Temperature – the highs and lows
is a measure of the average energy of the particles that make up a substance. It relates to the idea of hotness and coldness. If an object feels hotter, generally it has the higher .
Heat is a measure of the total amount of thermal energy in a body. Although a cup of boiling water and a full kettle of boiling water both have the same (100°C), the amount of heat or thermal energy present in the water of the full kettle is far greater then the water in the cup.
Heat flows from a hotter object to a colder one. If no net heat flow occurs between two objects, the objects have the same .
Temperature scales – Celsius, Fahrenheit and Kelvin
Three scales are in general use worldwide today. In scientific reports, only two of them are used – and .
, also known as centigrade, is a scale that is named after the Swedish astronomer Anders (1701–1744). 0°C is defined as the freezing point of water and 100°C as the boiling point of water, both at standard atmospheric pressure.
The scale is named after the 18th century German physicist Daniel Gabriel . The freezing point of water is defined as 32°F and the boiling point of water as 212°F.
The scale is a scale based on a theoretical point at which all thermal energy in any material is reduced to 0. This point is known as and is defined as zero (0 K). On the scale, it is -273.15°C.
The scale and the are named after the British physicist and engineer William Thomson, 1st Baron (1824–1907).
A unit has the same size as the degree: 1 K = 1°C. is zero (0 K) or -273.15°C, and 0°C is 273.15 K.
Temperature scales compared
Three temperature scales are in general use worldwide today. In scientific reports, only two of them are used – Celsius and Kelvin.
In scientific formulae, articles and reports, is frequently given in the unit . The symbol ‘T’ is often used in scientific formulae to represent in .
Low temperature – superconductivity
Superconductors are materials that lose all resistance to electric current when cooled to a certain . This – the critical – depends on the structure and composition of the material.
The advantage is that larger electric currents can be carried through thinner wire, with minimal energy losses.
At the present time, liquid helium is the coolant most often used in superconductor technologies.
Helium exists in liquid form only at extremely low temperatures. The boiling point of helium-4 is -269°C or 4 K at standard atmospheric pressure.
Dutch physicist Heike Kamerlingh Onnes first liquefied helium-4 in 1908. By using liquid helium as a coolant, he discovered superconductivity.
Researchers at Industrial Research Limited (IRL) in Wellington, New Zealand, have developed a ceramic material that becomes superconductive when cooled with liquid nitrogen (-196°C or 77 K). The critical of the ceramic is high compared with that of the alloys found in high-field magnets that are part of hospital MRI scanners. Superconducting magnets that make use of this technological advance are far cheaper to run.
Liquid helium and nitrogen compared
If liquid helium is cooled to -271°C or 2 K, it becomes a superfluid. In this state, it can flow freely, even upwards, with little apparent friction .
Liquid nitrogen.
Liquid nitrogen is a common laboratory coolant. With a boiling point of -196°C, it is cold enough to instantly freeze moist air in its vicinity. The ‘smoke’ is made up of tiny ice crystals.
Liquid helium
When liquid helium is cooled to -271°C, it becomes a superfluid. These liquids show unusual properties such as being able to creep along surfaces as shown in the diagram.
Design: Aarchiba, SVG rendering: Júlio Reis
High temperature – advanced ceramics
The use of in firing ceramics is critical to the hardening process. Traditional clay-based ceramics are normally heated in a kiln to temperatures within the range 1,100–1,300°C.
With some of the new high-performance ceramics, temperatures up to 1,800°C are needed. Specially designed furnaces have been developed to meet this need.
Use of temperature in firing ceramics
In this video, Dr Ian Brown, a senior research scientist with Industrial Research Limited, talks about the critical role that high temperature plays in the firing of ceramic materials. He explains the process known as ‘sintering’, which requires extremely high temperatures.
In the production of advanced ceramics, finely milled powders are shaped into a green body, and this is then heated to a very high that allows the fine particles to fuse at their edges. This process is known as sintering.
Nature of science
Science research is often driven by identification of potential technological applications. The development of a ceramic material that conducts at a higher has resulted in a from costly liquid helium as a coolant to cheaper liquid nitrogen.
