## 1 Introduction  
ZrO\({}_{2}\) material has good physical and chemical properties such as visually good color, high chemical stability, excellent anti-corrosive properties, high tensile strength, high hardness, and good mechanical and electrical properties [1; 2]. Zirconia is used in a broad spectrum of applications, such as refractory products, ceramics, and electronic devices [3; 4; 5; 6; 7]. It is widely utilized in corrosive environments, and zirconium alloys can be used in pipes, steel alloys, and flame retardant coatings. Another anomalous property of zirconia-based materials is their high strength and low thermal conductivity, and some of the zirconium-oxide-containing ceramics can conduct oxygen ions [8; 9; 10; 11; 12]. Because of these properties, the zirconium-oxide-based materials are regarded as prominent materials compared to alumina ceramics [13; 14]. Due to its high-temperature resistance, ZrO\({}_{2}\) is used as filler in intumescent flame retardant coatings (IFRCs) [15; 16; 17]. The chemical entities or substances that have the ability to withstand direct flame and can increase the ignition resistance are called flame retardants. These are added to materials that do not have flame retardancy in order to improve their flame resistance properties [18]. Flame retardant materials are of two types: external and internal [19]. Flame can be inhibited by two methods: The first method is restricting the atmospheric oxygen from reaching the material by releasing non-combustible gases; and the second method depends on the thermal behavior of the flame retardant, which lead to reducing the heat at surface of the material and finally results in the extinguishing of the flame of the burning material [20]. Materials such as nitrogen, phosphorous, halogenated (organic), and non-halogenated (inorganic) substances or molecules can be used as flame retardant agents; these agents can increase the flame retardant properties of a material. IFRC is considered as the most efficient and inexpensive way to safeguard products from fire and is usually applied on plastics, wood, and fabrics. It protects the materials against fire without changing the properties of the coated substances [21]. Intumescence is the phenomenon in which a substance swells upon heating and forms multi-cellular layers [22]. These layers act as thermal barriers that inhibit the flow of heat towards the material thereby protecting them against fire. The intumescent coating is usually composed of three parts: charring agent, acid source, and foaming agent. The quantities of these constituents must be optimized for the formation of an effective IFRC. Furthermore, inorganic fillers can also be added to these coating compositions for the improvement of flame retardant properties [23; 24]. Very recently, it has been observed that the addition of inorganic fillers can sufficiently improve char morphology, thermal resistance, and fire retardation [25; 26; 27]. Nanofilers, on reaction with phosphate, can induce a synergistic effect in IFRCs. The well-known synergistic candidates reported to date included TiO\({}_{2}\) nanoparticles (NPs) [28] and SiO\({}_{2}\) NPs [29]. However, other types of nanofillers still need to be tested in order to identify their function in synergism for an intumescent scheme [30; 31; 32]. Previously, the zirconium and zirconium-containing fillers were incorporated in different flame retardant coatings in anticipation of obtaining enhanced properties [33; 34; 35; 36; 37; 38; 39]. An increase in the char residue, limit of oxygen index (LOI), and peak heat release rate (PHRR) values have been reported for coating samples containing zirconium silicate and zirconium phosphate. However, in the present work, the zirconia was added to the chitosan- and melamine-based epoxy coating. Compared to the previous works, zirconium oxide shows enhanced flame retardant properties in this system. In this study, the impacts of ZrO\({}_{2}\) inorganic nanofillers in the intumescent coating were explored as a fire-retardant composition coating.