All posts by david02pd2014

Carbon Nanotubes: An Allotrope Worth More than Diamonds?

Recently I read a BBC article that both confused and intrigued me. The article was about a Stanford University engineering team and their creation, the “first computer built entirely with carbon nanotubes.” (Morgan, 2013) This reminded me of graphene, a singular sheet of covalently bonded carbon atoms in hexagonal rings, that had come up in class. Remember that graphite is one of the allotropes of carbon along with diamond and the C60 fullerene and that graphene is a single layer of the carbon sheets that make up graphite. (Graphene: World-leading Research and Development, 2012) Interestingly enough, India and Vhristi have both written on graphene, and nanotubes respectively, but through wider and more introductory lens; I hope to focus my research on the application of nanotubes in electronics. Thus with this foundation, I decided to investigate further the one claim the article brought up that really fascinated me, that carbon nanotubes could eventually replace silicon chips as the linchpin of modern electronics. (Hsu, 2013)

Carbon Nanotube Arrangements
Carbon Nanotube Arrangements

Single-walled carbon nanotubes are sheets of graphene rolled up into a cylinder; depending on the direction in which the sheet is rolled, the nanotube will possess different physical properties. (Nanocyl, 2009) Extreme strength, up a hundred times stronger than steel, while maintaining lightness is one of the characteristics that have made scientists so interested in carbon nanotubes. (Bonsor & Strickland, 2007) The other is the ability to act as a semiconductor, a substance with conductivity less than that of most metals but greater than that of an insulator. (Forbus) Currently, the heart of the ubiquitous tablets, computers, and smartphones is the silicon transistor, a semiconductor switch that allow for the control of electrical signals. (Brain, 2001) To keep up with society’s demand for smaller, lighter, and faster devices, engineers have had to shrink transistors. (Hsu, 2013) However as silicon transistors get smaller, with the smallest being Intel’s 22-nanometer Ivy Bridge model, more of the energy that goes in is transformed into heat and wasted. This physical limitation has prompted research into carbon nanotubes as an alternative because of their minute size and “energy-efficiency at small sizes.” (Hsu, 2013)

So, after establishing that carbon nanotubes, theoretically, could outclass the silicon chip I went back to the BBC article to ask: what does this ‘landmark computer’ really mean for the future of carbon nanotube technology? While the computer the Stanford team, led by Subhasish Mitra and H.S. Philip Wong, created is only an elementary prototype that can only count to 32, it is definitive proof a computer could be made solely from nanotubes. (Morgan, 2013) The process in which they arrived at the computer also made great strides in use of nanotubes in electronics. The team aligned the naturally misaligned nanotubes in chips with only 0.5% disparity, designed an algorithm to bypass those that were skewed, and vaporized the “metallic” nanotubes that always conducted electricity. (Shulaker, Hills, Patil, Wei, Chen & Wong, 2013) Although these improvements have streamlined the process of creating carbon nanotube based nanoelectronics the 8000-nanometer transistors are still far from being able to compete economically or technically with silicon chips. (Palmer, 2012)

Carbon Nanotube Transistor
Carbon Nanotube Transistor

Given that silicon chips will eventually reach their limits, this test has shown that carbon nanotubes are progressing as a viable replacement for the current industry standard. (Hsu, 2013) An economic implication of this development is that if the nanotubes keep making significant progress, this possibly more efficient option to the silicon chip will be met with great demand in our technology driven society from firms and governments, the former to produce the next-generation of electronics, and the latter to improve domestic technological and military infrastructure. Just like the silicon chip allowed for a surge in technological innovation, carbon nanotubes could too engender its own rush of progress. A more short-term implication of this auspicious advancement will be reenergized investment and resources dedicated to nanotube research by firms and laboratories not wanting to be beaten to the possible patent of the next half century. But for carbon nanotubes to make the transition from laboratory to factory to store shelf will be costly and time-consuming. One must consider the economic and technological quandaries that will undoubtedly arise as this technology advances, as with all innovations. How can we mass-produce carbon nanotube transistors? How do we maintain a high quality when dealing with such tiny basic components? Each is a question that must be resolved before this new technology hits the shelves.

But I have to say, after reading about the nanotube computer I felt genuinely excited. I know that many obstacles stand in the way of carbon nanotube devices, especially the development of a cost-effective means of mass-producing nanotube transistors. On the surface this seems like a classic case of a scientifically sound theory without any means of practical execution but in this case I have hope. Ever since I have remembered I’ve been waiting for that futuristic advancement that really ushers in a new technological age like home computers and mobile phones did in the 1990s. If this it, I have hope that some combination of entrepreneurship, capitalism, and scientific curiosity will see carbon nanotube technology commercially possible, if not in our smart houses, supercomputers, and flying cars.

References:

BBC. (2011, May 04). Intel unveils 22nm 3d ivy bridge processor. Retrieved from http://www.bbc.co.uk/news/technology-13283882

Brain, M. (2001, April 25). How semiconductors work. Retrieved from http://electronics.howstuffworks.com/diode1.htm

Forbus, K. D. (n.d.). http://www.qrg.northwestern.edu/projects/vss/docs/power/3-whats-a-semiconductor.html. Retrieved from http://www.qrg.northwestern.edu/projects/vss/docs/power/3-whats-a-semiconductor.html

Hsu, J. (2013, September 26). Carbon nanotube computer hints at future beyond silicon semiconductors. Scientific American, Retrieved from http://www.scientificamerican.com/article.cfm?id=carbon-nanotube-computer-hints-at-future-beyond-silicon

Morgan, J. (2013, September 25). First computer made of carbon nanotubes is unveiled. Retrieved from http://www.bbc.co.uk/news/science-environment-24232896

Nanocyl. (2009). Single-wall nanotubes (swnt). Retrieved from http://www.nanocyl.com/en/CNT-Expertise-Centre/Carbon-Nanotubes/Single-wall-Nanotubes-SWNT

Palmer, J. (2012, October 12). Carbon nanotubes fit by the thousands onto a chip. Retrieved from http://www.bbc.co.uk/news/science-environment-20086402

Shulaker, M. M., Hills, G., Patil, N., Wei, H., Chen, H. -., & Wong, H. -. P. (2013). Carbon nanotube computer. Nature, (501), 526-530. Retrieved from http://www.nature.com/nature/journal/v501/n7468/full/nature12502.html

(Graphene: World-leading Research and Development, 2012)The University of Manchester.(2012). Graphene is going to revolutionize the 21st Century. Retrieved 24 December, 2012, fromhttp://www.graphene.manchester.ac.uk.

Image Sources:

Groeben, N. V. D. (Photographer). (2013, September 25). Hand holding cnt wafer [Web Photo]. Retrieved from http://news.bbcimg.co.uk/media/images/70097000/jpg/_70097572_handholdingcntwafer.jpg

How Stuff Works. (Designer). (2007, October ). Nanotechnology [Web Photo]. Retrieved from http://static.ddmcdn.com/gif/nanotechnology-6.gif

The ‘Plaster of Paris’ Explored

Over the Chinese New Year break, I had to opportunity to relive one of my favorite art experiences from middle school, carving plaster, more specifically Plaster of Paris or Gypsum. (Chemistry Daily, 2007) After day four of carving I became acutely aware of the physical properties of Gypsum, its softness and hygroscopic qualities (ability to take moisture out of the air) to name a few and began to wonder what made the substance that way. Gypsum, formally known as calcium sulfate dihydrate (CaSO4.2H­­20) is a mineral, which is chemically defined as being a “naturally occurring inorganic element or compound having [homogenous crystalline structure, chemical composition], and physical properties.” (Kentucky Geological Survey, 2005)

The calcium sulfate dihydrate is comprised of sheets of intramolecular ionic bonded Ca2+ and So42- ions held together by the intermolecular hydrogen bonding of water. The dihydrate means that for every molecule of calcium sulfate there are two molecules of water attached to the sulfate ion with coordinate covalent bonds. (Kauffman, 2013) Due to the weak intermolecular hydrogen bonding, calcium sulfate dihydrate is quite soft, as these bonds being easily broken, a physical property I am very thankful for. Now for most commercial applications, Gypsum is typically sold and kept as a grind up power, that has been calcined, or had its moisture removed with intense heat, as calcium sulfate hemihydrate (one water molecule for every two calcium sulfate molecules).(Lafarge Prestia , 2000) The reaction is shown by:

CaSO4.2H2O + Heat → CaSO4.0.5H2O + 1.5H2O

Depending on at what pressure this reaction occurs at, a product with different physical properties is formed. Alpha plaster is formed when calcium sulfate dihydrate is calcined at about 150 degrees Celsius in an autoclave (a heated, pressurized container for chemical reactions) at higher than atmospheric pressures. Beta plaster on the other hand is calcinated at atmospheric pressure. (Lafarge Prestia , 2000) Manufactures do this to control the shape and size of crystal growth in the plaster, with alpha plaster having larger crystals, a higher mechanical strength, and low porosity while beta plaster has smaller crystals, lower mechanical strength, and higher porosity. (National Research Development Corporation) This reaction can be taken further to the point where calcium sulfate becomes an anhydride (compound with water removed) and all of the water of crystallization evaporated. In this form there are no polar water molecules to interfere with the ionic lattice formed by electrostatic attractions of Ca2+ and So42- ions, so it’s hardness increases dramatically. (Chemistry Daily, 2007) However this reaction is actually reversible, with the anhydride or hemihydrate form reverting back in an exothermic reaction to the dihydrate form if introduced to enough water. I had found the reaction that I crudely did to create the plaster for my sculpture, which was using beta plaster.

CaSO4.0.5H2O + 1.5H2O → CaSO4.2H2O + Heat

It turns out this material I used for an art project has roots stretching back 9000 years to the Anatolia region. Throughout history Gypsum has had various applications, from being used in Egyptian monuments to modern day drywall, with most stemming out of the field of construction. (Lafarge Prestia , 2000) There are some of the historical uses, where due to its ability to protect internal structures from fire it was used to cover the exteriors of houses. More specific and diversified uses for calcium sulfate have developed over time, some requiring particular physical attributes like “setting times, fluidity, viscosity, their hardening kinetics, their permeability (through pore [size]), their mechanical strengths, [and] their resistance to abrasion.” These conditions are met through a combination of alpha plasters, beta plasters, and neutral fillers. (Lafarge Prestia , 2000)

Calcium sulfate’s uncanny ubiquity in modern life, from the molds used to fashion ceramic molds or dentures, to the internal walls and ceilings in most buildings, to the decorative art on the outside of the building, to its discovery on mars (Webster & Cole, 2011) all remind me of how much a single substance can impact the direction of human society and culture. Additional uses for calcium sulfate include agricultural applications to increase the water penetration and aeration of sour (lime lacking) soil but run the risk of excess sulfate tainting the groundwater. Also just recently medical applications for calcium sulfate, acting as a bone void filler to be introduced slowly into the body at the same rate as new bone growth, have been posited. (Tangri, Prasad, Suri & Agrawal, 2004) All these from a single mineral, but while considering its uses one must also ponder the process it takes to produce. The arduous industrial process involved with mining, classifying, processing, and distributing this one mineral puts into perspective how much of the production line we as consumers are not typically aware of. (Lafarge Prestia , 2000) However based on the recent applications of this substance, calcium sulfate will be continued to be an integral but underemphasized part of people’s lives.

References:

Chemistry Daily. (2007, January 04). Plaster. Retrieved from http://www.chemistrydaily.com/chemistry/Plaster_of_paris

hydrate. (2013). In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/topic/278148/hydrate

Kentucky Geological Survey. (2005, December 12). Many definitions of minerals. Retrieved from http://www.uky.edu/KGS/rocksmn/definition.htm

Lafarge Prestia (2000, December 11). Caso4?,h20. Retrieved from http://www.lafargeprestia.com/caso4___h2o.html

National Research Development Corporation. National Research Development Corporation, (n.d.). High strength plaster of paris – alpha plaster. Retrieved from website: http://www.nrdcindia.com/pages/highplas.htm

Tangri, R. P., Prasad, R., Suri, A. K., & Agrawal, P. R. Bhabha Atomic Research Centre, Materials Processing Division. (2004). α-calcium sulphate hemihydrate as bone substitute. Retrieved from website: http://www.barc.gov.in/publications/nl/2004/200406-2.pdf

Webster, G., & Cole, S. (2011, December 07). Nasa mars rover finds mineral vein deposited by water. Retrieved from http://marsrover.nasa.gov/newsroom/pressreleases/20111207a.html

Images Cited:

Guidechem. (Producer). (2010). Calcium sulfate dihydrate. [Web Photo]. Retrieved from http://www.guidechem.com/products/10101-41-4.html

Lafarge Prestia (Producer). (2000). Plaster manufacture. [Web Photo]. Retrieved from http://www.lafargeprestia.com/caso4___h2o.html

Smith, S. E. (Photographer). (2003). Calcium sulfate dihydrate. [Web Photo]. Retrieved from http://www.wisegeek.com/what-is-calcium-sulfate.htm