/3)O3 (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B2O5) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q × f =16 000 GHz, ɛr=35, and τf=22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B2O5) ceramic sintered at 875°C for 2 h.  相似文献   

19.
Subsolidus phase relations in the system iron oride-Al2O2-Cr2O3 in air and at 1 atm. O2 pressure have been studied in the. temperature interval 1250° to 1500°C. At temperatures below 1318° C. only sesquioxides with hexagonal corundum structure are present as equilibrium phases. In the temperature interval 1318° to 1410°C. in air and 1318° to 1495° C. at 1 atm. O2, pressure the monoclinic phase Fe2O3. Al2O3 with some Cr2O3 in solid solution is present in the phase assemblage of certain mixtures. At temperatures above 1380°C. in air and above 1445°C. at 1 atm. O2 pressure a complex spinel solid solution is one of the phases present in appropriate composition areas of the system. X-ray data relating d- spacing to composition of solid solution phases are given.  相似文献   

20.
The phase diagram for the CuO-rich part of the La2O3─CuO join was redetermined. La2Cu2O5 was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu7O19 had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La2O3─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La1.9Ca1.1Cu2O5.9 and LaCa2Cu3O8.6, were stable at these temperatures, with three binary phases, Ca2CuO3, CaCu2O3, and La2CuO4. La2Cu2O5 and La8Cu7O19 were stable only at 1020°C, and did not support solid-solution formation.  相似文献   

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