CaO TiO2 Research Articles

Direct Production of Ti–Fe Alloy in Liquid by Electrowinning in Molten Slag

Aiming at the direct production of Ti–Fe alloy, its direct electrowinning has been attempted in a CaF2–CaO–TiO2–FeO bath by using a direct-current electro-slag remelting unit. The experiments were carried out in the slag where the molar ratio of CaO to TiO2 was fixed as 1.5, and the influence of the molar ratio of FeO to TiO2 was mainly investigated. The experimental results proved that Ti–Fe alloy in liquid could be obtained at the limiting bath compositional range. At the molar ratio of FeO to TiO2 was 0.90, both the Ti content in the deposit and the cathodic current efficiency were the best under the conditions in this study; the Ti content reached about 50 wt%, and the cathodic current efficiency also did about 50% at best.

Hydrothermal formation and conversion of calcium titanate species in the system Na 2O–Al 2O 3–CaO–TiO 2–H 2O

The hydrothermal formation and conversion of titanate species in the system Na 2O–Al 2O 3–CaO–TiO 2–H 2O was investigated based on the thermodynamic calculation and systematic experiments. Experimental results show that the reaction product of anatase with aluminate solution is sodium tri-titanate (Na 2O·3TiO 2), and that kassite (CaO·2TiO 2·H 2O) is formed by the reaction of sodium tri-titanate with calcium hydroxide (Ca(OH) 2) and sodium aluminate solution with high free caustic concentration at elevated temperatures. The results also show that there are two reaction paths for the formation of perovskite (CaTiO 3), one is the direct reaction of sodium tri-titanate with calcium hydroxide, and the other is the conversion of kassite with calcium hydroxide and sodium aluminate solution at elevated temperatures. In addition, the aluminum species in the sodium aluminate solution play a very important role in the process of kassite formation and its conversion to perovskite. The findings provide a potential method for the efficient preparation of titanate species and enhance the understanding of the scaling of heat exchanger surfaces in the Bayer process alumina refinery which is a result of titanate formation.

Titanium and Strontium-doped Phosphate Glasses as Vehicles for Strontium Ion Delivery to Cells

This study investigated the use of a Ti-containing quaternary phosphate glass system P(2)O(5)-Na(2)O-CaO-TiO(2) as a vehicle for strontium ion delivery to cells. Four glass compositions were manufactured: 0.5P(2)O(5)-0.15Na(2)O-0.05TiO(2)-(0.3 - x)CaO-xSrO (x = 0, 0.01, 0.03, and 0.05). Structural characterization revealed that sodium calcium phosphate is the dominant phase in all the glasses. Degradation studies demonstrated highly linear glass degradation, with Sr-containing glasses degrading at higher rates than the Sr-free glass. Biocompatibility studies using MG63 cells showed that the Sr-containing glasses possess excellent cell attachment and growth, particularly over short periods (~4 days).

Synthesis and photoluminescence of Ca–(Sn,Ti)–Si–O compounds

The phase relation of the compounds prepared in the CaO–SnO 2–SiO 2 system at 1673 K and in the CaO–TiO 2–SiO 2 system at 1573 K was investigated in order to explore new Ti 4+-activated stannate phosphors. Solid solutions of Ca(Sn 1− x Ti x )SiO 5 and Ca 3(Sn 1− y Ti y )Si 2O 9 were synthesized at x = 0–1.0 and y = 0–0.10, respectively, and their crystal structures were analyzed by powder X-ray diffraction. Photoluminescence of these solid solutions was observed in a broad range of a visible light wavelength region under ultraviolet (UV) light excitation. The peaks of the emission band of Ca(Sn 0.97Ti 0.03)SiO 5 and Ca 3(Sn 0.925Ti 0.075)Si 2O 9 were at 510 nm under excitation of 252 nm and at 534 nm under excitation of 258 nm, respectively. The absorption edges estimated by the diffuse reflectance spectra were at 300 nm (4.1 eV) for CaSnSiO 5 and at 270 nm (4.6 eV) for Ca 3SnSi 2O 9, suggesting that the excitation levels in Ca(Sn 1− x Ti x )SiO 5 were above the band gap of the host, although the levels in Ca 3(Sn 1− y Ti y )Si 2O 9 were within the band gap and near the conduction band edge.

Hydroxyapatite Coating on Ti-6Al-4V Alloy by an Electrolytic Process and with Heat-Treatment

The effect of the heat-treatment on the calcium phosphate deposited on Ti-6Al-4V substrate by an electrolytic process has been investigated. The calcium phosphate were deposited in a 0.04M Ca(H2PO4)2･H2O (MCPM) solution on Ti-6Al-4V substrate at 60 °C, 10V and 80 Torr for 1h, and calcined at different temperature for 4h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterized the deposited samples. The XRD pattern of as-deposited sample contain the phase of dicalcium phosphate (DCPD) and HAP. When calcined at 400 °C for 4 h, the DCPD phase is vanished and HAP becomes the major phase. The XRD pattern reveals that the intensity of HAP and Ca2P2O7 (CPP) decreases, but the β-TCP, CaO and rutile TiO2 also shows up.

Effect of ZrO 2 addition on crystallization behaviour, porosity and chemical–mechanical properties of a CaO–TiO 2–P 2O 5 microporous glass ceramic

2–6 mol% ZrO 2 was added to a base glass composition of P 2O 5 31.25, CaO 43.75, TiO 2 25 (mol%) at the expense of TiO 2. The prepared glasses were crystallized to bulk glass ceramics containing the major phases of β-Ca 3(PO 4) 2 and CaTi 4(PO 4) 6. DTA was utilized to determine the appropriate phase separation–nucleation and crystallization temperatures. The crystalline products and resulting microstructures were examined by XRD and SEM. The β-Ca 3(PO 4) 2 phase was dissolved out by leaching the resulting glass ceramics in HCl, leaving a porous skeleton of CaTi 4(PO 4) 6. It was shown that ZrO 2 addition resulted in reduction of volume porosity and mean pore diameter while the specific surface area was increased. The smallest median pore diameter and largest surface area were 8.6 nm and 32 m 2 g −1 respectively obtained for the specimen containing 6 mol% ZrO 2. The ZrO 2 addition also improved the chemical durability and bending strength of porous glass ceramics.

Phase separation, crystallization and leaching of microporous glass ceramics in the CaO–TiO2–P2O5 system

Microporous glass ceramics belonging to the CaO–TiO 2 –P 2 O 5 system were prepared with the assumption of a 2:1 mole ratio for β-Ca 3 (PO 4 ) 2 :CaTi 4 (PO 4 ) 6 , the anticipated crystalline phases in the end product. The glasses formulated according to the above composition were melted and cast onto a steel mold and were crystallized to glass ceramics containing the above phases. Dilatometric/differential thermal analysis (DTA) techniques were utilized to determine the appropriate phase separation–nucleation and crystallization temperatures. The crystalline products and resulting microstructures in various stages of process were determined and observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By leaching the resulting glass ceramics in HCl, β-Ca 3 (PO 4 ) 2 was dissolved out leaving a porous skeleton of CaTi 4 (PO 4 ) 6 . It was found that the volume porosity, specific surface area and mean pore diameter of microporous glass ceramics can be managed through the proper selection of heat treatment conditions. In the optimized conditions for fabricating glass ceramics of minimum mean pore size the values of 41 ± 4%, 26 ± 3 m 2 /g and 14.3 ± 2 nm were obtained for porosity, surface area and pore diameter respectively.

Highly active NiO–CaO photocatalyst for degrading organic contaminants under visible-light irradiation

Abstract A series of NiO–CaO photocatalysts have been successfully prepared by a precipitation–calcination method. The specimen was characterized by powder X-ray diffraction and UV–vis diffuse reflectance spectra. The UV–vis diffuse reflectance spectra revealed that the NiO–CaO samples exhibited absorptions in a wide visible-light range of 400–600 and 700–800 nm. These results showed that the NiO–CaO samples might possess excellent photocatalytic performances in the wide visible-light region. By using photocatalytic degrading methyl blue as the model reaction, the NiO–CaO samples showed higher photocatalytic activity than those of NiO, CaO, and commercial TiO 2 under visible-light illumination.

Novel porous TiO 2 glass-ceramics with highly photocatalytic ability

A porous TiO 2 glass-ceramics with high photo-oxidative activity was successfully obtained from the SiO 2–Al 2O 3–B 2O 3–CaO–TiO 2 glass system. Rutile-type TiO 2 was observed in the crystallization temperature range of 973–1173 K. The band gap of the glass-ceramics coincided approximately with that of rutile-type TiO 2. The photocatalytic activity of this glass-ceramics was about four times larger than that of a TiO 2-coated photocatalyst fabricated by the sol–gel process. Furthermore, as this porous TiO 2 glass-ceramics contained TiO 2 in composition form, it could prevent peeling of the TiO 2 from the substrate. As well, this glass-ceramics can be easily shaped into sheets, tubes, rods, etc.

Pyrochlore formation, phase relations, and properties in the CaO–TiO 2–(Nb,Ta) 2O 5 systems

Phase equilibria studies of the CaO:TiO 2:Nb 2O 5 system confirmed the formation of six ternary phases: pyrochlore (A 2B 2O 6O′), and five members of the (110) perovskite-slab series Ca n (Ti,Nb) n O 3 n +2, with n=4.5, 5, 6, 7, and 8. Relations in the quasibinary Ca 2Nb 2O 7−CaTiO 3 system, which contains the Ca n (Ti,Nb) n O 3 n +2 phases, were determined in detail. CaTiO 3 forms solid solutions with Ca 2Nb 2O 7 as well as CaNb 2O 6, resulting in a triangular single-phase perovskite region with corners CaTiO 3–70Ca 2Ti 2O 6:30Ca 2Nb 2O 7–80CaTiO 3:20CaNb 2O 6. A pyrochlore solid solution forms approximately along a line from 42.7:42.7:14.6 to 42.2:40.8:17.0 CaO:TiO 2:Nb 2O 5, suggesting formulas ranging from Ca 1.48Ti 1.48Nb 1.02O 7 to Ca 1.41Ti 1.37Nb 1.14O 7 (assuming filled oxygen sites), respectively. Several compositions in the CaO:TiO 2:Ta 2O 5 system were equilibrated to check its similarity to the niobia system in the pyrochlore region, which was confirmed. Structural refinements of the pyrochlores Ca 1.46Ti 1.38Nb 1.11O 7 and Ca 1.51Ti 1.32V 0.04Ta 1.10O 7 using single-crystal X-ray diffraction data are reported ( Fd3 m (#227), a=10.2301(2) Å (Nb), a=10.2383(2) Å (Ta)), with Ti mixing on the A-type Ca sites as well as the octahedral B-type sites. Identical displacive disorder was found for the niobate and tantalate pyrochlores: Ca occupies the ideal 16 d position, but Ti is displaced 0.7 Å to partially occupy a ring of six 96 g sites, thereby reducing its coordination number from eight to five (distorted trigonal bipyramidal). The O′ oxygens in both pyrochlores were displaced 0.48 Å from the ideal 8 b position to a tetrahedral cluster of 32 e sites. The refinement results also suggested that some of the Ti in the A-type positions may occupy distorted tetrahedra, as observed in some zirconolite-type phases. The Ca–Ti–(Nb,Ta)–O pyrochlores both exhibited dielectric relaxation similar to that observed for some Bi-containing pyrochlores, which also exhibit displacively disordered crystal structures. Observation of dielectric relaxation in the Ca–Ti–(Nb,Ta)–O pyrochlores suggests that it arises from the displacive disorder and not from the presence of polarizable lone-pair cations such as Bi 3+.

Preparation of porous titanium phosphate glass-ceramics for NH 3 gas adsorption with self-cleaning ability

Porous glass-ceramics with a skeleton of γ-Ti(HPO 4) 2·2H 2O crystals are derived from glasses in the Li 2O–CaO–TiO 2–P 2O 5 system by utilizing spinodal-type phase separation, crystallization and subsequent acid treatment of the resulting glass-ceramics. The glass-ceramics have both micro-sized (1–2 μm) and nano-sized pores (5–30 nm), and they adsorb polar molecules. In the present work, porous TiO 2 layers of 200–500 nm thickness were successfully deposited on the surfaces of the glass-ceramics by an infiltration of Ti(OCH(CH 3) 2) 4 and water vapor treatment at 100 °C under 100% relative humidity. X-ray diffractometry and laser Raman spectroscopy revealed the formation of anatase crystals. The resulting anatase-modified porous glass-ceramics show high activities for NH 3 adsorption as well as for photodecomposition of the adsorbed NH 3 molecules.

Physicochemical studies of phosphate based P2O5–Na2O–CaO–TiO2 glasses for biomedical applications

Glasses P2O5–Na2O–CaO–TiO2 with different TiO2 contents and fixed P2O5 (45wt%) and CaO (24wt%) have been prepared employing the normal melting and annealing technique. Measurements such as ultrasonic velocity, attenuation, solubility and pH have been carried out in all the compositions of the glasses. It is interesting to note that the above measured ultrasonic parameters exhibit an abnormal behavior (minimum) at 0.5wt% of TiO2 content, beyond which an increase in these parameters with increasing TiO2 content is observed. The maximum pH values and Ca2+ ion release have been observed for the TiO2 free glass those compositions with and the low TiO2(⩽1.0wt%) content. As the content of the TiO2 increases, the solubility of the glasses decreases. The observed weight loss reveals two stages of phosphate dissolution kinetics i.e. the first stage, in which the weight loss is proportional to t1/2, and a second stage in which a linear behavior is observed.

Characterization of CaO–TiO2 and V2O5/CaO–TiO2 catalysts and their activity for cyclohexanol conversion

Influence of CaO on TiO2 (anatase) phase stabilization and dispersion behaviour of V2O5 over CaO–TiO2 mixed oxide support have been investigated using XRD, FTIR, Raman, XPS, and BET surface area techniques. The CaO–TiO2 binary oxide (1:1 molar ratio) was synthesized by a homogeneous co-precipitation method from ultrahigh dilute solutions of the corresponding chlorides and calcined at various temperatures from 723 to 1273K. On the calcined CaO–TiO2 support (723K) various amounts of V2O5 (2.5–10wt.%) were deposited from ammonium metavanadate by a wet impregnation method and calcined at different temperatures. Conversion of cyclohexanol to cyclohexanone/cyclohexene was performed as a model reaction to assess the acid–base properties of the prepared catalysts. The CaO–TiO2 composite oxide exhibits reasonably high specific surface area and high thermal stability up to 1273K retaining titania-anatase phase. The deposited V2O5 over CaO–TiO2 support is present mostly in a dispersed form. Further, a strong and preferential interaction between the basic CaO and the dispersed V2O5 leads to the formation of CaVO3 and the physicochemical properties of the prepared catalysts are clearly reflected in their catalytic activity.

Surface-Enhanced Raman Spectroscopy Using Silver-Coated Porous Glass-Ceramic Substrates

Surface-enhanced Raman scattering (SERS) has been studied using a silver-coated porous glass-ceramic material as a new type of substrate. The porous glass-ceramic is in the CaO-TiO2-P2O5 system prepared by controlled crystallization and subsequent chemical leaching of the dense glass-ceramic, leaving a solid skeleton with pores ranging in size from 50 nm to submicrometer. Silver was coated on the surface of the porous glass-ceramic by radio frequency (RF) sputtering or e-beam evaporation in vacuum. SERS spectra of excellent quality were obtained from several dyes and carboxylic acid molecules, including rhodamine 6G, crystal violet, isonicotinic acid, and benzoic acid, using this new substrate. This new substrate showed a good compatibility with these molecules. The porous glass ceramic with a nanometer-structured surface accommodated both test molecules and silver film. The absorbed molecules were therefore better interfaced with silver for surface-enhanced Raman scattering.

Models for optical properties in the system Li2O–Na2O–MgO–CaO–TiO2–ZrO2–SiO2

Using experimental design, 15 high titania glasses in the system Li2O–Na2O–MgO–CaO–TiO2–ZrO2–SiO2 were prepared and their refractive indices, dispersions and densities determined. Polynomial models were derived to describe the relationships between properties and glass composition. The refractive index and dispersion models were linear, while the density model required second degree terms for an adequate fit to experiments.

Mass Spectrometric Study of the Thermodynamic Properties of Melts in the CaO–TiO2–SiO2System

The composition of the vapor over melts in the CaO–TiO2–SiO2 system, activities of the melt components, and Gibbs energies of formation are determined by high-temperature mass spectrometry upon evaporation from tungsten cells in the temperature range 1800–2200 K. It is demonstrated that the positive deviation of the SiO2 activity from ideal behavior in melts of the CaO–TiO2–SiO2 system at constant mole fraction ratios CaO/TiO2 equal to 2.33 and 1.5 is caused by the presence of titanium dioxide. The SiO2 activity decreases in the case when CaO is added to SiO2 and increases when TiO2 is introduced into the system under investigation.

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.

The systems Zr(Nb,Ti)( R)O 2− δ, R=Yb, Ca—optimization of mixed conductivity and comparison with results of other systems ( R=Y and Gd)

In this work we address the optimization of mixed conductivity in fluorite compounds based on zirconia. Phase relations of the new systems YbO 1.5–NbO 2.5–ZrO 2, and CaO–NbO 2.5–ZrO 2 are presented. The limit of the cubic defect fluorite phase in YbO 1.5–NbO 2.5–ZrO 2 closely resembles that of the system YO 1.5–NbO 2.5–ZrO 2, whilst in CaO–NbO 2.5–ZrO 2 is narrow extending to include composition Ca 0.255Nb 0.15Zr 0.595O 1.82 at 1500°C. The influence of dopant ion size, charge and composition on ionic conduction is assessed and parallels are drawn with the systems YO 1.5–NbO 2.5–ZrO 2 and YO 1.5–TiO 2–ZrO 2. Comparison of these results with published data on the Ti containing systems CaO–TiO 2–ZrO 2, GdO 1.5–TiO 2–ZrO 2 shows that the highest mixed conducting compositions can only be offered in the system YO 1.5–TiO 2–ZrO 2 out of all the systems here studied.

Preparation of ion exchangers in the hydrogen form from M1+xTi2P3–xSixO12 (M = Li, Na) crystals and glass-ceramics and their characterization

Inorganic ion exchangers in the hydrogen form were prepared by two different methods and their properties were investigated. The first method was a conventional one; the precursors, LiTi2(PO4)3 and Na1+xTi2P3¬xSixO12 (x = 0, 1, 1.5), were prepared by solid-phase reactions and the corresponding ion exchangers in the hydrogen form, HTP(Li) and HTPS(Na) (x = 0, 1, 1.5), were obtained by acid treatment of the precursors. In the other method, Na1+xTi2P3¬xSixO12–β-Ca3(PO4)2 (x = 0, 1) glass-ceramics were first formed by the crystallization of Na2O–CaO–TiO2–P2O5–(SiO2) glasses and then sodium ions in the Na1+xTi2P3¬xSixO12 (x = 0, 1) phases were displaced by protons and the β-Ca3(PO4)2 phase was dissolved out by acid treatments to obtain ion exchangers in the hydrogen form, gcHTPS(Na) (x = 0, 1). The leaching ability of sodium ions from the precursors, the specific surface areas and the ion exchange rates were higher for ion exchangers prepared via glass-ceramics than for the corresponding ion exchangers prepared conventionally. The ion exchangers prepared did not show any specific affinity toward Group 1 metal ions except for HTPS(Na) (x = 1) and gcHTPS(Na) (x = 0), for which a slight affinity toward sodium and/or lithium ions was observed. HTPS(Na) (x = 1) and gcHTPS(Na) (x = 1) were found to be slightly 6Li-specific; the single-stage separation factor, S, for the lithium isotopes was 1.002 and 1.004 under basic conditions at 25 °C respectively. In contrast to the other ion exchangers, HTP(Li) has a layered structure with an interlayer distance of 10.0 A. The S value on HTP(Li) was 1.012 under basic conditions at 25 °C. A strong feature of this system is the fast ion exchange rate; the monovalent ion–monovalent ion exchange equilibrium was attained within three minutes at 25 °C.

Bonding and chemical shifts in aluminosilicate glasses: importance of Madelung effects

A detailed study of the XPS binding energy shifts of Si 2p, O 1s and Zr 3d in a series of aluminosilicate glasses (a three oxide glass: SiO 2–Al 2O 3–CaO, three four-oxide glasses: SiO 2–Al 2O 3–CaO–TiO 2, ZrO 2 or CeO 2, along with a six-oxide glass SiO 2–Al 2O 3–CaO–TiO 2–ZrO 2–CeO 2) is presented. Their composition is such that these glasses have the same mean electronegativity, so that no changes in the atomic charges is expected. The binding energy shifts are interpreted in terms of initial and final state effects, and the balance of charge transfer contribution and electrostatic effects is discussed. Referred to the ternary glass, the binding energy shifts of the Si 2p, O 1s and Zr 3d lines in the complex glasses are due to an initial state effect, as the extraatomic relaxation is similar along the glass series. These shifts originate from electrostatic Madelung effects, likely coming from a structural change induced by the presence of the other oxides TiO 2, ZrO 2 and CeO 2. These structural effects make it impossible to deduce information on the atomic charges directly from the binding energy shifts, even in a qualitative way.