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Let there be light Biting the currency - Part

Bite a coin was a necessary precaution when its value depended on the material that formed. A surface layer could mimic the characteristics of gold, hiding a much cheaper composition. And is that a thin layer of gold can do great things.

Fortunately there are many applications that do not involve fraud. Getting the properties of gold for a cheap material has great advantages but is not without problems. The first is how to position and attach it. The easiest method is purely mechanical. Gold is tremendously ductile and malleable , which allows the formation of extremely thin sheets (up to ten thousandth of a millimeter thick). In the form of gold leaf was used for millennia to decorate all kinds of objects.
Although chemical reactions can be used to coat an object, are of little use for gold is a very reactive element ( except mercury). The comment on another occasion.

The method used is electricity. The electroplating is the coating of a material using electricity. To oversimplify, it would be something to reverse the operation of a battery. Instead of getting electricity from a chemical reaction, uses electricity to form a thin layer of material attached to a piece that acts as an electrode. Using many materials such as zinc and cadmium but gold has its place. Its very low emissivity (0.02) makes it highly valued as insulation against radiation. Do I have to protect a satellite from solar radiation? Nothing better than a sheet of mylar covered in gold. It is so effective that is used in infrared mirrors when looking for top quality. The picture below is part of a mirror I travel to Mars in the failed Mars mission Surveyor.





course useful as a mirror also be applied in a laser . Gold covers the resonant cavities to reduce losses and maximize power.

Its superb electrical conductivity and resistance to oxidation should use in electrical connections especially important, for example in the electronics of the airbags. You can also save the vision of astronauts against solar radiation covering their viewers. Or you can protect the crew of some war planes electronics of the electromagnetic radiation produced . But gold will not only serve to hide and protect. One of the many methods used to prepare samples electron microscope is covered with a thin conductive layer. For example, a layer of gold.
And if it is true. It is also used in jewelry. But while consuming much of its production still seems a less interesting.


Category: Chemistry

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propeller against

The Great Eastern, the largest vessel of its time, complete a very special mission in 1866. It was the only one capable of carrying the 4,260 miles the first transatlantic telegraph cable. This milestone is worth an entry by itself, but today we are talking about the propulsion of the boat. It had six masts for sails, two paddle wheels and was the first to bring a propeller. Now, that is redundancy.

The pallets were proposed as means of propulsion long before steam engines. Vitruvius, a Roman engineer the time of Julius Caesar, suggested using animal power to drive and shift paddles a boat. It was a way to replace the slaves used as a propulsive force in the Roman galleys.








It was not until the advent of steam engines that began to spread. First, in combination with candles for periods of quiet and then as the main thrust. For several decades the blades, in the rear and the sides of the boats, were the preferred form of mechanical propulsion. And indeed they had many advantages. The blades were easy to manufacture and easy to repair. Represent a proven, known and reasonably effective. In return they were very vulnerable, especially when mounted on the sides, which caused problems in military vessels. Were not very useful in case of bad weather, because the waves were taking them out of the water too often.





The alternative was the propellers but was not free of problems and enemies. Its manufacture was more complicated, especially in large sizes, and the need to define very precisely the shape and dimensions. Its axis penetrating the hull below the waterline and could cause seepage through the joints or even break. Not to mention the repairs. A damaged propeller had to be taken underwater or repaired in dry dock. Could your compensate for this performance?

The British decided to try it. In 1845 he made a series of races between two corvettes, Rattler and Alecto, very similar but fitted with a propeller and a paddle. Between testing and racing highlights one where you can see in the two boats and propeller Rattler dragged nearly 3 miles per hour at Alecto. The fate of the blades was determined and all new Royal Navy vessels were built with no propellers and blades.


As we can see the propeller in marine propulsion have only century of history. And, like others, was a new technology whose success was unclear. I wonder which of the continue their current path.


Category: History of science

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Pallets New year, new life, new contest.

For once, I will introduce a competition to see how it goes. It is a competition organized annually by the online newspaper "20 minutes". In particular, this blog appears in the category "Science and Environment ." 103 enrolled, including some of my favorites, so competition will be tough. If you believe that you deserve, you can vote for Science pocket this link or directly by clicking the icon on the left.

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