Method for synthesizing diboride powder by dry route

A method for synthesizing a diboride powder MB2, where M is a chemical element belonging to group 4 of the periodic table, by reducing an oxide of said M, comprising:

• preparing a mixture of raw materials comprising:
• a) a powder whose mass content of said oxide MO2 is at least 95% and
• b) a powder comprising a boron oxide or a precursor of a boron oxide, the boron content of which, expressed in B2O3, is at least 30%;
• and
• c) a metal powder of at least one reducing element R, R being selected from Al, Si, Ti, Zr, Hf, Y, Sc, the lanthanides;
• and
• d) an oxide powder of an alkali element A, having a A2O mass content of at least 70%, in respective proportions leading to the following balance reaction, expressed according to said MO2, B2O3, R and A2O:
• MO2+B2O3+yR+xA2O→MB2+A2xRyO5+x (3)
• heating said mixture in an enclosure under a rare gas flow, at a temperature above 600° C. and below 1500° C.,
• said mixture of raw materials having the following characteristics:
• a median particle diameter of said powder comprising the oxide MO2 is between 1 and 100 microns, and
• a median particle diameter of the powder comprising a boron oxide or a boron oxide precursor is between 5 and 200 microns;
• and
• x is greater than or equal to 1
• y is greater than 0.5.