High temperature high pressure capsule for processing materials in supercritical fluids

A high pressure, high temperature capsule for containing at least one material and solvent that becomes a supercritical fluid in a substantially air-free environment, said capsule comprising:

• a) a closed end;
• b) at least one wall adjoining said closed end and extending therefrom;
• and
• c) a sealed end adjoining said at least one wall opposite said closed end, said sealed end comprising a plug that is cold-welded to said at least one wall,
• wherein said at least one wall, said closed end, and said sealed end define a chamber therein for containing said at least one material and said solvent,
• wherein said capsule is formed from a deformable cold-weldable material, and
• wherein said capsule is fluid impermeable and chemically inert with respect to said at least one material and said supercritical fluid.

A method of filling a high pressure, high temperature capsule with at least one material and a solvent that becomes a supercritical fluid in a substantially air-free environment, said capsule having at least one wall, a closed end, and an open sealable end defining a chamber therein for containing said at least one material and said supercritical fluid, the method comprising the steps of:

• a) providing the capsule;
• b) providing the at least one material to the chamber;
• c) providing a solvent source, wherein the solvent source contains the solvent and is connectable to a vacuum manifold;
• d) connecting the solvent source to the vacuum manifold;
• e) inserting the at least one material into the chamber;
• f) placing the chamber of the capsule in fluid communication with the vacuum manifold and evacuating the chamber to a predetermined pressure;
• g) cooling the chamber to a temperature below a predetermined temperature;
• h) placing the chamber and the solvent source in communication with each other through the vacuum manifold;
• and;
• i) providing a portion of the solvent into the chamber, thereby filling the open-ended capsule to a predetermined level.

A method of sealing a high pressure, high temperature capsule containing at least one material and a solvent that becomes a supercritical fluid at high temperature and high pressure in a substantially air-free environment, said capsule having at least one wall, a closed end, and an open sealable end defining a chamber therein for containing said at least one material and said solvent, the method comprising the steps of:

• a) providing the capsule containing the at least one material;
• b) placing the chamber of the capsule in communication with a vacuum manifold and evacuating the chamber to a predetermined pressure;
• c) filling the chamber with a predetermined quantity of the solvent;
• and
• d) sealing the open sealable end of the capsule.

An apparatus for sealing a high pressure, high temperature capsule with a cold-weldable plug to a form a substantially air-free chamber within said capsule, said apparatus comprising:

• a) a movable ram for inserting said cold-weldable plug into an open sealable end of said capsule;
• b) a mechanical support for supporting said capsule and guiding said ram,
• wherein said mechanical support and said ram form an air-tight inner chamber;
• and
• c) a vacuum inlet passing through said mechanical support to said air-tight inner chamber, wherein said vacuum inlet provides communication between said air-tight inner chamber and a vacuum manifold,
• wherein said cold-weldable plug is cold-welded to at least one wall of said capsule when said cold-weldable plug is inserted into said open sealable end and a pressure is applied to said ram.

A gallium nitride single crystal, wherein the gallium nitride single crystal is formed by:

• providing at least one gallium nitride source material to a high pressure, high temperature capsule, the capsule having at least one wall, a closed end, and an open sealable end defining a chamber therein for containing said at least one gallium nitride source material and a solvent that becomes a supercritical fluid at high temperature and high pressure;
• placing the chamber of the capsule in fluid communication with a vacuum manifold and evacuating the chamber to a predetermined pressure;
• filling the chamber with a predetermined quantity of the solvent;
• sealing the open sealable end of the capsule;
• disposing the sealed capsule within a pressure vessel comprising a pressure transmission medium surrounding the capsule for maintaining an outer pressure on the capsule, a heating element insertable in the pressure transmission medium such that the heating element surrounds the capsule, a restraint to contain and hold in place the capsule, the pressure transmission medium, the heating element, and at least one seal between the restraint and the pressure transmission medium;
• and subjecting the capsule to high pressure, high temperature conditions, wherein the solvent contained within the sealed capsule becomes a supercritical fluid and generates a predetermined pressure within the sealed capsule, and wherein the supercritical fluid reacts with the at least one gallium nitride source material to form the gallium nitride single crystal.