Paul Louis Heroult

Caroline Noller has delved into the secrets of six of our world’s most important materials – those that contribute most of our carbon emissions. Here is part two of her investigations:


25 March 2011 – Paul Louis Heroult (1863-1914) is the enigma behind the invention of aluminium with electro-chemistry in 1886, and the Steel electric arc furnace in 1901.

Known for an unruly, highly strung personality, some claim Heroult’s inventions “appeared suddenly, out of the blue, a stroke of common sense, or of genius, sometimes during a lively game of billiards, his favourite pastime” .

Such is the elegance and simplicity of both of these inventions that they remain virtually unaltered and almost completely dominate the technology horizon of today’s steel and aluminium industries.

“Silver from Clay”  was the popular description of aluminium at the time it caught the attention of Napoleon III. However, the difficulty of its manufacturing rendered it as costly as silver and gold. Back then it sold for about US$12 per pound (equal to about US$413,000 a tonne today ), which restricted its use to jewellery and other luxuries.

Captivated by its potential to “lighten and brighten the accoutrements of his army ”, Napoleon invested a substantial sum in its further research and commercial development. Unfortunately, these efforts failed as the stubbornness of the bonds between aluminium and its compounds meant that it remained reserved for exotic purposes until the age of electricity.

At 23, Heroult, captivated by aluminium since the age of 15, experimented with a method of electrolysis reduction supported by the purchase of a Breguet electric dynamo (a generator) with his mother’s last 50,000 Francs .

The heat generated from the chemical bath formula and electric current achieved success at a fraction of the cost of prevailing methods and Heroult immediately applied for a patent (FP 175,711 issued on 23 April, 1886).

The commercialisation of the process using this method in France and America resulted in a drop in price to US$4 almost overnight, but due to an almost complete ignorance regarding its use or methods of casting, the market remained extremely limited.

Heroult’s American counterpart, Charles Martin Hall (Alcoa’s founder), achieved the backing of the powerful Mellon family and was able to offer the metal at prices as low as US$2 per pound in an attempt to widen the market . The investment in an intensive campaign of familiarisation as well as prices below US$1 per pound saw success in a rapid widening of the market.

Early uses

The oldest known application of aluminium still in service today is the dome of the San Gioacchino church in Rome . The architect used it instead of lead because of its lightweight properties, and it allowed windows to illuminate the choir.

However, aluminium remained on the fringe of building until 1931 when Hall’s firm Alcoa sponsored the creation of Aluminaire House to highlight its use in buildings and exhibited it at the Architectural League of New York.

Hall’s brief to architects was to create a modern, prefabricated light-filled house to showcase aluminium’s mass production, lightweight and low-cost qualities.

Not satisfied with the response from architects, Hall next sponsored its use for aluminium-framed windows for the Empire State Building (1932), and then the development of Alcoa’s Pittsburgh headquarters in 1950, designed to maximise the use of aluminium in all aspects of the building. Today the construction sector accounts for 26 per cent of global consumption.

Environmental credentials

But, with a carbon footprint of between 10 and 20 tonnes per tonne of primary metal , it faces substantial economic and environmental sustainability challenges.


Heroult’s other significant contribution, the electric arc furnace, is critical to the steel industry and still the basis for 40 per cent of global production .

This technology is 50 per cent more energy efficient per tonne of steel than the traditional Bessemer blast furnace, and is the only practical means for recycling scrap and waste steel into new steel.

The other benefit was a radical reduction in capital cost: only 20 to 30 per cent of that of the blast furnace. This was partly responsible for driving the evolution of the steel-framed skyscraper. The major weakness is the need for a ready supply of scrap steel, limiting their locations, and which explains why they are most prevalent in the US and Europe, where recycling infrastructure is extensive.

The Bessemer process was the first inexpensive industrial method for the mass-production of steel invented by Sir Henry Bessemer and patented in 1855.

Bessemer purchased a similar patent from a rival who had fallen on hard times and continued to improve the method.

Until this breakthrough, steel was expensive to produce and so its use was limited to higher order applications.

Equitable Life Assurance Building

Early uses

The coming together of Bessemer’s cheap, mass-produced steel and François Hennébique’s reinforced concrete heralded the era of the skyscraper.

Popularly considered the world’s first skyscraper with steel and concrete in its structure was the Equitable Life Assurance Building in New York City (1870). At eight storeys and 43 metres in height, it is small compared to modern skyscrapers, such as the Burj in Dubai (160 storeys and 828 metres high), but it completely transformed the economics of the commercial office market.

Environmental credentials

In 2008, the steel industry accounted for seven per cent of total global carbon emissions, the largest component of all industrial emissions.

If the cost of carbon was internalised, steel prices could increase by up to 40 per cent and the flow-on effect to building would be significant. Although the carbon footprint of a tonne of recycled steel is half that of its virgin sister, the ability to recycle steel efficiently is constrained by its necessary infrastructure, particularly in Australia.


The Romans delivered cast glass to the world in 100 AD, first as a material for mosaic floor decorations, a status symbol of rich and powerful households in Herculaneum and Pompeii, and later in the windows of the same households.

Its poor optical quality and limited size meant it was better suited to floors than windows.

Yet again, the fall of Rome saw the loss of skill and knowledge not rediscovered until the Middle Ages and then dominated by the Venetians around 1200 AD.

So important was glass to the economic development of Venice that glassmakers were isolated to the island of Murano under a municipal order (Ordinance 1271)  and lived under threat of execution if they attempted to escape or give away their knowledge to outsiders.

Seeing the value in glass, the French offered significant incentives to Italian glassmakers keen to escape their bonds, including French nationality and a permanent respite from income tax . This investment paid dividends with the French perfecting the art of polished plate glass for windows and mirrors.

Early uses

The assistance of Venetian defectors resulted in the most famous of glass applications in the Hall of Mirrors at the Palace of Versailles (1684). Today, just four companies control 70 per cent of global float glass supply, the largest of which is Pilkington/NSG, whose namesake, Sir Alistair Pilkington, invented the modern float glass process in 1953 .

Environmental credentials

Accounting for two per cent of global greenhouse emissions in 2005, the glass industry is set to expand to meet rapidly growing demand, driven by ever-increasing building energy efficiency regulations.

These regulations are driving double-glazing as the design response, however, a lifecycle approach is necessary as the extra carbon embodied in the additional glass and supporting aluminium frame can result in a total increase in the carbon intensity of a building.

In the event that carbon emissions were internalised it would increase the cost of laminated glass by as much as 60 per cent at carbon price of US$40 per tonne, which could radically alter the use of glass in buildings.

The future

The story of how these materials have come to dominate our buildings is inextricably linked to the corporate legacies of their creators.

One the one hand, access to cheap, abundant and versatile materials has delivered extraordinary social benefits to the developed and now developing world.

However, we cannot ignore the sheer scale of their emissions impact if we are to sustainably support another three billion people on the planet, all with the same high standard of built environment.

The economic barriers to investment in a new generation of energy and emissions efficiency for industrial production are vast, and the impact of which would be terminal for the building sector in absence of a paradigm shift in construction and design methodologies.

6.  Christian Bickert, Orleans, 1986, cited in

7.    Wallace, DH, 1937, Market Control in the Aluminium Industry

8.  accessed 1 November 2010

9.    Wallace, D.H., ibid

10.    Chemical Heritage Foundation, “History of Electrochemistry” 2008

11.    World Aluminium Industry, Australian Mineral Economics, 1980

12.    Christian Vargel, Corrosion of aluminium, Ch. C5, 1989

13.    Range of figures reflect the carbon intensity of the variety of primary energy sources

14.    IEA, 2009, Energy Technology Status and Outlook

15., accessed 1 November, 2010


17.    Jamie Austin, History of Murano Glass, 2005

18.    Glass Association of Australia, The Flat Glass Industry and Global Market Structure,