GB761050A - Improvements in or relating to methods and means for producing phosphors - Google Patents

Abstract

Trans-stilbene is prepared by the reduction of benzoin and recrystallization twice from ethanol and once from trichlorethylene. To reduce the benzoin content the ethanolic solution is treated with a mixture of hydroxylamine hydrochloride and sodium acetate to form benzoin oxime which remains in solution. Further purification may be obtained by crystallizing from the melt or scrubbing with n-pentane and also by distillation at about 180 DEG C. and 2 mm. of mercury pressure. The stilbene is subsequently crystallized from the melt to form single crystals (see Group III).ALSO:<PICT:0761050/III/1> <PICT:0761050/III/2> <PICT:0761050/III/3> <PICT:0761050/III/4> <PICT:0761050/III/5> <PICT:0761050/III/6> Single crystals of substances, e.g. stilbene, tolane, naphthalene and anthracene, suitable as phosphors for measuring nuclear radiation, are grown from the melt by passing vessels containing the substance and of the shape shown vertically downward through a furnace while initiating crystallization at the apex of the cone or the extremity of the capillary depending therefrom. The baffles 3, 8, 9, 17, 23 and/or the capillaries 4, 14 or 24 prevent entry into the main body of the liquid in the vessel of more than one growing crystal. The orifices in the baffles and the diameters of the capillary tubes are approximately 1 mm. in size. In the vessel of Fig. 2 the line joining the orifices in the baffles 8, 9 makes an angle with the wall of the cylindrical part of the vessel. A change in orientation of the growing crystal in a bent capillary may be obtained by suitable choice of freezing rate. In an example purified stilbene is crystallized in a vessel according to the invention by supporting the vessel in a brass cup carried by a screwed brass rod, the cup being insulated from the vessel and the tip of the vessel touching the rod, the rod being moved downwards by a threaded sprocket at 2.5 to 3 inches per day to cause the vessel to move through a furance. A temperature gradient of 20 DEG C. per inch is maintained between the upper and lower parts of the furnace, the air temperature in the upper part being 140 DEG C. \sB 2 DEG C. and in the lower part 100 DEG C. \sB 2 DEG C. The orientation of the crystal grown in a vessel having a baffle wth a bent capillary attached depends on the angle at which the capillary joins the baffle.