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Home metallurgy

File:Bismuth-crystal.jpg

My father was a teacher of material science in a professional school, teaching young people learning some metalworking profession. So as a child, I learnt already something about heat treatment of steel, about “Austenite” and “Martensite”, the “lattice face centered crystal system” and other stuff you can nowadays look up in the internet if you really want to know what that is.

In my childhood and youth, I was used to seeing models of metal crystal lattice structures (made by my father from little plastic pearls representing atoms) as well as photographs of iron or copper crystals viewed through a microscope, and similar things.

One time, I think I was maybe 13 or 14 years old, my father had bought a bar of bismuth, (in case you don’t know, that is a heavy metallic chemical element, number 83 in the periodic table) and we spend one summer afternoon making bismuth crystals (like the one shown on the picture above). He had brought a Bunsen burner. In the house, there was an old kitchen (unused at the time) that was suitable for the purpose, having a gas tap where the Bunsen burner could be connected and a marble table. My father had brought a melting crucible with a tripod and a pair of crucible tongs.

File:Tiegelzange.jpg

He put the melting pot on the tripod and lit the Bunsen burner. A blue flame emerged. He put it under the crucible and put some pieces of the bismuth inside and then we waited for the metal to melt. Bismuth melts at 271.4 ° C, no problem for a Bunsen burner, so we did not have to wait too long and the pot was filled with liquid metal with a slightly yellowish color, a little bit like gold, a little bit like silver.

Then the Bunsen burner was extinguished. With a piece of card board my father removed some oxides and impurities from the surface. Then we waited for the liquid to cool. Soon, we could see patches of something like a crust on top of the liquid.

Bismuth, my father explained to me, is one of very few materials for which the solid form is less dense than the molten form. The familiar example for this is water ice. Ice swims on top of the water, while in most materials, the solid form would sink. But in the case of Bismuth, it floats.

After some time, before the crust covered the surface completely, he took the tongs, used it to grab one of the pieces floating in the melt, took it out and turned it around quickly. Now I could see that the solid Bismuth had grown down into the cooling liquid and had formed a beautiful crystal with a step-like structure that is typical for this material, in some places forming little spiral -like structures or structures looking like small amphitheaters. We tried it again and I also took out a little piece. He said that in order to get larger ones you had to wait for longer, but if you waited too long the crystal growing down into the melt would attach to those that were growing from the walls of the vessel at the same time. The ones we got measured between about one and three centimeters, but he later showed me a larger one. When the crystals cooled, the surface oxidized in the air. The thin layer of metal oxide is shimmering in colors resembling those of soap bubbles or spilled oil films. Each of the crystals was unique and different and all where very beautiful.

My father had also brought a gas bottle filled with nitrogen gas, with a rubber hose attached to it. He opened the tap of that bottle and nitrogen gas started streaming out. He took another crystal out of the melt and put it into the nitrogen stream while it was cooling. Since the crystal was deprived of oxygen this way, it did not form the colorful oxide layer. It retained a gold-like color.

Years later, on a visit to a trade fair where minerals, crystals, fossils and the like where sold, I saw such crystals for sale. They wanted horrendous prices for one, more than ten times the actual costs, and claimed that growing one took several days in a special furnace, in a complicated process. I knew better, it had been as easy as cooking a soup and had taken us maybe an hour or two.

My early exposure to metal and mineral crystals, microscopic images of them and similar things is probably one of the things that primed my interest for abstract art. Witnessing how these crystals were made was really a unique experience. The emergence of such beautiful objects – with a complex, unforeseeable and uncontrollable structure, all of them similar and each of them unique – from a hot, shimmering liquid is a magical moment. It is something special, at the border between science and art. These experiences are among the most valuable things I inherited from my father.

(The pictures are from http://commons.wikimedia.org/wiki/File:Bismuth-crystal.jpg?uselang=de and http://commons.wikimedia.org/wiki/File:Tiegelzange.jpg)

9 thoughts on “Home metallurgy

  1. A pleasant memory of a useful learning experience. Something worth saving.

    Not only did you learn something about metallurgy, the knowledge you gleaned from that day with your dad also helped teach you a valuable lesson about capitalism later in Life.

    • Even if one takes the other cost the man had into account, like driving to the trade show, renting a stand and so on, I think he made a very high profit and the story he told was simply a lie. This was probably just a small one person business, but I am sure comparable things are very wide spread in big business as well.

      • Indeed. Profit can only be made by one at the loss of another. Profit means getting more out of a closed system than is put back in. Defies the basic laws of physics. Unsustainable.

        Sorry nannus. Very far off from your post, which is a very positive and uplifting story.

        • No problem, that aspect is part of the story. And you are right. Earth is a system with limited resources and where profit seems to come from “growth” it comes from future generations.
          And it is not so far off. The laws of physics you are talking about are those of thermodynamics and they also guide the behavior of molten metal in a furnace. The order of a crystal is unlike that of a living organism or a civilization. These are dynamic systems. In a molten metal over a Bunsen burner, convection streams form. Hot liquid is rising, cold liquid is sinking and a regular pattern of convection cells is forming. It takes energy in a low entropy form and dissipates it into a high entropy form (heat radiation). This is what Ilya Prigogine called dissipative systems. Convection cells are one of the simplest examples, life and civilization are more complex ones. Remove the Bunsen burner (the supply of resources) and the process grinds to a halt and the ordered pattern brakes down. The crystals that form are order of another kind, they are static and dead.

  2. Thinking about it another day, I am not so sure again how old I was, maybe only 12. It is also possible that I am mixing up two memories. It is possible we melted the metal on a gas cooker in a flat vessel and we used the crucible on the tripod in my father’s school’s laboratory on another day where I accompanied him a couple of times for watching interesting experiments or looking through a microscope. Memories can get a bit blurred over the years an this was about 40 years ago.

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