Titania Pigment Research Articles

Low temperature synthesis and characterization of rutile TiO2-coated mica–titania pigments

Rutile TiO2-coated mica–titania pigments were prepared by hydrolysis of TiCl4 ethanolic solution in water at 70 °C. MnO2 as a rutile promoting additive was deposited onto mica prior to TiO2. X-ray diffraction and Raman spectra analysis verified that use of only 2.07 wt% MnO2 with respect to mica weight began to provide a complete rutile TiO2 coating without calcination. The rutile promoting effects of MnO2 could be ascribed to the structural similarity of rutile and pyrolusite. Scanning electron microscopy analysis showed that MnO2 also had a pronounced effect on the morphology of TiO2 coatings. The prior deposition of MnO2 onto mica lead to the formation of rutile TiO2 films composed of highly oriented fine needles on the mica surface and nanoflower structures on the needle structures. The as-obtained rutile-TiO2 coated mica–titanium pigments are shown to exhibit a high photostability under UV illumination.

The effect of iron ions on the anatase–rutile phase transformation of titania (TiO2) in mica–titania pigments

Abstract Rutile TiO 2 -coated mica–titania pigments were prepared by hydrolysis of titanium tetrachloride in the presence of Fe 3+ . After calcination at 700 °C for 2 h, TiO 2 nanolayers in rutile phase were formed on the mica surfaces. The morphology and the anatase–rutile transformation were probed by scanning electronic microscopy (SEM) and X-ray diffraction (XRD) respectively. SEM micrographs show that the dopants enhance the growth of particles of TiO 2 thin layers. The change of lattice parameters confirms that Fe 3+ enter anatase structure and affect the anatase–rutile transformation. For the iron loading regime studied here, the anatase–rutile transformation is inhibited at low dopant levels with respect to undoped titania. While the anatase–rutile transformation is promoted as iron loading is increased. Moreover, synthesized pH value also has a pronounced effect on the anatase–rutile transformation and a highly acidic environment favors the formation of rutile.

Rheology of titania pigment slurry

The influence of polymeric dispersants containing different functional groups on the suspension behaviour of titania pigment slurry was investigated. The dispersants chosen were polyacrylic acid and modified polyacrylamides including homo and copolymers modified with carboxylate and/or hydroxyl groups. The pigment slurry rheology was strongly affected by both pH and dispersant chemical groups. The inorganic coating layer on the titania surface is not smooth, but rough or porous. The surface roughness of the pigment can generate additional contribution to the affinity of the dispersants for adsorption.

SiO2 coated pure and doped titania pigments: low temperature CVD deposition and quantum chemical study

We report the in-flight CVD coating with smooth 1-2 nm thick SiO(2) of pure and doped rutile particles via the oxidation of SiCl(4) vapour introduced in the high temperature zone of a purpose built thermal reactor. The effectiveness of the coatings was determined by a combination of electron microscopy, surface analysis and photocatalytic measurements. No excess Cl was detected on the coated pigment particles indicating the complete oxidation of the SiCl(4) precursor. In conjunction with the experimental outcomes of this optimised deposition process, we use first-principles density functional and semi-empirical quantum chemical calculations to examine the underlying electronic processes which determined the morphology and photocatalytic properties of the coated titania. We highlight the presence of low lying valence electronic states which reduce photocatalytic activity, and as a consequence decrease the population of photo-excited titania electrons which transfer to the surrounding matrix. Born-Oppenheimer molecular dynamics (MD) simulations indicate that the coating process is completed within the order of 10 ps.

Modified silica sols: titania dispersants and co‐binders for silicate paints

PurposeThe purpose of this paper is to investigate epoxysilane‐modified silica sols as surfactant‐free inorganic pigments dispersants and as co‐binders/reinforcing agents for silicate paints.Design/methodology/approachThe performance of epoxysilane‐modified silica sols as dispersants for titania was studied using a polyacrylate‐based dispersant as reference. Furthermore, the effect of the addition of silica sols, with or without silane modification, to potassium silicate on binder properties was investigated.FindingsSignificant improvements were obtained in stability towards settling in water‐based titania pigments pastes and in light‐scattering efficiency (as much as 50 per cent) for the optimal size of the silica particle of 5 nm. The number of silane molecules per nm2 silica particle surface must exceed a critical value of at least 1 molecule of epoxysilane per nm2 particle surface. Additionally, improved stability towards gelling, water resistance and film‐forming properties of sol‐silicate binder mixes were achieved for epoxysilane‐modified silica sols.Research limitations/implicationsOnly epoxysilane‐modified silica sols were studied in this report. Titania pigment was examined but other important pigments (e.g. iron oxides) remain to be studied. In addition, only sol‐silicate mixes were investigated and not fully formulated silicate paints.Practical implicationsA method that produces stable, high‐performing, surfactant‐free inorganic pigments pastes. Furthermore, stable, high‐ratio, sol‐silicate binders can be obtained with improved water resistance and film properties for use in silicate paints.Originality/valueThe present method provides an easy route to obtain stable surfactant‐free inorganic pigments pastes, as well as makes stable, high‐ratio, sol‐silicate mixes/paints.

Temperature-resolved synchrotron X-ray diffraction of nanocrystalline titania in solvent: the effect of Cr–Sb and V–Sb doping

Nanocrystalline titania pigments were produced by high temperature-forced hydrolysis in a coordinating high-boiling solvent (and water for reference). The effect of synthesis conditions and co-doping with Cr–Sb and V–Sb on particle size and anatase-to-rutile transformation (A → R) was studied by temperature-resolved synchrotron X-ray diffraction. The experiments were performed directly on low concentration (3.5 vol.%) as-synthesized suspensions of titania nanoparticles (up to 230 °C) and on the corresponding dried powders (up to 950 °C). Crystallite size of as-synthesized nano-anatase is around 20 nm (glycol) or 70 nm (water); it exhibits a slow growth rate up to the onset temperature of the A → R. Phase composition and crystallite size are drastically influenced by both synthesis conditions and doping. Synthesis in water resulted in the simultaneous occurrence of anatase and brookite; transformation into rutile begins early but with a slower rate with respect to glycol-based samples. Doping affected the A → R, whose onset temperature in undoped titania (700 °C) was lowered to 650 °C (V–Sb) or prevented up to 950 °C (Cr–Sb). Both (V–Sb) and (Cr–Sb) dopings reduced the volume thermal expansion rate of anatase.

Surface pinking in titanium dioxide/lead stabiliser filled PVC profiles

The “pinking” phenomenon which is known to occur in white PVC profiles has been investigated in detail in terms of test evaluations and analysis methods for determining the mechanism and nature of the species responsible. An artificial weathering test method using a Microscal unit with submersion of samples in water was established where colour measurements and FTIR analysis proved the similarity of functional groups present to those in naturally pinked samples. Analysis of the artificially pinked samples using hydroperoxide concentration analysis, fluorescence spectroscopy, microscopic FTIR and scanning electron microscopy showed that artificially pinked samples presented a more extended degree of degradation than samples that remained white during the exposure in the Microscal Unit. Short chain conjugated polyenes were also identified as the most likely functional groups responsible for the development of the pink colour and interactions between the titania pigment and the lead stabilisers would seem to have an influence in the pinking development. In addition, it was found that there was an increase in production of hydroperoxy radicals at the onset of colour development. Addition of trace lead dioxide accelerated the production of pinking. Different titanium dioxide grades used in the PVC profiles showed differences in pinking in the artificial test, also an increase in the titanium dioxide concentration decreased the formation of the pinking colouration in artificial conditions The use of different analysis methods (Microwave Dielectric Spectroscopy and ESR) showed differences in carrier radical production and carrier radical trapping between the pigments used suggesting that a small difference in the coatings could play an important part in the pinking phenomenon. Finally, a mechanism was proposed involving a redox reaction between the titanium dioxide and the lead stabiliser that could facilitate the production of short polyene chains in the PVC matrix producing the pink colouration.

Stabilisation of titania pigment particles with anionic polymeric dispersants

The stabilisation of titania pigment in dry water-based paint films with anionic polymeric dispersants containing carboxylate groups was investigated. The results were compared to those obtained from rheological analysis of titania pigment suspensions. The polymeric dispersants chosen were polyacrylic acid and polyacrylamides copolymer modified with carboxylate groups. AFM and TEM were used to assess the distribution of the titania pigment particles in the surface and bulk, respectively, of the paint films which were then compared to the gloss and surface roughness of these films. In the absence of a dispersant, the pigment distribution in the paint films was not uniform and relatively large pigment aggregates appeared at the surface, resulting in a rough surface and low gloss. However, anionic polymeric dispersants decreased surface roughness and increased the gloss of the dry paint films, with the dispersant concentration considerably enhancing pigment distribution in the paint films. An inverse correlation of paint film gloss with surface roughness was observed. The optimum pigment distribution in the dry state was found at dispersant concentrations much higher than those needed to obtain minimum yield stress in aqueous suspensions. This suggests that in the dry state, electrostatic stabilisation is substantially reduced or possibly absent, therefore a higher dispersant concentration is needed to achieve pigment stabilisation.

Influence of hydrolysis in sulfate process on titania pigment producing

Using industrial titanyl sulfate solution as feedstock, titania white pigment was prepared by self-generated seeded thermal hydrolysis method. The influence of some factors (such as F value, volume ratio of pre-adding water to TiOSO 4, heating rate and pH of pre-adding water) on the structure and pigment properties of the as-prepared slurry metatitanic acid and titania samples were studied. The samples were characterized by XRD, particle size distribution, SEM and pigment properties test. The results show that all samples show anatase phase, and the calcined samples prepared under suitable conditions are with narrow particle size distribution and good pigment properties. All these influencing factors have great impacts on the hydrolysis velocity, nucleation rate, crystal growth rate, particle size distribution, crystal structure and pigment properties. The suitable F value is 1.73–1.93, the volume ratio of pre-adding water and TiOSO 4 solution is 0.28:1, the optimum heating rate is 0.94–1.33 °C/min and pH of the pre-adding water should be at near-neutral range.

Electronic properties of oxygen-deficient and aluminum-doped rutileTiO2from first principles

The electronic properties of stoichiometric, defective, and aluminum-doped rutile $\mathrm{Ti}{\mathrm{O}}_{2}$ have been investigated theoretically with periodic quantum-chemical calculations. Theoretical results obtained with the Perdew-Wang density functional method [Phys. Rev. B 45, 13244 (1992)] and with a density functional-Hartree-Fock hybrid method are compared. Occupied defect states are observed in the band gap of rutile due to the presence of oxygen vacancies, which is in accord with previous theoretical studies and the experimentally observed coloring. For the investigation of aluminum doping, three different situations have been considered: substitution of a single Ti atom by an Al atom, cosubstitution of Ti by Al and O by Cl, and substitution of two Ti by two Al combined with the formation of an O vacancy. In the last two cases, aluminum doping does not introduce band gap states, and the band gap is even increased compared to undoped rutile. We conclude that stoichiometric Al doping reduces pigment coloring induced by oxygen vacancies in rutile and also suppresses the photocatalytic activity of titania pigments.

Removal of chrome spinels from Murray Basin ilmenites by low temperature roasting

Ilmenite concentrates from the Murray Basin deposits of southeastern Australia contain discrete grains of chrome spinels as a major impurity that must be removed for the ilmenite to become a satisfactory feedstock for the sulphate route to titania pigment production. Conditions were established for a magnetising roast of the ilmenite samples, followed by a magnetic separation, that produced products with (≤0·1 wt-%Cr2O3. The roasting conditions were adjusted to keep the crystallite size of any rutile formed during the roast to <10 nm. Under these conditions the rutile was appreciably soluble in sulphuric acid so that the roast products had satisfactory digestion properties. The roasting conditions are a sensitive function of the mineralogy of the ilmenite grains resulting from chemical weathering in the deposits. For mildly weathered ilmenite concentrates from the southern Murray Basin, containing intimate fine grained associations of ilmenite and pseudorutile, magnetising roasts at <650°C in slightly reducing fluidising gases gave magnetic products containing, <0·1 wt-%Cr2O3 at >80 wt-% recovery, with high solubilities in sulphuric acid. However, similar conditions were not effective for ilmenite concentrates from the central Murray Basin that contain mixtures of unweathered Mg rich ilmenite and highly weathered ilmenite. The strongly weathered ilmenite contains high levels of intra grain chromia (0·2 wt-%Cr2O3) and generates high levels of rutile on roasting, making it difficult to obtain acceptable sulphate route feedstocks from this ilmenite.

Degradation of carboxylated styrene butadiene rubber based water born paints. Part 1: Effect of talc filler and titania pigment on UV stability

The photo-oxidation of cast self-supporting films of a carboxylated styrene butadiene random copolymer (c-SBR) containing talc and TR92 (coated rutile) (both separately and together) has been investigated using ATR-FTIR, toluene swelling measurements and DSC (for T g determination). An imaging chemiluminescence (ICL) method was also used to depth profile the oxidation. Both the wavelength of the UV source and the presence of filler and pigment were found to affect the major degradation products and the propensity for surface crosslinking. At relatively low levels (<50 phr) talc showed an optimum UV stabilising effect at the irradiated surface (as measured by ATR-FTIR determination of carboxylic acid carbonyl index), though, due to iron impurities in the talc, higher loadings impaired the stabilisation performance. However, due to a physical barrier effect (verified using ICL), T g measurements indicated a progressive increase in overall stabilisation with increasing talc loading. As expected, TR92 significantly retarded surface photo-oxidation and was manifested as slow growth of the carbonyl absorption bands. Carboxylic acid was by far the major component of the latter bands throughout the entire exposure period. Even at advanced stages of oxidation, αβ-unsaturated carbonyl species were the major surface photo-oxidation products in samples containing talc. Interestingly talc also led to significant surface crosslinking whilst the TR92 did not.

Ceramic application of mica titania pearlescent pigments

Mica-based pearlescent pigments are widely applied in plastics, cosmetics, automobiles coatings among others, but they seem to be not explored by the ceramic industry. In this work, the potential of two commercial special effect pigments (with gold and silver lustre, respectively) in the decoration of ceramic tiles was appraised by testing them dispersed into several ceramic coatings fired in a wide range of temperatures (700–1150 °C). The pigments were characterized by XRD, FTIR, SEM, XRF and PSD, while their technological behavior was assessed by determining phase composition (XRD) and colorimetric parameters (DRS) of ceramic materials, including a Pearlescence Index. Results indicate that mica titania pigments are stable in glassy coatings up to 900 °C, any deterioration of their optical properties being due to anatase-to-rutile and muscovite-to-feldspar transformations occurring at higher temperatures or after long firing times. The pigment type with a gold shine is particularly suitable for third fire decoration of ceramic tiles, involving low temperatures and fast firing schedules, where it can replace expensive precious metals lustres. Moreover, a certain satin effect was appreciable in porcelain stoneware tiles, unexpectedly persistent after firing at 1200 °C.

Chemical variability in chrome spinel grains from magnetically fractionated ilmenite concentrates: implications for processing

Detrital chrome spinels are contaminant grains within ilmenite rich heavy mineral concentrates found along the southeast coastline of Africa and in the Murray Basin region of southeastern Australia. Separation is often difficult because of overlaps of physical properties between the chrome spinels and ilmenite. The presence of even minor levels of chromia in the concentrates will downgrade their market value as potential feedstocks for the production of titania pigment. In the present paper, the chemistry and distribution of chrome spinels in magnetically fractionated ilmenite concentrates from both regions are characterised using electron microprobe imaging and analysis techniques to establish the chemical and mineralogical factors that impact on their separation behaviour. Results show that the South African sample contains two chemically and magnetically distinct chrome spinel groups. The first group is dominated by a strong trend that reflects the mutual substitution between Al3+ and Cr3+ while the second group is characterised by compositions containing abundant Fe3O4 magnetite component. The presence of these two spinel groups means that physical separation from the ilmenite is relatively straightforward using simple roasting and magnetic separation procedures. In comparison, the Murray Basin chrome spinels exhibit broad chemical variation that results in no clear separation based on magnetic response. The broad spread in composition and magnetic susceptibility of the chrome spinels is responsible for the previously observed difficulties in developing successful separation methods.

Titania pigment particles dispersion in water-based paint films

The distribution of titanian pigment, in dry water-based paint films in the presence of polymeric dispeersants containing different functional groups was investigated. The polymeric dispersants chosen were polyacrylic acid and polyacrylamide momo-and copolymers modified with hydroxyl and/or carboxylate groups. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to assess the distribution of the titania pigment particles in the surface and bulk, respectively, of the paint films, which was then compared to the gloss and surface roughnes of these films. In the absence of dispersant, the pigment distribution in the paint film was not uniform and relatively large pigment aggregates appeared at the surface, resulting in a rough surface and low gloss value. All dispersants both decreased surface roughness and increased the gloss of the dry paint film, with the dispersant type considerably enhancing the pigment dispersion in the dry paint film, in agreement with results obtained in aqueous pigment suspensions. In the presence of polyacrylamide homopolymer, the paint gloss increased slightly and further increased with the hydroxyl-modified polyacrylamide copolymer. The paint gloss was highest in the presence of polyacrylic acid or carboxylate/hydroxyl-modified polyacrylamide.

Detrital chrome-spinel grains in heavy-mineral sand deposits from southeast Africa

AbstractDetrital chrome-spinels are contaminant grains within ilmenite concentrates produced from heavy-mineral deposits along the coast of southeast Africa. The presence of even minor levels of chromia in the predominantly ilmenite-rich concentrates, downgrades their market value as potential feedstocks for the production of titania pigment. An understanding of their composition can assist in their removal from the ilmenite concentrates.Compositions from a database of close to 900 chrome-spinel analyses shows the major element components and their ranges (in wt.%) are: Cr: 0.4-45.3, Al: 0.0-31.0, Fe: 8.5-69.6 and Mg: 0.0-12.2. Minor components include Ti: 0.1-11.4 and Zn: 0.0-13.7.The chrome-spinel data fall into two compositionally distinct groups. The first group of spinels is dominated by a strong trend reflecting the mutual substitution between Al3+ and Cr3+ in the spinel structure. The second group of spinels is characterized by compositions containing abundant Fe3O4magnetite component. The clear division between chrome-spinel compositional types indicates the grains are derived from at least two chemically dissimilar provenances.The compositional differences between the chrome-spinel groups has a positive impact on subsequent ilmenite upgrading treatments as the spinels which contain the highest magnetite component are easily removed via low-intensity magnetic separation procedures.

Coating of Silica on Titania Pigment Particles Examined by Electroacoustics and Dielectric Response

The coating of titania with a hydrous silica layer was investigated by electroacoustics, high-frequency dielectric response (DR), IR spectroscopy, and TEM microscopy. The shift in the isoelectric point measured by electroacoustics was the most sensitive indicator of silica coverage of the titania surface. Changes in the shape of the zeta potential pH dependence corresponding to formation of silica multilayers were accompanied by small changes in the IR spectra and TEM thickness. The coatings formed at 90 °C were dense and smooth and extended up to 10 nm from the titania surface. Changes in the dielectric constant of the coated pigment occurred over three domains and corresponded to changes in the nature of the adsorbing silica layer. At low concentrations, the relative permittivity of the coating layer was ∼5 but at higher concentrations it was ∼20, indicating greater hydration of the multilayer.

Influence of polymer functional group architecture on titania pigment dispersion

The influence upon adsorption of polymers containing different functional groups on the dispersion behaviour of titania pigment particle has been investigated at pH 6.0 and 9.5. The polymers chosen are polyacrylic acid and modified polyacrylamides including homo and copolymers modified with carboxylate and/or hydroxyl groups. A range of experimental methods including polymer adsorption isotherms, zeta potential, rheology and particle size measurements were used to assess the dispersion effect of the polymers. Adsorption of polyacrylic acid and anionic polyacrylamide copolymers onto the titania pigment surface is greatest when electrostatic repulsion is absent. At low pH values, below the pigment isoelectric point (iep), the adsorption density of the anionic polymers on titania pigment was high whilst at higher pH values, above the pigment iep, the adsorption density decreased. However, the adsorption of non-ionic polymers on titania pigment was less influenced by the pH. The presence of carboxylate functional groups in both polyacrylic acid and anionic polyacrylamide copolymer altered the titania pigment dispersion behaviour, reducing the suspension yield stress and mean particle size. The polyacrylamide homopolymer had negligible effect on the pigment dispersion properties at pH 9.5, while it caused pigment particle aggregation at pH 6.0. The hydroxyl-modified polyacrylamide had also a de-stabilisation effect on the pigment dispersion at pH 6.0, but decreased the yield stress and the mean particle size at pH 9.5. The stabilisation effect of both anionic and non-ionic polymers was pH-dependent. The dispersion properties of the pigment particles are largely predicted by DLVO theory.

Effects of chemical functional groups on the polymer adsorption behavior onto titania pigment particles

The effects of functional groups on polymer adsorption onto titania pigment particles have been investigated as a function of pH and ionic strength using polyacrylic acid and modified polyacrylamides. The polyacrylamides include the homopolymer, an anionic copolymer with hydroxyl and carboxylate group substitution, and a nonionic copolymer with hydroxyl group substitution. Adsorption isotherms and infrared spectroscopy were used to examine the polymer–pigment interactions. The adsorption of the polyacrylic acid and anionic polyacrylamide on titania pigment is greatest when electrostatic repulsion is absent or reduced. At low pH values, below the pigment isoelectric point (IEP), or at high ionic strength, the adsorption density of the anionic polymers on titania pigment is high, while at higher pH values above the pigment IEP, the adsorption density decreases. But the adsorption of nonionic polymers on titania pigment is not influenced by either ionic strength or pH. Acrylamide groups were found to hydrogen bond with the titania pigment surface, independent of pH. With the inclusion of hydroxyl functional groups into the polyacrylamide chain, the polymer adsorption density increased without increased adsorption affinity. Carboxylate functional groups in the anionic polymers strongly interact with the pigment surface, producing the highest adsorption density at low pH values. All polymers exhibit Langmuir adsorption behavior with hydrogen bonding found as the dominant mechanism of adsorption in addition to electrostatic interaction occurring for the anionic polymers.

Sodium stearate adsorption onto titania pigment

The interaction of sodium stearate with titania pigment particles from aqueous suspension has been investigated using thermal analysis and infrared spectroscopy combined with electrochemical studies. Thermogravimetric analysis (TGA) was used both to determine the adsorption isotherm and to investigate the interaction behavior. Monolayer coverage is determined to be 0.95 mg/m 2; however, unlike the case with organic solvents, multilayer adsorption occurs. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, combined with TGA, revealed that the surface monolayer is chemically bound. DRIFT spectroscopic data also indicated that the stearate bridged across two aluminum atoms. Subsequent stearate layers were physisorbed to the stearate monolayer and were readily removed with acetone washing.