Formation of tin dioxide pore structure

Formation of tin dioxide pore structure has been studied under various hydrogel precipitation conditions. Desired volumes of micro-and mesopores can be obtained when the pH and precipitation temperature are controlled. A relationship between the initial salt hydrolysis rate and the oxide phase nucleation rate appears to be of key importance. Peculiarities of thermal treatment of tin dioxide xerogel are shown.     

Tantalum oxide-modified calcium phosphate coatings on titanium for biomedical applications

A combination of plasma-electrolytic oxidation method with extraction-pyrolytic technique was used for preparation of layered coatings with a developed surface relief. The coating surface is composed of segments enriched in tantalum oxide, alternating with those containing titanium oxides and calcium and phosphorus compounds.     

Formation of titanium dioxide nanostructures in the interlayer space of clay minerals

Kaolin and montmorillonite are intercalated through their consecutive two-stage treatment with dimethyl sulfoxide (DMSO) and TiCl₄ vapors. It is established that, at 293 K, this process is kinetically hindered irrespective of the mobility of adjacent structural layers in the minerals. As the temperature is elevated to 393 K, the first stage markedly accelerates, thus making it possible to synthesize kaolin-DMSO and montmorillonite-DMSO intercalates in real time with interplanar spacings d ₀₀₁ = 11.4 and 23.18 Å, respectively, and the degree of intercalant incorporation up to 40 wt %. The replacement of DMSO by TiCl₄ leads to the formation of kaolin-TiCl₄ (d ₀₀₁ = 13.1 Å) and montmorillonite-TiCl₄ (d ₀₀₁ = 15.3 Å) intercalates, amorphization of the minerals, subsequent hydrolysis of intercalated TiCl₄, and the formation of hydrated titanium dioxide. The thermal transformation of the latter within a temperature range of 573–673 K is accompanied by the formation of anatase nanoclusters possessing high photocatalytic activity.     

Formation and structure of titanium alkyl phosphates

Titanium alkyl phosphates (TiAP) synthesized by the reactions of Ti(SO(4))(2) with monohexyl, monooctyl, and monodecyl phosphates in aqueous media were characterized by various means. The XRD patterns of TiAP showed a strong diffraction peak and two weak ones below 2theta=15 degrees. The TiAP particle prepared using octyl phosphate gave rise to the lattice patterns having uniform alternating spacings of ca. 0.7 and ca. 2.0 nm. When treated at 900 degrees C, TiAP crystallized as TiP(2)O(7). The chemical formula could be shown as (ROPO(3))(2)Ti.0.44H(2)O. These facts suggest that the TiAP is composed of a multilayer alternating bimolecular layer of alkyl phosphates and hydrated titanium phosphate phase. Alkyl groups in the layers were removed by outgassing above 300 degrees C to give the materials having mesopores with a diameter of ca. 2 nm.     

Formation of hydrated titanium dioxide from seeded titanyl sulphate solution

The paper analyses the influence of various kinds and amounts of titanium dioxide nuclei addition to a solution of titanyl sulphate on the conversion degree of TiOSO₄ to hydrated titanium dioxide and sulphuric acid. An industrial solution of titanyl sulphate used to produce titanium white was used in the present investigations. It was found that the course of hydrolysis clearly depended on the investigated parameters. The anatase nuclei calcined at 373 K and 333 K and rutile nuclei increased the degree of titanyl sulphate hydrolysis as compared to non-nucleation hydrolysis. The final degree of hydrolysis was by 1–2 % higher than that achieved without any nuclei addition. The constant rates of both colloidal intermediate and final crystalline products formation were higher in the hydrolysis process with both anatase nuclei after heat treatment at lower temperature and rutile nuclei in comparison to the same processes conducted in the absence of these nuclei. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Adsorption of the halogens on cerium dioxide

Summary CeO₂, alone or mixed with La₂O₃, is used as halogen adsorbent in the determination of carbon and hydrogen. Quantitative data are given on the adsorption of the single halogens on various samples of pure CeO₂ and La₂O₃. Retention of CO₂ and the influence of several parameters of special interest in the carbon and hydrogen determination, have been examined. It has been found that the conditions for optimum adsorption of the halogens are a large surface and relatively low adsorption temperature. Unfortunately these conditions cannot be applied in the determination of carbon and hydrogen.

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Zusammenfassung CeO₂ allein oder im Gemisch mit La₂O₃ wurde als Adsorbens für Halogen bei der CH-Bestimmung verwendet. Quantitative Angaben über die Adsorption der einzelnen Halogene an verschiedenen Mustern von reinem CeO₂ und La₂O₃ wurden gebracht. Die Retention von CO₂ und der Einfluß einzelner Parameter, die für die CH-Bestimmung von besonderem Interesse sind, wurden geprüft. Die besten Bedingungen für die Adsorption der Halogene sind große Oberfläche und relativ niedere Temperatur. Beide Bedingungen können leider bei der CH-Bestimmung nicht eingehalten werden.

     

Effect of silicon dioxide on the formation of the phase composition and pore structure of titanium dioxide with the anatase structure

The formation of the structure of titanium dioxide modified with silicon dioxide, which was introduced as tetraethyl orthosilicate, was studied. It was found that the formation of the nanocrystalline structure of TiO₂ occurred upon the modification of titanium dioxide with silicon dioxide. This nanocrystalline structure of TiO₂ was formed by highly dispersed anatase particles of size 6–10 nm stabilized by silicon oxide layers, which were formed upon the decomposition of tetraethyl orthosilicate. An increase in the modifier concentration resulted in a deceleration of the growth of anatase particles and an increase in the temperature of the phase transition of anatase to rutile. It was found that the anatase phase in the samples containing 5–15 wt % SiO₂ was stable up to 1000°C. The stabilization of highly dispersed anatase particles facilitated the retention of the developed fine-pore structure of xerogels with a pore diameter of 4 nm up to 900°C.     

Electronic conductivity in nonstoichiometric cerium dioxide

The electrical conductivity of sintered specimens of nonstoichiometric CeO_2?x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10^?22 atm). The isothermal compositional dependence of the electrical conductivity of CeO_2?x was determined by combining recently obtained thermodynamic data, x = x(P_O2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression

$\text{σ=410[x]e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{ohm cm}\text{)}{}^{\mathrm{?1}}$

over the temperature range 750–1500°C and from x = 0.001 to x = 0.1.This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentration

$\text{n}{}_{\mathrm{ce}}\text{′}{}_{\mathrm{ce}}\text{=}\text{8x}\text{a}{}_0{}^3$

where n_Ce′Ce is the number of Ce′_Ce per cm³ and a₀ is the lattice parameter and (b) the electron mobility

$\text{μ=5.2(10}{}^{\mathrm{?2}}\text{)e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{cm}{}^2\text{/}\text{V sec}\text{)}$

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The effect of the ionic environment during precipitation on the structure of hydrous titanium dioxide

Summary Samples of titanium dioxide have been prepared by hydrolysis of alkyl titanates in sulphuric acid solution of differing concentrations. The sulphate content of the resulting precipitate has been determined, and the specific surface and pore volume investigated by sorption methods. The results show that the surface properties of the oxide are determined by the conditions of hydrolysis and subsequent precipitation. It has been found possible to reproduce within a few per cents the surface area and the pore volume of the samples. A model has been put forward to account for the observed phenomena, and an equation relating the specific surfaceS of the precipitate with the activityn of sulphate ions in the hydrolysing medium has been deduced:S=S ₀−k√n whereS ₀ andk are constants.

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Zusammenfassung Proben von Titandioxyd wurden durch Hydrolyse von Alkylanaten in Schwefels?urel?sung verschiedener Konzentration pr?pariert. Die Sulfatgehalte des resultierenden Niederschlags wurden bestimmt und die spezifische Oberfl?che und das Porenvolumen durch Sorptionsmethoden untersucht. Die Ergebnisse zeigen, da\ die Oberfl?cheneigenschaften des Oxydes durch die Bedingungen der Hydrolyse und die anschlie\ende F?llung bestimmt werden. Es war m?glich, die Oberfl?che und das Porenvolumen der Proben innerhalb weniger Prozente zu reproduzieren. Es wurde ein Modell entworfen, die beobachteten Ph?nomene zu erkl?ren, und eine Gleichung abgeleitet, die die spezifische Oberfl?cheS des Pr?zipitates mit der Aktivit?tn der Sulfationen im hydrolysierenden Medium in Beziehung setzt:S=S ₀−k√n;S ₀ undk=const.

     

Thermodynamics of adsorption of cerium on lead dioxide

Adsorption of cerium on lead dioxide from aqueous solutions has been studied as a function of shaking time, amount of adsorbent, pH, concentration of the adsorbate and temperature. The adsorption process is endothermic and the distribution coefficient (K_D) increases with increasing temperature. The data fit very well the Langmuir, Freundlich, and Dubinin-Raduskevich Isotherms and their corresponding constants were calculated. H^o and S^o were calculated from the slope and intercept of plots of lnK_D vs. 1/T. G^o values decreases with increasing temperature, showing that the adsorption of Ce(III) is more favorable at high temperature. The endothermacity of the adsorption process is discussed.     

High-temperature capture of molecular hydrogen by cerium dioxide

Conclusions The high-temperature activated chemisorption of hydrogen on reduced cerium dioxide, i.e., CeO_1.85, has been discovered. Appreciable desorption of the chemisorbed hydrogen occurs only at 350°C and is completed at 700°C. This type of strong chemisorption of hydrogen can be classified as the high-temperature capture of molecular hydrogen by cerium dioxide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2194–2196, October, 1979.     

Visible spectrum of titanium dioxide

The electronic spectrum in the region 17?500 cm(-1) to 18?850 cm(-1) of a cold molecular beam of TiO(2) has been investigated using laser induced fluorescence (LIF) and mass-resolved resonance enhanced multi-photoionization (REMPI) spectroscopy. Bands at 18?412 cm(-1), 18?470 cm(-1) and 18?655 cm(-1) were recorded at a resolution of 35 MHz, rotationally analyzed, and assigned as the ?(1)B(2) (0,1,2) ←X[combining tilde](1)A(1) (0,0,0), ?(1)B(2) (1,0,0) ←X[combining tilde](1)A(1) (0,0,0) and ?(1)B(2) (1,1,0) ←X[combining tilde](1)A(1) (0,0,0) transitions. The dispersed fluorescence from the ?(1)B(2) (0,1,2) and ?(1)B(2) (1,0,0) levels were combined with previous results to produce an improved set of vibrational parameters for the X[combining tilde](1)A(1) state. The optical Stark effect in the ?(1)B(2) (0,1,2) ←X[combining tilde](1)A(1) (0,0,0) and ?(1)B(2) (1,0,0) ←X[combining tilde](1)A(1) (0,0,0) bands were recorded and combined with earlier results for ?(1)B(2) (1,1,0) ←X[combining tilde](1)A(1) (0,0,0) to determine the permanent electric dipole moment for these states. The origin and harmonic vibrational constants for the ?(1)B(2) state are determined to be: T(000) = 17?593(5) cm(-1), ω(1) = 876(3) cm(-1), ω(2) = 184(1) cm(-1), and ω(3) = 316(2) cm(-1). A normal coordinate analysis was performed and Franck-Condon factors calculated.     

Raman spectra of titanium dioxide

First-order Raman spectra have been recorded at room temperature for the anatase and rutile phases of polycrystalline titanium dioxide using an argon ion laser as exciter. The high-temperature rutile phase was found to be stabilized at temperatures below 450°C. Anatase transforms to rutile phase at ～750°C. All the Raman active fundamentals predicted by group theory are observed.