# Understanding the Nature of Glass

This is from over a month ago, but there was a wonderful article for all the closet material scientists out there in the New York Times on Glass a few weeks ago.

Here is an except:

It is well known that panes of stained glass in old European churches are thicker at the bottom because glass is a slow-moving liquid that flows downward over centuries.

Well known, but wrong. Medieval stained glass makers were simply unable to make perfectly flat panes, and the windows were just as unevenly thick when new.

The tale contains a grain of truth about glass resembling a liquid, however. The arrangement of atoms and molecules in glass is indistinguishable from that of a liquid. But how can a liquid be as strikingly hard as glass?

“They’re the thickest and gooiest of liquids and the most disordered and structureless of rigid solids,” said Peter Harrowell, a professor of chemistry at the University of Sydney in Australia, speaking of glasses, which can be formed from different raw materials. “They sit right at this really profound sort of puzzle.”

It’s a great article, and a wonderful exploration of an area of material science that most people assume they know more about than they do.

New York Times: The Nature of Glass Remains Anything But Clear

Enjoy.

# Diamond is NOT the Hardest Material (Who Knew?)

News flash. Two years late. Diamond is not the hardest known material. There are at least three known substances that are harder: Rhenium Diboride, Ultrahard Fullerite and Aggregated Diamond Nanorods.

I’m a little worried. I think this is what happens when you grow older. Technology has just outdated one of those simple scientific truths I learned about in school. What’s worse is that it took me almost two years to find out about it.

But before I get into a self-pitying “science is for the young” groove, let me tell you what I’ve learned so far.

First, a big thank you to Business Week. Yes, that’s right, Business Week. Not known for it’s scientific coverage, but the May 7, 2007 issue had a snippet on page 79 about the successful effort to create a substitute for industrial diamonds for slicing through steel. Apparently, the diamond reacts with the steel to form by-products that dull the blade. Scientists at UCLA have discovered a mixture of Boron and Rhenium that is hard enough to scratch diamond, and doesn’t react with steel. Press release dates to April 19, 2007, so it’s a pretty recent discovery.

In all fairness, Rhenium DiBoride is only harder than diamond in certain directions, due to its layered structure. But reading about it sent me to the web – what other substances have been discovered that are harder than diamond? Somehow, learning that diamond wasn’t the hardest material bar none made me realize that I last took Material Science coursework at Stanford in 1992.

Fortunately, in the 15 years since that coursework, a lot has happened to help me get up to speed in a matter of minutes. And I am glad I did, because new materials are just too cool.

First, let’s start with the simpler one: Ultrahard Fullerite. Fullerene is a form of carbon based on the $C_{60}$ structure of buckyball-fame. From Wikipedia:

Ultrahard fullerite ($C_{60}$) is a form of carbon which has been found to be harder than diamond, and which can be used to create even harder materials, such as aggregated diamond nanorods.

Specifically, it is a unique version of fullerene (which is a class of spherical, ellipsoidal, or tubular carbon molecules) with three-dimensional polymer bonds. This should not be confused with P-SWNT fullerite, which is also a polymerized version of fullerene. It has been shown[1][2] that when testing diamond hardness with a scanning force microscope of specific construction, ultrahard fullerite can scratch diamond.

Very cool, but now, of course I’m thinking, “Tell me more about these aggregated diamond nanorods!” (I’m sure you were thinking the same thing.)

That, my friends, is a thing of beauty. According to this article at the European Synchotron Radiation Facility, Aggregated Diamond Nanorods are the least-compressible known material. To be specific, the density of ADNR is 0.2% to 0.4% greater than Diamond. ADNR is also 11% less compressible than diamond, and has an isothermal bulk modulus of 491 GPa (gigapascals) compared to just 442 for diamond.

Of course, I’m only reading about this now. PhysicsWeb.org had the coverage on this discovery in Germany back on August 26, 2005. (it’s actually a very clear & well written piece.) You can bet that the PhysicsWeb RSS feed is going into my reader tonight…

Wikipedia has a very nice summary here as well.

Oh well, better late than never. My guess is that one or two people out there also missed this, which is why I’m posting it tonight.

Now, I think we just need to find a way to start a luxury jewelry business that specializes in ADNR-based engagement rings. Why settle for diamond, which can get scratched so easily? We could make a fortune on this one on the high end…

Update (1/4/2010):  See the comment from January 2010 below, but it seems Rhenium DiBoride is no longer assessed as harder than diamond.

# Mentos & Diet Coke Rockets

How is it possible that I have not made one of these before?

Diet Coke & Mentos Rocket on YouTube

Based on the well known Diet Coke & Mentos experiments… just do a search for “diet coke mentos” on YouTube.

What an easy way to waste 30 minutes…

… but this does seem like a fun father/son outing at some point.  Here is a nice web page on the science behind the Diet Coke/Mentos geyser effect.

# Invisibility & Cloaking Experiment Successful

Any fan of Star Trek knows all about “cloaking” technology.  Well, we’re one step closer as of yesterday.

LiveScience.com – Scientists Create Cloak of Partial Invisibility

Interestingly, while groundbreaking, the basic concept for cloaking has been worked out quite well in the science fiction community.  This experiment seems to confirm the basic approach:

Bend light around you, and there will be no reflection of light for an observer to see.   The experiment used the latest technology in metamaterial fabrication, and was limited to the microwave spectrum.  It also wasn’t perfect, with some small amount of distortion & reflection.

Still, it’s an impressive demonstration, and it’s extremely likely that this technology will progress with nano-materials to true cloaking capability at a variety of wavelengths, including visible light.

Most of the coverage I’m reading argues that this will be of limited use, largely because unlike Harry Potter, when you bend light around you, none of it is captured resulting in an inability to “see” outside of the cloak.  You are invisible to others, but others are invisible to you.

It seems to me that there is an easy solution to this:  the device in the cloak needs to be able to capture a percentage of light hitting it so it can “see”, but then have an energy source to duplicate the signal with sufficient fidelity to make it appear that the light was never captured at all.

I love seeing metamaterials play a strong role here.  As a trivia point, I originally planned to major in Molecular Biology at Stanford.  But my freshman year, I took an introductory course in Material Science & Engineering, and I fell in love with the science.  I ended up majoring in Computer Science, but Material Science was my “first love” in the Engineering School.

The advances in materials are every bit as breathtaking as the advances in software these days.  There is something magical about creating these materials with almost magical properties.

Any sufficiently advanced technology is indistinguishable from magic.”
— Arthur C. Clarke

# Welcome to Ununoctium (Element 118)

Just a quick article that I had to post.

The Seattle Times: Nation & World: Heaviest known element created

Ever since I learned about basic chemistry, I’ve had an unnatural affection for the periodic table. What an amazingly elegant and simple roadmap to understanding the composition of matter.

I’m not sure what we’re learning at this point as we built heavier and heavier elements, but for some reason, I still love the fact that we have scientists pushing forward our understanding of matter in this way.  This one was particularly interesting, because there has always been something special about the noble gases, and this one was the blank spot on that last row.

Let’s hope they give it a better name than Ununoctium