**Abstract**

Titanium dioxide (TiO2), owing to its non-toxicity, chemical stability, and low cost, is one of the most valuable ceramic materials. TiO2 derived coatings not only act like a ceramic protective shield for the metallic substrate but also provide cathodic protection to the metals against the corrosive solution under Ultraviolet (UV) illumination. Being biocompatible, TiO2 coatings are widely used as an implant material. The acid treatment of TiO2 promotes the attachment of cells and bone tissue integration with the implant. In this chapter, the applications of TiO2 as a corrosion inhibitor and bioactive material are briefly discussed. The semiconducting nature and high refractive index of TiO2 conferred UV shielding properties, allowing it to absorb or reflect UV rays. Several studies showed that a high ultraviolet protection factor (UPF) was achieved by incorporating TiO2 in the sunscreens (to protect the human skin) and textile fibers (to minimize its photochemical degradation). The rutile phase of TiO2 offers high whiteness, and opacity owing to its tendency to scatter light. These properties enable TiO2 to be used as a pigment a brief review of which is also addressed in this chapter. Since TiO2 exhibits high hardness and fracture toughness, the wear rate of composite is considerably reduced by adding TiO2. On interacting with gases like hydrogen at elevated temperatures, the electrical resistance of TiO2 changes to some different value. The change in resistance can be utilized in detecting various gases that enables TiO2 to be used as a gas sensor for monitoring different gases. This chapter attempts to provide a comprehensive review of applications of TiO2 as an anti-corrosion, wear-resistant material in the mechanical field, a UV absorber, pigment in the optical sector, a bioactive material in the biomedical field, and a gas sensor in the electrical domain.

**Keywords:** Titanium dioxide, properties, applications, corrosion resistance, wear resistance, UV absorber, biomaterials, gas sensors

### **1. Introduction**

Titanium dioxide (TiO2) is a naturally occurring oxide of titanium. It is also referred to as titanium (IV) oxide or titania. TiO2 is a cheap and widely available white oxide

ceramic having a molecular mass of 79.86 g/mol, a density of 3.9–4.2 g/cm3 , a refractive index in the range of 2.5–2.75, and Mohs hardness of 5.5–7 [1]. It occurs in three crystalline forms: rutile, anatase, and brookite. Both rutile and anatase have a tetragonal structure, whereas brookite has an orthorhombic structure. In industrial applications, only anatase and rutile phases of TiO2 are used [1]. TiO2 also serves as a semiconductor, with a band gap of 3.2 eV for anatase and 3.0 eV for rutile. TiO2 is non-toxic, chemically as well as photo-chemically stable, non-flammable, and biocompatible [2]. TiO2 is often deposited as thin films or thick film coatings to impart anti-wear and corrosion-resistant properties [3]. It is also used in gas sensing and biomedical applications. Because of its UV absorption ability, TiO2 has also been used in sunscreens. TiO2 is also suitable to be used as white pigments. In the past few decades, research activities on nanomaterials have grown rapidly since materials in nano size exhibit completely different properties as compared to their bulk properties. As a result, TiO2 is one of the most extensively used nano-size materials and is found to be useful in a wide range of applications [4].
