Temperature – the hot and the cold

Temperatures from absolute zero to 2000°C play a critical part in the world of ceramics. From the very low needed in superconductivity to the very high needed in ceramic production processes.

Select a white circle or bar in the thermometer for more information.

Transcript

Lord Kelvin

0K or -273.15°C is the theoretical lower limit of temperature.

Absolute zero is the name given to this point. It is the temperature at which no more heat can be removed from a substance.

William Thomson, Lord Kelvin (1824–1907) developed the concept of ‘absolute zero’ and proposed a temperature scale starting at this point. This scale, named in his honour is the Kelvin temperature scale.

Image: Public Domain

Liquid helium

4K or -269°C is the boiling point of liquid helium. When mercury is cooled to this temperature it enters a superconductive state.

When cooled to 3K, liquid helium becomes a superfluid. It travels up and over the walls of the container forming a drop on the container bottom. Superfluidity is a very rare phenomenon that occurs at ultra-cold temperatures. The key characteristic is zero viscosity.

Learn more about superconductivity.

Image: Public Domain

Liquid nitrogen

77K or -196°C is the boiling point of liquid nitrogen. Liquid nitrogen is relatively cheap to make and is extensively used as coolant.

The ladle holds boiling liquid nitrogen at -196°C. Moist air in close proximity to the ladle is rapidly cooled, the result being the formation of tiny ice crystals. This gives the impression that the liquid nitrogen is ‘smoking’.

Image: Sascha Meinrath

High temperature superconductors

105K or -168°C is the superconductive critical temperature for a ceramic material known as BSCCO 2223. Superconductivity research scientists Jeff Tallon and Bob Buckley based at Industrial Research Limited in Wellington developed this ceramic. The coolant used is liquid nitrogen, a far cheaper option than liquid helium.

Learn more about the work of IRL researchers on High temperature superconductors.

Image: Industrial Research Limited

Mercury’s freezing point

235K or -38°C is the freezing point of liquid mercury. Mercury thermometers have a limited ‘cold’ measuring range as a result of this.

Image: Bionerd, Creative Commons 3.0

Freezing point of water

At a temperature of 0°C or 273 K and a pressure of 1 atmosphere water freezes. This temperature and pressure is known as STP, which stands for standard temperature and pressure.

Image: Public Domain

Standard room temperature

298K or 25°C is often taken as standard room temperature.

Image: The University of Waikato Te Whare Wānanga o Waikato

Living systems temperature range

The climate temperature range for human habitation ranges from 223K or -50°C to 323K or 50°C. Living systems operate over a very small range of temperature. Desert highs to polar lows.

Image: Igloo, Public Domain. Sahara Desert, courtesy of Luca Galuzzi, Creative Commons 2.5

Fahrenheit 451

506K or 233°C is the temperature at which paper heated in air spontaneously combusts. A novel written by Ray Bradbury called Fahrenheit 451 is based on this. On the Fahrenheit temperature scale 506K is 451°F.

Image: Ilya Akinshin, 123RF Ltd

Mercury’s boiling point

611K or 338°C is the boiling point of mercury. Mercury thermometers have a limited ‘hot’ measuring range as a result of this.

Image: Public Domain

Molten aluminium

933K or 660°C is the melting point of aluminium. O-Sialons developed at IRL are used to make pipes, tubes, and conduits to contain, transfer, and mould molten aluminium.

Image: Sorapol Ujjin, 123RF Ltd

Porcelain

Porcelain is a traditional ceramic made from types of fine grained clay and additional minerals. Porcelain is often translucent when held to the light and is finer than stoneware or coarse earthenware.

Porcelain is fired in a kiln at temperatures between 1,200 and 1,400°C. The toughness, strength, and translucence of porcelain, relative to other types of traditional ceramics, arises mainly from vitrification.

Image: Public domain

Stoneware

Stoneware is a type of pottery that is impermeable and vitrified. Stoneware clay is fired in a kiln at temperatures between 1100°C to 1300°C.

Image: Staffordshire plate, ca. 1850, Petri Khrohn, Creative Commons 3.0 and Crown Lynn lunch plate, The University of Waikato Te Whare Wānanga o Waikato.

Earthenware

Earthenware is one of many terms for on object made from clay that hardens at lower temperatures – usually between 1,000 to 1,150°C.

Earthenware is very porous and needs to be glazed to be food safe. Terracotta bricks and garden pots are common examples of earthenware. Minton majolica is a collectable glazed example.

Image: Terracotta bricks and garden pot, Sailko, Creative Commons 3.0, Minton glazed Majolica tiles, Clem Rutter, Creative Commons 3.0

Traditional ceramics

Traditional ceramics (pottery) are fired within the temperature range 1100°C to 1400°C. Earthenware is at the low end, followed by mid range stoneware, and finally high range porcelain. Temperature plays a critical role in the production of these different types of pottery.

The style and presentation of ceramics can vary – the firing temperature does not mean that all porcelain is fine and elegant and all earthenware is rustic and homemade looking. 

Image: The University of Waikato Te Whare Wānanga o Waikato. Earthenware mug and terracotta pot, Public domain; Stoneware pink Crown Lynn teacup, Auckland Museum, CC BY 4.0, and Temuka pie dish, Public domain; Qing-dynasty porcelain teacup (ca. 1690), Public domain, and Royal Doulton plate with koru design, Auckland Museum, CC BY 4.0.

Specialised high temperature oven

Advanced ceramics generally require higher firing temperatures than traditional ceramics. Temperatures in the range 1700°C to 2000°C are frequently used. Special high temperature ovens have been developed to achieve these temperatures.

Image: The University of Waikato Te Whare Wānanga o Waikato