Kinetics of anatase transition to rutile TiO2 from titanium dioxide precursor powders synthesized by a sol-gel process

Kinetics of anatase transition to rutile TiO₂ from titanium dioxide precursor powders synthesized by a sol-gel process have been studied using differential thermal analysis (DTA), X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED) and high resolution TEM (HRTEM). The DTA result shows residual organic matter decomposed at 436 K. The transition temperature for amorphous precursor powders converted to anatase TiO₂ occurred at 739 K. Moreover, the full anatase transition to rutile TiO₂ occurred at 1001 K. The activation energy of anatase TiO₂ formation was 128.9 kJ/mol. On the other hand, the activation energy of anatase transition to rutile TiO₂ was 328.4 kJ/mol. Mesoporous structures can be observed in the TEM image.     

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。     

The critical size mechanism for the anatase to rutile transformation in TiO2 and doped-TiO2

A series of titania and doped titania materials have been prepared from sol–gel methods using a titanium isopropoxide precursor. Powder X-ray diffraction (PXRD) and secondary electron microscopy (SEM) have been used to follow the anatase to rutile transformation (ART) phase change in this system. PXRD was used to estimate the relative amounts of each phase and the average particle size at a series of temperatures. Importantly, very careful choice of reaction precursors were made so that a wide range of similar samples could be compared, thus removing effects due to preparation. It was found that doping with Si, Zr, Al and tertiary mixtures of these produced an elevated ART temperature whilst Co, Mn and V had the opposite effect. The most likely explanation for the elevation in the ART temperature is the presence of dopant strain fields, which limit mass transport in the system. Lowering of the ART temperature is probably related to creation defect sites, which provide low energy mass transport routes. It was also found that in the majority of samples, the mechanism for phase change was related to attaining a critical particle size. This was measured at around 450 Å independent of the dopant used. Results are discussed in terms of previous work.     

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.     

钛液水解工艺对金红石二氧化钛消色力的影响

以工业钛液为原料,采用外加晶种常压水解工艺制备了金红石型二氧化钛,研究了水解钛液的组成和操作参数对二氧化钛消色力的影响。实验结果表明：二氧化钛消色力（Tcs）和蓝相光谱值（Scx）随晶种添加量的增加先增大后减小,随判灰延时时间的增加先增大后减小,随钛液F值的增加先稍有增加后明显降低,随钛液二氧化钛质量浓度的增大而增加。在钛液F值（游离硫酸加上与钛结合的硫酸之和与二氧化钛质量浓度的比值）为1.90左右、铁钛比（铁元素与二氧化钛质量浓度的比值）＜0.5、二氧化钛质量浓度为190~200 g/L、晶种添加量（晶种中二氧化钛质量与对应批次水解浓钛液中二氧化钛质量的比值）为2.0%~2.2%、灰点为“基点+20 min”、熟化时间为0~30 min、稀释水在二沸后100 min加入的条件下进行水解,经过一次洗涤—漂白—二次洗涤—盐处理—煅烧,所得金红石型二氧化钛的消色力更好。     

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.     

Effect of zircon and anatase titanium dioxide nanoparticles on glass fibre reinforced epoxy with mechanical and morphological studies

In recent years, researchers have been interested in incorporating inorganic nanoparticles into thermosetting epoxy composites to improve their mechanical properties. This research explores the diffusion of ball milled zircon (ZrSiO₄) and anatase TiO₂ nanoparticles with glass fibre reinforced epoxy polymer (GFRP) composites at the same weight percentages (0:0, 2.5:2.5, 5:5, and 7.5:7.5) to improve mechanical properties. The ZrSiO₄ and TiO₂ nanoparticles were prepared by an ultrasonic liquid processor, and composites were fabricated using the compression molding technique. The void percentage was calculated from the theoretical and measured densities of composites. Mechanical tests were conducted in accordance with ASTM standards. The particle sizes of zircon and titanium dioxide were calculated as 70.5 nm and 64.5 nm, respectively, using field emission scanning electron microscopy (FESEM), which reveals the fibre pullout, damaged interfaces, filler dispersion, and voids in specimens. The chemical composition, crystalline structure, and size were determined using X-ray diffraction (XRD). It was found that the GFRP composite with Zircon and TiO₂ incorporated at a concentration of 5:5 wt% has a greater tensile strength of 74.34%, a tensile modulus of 18.14%, a flexural strength of 33.55%, a flexural modulus of 33.61%, a shore "D" hardness of 4.66%, and a capacity to absorb energy of 61.14% in notched specimens with neat GFRP. With filler addition, the percentage of elongation at failure in the 5:5 wt percent for the tensile test is 44.36%, and the flexural test is 24.38% higher than the neat sample. Hence, this work improves the GFRP composites' mechanical and structural properties.     

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.     

深还原钛渣硫酸法制取钛白实验研究

以含钛铁精矿直接还原冶炼的含钛物料（深还原钛渣）为原料,对硫酸法制取颜料级钛白粉的工艺进行了研究。实验结果表明,深还原钛渣具有良好的酸解性能,酸解率可达97%;酸解后得到的钛液过滤性能好;但酸解钛液中氧化镁和氧化铝浓度过高,所以直接以该钛液为原料制得的钛白颜料性能差。采用深还原钛渣和钛精矿按一定比例混合酸解,可以避免钛液杂质含量过高对最终钛白产品质量造成的影响。深还原钛渣较佳用量为不高于钛原料总质量的20%。     

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 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.     

A geometric model of growth for cubic crystals: Diamond

A mathematical and software implementation of a geometrical model of the morphology of growth in a cubic crystal system, such as diamond, is presented based on the relative growth velocities of four low index crystal planes: {100}, {110}, {111}, and {113}. The model starts from a seed crystal of arbitrary shape bounded by {100}, {110}, {111} and/or {113} planes, or a vicinal (off axis) surface of any of these planes. The model allows for adjustable growth rates, times, and seed crystal sizes. A second implementation of the model nucleates a twinned crystal on a {100} surface and follows the evolution of its morphology. New conditions for the stability of penetration twins on {100} and {111} surfaces in terms of the alpha, beta, and gamma growth parameters are presented.     

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.