Patent GB-1123806-A (GB)
Title: Inorganic crystalline powders
Inventor: BARRINGTON JONATHAN
IPC: H01F1/11
Filed: 1965-11-10
Abstract: Powders of silicon carbide, boron carbide, titanium carbide, tungsten carbide, molybdenum disilicide, tungsten, molybdenum and beryllium having a strained crystal lattice, an average particle size of less than 500m  and as sonall as 0.5 to 2m  and exhiluting a broadening, B(d) of the X-ray diffraction lines of a peak corresponding to lattice spacing, d, measured at half intensity and measured in degrees 2#q, #q being the diffraction angle at which X-ray deflection occurs, such that a plot of B (d) cos #q versus sin #q produces a straight line intercepting the ordinate above the origin and having a positive slope above 0.02 are produced by subjecting a powder which has a bulk density of at least 10% of its crystalline density and an average particle size no greater than 4500m  to a shock wave generated by detonation of an explosive mixture having a detonation velocity of at least 1500 meters per second and comminuting the resulting agglomerate. The powders may be cold pressed and sintered under vacuum.  The powder to be treated may be contained in a metal tube surrounded by the explosive charge or in a metal container having one end covered by a disc of the explosive. Alternatively, the powder may be contained in an annulus defined between two concentric tubes, the innermost tube being concentric about an air-filled tube closed at both ends and the outer tube being surrounded by an explosive.  The whole assembly is submerged under water which flows into an annulus between the inner tube and the air-filled tube.  In a modification the powder is again contained in an annulus defined between two concentric tubes but the tubes are disposed within a metal die submerged under water, and the explosive is in the form of a linear charge located concentrically within the innermost tube.ALSO:The invention comprises a brittle readily sinterable inorganic powder having a strained crystal lattice, an average particle size of less than 500 m , and exhibiting a broadening, B (d), of the X-ray diffraction lines of a peak corresponding to lattice spacing, d, in Angstroms, measured at half intensity and expressed in degrees 2#q after correction has been made for instrumental broadening, #q being the diffraction angle at which X-ray reflection occurs, such that a plot of B (d) cos #q versus sin #q produces a straight line intercepting the ordinate above the origin and having a positive slope above 0.02.  The powder is prepared by passing a shock wave generated by detonation of an explosive charge having a detonation velocity of at least 1500 metres per second through a brittle, inorganic, crystalline powder which has a bulk density of at least 10% of its crystalline density and an average particle size no greater than 4500 microns, and comminuting the resultant agglomerate into its constituent particles.  The ratio of explosive charge to powder may be 0.01 to 10 and the shock wave may have a velocity of at least 600 metres per second which imparts a particle velocity of at least 300 metres per second to the powder particles.  The explosive charge surrounds and is contiguous with a metal container holding the inorganic powder or vice versa and the whole system may be immersed in water. Alternatively the explosive charge is in contact with one side of a metal container holding the powder. The treated powder may be pressed and sintered.  The inorganic powder may be an oxide, carbide, nitride, boride, telluride, silicide, titanate, ferrite or intermetallic.  As examples, there is given alumina, barium ferrite, barium titanate, silicon carbide, boron carbide, magnesium oxide, titanium carbide, tungsten carbide, bismuth telluride, zirconia, molybdenum disilicide and g Fe2O3.