# 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.

- **Patent:** US 400664
- **Original title:** Process of reducing aluminium from its fluoride salts by electrolysis
- **Owner:** Individual
- **Granted:** 1889
- **Status:** Public domain (expired)
- **Times cited:** 18
- **Field:** mechanical, energy, materials

## What it does

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 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

## 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.

## Real-world examples

1. Modern aluminum smelting plants
2. Production of aluminum foil
3. Manufacturing of lightweight automotive parts
4. Aerospace structural components

## Why it matters

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.

## 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

**Full plain-English explainer:** https://patentbrief.org/patent/us/400664/hall-process-aluminum-smelting

**Original patent:** https://patents.google.com/patent/US400664

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


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