Design guidelines for titania-silica-alumina ceramics with tuned anatase to rutile transformation

Titania-based ceramics with adjustable anatase-rutile fractions were obtained by milling of anatase, quartz and corundum precursors, uniaxial pressing and firing at 1100?°C. The influence of silica and alumina, combined with milling time and compaction pressure, was studied by design of experiments. The L9 orthogonal array with a three-level noise factor was employed. Firing of pure titania at 1100?°C yielded complete anatase to rutile transformation (ART), whereas stabilized samples show that an optimum amount of 9% silica and 33% alumina reduces phase transformation to only about 5?wt% rutile. An extended correlation matrix combined with analysis of variance (ANOVA) was applied to assess the combined effects of quartz, alumina, milling time and uniaxial compressing pressure on relative density, and anatase to rutile transformation. Results show absence of ART after milling, and controlled partial conversion of anatase to rutile after firing. Very good fitting was obtained by multivariate analysis on considering first and second order terms for dependence on silica contents and interactions between silica and each of the remaining factors, including milling time. This empirical dependence could be interpreted on a sound physicochemical basis, allowing the prediction of suitable compositions and processing conditions to obtain rutile-free samples by conventional ceramic processing, and to design ceramic samples with controlled fractions of anatase and rutile.     

熔盐法处理富钛渣制备金红石型TiO_2

工业生产钛白粉的方法主要有硫酸法和氯化法两种,但这两种方法都存在环境污染严重的问题。本文提出了一种常压、低温下钠碱熔盐分解富钛渣制备金红石型二氧化钛的新工艺,从生产源头消除了对环境的污染,实现钛资源的可持续发展。介绍了该反应的制备、水洗、固相离子交换-水解耦合和煅烧过程。实验结果表明,该工艺可以制得理想的金红石型二氧化钛,二氧化钛含量为96.66%。     

Conditions for the production of pigmentary titanium dioxide of rutile and anatase modifications by ilmenite processing with ammonium fluoride

The process of ammoniac precipitation of hydrated titanium dioxide from a solution of ammonium hexafluorotitanate obtained during ilmenite processing by ammonium fluoride with the further sublimation separation of titanium tetrafluoride has been studied. The dehydration of hydrated titanium dioxide has been studied. The phase structure of titanium dioxide, depending on the thermal treatment and precipitation conditions, has been investigated. The size of the sample particles has been studied with the method of electron microscopy. The conditions of rutile and anatase pigments production have been determined.     

Patterning of periodic high-aspect-ratio nanopores in anatase titanium dioxide from titanium fluoride hydrolysis

We report straight pores in titanium dioxide produced by a pattern transfer method with titanium fluoride hydrolysis. The resulting films on fluorine-doped tin oxide had pores with diameters of 30 nm and depths of 500 nm, corresponding to aspect ratios of 1:17.     

Synthesis of few-to-monolayer graphene on rutile titanium dioxide

We demonstrate a chemical-vapor-deposition (CVD)-based approach for the direct synthesis of graphene on insulator with high-dielectric-constant (high-κ). Rutile titanium dioxide (TiO₂), an insulator with reported k value of 80–125, is selected as the growth-initiating layer for graphene. A two-step CVD process is shown to grow graphene directly on TiO₂ crystals or exfoliated ultrathin TiO₂ nanosheets without using any metal catalyst. Various material characterization techniques confirm the growth of few-to-monolayer of graphene. Annealing of the growth substrate at 1100 °C under atmospheric pressure, prior to the low-pressure CVD process, is needed for activating nucleation sites in subsequent graphene synthesis. Electrical behavior of a field-effect transistor fabricated on the graphene/TiO₂ heterostructure shows p-type doping in the CVD-synthesized graphene.     

聚酯用金红石型二氧化钛浆料的分散性能研究

研究了聚对苯二甲酸乙二醇酯(PET)用金红石型二氧化钛(TiO_2)粉体在乙二醇(EG)中的分散性和稳定性,考察了pH值、分散剂六偏磷酸钠(SHMP)用量和研磨时间对金红石型TiO_2浆料分散性能的影响以及在原位聚合法制PET中的应用情况。结果表明:在pH值为6.5~10.0时,金红石型TiO_2水溶液的Zeta电位绝对值小于30 mV,当在其中加入质量分数为1.6%(相对金红石型TiO_2)的SHMP时,其Zeta电位绝对值为50.1 mV;质量分数为50%的金红石型TiO_2-EG浆料(SHMP质量分数为1.0%)研磨时间为20~60 min时,TiO_2在浆料中的分散效果最好;金红石型TiO_2-EG浆料研磨分散后放置48 h,TiO_2粒子粒径分布稍有变宽,没有出现明显的团聚;将没有静置的金红石型TiO_2-EG浆料应用于PET的原位聚合中,所制得的半消光PET切片中的TiO_2粒子分散良好,直径小于1 000 nm,没有出现明显的二次团聚现象。     

Influences of saturation ratios on crystallization of anatase titanium dioxide by a titanium alkoxide hydrolysis

Influences of supersaturation in a tetraethyl orthotitanate (TEOT) solution on the degree of crystallinity of product particles in the case of a hydrolysis reaction of TEOT were indicated and the crystallization phenomena of anatase titanium dioxide (TiO₂) were discussed. Changes in saturation ratios with experimental durations were examined for the various amount of acetylacetone added into a TEOT solution. At the initial stages of TEOT hydrolysis operations, the degree of crystallinity of product particles was lower for the longer hydrolysis durations but the degrees became almost constant in the later stages of TEOT hydrolysis operations, although the supersaturation of titanium oxide in a TEOT solution was remained. Rapid increase in supersaturation of titanium oxide in a TEOT solution and consequent nucleation of amorphous titanium oxide would be restrained by addition of acetylacetone into a TEOT solution because the concentrations of titanium oxide in a saturated TEOT solution increased with the amount of acetylacetone.     

A multiple-scattering approach to the study of X-ray absorption spectra of anatase and rutile

Theoretical computations of the X-ray absorption spectra of the crystalline forms of TiO₂, rutile and anatase, have been carried out in order to analyze the influence of multiple scattering contributions to the absorption coefficient. The cluster size used in the computations after making a detailed study of shell contributions, has been 75 atoms for rutile and 63 for anatase. This work has been envisaged as a suitable starting point to the analysis of experimental data for the more complicated TiO₂ amorphous systems involved in catalytic processes.     

A new model for surface reaction-controlled growth of crystals from solution

A new model is proposed for the surface reaction-controlled growth of crystals from solution. It is based on a concept of ‘travelling’ steps instead of surface diffusion of adsorbed growth units. It is also shown how to take into account the mass transfer effects in the general case of solution growth.     

Theoretical analysis of light scattering properties of encapsulated rutile titanium dioxide pigments in dependent light scattering regime

Using numerical simulation, we study and compare the optical properties of model systems representing three types of scatterer: (a) standard TiO₂ pigments, (b) standard TiO₂ pigments encapsulated by a hard polymer shell and (c) standard TiO₂ pigments encapsulated by a layer of air and a polymer shell. Calculations are performed taking into account multiple and dependent light scattering regimes. Assuming an equivalent amount of TiO₂ in each system, results show that a standard TiO₂ pigment particle encapsulated by air could be a better opacifier than a standard un-encapsulated TiO₂ pigment because the presence of air could provide: (a) additional volume to the existing particle to scatter light; (b) better redistribution of the scattered field in the backward hemisphere; (c) a scattering cross-section less affected by crowding and (d) spacing effects due to the presence of the thin hard polymer shell which is required to encapsulate the air layer. Nonetheless, results also suggest that such benefits could probably not be exploited in real paint systems as encapsulated TiO₂ would only be more efficient than standard TiO₂ in a range of pigment volume filling fractions (PVC) that would not generate enough scattering efficiency to yield complete hiding as required by international standards.     

A mixture of anatase and rutile TiO2 nanoparticles induces histamine secretion in mast cells

Background  

Histamine released from mast cells, through complex interactions involving the binding of IgE to FcεRI receptors and the subsequent intracellular Ca²⁺ signaling, can mediate many allergic/inflammatory responses. The possibility of titanium dioxide nanoparticles (TiO₂ NPs), a nanomaterial pervasively used in nanotechnology and pharmaceutical industries, to directly induce histamine secretion without prior allergen sensitization has remained uncertain.     

Theoretical study of the scattering efficiency of rutile titanium dioxide pigments as a function of their spatial dispersion

We propose an original theoretical framework to model the scattering efficiency of white paint films as a function of the volume fraction and spatial state of dispersion of rutile titanium dioxide pigments, taking into account electromagnetic couplings. Numerical calculations are performed using a multiple T matrix formalism on an “elemental” volume extracted from the bulk of the paint and which we model as pigments and fillers in a polymer matrix. Qualitative studies show that, due to the dependent scattering phenomenon, the size of fillers can modulate the magnitude of loss in scattering efficiency by modifying the spatial state of dispersion of the pigments in the polymer matrix. In particular, fillers whose size is comparable to the dimension of the pigments improve the scattering efficiency by impeding crowding. It is also shown that the optical properties of the bulk material at arbitrary concentration can be approximated by extrapolating the optical properties calculated on a limited number of scatterers.     

A mechanistic growth model for inorganic crystals: Growth mechanism

Inorganic crystals grown from solution find wide application. A mechanistic growth model based on the spiral growth mechanism that operates at low supersaturation on inorganic crystal surfaces is presented. The long‐range electrostatic interactions on inorganic crystal surfaces are captured by methods developed in our previous article (Dandekar and Doherty, AIChE J., in press). The interactions of kink site growth units with the solvent molecules partially determine the growth kinetics. Relevant experimental parameters are systematically accounted for in the expression for the kink incorporation rate along step edges on the crystal surfaces. The growth model accurately predicts the asymmetric growth spirals on the surface of calcite crystals. The effect of supersaturation and ionic activity ratio on the step velocities of the acute and obtuse spiral edges is also correctly captured. This model can be used to predict the shapes of solution grown inorganic crystals and to engineer the growth process to design inorganic solids with functionally desirable shapes. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3720–3731, 2014     

The growth of interfacial compounds between titanium dioxide and bismuth oxide

The growth of interfacial compounds between TiO₂ and Bi₂O₃ during transient liquid phase bonding at 900, 1000 and 1100 °C for various times was investigated. The microstructures and compositions of compounds in joints were analyzed by means of SEM and EPMA. It was found that the compound Bi₄Ti₃O₁₂ forms initially and replaces the Bi₂O₃ interlayer. Bi₂Ti₄O₁₁ then arises at the interface between Bi₄Ti₃O₁₂ and TiO₂ and the metastable Bi₂Ti₂O₇ phase appears last at the interface between Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁. The modes and activation energies of the growth of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ were determined respectively. Holes in the middle of the joint heated at 1100 °C for 24 h were also found.     

改性钛白废渣对选矿废水中硫化物的去除

采用改性钛白废渣去除选矿废水中的硫化物,探讨了改性钛白废渣的投加量、反应时间、pH等因素对选矿废水中硫化物去除效果的影响,通过正交试验得到了改性钛白废渣处理选矿废水的最佳工艺条件.结果表明:对S2-质量浓度为3.58mg/L、pH为8.2的选矿外排废水,在常温条件下加入1.0g/L的改性钛白废渣,充分搅拌40min后,...     

A new kinetic model for titanium dioxide mediated heterogeneous photocatalytic degradation of trichloroethylene in gas-phase

This paper focuses on the kinetics of photocatalytic removal and carbon mineralization of gaseous trichloroethylene (TCE) on near-UV irradiated TiO₂ Degussa P25. Experiments were carried out in a flat-plate photoreactor at TCE inlet concentrations of 100–500 ppmv, relative humidities (RH) of 0–62% and gas residence times of 2.5–60.3 s. Gas residence time distribution (RTD) curves revealed an axial dispersed plug flow in the photoreactor with Peclet numbers above 59.4. For all experimental conditions, the carbon mineralization efficiency (5.1–73.0%) was lower than the removal efficiency (8.6–99.9%) and dichloroacetylchloride (DCAC) was detected as a gas-phase degradation product. TCE removal efficiencies increased with lower TCE inlet concentrations, lower RH and higher gas residence times. Evaluating different kinetic models by least squares analysis, it was shown that the Langmuir–Hinshelwood (LH) model could not give an adequate fitting to the experimental results. A new kinetic model, explicitly taking into account electron–hole pair reactions, was developed based on linear TCE adsorption–desorption equilibrium and first order reaction kinetics. The new kinetic model described the experimental results in a more accurate way, as exemplified by a more randomly distributed set of residuals and by a reduction of the sum of squares (SSQ) by a factor 1.7–8.5. The effect of TCE gas-phase concentration, RH and light intensity on adsorption–desorption kinetics, electron–hole concentrations and chemical conversion rates is discussed.     

Indirect electroreduction of o-nitrophenol to o-aminophenol on titanium dioxide coated titanium electrodes

The heterogeneous catalytic redox behaviour of a titanium dioxide coated titanium electrode surface was investigated with and without o-nitrophenol using cyclic voltammetry. A comparison of the cyclic voltammograms recorded in the absence and in the presence of o-nitrophenol confirmed the catalytic reduction of o-nitrophenol by the surface Ti⁴⁺/Ti³⁺ redox system present on the electrode surface. Preparative scale experiments were also carried out using a Ti/TiO₂ electrode of large surface area and the redox behaviour of the electrode was confirmed by the isolation of o-aminophenol with high current efficiency and yield.     

钛白废酸中金属盐的脱除

介绍了CNⅢ型酸液除盐净化器脱除废酸金属盐的工作原理和工艺流程.工业应用表明,CNⅢ型酸液除盐净化器可实现废酸中的酸盐分离,净化后废酸浓缩可避免管道和换热器堵塞,并可提高废酸的浓缩倍数,具有显著的环境效益和经济效益.     

Formation of anatase from titanium(IV) preasphaltenes complexes under coal liquefaction conditions

Solvent refined coal preasphaltenes from stable complexes with bis(cyclopentadienyl) Ti(IV) dichl-oride. On heating at 450 °C under 6.9 MPa H₂ atmosphere in tetralin, partial conversion of the BTD-preasphaltenes complex to anatase, Ti0₂ is observed. Preasphaltenes complexes of Ti may be involved in hydrodesulphurization catalyst deactivation by Ti0₂ in coal liquefaction processes.     

Selective growth of palladium and titanium dioxide nanostructures inside carbon nanotube membranes

ABSTRACT: Hybrid nanostructured arrays based on carbon nanotubes (CNT) and palladium or titanium dioxide materials have been synthesized using self-supported and silicon-supported anodized aluminum oxide (AAO) as nanoporous template. It is well demonstrated that carbon nanotubes can be grown using these membranes and hydrocarbon precursors that decompose at temperatures closer to 600°C without the use of a metal catalyst. In this process, carbonic fragments condensate to form stacked graphitic sheets, which adopt the shape of the pores, yielding from these moulds' multi-walled carbon nanotubes. After this process, the ends of the tubes remain open and accessible to other substances, whereas the outer walls are protected by the alumina. Taking advantage of this fact, we have performed the synthesis of palladium and titanium dioxide nanostructures selectively inside carbon nanotubes using these CNT-AAO membranes as nanoreactors.