Iodine tungsten lamp has ignition capacity. An iodine tungsten lamp is a kind of tungsten filament lamp filled with iodine vapor for a chemical reaction. It is often used in indoor and outdoor lighting places with high illumination requirements and high installation points. This kind of lamp has a high degree of thermal light source, and there is a risk of burning combustibles on the outer wall of the lamp tube in a short time. Therefore, it is of great significance to understand the ignition ability of iodine tungsten lamp to combustibles for fire prevention and fire investigation.

The standard molar enthalpy change for the reaction of tungsten diiodide (WI₂) is -70.61 kJ/mol. it is defined as the thermodynamic energy change between the reactants (i.e., W and I₂) required for the formation of 1 mol of WI₂ and its corresponding reaction product (i.e., the WI₂ gas) under the standard condition. Specifically, the enthalpy of formation of the reaction of tungsten diiodide can be determined by determining the standard molar enthalpy of formation of tungsten, iodine, and tungsten diiodide, a value that can be obtained by experimental measurement.

The standard molar enthalpy of formation of tungsten diiodide is -8.37 kJ/mol. The standard molar enthalpy of formation of tungsten diiodide, Δ_fH_m^θ(WI₂, g, 298 K), is defined as the standard molar enthalpy of formation for the reaction to produce the substance tungsten diiodide (ν_B=+1) from the monomers of the reference state at 298 K. The standard molar enthalpy of formation is -8.37 kJ/mol.

The type of crystal structure of tungsten diiodide is an orthorhombic crystal system, space group Bbem (No. 64), with lattice parameters a = 1258 pm, b = 1259 pm, and c = 1584 pm, and is a crystal cell with hexahedra. Each hexahedron has a tungsten atom in the center surrounded by six iodine atoms, forming a tungsten-iodine octahedron. The tungsten and iodine atoms are located at positions (0,0,0) and (0.5,0.5,0.5), respectively. The crystal has a layered structure with each layer consisting of tungsten-iodine octahedra, with neighboring layers interacting with each other through weak van der Waals forces.

The indirect preparation method of tungsten diiodide does not aim at obtaining the product directly but is a method of preparing other tungsten iodide compounds before preparing the final product. The indirect preparation method develops based on the direct preparation method and chooses tungsten iodide compounds that are easier to prepare relative to tungsten diiodides, such as tungsten triiodide (WI₃) and tetraiodide (WI₄), as intermediate products, to reduce the requirements and uncontrollable factors of the reaction conditions and to improve the yield of tungsten diiodide.

In tungsten diiodide, the tungsten element has a valence of +2, and the iodine element has a valence of -1. Therefore, the quantity ratio of iodine to tungsten in tungsten diiodide is 2:1, which is determined according to the principle of electroneutrality.

Tungsten hexachloride (WCl₆), as one of the reactants, can be reacted with hydrogen iodide (HI) to prepare tungsten diiodide, but attention should be paid to the temperature of the reaction to reduce the chances of the formation of other products.

There can be two methods of preparing tungsten diiodide using tungsten hexacarbonyl, the main difference between the two being in the choice of temperature.

The high-temperature chemical method of tungsten diiodide is legally produced by the reaction of elemental tungsten and elemental iodine at temperatures between 600 and 800°C: W+I₂→WI₂. Generally, the temperature selected for the reaction is 800°C, and tungsten diiodide is produced using the reaction of tungsten powder with iodine.

There are three direct preparation methods for tungsten diiodide, which are obtained by high-temperature chemotaxis, halide exchange reaction, and reaction of tungsten hexacarbonyl with elemental iodine. Meanwhile, tungsten diiodide can also be obtained by indirect method.