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NNadir

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A nice little table of the technologies utilizing the lanthanide elements.

I am not going to fully cover the paper from which this graphic comes, because it is on the subject of recovering elements from flowback water from the "fracking" industry in China.

The paper is this one: Rare Earth Elements Occurrence and Economical Recovery Strategy from Shale Gas Wastewater in the Sichuan Basin, China (Liu et al., ACS Sustainable Chem. Eng. 2020, 8, 32, 11914–11920)

As I have made clear, many times, I oppose all dangerous fossil fuels, the mining of all dangerous fossil fuels, and frankly, any technology which attempts to claim to mitigate the tragedy, because all of these attempts have and will prove trivial as compared to dangerous fossil fuels.

One of the huge waste profiles of dangerous natural gas - which many people who believe that so called "renewable energy" ignore based on their toxic fantasy that dangerous natural gas is "transitional" - is flow back water, the chemical and mineral laced water that is used to hydraulically shatter rocks permanently in the earth's crust so our generation can work to get the last molecule of methane burned and its waste, carbon dioxide, dumped into the planetary atmosphere, this at the expense of all future generations.

Many putative "green" technologies actually depend heavily on lanthanide elements, the overwhelming majority of which are mined and processed in China, often under decidedly dirty conditions that are hardly "green."

These elements, once thought as laboratory curiosities - I don't think we spent more than 5 minutes discussing them in my high school chemistry class when I was a child - are now key to many technologies.

This graphic from the paper shows how things have changed in my (long) lifetime, and how many technologies rely on access and purification of these elements which are, in general, not "renewable."



The caption:

Figure 1. (a) Range of applications for REEs in many fields. (b) Water samples collected from different sites in Sichuan Basin, China.


With the exception of scandium (Sc) (which could in theory be made via the neutron irradiation of calcium) all of the elements listed in this table up to (and more or less including) gadolinium (Gd) are present in used nuclear fuels, although some of them would require fairly long cooling before being available for non-nuclear applications and/or applications in closed systems. (Some closed system applications would be improved by using the radioactive forms of these elements rather than the stable form, but that's not current practice.) Others, such as yttrium, lanthanum, praseodymium, neodymium, would require very short (or no) cooling times, cerium only moderate cooling times. However the same energy to mass ratio that makes nuclear fuels superior in a purely environmental sense to all other forms of energy, means that the amounts available would more or less be trivial when compared to those available from the ores we are working so hard to deplete.

One of the elements listed, promethium, does not occur on earth except in minuscule amounts, from spontaneous fission in uranium ores. It has no stable, non-radioactive isotopes. Pm-147 can, and has been isolated from used nuclear fuels, but its use in signage, lighting and batteries has been limited because regrettably, nuclear fuel recycling has been limited.

I knew of most of these applications, but it was nice to see them all in one place, and I thought I'd post it.

I hope you're having a wonderful weekend.

Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes

The paper I will discuss in this post is this one: Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes (Vladislav Kamysbayev, Alexander S. Filatov, Huicheng Hu, Xue Rui, Francisco Lagunas, Di Wang, Robert F. Klie, Dmitri V. Talapin, Science 21 Aug 2020: Vol. 369, Issue 6506, pp. 979-983)

My son decided that he wanted to go into materials science while still in high school, and as such, we visited the Materials Science Departments of the various universities during the touring process. I attended the majority of them, but my wife took my son to Drexel University where, I learned afterward, the great Egyptian-American scientist Michel Barsoum actually came to speak to the prospective students, this, ironically on the very day I had acquired access to his book, MAX Phases: Properties of Machinable Ternary Carbides and Nitrides



Of course, if I had attended, any effort on my part to have engaged Dr. Barsoum would have distracted from his mission, which was to convince promising students to come to Drexel where, according to my wife, he promised, if they worked hard, even freshman undergraduates could be invited to work in his lab.

Drexel made my son a decent offer but the university he ultimately attended made him a great offer, and anyway, my son really found the idea of attending a university located right in a major metropolitan area distasteful, which is why he refused to even look at NYU, Columbia or MIT, not that any of these universities would have made him an offer we could have afforded to accept, or for that matter, even admitted him. So he didn't go to Drexel, and he didn't get to work with Michel Barsoum, even though his father had been discussing the MAX phases with him for some time.

In my opinion, however, Dr. Barsoum is one of the most important scientists of our time. He did not discover the MAX Phases, but he recognized them for what they were, greatly expanded on the knowledge of their chemistry and properties, and as published with scientists all over the world on the subject.

The MAX phases (which Dr. Barsoum named) have many of the important features of ceramics, resistance to high temperatures, resistance to harsh chemicals, while possessing some of the important properties of metals, specifically, machinability, as they lack the brittle nature of ceramics. I came across them in connection with my interest in high temperature materials and chemical resistance given my interest in nuclear reactors as well as in thermochemical carbon dioxide and water splitting using them in order to make for a sustainable world, something that we are no closer to doing than when I was a child; in fact we are living in a less sustainable world than the one into which I was born. (History will not forgive my generation, nor should it.) In any case, structurally, MAX phases consist of layers of atoms in a fairly precise arrangement, and this, as Dr. Barsoum and others have taught the world, leaves them capable of offering new opportunities in materials science in many areas.

One area in which Dr. Barsoum has further pioneered the applicability of these materials is in their use in preparing "MAXenes" which are two dimensional layered materials having a single molecule thickness. Although the MAX phases are notable for their chemical resistance, there are some which do react with chemicals. The most famous MAX phase - there are many, but the most famous - is Ti3SiC2. If this phase is treated with hydrofluoric acid, the silicon in them can be dissolved, leaving a two dimensional series of layers of Titanium carbide. The invention of the FFC Cambridge process should make titanium metal readily available in the future at reasonable prices, and the properties of its carbides (and indeed, the already widely used nitride) are very, very, very, exciting.

Much of what is written today on the subject of two dimensional materials these days relates to graphene and graphene nitride. MAXenes open up a much larger segment of the periodic table to these types materials.

Modification to MAXene titanium carbides is the subject of the paper under discussion and it extends the elements of the period table to two dimensional materials to the halides.

From the introduction to the paper:

Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) (1) have been actively studied for applications in supercapacitors (2), batteries (3), electromagnetic interference shielding (4), composites (5, 6), and catalysts (7). MXenes are typically synthesized from the corresponding MAX phases (Fig. 1A), where M stands for the transition metal (e.g., Ti, Nb, Mo, V, W, etc.) and X stands for C or N, by selectively etching the main group element A (e.g., Al, Ga, Si, etc.). The etching is usually performed in aqueous hydrofluoric (HF) solutions, rendering MXenes terminated with a mixture of F, O, and OH functional groups, commonly denoted as Tx. These functional groups can be chemically modified, unlike the surfaces of other 2D materials such as graphene and transition-metal dichalcogenides. Recent theoretical studies predict that selective terminations of MXenes with different surface groups can lead to remarkable properties, such as opening or closing bandgap (8), room-temperature electron mobility exceeding 104 cm2/V⋅s (9), widely tunable work functions (10), half-metallicity, and 2D ferromagnetism (11). Covalent functionalization of MXene surfaces is expected to uncover new directions for rational engineering of 2D functional materials

The surface of MXene sheets is defined during MAX phase etching. Electrochemical and hydrothermal methods have been recently applied for etching MAX phases without resorting to HF solutions, but the use of aqueous solutions introduces a mixture of Cl, O, and OH surface groups (12, 13). The etching of Ti3AlC2 MAX phase in molten ZnCl2 and several other Lewis acidic molten salts above 500°C results in Ti3C2Cl2 MXene with a pure Cl termination (14, 15). Because etching of MAX phases in molten salts eliminates unwanted oxidation and hydrolysis, we used a variation of this method for synthesis of Ti3C2Cl2, Ti2CCl2, and Nb2CCl2 MXenes in CdCl2 molten salt (figs. S1 to S5). Moreover, the use of Lewis acidic CdBr2 allowed us to extend the molten salt etching route beyond chlorides to prepare the first Br-terminated Ti3C2Br2 and Ti2CBr2 MXenes (Fig. 1, B and C, and figs. S6 and S7)...


Figure 1:



The caption:

Fig. 1 Surface reactions of MXenes in molten inorganic salts.
(A) Schematics for etching of MAX phases in Lewis acidic molten salts. (B) Atomic-resolution high-angle annular dark-field (HAADF) image of Ti3C2Br2 MXene sheets synthesized by etching Ti3AlC2 MAX phase in CdBr2 molten salt. The electron beam is parallel to the [21¯1¯0] zone axis. (C) Energy-dispersive x-ray elemental analysis (line scan) of Ti3C2Br2 MXene sheets. a.u., arbitrary units. HAADF images of (D) Ti3C2Te and (E) Ti3C2S MXenes obtained by substituting Br for Te and S surface groups, respectively. (F) HAADF image of Ti3C2⬜⬜2 MXene (⬜ stands for the vacancy) obtained by reductive elimination of Br surface groups.


Here is a excerpted brief discussion of the chemical processing of these phases:

The transition-metal atoms from the outer layers of MXene sheets (Ti, Mo, Nb, and V) form relatively weak M-Cl and M-Br bonds, in comparison to M-F and M-OH bonds typical for MXenes with Tx surface groups. This point can be demonstrated by the enthalpies of formation for TiBr4 (−617 kJ mol−1) and TiCl4 (−804 kJ mol−1) versus TiF4 (−1649 kJ mol−1), as well as by direct comparison of the bond energies (table S1). Strong Ti-F and Ti-O bonds make it difficult to perform any postsynthetic covalent surface modifications of MXenes (16). In contrast, Cl- and Br-terminated MXenes with labile surface bonding act as versatile synthons for further chemical transformations.

MXene surface exchange reactions typically require temperatures of 300° to 600°C, which are difficult to achieve using traditional solvents. We instead used molten alkali metal halides as solvents with unmatched high-temperature stability, high solubility of various ionic compounds, and wide electrochemical windows (17–19). For example, Ti3C2Br2 MXene (Fig. 1B) dispersed in CsBr-KBr-LiBr eutectic (melting point: 236°C) reacted with Li2Te and Li2S to form Ti3C2Te (Fig. 1D and figs. S8 to S10) and Ti3C2S (Fig. 1E and fig. S11) MXenes, respectively. The reactions of Ti3C2Cl2 and Ti3C2Br2 with Li2Se, Li2O, and NaNH2 yielded Ti3C2Se, Ti3C2O, and Ti3C2(NH) MXenes, respectively (figs. S12 to S16). The multilayers of Ti3C2Tn MXenes (T = Cl, S, NH) were further treated with n-butyl lithium (n-BuLi) resulting in Li+ intercalated sheets (fig. S17) with a negative surface charge (Fig. 2A and fig. S18)


A graphic on delamination of the MAXenes:



The caption:

Fig. 2 Delamination of multilayer Ti3C2Tn MXenes.

(A) Schematic of delamination process. (B) Photographs of stable colloidal solutions of Ti3C2Tn MXenes (T = Cl, S, NH) in NMF exhibiting Tyndall effect. (C) TEM image of Ti3C2Cl2 MXene flakes deposited from a colloidal solution. (Inset) Fast Fourier transform of the circled region, showing crystallinity and hexagonal symmetry of the individual flake. (D) XRD patterns of multilayer MXene and delaminated flakes in a film spin coated on a glass substrate.


There is considerable discussion in the paper of various means and results of characterization, including a discussion of the electrical properties of these materials.

The above examples show that the composition and structure of MXenes can be engineered with previously unattainable versatility. Chemical functionalization of MXene surfaces is expected to affect nearly every property of these materials, and we found that the surface groups defined the nature of electronic transport in Nb2CTn MXenes. Figure 4, A and B, shows temperature-dependent four-probe resistivity (ρ measured on cold-pressed pellets of Nb2CTn (T = ⬜, Cl, O, S, Se) MXenes (fig. S41), all synthesized by the procedures described above. Figure 4A also compares the conductivity of the parent Nb2AlC MAX phase with that of Nb2CCl2 MXene. Above 30 K, both MAX phase and MXene samples showed similar specific resistivity, which decreased when the sample was cooled. This temperature dependence is often associated with metallic conductivity. The ultraviolet photoelectron spectroscopy (UPS) confirmed nonzero density of electronic states at the Fermi energy EF (fig. S42), which is also consistent with a metallic state.


Figure 4:



The caption:

Fig. 4 Electronic transport and superconductivity in Nb2CTn MXenes.
(A) Temperature-dependent resistivity for the cold-pressed pellets of Nb2AlC MAX phase and Nb2CCl2 MXene. (Inset) Magnetic susceptibility (i.e., ratio of magnetization to magnetizing field strength) of Nb2CCl2 MXene as a function of temperature. FC and ZFC correspond to the field cooled and zero-field cooled measurements, respectively. emu, electromagnetic unit. (B) Temperature-dependent resistivity for the cold-pressed pellets of Nb2CTn MXenes. (Inset) Resistance as a function of temperature at different applied magnetic fields (0 to 8 T) for the cold-pressed pellets of Nb2CS2 MXene.


I never get too excited about applications of niobium, since niobium is a monoisotopic (A = 93) element that is subject to depletion of resources and which cannot be obtained from used nuclear fuel owing to the long half-life of its parent, Zr-93.

In any case, the authors continue:

However, when the Nb2CCl2 MXene was cooled below 30 K, the resistivity started increasing, possibly indicating the onset of localization. A sharp drop of resistivity by several orders of magnitude occurred at a critical temperature Tc ~ 6.0 K (Fig. 4A), which is reminiscent of a superconductive transition. The magnetic susceptibility measurements showed the development of a strong diamagnetism below 6.3 K that we interpreted as the Meissner effect (Fig. 4A). From the magnitude of zero-field cooled data at 1.8 K, we estimated the lower bound for the superconducting volume fraction of Nb2CCl2 MXene as ~35%. Consistent with superconductivity, the transition broadened, and Tc shifted to lower temperatures with the application of an external magnetic field (Fig. 4B and fig. S43). In contrast, the parent Nb2AlC MAX phase exhibited normal metal behavior down to the lowest measured temperature (1.8 K), which is consistent with a previously reported Tc ~ 0.44 K for Nb2AlC (28). For reference, Nb2CTx MXene with mixed O, OH, and F termination prepared by the traditional aqueous HF etching route shows two orders of magnitude higher resistivity and no superconductivity (fig. S44) (29).


In the conclusion the authors suggest a breakthrough in MAXene processing:

The MXene exchange reactions represent an exciting counterexample to the traditional perception of solids as entities that are difficult to postsynthetically modify. We showed that chemical bonds inside an extended MXene stack can be rationally designed in a way that is more typical for molecular compounds. Other MXene structures could be enabled by the combinations of etching and substitution reactions using Lewis acidic and Lewis basic molten salts, respectively.


It's a cool paper on what I regard as an important area in the future of materials science.

I trust you are having a pleasant weekend and enjoying the excitement over our outstanding virtual Democratic Party and are filled, as I am, with feelings of hope.














Five charts that will change everything you know about mud

The current issue of Science, has a number of articles, and a cover, devoted to mud.

Special Issue: A World of Mud



They are news items, not research papers.

One is called, as the title here indicates: Five charts that will change everything you know about mud (By David Malakoff, Nirja Desai, Xing Liu, Science, August 21, 2020.)

(One may need a subscription to open the paper, I'm not sure.)

An excerpt from the introduction:

Glop. Mire. Ooze. Cohesive sediment. Call it what you want, mud—a mixture of fine sediment and water—is one of the most common and consequential substances on Earth. Not quite a solid, not quite a liquid, mud coats the bottoms of our lakes, rivers, and seas. It helps form massive floodplains, river deltas, and tidal flats that store vast quantities of carbon and nutrients, and support vibrant communities of people, flora, and fauna. But mud is also a killer: Mudslides bury thousands of people each year.

Earth has been a muddy planet for 4 billion years, ever since water became abundant. But how it forms and moves have changed dramatically. About 500 million years ago, the arrival of land plants boosted the breakdown of rock into fine particles, slowed runoff, and stabilized sediments, enabling thick layers of mud to pile up in river valleys. Tectonic shifts that gave rise to mountains, as well as climate changes that enhanced precipitation, accelerated erosion, and helped blanket sea floors with mud hundreds of meters thick. Over time, many mud deposits hardened into mudrock, the most abundant rock in the geologic record, accounting for roughly half of all sedimentary formations.

Now, humans are a dominant force in the world of mud. Starting about 5000 years ago, erosion rates shot up in many parts of the world as our ancestors began to clear forests and plant crops. Even more sediment filled rivers and valleys, altering landscapes beyond recognition. In some places dams and dykes trapped that mud, preventing fresh sediment from nourishing floodplains, deltas, and tidal flats and causing them to shrink (see graphic below). And industrial processes began to produce massive quantities of new forms of mud—mine and factory waste—that is laden with toxic compounds and often stored behind dams that can fail, unleashing deadly torrents...


A few of the five charts:







An interesting read, these news items.

Something about my EKG is freaking medical people out.

Twenty-seven years ago, after an EKG, and echocardiogram, a stress echocardiogram, and finally an angiogram, my cardiologist at the time - not the most pleasant guy in the world, truth be told - told me that every time someone took my EKG, they were going to freak out and send me for all kinds of tests, if not hospitalize me. (This actually took place after two hospitalizations, one involving a stay in an ICU.)

So I just went through my third or fourth - I can't remember how many more - stress echo.

Now I just tell this story with every EKG freak out, and nobody gets excited, but they do get "concerned," with far more class than Susan Collins could ever muster.

However in the most recent freak-out my general physician did tell me that I'm older now, fatter now, with (managed) high blood pressure (why, oh why, do I ever post in E&E here) and that my EKG had "changed," and I should get it checked out.

So I went again.

A good time was had by all; wonderful nice techs, a very friendly and warm cardiologist. I got to get injected with a lipid formulation of the greenhouse gas SF6 as a contrast agent, got to talk a little about the chemistry of the gas.

"Looks good," the cardiologist told me. (Usually they don't tell you on the spot, but this is the first one where a cardiologist was in the room.)

I do have - I learned about 3 or 4 years ago when I'd developed a murmur - a mild mitral prelapse, this from a "normal" (non-stress) echocardiogram but no big deal.

I should lose weight, and I probably should stop talking about energy, engineering and climate change, especially in E&E.

But a good time was had by all.

Life is wonderful and then you die.

I will die - as my angiogram physician told me in a deadpan example of bad bedside manner, adding, after a pause, "but almost certainly not from heart disease."

Again...

A good time was had by all.

Life is wonderful and then you die.

He's on fire. Period, a President who can actually speak in complete sentences. Go Joe!!! n/t.

Obama's Speech Will Stand in the Pantheon of the Great Presidential Speeches from which He Drew.

I actually wept when I heard it not just the power, the sober emotion, but the brilliant way he drew upon the great speeches of other Presidents.

This speech, Obama's greatest, will live in history as one of the great American orations.

I consider that Lincoln made four of the greatest Presidential Speeches ever; obviously the Gettysburg Address, and the Second Inaugural, but I feel - as do others - that the Cooper Union address (made before he was President) and the often overlooked First Inaugural (which included the line - attributed to Seward - of "better angels of our nature" ) stand near the other two.

Then there is F.D. Roosevelt's first inaugural - "the only thing we have to fear is fear itself" - as well as his "four freedoms" speech in early 1941.

Another great (post-Presidency) speech in what I regard the great Pantheon is Theodore Roosevelt's "Citizenship in a Republic," and to these we may add, perhaps on a slightly lower level, but still among the great speeches, Dwight Eisenhower's farewell speech, Washington's Farewell, and perhaps Thomas Jefferson's first inaugural: "We are all Republicans; we are all Federalists."

Obama's speech should stand among these. For points, I reproduce the text (as provided by CNN) and highlight in bold the points where Obama showed his profound scholarship, his love and knowledge of our country's history, and his drawing on great American evocations of the past to make a new and novel statement of the importance of our country and evoke some of the antecedents among great American speeches that he evokes and makes his own.


Good evening, everybody. As you've seen by now, this isn't a normal convention. It's not a normal time. So tonight, I want to talk as plainly as I can about the stakes in this election. Because what we do these next 76 days will echo through generations to come.

I'm in Philadelphia, where our Constitution was drafted and signed. It wasn't a perfect document. It allowed for the inhumanity of slavery and failed to guarantee women -- and even men who didn't own property -- the right to participate in the political process. But embedded in this document was a North Star that would guide future generations; a system of representative government -- a democracy -- through which we could better realize our highest ideals. Through civil war and bitter struggles, we improved this Constitution to include the voices of those who'd once been left out. And gradually, we made this country more just, more equal, and more free.

(Draws on the Gettysburg "Conceived in liberty and dedicated to the proposition...a new birth of freedom)


The one Constitutional office elected by all of the people is the presidency. So at minimum, we should expect a president to feel a sense of responsibility for the safety and welfare of all 330 million of us -- regardless of what we look like, how we worship, who we love, how much money we have -- or who we voted for.

But we should also expect a president to be the custodian of this democracy. We should expect that regardless of ego, ambition, or political beliefs, the president will preserve, protect, and defend the freedoms and ideals that so many Americans marched for and went to jail for; fought for and died for.

(Gettysburg: "We cannot dedicate, we cannot consecrate this hallowed ground...the brave men...consecrated it far beyond our poor power to add or subtract" )

(FDR, The Four Freedoms: "I suppose that every realist knows that the democratic way of life is at this moment being directly assailed in every part of the world–assailed either by arms, or by secret spreading of poisonous propaganda by those who seek to destroy unity and promote discord in nations that are still at peace." )


I have sat in the Oval Office with both of the men who are running for president. I never expected that my successor would embrace my vision or continue my policies. I did hope, for the sake of our country, that Donald Trump might show some interest in taking the job seriously; that he might come to feel the weight of the office and discover some reverence for the democracy that had been placed in his care.

But he never did. For close to four years now, he's shown no interest in putting in the work; no interest in finding common ground; no interest in using the awesome power of his office to help anyone but himself and his friends; no interest in treating the presidency as anything but one more reality show that he can use to get the attention he craves.

Donald Trump hasn't grown into the job because he can't. And the consequences of that failure are severe. 170,000 Americans dead. Millions of jobs gone while those at the top take in more than ever. Our worst impulses unleashed, our proud reputation around the world badly diminished, and our democratic institutions threatened like never before.

(Lincoln's second: "If the lord wills that every drop of blood drawn with the lash be paid with another drawn with the sword...)

(Four Freedoms, as evoked above.)


Now, I know that in times as polarized as these, most of you have already made up your mind. But maybe you're still not sure which candidate you'll vote for -- or whether you'll vote at all. Maybe you're tired of the direction we're headed, but you can't see a better path yet, or you just don't know enough about the person who wants to lead us there.

So let me tell you about my friend Joe Biden.

Twelve years ago, when I began my search for a vice president, I didn't know I'd end up finding a brother. Joe and I came from different places and different generations. But what I quickly came to admire about him is his resilience, born of too much struggle; his empathy, born of too much grief. Joe's a man who learned -- early on -- to treat every person he meets with respect and dignity, living by the words his parents taught him: "No one's better than you, Joe, but you're better than nobody."

That empathy, that decency, the belief that everybody counts -- that's who Joe is.

When he talks with someone who's lost her job, Joe remembers the night his father sat him down to say that he'd lost his.
When Joe listens to a parent who's trying to hold it all together right now, he does it as the single dad who took the train back to Wilmington each and every night so he could tuck his kids into bed.

When he meets with military families who've lost their hero, he does it as a kindred spirit; the parent of an American soldier; somebody whose faith has endured the hardest loss there is.

For eight years, Joe was the last one in the room whenever I faced a big decision. He made me a better president -- and he's got the character and the experience to make us a better country.

And in my friend Kamala Harris, he's chosen an ideal partner who's more than prepared for the job; someone who knows what it's like to overcome barriers and who's made a career fighting to help others live out their own American dream.

Along with the experience needed to get things done, Joe and Kamala have concrete policies that will turn their vision of a better, fairer, stronger country into reality.

They'll get this pandemic under control, like Joe did when he helped me manage H1N1 and prevent an Ebola outbreak from reaching our shores.

They'll expand health care to more Americans, like Joe and I did ten years ago when he helped craft the Affordable Care Act and nail down the votes to make it the law.

They'll rescue the economy, like Joe helped me do after the Great Recession. I asked him to manage the Recovery Act, which jump started the longest stretch of job growth in history. And he sees this moment now not as a chance to get back to where we were, but to make long-overdue changes so that our economy actually makes life a little easier for everybody -- whether it's the waitress trying to raise a kid on her own, or the shift worker always on the edge of getting laid off, or the student figuring out how to pay for next semester's classes.

(T.R Citizenship in a Republic: "The pioneer days pass; the stump-dotted clearings expand into vast stretches of fertile farm land; the stockaded clusters of log cabins change into towns; the hunters of game, the fellers of trees, the rude frontier traders and tillers of the soil, the men who wander all their lives long through the wilderness as the heralds and harbingers of an oncoming civilization, themselves vanish before the civilization for which they have prepared the way."


Joe and Kamala will restore our standing in the world -- and as we've learned from this pandemic, that matters. Joe knows the world, and the world knows him. He knows that our true strength comes from setting an example the world wants to follow. A nation that stands with democracy, not dictators. A nation that can inspire and mobilize others to overcome threats like climate change, terrorism, poverty, and disease.

But more than anything, what I know about Joe and Kamala is that they actually care about every American. And they care deeply about this democracy.

They believe that in a democracy, the right to vote is sacred, and we should be making it easier for people to cast their ballot, not harder.

They believe that no one -- including the president -- is above the law, and that no public official -- including the president -- should use their office to enrich themselves or their supporters.

(T.R: "As the country grows, its people, who have won success in so many lines, turn back to try to recover the possessions of the mind and the spirit, which perforce their fathers threw aside in order better to wage the first rough battles for the continent their children inherit. The leaders of thought and of action grope their way forward to a new life, realizing, sometimes dimly, sometimes clear-sightedly, that the life of material gain, whether for a nation or an individual, is of value only as a foundation, only as there is added to it the uplift that comes from devotion to loftier ideals." )


They understand that in this democracy, the Commander-in-Chief doesn't use the men and women of our military, who are willing to risk everything to protect our nation, as political props to deploy against peaceful protesters on our own soil. They understand that political opponents aren't "un-American" just because they disagree with you; that a free press isn't the "enemy" but the way we hold officials accountable; that our ability to work together to solve big problems like a pandemic depends on a fidelity to facts and science and logic and not just making stuff up.

(FDR, four freedoms: "In times like these it is immature–and incidentally, untrue–for anybody to brag that an unprepared America, single-handed, and with one hand tied behind its back, can hold off the whole world." )


None of this should be controversial. These shouldn't be Republican principles or Democratic principles. They're American principles. But at this moment, this president and those who enable him, have shown they don't believe in these things.

Tonight, I am asking you to believe in Joe and Kamala's ability to lead this country out of these dark times and build it back better. But here's the thing: no single American can fix this country alone. Not even a president. Democracy was never meant to be transactional -- you give me your vote; I make everything better. It requires an active and informed citizenry. So I am also asking you to believe in your own ability -- to embrace your own responsibility as citizens -- to make sure that the basic tenets of our democracy endure. Because that's what at stake right now. Our democracy.

(Pretty much all of T.R's speech.)


Look, I understand why many Americans are down on government. The way the rules have been set up and abused in Congress make it easy for special interests to stop progress. Believe me, I know. I understand why a white factory worker who's seen his wages cut or his job shipped overseas might feel like the government no longer looks out for him, and why a Black mother might feel like it never looked out for her at all. I understand why a new immigrant might look around this country and wonder whether there's still a place for him here; why a young person might look at politics right now, the circus of it all, the meanness and the lies and crazy conspiracy theories and think, what's the point?

Well, here's the point: this president and those in power -- those who benefit from keeping things the way they are -- they are counting on your cynicism. They know they can't win you over with their policies. So they're hoping to make it as hard as possible for you to vote, and to convince you that your vote doesn't matter. That's how they win. That's how they get to keep making decisions that affect your life, and the lives of the people you love. That's how the economy will keep getting skewed to the wealthy and well-connected, how our health systems will let more people fall through the cracks. That's how a democracy withers, until it's no democracy at all.

(FDR, first inaugural: "Yet our distress comes from no failure of substance. We are stricken by no plague of locusts. Compared with the perils which our forefathers conquered because they believed and were not afraid, we have still much to be thankful for. Nature still offers her bounty and human efforts have multiplied it. Plenty is at our doorstep, but a generous use of it languishes in the very sight of the supply. Primarily this is because the rulers of the exchange of mankind's goods have failed, through their own stubbornness and their own incompetence, have admitted their failure, and abdicated. Practices of the unscrupulous money changers stand indicted in the court of public opinion, rejected by the hearts and minds of men.

True they have tried, but their efforts have been cast in the pattern of an outworn tradition. Faced by failure of credit they have proposed only the lending of more money. Stripped of the lure of profit by which to induce our people to follow their false leadership, they have resorted to exhortations, pleading tearfully for restored confidence. They know only the rules of a generation of self-seekers. They have no vision, and when there is no vision the people perish.

The money changers have fled from their high seats in the temple of our civilization. We may now restore that temple to the ancient truths. The measure of the restoration lies in the extent to which we apply social values more noble than mere monetary profit."

FDR, Four Freedoms: "We must especially beware of that small group of selfish men who would clip the wings of the American eagle in order to feather their own nests." )


We can't let that happen. Do not let them take away your power. Don't let them take away your democracy. Make a plan right now for how you're going to get involved and vote. Do it as early as you can and tell your family and friends how they can vote too. Do what Americans have done for over two centuries when faced with even tougher times than this -- all those quiet heroes who found the courage to keep marching, keep pushing in the face of hardship and injustice.

Last month, we lost a giant of American democracy in John Lewis. Some years ago, I sat down with John and the few remaining leaders of the early Civil Rights Movement. One of them told me he never imagined he'd walk into the White House and see a president who looked like his grandson. Then he told me that he'd looked it up, and it turned out that on the very day that I was born, he was marching into a jail cell, trying to end Jim Crow segregation in the South.

What we do echoes through the generations.

(This refers to Lincoln's Message to Congress of 1863, which is my signature line on this website. Lincoln did not deliver this address but sent it in writing to Congress to be read by others.)


Whatever our backgrounds, we're all the children of Americans who fought the good fight. Great grandparents working in firetraps and sweatshops without rights or representation. Farmers losing their dreams to dust. Irish and Italians and Asians and Latinos told to go back where they came from. Jews and Catholics, Muslims and Sikhs, made to feel suspect for the way they worshipped. Black Americans chained and whipped and hanged. Spit on for trying to sit at lunch counters. Beaten for trying to vote.

(Lincoln, again, "...drawn with the lash...)


If anyone had a right to believe that this democracy did not work, and could not work, it was those Americans. Our ancestors. They were on the receiving end of a democracy that had fallen short all their lives. They knew how far the daily reality of America strayed from the myth. And yet, instead of giving up, they joined together and said somehow, some way, we are going to make this work. We are going to bring those words, in our founding documents, to life.

(Lincoln, Gettysburg, "Our forefathers brought forth...conceived in liberty and dedicated...a new birth of freedom...)


I've seen that same spirit rising these past few years. Folks of every age and background who packed city centers and airports and rural roads so that families wouldn't be separated. So that another classroom wouldn't get shot up. So that our kids won't grow up on an uninhabitable planet. Americans of all races joining together to declare, in the face of injustice and brutality at the hands of the state, that Black Lives Matter, no more, but no less, so that no child in this country feels the continuing sting of racism.

To the young people who led us this summer, telling us we need to be better -- in so many ways, you are this country's dreams fulfilled. Earlier generations had to be persuaded that everyone has equal worth. For you, it's a given -- a conviction. And what I want you to know is that for all its messiness and frustrations, your system of self-government can be harnessed to help you realize those convictions.

(Lincoln, Gettysburg: ...that government of the people, by the people, for the people, shall not vanish from the Earth)


You can give our democracy new meaning. You can take it to a better place. You're the missing ingredient -- the ones who will decide whether or not America becomes the country that fully lives up to its creed.

(ibid and A new birth of freedom, again...)


That work will continue long after this election. But any chance of success depends entirely on the outcome of this election. This administration has shown it will tear our democracy down if that's what it takes to win. So we have to get busy building it up -- by pouring all our effort into these 76 days, and by voting like never before -- for Joe and Kamala, and candidates up and down the ticket, so that we leave no doubt about what this country we love stands for -- today and for all our days to come.

(Lincoln, 2nd Inaugural, "With malice toward none; with charity for all; with firmness in the right, as God gives us to see the right, let us strive on to finish the work we are in; to bind up the nation's wounds; to care for him who shall have borne the battle, and for his widow, and his orphan to do all which may achieve and cherish a just, and a lasting peace, among ourselves, and with the world. all nations, Gettysburg, again, "...shall not vanish from the Earth." )


Stay safe. God bless.


I've almost certainly missed some of the evocations, but these are those that caught my eye.

Obama's speech will stand among the great speeches in US history precisely because of the beautiful and eloquent way in which he updates these American themes of democracy, decency, equality and justice, and delivers them in a way that is all his own, just as Lincoln at Gettysburg, drew upon Pericles funeral orations, the Declaration of Independence, and other historical speeches.

We are privileged, indeed, to have Obama's speech delivered to us in our direst times, filled with force and hope, power and responsibility.

It will stand in history, as another example of a great American triumph in rhetoric.

Just checked my car's tires.

They're Goodyear tires.

I'm one proud American!

Toward Sustainable Biologically Derived Anodes for Aluminum Production.

The paper I'll discuss in this post is this one: Synthesis and Characterization of Bio-pitch from Bio-oil (Ying Lu, Dazhi Li, Xianai Huang, Donald Picard, Roozbeh Mollaabbasi, Thierry Ollevier,* and Houshang Alamdari* ACS Sustainable Chem. Eng. 2020, 8, 31, 11772–11782)

The Hall-Heroult process responsible for the production of aluminum metal from alumina, Al2O3, is electrolytic in nature, which theoretically should result in the production of oxygen, but doesn't in practice, do so. In real practice, even though the reaction is most definitely driven electrochemically, the oxidized species does not represent oxide being converted to oxygen gas, but rather represents the oxidation of carbon to give carbon dioxide:



European Carbon and Graphite Association.

Under certain conditions, side products are formed, the greenhouse gas CF4, for example where fluorine source is the flourine gas released from the synthetic cryolite in the molten salt bath, and carbon monoxide, from the Boudouard reaction between carbon dioxide trapped in pores of the anodes and the anode carbon itself. (Other minor gases include tetrafluoroethylene) etc.

According to the information from the World Aluminum Institute the world produced 63,697,000 metric tons of aluminum in 2019. The amount of electricity consumed, also as reported by the World Aluminum Institute to produce aluminum in 2019 was 848,845 GWh. (Accessed 8/17/20) More than half of the world aluminum supply was produced in China - and despite all the bull you can read around here, say over at the E&E forum about how coal is dead - China still burns massive amounts of coal. The World Aluminum Institute, thus reports that of the 848,845 GWh reported to produce aluminum, 509,393 GWh was produced by burning coal. A good working figure for the carbon intensity of electricity produced by coal is 1,100 grams of carbon dioxide are produced for each kwh, meaning that the electricity generated by coal combustion alone in order to drive aluminum plants was 560,000,00 million tons.

This of course, excludes the carbon in the anodes, which are made with coal tar pitch and petroleum coke.

From the equation above, and the atomic weight of aluminum, 28.96 grams per mole, and the molecular weight of carbon dioxide, 44.095 grams per mole, and the ratio - at least at 100% yield (which is unlikely) - of 3 moles of carbon dioxide being produced for 4 moles of aluminum, we can see that 63,697,000 metric tons of carbon dioxide, one can easily calculate that the oxidation of the electrodes added about 27 million tons of carbon dioxide to the atmosphere.

Aluminum production for various technical reasons I will not discuss here, needs to be produced in continuous processes. Although a tiny amount of power was reported for so called "renewable energy" generated electricity by the World Aluminum Institute's 2019 figures, 23,099 GWh, or in the "percent talk" that advocates of so called "renewable energy" love so much, 2.7% of the total electricity produced. Since aluminum plants are required to operate continuously, this 2.7% probably represents almost in its entirety, the Icelandic production using geothermal energy, supplemented by hydroelectricity.

It is not possible to produce reliable continuous power using the much ballyhooed, but entirely ineffective, wind and solar industry, and therefore here, as elsewhere, it is not really possible to displace coal with wind and solar energy, despite so much rhetoric - all of it delusional on a Trumpian scale - to the contrary.

It is, of course, possible to produce continuous power using nuclear energy, which unlike wind and solar can displace nuclear, but despite this fact, nuclear energy contributed only 13,828 GWh to aluminum production, dominated by Europe and China. Hydro is a major player in aluminum production, producing about 40% as much electricity as coal does for this purpose (210,154 GWh) but we are fresh out of rivers to destroy for electricity generation. It does seem that the continual rise in anti-nuke fear and ignorance is slowing down a bit, and may be peaking, but the reality is that nuclear energy has been prevented from reaching its potential by successful appeals to fear and ignorance, and thus aluminum production on this planet is responsible for about 2% of the 35 billion tons of carbon dioxide humanity releases each year.

The point of this diatribe is that the amount of carbon that can be saved using the technology being explored in this paper, the displacement of coal tar pitch with biooil pitch is small, only about 27 million tons, but perhaps a worthwhile object of consideration, since the other metal that uses prodigious amounts of coke is the steel industry. Moreover, considerable amounts of carbon are present in steel alloys, meaning that this carbon in those alloys is sequestered.

Nevertheless, it is important to keep scale in mind when discussing climate change, but too often we don't. This explains why people can prance around obliviously pretending that solar and wind energy matter, when in fact they don't: The failure to appreciate scale.

From the paper's introduction, covering some of the ground I've discussed above:

Carbon anodes for the aluminum smelting process are manufactured using coal-tar-pitch (CTP), as a binder, and dry aggregates (calcined petroleum coke and recycled butts) as the filler material.(1) The CTP is a residual fossil carbon material obtained after the distillation of coal tar.(1) It contains very complex chemical compounds, mainly fused aromatic and heterocyclic hydrocarbons, including carcinogens, such as polycyclic aromatic hydrocarbons (PAHs). The CTP is the main source of PAHs released into the environment during the anode making process,(2) since most of the volatile matter contained in the dry aggregates of petroleum coke is being removed during the high temperature calcination process prior to the anode making process. The PAHs are reported to be human carcinogens and damageable to the environment.(3) Moreover, the demand for CTP is continually increasing, while its supply is decreasing due to the strict environmental regulations, forcing many coke plants to shut down. On the other hand, according to the International Aluminium Institute, the global aluminum production is increasing spectacularly, rising from 25 Mt/a in 2000 to 65 Mt/a in 2019. To overcome such an unprecedented increase in demand and shortage in supply, it is critical to develop a new and environmentally-friendly alternative binder, which possesses similar features as CTP to replace it in the anode manufacturing process.

Biomass is a well-known renewable, sustainable, and environmentally-friendly carbon source. Consequently, it could be a potential alternative source to produce binder for carbon anode making.(4,5) The pyrolysis of biomass can produce solid bio-carbon, liquid bio-oil, and a gas phase, which is the result of chemical reactions involving the molecular breakdown of large molecules into smaller ones at high temperature and in the absence of oxygen. Attributable to the removal of oxygen-rich volatile matters of biomass during the pyrolysis process, the resultant products have a higher heating value.(6)


The "oxygen-rich volatile matters" are probably dominated by methanol, which years ago, when I was a kid, used to be sold in hardware stores as "wood alcohol." Almost all of the methanol now produced on earth is not from the destructive distillation of wood, but rather by the partial oxidation of dangerous natural gas's methane component, or else hydrogenation of carbon dioxide (or monoxide) using hydrogen produced by the reformation of dangerous natural gas.

What the authors explore here is a particular approach to converting "biooil" - the subject of much discussion in the scientific literature - into "biopitch" to be used as a binder to make anodes for Hall-Heroult aluminum production reactors:

...Some specific properties of bio-pitch are important parameters to determine its potential to replace CTP. The critical properties of pitch as a good binder to produce carbon anodes with good quality are (i) good binding to dry aggregate particles, (ii) high coking value during anode baking, and (iii) low impurities (such as sulfur and ash content). Moreover, the binder should have a good wettability to cover the surface of coke particles and have the required rheological properties to penetrate into coke pores to enhance the pitch/coke, thus improving the mixing and compaction behavior of the anode paste.(13,14) The published literature is, however, still lacking the detailed and systematic analysis of the properties of bio-pitches obtained from different distillation conditions targeted for use in anode formulation. This study focuses on the property characterizations of bio-pitches extracted from the same bio-oil using different synthetic process conditions to reveal its potential as an alternative binder for the carbon anode...


The properties are described as such:

Some specific properties of bio-pitch are important parameters to determine its potential to replace CTP. The critical properties of pitch as a good binder to produce carbon anodes with good quality are (i) good binding to dry aggregate particles, (ii) high coking value during anode baking, and (iii) low impurities (such as sulfur and ash content). Moreover, the binder should have a good wettability to cover the surface of coke particles and have the required rheological properties to penetrate into coke pores to enhance the pitch/coke, thus improving the mixing and compaction behavior of the anode paste.(13,14) The published literature is, however, still lacking the detailed and systematic analysis of the properties of bio-pitches obtained from different distillation conditions targeted for use in anode formulation. This study focuses on the property characterizations of bio-pitches extracted from the same bio-oil using different synthetic process conditions to reveal its potential as an alternative binder for the carbon anode.


"CTP" here is "coal tar pitch."

A brief description of "biooil" is provided:

The pyrolysis of biomass results in a dark brown, free-flowing liquid having a distinctive smoky odor, called bio-oil. Bio-oil is a complex mixture consisting of water and organic chemicals. Organic components consist of acids, alcohols, aldehydes, ketones, esters, phenols, guaiacols, syringols, sugars, furans, alkenes, aromatics, nitrogen compounds, and miscellaneous oxygen-containing compounds.(7,8) The distribution and content of these compounds mostly depend on the type of biomass and on their pyrolysis conditions (pressure, temperature, holding time, and heating rate). Their average molecular weight varies in the range of 300–1000 g/mol.(7,8) Usually, high oxygen content (in the range of 35–40 wt %) and water content (in the range of 15–30 wt %) in bio-oil result in the instability of bio-oil.(9,10)


The process utilized in the paper is vacuum pyrolysis, heating the biooil in a vacuum at different temperatures and for different periods of time.

They purchased the biooil from a supplier. Reportedly the biomass source was largely softwood sawdust, 80% pine, 20% cedar.

The experimental conditions are briefly described as such:

Since the boiling point of the aqueous fractions is lower than that of the oily fractions, the aqueous fraction was extracted from the bio-oil earlier than the oily fractions. Both aqueous and oily fractions were analyzed by gas chromatography–mass spectrometry (GC-MS). Bio-pitch is the residual fraction left in the flask after the distillation process, which becomes a solid material (high viscosity) when cooled to room temperature. The various experimental conditions used in this study are shown in Tables 1 and S2. The final temperature ranged from 160 to 260 °C with a stepwise increase of 20 °C, while the holding time was maintained at 3.5 h and the pressure was held at 35 Torr (samples BP-1 to BP-6). For the samples BP-7 to BP-10, the distillation temperature was kept at 180 °C, while different holding times and pressures were employed.


Table 1:



"Coking Value" is a property defined by the fractions extracted into various solvents: Batia [iet al., Journal of Materials Science volume 22, pages3847–3850(1987)]

Some pictures from the text:



The caption:

Figure 1. Correlation between (a) yield and softening point, (b) yield and coking value, (c) softening point and coking value, and (d) softening point and viscosity at 178 °C of bio-pitch samples.




PAH's (polyaromatic hydrocarbons, aka, PNA (polynuclear hydrocarbons) are the most carcinogenic components of coal tar:

The caption:

Figure 2. Correlation between bio-pitch yield and PAH content.




The caption:

Figure 3. (a) FTIR of bio-oil and bio-pitches from three different holding times (3.5, 9.5, and 25.5 h). (b) AreaCOOH/OH/AreaAliphatic calculated from FT-IR results for bio-pitches from three different holding times.




The caption:

Figure 4. MALDI-TOF mass spectrum of bio-pitch.


MALDI is "Matrix assisted laser desorption ionization," a mass spectrometry technique for determining the structure of molecules.



The caption:

Figure 5. Gas chromatograms and FTIR spectra of the distilled fractions.




The caption:

Figure 6. Polymerization of bio-oil showing several possible linkages.




The caption:

Figure 7. Molecular weight distribution curves for bio-oil and bio-pitches with different holding times (3.5, 9.5, and 25.5 h).




The caption:

Figure 8. Correlation between (a) bio-pitch yield and molecular weight, (b) molecular weight and softening point, (c) C content and coking value, and (d) O content and coking value.




Figure 9. Correlation between aromaticity and C/H ratio.


From the conclusion:

In this study, bio-pitch was synthesized from bio-oil using thermal conditions under vacuum. The effect of the synthetic conditions on bio-pitch properties was evaluated, aiming at generating insights to prepare a suitable material to replace coal-tar-pitch in the anode manufacturing process. The following conclusions have been obtained from the analysis of the results. When the distillation time and temperature increased, the yield of bio-pitch decreased. This is associated with the release of volatile compounds under the vacuum range used in this study (10–50 Torr). The C/H ratio and aromaticity of the produced bio-pitches were also increased by increasing distillation time and temperature, indicating the formation of aromatic structures, which were confirmed by the elemental analysis and NMR results. The properties of bio-pitch are determined by molecular structure and mainly interrelated, as identified by various analyses...

...Finally, a hypothetical reaction mechanism of bio-pitch synthesis from bio-oil was proposed on the basis of the chemical analysis of bio-oil and bio-pitch. The physical properties of the bio-pitch were characterized and compared to those of coal-tar-pitch. Compared to coal-tar-pitch, all bio-pitch samples exhibited much lower PAHs, quinoline insolubles, and sulfur contents, representing significant health and environmental advantages as a binder in the anode formulation. It was shown that some distillation conditions, i.e., temperature, heating rate, and pressure, are important parameters to adjust the softening point of the bio-pitch and its viscosity, both being important anode manufacturing parameters. Further investigation is required to evaluate other characteristics of bio-pitch in order to develop a new and environmentally-friendly alternative binder in the anode formulation and to confirm its appropriateness for replacing coal-tar-pitch...


From my perspective, an optimal approach to removing carbon dioxide from the air will depend on having an economic incentive for doing so, the key to this being useful materials. Coupled with the only sustainable form of energy that exists, nuclear energy, it seems remotely possible - although by no means certain - that we can reverse the indifference and self delusion that have led to the destruction of the planetary atmosphere. Some of it will involve little steps, like anodes from biomass, and some other large steps, like displacing all dangerous fossil fuel plants with nuclear plants, rendering so called "renewable energy" - which is decidedly not sustainable precisely because of its mass requirements - unnecessary and superfluous.

These ideas of mine are, of course, not popular, but I have convinced myself it would be morally unacceptable, for me personally at least, not to state them.

This little paper made me quite happy, since the issue of anodes has been troubling me for some time, given my fondness for metallurgy and my excitement over the new vistas opened by the Cambridge FFC process, and electrolytic process similar to that of the Hall-Heroult process long in use for aluminum.

I hope and trust that even in the age of Covid, some part of your summer has been pleasant and rewarding.

Susan Collins tweets: she sent a LETTER to the Post Office that she's concerned about their service.

You can't make this stuff up.

Sen. Susan Collins
@SenatorCollins
The USPS continues to be a lifeline amid COVID-19, especially for seniors, veterans, & those in rural areas who rely on mail delivery for essential goods. I sent a letter calling for the USPS to promptly address the delays in mail delivery.

https://collins.senate.gov/newsroom/senator-collins-calls-usps-address-delays-mail-delivery

https://twitter.com/SenatorCollins/status/1294070606544216064

A mathematical model reveals the influence of population heterogeneity on herd immunity to SARS-CoV2

The paper to which I'll refer is this one: A mathematical model reveals the influence of population heterogeneity on herd immunity to SARS-CoV-2 (Tom Britton1,*, View ORCID ProfileFrank Ball2, View ORCID ProfilePieter Trapman1, Science 14 Aug 2020: Vol. 369, Issue 6505, pp. 846-849)

The scientific publishing community has made all SARS-Cov-2 papers open sourced. There is no need for me to excerpt all that much of it, but it does note that something that all of here know, even if the ignorant white supremacist in the White House is as clueless on this subject as he is on all others: In diversity is strength.

The paper, however, does not actually refer to ethnic diversity, but rather to diversity in age and activity levels, as well as the diversity in restrictions utilized. This, of course is good news.

A few brief excerpts:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally despite the many different preventive measures that have been put in place to reduce transmission. Some countries aimed for suppression by extreme quarantine measures (lockdown) and others aimed for mitigation by slowing the spread using certain preventive measures in combination with protection of the vulnerable (1). An important question for both policies has been when to lift some or all of the restrictions. A closely related question is if and when herd immunity can be achieved. Herd immunity is defined as a level of population immunity at which disease spreading will decline and stop even after all preventive measures have been relaxed. If all preventive measures are relaxed when the immunity level from infection is below the herd immunity level, then a second wave of infection may start once restrictions are lifted.

By 1 May 2020, some regions and countries reached high estimates for the population immunity level; for example, 26% of the population was infected (with a large confidence interval) in the metropolitan Stockholm region, as shown by a mathematical model (2). At the same time, population studies in Spain showed that in the second half of May 2020, >10% of the population of Madrid had antibodies for coronavirus disease 2019 (COVID-19) (3). It is debatable whether (classical) herd immunity for COVID-19, which is believed to lie between 50 and 75%, can be achieved without unacceptably high case fatality rates (4–6).


There is then a discussion on the likely impact of vaccination on herd immunity, depending on the efficacy of the vaccine.

A figure from the paper:



The caption:

Fig. 1 Overall fraction infected over time.
Shown is a plot of the overall fraction infected over time for the age and activity structured community with R0 = 2.5 for four different preventive levels inserted 15 March (day 30) and lifted 30 June (day 135). The blue, red, yellow, and purple curves correspond to no, light, moderate, and severe preventive measures, respectively.


An interesting read, I think.

Have a nice weekend.
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