September 15, 2017

Oh oh. A plutonium powered satellite hit the atmosphere and the SNAP device vaporized.

As the beautiful Cassini mission comes to an end, I am reminded that television physicist with a cool hair cut, Michio Kaku, opposed the mission, since he was concerned it would crash into the earth, the plutonium RTG - the same kind of device that ironically went to, um, Pluto (for which the element is named) - and wipe out all life on Earth.

And Michio Kaku would know, since he's a famous physicist who appears on TV all the time.

And, now, I have the unpleasant duty to inform you that the very event he feared has happened, and has been reported in a major scientific journal; be scared; very scared.

Here's the report: Atmospheric Burnup of a Plutonium-238 Generator (P. W. Krey, Science 158 (3802), 769-771 1967)

Excerpts from the text:

Now the bad news:



I conclude we're all going to die.

As for Michio Kaku, I have had occasion to watch him on TV. He has a very cool haircut and it makes his kind of slightly supercilious lectures a little bit more tolerable. I can't say I've watched a lot of his shows, but he certainly does seem to know something about stars and stardom.

But again, I haven't watched him too much. I'm not all that much into television physicists.

I will say this. Scrolling ten minutes through Cassini pictures is, for me at least, worth a lifetime of Michio Kaku television appearances.

Just this morning I was reminding of reading, a few years back, Jared Diamond's fabulous book, COLLAPSE: HOW SOCIETIES CHOOSE TO FAIL OR SUCCEED

In it he tells the story of the demise of the Greenland Norse, who he concludes died out because unlike the Inuit, who survived quite well in exactly the same region, even further North than the Norse, the Greenland Norse had some kind of cultural prohibition, a CULT prohibition perhaps, against eating Salmon.

This he concludes from the presence or absence of salmon bones in archaeological sites related to the two cultures. The Norse, he claims, would only eat grain and grain fed domestic animals, and died out, when the temporary warm spell that brought them to Greenland ended. The Inuit lived, eating Salmon, just as they had done for thousands of years.

This is actually relevant to the issue of plutonium burning up in the atmosphere in 1964. (Actually metric ton quantities of it were vaporized in nuclear testing before the SNAP9A plutonium RTG vaporized, but it was generally the 239-isotope and not the more radioactive 238 isotope that powers spacecraft.)

Our atmosphere is collapsing, more rapidly than ever before. We have a cult of so called "renewable energy" to address it, and we've spent trillions of dollars on this cult in just the last ten years, with the result that the rate of the collapse of the atmosphere is increasing, not decreasing.

It has been shown that in the last half a century, the fuel that displaced the most dangerous fossil fuels was nuclear fuel, including a healthy amount of plutonium. There are more than sixty billion tons of carbon dioxide that didn't get dumped into the atmosphere because of plutonium and uranium.

We, however fear plutonium just like the Norse apparently feared Salmon.

Diamond's right; societies choose to fail, apparently in the 21st century, it's all one society, spread across the planet.

And we are failing. In the next two weeks or so, we will reach the annual minimum for the sinusoidal seasonal variation in carbon dioxide atmospheric concentrations. It will come in at above 403 ppm. Ten years ago, the time at which our two trillion dollar expenditure on wildly popular so called "renewable energy" started, it was 381 ppm.

We'd all like to believe that all the responsibility for climate change resides on the right. But just as Lincoln blamed slavery on the South and the North in his 2nd Inaugural address, we on the left have our own guilt in the issue of climate change.

I personally think we should eat the salmon, but I predict we won't.

I'm sorry for this post, but I stumbled across this old paper while researching modern thermoelectric materials, a fascinating subject, and I just couldn't resist this note.

Have a wonderful Friday tomorrow and a wonderful weekend.

September 13, 2017

North Dakota.

September 6, 2017

My Favorite Things

September 4, 2017

Computational Screening of 670,000 Materials For Optimal Separation of Krypton From Xenon.

As I poke around this long weekend through scientific papers that I was inspired to collect but never actually read and filed properly I came across a really cool one, this one: What Are the Best Materials To Separate a Xenon/Krypton Mixture?

(Cory M. Simon†, Rocio Mercado‡, Sondre K. Schnell†§, Berend Smit†?, and Maciej Haranczyk*¶ Chem. Mater., 2015, 27 (12), pp 4459–4475)

Xenon and Krypton are very rare gases in the Earth's atmosphere, from which they are obtained industrially, because they are very useful, at considerable expense. (The most common use for xenon is in automotive headlights because its excited states decay to produce light that is very similar to daylight.)

The authors of the cited paper do quite a nice job in describing some of the background on these two gases, and I'll quote what they say in their introduction:

The noble gases xenon (Xe) and krypton (Kr) have several important applications.28 Xenon is used as an anesthetic 29?31 and for imaging 32 in the health industry and as a satellite propellant in the space industry.33 Both xenon and krypton are used in lighting,34 in lasers,35,36 in double glazing for insulation,37,38 and as carrier gases in analytical chemistry.39 Since krypton and xenon are present in Earth’s atmosphere at concentrations of 1.14 and 0.087 ppm, respectively,40 the conventional method to obtain xenon and krypton is as a byproduct of the separation of air into oxygen and nitrogen by cryogenic distillation.41 This byproduct stream from air separation consists of 80% krypton and 20% xenon.42 At Air Liquide, this mixture is compressed to 200 bar and stored in cylinders, then sent to a separate Xe?Kr separation plant to undergo another cryogenic distillation to obtain pure xenon and pure krypton.43 Cryogenic distillation for the separation of krypton and xenon has a very high energy and capital requirement, reflected by the cost of high-purity xenon, about $5000/kg.44

Both gases are considered in general general to be inert, and until 1962 they were thought not to exhibit any kind of chemistry at all. Since that time, it has been discovered that both gases can, in fact, react to form compounds, krypton only at very low temperatures. The chemistry of xenon, by contrast, is quite extensive. (I touched briefly on the discovery of xenon chemistry here: Neil Bartlett's superpowerful oxidants NiF6- and AgF4- and the preparation of RhF6.)

As noted by the authors, the separation of these two gases is energetically and economically expensive, and the purpose of their paper is to examine, by computer modeling, approaches to designing materials that can reduce the costs of their separation by a technique known as "pressure swing absorption," PSA which relies on a process in which a gas consisting of multiple components is pressured in a chamber in the presence of a solid material that has a capability to absorb one component in preference to another. (Home oxygen generators for medical use, and nitrogen generators in some scientific laboratories utilize a PSA approach to separate these bulk gases.)

It is possible to exploit, I suppose, the chemical differences between the gases to effect their separation, however in most cases the chemistry involves the use of highly reactive, corrosive and toxic fluorine gas. In the presence of water, xenon fluorides can hydrolyze to form xenon oxides which can be highly explosive.

By contrast, pressure swing absorption is orders of magnitude safer and most probably considerably cheaper.

Modern computers are extremely powerful compared with computers from even a short time ago, but computational power is not necessarily cheap or free when one considers very, very, very complex calculations.

Nevertheless in silico calculations can save far greater expense in screening for molecular structures - be they involved in medicinal chemistry or in materials chemistry, such as being explored here - that accomplish these kinds of tasks.

Candidate materials for the separation of these gases exist in quite an array of differing types, again, I'll let the authors describe them:



The separations, as the author's note, in a pressure swing situation rely mostly on the size difference between the two types of atoms: The mean diameter of a xenon atom is 198.5 picometers, of krypton 183 picometers, a small, but significant difference. The idea is to structure the pores in materials so that xenon cannot fit into the pores while krypton can, or conversely that krypton can easily diffuse out of the pores while xenon can do so only slowly. Besides size, differences in their electronic structure - which accounts for the differences in their chemistry - can also be exploited without actual chemical reactions taking place.

Their computational approach, which they describe as considerably streamlined in terms of the computational algorithms utilized previously for one class of possible absorbents, metal organic frameworks (MOF), the previous approach being described as "brute force" is described in the following text:



The authors in this screening process describe two known materials which may be useful in these separations:



This paper has been cited extensively since its publication two years ago, and it might be fun, if I find the time once my favorite academic libraries reopen after the holidays, to look into these citations to see if these predictions have been experimentally confirmed.

It is interesting to note that isotopic ratios of these gases tell us a lot about the history of this planet, owing to the fact that actinide elements, for example, long lived plutonium-244 - which is known to have been a constituent of the early Earth (because of xenon isotopes) - spontaneously fission in a characteristic way that causes a traceable signature of geological history.

(See for example: Xenon isotope constraints on the thermal evolution of the early Earth (Nicolas Coltice a,⁎, Bernard Marty b, Reika Yokochi c, Chemical Geology 266 (2009) 4–9))

As the authors of the original paper note, these separations would also be valuable in the processing of used nuclear fuels, because both elements are fission products. No radioactive isotopes of xenon are very long lived in nuclear fuels; they rapidly decay into other isotopes. Xenon-135 has the highest neutron capture cross section of any nuclide known, it is rapidly converted into non-radioactive xenon-136 in the neutron flux in the core of nuclear reactors. Because of this, it does not accumulate, and in any case its half life is on the order of hours, not days. (The presence of xenon-135 in reactor cores where it is the cause of an effect known as "xenon poisoning" played a role in the very stupid decisions made by the operators of the Chernobyl reactor that exploded: Their decisions, made late at night, to remove the control rods from the reactor was intended to overcome xenon poisoning effects.)

Fission gases contained in fuel rods are therefore highly enriched in these valuable gases, and in theory they could be collected from used nuclear fuel for use, especially xenon.

Krypton contains one relatively long lived radioactive isotope, krypton-85, and its detection has been utilized to identify nuclear explosions (both atmospheric and underground) as well as reprocessing of nuclear fuels around the world, since it is generally vented to the atmosphere rather than recovered for use. (Radiokrypton-85 I think is possibly a very useful material for providing a continuous portable light source for remote locations or as a continuous power source.) Venting it to the atmosphere is probably not a very dangerous practice however, certainly not at the level of venting dangerous fossil fuel waste to the atmosphere, since dangerous fossil fuel waste and dangerous biomass combustion waste combine to cause 7 million deaths every year.

Krypton 85 can also be stored to provide a source of non-radioactive rubidium-85 which would be less radioactive than natural rubidium, since the latter contains the naturally occurring long lived radioactive isotope rubidium-87. However, except for esoteric research purposes, I cannot imagine that there is much call for isotopically pure rubidium-85, but hey, you never know.

Some folks might find all of this stuff as interesting as I do.

Enjoy the rest of the labor day weekend.

September 3, 2017

Trump Administration Announces New $20 Bill Design Honoring Harriet Tubmans Owners

The Trumpist $20 bill

September 2, 2017

Nature: Cassini's 13 Years of Stunning Saturn Science - in Pictures.

Cassini’s 13 years of stunning Saturn science — in pictures

It's brief, but opened sourced; I recommend taking a look at the PDF version.

I love this graphic:

http://www.nature.com/polopoly_fs/7.46007.1504091141!/image/casinis-journey.jpg_gen/derivatives/landscape_630/casinis-journey.jpg

The mission was launched 20 years ago, in 1997. The world seemed so full of hope then; Bill Clinton was President, and even though that racist freak Newt Gingrich was in control of the House of Representatives, it seemed like the country was on the right track in spite of his ignorance now matched by other racists, Paul Ryan and the worst racist in the Senate, Mitch McConnell.

These creeps would have never funded science like this.

No one thought, in 1997, especially not me, that the entire country would be controlled by Neo Nazis who hated science, but here, 20 years later we face this.

The United States was a great nation in 1997; a nation that could launch the Cassini mission. It is terrible how far we have fallen in so short a time.

Let us hope and work to make it that kind of nation again, not a nation of Klansmen, but a great nation that can do things like Cassini. Let this not be the last outstanding space science and engineering to come from our country!

September 2, 2017

The separation of samarium, europium and neodymium from other lanthanides by distillation.

Going through some old unsorted files among the papers I've collected over the years, I came across an oldie but goody, this paper:

Technique for Enhanced Rare Earth Separation. (Tetsuya Uda,1* K. Thomas Jacob,2 Masahiro Hirasawa1, Science 289 2326-2329 2000) The term "Rare Earths" is a colloquial term for "lanthanides" and as generally ill advised since the lanthanides are not really rare although they, like many other elements in the periodic table are subject to depletion, and within one century, reserves of them are expected to be depleted.

If we cared about future generations, this would upset us, but we don't care about future generations so I guess it's OK with us.

The extraction and separation of lanthanides as a class - they always occur in combination with one another albeit in varying proportions along with the radioactive potential nuclear fuel, the element thorium - is very dirty and energy intensive chemistry, particularly when such separations are exempt from environmental laws or where environmental laws are not enforced. (Many of the lanthanides themselves, lanthanum, neodymium, samarium among them have long lived naturally occurring radioactive isotopes.)

The world sources of the lanthanides are dominated by Chinese production.

These elements are very important in any devices involving magnetism, which is most of our electronic stuff like hard disks and similar devices and, on a macroscopic scale things like generators, most notably in wind turbines and electric cars, neither of which are as "green" as advertised, and neither of which represent efficient utilization of materials, since both have low capacity utilization.

Since the chemistry of all of the lanthanides are very close the separation of them from one another is an industrially challenging procedure, generally involving industrial scale chromatography or solvent extraction.

This paper is interesting because it describes a process for separating the lanthanides from molten salts by distillation by exploiting the differing stability of their +2 oxidation state, which are, apparently appreciably volatile. Distillation in general is a cleaner process than either solvent extraction or chromatography, at least where clean energy is available. (Distillation is also utilized to make some very dirty fuels; probably the largest use of distillation in the world is to refine petroleum, a very dangerous and unsustainable fuel.)

Some text from the paper, beginning with the introductory paragraph which succinctly says (without sarcasm) what I touched on above:

Some process description:



Some notes on material efficiency:



Separation factors such as 570 for neodymium to samarium were obtained.

It's been 17 years since this paper was published, and I have no idea whether the techniques described herein have ever found industrial application, many ideas - even exceptionally good ideas - do not go commercial. The paper has, however, been cited 89 times according to Google Scholar.

I find it interesting for its utility for the recovery of lanthanides from used nuclear fuels, where they occur as potentially valuable fission products.

Enjoy the holiday weekend.

September 2, 2017

An interesting thesis on the utility of MAX phases in the manufacture of turbine blades.

I'm sorting through some papers I collected back in 2015 but never got around to filing correctly after being diverted by other topics.

I came across a nice graduate thesis in my files that involve my interest in refractory materials, materials which exhibit high strength and corrosion resistance at very high temperatures. It's rather old, 17 years old to be precise, but it touches on the vapor phase synthesis or a remarkable class of materials, the MAX phases.

The thesis is in the public domain. It is here: Simulation of Diffusion Processes in Turbine Blades and Large Area Deposition of MAX Phase Thin Films with PVD

(Don't be put off by the acknowledgements in German; the thesis itself is in English.)

The industrial importance of refractory materials cannot be underestimated, they are essential components of jet engines, and regrettably - given the decision of our generation to strip all future generations of a safe and sustainable planet by enthusiasm for the dangerous fossil fuel "natural" gas, albeit with an idiotic and fraudulent so called "renewable energy" fig leaf - combined cycle dangerous natural gas power plants.

From a materials science perspective, all modern turbines, jet engines as well as dangerous natural gas plants, rely on what are known as "superalloys." A useful and informative monograph on the topic and properties of superalloys is this one: Superalloys: Alloying and Performance

In many turbines, especially gas turbines, superalloys actually function at temperatures higher than their melting point; this is possible only because they are generally coated with ceramic thermal barrier coatings, typically zirconium dioxide bonded to the superalloy surface with an alumina bonding agent. A paper I like a lot on this subject was published some years back by the great materials science engineer Emily Carter, now the Dean of Engineering at Princeton University: Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

Superalloys are generally nickel based, but their performance is very much a function of their alloying agents. I referred to the aformentioned monograph in a post elsewhere sometime back relating to the important superalloy alloying element rhenium , which may property considered to be the rarest occurring stable element on earth; we will run out of it and do so soon, but maybe not fast enough.

That post is here: Technetium: Dangerous Nuclear Energy Waste or Essential Strategic Resource?

(Hopefully the depletion of rhenium reserves will effect the economics of dangerous natural gas in a more obvious way than the current generation is loathe to recognize. Some people, venal people, badly educated people or people who are simply indifferent and too lazy to think say natural gas is "cheap." It isn't. The real costs of dangerous natural gas are obscured by the fact that this fuel is allowed to kill people at will with almost no note as well as the fact that its users are allowed to dump an intractable waste form from it that can never and will never be contained and will destroy most major ecosystems on this planet, carbon dioxide. All future generations will pay for our terrible decision to use natural gas. Humanity will be paying for the natural gas we burn today forever. Don't worry, be happy: Current models of climate economics assume that lives in the future are less important than lives today, a value judgement that is rarely scrutinized and difficult to defend. Screw future generations; we have our own problems.)

MAX phases are ternary alloys that have the properties of both metals and ceramics. They are extremely refractory like very high temperature ceramics such as borides, silicides, nitrides and carbides (and in fact, formally they are either nitrides or carbides) but they have properties that ceramics lack: They are machinable, often flexible rather than brittle, and they can conduct both heat and electricity. MAX phases are ternary, and consist of three elements, one of which is an early transition element, one is a early non metal or semi-metal and one which is, again, either carbon or nitrogen. The most famous and most widely studied MAX phase is Ti3SiC2.

Dr. Walter has a nice brief description of the MAX phases in her thesis, albeit that some of her remarks are now dated:

Michel Barsoum at Drexel University - a world leader in MAX phase research - has characterized a large number of MAX phases since Dr. Walter's thesis was published. (My son met Dr. Barsoum during an open house during his college search process, ironically and entirely coincidentally at precisely the same time I was reading Dr. Barsoum's book; my son was admitted to Drexel, but chose another university.)

Anyway, the thesis is interesting, if only for the account of a novel approach to synthesizing the MAX phases, a vapor phase approach. If I were researching this topic, I'd choose a different approach, and perhaps someone already has done what I would do, but again, it's interesting. Titanium silicon and carbon are some of the most common elements on the planet, and the discovery of the FCC process for titanium reduction a few years back now makes this metal industrially more accessible. While I detest natural gas and its defenders, I'm not against high temperature turbines; I think we need them.

I note that turbines operating at very high temperatures can achieve very high thermodynamic efficiency and high temperatures do not require filthy fuels like natural gas; they are accessible with nuclear energy.

Enjoy the holiday weekend.