Pique the Geek (Elements) 20120708: Boron – Widely Used and Uncommon

(9 pm. – promoted by ek hornbeck)

If you follow this series closely, you will remember that the last element that we covered was lithium, and so the next one should be beryllium.  However, I wrote about beryllium recently and so you can just follow the link.

Last week I wrote about fireworks safety, and my piece was prescient and unfortunately evidently not read by some unfortunate youths in Arkansas.  My friend, who often comments here using the handle justasabeverage, sent me the newspaper article by email the other day that covers the topic after the fold.

Arkansas teen killed after sparkler bomb explodes

The Associated Press

BUCKNER, Ark. – An Arkansas teenager was killed and another was injured when their homemade sparkler bomb exploded before they could back away safely, authorities said Thursday.

The teens, who were celebrating the Fourth of July, used electrical tape to bind sparklers together and lit another sparkler to act as a fuse. The bundle detonated sooner than expected as one of the teens was placing a 5-gallon bucket over it, said Pete Richardson, Lafayette County’s chief sheriff’s deputy.

Wrapping together sparklers “makes a pretty awesome bomb,” Richardson said.

Both teens were taken to the hospital, where 17-year-old Justin Smith, of Buckner, died. Authorities didn’t release the injured teen’s name, but said he is in stable condition and from nearby Mount Holly.

Two other people witnessed the blast but were not injured.

Lafayette County is under a burn ban, which means fireworks are illegal unless a resident receives written permission to ignite them. Richardson said he didn’t know if the teens had permission to use fireworks.

I noticed on a box of sparklers that I bought the other day for The Girl and The Little Girl that it says, “Light only one sparkler at a time” on it.  Too bad those kids in Arkansas did not heed the warning.

Boron, with an atomic number (Z) of 5, is one of the more uncommon light elements.  Whilst few of us have seen elemental boron (I have, because we used it as a fuel for delay trains whilst I was a professional pyrotechnician), almost everyone has seen its compounds or products made from them.  Actually, the boron that I used in pyrotechnics was not really pure, but contaminated with a little carbon.  Highly purified boron is difficult to make is is used mainly in the electronics industry.

Most people are familiar with borax, either from the laundry or from hand cleaners.  Borax is sodium borate decahydrate, Na2B4O7.10H2O.  However, X-ray crystallographic studies indicate that the formula is actually Na2[B4O5(OH)4]·8H2O.  It is used in the laundry in two ways.  Most people use it to boost the cleaning power of laundry detergent by adding it to the wash.  Since borax solutions are bactericidal, these solutions will keep smelly laundry, such as diaper pail contents, from smelling until washing.  It also inhibits the growth of mold, so clothes in a borax solution will “keep” until laundry time and not smell.

Because of its antimicrobial properties, borax is used as a food preservative for many decades.  It is not allowed to be used for that purpose in the US, and according to Harold McGee in his wonderful On Food and Cooking, caviar imported into the US is inferior to that eaten other places because a little borax is added to replace quite a bit of salt, so caviar in the US is saltier and less sweet than caviar where borax is legal for food use.

I have used borax for brazing and hard soldering metals, because it forms a flux in which oxides dissolve that thus are removed from the joint by floating them out of it.  This allows for a good, tight joint.  Because it is so good at dissolving metal salts, it was used for years for color tests for different metals and still is to a small extent for “fast and dirty” work but has been replaced by modern optical analyses to a great extent.

There are so many uses for borax that I could write a whole piece about that topic, but one last one that you may have experience with is the goopy toy stuff called Slime.  Borax and polyvinyl alcohol are mixed with water and Slime is the result.  If you use polyvinyl acetate instead, you get Elmer’s Glue-All.

Boric acid is another compound that you may have handled.  It is popular in eye drops because the boron helps to preserve the drops and also is used as a buffer to make the pH of the drops the same as tears so they do not irritate the eye.

Boric acid is also used as a relatively nontoxic insecticide.  Boron compounds are toxic to lower forms of life much more than to mammals, so it is safe to use boric acid around children and pets.  In places where cockroaches are really bad, sometimes builders will put boric acid in new construction before the drywall is installed.  This provides a reservoir of insecticide for the life of the home.  Boric acid is a solid, by the way.

A large use of boron compounds is to produce borosilicate glass.  The brand that most think of is Pyrex, and that name is owned by Corning Glass.  This glass contains around 15% of boron as boron oxide (B2O3), the rest being mostly sand (very pure, white sand).  This glass is stronger than standard soft glass and has a much lower coefficient of thermal expansion.  This means that borosilicate glass is much less apt to break due to thermal shock.

Corning still makes Pyrex for scientific and industrial use, but leased the name to another company for bakeware.  Modern Pyrex bakeware is regular soft glass that has been tempered, so do not get confused.  All US Pyrex bakeware manufactured since 1998 is soft glass.

Elemental boron does not exist in the crust of the earth, but as compounds, mostly containing sodium and oxygen along with the boron.  It was used in antiquity to produce glazes on pottery (and is still used for this purpose, since a glaze is essentially a glass).  The word boron is probably derived from the Persian word  بوره (burah), the name in that language for borax.

Boron compounds were relatively rarely encountered until comparatively recently.  Boron itself was produced in 1808 by the brilliant British chemist Sir Humphrey Davy.  Davy also discovered sodium, potassium, and other elements.  Except for pyrotechnical and electronics work, elemental boron has few uses.

Aside from the consumer uses mentioned previously, boron has a large number of industrial and scientific uses in the form of compounds.  For example, boron carbide (the formula is somewhere betwixt B12C2 and B12C3) is extremely hard (~9.5 on the Mohs scale) and extremely tough.  It is widely used as an abrasive, but also for armor and other applications where a very hard and tough material is needed.  The ceramic inserts that you hear about for body armor are made of boron carbide.  It also has nuclear applications that we shall discuss later.

Boron nitride (BN) is a strange material.  Boron has Z=5, carbon has Z=6, and nitrogen has Z=7.  Thus, BN has the same number of electrons as carbon, and so is said to be isoelectronic with carbon.  Like carbon, BN can form a hexagonal crystal lattice in layers, just like graphite.  It can also form a three dimensional network with a cubic structure, just like diamond.  In fact, both of those structures are known, and the hexagonal one is soft like graphite and the cubic one is almost as hard as diamond.  It also has a very high thermal conductivity.  Since it is less reactive under many circumstances than diamond, it is used as a replacement for diamond in many industrial applications.  It is also cheaper than diamond and can be made into large pieces.

Boron forms organic compounds with carbon that are very useful.  Diborane (B2H6 and its derivatives can add to a double bond in an alkene, often very selectively with respect to other nearby groups.  These organoboranes can then be further manipulated to produce excellent yields of single products where many other approaches produce mixtures of two or more products that must be separated to get the desired one.  This reaction is called hydroboration and won the Nobel Prize for H. C. Brown in 1979.

There are many organic compounds of boron, and lots of them are pyrophoric, bursting into flame when exposed to air.  Normally this is got a good thing, but they can be used as ignitors for jet and rocket engines.  The most advanced jet of its time, the SR-71 Blackbird, used triethylborane to ignite its engines, as did the Saturn V rocket that took us to the moon.

A binary compound of boron and magnesium, magnesium diboride (MgB2) is superconductive below 39 K.  Since this material is far less expensive than many other superconductors and is easy to form, it is expected to become very widely used in future and is already finding applications in things like MRI.

Another interesting electromagnetic property of boron is its use in neodymium magnets, the strongest permanent magnets currently known.  It is just a small part of the formula, but the material represented by the formula Nd2Fe14B are the most powerful that can be had.  They are so powerful that care has to be taken with them because fingers can be broken when two relatively small ones try to come together.

Boron has a significant role in biological processes, but the exact mechanisms are not well known.  It is an essential plant micronutrient, but too much causes plants to be stunted.  Rodent studies show that it is essential for them, but how much is debatable.  My multivitamin has 75 micrograms, but the RDA has not been established for boron.  In a very interesting study conducted by USDA indicated that very small amounts of boron (around 3 milligrams per day) reduced calcium excretion and boosted activity of estrogen and vitamin D in postmenopausal women, and the implications for that may be very significant as it could be a safe and cheap treatment for the prevention of osteoporosis.  Whilst I do not give medical advice, it seems that a tiny bit of laundry borax on the tip of a finger might do a body well.

The nuclear applications of boron are interesting.  There are two stable isotopes of boron, 10B and 11B.  The lighter one is at about 20% abundance and the heavier the remaining 80%.  This makes sense, because generally odd/even nuclei are more common than odd/odd ones.  It turns out that 10B is an excellent absorption material for neutrons and it is used in the nuclear power industry for just that, either as control rod filling or as boric acid dissolved in the cooling water when reactors are refuelled until the rods are not so hot.  It is also proposed for use in spacecraft to absorb neutrons given off from cosmic ray bombardment of the craft.

An interesting medical use for 10B is in radiotherapy for cancer.  When 10B absorbs a neutron, it gives off an alpha particle and a 7Li atom, both of which are quite energetic and highly ionizing.  By choosing the proper boron compound, the 10B concentrates at the tumor area and allows low energy neutrons that in themselves do not do much to cause those very energetic fragments to target cancer cells with little collateral damage to healthy cells.

On the other hand, 11B interacts with radiation hardly at all.  One plan is to use it to shield delicate electronics on spacecraft from the 7Li and alpha particles produced when the 10B absorbs the neutrons.  It is truly amazing what one little neutron can do!

So, where do we get boron?  It is actually quite a rare element, and we shall go into that in a bit.  Most of the boron used in the US comes from California, near a town called, interestingly enough, Boron.  About half the world market supply comes from that one mine.  It is mined using open pit technology, then the ore is treated with water to extract the soluble borates.  After refining, it is marketed as borax whence comes all of the other boron products.  The nation of Turkey comes in second, but it has much larger borate deposits than the US has.  Their mining industry just has not developed as much as ours has.

Borate mining became a big deal in the 1880s when the California deposits were discovered.  The trademark “Twenty Mule Team Borax” is actually very apt, because the mining operation actually used teams of 20 mules to haul huge wagons of borax to the rail spur near Death Valley from 1893 to 1889 when the rail spur was extended.  That trademark has been active since it was registered in 1894 (actually it was used for a couple of years before being registered).

So how can there be such huge deposits for such a rare element?  It is because of its solubility in water.  When land containing borates is flooded, lakes form.  Later, in arid places, the lakes eventually dry out and the salts are concentrated.  That is why the borate ore has to be refined because salts other than borates are in the deposits.

Cosmically, boron is quite rare.  There is no mechanism to make it in stars, and it appears not to be formed in significant amounts in supernovae.  That leaves cosmic ray spallation, and we talked about it in the lithium piece from two weeks ago to which I gave the link earlier.  This is an inefficient way to make nuclei, and that accounts for why there is so little boron in the universe compared to most other light elements.  Most of the boron was formed early in the universe when it was much smaller.  The flux of cosmic rays is much too small in our 13+ billions of years old universe to be significant now.  An example of a spallation reaction is the formation of the alpha particle and 7Li from 10B mentioned previously.

That about covers what I wanted to say about boron this evening.  I barely scratched the surface, and boron is a fascinating element.  I should mention that the known isotopes of boron range from 6B to 19B, but none have a half life more than 20 milliseconds are have no use other than theoretical physics research, and they are not used for anything except to determine their properties to refine theory.

Before I go, I should mention a couple of personal things.  The cold front came through a couple of hours ago and we dropped from 101 degrees F to about 84 degrees F now.  The other thing is that I do not know exactly what the outside temperature is because Jace (the new kitten that The Girl and I got for The Little Girl) chewed through the buggering lead wire from the outdoor sensor.  I  have soldered the lead back, but have not yet put it in place outside.  I should have gotten a wireless one years ago.  Now I have to figure out how to protect the repaired lead or he will just do it again.

Well, you have done it again!  You have wasted many more einsteins of perfectly good photons reading this spallated piece.  And even though Allen West realizes that he really sounds like an idiot by stating that President Obama wants to enslave the people when he reads me say it, I always learn much more than I could possibly hope to teach by writing this series.  Thus, please keep those comments, questions, and corrections coming.  Tips and recs are also greatly appreciated.  Remember, no science or technology issue is off topic here.  I shall remain here tonight as long as comments warrant, and shall return tomorrow at around 9 PM Eastern for Review Time.

Warmest regards,


Crossposted at

The Stars Hollow Gazette,

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  1. Z=5?

    Warmest regards,

  2. I very much appreciate it.

    Warmest regards,


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