Pt nanowires have been produced by FIB deposition of Pt thin films in a commercial Ga+ focused ion beam (FIB) system, followed by cross-sectional sputtering to form electron transparent Pt nanowires. The thermal stability of amorphous FIB manufactured Pt wires has been investigated by in-situ thermal cycling in a TEM. The Pt wires are stable up to 580-650°C where partial crystallization is observed in vacuum. Facetted nanoparticles grow on the wire surface, growing into free space by surface diffusion and minimising contact area with the underlying wire. The particles are fcc Pt with some dissolved Ga. Continued heating results in particle spheroidization, coalescence and growth, retaining the fcc structure.