Phase Transitions 3

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The next phase transistion is taking place. In the previous one, whole cristals changed their configuration at once, in a process one may think of as a shearing of the whole molecular lattice. You may think of a group of soldiers turning on comand. The next phase transition, however, is a “civilian” transformation. Below a certain temperature, the old crystal lattice becomes instable. The transformation starts accidentally in some places, probably triggered by some faults in the crystal lattice. Then, one by one, molecules are shifting from the old to the new lattice, so the crystalites of the new conformation are growing bit by bit. For some time, the two phases coexist, but if the temperature goes down further, the new crystalites take over, obliterating most of the history of what was there before.

So from liquid to solid, from one solid phase to another solid phase and now to the third one, this is the fourth phase transition happening in this material.

Look at the previous phases of the Phase Transitions series to see more.

WAITING TO HAPPEN

nannus:

This is the second time I am reblogging a post of an artist I find remarkable on The Kellerdoscope. To me, the paintings of Ashley Sullivan are mesmerizing. Some are pure abstracts, some are landscapes, some are cityscapes or show industrial motives, with varying degrees of abstraction. Many of them are magic for me. I had a hard time deciding which of these paintings to choose. Just have a look yourself.

Originally posted on ASHLEY SULLIVAN:

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AUGUST 2014

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Rolf Keller – In Memoriam

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My grandfather Rolf Keller, the artist who created many of the drawings and paintings on this web site, as I remember him. He was fond of smoking, especially cigars. This picture was taken in a restaurant at river Elbe in Hamburg.

I think the film used was from East German (GDR-) production; all of these pictures have this violet tint. I decided not to try a color correction. This is how they are actually looking. They are contemporary documents and the properties of the film material are part of that.

The next one is also a slide, but on a black-and-white film. My father was a student back then and could not afford the expensive color slide films, so he used the cheaper black and white slide films instead or the color films from East German production that my grandfather brought along.

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This picture was probably taken in the port of Hamburg during a visit. Hamburg is in West Germany, Karl-Marx-Stadt, where Rolf Keller was living, was in the East. Young people were normally not allowed to visit the West, but for old people, this was possible. I cannot date these pictures at the moment, but might be able to do so later. In any case, they are from the 1960s.

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This picture is probably from the same visit to Hamburg as the first one.

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Rolf Keller’s grave in Chemnitz, photographed probably in 1984 (so the city’s name was still “Karl-Marx-Stadt”). It is displaying his 24-logo – he had started his business as a self-employed graphics artist in 1924. This grave probably does not exist any more.

All pictures: Svend Keller. The pictures are digitized slides or sections thereof.

Phase Transitions 2

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This is a view of the same material as in Phase Transitions 1. What has happened? Well, there was an intermediate stage. The lines visible in that one are maybe just cracks, but I don’t know. The material is cooling and that is putting it under some tension:
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But the third stage (the picture above) is different. What has happened there? The material has been cooling and then it underwent another phase transition, this time from one solid state into another solid state. The molecules in the crystals arranged themselves into another configuration. This is called a lattice transformation. Energy is released in this process. It is happening at a certain temperature during the cooling process.

The problem is that the angles of the crystals are changing during this transformation. As a result, the crystals don’t fit again into their places between the other crystals. They are put under tension. This is causing them to “zig-zag” in a process called “twinning”. You can see this at the border of the crystal. The lattice of molecules goes in one direction, then flips into its mirror image in the next section. The resulting stripes appear very quickly (with something like the spee of sound in the material). They appear not all at once but several of them might appear at the same time (as far as you can see). This changes the pattern of tension, so another set of stripes appears a moment later, and so on, until a relatively stable configuration is reached.

The result is a complex pattern of stunning beauty, with a mix of order and disorder.

The yellow section down in the center is a harbinger of things to come, but you will have to wait until next time before I am going to post that. And I am probably going to post some other stuff in between. So that is the cliff hanger here :-) .

The following pictures might illustrate what is happening in a crystal during twinning. This is, of course, a very simplified model (these models where built by Svend Keller for his material science lessons). The molecules in the organic crystals are not simple spheres, they have more complex shapes. But what you can see here are two octaedral crystals consisting of spherical “atoms” (plastic spheres), The third “crystal” in the middle shows an intermediate stage. The models consists of stacked layers of shperes. The spheres in each layer are glued together. If you push the blue sphere to the left, the middle “crystal” will “flip” from one configuration to the other. If you flip between the second and third image, you may get an idea what happens during twinning. This is also called lattice shearing.

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This is also called lattice shearing.

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All pictures: Svend Keller

Phase Transitions 1

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This is the first of a new series of posts that will show abstract photographs made by Svend Keller during the 1970s or 1980s (I don’t know exactly). I hope you will enjoy them. Actually, these are microphotographs. Details can be found in my previous article Organic Martensite.

A phase transition is a change from one phase to another. Phases are different states of matter, e.g. liquids and solids. On this image, you can see some crystals (colored areas, solid phase) and some rests of liquid, molten material between them (colorless areas, liquid phase). The colors are the result of an optical effect involving polarized light. In the crystalized areas, the molecules are ordered into a regular configuration, a crystal lattice. This ordered configuration has different optical properties in different directions, resulting in this optical effect. In the molten material, the molecules appear in all possible directions, so it has the same optical properties in all directions and does not influence polarized light in any specific way. The needle-like strokes are the first signs of another phase transition, from one solid phase to another one that has a different crystal configuration. More of that in later posts.

When the crystals start growing, they look like this (this is another sample and I don’t know if the same mix of substances was used):

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In this image, the molten liquid appears black, the crystals white or grey. You can see here that these crystals are branching (this is called dendritic growth). In the first picture, some crystals are parallel because the branched off from a common “parrent”. In fact, they are part of the same crystal.

One reason for the dendritic growth, i.e. the feather-like branching, is probably that the growing crystals increase the temperature in their surrounding (the phase transition results in the release of heat). Only a little distance away from one of the growing needles, the temperature is right again for the crystal to grow further, resulting in branching. This can happen in a fractal fasion.

There might be another reason contributing to the dendritic growth. The molten material is a mix of two different organic substances. In the crystals, these appear in some fixed ratio, depending on the structure of the crystal lattice. Of one component, there is more than what is “needed” in the crystals, the other one is a “minority component”. As a result of crystal growth, the remaining liquid is depleted of the minority component. Since the remaining substance for itself has a different (and in this case: lower) melting point, it remains liquid and the needles cannot grow thicker. Where a branch meets another one, it depleets the surrounding liquid, so the other crystal has some little indentation there because there was not enough material left (but this might also be a result of remelting because the newly growing branch releases heat). This is probably one of the reasons why the crystals branch: each branch reduces the minority component in the liquid around it, so directly besides the branch, the parent crystal cannot grow thicker. Only a little distance away there is anough of the other material again and another branch starts growing, resulting in a feather-like structure. These are just hypotheses, however. Some scientific research would be required to find out the exact mechanisms at work here.

However, you may leave this to the scientists and just enjoy the pictures for their beauty.

The blurring on the lower side is caused by the fast growth. If you watch this under a microscope, you can see the needles grow. The speed depends on the temperature. Unfortunately, I don’t have any film of this. It is fun to watch.

The motto of this blog is “Natural and Artificial”. Is this natural? Is it artificial? Or both? Maybe natureficial?

Portrait of Rolf Keller, by Rudolf Kraus

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A portrait showing Rolf Keller, drawing. This drawing was made by Rudolf Kraus, another artist living in Karl-Marx-Stadt (today Chemnitz) at the time. The drawing (pen and (probably) black chalk, ca. 14.3 cm x 21.5 cm), signed “Rudolf Kraus, Nov. 22nd, 1956) used to be hanging in my parents living room, so I grew up seeing it. This is the form my grandfather was present most of the time. It is now hanging in my living room.

A caricature made by Herbert Reuter, yet another artist, on January 4th 1962, shows Rudolf (“Rudi”) Kraus, among others. Here is a clipping of it showing Rudolf Kraus (showing this caricature completely needs more preparation to explain the context, so I am not going to do that today):

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Rudolf Kraus is mainly known for works in public places. After the end of the German Democratic Republic, many of these, often in the style of socialist realism, were not thought to be worth keeping and where destroyed during building projects. Looking at the pictures in the Wikipedia article (linked to the name above), I tend to agree. However, the low artistic quality was obviously not due to missing ability on the side of the artist, as the drawing above is of high quality and is attesting the abilities of the artist. Rather the bad taste and ideological thinking of the people in the awarding authorities seems to be responsible. I don’t know how he was thinking about the political system, maybe he simply had no choice.

But I suspect that there must be quite some drawings or other private works of this artist, mostly probably in private collections, so his real oeuvre remains to be discovered.

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This pen drawing, made by Svend Keller in 1949, is an illustration for a newspaper article. Below you can see the finished article, as it was probably published in a local newspaper of Chemnitz (yet to be identified, however I have no proof at the moment the article actually appeared in print, but it probably did). This is one of the very few examples where Svend Keller actually worked commercially in his newly learnt profession as a Graphics Designer. It looks like Svend Keller designed for himself a logo to be used for such purposes (probably a stylized “K”, above the name) but I have not seen it anywhere else yet. I don’t know if other newspaper illustrations by Svend Keller exist. To find out, one would have to screen the old papers from Chemnitz, if they still exist in some library or archive, probably as microfilm. As you can see, in the printed version of the drawing, the top part of the drawing was sacrificed. Perhaps drawings played a greater role in newspapers and magazines in those days than they did later when they where largely replaced by photography.

The author of the article signed “Knudsen”. I have not yet identified who he was. Among the drawings of my father, I have found a print (probably a lithography) showing some rocks in Elbsandsteingebirge, also signed “Knudsen”. I have also seen the name being mentioned in one of Rolf Keller’s letters, but I have not yet evaluated those letters systematically. The article is a reportage describing efforts to remove the ruins at one place in Chemnitz where a new square (“Kollwitzplatz” was being built). If the author of the article is the same person (which is likely since in Germany this is a rare name) who made that print, he was probably a graphics artist as well. Maybe he was working as a freelance author for the local newspapers, providing both articles and drawings. But again, only an investigation into archives and libraries could answer that question.

A rough translation is following below. I can only give an idea of the text here, I don’t know how to capture the subtleties of the slightly propagandistic language of some sections. Remember we are here in eastern Germany, in the Soviet occupation zone, a few months before the foundation of the GDR (DDR). For example, an expression like “das schaffende Chemnitz” (literally “the working Chemnitz”, where the word “schaffen” has a connotation of “to bring into being”) seems to be communist jargon. I have translated it here simply “the workers of Chemnitz”. Probably a native speaker of English with some knowledge of Soviet jargon could come up with a better translation.

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Translation:

Chemnitz

28th of March 1949.

 

Where the Kollwitz-square is forming

Once again, spring is coming into our city, accompanied by many hopes and wishes. With strengthened effort, people work on the rebuilding of the heavily destroyed Chemnitz.

Behind the museum as well, callused worker’s fists are clenching harder. Here, the new Käthe-Kollwitz-Square is forming that is supposed to unite the workers of Chemnitz on Mai 1st into a tremendous peace rally. Ruins are being blasted; a steam shovel is loading the narrow-gauge railway removing the debris.

In the evening the colossus is still digging its giant shovel into the debris. The day’s planned target has to be accomplished. The machine is screeching and making noise. Enormous chunks of debris are thudding into the trolleys. Suddenly, a heavy, elongate steel object is clamped between the digging teeth. A bomb! – For four years, the unexploded bomb had been lying in the ruins, witness of a night of horror. Now, one push is forwarding it into the light of the day. In an instant, the square is deserted. But the operator is keeping his nerve. Gently, he lets the 250 kg chunk glide to the ground.

On the next day, the removal of debris is continued as if nothing has happened. Even an American bomb cannot stop the work!

At noon, two blasts are to be conducted. To prevent a mishap, the unexploded bomb is “screened” by T-beams and boulders. A contingent of the People’s Police closes off the surrounding streets. Two explosions – the walls are collapsing -, work can continue. But now the bomb has to be removed. Defusing it is impossible, the detonator is seized up by rust and such old explosive devices are treacherous things. The power shovel must load the chunk into a trolley. “Well, you can sit inside it!” the machinist is saying.

But then he is doing I nevertheless. Four venturous men are clasping the bomb with a chain and fix it to the giant. It is lifted more gently than a raw egg and loaded into one trolley ready for it. Carefully, it is taken away. At the street, the unexploded bomb is loaded onto a police truck allocated for it, gazed at by many passersby, to be exploded in Rabensteiner forest.

On the Käthe-Kollwitz-square, people are already working again to remove the remains of the war.