You can freely build on How Charles Hall Invented Modern Aluminum Production

What this patent covers

The patent details a method for isolating aluminum by dissolving aluminum oxide in a bath of molten cryolite. An electric current is then passed through this mixture, causing the aluminum to separate and collect at the bottom of the vessel. This process effectively lowers the melting point of the aluminum ore, allowing it to be processed at temperatures that are commercially practical.

What is now free to use

All 0 claims of US 400664 are in the public domain. Specifically:

The 0 dependent claims add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover chemical reduction methods that rely on heat alone without electrolysis

• Does not cover the refining of aluminum from non-fluoride salts

• Does not cover the specific design of the industrial smelting pots used in modern plants

Who is building on this today

Major global aluminum producers like Alcoa, which traces its roots back to the company founded to exploit this patent, continue to refine this fundamental electrolytic process.

Products built on expired version of this technology

How to cite this patent in your documentation

Individual. US Patent 400664. Process of reducing aluminium from its fluoride salts by electrolysis. Granted 1889, expired 1906. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.