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1.
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   

2.
Data obtained by quenching, thermal, and high-temperature X-ray techniques are presented for the three binary systems CaF2–BeF2, MgF2–BeF2, and LiF–MgF2. The systems CaF2–BeF2 and MgF2–BeF2 are presented as weakened models of the systems ZrO2–SiO2 and TiO2–SiO2, respectively. The compound CaBeF4 is a model of ZrSiO4 (zircon). New data obtained for the system LiF–MgF2 explain many discrepancies among the results of previous authors. Solid solution is almost complete between LiF and MgF2 at elevated temperatures, but a small gap occurs at the eutectic (735°C.) with extensive exsolution at lower temperatures.  相似文献   

3.
Phase equilibrium relations in the system PbO–TiO2–ZrO2 were studied by quenching in the range where the PbO content is 50 mole % and more. Isotherms were examined at 1100°, 1200°, and 1300°C and tie lines were determined between the liquid and solid solution in equilibrium. The incongruent melting point of PbZrO3 was 1570°C and the equilibrium between liquid, PbO-type solid, and PbZrO3 is peritectic. Pb(Zr,Ti)O3 solid solutions containing more than 14 mole % PbZrO3 decomposed to liquid, ZrO2, and Pb(Zr,Ti)O3 and the decomposition temperature rises from 1340° to 1570°C with increasing PbZrO3 content. The system PbTiO3–PbZrO3 should not be treated as a binary, but as a section of the ternary system.  相似文献   

4.
Zirconolite (CaZrTi2O7) is a mineral that has a high containment capacity for actinides and lanthanides and is considered to be a good candidate for the immobilization of radioactive wastes. The glass–ceramic technique seems to be a very suitable and convenient method to produce zirconolite crystals by precipitating them in a specific glass matrix. In this study, development of a new zirconolite-based glass–ceramic belonging to SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O) system was investigated. The presence of PbO, together with B2O3 and K2O, allowed the preparation of a X-ray diffraction (XRD) amorphous glass with a relatively high concentration of ZrO2 and TiO2, which was successfully converted to a glass–ceramic containing 34 wt% of zirconolite after heating at 770°C for 4 h. Differential thermal analysis, XRD, scanning electron microscope, and energy dispersive X-ray spectroscopy were used to determine the crystallization conditions, identify the crystallized phases, determine their compositions and quantities and observe and analyze the microstructures. The zirconolite crystals showed a platelet morphology with a monoclinic structure characterized by a =1.246 nm, b =0.7193 nm, c =1.128 nm, and β=100.508°.  相似文献   

5.
In this work several complementary techniques have been employed to carefully characterize the sintering and crystallization behavior of CaO–Al2O3–ZrO2–SiO2 glass powder compacts after different heat treatments. The research started from a new base glass 33.69 CaO–1.00 Al2O3–7.68 ZrO2–55.43SiO2 (mol%) to which 5 and 10 mol% Al2O3 were added. The glasses with higher amounts of alumina sintered at higher temperatures (953°C [lower amount] vs. 987°C [higher amount]). A combination of the linear shrinkage and viscosity data allowed to easily find the viscosity values corresponding to the beginning and the end of the sintering process. Anorthite and wollastonite crystals formed in the sintered samples, especially at lower temperatures. At higher temperatures, a new crystalline phase containing ZrO2 (2CaO·4SiO2·ZrO2) appeared in all studied specimens.  相似文献   

6.
Equilibrium relations in the system NiO–TiO2–SiO2 in air have been investigated in the temperature range 1430° to 1660°C. The most conspicuous feature of the phase relations is the existence of a cation-excess spinel-type phase, in addition to NiO and NiTiO3, on the liquidus surface and at subsolidus temperatures down to 1430°C. Three invariant points have been located on the liquidus. There is a peritectic at 1540°C characterized by coexisting NiO ( ss ), spinel( ss ), cristobalite, and liquid of composition 47 wt% NiO, 29 wt% TiO2, and 24 wt% SiO2. Two eutectics are present, one at 1480°C, with spinel( ss ), NiTiO3, cristobalite, and liquid (42 wt% NiO, 43 wt% TiO2, and 15 wt% SiO2), as the coexisting phases. The other is at 1490°C with NiTiO3, rutile, cristobalite, and liquid (32 wt% NiO, 56 wt% TiO2, and 12 wt% SiO2). A liquid miscibility gap extends across the diagram from the two bounding binary systems NiO–SiO2 and TiO2–SiO2.  相似文献   

7.
The wettability of binary and ternary glasses belonging to SiO2–Al2O3–ZrO2 diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO2–Al2O3–ZrO2 (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO2 slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo5+, Mo4+, and Mo6+. After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo6+.  相似文献   

8.
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   

9.
Thin films of crystalline TiO2 were deposited on self-assembled organic monolayers from aqueous TiCl4 solutions at 80°C; partially crystalline ZrO2 films were deposited on top of the TiO2 layers from Zr(SO4)2 solutions at 70°C. In the absence of a ZrO2 film, the TiO2 films had the anatase structure and underwent grain coarsening on annealing at temperatures up to 800°C; in the absence of a TiO2 film, the ZrO2 films crystallized to the tetragonal polymorph at 500°C. However, the TiO2 and ZrO2 bilayers underwent solid-state diffusive amorphization at 500°C, and ZrTiO4 crystallization could be observed only at temperatures of 550°C or higher. This result implies that metastable amorphous ZrTiO4 is energetically favorable compared to two-phase mixtures of crystalline TiO2 and ZrO2, but that crystallization of ZrTiO4 involves a high activation barrier.  相似文献   

10.
Silver and gold nanoparticles were synthesized by the sol–gel process in SiO2, TiO2, and ZrO2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag+ and Au3+ ions in sol–gel systems. Various ligands of the metal ions were tested, and for each system it was possible to find a suitable ligand capable of stabilizing the metal ions and preventing gold precipitation onto the film surface. Thin films were prepared by spin-coating onto glass or fused silica substrates and then heat-treated at various temperatures in air or H2 atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO2 film at 600°C and the TiO2 and ZrO2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO2 and ZrO2 films, respectively. The films were characterized by UV–vis optical absorption spectroscopy and X-ray diffraction, for studying the nucleation and the growth of the metal nanoparticles. The results are discussed with regard to the embedding matrix, the temperature, and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO2 and ZrO2 films may hinder the growth of Ag and Au particles.  相似文献   

11.
By a progressive weight percent substitution of TiO2 for SiO2 at various rations of concentration of K2O and PbO, the entire region of glass formation in the quaternary system K2O–PbO–SiO2–TiO2 was covered with 51 glass compositions. The properties of these glasses were determined and studied with respect to the role of TiO2 in the system. The results indicated that the dielectric constant increased progressively with increasing TiO2 concentration whereas the dissipation factor showed an overall decrease, when measured at 1 Mc and 25°C. Density and the refractive index increased progressively with increasing TiO2 concentration but deviated from the additive relation. Chemical durability, expansivity, and softening temperature vs. composition curves showed definite inflections. The effect of TiO2 on oxygen packing indicated that Ti4+ strengthens the network in lower concentrations and weakens the network in higher concentrations in this system. It appears to be likely that Ti4+ changes its coordination number form 4 to 6.  相似文献   

12.
High-energy ball milling initiates a solid-state reaction in an equimolar mixture of TiO2 and ZrO2. The first stage of ball milling induced the transformation of anatase TiO2 to high-pressure phase TiO2 (II), isostructural with ZrTiO4. The formation of solid solutions monoclinic ZrO2/TiO2 and TiO2 (II)/ZrO2 was observed in the intermediate stage. Afterward, a nanosized ZrTiO4 phase was formed in the milled product from the TiO2 (II)/ZrO2 solid solution. The sintering of the milled product at a temperature <1100°C was examined in situ by Raman spectroscopy. The full solid-state reaction toward ZrTiO4 ceramic is completed at a temperature considerably lower than reported in the literature.  相似文献   

13.
The solubility of TiO2 in tetragonal ZrO2 is 13.8±0.3 mol% ui 1300°C, 14.9±0.2 mol% at 1400°C, and 16.1±0.2 mol% at 1500°C. These solid solutions transform to metastable monoclinic solid solutions without compositional change on cooling to room temperature.  相似文献   

14.
Metastable tetragonal ZrO2 phase has been observed in ZrO2–SiO2 binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO2 tetragonal stabilization in binary oxides such as Y3O2–ZrO2, MgO–ZrO2, or CaO–ZrO2. In these binary oxides, oxygen vacancies cause changes or defects in the ZrO2 lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO2–SiO2 binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO2 crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O groups). In this paper, FT-IR and 29Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples.  相似文献   

15.
The effect of Y2O3 content on the flexure strength of melt-grown Al2O3–ZrO2 eutectics was studied in a temperature range of 25°–1427°C. The processing conditions were carefully controlled to obtain a constant microstructure independent of Y2O3 content. The rod microstructure was made up of alternating bands of fine and coarse dispersions of irregular ZrO2 platelets oriented along the growth axis and embedded in the continuous Al2O3 matrix. The highest flexure strength at ambient temperature was found in the material with 3 mol% Y2O3 in relation to ZrO2(Y2O3). Higher Y2O3 content did not substantially modify the mechanical response; however, materials with 0.5 mol% presented a significant degradation in the flexure strength because of the presence of large defects. They were nucleated at the Al2O3–ZrO2 interface during the martensitic transformation of ZrO2 on cooling and propagated into the Al2O3 matrix driven by the tensile residual stresses generated by the transformation. The material with 3 mol% Y2O3 retained 80% of the flexure strength at 1427°C, whereas the mechanical properties of the eutectic with 0.5 mol% Y2O3 dropped rapidly with temperature as a result of extensive microcracking.  相似文献   

16.
It has been shown that polydimethylsiloxane (PDMS)–CaO–SiO2–TiO2 and poly(tetramethylene oxide) (PTMO)–CaO–TiO2 hybrids form apatite on their surfaces in a simulated body fluid (SBF) and show mechanical properties similar to those of human cancellous bones. In the present study, changes, caused by soaking in SBF, were measured in the mechanical properties of PDMS–CaO–SiO2–TiO2 hybrids with different CaO and TiO2 contents and PTMO–CaO–TiO2 hybrids with different CaO contents. Significant decreases in the strength and strain at failure of the hybrids were observed for the PDMS–CaO–SiO2–TiO2 hybrids with high CaO or TiO2 contents and PTMO–CaO–TiO2 hybrids with a high CaO content after soaking in SBF for 4 w. This indicates that incorporation of a large amount of CaO component into the hybrids should result in the deterioration of the hybrids in the body environment.  相似文献   

17.
Ceramic photonic crystals with diamond structure were fabricated using stereolithography and successive sintering. The green body of an epoxy resin incorporating 10 vol% TiO2–SiO2 was formed by stereolithography and then heated in air at 1100°–1400°C for 2 h. The sintered products maintained the diamond structure with a linear shrinkage ratio of about 57% and a porosity of 38%. The ceramic photonic crystal with eight unit cells showed a photonic band gap at the center frequency of 23.5 GHz. This fabrication method of three-dimensional (3D) ceramic photonic crystals is applicable to other 3D structural ceramics and does not require any molding techniques.  相似文献   

18.
In this paper concerning the synthesis of microporous ceramic membranes, we focus on the preparation and ther- mal stability of unsupported microporous TiO2-ZrO2, mixed-oxide membranes. It has been observed that, by add- ing up to 20% ZrO2, into TiO2, or up to 10% TiO2, into ZrO2, these microporous membranes display improved thermal stability. They can be fired up to 500°C for 0.5 h without closing micropores. However, membranes containing almost equal percentages of each component have lost microporous features and have low surface areas and low porosities. A phase diagram of a two-component TiO2- ZrO2, mixed-oxide membrane has been prepared based on DTA and X-ray diffraction data in order to better under- stand the microstructure changes upon firing.  相似文献   

19.
Anatase-type TiO2 powder containing sulfur with absorption in the visible region was directly formed as particles with crystallite in the range 15–88 nm by thermal hydrolysis of titanium(III) sulfate (Ti2(SO4)3) solution at 100°–240°C. Because of the presence of ammonium peroxodisulfate ((NH4)2S2O8), the yield of anatase-type TiO2 from Ti2(SO4)3 solution was accelerated, and anatase with fine crystallite was formed. Anatase-type TiO2 doped with ZrO2 up to 9.8 mol% was directly precipitated as nanometer-sized particles from the acidic precursor solutions of Ti2(SO4)3 and zirconium sulfate in the presence and the absence of (NH4)2S2O8 by simultaneous hydrolysis under hydrothermal conditions at 200°C. By doping ZrO2 into TiO2 and with increasing ZrO2 content, the crystallite size of anatase was decreased, and the anatase-to-rutile phase transformation was retarded as much as 200°C. The anatase-type structure of ZrO2-doped TiO2 was maintained after heating at 1000°C for 1 h. The favorable effect of doping ZrO2 to anatase-type TiO2 on the photocatalytic activity was observed.  相似文献   

20.
Equilibrium phase diagrams for the systems NdCl3–CaCl2 and NdCl3–NaCl were determined by differential thermal analysis. A simple eutectic was observed at 59 ± 1 mol% CaCl2 and 600°± 2°C in the NdCl3–CaCl2 system. A compound NaCl.3NdCl3 which melts incongruently at 545°± 5°C to NdCl3 and a liquid containing approximately 47 mol% NaCl, and a eutectic at 68 mol% NaCl and 439°± 2°C were found in the NdCl3–NaCl system. On the basis of agreements between the activities calculated by the Clausius–Clapeyron equation and Temkin's model using the present data for the NdCl3–CaCl2 system and the literature data for the PrCl3–CaCl2 system, the melts in the former system consist of Nd3+, Ca2+, and Cl ions and in the latter system of Pr3+, Ca2+, and Cl ions. The above approach indicates the presence of Na+, Cl, and NdCl2-5 ions in the NaCl-rich melts and Nd3+, Cl, and NdCl4 in the NdCl3-rich melts in the NdCl3–NaCl system. Analogous ions were indicated in the melts of the PrCl3–NaCl system.  相似文献   

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