Gases and Plasmas
We live in a gaseous atmosphere and are influenced by its composition, behaviour and structure. Use is made of gas properties in our everyday lives – from perfumes and aftershaves to carbonated drinks to baking the perfect sponge cake to pumping up car/bicycle tyres.
When this state of matter is subjected to heat or electrical stimulation, it can transform into the fourth state of matter known as plasma. Natural atmospheric events such as lightning and auroras have a captivating and at times frightening quality. They are demonstrations of some of the properties of plasmas. Plasmas comprise the majority of the universe, and in terms of our atmosphere, some physicists have likened it to “living in a bubble of unionised gas surrounded by a plasma”.
Gases and plasmas are all around us, and we can better understand their properties and uses by investigating them in more detail.
States of matter
Matter is anything that occupies space and has mass. All physical objects are composed of matter, and an easily observed property of matter is its state or phase. The classical states of matter are solid, liquid and gas. Several other states, including plasma and Bose-Einstein condensate, do exist, but it is the classical states that can transition directly into any of the other classical states.
The gaseous state
The gaseous state is truly chaotic on the molecular level. It is the rapid, random motion of the spaced out gaseous particles that supports this description. This kinetic-molecular model helps to explain some of the properties of gases.
Converting states of matter from one form into another requires the involvement of heat energy. This ‘hidden heat’ (so called because, as the change occurs, there is no change in temperature) is referred to as ‘latent heat’.
The plasma state
Our daily experience confirms a world made up of solids, liquids and gases. However, at about 80 km above the Earth’s surface, the atmosphere is no longer made up of gas. Instead, it is made up of ionised gas, which consists of a balanced mix of electrons, positive ions and neutral particles. This state is called plasma.
Lightning is a large-scale natural spark discharge that occurs within the atmosphere or between the atmosphere and the Earth’s surface. On discharge, a highly electrically conductive plasma channel is created within the air, and when current flows within this channel, it rapidly heats the air up to about 25 000°C. The lightning channel is an example of terrestrial plasma in action.
Within the Sun’s plasma core, nuclear fusion reactions occur, releasing huge amounts of energy. Attempting to mimic this process on Earth has been the goal of some nuclear physicists for more than half a century. Progress has been slow, and the main reasons for this are linked to making, controlling and containing extremely high-temperature plasma within which hydrogen nuclei can fuse to form heavier helium nuclei.
Meet the scientists
Otago University’s Associate Professor Craig Rodger is regarded as New Zealand’s lightning expert. He was a major player in setting up the worldwide lightning location network (WWLLN), and his research interests include upper-atmosphere transient luminous events as well as coronal mass ejections from the Sun.
Dr Eric Scharpf is a partner in safety and automation consultancy firm exida and is widely recognised as an expert in chemical process safety, efficiency analysis and optimisation. He also works part-time in the Energy Studies section of the Physics Department at the University of Otago. One of his recent research areas has dealt with heat pump efficiencies used in the timber industry.
Associate Professor Bob Lloyd is the Director of the Energy Studies programme at Otago University. With a keen interest in renewable energy and energy conservation, Bob has been following developments in the nuclear fusion projects being run at the JET facility in the UK.
Professor Margaret Hyland is Deputy Dean of the Faculty of Engineering at the University of Auckland. Her area of expertise is in the chemical and materials engineering field. One of her research projects is focused on the use of high-temperature plasmas to assist in the deposition of thin ceramic coatings on metal substrates.
Dr Steven Matthews is a senior lecturer in the School of Engineering and Advanced Technology at Massey University in Auckland. His plasma spray gun research is focused on two main areas – plasma spray-coating magnesium-based medical implants with hydroxyapatite and the plasma spraying of titanium coatings.