Method of forming a coating

A method of forming a coating within an internal pathway, comprising:

• providing a body having an internal surface which defines an internal pathway within the body, the body having an inlet and an outlet both communicating with the internal pathway for passage of a fluid successively into the inlet then through the internal pathway and then out of the outlet;
• introducing a liquid solution into the internal pathway so as to fill at least a portion of the internal pathway with the liquid solution, the liquid solution comprising a solute capable of undergoing thermal decomposition, wherein said at least a portion of the internal pathway forms at least 50% of the length of the internal pathway;
• heating the liquid solution while the liquid solution fills said at least a portion of the internal pathway to a sufficient temperature so that the solute undergoes thermal decomposition to form a decomposition product within said at least a portion of the internal pathway;
• the heating forming a coating comprising the decomposition product on at least a part of the internal surface wherein said at least a part of the internal surface borders the internal pathway.