Monthly Archives: April 2022

A more accurate permeation tester

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There are two ASTM-approved methods for measuring the gas permeability of a material. The equipment is very similar, and REB Research makes equipment for either. In one of these methods (described in detail here) you measure the rate of pressure rise in a small volume.This method is ideal for high permeation rate materials. It’s fast, reliable, and as a bonus, allows you to infer diffusivity and solubility as well, based on the permeation and breakthrough time.

Exploded view of the permeation cell.

For slower permeation materials, I’ve found you are better off with the other method: using a flow of sampling gas (helium typically, though argon can be used as well) and a gas-sampling gas chromatograph. We sell the cells for this, though not the gas chromatograph. For my own work, I use helium as the carrier gas and sampling gas, along with a GC with a 1 cc sampling loop (a coil of stainless steel tube), and an automatic, gas-operated valve, called a sampling valve. I use a VECO ionization detector since it provides the greatest sensitivity differentiating hydrogen from helium.

When doing an experiment, the permeate gas is put into the upper chamber. That’s typically hydrogen for my experiments. The sampling gas (helium in my setup) is made to flow past the lower chamber at a fixed, flow rate, 20 sccm or less. The sampling gas then flows to the sampling loop of the GC, and from there up the hood. Every 20 minutes or so, the sampling valve switches, sending the sampling gas directly out the hood. When the valve switches, the carrier gas (helium) now passes through the sampling loop on its way to the column. This sends the 1 cc of sample directly to the GC column as a single “injection”. The GC column separates the various gases in the sample and determines the components and the concentration of each. From the helium flow rate, and the argon concentration in it, I determine the permeation rate and, from that, the permeability of the material.

As an example, let’s assume that the sample gas flow is 20 sccm, as in the diagram above, and that the GC determines the H2 concentration to be 1 ppm. The permeation rate is thus 20 x 10-6 std cc/minute, or 3.33 x 10-7 std cc/s. The permeability is now calculated from the permeation area (12.56 cm2 for the cells I make), from the material thickness, and from the upstream pressure. Typically, one measures the thickness in cm, and the pressure in cm of Hg so that 1 atm is 76cm Hg. The result is that permeability is determined in a unit called barrer. Continuing the example above, if the upstream hydrogen is 15 psig, that’s 2 atmospheres absolute or or 152 cm Hg. Lets say that the material is a polymer of thickness is 0.3 cm; we thus conclude that the permeability is 0.524 x 10-10 scc/cm/s/cm2/cmHg = 0.524 barrer.

This method is capable of measuring permeabilities lower than the previous method, easily lower than 1 barrer, because the results are not fogged by small air leaks or degassing from the membrane material. Leaks of oxygen, and nitrogen show up on the GC output as peaks that are distinct from the permeate peak, hydrogen or whatever you’re studying as a permeate gas. Another plus of this method is that you can measure the permeability of multiple gas species simultaneously, a useful feature when evaluating gas separation polymers. If this type of approach seems attractive, you can build a cell like this yourself, or buy one from us. Send us an email to reb@rebresearch.com, or give us a call at 248-545-0155.

Robert Buxbaum, April 27, 2022.

Hypochondriacs anonymous: the first step is admitting you don’t have a disease.

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I’m writing a book about reverse psychology; please don’t buy it.

This one’s not by Rappaport

The judge said I had to keep 6 feet away from my ex-wife. So I buried her under the patio.

Robert Buxbaum: the above 3 jokes are from Jack Rappaport — He sometimes sells jokes. April 13, 2022. The ones below are from Gahan Wilson, and the one at right, I don’t know.

These last two are from Gahan Wilson

Ukraine looks like Vietnam or the beginnings of WWI

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The press and our Russian experts claim we’re helping in Ukraine, protecting it from a Russian invasion. I suspect they are wrong, and that our help and protection will prove to be as deadly to all as in the Vietnam war. I’m also uncomfortable with their presentation their framing of Putin as an out of touch autocrat. Putin has popular support, and acts with a strong sense of history, as I see it, just not our version of history. In the Russian version, it was Russia that stopped the Nazis — of Germany and Ukraine. We are not the heroes of WWII in their telling; I doubt we’ll be the heroes of this conflict either.

We have a habit of seeing ourselves as saving heroes as we enter other people’s conflicts. It is how we got into Vietnam, to save the South from the North. It’s also how Europe got into WWI: Russia was saving Serbia, Germany was saving Austria, etc (see cartoon below). We meddle our way, and leave much later than we planned. The result, as in Vietnam and Afghanistan is far more death and destruction than if we’d minded our own business. And US war-dead too. In Vietnam 58,000 US deaths. In Afghanistan 2,400 US dead. and no obvious accomplishment. As Henry Kissinger famously commented: “It’s dangerous to be America’s enemy, but deadly to be America’s friend.”

European aggression in WWII started with the good intention of preventing aggression. It got out of hand, as I fear our good intentions will in Ukraine.

The US troops we’ve sent to Ukraine are not called soldiers. They are “fighting advisors” sent to help the Ukrainians use our weapons. In WWI and Vietnam, fighting advisors are called invaders; it’s how we got drawn into Vietnam. The Russians claimed to send advisors when they entered the Crimea and later the Dundas. We called it an invasion. We can’t be that blind to our own words. Sooner or later, the advisors will start killing each other– something we’ll call an unprovoked attack. Our high tech aid including anti-tank missiles are reported to have killed some 10,000 Russians so far. We don’t seem to think the Russians will mind, or that they’ll give up as the body count mounts. In Vietnam, the more we killed with our high-tech weapons, the more the Vietnamese on both sides called us the villains, and the more Vietnamese joined the fight against us. That’s the future I fear for Ukraine, or worse. The conflict in WWI spiraled quickly beyond the borders of Serbia to include the whole world, and continued through WWII.

Our approach to diplomacy is counterproductive too, in my opinion, and similar to Vietnam too. We call Putin a terrorist, a madman and a narcissist, and then we begin talks with him to end the war. Biden has asked to have Putin removed by assassination.Does he think this will help, or if Putin is removed his successor will be a friend of the US? We demonized Ho Chi Minh, and propped up our favored, corrupt leaders. Minh was popular, as is Putin, and both have valid reasons for opposing us. Putin worries about the expansion of NATO. It’s not an illegitimate worry given Russian history of repeated invasions from the west.

Our desire to remove Russian leadership is a long-standing mistake. It does not lead to peace, or good negotiation, nor even peaceful co-existence.

Russia has been invaded many times. US schools mention Napoleon’s invasion in 1812 and the German’s in 1941, but there are more. They were invaded by the Germans in WWI too, and by the Ukrainian Cossacks in the days of Khmelnytsky, 1646-57. Before that the Polish Lithuanians, 1609-1618, the Swedes, 1701-1709, and in the early days, it was Tartars, Mongols, who invaded and ruled Russia from about 1225 til they joined with the Russian Tzars about 1650. Add to that, our help in the war of the Whites vs the Reds (1917-23) that produced Ukrainian independence — I talk about the relevance here. With a history like that, Russia has every reason to worry about NATO expansion. We should be cognizant of this and stop calling Putin a madman. Let’s accept the Russian version of history, and the sitting ruler of Russia.

Some cite the Budapest memorandum that lead to the removal of “Ukrainian” nuclear weapons –– read it here. It’s short, only 1 page, and deliberately vague. it was signed by Putin’s predecessor, Boris Yeltsin, for the Russian Federation, along with representatives for Ukraine, The US, and The UK. The missiles were not Ukrainian, they were Soviet, and pointed at us. As a result of that agreement, they were dismantled and moved into Russia. There is no sense that this is an invitation for us to protect Ukraine against Russia. The co-signers sort-of agree to protect Ukraine from outsiders (Germany, Turkey,..?), but that’s not clear. We commit ourselves to peace in the region, and can claim that Russia violated the peace first, but there’s no invitation for us to violate it second. Until recently, the UK provided no military aid. China and most of the EU still trades with Russia; if they see a villainy, it’s not enough to stop trade.

Robert McNamara was Secretary of Defense under Kennedy and Johnson, and a key “Whiz Kid” pushing for war in Vietnam. Years later, he decided Vietnam was a mistake. A sad cartoon: the veterans are walking past the grave monument for the 58,000 US dead. I worry we’ll have a similar cartoon after this war.

In my opinion, our best course is to reduce our military aid to providing only basics: bullets, blankets, food… We should reopen discussions with Putin, not demonize him, or try to remove him. Ukraine will likely fight on even without our high-tech weapons. Perhaps they’ll buy from Europe, or from independent dealers. The death rate on both sides will be lower and peace will come quicker without us. Crimea might remain Ukrainian or Russian, but that will not be our decision. We’ve done enough damage for now. It took many years after the end of the Vietnam war for the instigators admit is was a mistake.

Robert Buxbaum April 3, 2022. Much of my thinking about Vietnam comes from Francis Fitzgerald’s wonderful book “Fire in the Lake”. I see it all happening again here. Also worth reading is this 2014 letter by Henry Kissinger about how to negotiate a peace: “Damning Putin is not a foreign policy; it’s an alibi for the lack of one.” It’s a nice insight. He seems to understand diplomacy about as well as anyone.