Download FROM STARS TO CARS December 2012

FROM STARS TO CARS
December 2012
.
From Stars to Cars
1. Imagine.
Did you know that your car came from outer space? Of course, it’s not an alien vessel, but it is
made mostly of steel, which in turn is made mostly from iron, and iron - as we shall discover - is a
very special element.
Here on earth we rely heavily on iron and steel. Without steel, we would have no cars, trucks,
planes and ships, no tall buildings, factories or bridges. Modern society would not be, well,
modern without it. The world relies so much on steel, that it now produces an incredible 1.5
billion metric tons per year. Compare that to 44 million metric tons of aluminum, the second most
widely used metal, and 80 million metric tons of polyethylene (PE), by far the most common
plastic. If we rely on steel to such an extent, might we run out of iron ore, the primary ingredient of
steel? Luckily, there is no need to worry, since iron is the fourth most abundant element in the
earth’s crust, and even the most abundant in the earth as a whole. By mass, nearly one third of
the earth and 5% of its crust is iron. As a result, the top 10 meters of the continental crust alone
contain over 270,000 billion tonnes of iron. With this much iron, we could maintain our current
production level for the next 180,000 years and beyond. This may lead to the question, how
come there’s so much iron, and how did it get here anyway? It turns out that the story of iron’s
abundance on earth is the story of the universe itself.
Let us take a ride back in time and see where this car really started.
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2. Life of a Star
Approximately three minutes after the big bang, the universe cooled to a giant soup of mostly
hydrogen, with traces of helium, deuterium, and lithium. A short while later - about 375 million
years - gravity pulled the hydrogen atoms together to form huge gas clouds which subsequently
collapsed creating conditions where millions of densely-packed hydrogen atoms whizzing around
one another in very close proximity. Hydrogen, with one positive proton at its nucleus and one
electron at its shell, will normally avoid another hydrogen atom because two positive nuclei tend
to repel each other like similar poles on a magnet. However, at high temperatures- about 15
million degrees F - they will smash and stick together in a process known as nuclear fusion. The
proton-proton chain fuses hydrogen nuclei, creating a new element, Helium4, with a nucleus of
two protons and two neutrons. The fusion of hydrogen into helium creates a large amount of
energy from its small mass, and it is this in the form of light and heat, that makes most stars,
including our own sun, shine.
Fig 1. Formation of Helium 4
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Children of the Stars – The Triple Alpha Process
Now there is hydrogen and helium, but what about the other elements? How did they come to
be? The next stage in stellar nucleosynthesis is Helium burning, via the Triple Alpha Process.
Once there is sufficient helium in a star and its temperature is high enough, three helium-4 nuclei,
(also called an alpha particle), will fuse into Carbon12 nuclei (six protons and 6 neutrons).
Additionally, some of these Carbon12 nuclei will fuse with another alpha particle and become
Oxygen16. Oxygen and carbon are considered the 'ash' of helium burning. They are the most
abundant elements after hydrogen and helium in the universe and are the building blocks of life
as we know it. Middle-sized stars end their lives when they have exhausted their helium and end
up with carbon cores. However at this point large stars (>8 solar mass), will start to contract, heat
up further, and carbon burning begins, enabling the synthesis of elements such as neon (10
protons), sodium (11 protons), magnesium (12 protons), and silicon (14 protons).
Fig 2. The triple-alpha process
The Star’s Last Day
The fusion of silicon is the final stage of stellar nucleosynthesis. Silicon burning works via the
Alpha Process, which creates new elements by adding the equivalent of one helium nucleus (two
protons plus two neutrons) per step, starting with the silicon nuclei, and then to the resulting
heavier fusion products. Thus, we get sulfur (16 protons); argon (18 protons); calcium (20
protons); titanium (22 protons); chromium (24 protons); and finally iron, with its 26 protons. Up
until iron, each addition of a helium nucleus generated energy and kept the star burning. After
iron, there is no more fusion. If an alpha particle is added to iron, it creates nickel-56, which is
unstable and quickly decays back into iron and adding an alpha particle to nickel consumes
rather than generates energy. The stellar fire has run out of fuel and within minutes begins to
collapse. The center of the star is crushed into a neutron star or a black hole and the outer layers
are blasted into space in a giant Supernova explosion. The entire silicon burning process—and
therefore the creation of iron in an individual star - takes just one day, yet incredibly, it is the sixth
most abundant element in our universe.
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Fig 3. Super Nova 1979C, may be the youngest black hole in the known universe Source:
NASA
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3. The Journey to Earth
Now we know how the iron is created, but how did the iron atoms get from their stellar birthplaces
to earth? After the supernova has blown off its layers, large clouds of interstellar matter begin to
gather and subsequently collapse, just like the original hydrogen soup, forming a new generation
of stars. Our own sun is one of these, a youngster at only 4.5 billion years old. That same cloud of
interstellar matter that formed the sun also formed the planets around it. The gravitational pull of
the sun is stronger for heavier elements and their condensation point higher. Once these
elements condensed into solid particles, they orbited the sun at a similar speed, gradually sticking
together and growing larger through accretion. This is why the planets closer to the sun; Mercury,
Venus, Earth and Mars, (also known as the terrestrial planets) contain lots of iron, while the
planets that formed further away from the sun like Saturn and Jupiter, are mostly made of lighter
elements such as hydrogen and helium.
Earth’s abundance of iron is, in the true sense of the word, a gift from the universe. It is the final
element to be created before the stars extinguish and explode, spreading their remains
throughout the universe for new stars and planets to arise from the ashes.
However, iron’s success is not just the story of 26 protons, it is also the story of 26 electrons. The
properties of iron’s electron shells are equally important for making its prodigy, steel, the
sustainable material of choice.
Iron on our Planet - Perfect Chemistry
The periodic table of chemical elements (below) organizes the elements based on their atomic
numbers, electron shell configurations and chemical properties. Elements are presented in
increasing atomic number, and elements with the same number of valence electrons are
arranged together in groups, which are represented on the table in 18 vertical columns. There are
four distinct regions in the table, known as blocks, which correspond to the sub shell in which the
‘last’ electron resides. The s-block comprises groups 1 and 2 (alkali metals and alkaline earth
metals) as well as hydrogen and helium. The p-block comprises the last six groups, which are
groups 13 to 18 including all metalloids. The f-block, often shown below the rest of the table,
comprises the lanthanides and actinides. The d-block comprises groups 3 to 12 and contains all
of the transition metals including iron.
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Fig 4. The periodic table of elements
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4. Special Bonds
While the protons in an atom’s nucleus give an atom its identity, it is the electrons, arranged in
shells around the nucleus, which define the way they relate to each other. Any solid material is
made up of a vast number of atoms bonded together. Atoms want to bond with each other
because they are all trying to become stable or ‘happy’ which is achieved by filling, emptying, or
half-filling the valence shell. Noble gases, such as Helium, Neon, and Argon, are completely
happy to be on their own - they have completely filled valence electron shells and virtually do not
bond at all with other elements, even themselves. , With its 3 valence electrons, Aluminum has
more difficulty finding a fulfilling atom to bond with, and once it does, is reluctant to let go.
Magnesium is even more clingy with only two valence electrons - it has few bonding options and
may be considered something of a ‘social misfit’ on the periodic table. Part of what makes iron so
successful is its balanced nature - 26 electrons, 8 in the valence shell, which enables it to bond
and unbond easily with a wide range of other elements. How an element bonds with itself and
other elements determines, largely, its usefulness as a structural material.
Primary Production – Isolating the Element
Metals such as iron, aluminum, and magnesium are rarely found in pure form in nature, but
typically as oxides, (bonded to oxygen). Before we can do useful things with these elements, we
must separate – unbond - the metals from the oxygen. It takes roughly four times less energy to
reduce iron oxides than reducing alumina and magnesia, using the theoretical minimum value,
giving iron a significant sustainability advantage. This is due to oxygen’s 6 electron valence shell,
which creates a tighter bond with magnesium’s2 and aluminum’s 3 valence electrons than they
do with iron’s stable 8. Iron is willing to let go with less of a struggle! It is, if you will, in the ‘sweet
spot’ of the periodic table with regards to bonding. While the theoretical minimum values in the
table are informative, the actual energy required to produce pure metal from ore is actually much
larger. Energy is needed to extract the metal ores from the earth’s crust and preprocess them,
since they are not simply made of pure metal oxides and even the actual reduction of the metal
oxides requires much more energy than shown, since real processes suffer from inefficiencies. A
considerable amount of heat is lost in furnaces and it takes around 3 MJ of fuel to generate 1 MJ
of electricity. The table below lists the theoretical minimum reduction energies for some metal
oxides and the average global primary production energy. In comparison, the energy content of
1kg gasoline is about 42.5 Megajoules (MJ).
Table1. Theoretical Minimum Reduction Energies for Some Metal
Oxides
Theoretical
Avg. global
Chemical
minimum
primary
Synonyms
Formula
reduction energy
production
MJ/kg
energy MJ/kg
Alumina
31.1
140
A1203
Magnesia
24.8
170-350
MgO
Hematite
7.4
20
Fe2O3
Magnetite
6.7
20
Fe3O4
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Alloys are Allies
The pure metals are not very useful as structural materials, since they lack in strength and
hardness. Adding other elements creates alloys with greatly improved physical characteristics.
Figure 5 (below) shows the two ways we can add alloying elements. Interstitial alloying elements
must be small enough to fit between the metal atoms, like the carbon that turns iron into steel.
Substitutional alloying elements replace metal atoms and therefore need to be roughly the same
size. Many of iron’s surrounding d-block transition metals have a similar atomic radius, which
gives iron an extraordinary range of substitutional alloying elements, such as titanium (Ti),
vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zirconium (Zr), niobium
(Nb), and molybdenum (Mo). Each of these alloying elements has a unique effect on steel
properties, providing an infinite number of combinations, which allow customized grades to meet
the vast range of society’s needs.
Fig5. Two ways to add alloying elements: Interstitial and Substitutional
The range of steel properties is further widened by the many different crystal structures into which
iron atoms can be arranged, thus increasing its scope of abilities. Figure 6 (below) shows the
unique triple-phase microstructure of transformation induced plasticity (TRIP) steels. TRIP steels
obtain their combination of high strength and enhanced formability, not just through their alloying
elements, but also through their three crystal structures, which turns them into sophisticated
composite materials.
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Fig6. The triple-phase microstructure of Transformation Induced Plasticity (TRIP) steels
Sustainability and Recycling
Metal atoms share their valence electrons not just with their neighbors but also with all atoms in
the structure. This accounts for many physical properties of metals like strength, malleability,
ductility, thermal, and electrical conductivity. It also makes metals uniquely recyclable. Metals can
be molten and re-formed repeatedly - a critical property for a truly sustainable material. The
theoretical minimum energy required to melt a metal depends on its melting temperature, its heat
capacity, and the energy required to turn a solid to a liquid, called enthalpy of fusion. For
magnesium, aluminum, and steel, this theoretical minimum energy is approximately 1 MJ per kg
of metal, however actual values for scrap recycling are considerably higher since they account for
additional processes like scrap collection and process inefficiencies. The table below shows the
global average total amount of energy required for turning scrap into secondary metal
Table2. Global Average Total Amount of Energy Required to
Turn Scrap Into Secondary Metal
Material
Energy Required
MJ/kg
6.4
Steel
12.8
Aluminium
12.1
Magnesium
This is dramatically less than the energy needed to turn ore into primary metal, a large portion of
which can be regarded as an energy investment rather than an expenditure. We all know
investments can go wrong if not managed properly, and this is no less true for metal recycling.
Steel scrap contains not only iron, but also all elements of the different alloys and any
contaminants that were added during the material’s life cycle. The main method to remove
undesired elements from molten steel scrap is to oxidize them and either boil them off or remove
them with the slag. It is here that Iron has an edge on aluminum, magnesium and all other metals,
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which require a more complex and costly purification process. Just blowing oxygen through it can
purify molten steel scrap. Almost every contaminant or alloy (save copper and tin, which are
easily limited,) will oxidize before iron, making steel infinitely recyclable at half the energy input of
either Aluminum or Magnesium.
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5. Driving Home
Examining this evidence, it is clear that steel, the material of the industrial revolution, is also the
right material for the green revolution. Steel’s primary inputs are abundant and its primary
production requires only a modest amount of energy. The small amount of energy needed to melt
and re-form steel, together with the easy ability to purify it, makes it uniquely recyclable. It is
flexible, thanks to iron’s sweet spot on the periodic table, enabling the wide range of atomic
alliances to suit all grades and purposes. Finally, the possibilities of combining iron with other
elements and arranging them in novel ways are unparalleled and vast, which is why and how
steel keeps reinventing itself.
Iron’s journey has been long, and it is still not over - there are so many ways we can keep
exploring the possibilities of how it has shaped - and may save - our planet and civilization. So
next time you get into your car, remember to thank your stars for steel.
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Sources:
The sources behind Stars to Cars can be found in two background papers, available at
www.worldautosteel.org. They are:


Scientific Background Paper: Iron’s Place and Role in the Universe
Scientific Background Paper: The Chemistry Behind Stars to Cars
Acknowledgements:
Special thanks to Lisa Lamb and Dr. Roland Geyer of GeyerLamb Communications for putting
science and sustainability into words we can all understand. Special thanks also to Professor
Leroy Laverman, University of California at Santa Barbara for contributing imagery and chemistry
expertise. Special recognition to Ed Opbroek and Kate Hickey, WorldAutoSteel, and George
Coates and Russ Balzer, Phoenix Group, for painstaking edits. And sincerest appreciation and
thanks to Jody Shaw, United States Steel Corporation, for being the catalyst and inspiration for
this book and its exciting subject matter.
Finally, we wish to acknowledge with thanks the 18 WorldAutoSteel member companies and their
employees, who dedicate every day of their lives all over the world to make steel a better product
for the environment.
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