| abstract |
1470501 Electrical stress-controlling compositions RAYCHEM Ltd 19 March 1974 [20 March 1973] 13352/73 Heading C3P Compositions for controlling electrical stress at cable junctions and terminations comprise a polymeric material having dispersed therein a particulate compound selected from (a) compounds having a perovskite-type structure other than Sr, Mg, Ni and Ba titanates; (b) compounds having a spinel crystal structure selected from A<SP>II</SP>B<SP>III</SP> 2 O 4 where A is Mg, Co, Cu, Zn or Cd and B is Al, Cr, Fe, Mn, Co or V provided that when A is Mg B cannot be Al, when A is Cu B cannot be Cr and when A is Zn B cannot be Fe, and A<SP>IV</SP> B<SP>II</SP> 2 O 4 where A is Ti or Sn and B is Zn, Co, Ni, Mn, Cr or Cd; (c) compounds having an inverse spinel structure, other than stoichiometric Fe 3 O 4 ; (d) compounds having a mixed spinel crystal structure; (e) MoSe 2 , MoTe 2 , MnO 2 and SnO 2 ; (f) AgI, Prussian blue, Rochelle salt and other alkali metal tartrates, ammonium fluoroberyllate, thiourea, triglycine sulphate, ammonium sulphate and compounds of formula XH 2 YO 4 where X is K, Rb or Cs and Y is P or As; (g) Si 3 N 4 ; (h) a mixture of stoichiometric or non- stoichiometric Fe 3 O 4 with barium titanate, MoS 2 or a metal powder selected from Fe, Al, Cu, Mn, Cr, Pb, Ni, Zn or Ag; and (i) a mixture of barium titanate and a carbon black; the total weight of the compounds in the filler being at least 10 per cent by weight of the polymeric material and the material having a γ-value, at least at some direct current stress between 0À01 kV/mm. and 10 kV/mm., of at least 1À5. The compositions may also contain electrically conductive particulate fillers and/or silicon carbide, and may be used in cable insulation and for the manufacture of heatshrinkable tubes for cable terminations. Many suitable polymers, compounds and fillers are specified and examples describe compositions comprising components selected from EP and EPDM rubbers, polyethylene, ethylene/ethylacrylate copolymer, ionomer resins, vinylidene fluoride / hexafluoropropylene copolymers chlorinated polyethylene and chlorosulphonated polyethylenes; non-stoichiometric Fe 3 O 4 , Co 3 O 4 , strontium titanate, barium stannate, molybdenum ditelluride, molybdenum diselenide, silicon nitride, copper chromite, cobalt ferrite, Mn 3 O 4 , copper manganite and magnesium ferrite; and optionally finely divided carbon black, aluminium, copper, iron, manganese, chromium, lead, nickel, nickel/aluminium, zinc or silver. |