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1.
Phase relations in the system NiO–TiO2 have been determined by heating oxide mixtures in air at selected temperatures in the range 1300° to 1750°C for sufficient periods of time to attain equilibrium, followed by rapid quenching to room temperature. The phases have been characterized by optical microscopy, X-ray diffraction, and electron microprobe analysis. The most striking feature is the presence, above 1430°C, of a spinel-type phase that decomposes below this temperature to a mixture of remnant spinel, NiO of periclase-type structure, and NiTiO3 of ilmenite-type structure. There are two peritectic points in the system, one at 1730°C where spinel, NiO, and liquid coexist in equilibrium, and one at 1610°C where spinel, NiTiO3, and liquid are the coexisting phases. A eutectic is present at 1570°C, with NiTiO3, rutile, and liquid coexisting in equilibrium. Rapid transformation of the spinel phase, even during rapid quenching, imposes uncertainties on the interpretation of the experimental data obtained, but the equilibrium-phase relations are deduced essentially as shown in the phase diagram presented. Results of a small number of calculated activities of NiO in oxide-phase assemblages involving the spinel phase at high temperatures (∼1500°C) lend support to the interpretation of the phase relations as presented in this paper.  相似文献   

2.
Liquidus and solidus phase relations have been determined for the system iron oxide–NiO–SiO2 under strongly reducing conditions obtained by using CO2–CO gas mixtures in controlled proportions. The phase relations were determined with the well-known quenching method: oxide mixtures were equilibrated in vertical tube resistance furnaces, followed by quenching to room temperature and identification of phases with transmitted- and reflected-light microscopy and X-ray diffraction. Three crystalline phases are present on the liquidus surface: olivine (Fe2SiO4–Ni2SiO4 solid solutions), oxide ("FeO"–NiO solid solutions), and silica (tridymite or cristobalite, depending on temperature). The "ternary peritectic" point where these three phases coexist with liquid is at 1571°C, with a liquid composition of approximately 19 wt%"FeO", 47 wt% NiO, 34 wt% SiO2.  相似文献   

3.
A furnace for use in conjunction with the X-ray spectrometer was developed which was capable of heating small powdered specimens in air to temperatures as high as 1850°C. This furnace was also used for the heating and quenching of specimens in air from temperatures as high as 1850°C. An area of two liquids coexisting between 20 and 93 weight % TiO2 above 1765°± 10°C. was found to exist in the system TiO2–SiO2, which is in substantial agreement with the previous work of other investigators. The area of immiscibility in the system TiO2–SiO2 was found to extend well into the system TiO2–ZrO2–SiO2. The two liquids were found to coexist over a major portion of the TiO2 (rutile) primary-phase area with TiO2 (rutile) being the primary crystal beneath both liquids. The temperature of two-liquid formation in the ternary was found to fall about 80°C. with the first additions of ZrO2 up to 3%. With larger amounts of ZrO2 the change in the temperature of the boundary of the two-liquid area was so slight as to be within the limits of error of the temperature measurement. Primary-phase fields for TiO2 (rutile), tetragonal ZrO2, and ZrTiO4 were found to exist in the system TiO2–ZrO2–SiO2. SiO2 as high cristobalite is known to exist in the system TiO2–ZrO2–SiO2.  相似文献   

4.
Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al2O3 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 MnAl2O4–NiAl2O4 solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2O4 from 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 distribution models.  相似文献   

5.
The phase relations of the systems ZrO2–TiO2 and ZrO2–TiO2–SiO2 were investigated. X-ray diffraction techniques served as the principal means of analysis. The binary system ZrO2–TiO2 was found to be one of partial solid solutions with no intermediate compounds. A eutectic point was found to exist at 50 to 55 weight % ZrO2 and 1600°C. A preliminary investigation of the ternary system ZrO2–TiO2–SiO2, although not extensive, resulted in a better understanding of this system, with a fairly accurate location of some of its boundary lines. A eutectic point was located at 2% ZrO2, 10% TiO2, and 88% SiO2 at approximately 1500°C.  相似文献   

6.
In this work, the liquidus of synthetic CaO–SiO2–MgO–Al2O3–CrO x slags is evaluated in the industrially relevant compositional domain. Equilibrium experiments are carried out at 1500°C and partial oxygen pressure ( p O2) 10−11.04 atm, and at 1600°C and p O2=10−10.16 and 10−9.36 atm. The studied basicities (CaO/SiO2) are 1.2 and 0.5. Al2O3 levels range from 0 to 30 wt%. Oversaturated liquid is sampled and phase relations are measured with quantitative electron probe microanalysis–wavelength dispersive spectroscopy (EPMA–WDS). The results are compared with the commercially available FactSage thermodynamic databases. Qualitative agreement is always obtained. Also a good quantitative agreement is found at the higher basicity, especially for the spinel liquidus. A minor but systematic deviation can be observed for the eskolaite liquidus. At the lower basicity, the calculated phase diagram deviates strongly from the experimental results, probably due to missing ternary interactions in the database.  相似文献   

7.
Subsolidus phase equilibria in the system Fe2O3–Al2O3–TiO2 were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M3O5 solid solution series between end members Fe2TiO5 and Al2TiO5, (b) a miscibility gap along the Fe2O3–Al2O3 binary, (c) an α-M2O3( ss ) ternary solid-solution region based on mutual solubility between Fe2O3, Al2O3, and TiO2, and (d) an extensive three-phase region characterized by the assemblage M3O5+α-M2O3( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe2O3–Al2O3–TiO2 system shows considerable discrepancy.  相似文献   

8.
9.
We characterized SiO2–TiO2 nano-hybrid particles, prepared using the sol–gel method, using high-resolution transmission microscopy. A few nanometer-ordered TiO2 anatase crystallites could be observed on the monodispersed SiO2 nanoparticle surface. The quantum size effect of the TiO2 anatase crystallites is attributed to the blue shift of the absorption band. The rough surface of the SiO2–TiO2 nano-hybrid particles was derived from the developed growth planes of the TiO2 anatase crystallites, grown from fully hydrolyzed Ti alkoxide that did not react with acetic acid during the crystallization process at 600°C thermal annealing.  相似文献   

10.
A complete solid-solution series exists between diopside (CaMgSi2O6) and its nickel analogue, "niopside"(CaNiSi2O6). Activity–composition relations within this solid solution, and the stability of the end member CaNiSi2O6, have been determined by equilibrating CaNiSi2O6 with SiO2, CaSiO3, and metallic Ni in atmospheres of known oxygen pressures. Within limits of accuracy of the experiments, the solution is ideal at 1350°C. From the experimental data obtained in the present investigation, the standard free energy (Δ G °) of formation of CaNiSi2O6 according to the equation CaO + NiO + 2SiO2= CaNiSi2O6 is calculated to be Δ G °=−165862 + 42.40 T J. Experiments in the system CaO–NiO–SiO2 have shown that the nickel analogue of the phase pseudo-enstatite (MgSiO3) is unstable with respect to SiO2 and nickel olivine (Ni2SiO4), and the nickel analogues of the phases akermanite (Ca2MgSi2O7) and monticellite (CaMgSiO4) are unstable relative to the phase assemblage pseudo-wollastonite (CaSiO3) plus NiO. In the system CaO–MgO–NiO–SiO2, however, substitution of Ni for Mg in these phases was observed. The percentage substitution of Ni for Mg in the phases is given in parentheses: diopside (100%), olivine (100%), enstatite (18%), akermanite (20%), and monticellite (57%).  相似文献   

11.
Liquidus phase equilibrium data are presented for the system Al2O3-Cr2O3-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 (6Al2O3-ICr2O3-93SiO2) coexists with a mullite solid solution (61Al2O3-10Cr2O3-29SiO2), a corundum solid solution (19Al2O3-81Cr2O3), 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   

12.
Phase relations at liquidus temperatures in the system iron oxide-TiO2-SiO2 have been determined in air. The equilibrium existence of the crystalline phases magnetite (ss), hematite (ss), pseudobrookite(ss), rutile(ss), and silica (tridy-mite or cristobalite) has been established. Three isobaric eutectic points are formed by the intersections of quaternary liquidus univariant lines of the system Fe-Ti-Si-O and the 0.21 atmosphere isobaric surface. The liquid misci-bility gaps present in the bounding "binary" systems iron oxide-Si02 and TiO2-SiO2 extend across the composition triangle representing the "ternary" system iron oxide-TiO2-SiO2. Liquidus temperatures decrease within the two-liquid region from approximately l <57Qa C. in the system iron oxide-SiO2 and 1780°C. in the system Ti(VSiO2 to 1540°C. at the cristobalite-rutile(ss) boundary curve which bisects the two-liquid region. Paths of equilibrium crystallization of representative mixtures are discussed with reference to a simplified projection into the plane FeOFe2O3-TiO2-SiO2 as well as in terms of the tetrahedron representing the system FeO-Fe2O3-TiO2-SiO2.  相似文献   

13.
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   

14.
The independent crystallization sequence of an Al2O3 component is modified in the presence of SiO2 and vice versa. Mixed SiO2-Al2O3, gel (28 wt% SiO2 and 72 wt% Al2O3) forms neither cristobalite nor γ-Al2O3 and corundum at 1000°C but forms Si-Al spinel; an amorphous aluminosilicate phase invariably also forms after the gel is heated. However, the composition of this amorphous aluminosilicate phase is not as yet known.  相似文献   

15.
The influence of co-additions of crystalline TiO2 and SiO2 fillers (10 wt% addition in total) to BaO–ZnO–B2O3–SiO2 glass on resultant properties was investigated from the viewpoint of applying the material to the barrier ribs of plasma display panels. The substitution of SiO2 for TiO2 reduced the dielectric constant significantly, while it maintained high optical reflectance and appropriate coefficient of thermal expansion (CTE) in the case when TiO2 alone was used. A 5–7.5 wt% SiO2 addition with 2.5–5 wt% TiO2 under the constraint of 10 wt% total fillers demonstrated an optical reflectance of about 55%, a CTE of about 8.3 × 10−6 K−1 (compatible with glass panels), and a dielectric constant of about 7.5, which are promising properties for the barrier rib application.  相似文献   

16.
A series of La2O3–HfO2–SiO2 glasses, approximately along the join 0.73SiO2–0.27( x HfO2–(1− x )La2O3), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B2O3) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO2 content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO2 content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO2 content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon.  相似文献   

17.
Solid-state compatibility and melting relations of MgAl2O4 in the quaternary system Al2O3–CaO–MgO–SiO2 were studied by firing and quenching selected samples located in the 65 wt% MgAl2O4, plane followed by microstructural and energy dispersive X-ray analysis. A projection of the liquidus surface of the primary crystallization volume of MgAl2O4 was constructed from CaO, SiO2 and exceeding Al2O3, not involved in stoichiometric MgAl2O4 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 Al2O3 impurities on the high temperature behavior of spinel materials was also discussed.  相似文献   

18.
Results of a study of phase equilibria in the system CaO–TiO2–SiO2 are presented. A prominent feature of the liquidus surface is a large two-liquid region which appears on the equilibrium diagram as a broad band extending from the SiO2-CaO side to the SiO2-TiO2 side of the triangle. Evidence for the liquid immiscibility and the significance of the resulting large high-temperature liquidus region in silicate technology are discussed. Representative paths of crystallization of liquids in the system under equilibrium conditions are outlined. It is shown that solid solution in the system is virtually nonexistent except for the small-scale substitution of Ti4+ for Si4+ in wollastonite. Indices of refraction of glasses are given. Composition and temperature are listed for the twelve liquidus ternary invariant points.  相似文献   

19.
Measurements of electrical resistance in the composition systems Al2O3–SiO2, SiO2–TiO2, Al2O3–Cr2O3, and MgO–NiO were made using, in general, dry-pressed disks about 3 cm. in diameter and 0.4 cm. thick and fired to 1500°C. In the Al2O3–SiO2 series minimum resistance was shown by the samples containing 50% SiO2, 50% Al2O3. The resistance of Al2O3 was increased by the addition of small amounts of Cr2O3. The same effect was observed in the higher temperature range with small additions of NiO to MgO. In other instances the addition of the relatively inert SiO2, Al2O3, and MgO to the semiconductors TiO2, Cr2O3, and NiO resulted in a dilution effect. The resistance of Cr2O3 was decreased by the addition of a slight amount of MgO.  相似文献   

20.
Phase relations within the "V2O3–FeO" and V2O3–TiO2 oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10−10, 2.99 × 10−9, and 2.31 × 10−8 atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M2O3, M3O5, and higher Magneli phases (M n O2 n −1, where M = V, Ti) were identified in the V2O3–TiO2 system. In the "V2O3–FeO" system, the solid-solution phases M2O3 and M3O4 (where M = V, Ti), as well as liquid, were identified.  相似文献   

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