Aluminum and zirconium oxynitride abrasive grains

Abstract

Corundum-zirconia abrasive grains containing more than 50 wt % of an alumina-zirconia eutectic mixture. The grains contain 0.3 to 3% nitrogen, and more than 75% of the zirconia crystals are cubic in shape. The abrasive grains are of particular use for making grinding wheels, abrasive fabrics and papers, polishing compounds and sprayed abrasives.

1 . Abrasive grains containing more than 50% of a eutectic alumina—zirconia mixture by weight, containing more than 0.3% of nitrogen, wherein less than 25% of the zirconia crystals are in monoclinic form  
   
   
       2 . Abrasive grains according to  claim 1  containing from 0.3% to 3% of nitrogen, preferably from 0.3% to 1% of nitrogen.  
   
   
       3 . Abrasive grains according to  claim 1  wherein more than 75% of the zirconia crystals are in tetragonal or in cubic form.  
   
   
       4 . Abrasive grains according to  claim 1  wherein more than 75% of the zirconia crystals are in cubic form.  
   
   
       5 . Abrasive grains according to  claim 1 , wherein most of the nitrogen is in zirconium nitride form.  
   
   
       6 . Abrasive grains according to  claim 1 , wherein the content of metallic aluminum is less than 0.1% by weight and the content of free aluminum nitride AlN is less than 0.1%.  
   
   
       7 . Abrasive grains according to  claim 6 , wherein the content of metallic aluminum is less than 0.01% and the content of free aluminum nitride AlN is less than 0.01%.  
   
   
       8 . Abrasive grains according to  claim 5 , wherein more than 90% of the nitrogen not combined in the form of zirconium nitride is combined in the form of aluminum oxynitride.  
   
   
       9 . Abrasive grains according to  claim 1 , wherein the total contents of zirconium and aluminum in the form of oxides, nitrides and oxynitrides expressed in the form of equivalent contents of oxides, are between 21 and 44% for ZrO 2  and between 57 and 80% for Al 2 O 3 .  
   
   
       10 . Abrasive grains according to  claim 1 , characterised in that they have a Knoop hardness equal to or greater than 19 GPa and a tenacity equal to or greater than 2.3 MPa 1/2 .  
   
   
       11 . Abrasive grains according to  claim 1 , having a Knoop hardness equal to or greater than 20 GPa and a tenacity equal to or greater than 2.7 MPa.m 1/2 .  
   
   
       12 . Process of manufacturing abrasive grains according to  claim 1 , by melting in an electric arc furnace with a load composed of alumina and baddeleyite, characterised in that a nitride material is added to this load composed of aluminum nitride and/or one or several aluminum oxynitrides.  
   
   
       13 . Process according to  claim 12 , wherein the nitride material is prepared by nitriding of a load composed of an alumina and aluminum powder mixture.  
   
   
       14 . Process according to  claim 12 , wherein the nitride and/or the aluminum oxynitrides react with zirconium during melting to form zirconium nitride.  
   
   
       15 . Process according to  claim 12 , wherein the mass melted in the electric furnace is cast and solidified quickly.  
   
   
       16 . Process according to  claim 15 , in which the fast solidification of the molten mass is obtained by pouring it on a cold support, wherein the mass of the cold support is equal to at least twice the mass of the molten mass, and wherein its temperature before casting is between 50° C. and 350° C.  
   
   
       17 . Process for preparation of abrasive grains according to  claim 1 , including the preparation of a mixture of aluminum nitride AlN and/or oxynitride Al X O Y N Z , alumina and zirconia powders, the reactive sintering of this mixture at a temperature between 1500° C. and 1600° C., and fast cooling of the sintered grains between 1100° C. and ambient temperature.  
   
   
       18 . Process according to  claim 17 , comprising a final washing of the grains with a solution with a pH between 2 and 7.  
   
   
       19 . Grinding wheels designed for grinding metals and metallic alloys or for precision grinding containing abrasive grains according to  claim 1 .  
   
   
       20 . Abrasive fabrics and papers designed for polishing containing abrasive grains according to  claim 1 .  
   
   
       21 . Polishing paste containing abrasive grains according to  claim 1.