Photography is so common that most people never give a moment’s thought to how remarkable the process is. Ordinary black-and-white photographic film consists of a celluloid strip that has been coated with a gelatin emulsion containing very tiny crystals, or “grains,” of a silver halide, usually AgBr. There is a considerable amount of art as well as science to making the film, and the recipes used by major manufacturers are well-guarded secrets. When exposed to light, the surfaces of the AgBr grains turn dark because of a light-induced redox reaction in which Br- transfers an electron to Ag+ producing atoms of elemental silver and Br2,which reacts with the gelatin emulsion. Those areas of the film exposed to the brightest light have the largest number of silver atoms, and those areas exposed to the least light have the smallest number.
2AgBr ---> 2Ag + Br2
Perhaps surprisingly in view of what a finished photograph looks like, only a few hundred out of many trillions of ions in each grain are reduced to Ag atoms, and the latent image produced on the film is still invisible at this point. The key to silver halide photography is the developing process, in which the latent image is amplified.
By mechanisms still not understood in detail, the presence of a relatively tiny number of Ag atoms on the surface of an AgBr grain sensitizes the remaining ions in the grain toward further reduction when the film is exposed to the organic reducing agent hydroquinone. Those grains that have been exposed to the strongest light—and thus have more Ag atoms—reduce and darken quickly, while those grains with fewer Ag atoms reduce and darken more slowly. By carefully monitoring the amount of time allowed for reduction of the AgBr grains with hydroquinone, it’s possible to amplify the latent image on the exposed film and make it visible.
Once the image is fully formed, the film is fixed by washing away the remaining unreduced AgBr so that the film is no longer sensitive to light. Although pure AgBr is insoluble in water, it is made soluble by reaction with a solution of sodium thiosulfate, Na2S2O3 called hypo by photographers.
AgBr (s) + S2O32-(aq) ---> Ag(S2O3)23-(aq) +Br-(aq)
At this point, the film contains a negative image formed by a layer of black, finely divided silver metal, a layer that is denser and darker in those areas exposed to the most light but lighter in those areas exposed to the least light. To convert this negative image into the final printed photograph, the entire photographic procedure is repeated a second time. Light is passed through the negative image onto special photographic paper that is coated with the same kind of gelatin–AgBr emulsion used on the original film. Developing the photographic paper with hydroquinone and fixing the image with sodium thiosulfate reverses the negative image, and a final, positive image is produced. The whole process from film to print is carried out billions of times and consumes over 3 million pounds of silver each year.
Every so often on a clear evening, residents of Alaska, Canada, and other far-northern parts of the world are treated to a breathtaking display of celestial fireworks—the so-called northern lights, or aurora borealis. The lights appear in many different forms—as curtains, arcs, rays, and gauzy patches—and in many different colors. All, however, result from the emission of light by energetically excited atoms, ions, and molecules in the upper atmosphere, the same kind of phenomenon that gives rise to atomic line spectra.
The aurora borealis is caused by a chain of events that begins on the surface of the sun with a massive solar flare. These flares eject a solar “gas” of energetic protons and electrons that reach Earth after about 2 days and are then attracted toward the north and south magnetic poles. (The Southern Hemisphere has its own display of lights called the aurora australis.) The energetic electrons are deflected by the earth’s magnetic field into a series of sheetlike beams, much as iron filings scattered around a magnet are deflected into a series of lines by the magnet’s field of force. The electrons then collide with O2 and N2 molecules in the upper atmosphere, exciting them, ionizing them, and breaking them apart into O and N atoms.
The energetically excited atoms, ions, and molecules generated by collisions with electrons emit energy of characteristic wavelengths when they decay to their ground states. The O2+ ions emit a red light around 630 nm; N2+ ions emit violet and blue light at 391.4 nm and 470.0 nm; and O atoms emit a greenish-yellow light at 557.7 nm and a deep red light at 630.0 nm. Protons in the solar gas are also responsible for part of the auroral display as they too collide with oxygen atoms when they descend into the upper atmosphere. The protons pull electrons from the oxygen atoms, yielding excited O+ ions and H atoms that give off still more colors when they return to their ground states. The hydrogen atoms, in particular, emit all the wavelengths of visible light in the Balmer series.
A group of researchers led by Professor Martyn Poliakoff at the University of Nottingham chemistry department are producing a live periodic table of elements using YouTube clips. They are working through each element providing descriptions and demonstrations. It's certainly informative and engaging, and shows some real chemistry in action.
There are already several alternative sources of energy. One of these alternative sources was originally intended for space programs but now, some studies are already considering it for car use. Hydrogen fuel cells are indeed gaining much attention in today's times when there is a great need for another energy source.
The hydrogen fuel cells are just like traditional batteries. A chemical reaction produces electricity and electrical charge. However, there is still a difference. You see, with batteries, power is produced if the cell is continuously supplied with hydrogen. To understand how the fuel cells work, read on.
The cell's size and hydrogen flow determines the electricity produced. When a chemical reaction occurs between air and hydrogen, three things are produced namely ? heat, water, and electricity. Fuel cells lower heat output as compared to other sources of energy like the fossil fuels. But still, there are advantages in using hydrogen fuel cells.
One obvious advantage is that fuel cells are clean since the byproducts are heat and water. These byproducts can't harm the environment. Fuel cells have efficiency rates ranging from 45-53% as compared to gasoline with only 20% efficiency rate.
Whenever electricity is required, you can use fuel cells. The size of fuel cells is scalable. Fuel cells can therefore be created small to power an MP3 player or even large enough to give a town its needed electrical power. Aside from providing electrical power to certain things, it can also supply the needed rotary power by cars.
At present, car manufacturers worldwide are looking at hydrogen fuel cells are an alternative to the combustion engines. There are already pictures of hydrogen powered vehicles online; if you want, you can check them out if you have the time. If ever the hydrogen powered vehicles will become a reality in the near future, the dependency of many countries to petroleum will be reduced and not only that, pollution will be cut down.
Currently, fuel cells are installed in some neighborhoods and industrial buildings to provide electrical power. Within the next 50-100 years, hydrogen fuel cells will completely replace petroleum since they have broad social and commercial applications. Remote settlements can now depend on fuel cells for power. Portable devices can also be provided with renewable power through the fuel cells.
Countries from all over the world are looking for a clean and dependable energy source. With the continued support from the government and commercial establishments, the use of fuel cells will soon be a guaranteed success.
Hydrogen fuel cells are truly great but there is one consideration. In order to produce fuel cells, energy is needed and at present, fossil fuels serve as the source of energy. Scientists and experts are still conducting studies and researches to find other ways to produce fuel cells safely. At the moment, fossil fuels are being used to produce the hydrogen fuel cells but hopefully, new sources of energy will be discovered to further improve its production.
Now you know what hydrogen fuel cells are all about. The fuel cells are not mainly used for providing electricity because currently the automakers are trying to manufacturer cars that are fueled by hydrogen.
British scientists are developing a new type of glass that can dissolve and release calcium into the body. This will enable patients to regrow bones and could signal a move away from bone transplants.
The porous glass, originally developed at Imperial College is capable of acting as an active template for new bone growth, dissolving in the body without leaving any trace of itself or any toxic chemicals. As it dissolves it releases calcium and other elements such as silicon into the adjacent body fluids, stimulating bone growth.
The glass activates genes present in human bone cells which encode proteins controlling the bone cell cycle and the differentiation of the cell to form bone matrix and rapid mineralisation of bone nodules. It is the release of soluble silica and calcium ions in specific concentrations that activate the genes. Gene activation occurs only when the timing sequence of the cell cycle is matched by that of the glass surface reactions and controlled release of the ions.
Partners at the Universities of Kent and Warwick have been carrying out experiments at the Science and Technology Facilities Council's world leading ISIS neutron source. Research at ISIS is showing exactly how the calcium is held in the glass and thereby precisely how it is released into the body. Professor Bob Newport at the University of Kent explains that it was when the material was studied at ISIS that the process became clear.
"Although variants of these bioactive materials are already in clinical use, and the role of calcium in these materials was already understood as being critical in terms of both the stability of the glass and its bioactivity, no direct and quantitative study of the calcium atoms within the glass network had been undertaken. Using ISIS to study the relationship between these atoms and the host silicate glass via techniques unique to neutron diffraction has enabled us to move forward with the programme. The key outcome of our experiments has been a full understanding, at the level of atomic arrangements, of why it is that calcium is able so easily to leave the glass at the rate required to generate the desired response."
By comparing samples made with natural calcium and with a calcium isotope it was possible for the first time to isolate the complex and subtle contribution of the calcium from that of all the other atoms present. Dr Andrew Taylor, Director of the ISIS neutron source commented, "To allow people to remain active, and to contribute to society for longer, the need for new materials to replace and repair worn out and damaged tissues becomes ever more important. We're pleased that at ISIS we can continue to contribute to cutting edge research that affects all our lives."
Further research is planned at the ISIS Second Target Station when it opens later this year. This will investigate glass/polymer hybrids and could be instrumental in developing mechanically stronger versions of the glass that would be load bearing and available for medical use in the context of joint replacement. If the extensive research goes as expected, clinical trials could be in place in the next five years.
Note: This story has been adapted from a news release issued by the Science and Technology Facilities Council
Dr. Gino DiLabio, Research Council Officer at Canada's National Institute for Nanotechnology (NINT) in Edmonton, Alberta, has been awarded the 2008 Journal of Physical Organic Chemistry Award for Early Excellence in the Field of Physical Organic Chemistry. This award is given annually to recognize the accomplishments of an individual working in the field of physical organic chemistry or applying the principles of this field to other areas. At the time of nomination, the recipient must be no more than six years from the beginning of the first independent appointment. The award was presented at the 32nd Reaction Mechanisms Conference held at the University of North Carolina, Chapel Hill. Dr. DiLabio gave an award presentation entitled “Linear Organic Nanostructures on Silicon Surfaces: A Platform for Studying Single Molecule Physics and Chemistry.” on June 27, 2008.
A member on NINT’s Molecular Scale Devices Group, DiLabio’s work focuses on the modeling of chemical processes leading to nanostructure formation on silicon surfaces. Dr. DiLabio also conducts research in the area of molecular electronics, including efforts to gain an understanding of the mechanism by which localized charged states on silicon surfaces can act as gates in models for molecular transistors.
Originally from Ottawa, DiLabio received his doctorate from Clarkson University, Potsdam, New York. He joined NRC in 2001 as a Research Officer at the Steacie Institute and moved to NINT in 2004. He has authored more than 70 papers and holds two patents. He is also an Adjunct Professor at of the Chemistry Department of Carleton University.
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