Hydrogen: Fuel or Foe?

Hydrogen is being viewed as an eventual alternative to fossil fuels. For metals such as steel, aluminium and magnesium, commonly used in automotive and energy technology, hydrogen is less than ideal.

Hydrogen can permeate the metals when filling the tank, or during various manufacturing processes. It can infiltrate the metal lattice through corrosion, during chromium-plating of car parts, or welding, milling or pressing.

Hydrogen can make these metals brittle and their durability deteriorates leading to sudden failure of parts and components such as the fuel tank, parts of the fuel cell, and even ordinary components like ball bearings.

Scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg are studying hydrogen-induced embrittlement in order to find materials and manufacturing processes that are compatible with hydrogen.

Reference:
Fraunhofer-Gesellschaft (2010, August 21). Hydrogen causes metal to break. ScienceDaily. Retrieved August 22, 2010, from http://www.sciencedaily.com­ /releases/2010/08/100816114831.htm

Study Questions

1. What is meant by the term fossil fuels?
2. Give three examples of commonly used fossil fuels.
3. Why are scientists looking at alternatives to fossil fuels?
4. Describe what is meant by a metal lattice.
5. Explain how hydrogen could infiltrate the metal lattice.
6. Explain how this infiltration of hydrogen into the metal lattice could lead to reduced ductility and brittleness.
7. List other physical properties of metals besides ductility and hardness.
8. List some chemical properties of metals.
   
9. How does steel differ from the other metals mentioned in the article above?
   

Reaction Mechanism for Ammonium Sulfates's Phase Transition

During a chemical reaction, the atoms in the reactants are rearranged to form new compounds. On a molecular level, the spatial arrangement of electrons and nuclei changes. While the structure of the reactant and product molecules can be measured the reaction mechanism, or the transient structures and molecular motions during a reaction, have remained unknown in most cases, but, this knowledge is a key element needed to understand the reaction.

Scientists at the Max-Born Institute in Berlin have now succeeded in making a "molecular movie" of the thermal phase transitions of ammonium sulfate which is a reversible reaction.

Using an advanced femtosecond laser system which generates a blue pulse of 50 femtosecond duration, they initiated the chemical reaction and then probed the structure of the excited material with high spatial resolution using a synchronised X-ray flash of 100 femtosecond duration. The X-ray pulse is diffracted off a powder made of small crystals, this is known as the Debye-Scherrer method. By simultaneously measuring the many different X-ray reflections they reconstructed the transient distances of atomic lattice planes and in turn the three dimensional distribution of electronic charge within the crystal. The "molecular movie" was created by taking X-ray snap shots at various times after triggering the reaction.

What they found is that the blue flash caused a release of both a proton from the ammonium ion and an electron from the sulfate ion. The proton and the electron then merged to form a hydrogen atom which jumped back and forth between two distant spatial positions.

Reference:
Michael Woerner, Flavio Zamponi, Zunaira Ansari, Jens Dreyer, Benjamin Freyer, Mirabelle Prémont-Schwarz, Thomas Elsaesser. Concerted electron and proton transfer in ionic crystals mapped by femtosecond x-ray powder diffraction. The Journal of Chemical Physics, 2010; 133 (6): 064509 DOI: 10.1063/1.3469779

Study Questions

1. Give the molecular formula for ammonium sulfate.
2. What is the oxidation state (oxidation number) for nitrogen in the ammonium ion?
3. What is the oxidation state (oxidation number) for sulfur in the sulfate ion?
   
4. Write a chemical equation for the overall reaction for the thermal phase transition of ammonium sulfate.
5. What is meant by the term reversible reaction? Explain your answer using the chemical equation above.
6. Draw Lewis structures (electron dot diagrams) for the ammonium ion and the sulfate ion.
7. Draw Lewis structures (electron dot diagrams) for each of the ions above immediately after the laser's blue flash initiates the reaction.
8. Using the new species above, give the oxidation state (oxidation number) for nitrogen and sulfur after the reaction is initiated. Compare these oxidation states to those in questions 2 and 3. Is this an example of a redox reaction? Explain your answer.
9. Define the terms Bronsted-Lowry acid and Bronsted-Lowry base.
10. Are any of the species described in the reaction mechanism for the thermal phase transition of ammonium sulfate acting as Bronsted-Lowry acids or Bronsted-Lowry bases. Explain your answer.
11. Define the terms Lewis acid and Lewis base.
12. Are any of the species described in the reaction mechanism for the thermal phase transition of ammonium sulfate acting as Lewis acids or Lewis bases. Explain your answer.

Hexagonal Boron Nitride

Graphene, a single-atom thick allotrope of carbon and an electrical conductor, is considered to be a possible successor to silicon in microelectronics applications.
Hexagonal boron nitride (h-BN) is an insulator. It is highly elastic and nearly as strong as graphene. Rice University scientists have found a way to implant sheets of h-BN into sheets of graphene, which controls the sheet's electronic character.
They have also found a way to deposit sheets of pure h-BN, 1 to 5 atoms thick, onto a copper substrate using a chemical vapour deposition process at about 1,000^oC. The h-BN material can then be transferred to other substrates. The size of h-BN sheets is limited only be the size of the copper foil and furnace used to grow it.
It should be possible to draw microscopic patterns of graphene and h-BN, useful in creating nanoscale field-effect transistors, quantum capacitors or biosensors.

Reference:
Li Song, Lijie Ci, Hao Lu, Pavel B. Sorokin, Chuanhong Jin, Jie Ni, Alexander G. Kvashnin, Dmitry G. Kvashnin, Jun Lou, Boris I. Yakobson and Pulickel M. Ajayan. Large Scale Growth and Characterization of Atomic Hexagonal Boron Nitride Layers. Nano Letters, 2010; 100722142755098 DOI: 10.1021/nl1022139

Study Questions

1. What is meant by the term allotrope?
2. What are the naturally occurring allotropes of carbon?
3. In what ways are these allotropes of carbon the same?
4. In what ways are these allotropes of carbon different?
5. If the formula for boron nitride is BN, what is the oxidation state (number) of boron?
6. Given the name hexagonal boron nitride, draw a possible Lewis Structure (electron dot diagram) for hexagonal boron nitride.
7. In what ways are graphite and hexagonal boron nitride the same?
8. In what ways are graphite and hexagonal boron nitride different?
9. Why is graphite a conductor while hexagonal boron nitride is an insulator?
   

Champagne Bubbles

Tiny bubbles are the essence of fine champagnes and sparkling wines.
The bubbles, formed during the release of large amounts of dissolved carbon dioxide, help transfer the taste, aroma, and mouth-feel of champagne. Scientists have thought that the act of pouring a glass of champagne could have a big impact on gas levels in champagne and its quality.
Scientists in France have studied carbon dioxide loss in champagne using two different pouring methods:

• pouring champagne straight down the middle of a glass
• pouring champagne down the side of an angled glass

They found that pouring champagne down the side of an angled glass preserved up to twice as much carbon dioxide in champagne compared to pouring it straight down the middle.
They also showed that cooler temperatures help reduce carbon dioxide loss.

Reference:
Liger-Belair et al. On the Losses of Dissolved CO2 during Champagne Serving. Journal of Agricultural and Food Chemistry, 2010; 58 (15): 8768 DOI: 10.1021/jf101239w

Study Questions

1. What is the formula for carbon dioxide?
2. Is carbon dioxide a polar or non-polar molecule?
3. What is the structural formula for ethanol?
4. Is ethanol a polar or non-polar molecule?
5. Would you expect carbon dioxide to dissolve in ethanol? Explain your answer.
6. Describe an experiment you could conduct to test the hypothesis that cooler temperatures reduce carbon dioxide loss in champagne.
   

Casting : Changes of State

The question of what happens when a material composed of more than one phase or state is heated or cooled is very important.
Many metal parts, for example, are made by casting. In the casting process liquid metal is poured into a mold and solidifies into the shape of the mold. As the liquid metal solidifies it forms tree-like structures called dendrites, and, if one of the dendrites breaks off it can lead to a change in the properties of the solidified material. The airplane industry has spent a long time developing solidification methods to avoid this problem when casting jet turbine blades.
Polymer solar cells use a complicated mixture of two polymers. When heated, the mixture evolves by a process that involves pinching which ultimately alters the properties of the mixture and the efficiency of the solar cell.
Scientists have been observing the heating process during which a rod-like phase or state embedded in another will break up into smaller domains just like droplets at the end of a stream of water, resulting in changes to the properties of the material. They have found that the shape of the interfaces during break up becomes universal, independent of the material used. This now allows them to predict the dynamics of the break-up process in a vast array of materials such as steel and polymers.

Reference:
Aagesen et al. Universality and self-similarity in pinch-off of rods by bulk diffusion. Nature Physics, 2010; DOI: 10.1038/nphys1737

Study Questions

1. Name the phase changes (changes of state) that can occur in each of the following situations:


• heating a solid


• heating a liquid


• cooling a liquid


• cooling a gas




2. Draw a sketch of the temperature-time graph expected for each of the following situations involving pure substances:
   


• heating a solid


• heating a liquid


• cooling a liquid


• cooling a gas




3. Explain why the temperature-time graph for the melting of ice differs from the temperature-time graph for freezing water.
4. Explain why the purity of a solid substance can be determined using its melting point.
5. Do you think the purity of a liquid substance could be determined using its freezing point? Explain your answer.
   
6. Explain what is meant by the term sublimation.
7. Give two examples of pure substances that undergo sublimation.

Grave Detection Techniques

Cadaver-sniffing dogs or ground penetrating radar are used to detect clandestine gravesites, but, these are not always useful if the body is buried under concrete.
Scientists at the National Institute of Standards and Technology (NIST) have developed a technique that can reliably detect biochemical changes in a decomposing cadaver.
The process uses an alumina-coated porous layer, open tubular (PLOT) column with a motorized pipette that pulls in air samples at ambient temperatures. The device detects trace amounts of ninhydrin-reactive nitrogen (NRN) that collects in air pockets above and close to grave-soil. The probe, slightly thicker than a human hair, can be inserted into the ground to detect decaying flesh.

Reference:
Tara M. Lovestead, Thomas J. Bruno. Detecting gravesoil with headspace analysis with adsorption on short porous layer open tubular (PLOT) columns. Forensic Science International, 2010; DOI: 10.1016/j.forsciint.2010.05.024

Study Questions

1. What is meant by the term ambient temperature?
2. What is the other major use for ninhydrin in forensic science?
3. Could this probe be used to distinguish between a human cadaver and a dead, decaying rat? Explain your answer.
4. Why do you think cadaver-sniffing dogs might not be useful if a body is buried under concrete?
5. Imagine you have been asked to set up an experiment to determine the effectiveness of this technique at different stages of decomposition. Describe how you would do this.
   

Lithiated Graphite in Fusion Reactors

Nuclear fusion powers the stars and could be used to supply clean energy on Earth. A nuclear fusion plant would produce ten times more energy than a conventional nuclear fission reactor.

Scientists have been investigating the "plasma-material interface", the region in a fusion reactor where the inner lining cones into contact with the extreme heat of the plasma. A major challenge in finding the right coatings to line fusion reactors is that the material changes due to extreme conditions inside the reactors where temperatures can reach millions of degrees.

One such lining material uses lithium which is applied to the inner graphite wall of the reactor and diffuses into the graphite creating an entirely new material called lithiated graphite.
During a fusion reaction, some of the deuterium fuel atoms strike the inner walls of the reactor and either "pumped", causing them to bind with the lithiated graphite, or returned to the core and recycled back to the plasma.
The intense thermal energy inside the reactor causes tiny micro- and nano- scale features to "self-organise" on the surface of the lithiated graphite under normal plasma-surface interaction conditions. The surface only continues pumping for a few seconds before being compromised by damage induced by the extreme internal conditions.

Reference:
Purdue University (2010, July 27). Promise for nuclear fusion test reactors, findings show. ScienceDaily. Retrieved July 28, 2010, from http://www.sciencedaily.com­ /releases/2010/07/100727142415.htm

Study Questions

1. Define nuclear fusion.
2. Write an equation to represent a nuclear fusion reaction that might take place in a sun.
   
3. Define nuclear fission.
4. Write an equation to represent the nuclear fission of uranium-235.
   
5. How are deuterium atoms similar to hydrogen atoms?
6. How are deuterium atoms different to hydrogen atoms?
7. Name another isotope of hydrogen and give its symbol.
8. Name two allotropes of carbon.
9. Discuss the ways in which the two allotropes are the same.
10. Discuss the ways in which the two allotropes are different.
    
11. Draw a structure for graphite.
12. Use the drawing above to describe how lithiated graphite might be formed.
13. Discuss how deuterium atoms in the fuel plasma could bind to lithiated graphite.