Diamond Soufflé

Graphite (as graphene)

Isn't it obvious looking at their structures why so many attempts to make synthetic diamonds fall flat and make graphite instead?

This is backed by thermodynamic data so argue only if you dare.

A Girl's Best Friend is the Blue Diamond*

The structure of graphene got me to thinking of that other form of carbon, viz., diamond:

3D movie: link

Why is diamond so tough, so adamant, so opposed to physical change? I think the answer is called "perfect covalency" but not in an electron sharing sense:

The paradox of the diamond is interesting. Its atoms are not arranged in a tight, closest-packing order. They lack the triangulation of sound architecture. In order for its remarkable rigidity to be understood, I assume that the electrons which surround this meager structure supply it with its resistance to deformation. This is one reason why I cannot assume that electron clouds can infiltrate one another like vapors or ghosts. link

Pure diamond is also colorless and transparent, so what gives fancy (colored) diamonds their colors? The answer is not simply: "there must be something blue inside." An impurity is involved, but not the usual colored metal atoms like iron or chromium found inside other gemstones. The impurities in blue and yellow diamonds are carbon's left- and right-hand periodic neighbors--boron and nitrogen--playing little tricks on the lattice electrons.

Take the perfect 3D lattice of carbon atoms pictured above. Now suppose that we could randomly go in and replace every millionth carbon atom with a boron atom without perturbing anything else. What we get is a boron-doped diamond lattice. Because boron has one less electron than carbon, the entire lattice structure of the diamond is riddled with electronic "holes."

Now it just so happens that reddish-orange light has just the right energy match to promote an electron on an adjacent carbon atom into a "hole" next door. That jump in turn creates a new "hole" and so the next neighbor carbon jumps at the chance to fill the new hole and so on and so forth throughout the entire diamond lattice. Really, a blue diamond is rather like a doped silicon p-type semi conductor. In fact, blue diamonds are semi-conductors--albeit rather expensive ones!

Because only reddish-orange light is absorbed, the remaining visible light appears bluish to our eye because the white light lacks its reddish-orange component: remember the color wheel and complimentary colors!

Likewise, water in a white bathtub appears bluish because it absorbs some of the reddish component of the incident white light. That's also why heat lamps are red too--they are more or less tuned to the wavelength (infrared) that water in food absorbs and converts to heat. Microwave ovens are even better at this.

So what makes yellow diamonds? The answer is slightly more complex. If nitrogen atoms, carbon's other nearest neighbor, are doped into the diamond lattice instead of boron, each nitrogen brings an extra electron into the lattice which is easily promoted to the existing conduction band of diamond by violet light--ergo yellow appearing diamonds. Yellow diamond is analogous to an n-type semiconductor. Here's a link explaining in more detail why blue diamonds are blue and why yellow diamonds are yellow: Link.

Meanwhile, here's a very pretty picture of the Hope Diamond:

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*I don't mean "blue diamond-shaped" Viagra either.

Whiffing Aromaticity

Aromatic chemistry.  The very name suggests something sweet and pleasant smelling. I still recall the distinct aromas of purified benzene, toluene, xylene(s), anisole, phenol, benzaldehyde, benzylchloride, aniline, styrene, and naphthalene. It's been over a decade since I whiffed any of those but I'm certain I could score 100% on a blindfolded aroma test for all of them.

Those names are fascinating--despite the stylized suffixes "ene" and "ol".  Many are old words derived from older languages like Greek, Persian, Arabic and those of other ancient trading cultures.  The root words were probably once familiar to everyday people in those cultures, much like the ancient substance called myrrh.  If there were an aromatic hydrocarbon derived from myrrh, I'm certain that chemists would have called it myrrhene.

Few of the aromatics smell bad.  But then again, I've always thought the smell of gasoline was rather pleasant. But some of them smell better than others, especially benzaldehyde (which smells like almond extract) and anisole (which smells like licorice). Not so with the saturated straight-chain hydrocarbons: methane, ethane, propane, butane, pentane, hexane, etc. The odors of those are much fainter.

Aromaticity has a whole nother meaning in chemistry, but that will have to wait for another time.

More Bloghetti Carbonara

Carbon dioxide is like the burned-out skeleton of a once juicy hydrocarbon. Drawing out the Lewis structure, the double bonds remind me of the radius and ulna bones in the forearm:

O=C=O

Soft tissues (which are mostly water) show up as lighter shadows in X-rays. Magnetic Resonance Imaging (MRI) is a complementary technique that locates water's hydrogen in soft tissues. And that's exactly what's missing in CO₂--all the hydrogen. Hydrocarbons get all the hydrogen and electrons sucked out of them when they burn, transferring them to electronically rapacious oxygen:

CH₄   +   2 O₂   →  CO₂   +   2 H₂O

Of course plants and bacteria carry out the reverse reaction, converting CO₂ to sugars, but it's possible to synthetically convert carbon dioxide into methanol or even methane using dihydrogen:

But making hydrogen requires energy too.  Making nitrogen fertilizers uses lots of hydrogen, so those serious about fuel supplies will also have to worry about food supplies.  I just wish the same people who talk about shutting down industries and exacting revenge would instead busy themselves with showing that alternatives can be successfully commercialized, because if they can't there's little sense in using them. Energy independence will not come from government investing in unworkable alternatives.  Energy independence can only come from the use and exploitation of domestic energy sources and this includes coal. Oil and related hydrocarbons are intrinsically cheap.  If we decide to move away from them because we don't like or can't shoulder the associated problems, e.g., keeping the free flow free, we'd better prepare for somebody else doing the dirty jobs. And to the winner goes the spoils.

Hydrocarbons: Still Our Old Friend

As I write this we're all still watching the horrible oil rig disaster unfold. Here are some spectacular photos of the event via Twitter.

Eleven dead already.  The entire Gulf of Mexico coastline threatened. Is there already talk of this catalyzing a move further away from oil? The fact is that oil and related hydrocarbons are still relatively cheap and plentiful. Or is the whole enterprise just too big to fail?  I worked for a time on a project devoted to making gasoline from natural gas. During this time I became familiar with the business phrase "shutdown economics" which in that case meant that any new technology had to be good enough to make the existing technology unprofitable and pay for the cost of recapitalization.

We'd all like for wind and solar energy to be cheaper. But we're not anywhere close to replacing hydrocarbons.

Get Your Carbs Here!

A single blogpost will just not cut it for carbon, the 6th element. There are so many interesting little sub-topics to cover like diamonds, graphite, buckyballs, and nanotubes. But that wouldn't even begin to touch on compounds, e.g., the hydrocarbons, which give us energy and which also fuel human conflicts past, present and future. And then there's carbon combining with other elements that I haven't reached yet- elements like nitrogen and oxygen: hello, CO₂ anyone? Of course that wouldn't get us to carbohydrates or even amino acids, let alone to proteins and things that make up living creatures. I'll probably end up doing several blog posts on carbon, but also keep moving ahead.

Many chemists fall so in love with carbon that they never get past it. Those chemists are called organic chemists. To help understand why carbon is so special, consider a "carbo-centric" version of the periodic table which any Organiker should love:

original

That chart used to be standard fare at German universities (and let's face it: until the end of WW II, the Germans were organic chemistry). Notice how carbon sits dead center in a row of nine elements, having an equal number of elements to its right and to its left. Here is that first row or period again, pulled out of the chart:

    He     Li    Be     B      C      N     O     F     Ne

Carbon is the first element beyond helium that is found (practically) pure in the elemental state. In general, when commingling, elements tend to gain or lose valence electrons to resemble the nearest noble gas: elements to the left of carbon (e.g., Li⁺, Be²⁺) achieve the electronic nobility of helium by doffing one or two electrons respectively; elements to the right (O^2-, F^-) achieve the nearest noble gas configuration of neon by gaining one or two electrons; elements in the middle (B, C, N) tend to neither completely gain nor to lose electrons, but rather, to share electrons with other elements. These tendencies are a consequence of electronegativity. Carbon also forms so many compounds because of catenation. Catenation is just a fancy latinate word for "linking together"-something that carbon is good at doing, especially with itself.

Returning to the carbo-centric periodic table above, note that there is a similar row or period centered around silicon:

    Ne    Na     Mg    Al     Si      P      S      Cl    Ar

One might ask whether a similarly rich silicon chemistry exists. The short answer is no, because silicon can't self-catenate like carbon can.  Silicone polymers require the insertion of one oxygen atom between silicon "monomers." But some might argue that silicon-based life, created in our own image, has just begun to evolve--it just finds our oxygen-rich environment too hostile. 

Carnot Knowledge: Rudolf Diesel's Awesome Idea

Rudolf Diesel (1858-1913)

Ordinary gasoline engines are powered by the sparked ignition of gasoline vapor compressed with air. The heat of combustion and increased exhaust gas pressure drives pistons, doing useful work derived from the chemical energy stored in the fossil fuel. Gasoline engines behave according to the Otto Cycle and the ideas originally date from the mid-19th century.

Rudolf Diesel, a German engineer, understood the engines of his day and had the radical idea of compressing air inside the piston until it became so hot that fuel would spontaneously ignite when it contacted the hot pressurized air, thus not requiring a spark plug. In essence, Diesel reengineered the existing Otto cycle and invented engines that behaved according to the Diesel Cycle.

Diesel based his ideas on his understanding of the thermodynamics of heat engines, a young science begun by the French engineer Sadi Carnot and who later became known as the father of thermodynamics.

US Patent No. 542,846: "Method of and Apparatus for Converting Heat into Work (Link) was awarded to Diesel and has a clear and concise explanation of how and why diesel motors work. In Diesel's own words (or more likely those of his patent attorney):

The gases in the cylinder are now permitted to expand with gradual introduction of fuel and expansion is so regulated that the decrease in temperature by expansion counterbalances the heat produced by the combustion of the fresh particles of fuel. The effect of combustion will therefore not be increase in temperature or pressure, but increase in actual energy exerted.

Diesel also solved another important problem that still limits the efficiency of gasoline engines, viz., the tendency for gasoline motors to knock or ping due to "predetonation." Autoignition is precisely what diesel motors are supposed to do, albeit in a controlled way.  In a diesel motor, the air and fuel are pressurized separately and then mixed. Because diesel motors burn at hotter temperatures than gasoline engines do, they have a tendency to "burn air," forming nitrogen oxides from the normally inert N₂ and O₂ that make up the air we breathe. Precious metal catalysts are used to convert the nitrogen oxides back into oxygen and nitrogen.

Today, diesel motors find widespread use in nearly all commercial transportation applications: trucks, trains, ships, submarines, and, as I learned from Theo Boehm, even in aviation (BTW, did you know that aviation gasoline still has lead? Link--fine particles of lead oxide (or actually lead chloride or bromide) rain down on us everyday. Europeans use diesel motors far more commonly than we do for personal transportation.

I'm sold on diesels. I own a 2003 VW Golf Diesel (TDI) and I love it. It gets around 43 MPH on the highway and not much less in city because it's a stick. Another advantage to owning a diesel in CA is that they are exempt from smog-testing.