Immiscibility Area in the System TiO2–ZrO2–SiO2

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.     

A Study of the Phase Relations of ZrO2–TiO2 and ZrO2–TiO2–SiO2

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.     

Preparation of TiO2 Nanoparticles on Different SiO2 Supports by the Adsorption Phase Technique

The influence of supports on the preparation of TiO₂ nanoparticles by the adsorption phase technique is studied in detailed. Series temperature experiments of two types of supports (named as SiO₂ A and B) were used. Energy-dispersive analysis by X-ray indicates that the concentration of TiO₂ on both supports decreases with temperature increasing. TiO₂ quantity on SiO₂ A decreases sharply between 40° and 60°C, whereas the temperature range for SiO₂ B is between 30° and 50°C. X-ray diffraction (XRD) shows that grain size of TiO₂ particles on two SiO₂ surfaces is all below 7 nm. It is also shown by XRD that particles on SiO₂ A decrease sharply as in the quantity curve of TiO₂, but particles on SiO₂ B all change gradually and TiO₂ particles on SiO₂ B are more uniform in transmission electron spectroscopy. The similarly of both supports is considered to be the reason for the similar changes in Ti concentration, and the different characteristics of the internal/external surface lead to variant quantity and grain size, as well as characteristics of TiO₂.     

Degradation of Bioactive Polydimethylsiloxane–CaO–SiO2–TiO2 and Poly(tetramethylene oxide)–CaO–TiO2 Hybrids in a Simulated Body Fluid

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.     

Co-Additions of TiO2 and SiO2 Crystalline Fillers to Tailor the Properties of BaO–ZnO–B2O3–SiO2 Glass for Application to Barrier Ribs of Plasma Display Panels

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.     

Fluoride Model Systems: II, The Binary Systems CaF2–BeF2, MgF2–BeF2, and LiF–MgF2

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.     

Liquid–Solid Equilibria in the System NiO–TiO2–SiO2 in the Temperature Range 1430° to 1660°C

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.     

Sol–Gel-Processed SiO2/TiO2/Methylcellulose Composite Materials for Optical Waveguides

SiO₂–TiO₂–methylcellulose (MC) composite materials processed by the sol-gel technique were studied for optical waveguide applications. Dense, crack-free and homogeneous films as thick as 2 μm were obtained via the organic binder MC-assisted sol–gel process and single coating with low-temperature treatment. Light waveguiding in such hybrid film was demonstrated at a wavelength of 650 nm. About 1.1 dB/cm or lower propagation loss for the SiO₂ (80 mol%)–TiO₂ (20 mol%)–MC (22 wt%) film can be achieved. The effects of thermal treatment on the structure and properties of the gel films were also investigated.     

Chemical Interactions Between Cement and E-Glass Fibers with a CaO–BaO–SiO2–TiO2 Coating

E-glass fibers were coated with a 15CaO–15BaO–20SiO₂–50TiO₂ thin film by the sol–gel method. Mechanical and chemical tests were performed on coated and uncoated fibers in cement and cement extract solutions to investigate the interactions between cement and gel-glass film. The results show that the resistance of E-glass fibers to the alkali cement medium is enhanced by the 15CaO–15BaO–20SiO₂–50TiO₂ coating. The significant roles of TiO₂, CaO, and BaO in the protection fibers from the alkaline attack of cement are described. Some evidence is presented that the alkali corrosion of the coated fibers results in the formation of a thick and compact Ti film that suppresses further corrosion reaction.     

Preparation and Physical Properties of Radiofrequency-Sputtered Amorphous Films in the System AlPO4–TiO2

Amorphous films in the system AlPO₄–TiO₂ were prepared by an rf-sputtering method, and their physical properties, such as density, refractive index, and thermal expansion coefficient, and the infrared absorption spectra were measured. The thermal expansion coefficient increased linearly with increasing TiO₂ content. The results of the molar refractivity and the infrared absorption spectra indicated that the coordination number of titanium ions in these films is higher than that in SiO₂–TiO₂ glasses with a negative thermal expansion, in which Ti⁴⁺ ions are tetrahedrally coordinated. In order to confirm the coordination state of the titanium ions in these amorphous films, titanium K -band emission spectra were obtained by X-ray emission spectroscopy, revealing sixfold coordination. The higher coordination state of Ti⁴⁺ was considered to account for these amorphous films not exhibiting negative thermal expansion, as in the SiO₂–TiO₂ system.     

Influence of TiO2 on Properties of Glasses in the System K2O–PbO–SiO2–TiO2 and Its Relation to Structure

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.     

Formation and Sintering of TiO2 (Anatase) Solid Solution in the System TiO2-SiO2

In the TiO₂-SiO₂ system, anatase solid solutions (ss) containing up to similar/congruent ∼15 mol% SiO₂ are formed in the as-prepared state by the hydrazine method. The lattice parameters a and c decrease linearly from 0.3785 to 0.3776 nm and from 0.9514 to 0.9494 nm, respectively, with increased SiO₂ content. At high temperatures, the solid solutions by transformation decompose into rutile and amorphous SiO₂. The anatase(ss) powders have been characterized for particle size and surface area. They consist of very fine particles (7-25 nm). Surface areas at low temperatures are very high and do not drop below 60 m²/g at 1000°C. Nanostructured anatase(ss) ceramics, with greaterthan/equal to 99.5% of theoretical density and an average grain size of 72 nm, have been fabricated by hot isostatic pressing for 1 h at 850°C and 196 MPa. Their mechanical and electrical properties have been examined.     

Structural Changes of Sol–Gel-Derived TiO2–SiO2 Coatings in an Environment of High Temperature and High Humidity

Structural changes in sol–gel-derived TiO₂–SiO₂ coatings were found to proceed in an environment of high temperature and high humidity as follows: (1) dissociation of Si–O–Ti bonds in the coating by the attack of water vapor, (2) formation of Ti–O–Ti bonds, and (3) nucleation and growth of anatase TiO₂. The coating obtained with the addition of poly(ethylene glycol), PEG, reacts with water vapor more easily than the coating obtained without PEG, since the former is more porous than the latter due to the decomposition of PEG during heat treatment.     

Synthesis, Densification, and Phase Evolution Studies of Al2O3–Al2TiO5–TiO2 Nanocomposites and Measurement of Their Electrical Properties

Alumina–aluminum titanate–titania (Al₂O₃–Al₂TiO₅–TiO₂) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as-synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al₂O₃–TiO₂ nanocomposite, while at a higher temperature (1300°C) an Al₂O₃–Al₂TiO₅–TiO₂ nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties.     

Phase Equilibria in the System CaO-TiO2–SiO2

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.     

Preparation of NiAl2O4/SiO2 and Co2+-Doped NiAl2O4/SiO2 Nanocomposites by the Sol–Gel Route

NiAl₂O₄/SiO₂ and Co²⁺-doped NiAl₂O₄/SiO₂ nanocomposite materials of compositions 5% NiO – 6% Al₂O₃– 89% SiO₂ and 0.2% CoO – 4.8% NiO – 6% Al₂O₃– 89% SiO₂, respectively, were prepared by a sol–gel process. NiAl₂O₄ and cobalt-doped NiAl₂O₄ nanocrystals were grown in a SiO₂ amorphous matrix at around 1073 K by heating the dried gels from 333 to 1173 K at the rate of 1 K/min. The formations of NiAl₂O₄ and cobalt-doped NiAl₂O₄ nanocrystals in SiO₂ amorphous matrix were confirmed through X-ray powder diffraction, Fourier transform infrared spectroscopy, differential scanning calorimeter, transmission electron microscopy (TEM), and optical absorption spectroscopy techniques. The TEM images revealed the uniform distribution of NiAl₂O₄ and cobalt-doped NiAl₂O₄ nanocrystals in the amorphous SiO₂ matrix and the size was found to be ∼5–8 nm.     

The System KAlSiO4–Mg2SiO4–KAlSi2O6

Schairer's study (1954) on phase relations in the system KalSi₂O₆–Mg₂SiO₄–SiO₂ was extended to include the system KalSiO₄–Mg₂SiO₄–KalSi₂O₆. It is shown that this join is ternary; however, the relatively high vapor pressure of the condensed phases prohibits study by the usual quenching techniques. The apparent intersection of the (KalSiO₄–Mg₂SiO₄–SiO₃) join with the primary phase volume of spinel is attributed to loss of the alkali-silicate constituents by vapor transport. This results in the effective bulk composition being moved away from this join toward the primary phase volume of spinel in the system K₂O–MgO–Al₂O₃–SiO₂.     

Direct Formation and Photocatalytic Performance of Anatase (TiO2)/Silica (SiO2) Composite Nanoparticles

Anatase (TiO₂)/silica (SiO₂: 23.9–27.7 mol%) composite nanoparticles were directly synthesized from (i) the reaction of titanyl sulfate (TiOSO₄) and sodium metasilicate (Na₂SiO₃) under mild hydrothermal conditions, (ii) the acidic precursor solutions of TiOSO₄ and tetraethylorthosilicate (TEOS) by thermal hydrolysis, and (iii) the metal alkoxides, i.e., tetraisopropoxide (TTIP) and TEOS, by the sol–gel method. Their photocatalytic activities were evaluated by measurements of the relative concentration of methylene blue after UV irradiation. The as-prepared TiO₂/SiO₂ composite nanoparticles showed far more improved photocatalytic activity than the pure anatase-type TiO₂. The composite nanoparticles formed from (i) TiOSO₄ and Na₂SiO₃ as well as those from (ii) TiOSO₄ and TEOS showed fairly good photocatalytic activity, and it was better than that of those synthesized from (iii) the metal alkoxides, which was suggested to be due to the difference in crystallinity of the anatase.     

Effect of Sintering Aids on Microstructures and PTCR Characteristics of (Sr0.2Ba0.8)TiO3 Ceramics

The effects of liquid-phase sintering aids on the microstructures and PTCR characteristics of (Sr_0.2Ba_0.8)TiO₃ materials have been studied. The grain size of sintered materials monotonically decreases with increasing content of Al₂O₃–SiO₂–TiO₂ (AST). The ultimate PTCR properties with ρ_ht/ρ_rt as great as 10^5.61 are obtained for fine-grain (10-μm) samples, which contain 12.5 mol% AST and were sintered at 1350°C for 1.5 h. The quantity of liquid phase formed due to eutectic reaction between AST and (Sr,Ba)TiO₃ is presumably the prime factor in determining the grain size of samples. The grains grow rapidly at the sintering temperature in the first stage until the liquid phase residing at the grain boundaries reaches certain critical thickness such that the liquid–solid interfacial energy dominates the mechanism of grain growth.     

Fabrication and Microstructure Characterization of Continuous Porous TiO2/Al2O3 Composite Membrane

Using a multipass extrusion process, continuous porous Al₂O₃ body (∼41% porosity) was produced and used as a substrate to fabricate continuous porous TiO₂/Al₂O₃ composite membrane. The diameter of the continuous pores of the porous Al₂O₃ body was about 150 μm. The TiO₂ nanopowders dip coated on the continuous pore-surface Al₂O₃ body existed as rutile and anatase phases after calcination at 520°C in air. However, after aging of the fabricated continuous porous TiO₂/Al₂O₃ composite membrane in 20% NaOH at 60°C for 24 h, a large number of TiO₂ fibers frequently observed on the pore surface. The diameter of the TiO₂ fibers was about 150 nm having a high specific surface area. However, after 48-h aging period, the diameter of the TiO₂ fibers increased, which was about 3 μm. Most of the TiO₂ fibers had polycrystalline structure having nanosized rutile and anatase crystals of about 20 nm.