Metal Borides

Abstract

The invention is related to a boride of a metal of transition group four of the periodic table of the elements, wherein at least 40 wt. % of the particles have a grain size of more than 106 μm, determined by sieve analysis according to ASTM B 214, and these particles consist of grown, monocrystalline grains. The invention also relates to a cermet, wettable powder and a surface coating which contain the boride. The invention further relates to a process to prepare the boride. The invention additionally relates to a process to prepare a cermet or a wettable powder.

1 - 21 . (canceled) 
   
   
       22 . A boride of a metal of transition group four of the periodic table of the elements, wherein at least 40 wt. % of the particles have a grain size of more than 106 μm, determined by sieve analysis according to ASTM B 214, and these particles consist of grown, monocrystalline grains. 
   
   
       23 . The boride according to  claim 22 , wherein the metal of transition group four of the periodic table is a metal selected from the group consisting of titanium, zirconium, hafnium and mixtures thereof. 
   
   
       24 . The boride according to  claim 22  which is a titanium boride, zirconium boride or a mixed crystal comprising at least one of these borides. 
   
   
       25 . The boride according to  claim 22 , wherein the mean grain size of the sieve analysis according to ASTM B 214 is between 100 and 500 μm. 
   
   
       26 . The boride according to  claim 22 , wherein the mean grain size of the sieve analysis according to ROTAP ASTM B 214 is between 200 and 355 μm. 
   
   
       27 . The boride according to  claim 22 , wherein the monocrystalline grains have a glossy, smooth surface and round corners and edges. 
   
   
       28 . The boride according to  claim 22 , wherein the fraction thereof >106 μm exhibits less than 10% particles consisting of raspberry-like agglomerated fine primary crystals having a size of from 2 to 30 μm. 
   
   
       29 . The boride according to  claim 22  having a content of alkali or alkaline earth metal of less than 100 ppm. 
   
   
       30 . The boride according to  claim 22 , wherein 60 wt % to 70 wt % of the particles have a grain size of more than 106 μm, determined by sieve analysis according to ASTM B 214 
   
   
       31 . A process for the preparation of a boride of metals of transition group four by reacting boron carbide with at least one oxide of a metal of transition group four in the presence of carbon, which comprises carrying out the reaction in the presence of an alkali or alkaline earth metal salt having a high boiling point of at least 1800° C., boron carbide is used in excess, and the reaction is carried out at a temperature of more than 2000° C. 
   
   
       32 . The process according to  claim 31 , wherein the temperature is from 2100° C. to 2750° C. 
   
   
       33 . The process according to  claim 31 , wherein the alkali or alkaline earth metal salt used is at least one oxide, hydroxide or carbonate. 
   
   
       34 . The process according to  claim 33 , wherein the alkali or alkaline earth metal salt used is a salt selected from the group consisting of lithium oxide, magnesium oxide, calcium oxide, calcium hydroxide and calcium carbonate. 
   
   
       35 . The process according to  claim 31 , wherein the reaction is additionally carried out in the presence of B 2 O 3 . 
   
   
       36 . The process according to  claim 31 , wherein the alkali or alkaline earth metal salt is added in an amount of not more than one percent by weight of the reaction mixture. 
   
   
       37 . The process according to  claim 31 , wherein the calcium content of the reaction mixture is from 0.03 to 0.1 wt. %. 
   
   
       38 . A process to manufacture a cermet which comprises hot pressing, high-temperature isostatic pressing, low-temperature isostatic pressing/sintering or free sintering the boride according to  claim 22  in admixture with a metal binder component. 
   
   
       39 . A process for producing a wettable powder for surface coating by plasma spraying, HVOF or cold gas spraying, which comprises bonding the titanium boride according  claim 24  to a surface in the form of a ceramics hard material in a metal binder component and, owing to its smooth crystal surface and its round corners and edges, brings about frictional, sliding and wear properties of the coating. 
   
   
       40 . A surface coating comprising the boride according to  claim 22 . 
   
   
       41 . Cermet comprising the boride according to  claim 22 . 
   
   
       42 . The cermet according to  claim 41 , further comprising as metal binder component iron, copper, steel, stainless steel, MCrAlY, superalloys, Inconel, Hastalloy, V4A steel, or V2A steel. 
   
   
       43 . A wettable powder comprising the boride according to  claim 22  and at least one metal powder as binder component.