Patent GB-927492-A (GB)
Title: Improvements in or relating to magnetic test particles
IPC: H01F1/44
Filed: 1960-06-30
Abstract: 927,492. Magnetic materials. J. D. STEELE. June 30, 1960 [Aug. 3, 1959], No. 22992/60. Class 38 (2). [Also in Groups XXXVI, XL (a) and XL (b)] A paramagnetic radio-active powder comprises a carrier material bonded to paramagnetic particles by means of an adhesive, radio-active material being physically or chemically bonded to an exposed surface of the carrier. The magnetic material is preferably ferromagnetic and may be red or black iron oxide, iron produced by the carbonyl process, or aluminium. The preferred carrier material is an ion exchange or chelating substance to which the radioactive material is chemically attached. Suitable ion-exchange resins for positive radioactive ions are sulphonated cross-linked polystyrene and cross-linked acrylic acid resin, both in their sodium forms, and resins made by condensing formaldehyde with phenol msulphonic acid or with 5-resorcylic acid. For negative radio-active ions, quaternary ammonium derivatives of cross-linked polystyrene may be used. A resin carrier having metal chelating properties is made by reacting a copolymer of styrene and divinyl benzene first with monochloromethyl ether and then with a salt of imino-diacetic acid. Other suitable carriers are silica gel, diatomaceous earth, activated clays, zeolites, sulphonated coal, polyphosphates, porphyrins and phthalocyanines. The carrier is bonded to the magnetic particles preferably with an epoxy resin, but other suitable resins are mentioned. The radioactive material may be a radioisotope having a half-life of from several hours to 10,000 years. In examples, the magnetic materials used are ferromagnetic iron oxide powder and iron filings, to which the carriers are bonded by means of epoxy type resins. The carriers are sulphonated styrene resin, phenol-formaldehyde-sulphonic acid resin, activated bauxite, quaternary ammonium styrene resin in chloride form, a carboxylic acid resin made from acrylic acid and divinyl benzene in sodium form, and styrene-divinyl benzene resin having -CH 2 - N(CH 2 -COOH) 2  substituents. The ground carrier particles are treated with solutions containing Sc 46, Pm 147, Ce 144, Co 60, Cs 137, Tl 204, Au 198, Ra, S 35, Ta 182, and Eu 152 and 154. The powder may also contain fluorescent or colouring materials which may be introduced by addition to the resin mixture or to the radio-active solution. Suitable fluorescent substances are the azine of 2-hydroxy-1- naphthaldehyde, the axine of 2-aceto-1-naphthol, fluorescent zinc oxide or sulphide, Lumogen L Red Orange, or resinous fluorescent pigments as described in U.S.A. Specification 2,498,592. The final powder is suspended in an aqueous solution of a wetting agent or in kerosene or other organic liquid. The examples also describe the use of the radio-active magnetic powder for the detection or flaws in turbine blades and steel bars. The parts to be tested are magnetized and then treated with a slurry of the powder. Powder adheres near flaws and is detected by scintillation counters (for gamma rays) and Geiger-Muller counters (for beta particles). When a fluorescent material is present in the powder, the parts may also be inspected visually under ultra-violet light. The radioactive component may be incorporated in the powder at the place and time of use ; moreover, the powder itself and the bodies tested may be subsequently decontaminated from radio-activity. Specification 833,267 and U.S.A. Specification 2,267,999 also are referred to.