Roman Concrete

I hope all of you had a Merry Christmas and a Happy New Year, and 2023 is shaping up well for you. They say the end of the year is a time to look back, so why not look really back? Quite some time ago, I visited Rome, and I have always been fascinated by the Roman civilization, so why not start this year by looking that far back?

Perhaps one of the more rather remarkable buildings is the Pantheon, which has the world’s largest unreinforced concrete dome. That was built under the direction of Marcus Vipsanius Agrippa, the “get-things-done” man for Augustus. No reinforcement, and it lasted that long. Take a look at modern concrete and as often as not you will find it cracks and breaks up. Concrete is a mix of aggregate (stones and sand) that provides the bulk, and a cement that binds the aggregate together. We use Portland cement, which is made by heating limestone and clay (usually with some other material but the other material is not important) in a kiln up to about 1450 degrees Centigrade. The product actually depends to some extent on what the clay is, but the main products are bellite (Ca2SiO4) and alite (Ca3SiO5). If the clays contain aluminium, which most clays do, various calcium aluminosilicates are formed. Most standard cement is mainly calcium silicate to which a little gypsum is added at the end, which makes the end surface smoother.

Exactly what happens during setting is unknown. The first thing to note is that stone does not have a smooth surface at close to the molecular level, and further, stones are silicates, in which the polymer structure is perforce terminated at the surface. That would mean there are incomplete bonds. An element like carbon would fix this problem by forming double bonds but silicon cannot do that so these “awkward” surface molecules react with water to form hydroxides. What I think happens is the water in the mix hydrolyses the calcium silicate and forms silica with surface hydroxyls, and these eliminate with hydroxyls on the stone, with the calcium hydroxide also taking part, in effect forming microscopic junctions between it and stone. All of this is slow, particularly when polymeric solids cannot move easily. So to make a good concrete, besides getting the correct mix you have to let it cure for quite some time before it is at its best.

So what did the Romans do? They could not make cement by heating clay and lime up to that temperature easily, but there were sources where it was done for them: the silicate around volcanoes like Vesuvius. The Roman architect and engineer Vitruvius used a hot mix of quicklime (calcium oxide) that was hydrated and mixed with volcanic tephra. Interestingly, this will also introduce some magnesiosilicates, which are themselves cements, but magnesium may fit better than calcium onto basaltic material. For aggregate Vitruvius used fist-sized pieces of rock, including “squared red stone or brick or lava laid down in courses”. In short, Vitruvius was selecting aggregate that was much better than ordinary stone in the sense of having surface hydroxyl groups to react. That Roman concrete lasted so long may in part be due to a better choice of aggregate.

A second point was the use of hot mixing. One possibility is they used a mix of freshly slaked lime and quicklime and by freshly slaking the mix became very hot. This speeds up chemical reactions, and also allows compound formation that is not possible at low temperatures. By reacting so hot it reduced setting times. But even more interestingly, it appears to allow self-healing. If cracks begin to form, they are more likely to form around lime clasts, which can then react with water to make a calcium-rich solution, which can react with pozzolanic components to strengthen the composite material. To support this, Admir Masic, who had been studying Roman cement, made concretes using the Roman recipe and a modern method. He then deliberately cracked the samples and ran water through them. The Roman cement self-healed completely within two weeks, while the cracks in the modern cement never healed.

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Fusion Energy on the Horizon? Again?

The big news recently as reported in Nature (13 December) was that researchers at the US National Ignition Facility carried out a reaction that made more energy than was put in. That looks great, right? The energy crisis is solved. Not so fast. What actually happened was that 192 lasers delivered 2.05 MJ of energy onto a pea-sized gold cylinder containing a frozen pellet of deuterium and tritium. The reason for all the lasers was to ensure that the input energy was symmetrical, and that caused the capsule to collapse under pressures and temperatures only seen in stars, and thermonuclear weapons. The hydrogen isotopes fused into helium, releasing additional energy and creating a cascade of fusion reactions. The laboratory claimed the reaction released 3.15 MJ of energy, roughly 54% more than was delivered by the lasers, and double the previous record of 1.3 MJ.

Unfortunately, the situation is a little less rosy than that might appear. While the actual reaction was a net energy producer based on the energy input to the hydrogen, the lasers were consuming power even when not firing at the hydrogen, and between start-up and shut-down they consumed 322 MJ of energy. So while more energy came out of the target than went in to compress it, if we count the additional energy consumed elsewhere but necessary to do the experiment, then slightly less than 1% of what went in came out. That is not such a roaring success. However, before we get critical, the setup was not designed to produce power. Rather it was designed to produce data to better understand what is required to achieve fusion. That is the platitudinal answer. The real reason was to help nuclear weapons scientists understand what happens with the intense heat and pressure of a fusion reaction. So the first question is, “What next?” Weapons research, or contribute towards fusion energy for peaceful purposes?

Ther next question is, will this approach contribute to an energy program. If we stop and think, the gold pellet of frozen deuterium had to be inserted, then everything line up for a concentrated burst. You get a burst of heat, but we still only got 3 MJ of heat. You may be quite fortunate to convert that to 1 MJ of electricity. Now, if it takes, say, a thousand second before you can fire up the next capsule, you have 1 kW of power. Would what you sell that for pay for the gold capsule consumption?

That raises the question, how do you convert the heat to electricity? The most common answer offered appears to be to use it to boil water and use the steam to drive a turbine. A smarter way might be to use magnetohydrodynamics. The concept is the hot gas is made to generate a high velocity plasma, and as that is slowed down, the kinetic energy of the plasma is converted to electricity. The Russians tried to make electricity this way by burning coal in oxygen to make a plasma at about 4000 degrees K. The theoretical maximum energy U is given by

    U  =  (T – T*)/T

where T is the maximum temperature and T* is the temperature when the plasma degrades and the extraction of further electricity is impossible. As you can see, it was possible to get approximately 60% energy conversion. Ultimately, this power source failed, mainly because the cola produces a slag which damaged the electrodes. In theory, the energy could be drawn in almost 100 % efficiency.

Once the recovery of energy is solved, there remains then problem of increasing the burn rate. Waiting for everything to cool down then adding an additional pellet cannot work, but expecting a pellet of hydrogen to remain in the condensed form when inserted into a temperature of, say, a million degrees, is asking a lot.

This will be my last post for the year, so let me wish you all a Very Merry Christmas, and a prosperous and successful New Year. I shall post again in mid-January, after a summer vacation.

Meanwhile, for any who fell they have an interest in physics, in the Facebook Theoretical Physics group, I am posting a series that demonstrates why this year’s Nobel Prize was wrongly assigned as Alain Aspect did not demonstrate violations of Bell’s inequality. Your challenge, for the Christmas period, is to prove me wrong and stand up for the Swedish Academy. If it is too difficult to find, I may post the sequence here if there were interest.

Reducing Electricity Usage in Your Refrigerator

When thinking about battling climate change, did you know that a major electricity consumer in your house is your refrigerator? The International Institute of Refrigeration (yes, there are institutes for just about everything) estimates that about 20% of all electricity used is expended on vapour compression refrigeration. The refrigerator works by compressing a vapour, often some sort of freon, or in industry, with ammonia, and when compressed it gives off heat. When you ship it somewhere else and expand it, the somewhere else gets colder. This is also the principle of the heat pump and various air conditioning units. Compress gas here to add heat from a heat exchanger; ship the gas there and expand it, where it cools a heat exchanger. The compression and expansion of gas moves heat from A to B, hence the name heat pump. Also, the refrigerant gases tend to be powerful greenhouse gases. One kilogram of R410a has the same greenhouse impact as two tonne of carbon dioxide. Refrigerants leak into the atmosphere from faulty equipment or when equipment is not properly disposed of.

It is possible to heat or cool without any gas through the Peltier effect. Basically, when electric current passes between two conductors, heating or cooling effects may be generated. There are commercial solid-state such cooling systems, but they suffer from high cost and poor efficiency, in part because the effect is restricted to the specific junction.

There is an alternative. Some solid state materials can cool when they are subjected to strain, which is generated from an external field, such as  the electric or magnetic fields, or simply pressure. So far most efforts have been focused on the magnetic field, and one material, Mn3SnC apparently gives significant cooling,  but the magnetic field has to be greater than 2 tesla. That means expensive and bulky magnets, and additionally the refrigerator, if it used them, would have to be a “no-go” area for credit cards, and possibly people with a pacemaker. Even aside from direct messing with the pacemaker, losing all those bitcoin just because you wanted a cool beer could lead to medical problems.

However, there has been an advance. Wu et al. (Acta Materiala 237: 118154) have taken the Mn3SnC and coated it with a piezoelectric layer of lead zirconate titanate. Don’t ask me how they come up with these things; I have no idea, but this is certainly interesting. They probably do it by looking through the literature to find materials already known to have certain properties. Thus a piezoelectric effect is where you generate an electric voltage by applying pressure. Such effects are reversible so if you can generate a voltage by applying pressure to something, you can generate pressure by applying a potential difference. Recall that pressure also can generate a cooling effect. Accordingly, by applying an electric field to this coated material a cooling effect was obtained equivalent to that of a 3 tesla magnetic field. When the electric field is removed, the temperature returns to where it was. How useful will this be? Hard to tell right now. The temperature drop when applying a field of 0.8 kV/cm was slightly under 0.6 of a degree Centigrade, which is not a huge change while the voltage is tolerably high. Interestingly, if you apply a magnetic field you also get a temperature change, but in the opposite direction – instead of cooling, it heats. Why that is is unclear.

As you might guess, there is still a significant distance to go before we get to a refrigerator. First, you have to get the cooling into some other fluid that can transport it to where you need it. To do that you have to take the heat out of the cooling fluid, but that will heat up your unit, so you need another fluid to take the heat to where it can be dissipated. We have very roughly the same cycle as our present system except we are not compressing anything but we have two fluids. Except I rather think we will be, because pumping a fluid involves increasing its pressure so it flows. The alternative is to put the material across the rear wall of the refrigerator thus to cool the interior and have the heat dissipated out the back. The problem now is the change of temperature is rather small for the voltage. This is not so much a problem with fluids transporting it, but if the solids transport it, the solids are always heated by the environment so your temperature drop is from the room temperature. Half a degree is not very helpful, although you could increase the electric field. Unfortunately, to get a big enough temperature change you might be into the spark jumping region. Lightning in the kitchen! Finally, do you want the back of your refrigerator to be carrying even a kilovolt electric field? My guess is this effect may remain a curiosity for some length of time.

Economic Consequences of the Ukraine War

My last post mentioned the USSR collapse. One of the longer term consequences has been this Ukraine war. Currently, there have been problems of shelling of the Zaporizhzhia nuclear plant, and this appears to have happened in that our TV news has shown some of the smashed concrete, etc. The net result is the plant has shut down. Each side accuses the other of doing the shelling, but it seems to me that it had to be the Ukrainians. Russia has troops there, and no military command is going to put up with his side shelling his own troops. However, that is far from the total bad news. So far, Ukraine has been terribly lucky, but such luck cannot last indefinitely. There are consequences outside the actual war itself. The following is a summary of some of what was listed in the August edition of Chemistry World.

The Donbas area is Ukraine’s heavy industry area, and this includes the chemical industry. Recently, Russian air strikes at Sieverierodonetsk hit a nitric acid plant, and we saw images of the nitrogen dioxide gas spewing into the atmosphere.

Apparently, in 2017 Ukrainian shelling was around a chemical plant that contained 7 tonne of chlorine. Had a shell hit a critical tank, that would have been rather awkward. Right now, in the eastern Donbas there is a pipeline almost 700 km long that pipes ammonia. There are approximately 1.5 million people in danger from that pipeline should it burst; exactly how many depends on where it is broken. There are also just under  200,000 t of hazardous waste stored in various places. The question now is, with all this mess generated, in addition to demolished buildings and infrastructure, who will pay what to clean it up? It may or may not be fine for Western countries to use their taxes to produce weapons to give to Ukraine, but cleaning up the mess requires the money to go to Ukraine, not armament-making corporations at home.

The separation of the Donbas has led to many mines being closed, and these have filled with water. This has allowed mercury and sulphuric acid to be leached and then enter the water table. During 2019, a survey of industrial waste was made, and Ukraine apparently stores over 5.4 billion t of industrial waste, about half of which is in the Donbas. Ukraine has presumably inherited a certain amount, together with some of the attitudes, from the old Soviet Union. From experience, their attitude to environmental protection was not their strong point. I recall  one very warm sunny morning going for a walk around Tashkent. I turned a corner and saw rather a lot of rusty buildings, and also, unbelievably, a cloud. How could water droplets form during such a warm dry climate? The answer was fairly clear when I got closer. One slight whiff, and I knew what it was: the building was emitting hydrogen chloride into the atmosphere and the hydrochloric acid droplets were the reason for the rust.

Meanwhile, some more glum news. We all know that the sanctions in response to the Ukraine war has led to a gas shortage. What most people will not realize is what this is doing to the chemical industry. The problem for the chemical industry is that unlike most other industries, other than the very sophisticated, the chemical industry is extremely entangled and interlinked. A given company may make a very large amount of chemical A, which is then sold as a raw material to a number of other companies, who in turn may do the same thing. There are many different factories dependent on the same raw chemical and the material in a given chemical available to the public may have gone through several different steps in several different factories.

An important raw mixture is synthesis gas, which is a mix of carbon monoxide and hydrogen. The hydrogen may be separated and used in steps to make a variety of chemicals, such as ammonia, the base chemical for just about all nitrogen fertilizer, as well as a number of other uses. The synthesis gas is made by heating a mixture of methane gas and water. Further, almost all chemical processing requires heat, and by far the bulk of the heat is produced by burning gas. In Europe, the German government is asking people to cut back on gas usage. Domestic heating can survive simply by lowering the temperature, although how far down one is prepared to go during winter is another question. However, the chemical industry is not so easily handled. Many factories use multiple streams, and it is a simple matter to shut down such a stream, but you cannot easily reduce the amounts going through a stream because the reactions are highly dependent on pressure, and the plant is in a delicate balance between amount processed and heat generated.  A production unit is really only designed to operate one way, and that is continuously with a specific production rate. If you close it down, it may take a week to get it started again, to get the temperature gradients right. One possibility is the complete shutdown of the BASF plant at Ludwigshafen, the biggest chemical complex in the world. The German chemical industry uses about 135 TWhr of gas, or about 15% of the total in the country. The price of such gas has risen by up to a factor of eight since Russia was sanctioned, and more price rises are likely. That means companies have to try to pass on costs, but if they face international competition, that may not be possible. This war has consequences far beyond Ukraine.

Burying Carbon Dioxide, or Burying Cash?

In the last post, I expressed my doubt about the supply of metals for electric batteries. There is an alternative to giving up things that produce CO2 and that is to trap and sequester CO2. The idea is that for power stations the flu gases have the CO2 removed and pumped underground. That raises the question, how realistic is this? Chemistry World has an article that casts doubt, in my mind, that this can work. First, the size of the problem. One company aims to install 70 such plants, each capable of sequestering 1 million t of CO2. If these are actually realized, we almost reach 0.2% of what is required. Oops. Basically, we need to remove at least 1 billion t/a to stand still. This problem is large. There is also the problem of how we do it.

The simplest way is to pass the flu gases through amine solvents, with monoethanolamine the most common absorbent used. Leaving aside the problem of getting enough amine, which requires a major expansion of the chemical manufacturing industry, what happens is the amine absorbs CO2 and makes the amine carbonate, and the CO2 is recovered by heating the carbonate and regenerating the amine. However, the regeneration will never be perfect and there are losses. Leaving aside finding the raw materials actually synthesizing the amine takes about 0.8 MWh of energy, the inevitable losses mean we need up to 240 MWh every year to run a million tonne plant. We then need heat to decompose the amine carbonate, and that requires about 1 MWh per tonne of CO2 absorbed. Finally, we need a little less than 0.12 MWh per tonne of CO2 to compress it, transport it and inject it into the ground. If we wanted to inject 1 billion t of CO2, we need to generate something like 840 TWh of electricity. That is a lot of electricity.

We can do a little better with things called metal organic frameworks (MOFs).These can be made with a high surface energy to absorb CO2 and since they do not form strong chemical bonds the CO2 can be recovered at temperatures in the vicinity of  80 – 100 degrees C, which opens the possibility of using waste heat from power stations. That lowers the energy cost quite a bit. Without the waste heat the energy requirement is still significant, about half that of the amines. The comes the sting – the waste heat approach still leaves about 60% of what was absorbed, so it is not clear the waste heat has saved much. The addition of an extra step is also very expensive.

The CO2 content of effluent gases is between 4 – 15%; for ordinary air it is 0.04%, which makes it very much more difficult to capture. One proposal is to capture CO2 by bubbling air through a solution of potassium hydroxide, and then evaporating off the water and heating the potassium carbonate to decomposition temperature, which happens to be about 1200 degrees C. One might have thought that calcium oxide might be easier, which pyrolyses about 600 degrees C, but what do I know? This pyrolysis takes about 2.4 MWh per tonne of CO2, and if implemented, this pyrolysis route that absorbs CO2 from the air would require about 1.53 TWh of electricity per year for sequestering 1 million t of CO2.

When you need terawatt hours of electricity to run a plant capable of sequestering one million tonne of CO2, and you need to sequester a billion t, it becomes clear that this is going to take an awful lot of energy. That costs a lot money. In the UK, electricity costs between £35 – 65 per MWh, and we have been talking in terms of a million times that per plant. Who pays? Note this scheme has NO income stream; it sells nothing, so we have to assume it will be charged to the taxpayer. Lucky taxpayer!

One small-scale effort in Iceland offers a suggested route. It is not clear how they capture the CO2, but then they dissolve it in water and inject that into basalt, where the carbonic acid reacts with the olivine-type structures to make carbonates, where it is fixed indefinitely. That suggests that provided the concentration of CO2 is high enough, using pressure to dissolve it in water might be sufficient. That would dramatically lower the costs. Of course, the alternative is to crush the basalt and spread it in farmland, instead of lime. My preferred option to remove CO2 from the air is to grow plants. They work for free at the low concentrations. Further, if we select seaweed, we get the added benefit of improving the ecology for marine life. But that requires us to do something with the plants, or the seaweed. Which means more thinking and research. The benefit, though, is the scheme could at least earn revenue. The alternatives are to bankrupt the world or find some other way of solving this problem.

Banana-skin Science

Every now and again we find something that looks weird, but just maybe there is something in it. And while reading it, one wonders, how on Earth did they come up with this? The paper in question was Silva et. al. 2022. Chemical Science 13: 1774. What they did was to take dried biomass powder and exposed it to a flash of 14.5 ms duration from a high-power xenon flash lamp. That type of chemistry was first developed to study the very short-lived intermediates generated in photochemistry, when light excites the molecule to a high energy state, where it can decay through unusual rearrangements. This type of study has been going on since the 1960s and equipment has steadily been improving and being made more powerful. However, it is most unusual to find it used for something that ordinary heat would do far more cheaply. Anyway, 1 kg of such dried powder generated about 100 litres of hydrogen and 330 g of biochar. So, what else was weird? The biomass was dried banana skin! Ecuador, sit up and take notice. But before you do, note that flash xenon lamps are not going to be an exceptionally economical way of providing heat. That is the point; this very expensive source of light was actually merely providing heat.

There are three ways of doing pyrolysis. In the previous post I pointed out that if you took cellulose and eliminated all the oxygen in the form of water, you were left with carbon. If you eliminate the oxygen as carbon monoxide you are left with hydrogen. If you eliminate it as carbon dioxide you get hydrogen and hydrocarbon. In practice what you get depends on how you do it. Slow pyrolysis at moderate heat mainly makes charcoal and water, with some gas. It may come as a surprise to some but ordinary charcoal is not carbon; it is about 1/3 oxygen, some minor bits and pieces such as nitrogen, phosphorus, potassium, and sulphur, and the rest carbon.

If you do very fast pyrolysis, called ablative pyrolysis, you can get almost all liquids and gas. I once saw this done in a lab in Colorado where a tautly held (like a hacksaw blade) electrically heated hot wire cut through wood like butter, the wire continually moving so the uncondensed liquids (which most would call smoke) and gas were swept out. There was essentially no sign of “burnt wood”, and no black. The basic idea of ablative pyrolysis is you fire wood dust or small chips at a plate at an appropriate angle to the path so the wood sweeps across it and the gas is swept away by the gas stream (which can be recycled gas) propelling the wood. Now the paper I referenced above claimed much faster pyrolysis, but got much more charcoal. The question is, why? The simple answer, in my opinion, is nothing was sweeping the product away so it hung around and got charred.

The products varied depending on the power from the lamp, which depended on the applied voltage. At what I assume was maximum voltage the major products were (apart from carbon) hydrogen and carbon monoxide. 100 litres of hydrogen, and a bit more carbon monoxide were formed, which is a good synthesis gas mix. There were also 10 litres of methane, and about 40 litres of carbon dioxide that would have to be scrubbed out. The biomass had to be reduced to 20 μm size and placed on a surface as a layer 50 μm thick. My personal view is that is near impossible to scale this up to useful sizes. It uses light as an energy source, which is difficult to generate so almost certainly the process is a net energy consumer. In short, this so-called “breakthrough” could have been carried out to give better yields of whatever was required far more cheaply by people a hundred years ago.

Perhaps the idea of using light, however, is not so retrograde. The trick would be to devise apparatus that with pyrolyse wood ablatively (or not if you want charcoal) using light focused by large mirrors. The source, the sun, is free until it hits the mirrors. Most of us will have ignited paper with a magnifying glass. Keep the oxygen out and just maybe you have something that will make chemical intermediates that you can call “green”.

The Case for Hydrogen in Transport

In the last post I looked at the problem of generating electricity, and found that one of the problems is demand smoothing One approach to this is to look at the transport problem, the other major energy demand system. Currently we fill our tanks with petroleum derived products, and everything is set for that. However, battery-powered cars would remove the need for petrol, and if they were charged overnight, they would help this smoothing problem. The biggest single problem is that this cannot be done because there is not enough of some of the necessary elements to make it work. Poorer quality batteries could be made, but there is another possibility: the fuel cell.

The idea is simple. When electricity is not in high demand, the surplus is used to electrolyse water to hydrogen and oxygen. The hydrogen is stored, and when introduced to a fuel cell it burns to make water while generating electricity. Superficially, this is ideal, but there are problems. One is similar to the battery – the electrodes tend to be made of platinum, and platinum is neither cheap nor common. However, new electrodes may solve this problem. Platinum has the advantage that it is very unreactive, but the periodic servicing of the cell and the replacing of electrodes is realistic, and of course recycling can be carried out because unlike the battery, it would be possible to merely recycle the electrodes. (We could also use pressurised hydrogen in an internal combustion engine, with serious redesign, but the efficiency is simply too low.)

One major problem is storing the hydrogen. If we store it as a gas, very high pressures are needed to get a realistic mass to volume ratio, and hydrogen embrittles metals, so the tanks, etc., may need servicing as well. We could store it as a liquid, but the boiling point is -259 oC. Carting this stuff around would be a challenge, and to make matters worse, hydrogen occurs in two forms, ortho and para, which arise because the nuclear spins can be either aligned or not. Because the molecule is so small there is an energy difference between these, and the equilibrium ratio is different at liquid temperatures to room temperatures. The mix will slowly re-equilibrate at the low temperature, give off heat, boil off some hydrogen, and increase the pressure. This is less of a problem if you have a major user, because surplus pressure is relieved when hydrogen is drawn off for use, and if there is a good flow-through, no problem. It may be a problem if hydrogen is being shipped around.

The obvious alternative is not to ship it around, but ship the electricity instead. In such a scenario for smaller users, such as cars, the hydrogen is generated at the service station, stored under pressure, and more is generated to maintain the pressure. That would require a rather large tank, but it is doable. Toyota apparently think the problem can be overcome because they are now marketing the Mirai, a car powered by hydrogen fuel cells. Again, the take-up may be limited to fleet operators, who send the vehicles out of central sites. Apparently, the range is 500 km and it uses 4.6 kg of hydrogen. Hydrogen is the smallest atom so low weight is easy, except the vehicle will have a lot of weight and volume tied up with the gas pressurized storage. The question then is, how many fuel stations will have this very large hydrogen storage? If you are running a vehicle fleet or buses around the city, then your staff can refill as well, which gets them to and from work, but the vehicle will not be much use for holidays unless there are a lot of such stations.

Another possible use is in aircraft, but I don’t see that, except maybe small short-haul flights driven by electric motors with propellors. Hydrogen would burn well enough, but the secret of hydrocarbons for aircraft is they have a good energy density and they store the liquids in the wings. The tanks required to hold hydrogen would add so much weight to the wings they might fall off. If the main hull is used, where do the passengers and freight go? Another possibility is to power ships. Now you would have to use liquid hydrogen, which would require extremely powerful refrigeration. That is unlikely to be economic compared with nuclear propulsion that we have now.

The real problem is not so much how do you power a ship, or anything else for that matter, but rather what do you do with the current fleet? There are approximately 1.4 billion motor vehicles in the world and they run on oil. Let us say that in a hundred years everyone will use fuel cell-driven cars, say. What do we do in the meantime? Here, the cheapest new electric car costs about three times the cost of the cheapest petrol driven car. Trade vans and larger vehicles can come down to about 1.5 times the price, in part due to tax differences. But you may have noticed that government debt has become somewhat large of late, due to the printing of large amounts of money that governments have promptly spent. That sort of encouragement will probably be limited in the future, particularly as a consequence of shortages arising from sanctions. In terms of cost, I rather think that many people will be hanging on to their petrol-powered vehicles, even if the price of fuel increases, because the difference in the price of fuel is still a few tens of dollars a week tops, whereas discarding the vehicle and buying a new electric one involves tens of thousands of dollars, and with the current general price increases, most people will not have those spare dollars to throw away. Accordingly, in my opinion we should focus some attention on finding an alternative to fossil fuels to power our heritage fleet.

Solar Energy in India

There is currently a big urge to move to solar energy, and apparently India has decided that solar energy would greatly assist its plans to deal with climate change. However, according to a paper by Ghosh et al.in Environmental Research Letters, there is a minor problem: air pollution. It appears that while India is ranked fifth in the world for solar energy capacity, parts of it, and these tend to be the parts where you need the power, suffer from growing levels of particulate air pollution. There are two problems. First, the particles in the air block sunlight, thus reducing the power that strikes the panels. Second, the particles land on the panels and block the light until someone cleans the detritus off the panels.

I am not sure I understand why, but the impact on horizontal panels ranged from 10% to 16%, but the impact was much greater on panels that track the position of the sun (which is desirable to get the most power) as they suffered a 52% loss of power from pollution. Apparently if it were not for such pollution it was calculated (not sure on what basis – existing panels or proposed panels) to be able to generate somewhere between an additional six to sixteen TWh of solar electricity per year. That is a lot of power.

But if you are reducing the output of your panels by fifty percent, that means also you are doubling the real cost of the electricity from those panels prior to entering the grid because you are getting half the power from the same fixed cost installation. The loss of capacity translates into hundreds of millions of dollars annually. China has the same problem, with some regions twice as badly off as the Indian regions, although care must be taken with that comment because they are not necessarily measured the same way. In all cases, averaging down over area is carried out, but then different people may select different types of area.

So, what can be done about this? The most obvious approach is to alter the sources of the pollution, but this could be a problem. In India, the sources tend to be the use of kerosine to provide lighting and the use of dirty fuel for cooking and heating in rural villages.

The answer is to electrify them, but now the problem is there are 600,000 such villages. Problems in a country like India or China tend to be very large, although the good news is the number of people available to work on them is also very large. Unfortunately, these villages are not very wealthy. If you want to replace home cooking with electricity, and domestic heating with electricity, someone has to pay for electric ranges. One estimate is 80 million of them. Big business for the maker of electric cookers, but who pays for them when the rural people are fairly close to the poverty line. They cook with fuel like biomass that gets smoky because that is cheap or free. Their cookers may even be home-made, but even if not so, they would have to be discarded as they could not be used for electric cooking.

There are claimed to be other benefits for reducing such pollution. Thus reducing air pollution would reduce cloudiness, which means even better solar energy production. It is also claimed that precipitation is inhibited from polluted clouds, so it is concluded that with more precipitation that would wash more pollution from the air. I am not sure I follow that reasoning, because they have already concluded that they will have fewer clouds.

If they removed these sources of air pollution, they calculated that an extra three TWh per year could be generated from flat surface panels, or eight TWh per year could be generated from tracking panels. The immediate goal is apparently to have 100 GW solar installed. It will be interesting to see if this can be achieved. One problem is that while the economics look good in terms of money saved from increased solar energy, the infrastructure costs associated with it were neglected. My guess is the current air pollution will be around for a while. It also shows the weaknesses of many solar energy projects, such as setting up huge farms in the Sahara. How do you stop fine sand coating panels? An army of panel polishers?

Plastics and Rubbish

In the current “atmosphere” of climate change, politicians are taking more notice of the environment, to which as a sceptic I notice they are not prepared to do a lot about it. Part of the problem is following the “swing to the right” in the 1980s, politicians have taken notice of Reagan’s assertion that the government is the problem, so they have all settled down to not doing very much, and they have shown some skill at doing very little. “Leave it to the market” has a complication: the market is there to facilitate trade in which all the participants wish to offer something that customers want and they make a profit while doing it. The environment is not a customer in the usual sense and it does not pay, so “the market” has no direct interest in it.

There is no one answer to any of these problems. There is no silver bullet. What we have to do is chip away at these problems, and one that indicates the nature of the problem is plastics. In New Zealand the government has decided that plastic bags are bad for the environment, so the single use bags are no longer used in supermarkets. One can argue whether that is good for the environment, but it is clear that the wilful throwing away of plastics and their subsequent degradation is bad for it. And while the disposable bag has been banned here, rubbish still has a lot of plastics in it, and that will continue to degrade. If it were buried deep in some mine it probably would not matter, but it is not. So why don’t we recycle them?

Then first reason is there are so many variations of them and they do not dissolve in each other. You can emulsify a mix, but the material has poor strength because there is very little binding at the interface of the tiny droplets. That is because they have smooth surfaces, like the interface between oil and water. If the object is big enough this does not matter so much, thus you can make reasonable fence posts out of recycled plastics, but there really is a limit to the market for fence posts.

The reason they do not dissolve in each other comes from thermodynamics. For something to happen, such as polymer A dissolving in polymer B, the change (indicated by the symbol Δ) in what is called the free energy ΔG has to be negative. (The reason it is negative is convention; the reason it is called “free” has nothing to do with price – it is not free in that sense.) To account for the process, we use an equation

            ΔG = ΔH -T ΔS

ΔH reflects the change of energy between each molecule in its own material and in solution of the other material. As a general rule, molecules favour having their own kind nearby, especially if they are longer because the longer they are the interactions per atom are constant for other molecules of the same material, but other molecules do not pack as well. Thinking of oil and water, the big problem for solution is that water, the solvent, has hydrogen bonds that make water molecules stick together. The longer the polymer, per molecule that enhances the effect. Think of one polymer molecule has to dislodge a very large number of solvent molecules. ΔS is the entropy and it increases as the degree of randomness increases. Solution is more random per molecule, so whether something dissolves is a battle between whether the randomness per molecule can overcome the attractions between the same kind. The longer the polymer, the less randomness is introduced and the greater any difference in energy between same and dissolved. So the longer the polymers, the less likely they are to dissolve in each other which, as an aside, is why you get so much variety in minerals. Long chain silicates that can alter their associate ions like to phase separate.

So we cannot recycle, and they are useless? Well, no. At the very least we can use them for energy. My preference is to turn them, and all the organic material in municipal refuse, into hydrocarbons. During the 1970s oil crises the engineering was completed to build a demonstration plant for the city of Worcester in Massachusetts. It never went ahead because as the cartel broke ranks and oil prices dropped, converting wastes to hydrocarbon fuels made no economic sense. However, if we want to reduce the use of fossil fuels, it makes a lot of sense to the environment, IF we are prepared to pay the extra price. Every litre of fuel from waste we make is a litre of refined crude we do not have to use, and we will have to keep our vehicle fleet going for quite some time. The basic problem is we have to develop the technology because the engineering data for that previous attempt is presumably lost, and in any case, that was for a demonstration plant, which is always built on the basis that more engineering questions remain. As an aside, water at about 360 degrees Centigrade has lost its hydrogen bonding preference and the temperature increase means oil dissolves in water.

The alternative is to burn it and make electricity. I am less keen on this, even though we can purchase plants to do that right now. The reason is simple. The combustion will release more gases into the atmosphere. The CO2 is irrelevant as both do that, but the liquefaction approach sends nitrogen containing material out as water soluble material which could, if the liquids were treated appropriately, be used as a fertilizer, whereas in combustion they go out the chimney as nitric oxide or even worse, as cyanides. But it is still better to do something with it than simply fill up local valleys.

One final point. I saw an item where some environmentalist was condemning a UK thermal plant that used biomass arguing it put out MORE CO2 per MW of power than coal. That may be the case because you can make coal burn hotter and the second law of thermodynamics means you can extract more energy in the form of work. (Mind you, I have my doubts since the electricity is generated from steam.) However, the criticism shows the inability to understand calculus. What is important is not the emissions right now, but those integrated over time. The biomass got its carbon from the atmosphere say forty years ago, and if you wish to sustain this exercise you plant trees that recover that CO2 over the next forty years. Burn coal and you are burning carbon that has been locked away from the last few million years.

Thorium as a Nuclear Fuel

Apparently, China is constructing a molten salt nuclear reactor to be powered by thorium, and it should be undergoing trials about now. Being the first of its kind, it is, naturally, a small reactor that will produce 2 megawatt of thermal energy. This is not much, but it is important when scaling up technology not to make too great of leaps because if something in the engineering has to be corrected it is a lot easier if the unit is smaller. Further, while smaller is cheaper, it is also more likely to create fluctuations, especially with temperature, and when smaller they are far easier to control. The problem with a very large reactor is if something is going wrong it takes a long time to find out, but then it also becomes increasingly difficult to do anything about it.

Thorium is a weakly radioactive metal that has little current use. It occurs naturally as thorium-232 and that cannot undergo fission. However, in a reactor it absorbs neutrons and forms thorium-233, which has a half-life of 22 minutes and β-decays to protactinium-233. That has a half-life of 27 days, and then β-decays to uranium-233, which can undergo fission. Uranium-233 has a half-life of 160,000 years so weapons could be made and stored.  

Unfortunately, 1.6 tonne of thorium exposed to neutrons and if appropriate chemical processing were available, is sufficient to make 8 kg of uranium-233, and that is enough to produce a weapon. So thorium itself is not necessarily a form of fuel that is free of weapons production. However, to separate Uranium-233 in a form to make a bomb, major chemical plant is needed, and the separation needs to be done remotely because apparently contamination with Uranium-232 is possible, and its decay products include a powerful gamma emitter. However, to make bomb material, the process has to be aimed directly at that. The reason is, the first step is to separate the protactinium-233 from the thorium, and because of the short half-life, only a small amount of the thorium gets converted. Because a power station will be operating more or less continuously, it should not be practical to use it to make fissile material for bombs.

The idea of a molten salt reactor is that the fissile material is dissolved in a liquid salt in the reactor core. The liquid salt also takes away the heat which, when the salt is cycles through heat exchangers, converts water to steam, and electricity is obtained in the same way as any other thermal station. Indeed, China says it intends to continue using its coal-fired generators by taking away the furnaces and replacing them with a molten salt reactor. Much of the infrastructure would remain. Further, compared with the usual nuclear power stations, the molten salt reactors operate at a higher temperature, which means electricity can be generated more efficiently.

One advantage of a molten salt reactor is it operates at lower pressures, which greatly reduces the potential for explosions. Further, because the fuel is dissolved in the salt you cannot get a meltdown. That does not mean there cannot be problems, but they should be much easier to manage. The great advantage of the molten salt reactor is it burns its reaction products, and an advantage of a thorium reactor is that most of the fission products have shorter half-lives, and since each fission produces about 2.5 neutrons, a molten salt reactor further burns larger isotopes that might be a problem, such as those of neptunium or plutonium formed from further neutron capture. Accordingly, the waste products do not comprise such a potential problem.

The reason we don’t directly engage and make lots of such reactors is there is a lot of development work required. A typical molten salt mix might include lithium fluoride, beryllium fluoride, the thorium tetrafluoride and some uranium tetrafluoride to act as a starter. Now, suppose the thorium or uranium splits and produces, say, a strontium atom and a xenon atom. At this point there are two fluorine atoms as surplus, and fluorine is an extraordinarily corrosive gas. As it happens, xenon is not totally unreactive and it will react with fluorine, but so will the interior of the reactor. Whatever happens in there, it is critical that pumps, etc keep working. Such problems can be solved, but it does take operating time to be sure such problems are solved. Let’s hope they are successful.