Tin: a crackling metal
Why tin squeaks when bent
At room temperature, tin is a silvery-white metal that is easily fusible and malleable. When the temperature drops to 13.2°С, metallic white tin moves to a fragile non-metallic form – gray tin. This process self-accelerates, as the more white tin turns to silver, the swifter the subsequent transformation. The transformation also speeds up as the temperature drops. This phenomenon is called the “tin pest”. If you bend a piece of white tin, you can hear a characteristic squeak – a “tin cry”. It takes place because of the metal crystals rub against each other.
In the earth’s crust, tin is the 49th most abundant element. It is also encountered in the form of compounds. The most widespread mineral containing tin is cassiterite (SnO). Owing to certain of its special features, tin has played a key role in a number of historical events connected with its use.
The history of tin
Tin is one of the first metals that humanity encountered. In an alloy with copper, bronze was obtained, which was quite easy to melt and process. Humanity learned to smelt bronze around 3,300 BCE. Tin is mentioned in the Old Testament, and in the works of Homer. The use of bronze defined an entire era – the Bronze Age. Items from bronze and tin were found in Ancient Egypt, Greece, South America, India and other countries. Ancient bronze statues are well-known: the Colossus at Rhodes in Greece, and one of the symbols of Japan, the “Great Buddha” in the temple of Kotoku-yin in Kamamkura.
One of the sources of tin ore was the British Isles, which were called the Cassiterides. From this word, the main mineral was named that is used to obtain tin, cassiterite. The name of tin, “stannum” probably comes from the Sanskrit root “sta”, meaning “hard”.
Since ancient times, tin has not lost its importance for humans. Weapons, dishes and household items were made from it and its alloys. Due to its fusibility and wettability with other metals, tin was used in solders and in soldering metal containers. This led to the downfall of Robert Scott’s expedition. Fuel and food supplies were stored in metal containers soldered with tin. But because of the “tin pest”, the tin disintegrated and the kerosene leaked out.
The “tin pest” was well-known in Russia, as in the 18th century, in cold winters the pipes of church organs made from tin became brittle and crumbled at the touch!
Tin is such an important metal that there was even a war for the ownership of cassiterite deposits in the Democratic Republic of the Congo in the early 2000s! The ore is mined there manually, and people carry it on their backs to the highway for further transportation. But even these enormous efforts are considered to be justified.
Tin also played a role in science. On the 16th of October 1933, the German physicists Walther Meissner and Robert Ochsenfeld reported that they had studied tin at low temperatures, when it becomes superconductive, and they discovered that it starts to “repel” the magnetic field away from itself. The magnet then starts to “levitate” above the superconductor! This was called the “Meissner effect”.
Chemical properties of tin
In the laboratory tin can be obtained in several ways.
One of them is the reaction of tin salts with more reactive metals, for example zinc. Zinc will displace tin from its salts:
SnCl₂ + Zn → ZnCl₂ + Sn
Also, if we put a piece of zinc in a test tube with a solution of tin(II) chloride, beautiful needle-like tin crystals will start to grow on the surface of the zinc.
Additionally, tin may be obtained by the electrolysis of a tin chloride solution.
SnCl₂ →↯→ Sn↓ + Cl₂↑
Metallic tin is deposited on the cathode. If this process is carried out in a Petri dish, beautiful branched tin crystals form, to make a tin tree.
Tin is a more reactive metal than copper, for example. So tin displaces copper from its salts:
Sn + CuSO4 → SnSO₄ + Cu↓
Tin is resistant to the effects of air and moisture in ordinary conditions because of the presence of a oxide film. With concentrated hydrochloric acid, tin reacts slowly with the formation of hydrogen trichlorostannate(II):
Sn + 3HCl(conc.) → H[SnCl₃] + H₂↑
Tin chloride can be obtained in the reaction of metallic tin with hydrogen chloride gas.
Sn + 2HCl(gas) → SnCl₂ + H₂
Tin chloride is soluble in small amounts of water, and with dilution it is hydrolyzed with the formation of a white sediment - dihydrate tin (II) chloride:
SnCl₂(concentrated) + H₂O → [Sn(H₂O)Cl₂]↓
Where tin is used
All fans of electronics know about one the most important spheres for the application of tin – soldering. For a long time, an alloy of tin and lead was used in solders. But because of its toxicity, lead ceased to be used in solders. Tin solders melt at a higher temperature and are sometimes inclined to form “metal whiskers” – numerous fine shoots that appear on the surface of the metal, which look like hairs. Additionally, the problem of the “tin pest” had to be solved. A small amount of antimony or bismuth is added to the tin. Nevertheless, the majority of tin produced is used for solders. Tin is used in alloys and anticorrosive coatings for dishes and other items. Tin coatings have been used in cans since 1812, when the first can with this coating was made in London. Alloys containing tin are used for manufacturing superconductors, elements of nuclear reactors, and also for musical instruments. Bells are made from alloys of copper and tin, and organ pipes from an alloy of lead and tin.
Lead oxide is used in electronics and optics. Organics compounds of tin find an application in organic synthesis, the manufacturing of lithium ion batteries, and also in biocidal additives – substances that prevent the growth of bacteria, fungi, algae etc.
One interesting sphere for the application of tin is the manufacture of glass! To make smooth glass plates, suitable for windows, for example, for a long time various mechanical methods were used, such as putting heated glass between rollers, polishing etc. This laborious process still did not provide sufficiently smooth and even surfaces. A solution was found in the 1950s by the English engineer and businessman Sir Alastair Pilkington. Melted glass with a temperature of over 1,000 degrees Celsius is poured onto the surface of melted tin, a process which was subsequently named the “Pilkington process”. The glass cools on the smooth surface of the melted metal. The result is sheets of glass with a very smooth surface!
As you can see, tin is an element which has never lost its significance for humanity from ancient times up to the present day.
- Paul Parsons, Gail Dixon — The Periodic Table A visual guide to the elements;
- Norman N. Greenwood, Alan Earnshaw — Chemistry of the Elements (2nd ed.). Butterworth-Heinemann, 1997;
- Pilkington, L. A. B. (1969). "Review Lecture. The Float Glass Process". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 314 (1516): 1–25. Meissner, W. & Ochsenfeld, R. Naturwissenschaften (1933) 21: 787;
- W. MeissnerR. Ochsenfeld — Ein neuer Effekt bei Eintritt der Supraleitfähigkeit;
- The New York Times;
- Wikipedia/Meissner effect;
- Wikipedia/Float glass.