Lunch with a Lens

Aluminium (Al – Atomic Number 13). Or should I say Aluminum? Officially (IUPAC – The International Union of Pure and Applied Chemistry) say the former, and that’s the one I’m most used to – but in the United States Aluminum is the more common. IUPAC also accept this as a variant. The history of the name gets even more interesting, as it is this latter spelling that was first given by Humphry Davy in 1812 when he was working to isolate the metal from alumina (after he’d dismissed the name of Alumium).

Aluminium is the third most abundant element on earth, following Oxygen and Silicon – but is quite reactive so is rarely found as a native metal. The chief ore of Aluminium is bauxite – and I even remember from school geography that Australia and Brazil are the main producers – with cheap electricity being key to extraction. One thing I didn’t know – 5% of the electricity generated in the United States is consumed by Aluminium production!

Aluminium is light and resists corrosion (protected by a layer of Aluminium Oxide that forms when Oxygen from the air reacts with the surface or pure Aluminium, and these p[roperties make it perfect for use in the aerospace and other transportation industries – sometime on its own, but also as alloys which can increase its strength.  Another important use is for transmission of electivity – power lines benefit from the greater per weight conductivity compared to copper.  Aluminium foil and other forms of food packaging are more common uses of Aluminium – and an historically significant use was for the capstone for the Washington Monument.

Next up – Iodine!

Oxygen (O – Atomic number 8) is certainly something we couldn’t live without – or in fact couldn’t live at all if the concentrations in the atmosphere were much more or less.  But I guess if the levels had fluctuated more or been different then we wouldn’t have evolved quite the way we did. 

I found it much easier to concentrate on what Oxygen does to things as subjects for my photographs – is consumed when things burn – oxidises things, such as creating rust on iron, and is given off by the process of photosynthesis – from plants both in and under oceans – though not too deep as the process also requires light.

Industrially Oxygen is produced mostly by fractional distillation of liquefied air, with some being produced by passing over molecular sieves which absorb the nitrogen.  Main uses are the production of steel, and in the chemical industry for production of materials going into plastics and fabrics.  And of course life support.  Hospitals, divers, submariners and spacemen.  Oxygen is not used for blowing up the bags that fall at you in airplanes – but the oxygen is still flowing…

It always seems strange talking about discovering something that was there all the time (like America for example) but understanding the components of air and isolating the individual elements I think is a tangible discovery.  Two people are credited with Oxygen’s discovery – the Swede Carl Wilhelm Scheele (first) and England’s Joseph Priestley (first to publish) – although Antoine Lavoisier (and his wife) had a big part too in understanding what they had found.  

The isotopes of Oxygen – atomic weight 16, 17 and 18 – and their relative abundance and the fact that water containing these isotopes evaporates at different rates – which is also temperature dependant has helped with both dating and identifying temperature fluctuations in the past – by analysis of ice cores.

Tin (Sn – Atomic number 50) is a metal, except when it isn’t.  White Tin, or β Tin is a metal, but there is also another allotrope – α Tin – grey Tin which has no metallic properties at all.  This semi-conductor is stable under 13.2 °C, and can form from white Tin in a process known as Tin pest.  The most common uses of (white) Tin are as a component of solder and for coating steel to prevent corrosion – one example of which is to make ‘tins’ – or cans if you prefer. Solder was made from Tin and Lead – but other alloys with Tin are now used to avoid the toxic Lead.  Tin pest is more of a problem in Lead -free solder and can lead to joint integrity issues.  If you are not familiar with allotropes – carbon as diamond or graphite is a more common example.

The previous posting was about Yttrium – which had just one stable isotope – and in contrast Tin has 10 – due to it having a magic number of protons.  Tin has been used since around 3000 BC and its addition to copper to form alloys like bronze heralded in a new age.  Tin mines in Devon and Cornwall operated from around 2150 BC – with the last one closing as recently as 1998.  This made the region one of the earliest parts of Britain to trade with the rest of Europe and even the Middle East –  both before and after the Roman invasion.

The main mineral that has always been the primary source of Tin is cassiterite, and this is now classified as a conflict mineral due to the conflict waged over control of the land where large deposits are fund – such as in the eastern parts of the Democratic Republic of the Congo.  Companies in the United States that use materials that come from conflict minerals need to be able to audit their supply chains to prove the origins – following the 2010 Dodd-Frank Wall Street Reform and Consumer Protection Act.

Now for the photography connection – and Tin(II) Chloride – SnCl₂ – otherwise known as stannous chloride – is used in the ‘E-6’ photographic process for producing colour transparancies, or slides.  When I worked in a photo research lab the E-6 reversal bath was one of the formulations I worked on.  Stannous chloride is a reducing agent, and in the reversal bath it performs the same role that light does in exposing the silver halides that remains after the ‘First Developer’ has produced basically a black and white negative.  In print photography you take a negative – shine light through onto paper and then develop – for slides this all happens in the same piece of film.

The reversal bath prepares the reversed image by ‘exposing’ all the silver halide that has not been developed to a silver image in the first developer (which is a black and white developer)   and this silver halide can then be developed in the colour developer to product the positive image. The colour actually comes from dyes in the film reacting with the local oxidized developer in three layers sensitive to different parts of the spectrum.   A good article that show this effect weel is the Kodak one – Processing Solutions and their Effects.  The E-6 process applies to Kodak’s Ektachrome and Fuji’s Fujichrome and others – but probably the most famous transparency film – Kodachrome – goes through a slightly different process.  It has no dyes in the film (so the film can actually be thinner) but instead after first development it goes through a series of exposures to different coloured light and development in three different colour developers that contain the dyes – so building up the colour image without chemical reversal.  E-6 is a process you can do at home without too much difficulty – Kodachrome K-14 was much more involved – and I say ‘was’ as production of Kodachrome film ceased in 2009 and the last roles were processed in December 2010.

Next up in my photographic journey through the Periodic Table is Oxygen – and I might need to get a bit creative with a photo depicting O₂.

Yttrium (Y – Atomic number 39) is another transition metals (like Iron) and was named after the town in Sweden, Ytterby, where the mineral (Ytterbite) in which it was first found was picked up from a quarry. Today Yttrium has a number of uses – as its oxide it is added to glass for camera lenses to improve heat and shock resistance.  We have all starred at it as it was used for making phosphors, such as the red ones in used in televisions (non flat screen), and it is a regular additive to magnesium and aluminium alloys to improve strength  – and probably its most important current use is in the production of white LEDs. So a couple of photography related uses.

I must get a better lens for macros… Yttrium is fairly common – the 28th most abundant element in the earths crust, found in soil and sea water – and strangely found in cabbage (not enough to worry about though).  It is very similar to the lanthanides, its close neighbours in the periodic table, and mostly obtained from the same rare earth minerals.

The way it is used in white LEDs is interesting, as Cesium doped Yttrium Aluminium Garnet (YAG, Y₃Al₅O₁₂) – it is a phosphor that emits a yellow light.  As a coating in high brightness blue InGaN diodes this converts some of the blue light to yellow – giving an overall white light.  The spectrum coverage is not perfect though – so even though it appears white the colour rendering isn’t ideal.  It is a fascinating (to me anyway) topic colour rendering – and has always been a challenge for colour photography to get an accurate representation of scenes that match to the way our eyes interpret them.  The colour can be affected very much by the light source – and it the white light doesn’t cover the full visibile spectrum then some colours just won’t look as expected – and this can be further challenged by the viewing conditions.  More over at Wikipedia – and the book The Reproduction of Colour gives lots more detail for those interested.

On final fun fact – and I’m sure gas mantles are something that few will remember – but these were used for propane lanterns (I remember them from caravan holidays) and where often used in the science lab as a demonstration of Geiger counters – as they used to be made with thorium which is radioactive.  Yttrium has replaced thorium now, so I guess science teachers bought up the old stock to keep the demonstrations going!

That finishes my first word – Fe Br U Ar Y – so next up come Tin, Oxygen and Tungsten – one life giver between two metals often connected with war and conflict – and the word is Sn O W.

Argon (Ar – Atomic number 18) is the third most abundant gas in the atmosphere, after nitrogen and oxygen, and on the increase – albeit slowly.  Not really good for nothing – but good for doing nothing – one of the inert gases.  Most of its uses rely on this fact – whether it is keeping wine fresh or allowing metals to be welded in an inert atmosphere – or protecting the filament of a light bulb.

I was going to say that Argon replace the vacuum that had been used to allow filaments in early light bulb to glow without burning away – but not sure it makes sense that a vacuum can be replaced.  The word Argon comes from the Greek word  αργον – meaning lazy – as it can’t be bothered to react.  There are very few compounds of Argon – argon fluorohydride is one – but needs very low temperatures to survive (40 kelvin).  (Just in case you are wondering – like I was – the root for the Argonauts was Argo – from the word meaning swift)

In the intro I mentioned the volume of Argon in the atmosphere is increasing (around 0.94% currently) and this is due to the decay of ⁴⁰K to ⁴⁰Ar by electron capture.  This fact is also used for dating rocks – as the amount of Ar is indicative of the age or the rock.

Another good periodic table fact is that in early periodic tables by Mendelev, Potassium preceded Argon – as the order was first based on atomic mass – and even though Argon has one fewer protons than Potassium, the most abundant isotopes of Argon have more neutrons – and hence the relative atomic mass is higher for Argon.  The nature of Argon compared to Potassium seemed to fit the other order better – and the periodic table was soon changed to follow atomic number.

The excellent interactive Periodic Table from the Royal Society of Chemistry is the one seen in the background of these photographs.