Abstract: High chromium stainless steels having enhanced corrosion resistance are provided in which the steels have 25% to 35% by weight chromium; 0.1 to 5% by weight molybdenum; 0.1 to 6% by weight nickel; 0.0 to 4% by weight copper; 0.0 to 1% by weight titanium and/or niobium and/or vanadium; and, 0.02 to 5% by weight of a platinum group metal. The steels are particularly resistant to sulphuric and phosphoric acids.

Abstract: Particles are conveyed in a stream in a direction transverse to the width of the stream. Windows view individual width zones of the stream and optical fibres are associated with the windows to convey light passing through a window to a light detector. The windows are rapidly opened and closed and a processor is provided to determine which window passed light detected by the detector and accordingly which width zone of the stream the light emanated from. The windows preferably incorporate liquid crystal shutters which can be switched rapidly between light-transmitting and opaque states corresponding to open and closed states of the windows.