You'll never find big blocks of monocrystalline graphite in which you can machine an object having the properties you want. Big blocks of graphite can be found, but made of polycrystalline graphite (such as the one used for making electrodes for metallurgy), so its conductivity is isotropic. One way of doing a highly anisotropic material is using plates (1 cm-thick as maximum) made of compressed exfoliated graphite. The density of this material is 1 (i.e. the half of that of graphite), but the porosity is so narrow and closed that the material is impervious. From such plates, that you can purchased from Mersen company, you can cut elements for building a new object.

Alain

Can I use highly oriented pyrolytic graphite block as a suitable mould for maximum horizontal heat transfer? or there is any drawback of HOPG as a mould?

The problem is finding a big block of HOPG ... This should have a prohibitive cost, and I am even not sure that it exists. I have only seen small samples (of  few mm) of HOPG so far.

Alain

thanks..

while pouring the molten metal, lubricity and hardness of graphite mould with increasing temperature compensates the flow of metal or mould damage with high temperature??

what do you think Graphite mold and copper mould which one is better?

You can find the properties of this graphite in the attached file: many of them related to high-temperature applications.

Alain

sorry i dont know this language.. if  u have another file in english so please upload it