A process once used to produce pure metal, such as tungsten, titanium and zirconium, by the formation of metal iodides followed by their thermal decomposition on a hot tungsten filament. It was developed by Dutch chemists Anton Eduard van Arkel (1893–1976) and Jan Hendrik de Boer (1899–1971). It is also known as the iodide process or crystal bar process. The process has been replaced by the Kroll process.