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.     

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.     

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.     

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.     

Quaternary System Al2O3–CaO–MgO–SiO2: I, Study of the Crystallization Volume of Al2O3

Compatibility relations of Al₂O₃ in the quaternary system Al₂O₃–CaO–MgO–SiO₂ were studied by firing and quenching followed by microstructural and energy-dispersive X-ray examination. A projection of the liquidus surface of the primary phase volume of Al₂O₃ was constructed in terms of the CaO, SiO₂, and MgO contents of the mixtures recalculated to 100 wt%. Two invariant points, where four solids coexist with a liquid phase, were defined, and the positions of the isotherms were tentatively established. The effect of SiO₂, MgO, and CaO impurities on Al₂O₃ growth also was studied.     

Dissolution of MgO in CaO–"FeO"–CaF2–SiO2 Slags under Static Conditions

The dissolution of MgO in CaO–"FeO"–CaF₂–SiO₂ slags has been studied in the temperature range 1573°–1673° K under static conditions. The concentration profiles of Mg in the product Mg_1-xFe_xO solid-solution layer as well as slag were determined by EDS analysis. From this, the diffusivities of MgO in the slag and the. interdiffusivities in solid solution were estimated. The dissolution of MgO in CaO–"FeO"–CaF₂–SiO₂ slags increased with CaF₂ content.     

Nanostructure of TiO2 Nano-Coated SiO2 Particles

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.     

SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O), A New Zirconolite Glass–Ceramic System: Crystallization Behavior and Microstructure Evaluation

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°.     

Calcium Hexaluminate and Its Stability Relations in the System CaO–Al2O3–SiO2

By a combination of solid-state sintering and quenching experiments the validity of calcium hexaluminate as a stable phase and the extent of its primary field in the system CaO–Al₂O₃–SiO₂ have been established. The size of the primary field is considerably reduced from that suggested by earlier work. The anorthite-corundum-calcium hexaluminate invariant point has been relocated at 28.0% CaO, 39.7% Al₂O₂, and 32.3% SiO₂ and at 1405°± 5°C.     

Sintering and Crystallization of CaO–Al2O3–ZrO2–SiO2 Glasses Containing Different Amount of Al2O3

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.     

Quaternary System Al2O3–CaO–MgO–SiO2: II Study of the Crystallization Volume of MgAl2O4

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.     

Oxidation State of Chromium in CaO–Al2O3–CrOx–SiO2 Melts under Strongly Reducing Conditions at 1500°C

Equilibrium ratios Cr²⁺/Cr³⁺ of chromium oxide dissolved in CaO–chromium oxide–Al₂O₃–SiO₂ melts have been determined by analysis of samples equilibrated at 1500°C under strongly reducing conditions ( p _o2= 10^−9.56 to 10^−12.50 atm). The majority of the chromium is divalent (Cr²⁺) under these conditions and Cr²⁺/Cr³⁺ ratios at given constant oxygen pressures decrease with increasing basicity of the melts, expressed as CaO/SiO₂ ratios. In addition, Cr²⁺/Cr³⁺ ratios, at a given CaO/SiO₂ ratio, are relatively unaffected by the amount of Al₂O₃ present.     

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.     

Determination of CaO–SiO2–MgO–Al2O3–CrOx Liquidus

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.     

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.     

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.     

Crystallization Behavior of CaO–P2O5 Glass with TiO2, SiO2, and Al2O3 Additions

TiO₂ above 4 mol% is an effective nucleating agent for CaO–P₂O₅ glass which also contains substantial SiO₂ and Al₂O₃ additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β-Ca₂P₂O₇, whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca-P-Ti-Si-Al oxide phase surrounded by impure AlPO₄ dendrites. Metastable calcium phosphate grows on the AlPO₄ dendrites and later transforms to β-Ca₂P₂O₇.     

Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass-Ceramic

The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K₂O–CaO–SrO–BaO–B₂O₃–SiO₂ glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO₂) and pseudowollastonite ((Ca,Ba,Sr) SiO₃) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.