I take Isaac Asimov's book "The Intelligent Man's Guide to the Physical Sciences" as my baseline for the state of science as it was when he wrote the book (1959 - 60). In these posts I am reviewing what he reported and what's changed since. For this post I am starting with the chapter Asimov titled "Gases". I will then move on to the chapter he titled "Metals".
The traditional "phases" of materials are solid, liquid, and gas. Since the dawn of Chemistry it has been known that a material can transition from one phase to another as the temperature is changed. In 1787 Charles discovered the law now named after him. A gas contracts as it is cooled (and expands as it is heated). He also noted that the contraction amounted to one part in 273 if the temperature was what we now call 0 degrees Celsius. (In Asimov's time the equivalent temperature scale was called Centigrade. I am going to skip over the small technical differences between the Celsius and Centigrade scales. For our purposes they are essentially the same.) Charles wondered if there was an "absolute zero" that was 273 degrees colder than 0 Celsius.
It turns out he was on to something but it would be a long time before equipment existed to lower temperatures more than a few tens of degrees below zero Celsius. When the "atomic theory of gasses" was developed temperature could be related to tiny molecules of gas moving at high speeds and banging off of each other. A decrease in speed would accompany a decrease in temperature. This would naturally lead to a decrease in the average distance between molecules. And that would make the same amount of gas occupy less space.
In the 1860's the physicist Thompson discussed with Lord Kelvin the idea that at absolute zero (-273 degrees Celsius) all molecular motion would cease. It was obviously not possible to go slower than zero speed so no lower temperature was possible. Asimov pegs Absolute zero at -273.12 degrees Centigrade. We can now add several decimal places (plus make the adjustments necessary to switch from Centigrade to Celsius) but the value has changed little in the intervening time.
Quantum Mechanics tells us, however, that it is impossible for all motion to completely stop. The Heisenberg Uncertainty principle requires that even at absolute zero there is some motion still present. And it turns out that the amount of residual motion matters. Scientists are now able to reduce the temperature of small amounts of matter to a thousandth, a millionth, or even a billionth of a degree above absolute zero. And in some cases these tiny temperature changes cause the properties of the material to change due to quantum effects. The study of temperatures very near absolute zero is now is now an area that commands the energies of a relatively large scientific community. But that's getting ahead of the story.
The coldest temperatures available to early scientists were not much lower than 0 Celsius. But that just led to "out of the box" thinking. The first step along this path was to notice that some gasses could be liquified without lowering their temperature. All that was necessary was to raise their pressure. This worked well for Chlorine, Sulfur Dioxide, Carbon Dioxide, and a number of other gasses. Pressurizing gasses tends to heat them up. But if you pressurize a gas, cool it down, then depressurize it, it becomes very cold. That's how refrigeration works. And refrigeration extended the range of cold temperatures accessible to scientists.
Another trick is evaporation. The process of evaporation draws heat out of a liquid. At the microscopic level what's going on is that all liquids contain molecules traveling at different speeds. If a high speed molecule happens to fly above the surface of a liquid it may never come back. This is how evaporation works at the molecular level and this mechanism preferentially removes the speediest molecules from the liquid. And, just as with a gas, these speedy molecules are the warmest ones. So evaporation, by removing the warmest molecules, lowers the average temperature of the remainder. In other words, it cools the liquid down. This "evaporative cooling" technique is how "Swamp coolers" work.
So scientists found clever ways to use refrigeration, evaporation, or both to reach heretofore unreachably cold temperatures. By 1885 -110 Celsius was reachable. But this is only 40% of the way to absolute zero. And, more importantly, a number of common gasses, Hydrogen, Oxygen, Nitrogen, and others, stayed in their gaseous form at this temperature. In 1869 Andrews determined that gasses had a "critical temperature". Above the critical temperature the gas would not liquify no matter how much pressure was applied. That made it all the more was important to be reduce the temperature of these gasses still further.
The "cascade" method allowed temperatures to be further lowered. An evaporation/refrigeration process using one gas was used to lower the temperature a certain amount. Then a second evaporation/refrigeration process using a different gas was used to lower the temperature further. By using a cascade consisting of several stages Pictet managed to liquify Oxygen at -140. Others liquified Carbon Monoxide (-190) and Nitrogen (-195). But it wasn't until 1900 that Dewar managed to liquify Hydrogen at -240 by using a multi-stage process that depended on these tricks plus his own invention, a "Dewar bottle", what we now call a "thermos bottle". But we are now only 88% of the way to our goal. And, as is common in these situations, the closer you get the harder it is to make additional progress.
Now we make a couple of digressions, not compliments of me, but instead compliments of Mr. Asimov. He first digresses by noting that by 1895 Hampton had been able to turn laboratory scale techniques into ones that could be performed at industrial scale. A simple modification of the same basic technique made it possible to cheaply and easily manufacture Oxygen in either liquid or gaseous form. It could then be used in Acteline torches and as a component in liquid fueled rockets, to name just two of the many applications that this breakthrough made possible.
In his second digression Asimov takes a moment to talk about what makes a good rocket fuel. As the results are informative, I am going to summarize them here. (Feel free to consult the original if you want to know more.) The magic number that tells you how efficient a rocket fuel is is something called "specific impulse". The more the better. Mixing Kerosene and Oxygen yields a specific impulse of 242. Using Hydrogen and Oxygen gives you 350.
So a pound of Hydrogen-Oxygen performs as well as about a pound and a half of Kerosene-Oxygen. But, of course, in the former case the rocket is lighter to the tune of a half a pound. Solid fuels generally have a lower specific impulse. But they are cheaper and safer and easier to work with. This makes it much easier to understand the trade-offs involved in selecting the fuel to use in your rocket.
Among the options listed, liquid Hydrogen + liquid Oxygen is the best but the hardest to work with so when you factor everything in it is likely to be the most expensive option. Solid fuels are the easiest to work and so initially they look to be the least expensive option with but are not nearly as efficient. Kerosene + liquid Oxygen is somewhere in the middle both in terms of efficiency and ease of use. Elon Musk went with this middle choice for his Space-X rockets.
And I always thought that liquid Hydrogen + liquid Oxygen was the best (as in most efficient) chemical fuel. But Asimov says I am wrong. Both Oxygen and Hydrogen are normally molecules consisting of two identical atoms bonded tightly together. And it is the combining of molecular Hydrogen with molecular Oxygen that I have been talking about. But they both elements also have an "atomic" form consisting of a single atom.
And if you start out with "atomic" Hydrogen and let it combine with itself in a rocket motor to form molecular Hydrogen you get a hell of a lot of energy. The specific impulse of this configuration is 1,300. It is almost 4 times as efficient as what I thought was the best chemical fuel. It's not used because no one has been able to figure out how to store atomic Hydrogen in the necessary quantities.
Most people know where the end of the line is when it comes to liquifying gasses. The hardest gas to liquify is Helium. But in 1908 Onnes cracked the riddle and liquified Helium under high pressure at -255 Celsius. By applying more tricks to his already extremely cold liquid Helium he was able to get small quantities down to 4.2 degrees above absolute zero (now referred to as 4.2 K for "degrees Kelvin"). At that temperature Helium is a liquid at normal pressure. The lowest temperature he was able to achieve was 1 K.
Work at these temperatures allowed Onnes to discover super-conductivity. Under the right circumstances materials lose all resistance to the movement of an electric current. Mercury becomes a super-conductor at 4.12 K. Lead becomes one at 7.22 K. In Asimov's time the highest temperature at which super-conductivity was observed was 11.2 K. Things have changed a lot since. The first "high temperature" super-conductor was discovered in 1986. Since then many others have followed.
But the holy grail, a material that super-conducts at room temperature, is still only a dream. And there is now a two track contest. Some materials become super-conductive at relatively high temperatures but only if they are compressed to very high pressures. These materials are interesting but not that practical. Unfortunately, materials that super-conduct at normal pressure do so at much lower temperatures.
And the lack of even a hint of a realistic possibility of ever finding a room temperature super-conductor has led scientists to move the bar. A material that super-conducts at normal pressure and at or above the temperature of liquid Nitrogen would be immensely useful. Liquid Nitrogen is now considered so widely and inexpensively available that a material that super-conducts in a bath of liquid Nitrogen is now considered "good enough". But even this considerably relaxed goal is still well out of reach.
Most devices that employ magnets constructed from super-conducting material like the Large Hadron Collider (LHC) at the CERN laboratory that straddles the Swiss - French border, bathe them in a cooling fluid of liquid Helium. Using materials that super-conduct at higher temperatures could instead use a less demanding and less expensive non-Helium cooling system.
But so far, no one has figured how to get such a system to work well enough to be practical. That means that everyone needing the performance a super-conducting magnet delivers has ended up being forced to go with a liquid Helium cooling system. Moving to high-temperature super-conductors for practical applications is still a dream rather than a reality.
And both the super-conducting phenomenon and super-conducting materials were quite mysterious in Asimov's time. They are now less mysterious. There is now a theory called BCS that seems to be relatively successful in providing some insight. It involves something called "Cooper pairs". I don't understand it well enough to talk about it so I'll leave it at that.
Asimov goes into a number of the starling properties of super-conducting materials in general and liquid Helium in particular. In the interests of brevity I am going to skip over them except to note that the record low temperature achieved by this time was 0.00002 K.
As I noted above, scientists can do better now. And they have discovered and explored many more remarkable ultra-low temperature phenomenon. There is something called a Bose-Einstein Condensate that displays remarkable quantum mechanical properties. Then there is the "Cesium Fountain Clock". Feel free to search out the details on your own as they are fascinating. I am going to confine myself to noting that this type of clock is so accurate that over a period of 300 million years it will be off by a second or less and that two Cesium Fountain Clocks, NIST-f1 and NIST-f2, provide the official time standard for the US.
It turns out that an interest in low temperatures naturally led to an interest in high pressures. Pressures are often measured in "atmospheres". One atmosphere is 15 pounds per square inch (PSI). The pressure at the center of the earth is about 3 million atmospheres. By the 1880s scientists could produce 3,000 atmospheres (45,000 PSI) in the laboratory. In 1905 Bridgman achieved 20,000 atmospheres. And somehow this led to a discussion by Asimov of diamonds.
It took a while for scientists to prove that diamonds were just Carbon arranged in a specific crystalline configuration. It is easy to turn a diamond into another form of Carbon. Is it possible to go the other way? Yes, but it takes a lot of pressure. The first artificial diamonds were produced in 1955 in a lab owned by General Electric. The feat required pressures of 100,000 atmospheres combined with temperatures of 2,500 degrees Celsius.
Artificial diamonds were a curiosity at the time. They are now a business, albeit a modest one. The GE process has been improved upon but not by much. The more interesting recent development is the "Diamond Anvil Cell". Diamonds are extremely hard. If you take a diamond with a point on it (the part on the bottom in the setting of an engagement ring) and chop a very small part off of it, you get a small flat spot.
Now do the same thing to a second, similarly sized, diamond. Now glue one diamond, point out, to one jaw of a vise and the other diamond, also point out, to the other jaw. If everything is lined up properly all the pressure the vice generates as it is closed is focused into the space between the two tiny flat surfaces at the tips of the diamonds. If you put something into that tiny space you can subject it to fantastic pressures.
Now add a microscope. Remember that diamonds are transparent so you can see what is going on by looking through the flat surface of one or the other diamond at whatever you put between them. You can also shine lights through the diamonds or add other components to perform a wide variety of experiments under extremely high pressure.
Diamond Anvil Cells have become a common tool in labs that want to subject materials to extremely high pressures. Lots has been learned about the inside of the earth, for instance. Before the advent of the Diamond Anvil Cell, rocks and minerals thought to be common in the interior of the earth couldn't be subject to pressures high enough to reproduce those found at depth in the earth. Now they can.
Moving on to "Metals", the first thing to understand is that the definition of what is and is not a metal evolved from experience. The ancients became familiar with Gold, Silver, Copper, Iron, and Tin. They seemed to share similarities so they were lumped together as "metals". Fast forward to the present and Chemists scan the Periodic Table of the Elements and classify many elements as metals and others as non-metals. But more than anything, what they are doing is retrofitting things to fit the ancient conception of what was and was not a metal.
The ancients observed that a metal in it's pure state was shiny. You could form it into sheets by beating it with a hammer. Later it was found to conduct electricity and heat. So over time elements that seemed to have properties similar to known metals were added to the "metals" group. This resulted in some weird decisions.
Mercury is a metal even though it is liquid at room temperature. Why? Because it is shiny and conducts both heat and electricity well. So the fact that you couldn't form it into a sheet and beat it with a hammer was ignored. And so it went to the present day when, as Asimov notes, only about 20 of the (then) 102 elements in the periodic table are classified as non-metals. The rest are metals.
Then there are the Astronomers. They have an entirely different definition of a "metal". At the time of the Big Bang the universe consisted of about 90% Hydrogen (atomic number 1), 10% Helium (atomic number 2), a trace of Lithium (atomic number 3), and pretty much nothing else. To an astronomer a "metal" is anything that is not either Hydrogen or Helium.
They ignore the trace of Lithium that was also formed during the Big Bang and use "metal" as short-hand for any element created after the Big Bang. As Asimov goes with the Chemistry definition of "metal", I will too. But knowing this Astronomical definition of a "metal" may avoid some confusion. If you come across the word "metal" in an Astronomical context and something seems wrong it's because something actually is wrong. Astronomers are just being Astronomers. Once you understand this the confusion evaporates.
Anyhow, the first metal that came into wide use in ancient times was Copper. Warfare drives a lot of technological advances and "Copper" edged weapons were found to have advantages over stone edged weapons in a lot of contexts. And Copper, as it is found in the ground, often has some Tin mixed in. As a result, a lot of ancient "Copper" was actually Bronze. Bronze has more of the hardness that stone possesses but avoids stone's brittleness. Pure Copper, on the other hand, is quite soft.
It took a while for the ancients to figure out that they wanted to avoid pure Copper when they were making weapons and go with the Copper that contained a substantial amount of Tin. By between 3,500 BC (Egypt and other palaces) and 2,000 BC (Greece and other places ) years ago people figured out what the story was and were deliberately mixing Copper and Tin together in the correct proportions to get weapons grade Bronze. And that's where the "Bronze Age" got it's name.
Iron was known to have excellent properties from antiquity but the only known source for a long time was meteorites. Smelting, the deliberate manufacture of Iron from ore, was pioneered in Asia Minor in about 1,400 BC. Iron is much harder to make than Bronze as it requires much higher temperatures and careful attention to the carbon content of the resulting metal. The early product, called "Wrought Iron", did not have the strength and other properties we now associate with Iron due to all the impurities it contained.
By the middle ages the process was better understood and "Cast Iron", an Iron with fewer impurities, became widely available, It made much better weapons. But it tended to be brittle because (as was found out later) it had too much carbon in it (4-5%). Steel (what we would now call "Mild Steel") is low-carbon (0.2-1.5%) Iron. It is both stronger than and less brittle than Iron. But it is also very hard to make.
That is, until 1876 when Bessemer came up with his process for making Steel in large volumes using the simple and inexpensive process that was named after him. He invented the process to solve a different problem. Adding rifling (groves that caused the projectile to spin and, therefore, fly much straighter) to the barrels of cannons substantially increased their accuracy. But the added stresses were too much for the Iron or Brass cannons of the day. He needed something stronger and his "blast furnace" could make Steel, and that was exactly what was needed.
It turned out that Bessemer steel was inferior if it contained Phosphorus. Bessemer got around this by using ore that was Phosphorus free. But in 1875 Thomas figured out that lining blast furnaces with limestone and magnesia enabled the use of high Phosphorous ore. The lining removed the Phosphorous. Soon, suitably lined Bessemer-style blast furnaces took over everywhere and the "Age of Steel" got under way.
By 1900 steel was showing up everywhere. It was used in the rails trains rode on and in the trains themselves. It was used in the bridges that spanned rivers. It was in the skeletons of "skyscraper" buildings that rose above the street. It was in the pipes below the streets. It was in automobiles that rode on the streets. It was in appliances in the kitchen and more appliances in the laundry room. It showed up hundreds of consumer products large and small. It was in the factories that made everything else. And it revolutionized warfare.
The "Dreadnaught" was the first modern battleship. It set the pattern that continued to the end of World War II. The "tank", a weapon invented by the British during World War I, revolutionized how land battles were fought. Rifled artillery weapons, deployed both on land (most famously as the "Big Bertha" gun the Germans used to shell Paris during World War I) and at sea (also famously as the "16", or in the case of the Japanese "18", "main battery" guns found on the battleships that fought in World War II). And many of the battles fought during World War I were, in essence, artillery duels involving thousands of guns on each side.
But Bessemer Steel pouring straight out of a blast furnace was not the end of the "Steel" story. The "Carbon" and the "Phosphorus" stories got scientists to thinking "what would happen if we added a little of this or a little of that to Steel?" The answer turned out to be very interesting. Adding Manganese, Tungsten, Chromium, and other materials, could produce Steel with very beneficial properties. Most famously, adding the right amounts of Nickel and Chromium produces "Stainless Steel".
Progress has continued in this area since Asimov published but there have been no big breakthroughs. One candidate that ultimately failed is something called "Cor-Ten" Steel. Initially it rusts. But once a thin layer of rust has built up no more rust forms. In theory that makes it a good roofing material and it was used on a number of buildings.
The industry had high hopes for it at one point. But, although it worked exactly as advertised, it never caught on with the general public. So the Cor-Ten craze lasted only a short while. Nor has any other "magical new" kind of Steel caught on in a big way. There have been numerous small advances but no big breakthroughs when it comes to Steel.
But Steel (or the Iron that is its principal component) is not the only metal out there. Aluminum is a striking example of this. For most of history Aluminum was considered a rare and exotic material. It's not because Aluminum itself is rare. It is actually more common than Iron. But before 1886 pure Aluminum was very hard to come by. There are a few chemical processes that will break up molecules containing Aluminum. But they were either difficult or expensive to perform. This put Aluminum in the same category of "only for the rich" as Gold and Silver.
All this finally changed in 1886 when Hall figured out that the tight chemical bonds Aluminum formed could be broken by the application of electricity. This led to the "smelting" process still in widespread use. Since it takes a lot of electric power, smelters that turn bauxite (the most common ore that contains a large amount of Aluminum) into relatively pure Aluminum ingots are all located where cheap electricity is available in large quantities.
Aluminum has two advantages when compared to steel. It is light, weighing in at only a third the weight of steel. The second advantage is corrosion resistance. Like Cor-Ten Steel, Aluminum quickly forms a tough shell on any surface exposed to the air. Once a relatively thin shell has formed it does not continue to get thicker. The difference is that the public has accepted the shell Aluminum creates while they have not accepted the shell Cor-Ten creates. So we see Aluminum items like ladders all over the place but Cor-Ten items are rare.
Pure Aluminum is too soft to be of much use. But in 1906 Wilm developed an alloy by adding Copper and Magnesium to Aluminum. The resulting "Duralumin" quickly became a hit, especially in the airplane business. Duralumin is not very corrosion resistant. But if you add a thin surface layer of pure Aluminum you get "Alclad", which is. Work has continued to find new better Aluminum alloys. There have been successes, but the story is that same as with Steel. There have been a lot of small improvements but no big breakthrough.
And there was a lot of talk for many years of moving from Steel cars to Aluminum cars. But it turns out that Aluminum is far less versatile and far harder to work with than Steel is. So modern motor vehicles have a lot more Aluminum in them these days than cars of yore. (The Ford F-150 pickup truck is an example of this.) But they also still contain lots of Steel. Efforts to use Aluminum for engine blocks, for instance, have been largely unsuccessful.
And airplanes skipped over Steel and went from wood to Aluminum. Aluminum has ruled the roost as the metal of choice when it comes to airplanes from the '20s pretty much to this day. It looks like the material that is most likely to supplant it is carbon fiber. The Boeing 787 was a big bet on carbon fiber that seems to be paying off. But carbon fiber is even harder to work with than Aluminum.
It has been a long slow learning curve for the aerospace industry to figure out how to work with it. The auto industry has moved even slower. There are a few super-expensive cars that use substantial amounts of carbon fiber. But, so far, that's it. No one had a clue as to the possible existence of something like carbon fiber in Asimov's day.
Asimov next moves on to Magnesium. Magnesium is lighter and rarer than Aluminum. There is lots of Magnesium in the ocean. All salt water contains small amounts of it. But it was not then and is still not economically practical to extract Magnesium from salt water. Besides its expense, Magnesium has the additional problem that it is easy to get it to burn. And it burns really well. A "Magnesium flare" is very bright. It's also very dangerous to be anywhere near.
After Asimov published his book it was discovered that vast beds of "Magnesium Nodules" could be found on the sea floor in various parts of the ocean Several schemes were hatched to harvest these nodules. But none of them turned out to be feasible. So Magnesium never went mainstream. There are various niche uses for it but it is too expensive and hard to work with to come into widespread use. Are there any other interesting metals?
There are seven really common metals in the earth's crust, Asimov observes. We have already covered three: Iron, Aluminum, and Magnesium. The other four are: Sodium, Potassium, Calcium, and Titanium. Quoting Asimov, "Sodium, Potassium, and Calcium are far too active chemically to be used as construction materials." This line of thinking allows him to focus on Titanium.
Titanium is roughly half the weight of Steel while being stronger, more corrosion resistant, and possessing better tolerance of high temperatures than its competitors. It sounds like the wonder metal and it is. The only thing holding it up is the difficulty of procuring it and working with it. Asimov saw it as a potential metal of the future.
Titanium has found many in the intervening years. But the cost and difficulty of working with it have limited these uses to a few high value situations. One marquis use of it is in the SR-71 spy plane. There, its ability to withstand very high temperatures while maintaining most of its strength were critical. But each SR-71 costs a bloody fortune to build and maintain.
At present, Titanium is most commonly found inside jet engines. Modern jet engines have two sets of "compressor" blades. The front set operates in a cool and relatively benign environment. The back set are literally located in the middle of the flame of the jet. That environment is very hot and very chemically harsh. And it turns out the higher operating temperature at which you can run this rear part of the engine, the more efficient you can make the engine.
So engine makers figure out exactly how much punishment blades in the back part of the engine can withstand and design the rest of the engine accordingly. As new methods and materials come along that allow the blades to stand up under still more punishment the engine design is changed accordingly.
It's a fine line that is walked as any increase in operating temperature or other means of torturing the blades that can be safely withstood translates directly into increased engine performance and/or efficiency. But if you go too far really bad things happen. The engine explodes into very hot, very sharp, shrapnel. It's a good thing Tungsten and its alloys can withstand a truly astonishing amount of torture.
Both the operating temperatures and the efficiencies of modern jet engines far surpass anything an engineer of Asimov's day could have imagined would ever be possible. And that has enabled airlines to be profitable while charging far lower fares than anyone could have imagined back then. At the time the book was written the Boeing 707 had just come into service.
Back then, most planes were still propeller driven. People forget that the piston engines in propeller planes are complex and finicky. That means they require a lot of maintenance to keep them running well. Jet engines are far simpler and turn out to require far less maintenance. And they are way more fuel efficient, lighter, etc. But at that point airlines had little experience with jets and didn't know what to expect.
The obvious expectation is that the costs and performance of jets would be similar to that of propeller planes. It turns out that jets were faster so you could get more flights in per day. And they were more fuel efficient and required far less maintenance. And modern jets can fly a lot further. The longest range jets in today's inventory can fly directly from pretty much anyplace on the earth to pretty much anyplace else. Predicting that all these changes were going to happen would have been nearly impossible. It's not any one thing. It's the combination of all of them.
Asimov ends this chapter with a trenchant observation:
There is reason to think, however, that the older metals (and some non-metals, too) can be made far more "wonderful" than they are now.This observation has proven to be spot on. Progress consists of a combination of new discoveries and ways of making old things work better than anyone thought possible.
In the next installment we will move on to the section titled "The Particles". This will circle back to subjects covered previously. But it will dig deeper into them and that will allow me to discuss at greater length and in more detail the new discoveries and advances that have taken place AA - After Asimov.
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