A die or piston of a spark plasma sintering apparatus, wherein the die or piston is made from graphite and the outer surfaces of the die or piston are coated with a silicon carbide layer with a thickness of 1 to 10 micrometres, the silicon carbide layer being further optionally coated with one or more other layer(s) made from a carbide other than silicon carbide chosen from hafnium carbide, tantalum carbide and titanium carbide, the other layer(s) each having a thickness of 1 to 10 micrometres. A spark plasma sintering (SPS) apparatus comprising the die and two of the pistons, defining a sintering, densification or assembly chamber capable of receiving a powder to be sintered, a part to be densified, or parts to be assembled. A method of sintering a powder, densifying a part, or assembling two parts by means of a method of spark plasma sintering (SPS) in an oxidising atmosphere, using the spark plasma sintering (SPS) apparatus.