Most people, when asked what they thought the most expensive metal in the world was, would be inclined to say gold, silver, or even platinum. Although we consider these metals ‘precious’, and indeed they are close to the top of the list, they are by no means the most expensive and can all be trumped by one metal – Californium.
Californium is a rare earth metal and does not occur naturally on the planet. It is a radioactive metallic chemical element with the symbol Cf and atomic number 98. Not only is a gram of Californium worth US$27 million, it is second only to antimatter when it comes to the most expensive materials in the world.
The element was first made in the 1950s at the University of California Radiation Laboratory in Berkeley, hence the name Californium which it takes from its origins. It is a silver/white actinide metal with a melting point of 900 ± 30 °C. It is also exceedingly radioactive and just one microgram of Californium releases up to 170 million neutron particles every minute.
Uses of Californium include the detection of gold and platinum. At US$56 per gram for gold and US$60 per gram for platinum these 2 metals are still high on the list of the world’s most expensive elements, but far from the cost of Californium. It can also be used in a device called a neutron moisture gauge to detect oil/water bearing layers within wells.
More uses are expected to be discovered for Californium as at the moment only a few of its compounds are known.
Bells have long been used to herald significant events and are especially prominent during December as we enter the festive season. From ‘Jingle Bells’ to ‘Deck the halls…’, the references are constant. To get into the spirit of Christmas we decided to take on a special theme this month and explore the origins of bells and how they are made.
Bell making can be a complex procedure and the end result varies by country and culture, as well as purpose of course. East Asian bells, for example, tend to be barrel shaped, whilst Western bells have a tulip shape, often with a bulge near the rim. Bells that are intended to be rung are usually made by casting bell metal – a high copper bronze alloy – of a size that is correct for the pitch the bell is to produce. Fine tuning can be achieved by removing a precise amount of material from the inside of the bell, dependant on the tune one wants to produce.
The manufacture of bells has been important throughout the history of many civilizations with the earliest examples being made of pottery. In Britain, it takes its roots in monasticism and the early medieval period, when it was carried out predominantly by monks. References to large bells can be found in the works of Bede as early as 670 A.D. By the eighth century the use of bells had been incorporated into church services.
Bells intended to make sound are usually made of bell metal, as mentioned above. Bell metal is a hard alloy form of bronze, usually in approximately a 4:1 ratio of copper to tin. Bell metal ore is a sulfide of tin, copper and iron called stannite. Both tin and copper are fairly soft metals that will deform when struck – however, when alloyed together the two elements create a metal which is much harder and less ductile. It also has more elasticity than either of the metals alone. This allows for better bell resonance and causes the bell to vibrate when struck, which is necessary as the clapper can strike at speeds of up to 600 miles per hour. In Russia, silver is sometimes added to the mix too to produce a unique sonority and resonance.
Other metals which can be used include brass or iron. For a brief period in mid-nineteenth century England steel was tried, mainly for its economic cost compared to bronze, but it was not durable enough and manufacture ceased in the 1870s.