How Charles Hall Invented Modern Aluminum Production
This 1889 patent describes the Hall-Héroult process, which uses electricity to extract pure aluminum from its ore, making the metal affordable for everyone.
Original patent title: “Process of reducing aluminium from its fluoride salts by electrolysis”
This 1889 patent describes the Hall-Héroult process, which uses electricity to extract pure aluminum from its ore, making the metal affordable for everyone. Granted to Individual in 1889 with 18 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent NOT cover?
- 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
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The genius was realizing that molten cryolite acts as a solvent for aluminum oxide, allowing electrolysis to occur at a much lower temperature than melting the oxide alone.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Modern aluminum smelting plants
Production of aluminum foil
Manufacturing of lightweight automotive parts
Aerospace structural components
Why it matters
The bigger picture
Before this invention, aluminum was more expensive than gold because it was incredibly difficult to extract. This process transformed aluminum from a luxury material into a common industrial metal used in everything from airplanes to soda cans.
Filed
July 9, 1886
Granted
April 2, 1889
Market context
Who's building on this
Companies in this space
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.
Market impact
This patent effectively launched the modern aluminum industry, enabling the mass production required for the 20th-century boom in aerospace, construction, and consumer packaging.
Claim 1 — Plain English
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.
The clever bit
The genius was realizing that molten cryolite acts as a solvent for aluminum oxide, allowing electrolysis to occur at a much lower temperature than melting the oxide alone.
What it does not cover
- 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
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Early stage
Citation count
26/40
Moderately cited
Claim breadth
0/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$22K – $69K
Midpoint $43K · expired or expiring · industry ×2.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
Concepts involved
Citations
Patent lineage
Cite this patent
Charles, M. H. (1889). How Charles Hall Invented Modern Aluminum Production (U.S. Patent No. 400,664). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/400664/hall-process-aluminum-smelting
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Charles Hall Invented Modern Aluminum Production cover?
This 1889 patent describes the Hall-Héroult process, which uses electricity to extract pure aluminum from its ore, making the metal affordable for everyone.
Who owns patent US 400664?
Individual owns this patent, granted in 1889.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 400664 cited by?
This patent has been cited by 18 later patents that build on its ideas.
What problem does this patent solve?
Before this invention, aluminum was more expensive than gold because it was incredibly difficult to extract. This process transformed aluminum from a luxury material into a common industrial metal used in everything from airplanes to soda cans.
What does this patent NOT cover?
Does not cover chemical reduction methods that rely on heat alone without electrolysis
Same assignee
More from Individual
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