Inorganic halogen compounds layer

The molecules in crystalline chlorine, bromine and iodine are packed in a different manner, as shown in Fig. 11.1. The rather different distances between atoms of adjacent molecules are remarkable. If we take the van der Waals distance, such as observed in organic and inorganic molecular compounds, as reference, then some of the intermolecular contacts in the b-c plane are shorter, whereas they are longer to the molecules of the next plane. We thus observe a certain degree of association of the halogen molecules within the b-c plane (dotted in Fig. 11.1, top left). This association increases from chlorine to iodine. The weaker attractive forces between the planes show up in the plate-like habit of the crystals and in their easy cleavage parallel to the layers. Similar association tendencies are also observed for the heavier elements of the fifth and sixth main groups. 

Even minor loadings of layered clay in PNCs result in substantial reduction in flammabifity which has been attributed to the build-up of a protective char layer involving the clay [260]. Substantial improvement in the ablative properties of materials due to a. similar char formation has also been reported [261 ]. These properties could lead to the development of novel fire resistant composites without the use of halogenated compounds that have negative environmental impact and hydrated inorganic oxides that require substantial loading. 

Fluorine attacks all organic compounds except CF4. The inorganic compounds that react with fluorine include many, such as asbestos, that are relatively stable to the other halogens. Reaction with water often leads even to explosions. Metals react with fluorine at room temperature some form an impermeable fluorine layer on the surface which protects them against further corrosion, in particular Monel metal, nickel, aluminum, magnesium, iron, and steel. Glass is not attacked by fluorine if it is free from HF and dry. 

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