As a white pigment, titanium dioxide is used for cosmetic applications [1] . This oxide is well known to have a photocatalytic activity. Therefore, a certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. To repress this effect, technical processes of several kinds have been investigated and used. For example, as one such technique, composite particles with silicon oxide have been used [2] . However, these particle materials are too hard for use on a human face. Mild materials are required for use as a white pigment on a human face. In addition, one report has described that microfine titanium dioxide is adsorbed through the skin [3] . A novel white pigment that is not adsorbed must be used.

Phosphates have been used for ceramic materials, catalysts, adsorbent, fluorescent materials, dielectric substances, biomaterials, for metal surface treatment, as fertilizer, detergents, food additives, in fuel cells, pigments, and in other applications [4] [5] . Phosphate materials are well known to have high affinity for living organisms. Therefore, as a novel white pigment, phosphates are expected to be useful as cosmetics.

In earlier studies [6] [7] , we prepared a titanium phosphate pigment that had no catalytic activity with titanium chloride. The titanium chloride is difficult to treat because of the formation of smoke and undesirable precipitate. Generally, raw materials have influence on the formation and properties of materials. In the group of titanium compounds, titanium sulfate is also important compound to obtain titanium oxide as well as titanium chloride. Furthermore, the pH value in preparation is an important factor on the particle shape and size of phosphate materials [8] . The ultrasonic treatment was also found to be a useful method to control the particle shape [9] [10] .

In this work, titanium phosphates were prepared from titanium sulfate and phosphoric acid at pH 5, 7, and 9 with/without ultrasonic treatment. Their respective chemical compositions, powder properties, photocatalytic activity, colour phases, moisture retention, and smoothness of the obtained precipitates and their thermal products were studied for application to cosmetics.

The 0.1 mol/L of titanium sulfate solution was mixed with 0.1 mol/L of phosphoric acid solution in molar ratio of Ti/P = 3/4, and then adjusted to pH 5, 7, 9 with ammonia solution, respectively. This Ti/P ratio was decided from the chemical composition of Ti₃(PO₄)₄. The mixed solutions were treated with ultrasound for 10 minutes (26W, CITIZEN SW5800). For comparison, samples without ultrasound were also prepared. The precipitates were filtered off, washed with water, and dried. All chemicals were of commercial purity from Wako Chemical Industries Ltd. (Osaka Japan) and used without further purification.

A part of the precipitates was dissolved in a sulfuric acid solution. The ratios of phosphorus and titanium in the precipitates were also calculated based on the ICP results of these solutions using an SPS1500VR from Seiko Instruments, Inc. The chemical compositions of these materials were analyzed using X-ray diffraction (XRD). The XRD patterns were recorded on an X-ray diffractometer (MiniFlex; Rigaku Corp.) using monochromated CuKα radiation. Samples were heated at 100˚C in air conditions. These thermal products were also analyzed according to their XRD patterns.

The particle shapes and sizes of the precipitates, as well as their thermal products at 100°C, were estimated based on scanning electron microscopy (SEM) images and particle size distributions. The SEM images of the titanium phosphates were observed (JGM-5510LV; JEOL). The particle size distributions of these materials were measured using a centrifugal precipitation particle-size distribution (SA-CP3L, Shimadzu Corp.).

The cosmetic properties were estimated according to the photocatalytic activity, the color phase, the moisture retention, and the smoothness. The photocatalytic activity of samples was estimated with the decomposition of methylene blue by 365 nm radiation [11] [12] . The 0.01 g of sample was placed in 4 mL of methylene blue solution (1.0 × 10⁻⁵ mol/L), and then this solution was radiated. The decrease of the absorption at about 660 nm was estimated for 120 min. The color phase of phosphate pigments was estimated using ultraviolet-visible (UV-Vis) reflectance spectra with a UV2100 (Shimadzu Corp., reference compound; BaSO₄). The whiteness was also estimated with TES135 plus color analyser (TES Electrical Electronic Corp). For the moisture retention of the samples, 0.3 g per sample was mixed with 0.1 g of water, and the weight loss was then evaluated at 50°C (MS-70 Moisture Analyzer, A and D Instruments Co. Ltd.). The same weight loss over longer time meant high water retention of samples. The particle smoothness was measured on artificial leather with KES-SE objective evaluation of surface friction property (Kato Tech Co. Ltd.). The values of MIU and MMD respectively represent the slipping resistance and roughness of powders. Sample powders were spread on the leather. Then a sensor was run over these powders. The values of MIU and MMD were calculated respectively from the power to move a sensor and the pitching of a sensor. The values of MIU and MMD have no unit because these values are related with coefficient of friction and scattering, respectively.

Titanium phosphates were prepared from titanium sulfate and phosphoric acid at pH 5, 7 and 9 with/without ultrasonic treatment. All samples indicated higher Ti/P ratio than 0.75, which ratio is corresponding with Ti₃(PO₄)₄. This was caused from the formation of titanium oxide and hydroxide. All samples indicated high ratio at 15 µm in particle size distribution. These titanium phosphates had less photocatalytic activity to protect the sebum on the skin. Samples without heating indicated higher whiteness by ultrasonic treatment. Sample prepared at pH 7 without ultrasonic treatment had higher moisture retention than other samples. All samples obtained in this work had the suitable smoothness for cosmetics.

The authors are grateful to Dr. Takeshi Toyama, Nihon University, Japan, for smoothness measurements.