Sintering of Graphite

Sintered graphite and graphite-aided-sintering can be used for production of specialty materials such as:

  • Ultra high temperature, high strength materials for fighter jets nose
  • Polycrystalline diamond (PDC) drill bits
  • Anode for solid state batteries
  • Ultra thin heat dissipation sheets
  • Opaque quartz for infrared shielding

Ultra High Temperature Ceramics for Aeronautical Applications

A  boron-containing carbide ceramic powder can be prepared by ball milling a mixture of two metal powders and graphite powder followed by crushing and pressureless plasma sintering.

The manufacturing process includes:

  1. Ball milling and mixing two metal powders and graphite powder. The ball milling is performed at a rotating speed of 50-300 rpm for 1-5 hrs with ball to material ratio of 4-10:1.
  1. The mixture is crushed and undergo pressureless plasma sintering to obtain carbide powder. The sintering is done at 110-1800 ℃ for 15-60 mins at <5Pa pressure in a vacuum furnace. The temperature is increased at a rate of 5-150 ℃/min.
  1. The carbide powder is mixed with Boron Oxide powder (B2O3), graphite powder and sintered at high temperature.
  1. The sintered product is again crushed to produce ceramic powder.

Polycrystalline Diamond for drill bits

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Polycrystalline diamond can be prepared by making a graphite mixture with less than 0.01% impurity and subjecting it to high temperature and pressure sintering.

The manufacturing process includes:

  1. Forming graphite on a base material by thermal decomposition of a high purity (not less than 99.99%) hydrocarbon gas in a vacuum chamber at temperature greater than 1550 ℃. 
  1. Loading the  graphite on a substrate in a vacuum chamber and subjecting it to high temperature-pressure sintering to synthesize diamond. The pressure and temperature is maintained above 12 GPa and 1500 DEG C respectively.

Solid State Electrode for Batteries

A solid state electrolyte can be manufactured by sintering a mixture of graphite particles, amorphous carbon and a binder. 

Sintering is done in a reducing atmosphere at 900 to 1500 DEG C. The sintering process results in formation of a coating layer of amorphous carbon particles on the surface of graphite particles.

Negative electrode is prepared by coated graphite particles and scaly graphite particles with a binder containing styrene-butadiene rubber.

The negative electrode has 1 to 6% by mass scaly graphite particles and 92.7 to 97.7 percent by mass coated graphite particles.

The coated graphite particles have a specific surface area of 4-6 m2/g and a tapped bulk density greater than 0.9 g/cc. The scaly graphite has a specific area of 5-15 m2/g and a tapped bulk density greater than 0.05 g/cc.

Ultra thin heat dissipation sheets

A high performance ultra thin heat dissipation sheet can be prepared by sintering of graphene or graphite with a binder.

The manufacturing process includes:

  1. Preparing a heat dissipation film by sintering a composition of graphene/graphite powder solution and a binder (e.g., ethylcellulose resin).
  2. Subsequent deposition of graphene heat dissipation films by the aid of a graphene adhesive.

Opaque quartz glass for infrared shielding

Opaque quartz glass can be made by mixing a pore forming agent (graphite powder) to an amorphous silica powder by 0.04 % v/v followed by molding and sintering.

The mixture is heated at a temperature at which the pore forming agent is burnt off, followed by sintering of the silica until pores contained in the sintered body become are closed.

The graphite powder has an average particle size of 5-40 μm.

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