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These questions were asked on the 'Why Study Materials?' website and have been answered by members of the UK Centre for Materials Education
Why is glass transparent?
This is a very interesting question. What else can you think of that is transparent? Are they liquids, gases or solids? And what do we mean when we say that something is transparent? That we can see through it, I’m guessing is your answer, but it’s not the full answer. The energy that we call light is actually only part of a whole spectrum of energies called the electromagnetic spectrum. This spectrum includes all sorts of energy such as radio waves, microwaves, X-rays and even radioactive rays, as well as the light we can see. So, materials can be transparent to one type of energy but not to another, and glass is no exception, we can see through it but it is not transparent to X-rays. So, what’s the difference? How does the energy arriving at the material know what to do? Well, let’s look at the options for a packet of energy arriving at the surface of a material (these packets of energy are called photons). The first option is reflection; you’ve all looked in a mirror so you know how this works, the energy bounces off the surface, and, if it’s visible light, you’ll get an image, your face in the mirror, trees reflected in a lake. If this didn’t happen we really wouldn’t be able to see very much, other than sources of light, like the sun. Try looking at your face in a window; you’ll see that even glass is slightly reflective.
What’s next? Well, if the energy doesn’t bounce of the surface, it goes into the material and can either come out the other side, or be absorbed by the material. This absorption means the energy is transferred from the photon into the material, which causes the material to change in some way, usually to heat up. As with reflection, different materials absorb different energies of light, so some bounce off, and some are transferred to the material; this makes things appear to be different colours (we refer to the different energies of visible light as colours!). So, if a material reflects all the colours, it looks white, if it absorbs all the colours, it looks black. A good test of how much energy a material is absorbing is how much it heats up if you leave it in the sun.
The third option would be for the photon to go into the material and come out the other side, and this is what we would call transparency. But is it really that simple? Does the photon not interact with the material at all? Does it just pass straight through without changing? Well, no, it’s not that simple, especially in solids, there are no big holes that allow the light to just pass straight through, so what does happen? Well, we already know that different materials behave differently with different types of energy, so maybe what the material is made of is the answer.
Remember all the examples of transparent materials you thought of before? Hopefully one of them was diamond, which is nice and transparent, and also hopefully, graphite wasn’t one of your examples, because it isn’t transparent at all, not to visible light anyway. That’s strange though, aren’t diamond and graphite both made out of carbon? These two materials, both made entirely of carbon have widely different material properties and this is because of how the atoms are arranged; this is known as the lattice structure of the material. So, two materials with the same atoms, but a different lattice structure, can be the hardest substance known to man, or one of the softest. The arrangement of the atoms within a material allows the lattice to vibrate in certain modes, called phonons, which represent discrete ways in which the lattice can move. These phonons determine a number of the material’s properties, including transparency.
So the question now becomes not ‘why is a material transparent?’ but ‘when is material transparent?’. If the structure of the material allows a photon to be absorbed and turned into heat, the material isn’t transparent, but if the structure allows the photon to be absorbed and re-emitted, then it is. So really, light doesn’t travel straight through anything; the material just collects the light and then sends the same type of light out the other side. Think about that next time you look out the window.
by Dr Chris Russell
What alloys are used to make aeroplanes or coins?
Thanks for your questions. Here's some answers for you:
Generally, a number of different alloys are used in the Aerospace industry, ranging in uses from jet turbine blades to wings and fuselages. Aluminium alloys are very commonly used, as are alloys of:
Magnesium (a very light alloy)
Nickel (has excellent high temperature properties)
Titanium (lightweight, very strong and corrosion resistant)
Zirconia (can withstand very high temperatures so is used for coating parts of jet engines)
Historically, our 1p and 2p coins have been made from bronze, our silver coins (5p – 50p) from a copper-nickel alloy and our pound coins from a nickel-brass alloy. In 1992 the bronze coins were replaced with a copper-plated steel. £2 coins are made from a combination of copper-nickel (inner) and nickel-brass (outer).
There’s some interesting videos with some more details here on The Royal Mint’s website:
by Chris Taylor
What is the newest material for football boots and what is the best?
Please note this question was answered in 2008 and may no longer be correct
Traditionally, football boots have been made from leather, though these days a combination of man-made (synthetic) fibres are used either in addition to or in replace of leather. Using synthetic materials enables a lot of interesting and useful shapes to be created. Adidas produced their Predators back in 1996, using rubber ridges to help swerve the ball, and this year a company called Concave have developed a boot specifically shaped to cup the ball and increase the boot's sweet-spot. More info on them here: http://www.footy-boots.com/concave-football-boots-4586/
Most of these new materials carry copyrighted names and the exact compositions of them are difficult to find, but most appear to be a kind of polymer (plastic).
To answer your question more specifically, Nike were recently challenged to produce a boot with no financial restraints at all, to create something that would be the fastest and lightest boot on the market. They ended up with a boot made almost entirely from carbon fibre, which is a very strong yet very light composite material. You can read more about the boot here: http://www.footy-boots.com/nike-mercurial-sl/ Yours for only £240!
by Chris Taylor
Is stainless steel magnetic?
The simple answer is... it depends. It depends on what other elements have been alloyed to create the steel.
Basic stainless steel consists primarily of iron with approximately 11.5% chromium (by mass). This IS magnetic and is known as a "ferritic" (from iron) steel.
However, many stainless steels are known as "austenitic", and contain a greater amount of chromium and also another metal called nickel. It is the nickel which alters the steel's physical properties and makes it non-magnetic.
by Chris Taylor
What is the hardest metal in the world?
The hardest known metal alloy, and the hardest known metal in general, is a type of carbon steel, Alloy 1090. With a tensile strength of .84 GPa (122,000 psi) and a yield strength of .64 GPa (67,000 psi), carbon steel is surpassed in hardness only by very hard non-metals, such as ruby, diamond, or aggregated diamond nanorods.
by Dr Vanessa Cheel
What is Materials Science?
Every day we come into contact with many thousands of manufactured objects that are essential to modern life: the vehicles that we travel in; the clothes that we wear; the machines in our homes and offices; the sport and leisure equipment we use; the computers and phones that we can’t live without; and the medical technology that keeps us alive. Everything we see and use is made from materials derived from the earth: metals, polymers, ceramics, semiconductors and composites.
To develop the new products and technologies that will make our lives safer, more convenient, more enjoyable and more sustainable we must understand how to make best use of the materials we already have, and how to develop new materials that will meet the demands of the future. Materials Science and Engineering involves the study of the structure, properties and behaviour of all materials, the development of processes to manufacture useful products from them, and research into recycling and environmentally friendly disposal.
The basic building block of all matter is the atom and there are 94 different types that occur naturally on earth. These are ‘the elements’ and include hydrogen, oxygen, carbon, silicon, iron, copper, and aluminium. All materials are made up of these atomic building blocks but differ in their microstructure: the types of atom they contain, the pattern in which the atoms are arranged and the way in which the atoms are joined together. The central concept in Materials Science and Engineering is that the properties and behaviour of every material is dependant on its microstructure, and that microstructure can be controlled by the way in which the material is made and processed.
Materials Scientists test the mechanical, physical, chemical and electrical properties of materials and explore how these properties depend on the microstructures they engineer and observe using high powered microscopes. Materials Engineers apply this knowledge to select the most appropriate material and manufacturing process for any given application, to predict how a component will perform in service, and to investigate how and why materials fail.
The technological advances that have transformed our world over the last 20 years have been founded on developments in Materials Science and Engineering. Materials are evolving faster today than at any time in history; enabling engineers to improve the performance of existing products and to develop innovative technologies that will enhance every aspect of our lives. Materials Science and Engineering has become a key discipline in the competitive global economy and is recognised as one of the technical disciplines with the most exciting career opportunities.
Structure – how the atoms fit together. For crystalline materials, then this involves the size and shape of the crystals (usually called grains).
Microstructure – structure on a small scale so that a microscope is needed to see it.
Properties – measured behaviour, such as strength, electrical conductivity, stiffness or colour
Processing – changing the shape or properties of a piece of material, for instance by heating it, rolling it or stretching it.
Polymers – usually called plastics
Ceramics – brittle non-conductors such as pottery
What are Materials?
What do we mean by "materials"? The simplest definition is simply "stuff" - indeed Ivan Amato has written a whole book with this title, and it is very easy to read. There is natural stuff - wood, bone, straw, wool, cotton - and there is man-made stuff - steel, pottery, plastic, semiconductors, concrete, textiles, paper. People interested in materials are usually fascinated by two questions: "Why does each material behave the way it does?" and "How can I exploit the properties of a material to make something better or cheaper?"
The people who concentrate on the "Why?" question are Materials Scientists, and those who focus on the "How?" question are Materials Engineers. Both types of Materials specialists need to know what properties each material has and how they might be changed. Only very rarely can the answers be deduced using our bare hands and the naked eye, so the study of materials inevitably involves testing materials (that is, measuring their properties) and looking at their microstructure (using a microscope). The more theoretical side of the discipline is then to deduce how the properties (strength, transparency, flexibility, conductivity and so on) are related to the structure (crystal size, alignment of fibres, etc.). The challenge is then to use this knowledge to design and make materials which have better properties for our purpose.
Examples of this approach include the development of alloys which can be used at higher and higher temperatures in turbine engines and the development of plastics so resistant to breaking when bent that they can be used as hinges. Neither Engineers nor Materials specialists could do these things fifty years ago, yet today they are commonplace.
Professor Peter Goodhew
What is the name of the material most used for baby changing mats?
Baby mats are commonly made from a phthalate-free polyvinyl chloride (PVC).
(PVC is a plastic, technically a thermoplastic polymer, which is a plastic that will remelt when heated.)
Phthalates used to be added to PVC to increase its flexibility, but are no longer used here because of potential health risks.
by Chris Taylor
Why should I study M.Tech in Materials Sciences? What are the prospects?
There will be lots of career paths open to you with a qualification in Materials Science.
Materials graduates are sought after in many industries, including motorsport and aerospace, nanotechnology or biomechanical and medical applications, in technical areas ranging from manufacturing, processing and research to managerial roles such as production and sales.
How would you describe Materials Engineering to someone who knows nothing about it?
Materials Engineering is all about understanding what things around us of are made of and how we can produce things out of different materials so that they have different properties.
Materials Engineering can involve working on things in a very theoretical way, for example, carrying out tests to see how strong a material is in a laboratory. However, it can also be very practical, for example, working in a huge production plant manufacturing materials from raw products. Materials Engineering also takes you from the very small, such as nano-technology, to the very big, such as producing thousands of tons of steel a week in a blast furnace.
It is a very broad field – once you have studied the fundamental theory there are lots of different possibilities in terms of a career.
What is a normal working day of an Materials Engineer like?
From the Interview with Cheryl Anderson, read the whole interview here.
My current job involves working with the customers of a steel producer to understand why different material properties are important to them. Sometimes this means I am looking at tables of data or reading reports about how different manufacturing processes work. But much more I am involved in actually going out and meeting the customers and looking at their production facilities so that I can really understand how they use the steel that we make. For example, last week I visited a factory in Italy and in a few weeks I will be travelling to Eastern Europe. I also go to quite a lot of meetings, some only a few minutes long and some that are quite a lot longer, sometimes days!
To give you an idea of my week I have listed some of things that I was doing last week below:
• Monday – Write a report about a meeting that I had with a customer and prepare a presentation for the management team about how the visit went.
• Tuesday – Joint meeting with some other departments to discuss how we can improve the way in which we make our products. • Wednesday – Research on the internet about how certain materials are being used by some of our customers.
• Thursday – Travel to Italy, some meetings with the customer, a tour of their site and discussion about some technical issues that we are both interested in.
• Friday – more meetings with the customer; travel back to the UK – got back quite late!
What is a 'grain' and 'grain size'?
In metallurgy, "grain" refers to any of the small randomly distributed crystals of varying sizes that compose a solid metal. The structure and size of the individual grains determine the physical and mechanical properties of the metal.
For example in steel, decreasing the grain size will increase the strength and toughness of the steel.
You can find out more information if you search for "grain" here: http://www.matter.org.uk/matter_glossary/glossary.htm
What dissolves Al/Ti/Zr oxides?
There are many ways of dissolving the oxides of Al, Ti and Zr (alumina, titania and zirconia). There is no easy single answer, because the compounds can exist in different forms with different crystal structures and compositions.
However strong alkali (e.g. sodium hydroxide) will dissolve alumina, and probably the others. HF is also reported to dissolve titania and zirconia. Beware that these are all dangerous chemicals!
by Professor Peter Goodhew
Why is aluminium lighter than other materials?
Aluminium is lighter than many other materials because of its low density.
This is one of the main reasons why it is being used in car and aeroplane manufacturing.
Density is a physical material property which gives the ratio of mass to volume.
You can see how it compares to some other materials here:
Material Density, ρ (kg m-3)
It is much less dense than Iron (which Steel is made from).
You can find out some more information on aluminium (and all the other elements) here:
1. Do solids dissolve in water? If so which ones? 2. Do solids melt? If so which ones? 3. Do solids conduct electricity - if so which ones?
Do solids dissolve in water? If so which ones?
Yes, some solids will dissolve in water. They are commonly known as "water-soluble". Examples include salts and certain polymers (plastics). Searching for "water soluble materials" may help further.
Do solids melt? If so which ones?
Yes, some solids melt. Metals will melt, thermoplastics will melt, and glass will melt. Some solids will not melt into a liquid, and instead turn straight into a gas, this process is called Sublimation.
Do solids conduct electricity, and if so which ones?
Yes, some solids will conduct electricity. In order to do so, the material needs to have free roaming electrons within its molecular construction. Electrical conductivity is also dependent on temperature, so you have some materials that will only conduct if they are above/below a certain temperature. These materials are called semi-conductors, and include Silicon.
In addition, liquids like water will conduct electricity, which is why you should never use a water spray fire extinguisher to extinguish an electrical fire!
by Chris Taylor
What is the difference between glass and ceramics?
Glass is actually a type of ceramic.
The word Ceramic can be used to describe a number of materials, including: glass, enamel, concrete, cement, pottery, brick, porcelain, and chinaware.
Glass is a special type of ceramic, in that it has no crystalline structure, and is classed as an amorphous solid, meaning there is no long-range order of the positioning of its molecules.
You can find further information on Glass, Glass-ceramics and ceramics here:
by Chris Taylor