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Investigation into the physical properties of glass.

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Introduction

Investigation into the physical properties of glass. Introduction 2 I have been set the task of investigating the physical properties of glass. Glass is very widely used (20 billion sq ft of glass is manufactured every year) but the methods used to manufacture it and the properties it possesses aren't as widely known. I aim to not just cover the properties of normal window glass but also to cover the different types of glass that exist, including bullet proof, safety, tempered, one-way bullet proof, optical lenses and radiation proof glass. The different properties I aim to investigate include young's modulus, impact resistance, transmittance, reflection and refraction. How glass is made 7, 12 In this section the sources agreed about most things, where they didn't agree it was due to simplification aimed at a younger audience. This is a very brief explanation of how glass is made because the task was to investigate the physical properties of the chosen material. The only manufacturing processes I have covered are the processes that explain some of the properties of glass. Most transparent solids are made by melting and cooling a different solid, when the particles in the molten solid cool and solidify their structure changes and the particles don't have a regular crystalline structure anymore, they now have an amorphous structure with no covalent bonds which absorb light. Heating silica until it melts and then cooling it makes glass. Chemicals added to the silica prevent the glass from becoming brittle and decrease the melting point of the substance. This saves heat energy that is important to save on production costs. When the silica and added materials cool they aren't in any sort of order, the particles are positioned randomly, which gives glass one property of liquids, the random position of their particles. Added to this is the fact that the electrons in the newly formed glass don't absorb energy from the visible area of the spectrum. ...read more.

Middle

If a bullet hits the flexible material first the glass is forced away from the flexible material, the bullet can then breach the flexible material. This gives the person being shot at a chance to reply, which could be useful if you were being shot at. Smart windows 7, 1 Smart windows are a relatively new idea that aims to get rid of the need for blinds. The idea is that just by turning a knob your window will suddenly go from transparent, to translucent and then to opaque. One objective of this project is that the windows would save the company money in heating, lighting and air conditioning costs. I could see why this might work if blinds hadn't been invented but since blinds have been invented the only application for smart windows is a system where the windows automatically darken as the light levels outside increase. Even if I think the idea is a waste of time smart windows are apparently the future and the physics behind them is interesting. Suspended particle devices (sometimes called light valves or SPDs) are another type of smart window. SPDs work by particles aligning themselves when electricity passes through them. When the particles are aligned they allow light to pass through. These particles are suspended in a liquid film that allows the particles to move freely when the electricity isn't turned on. The liquid is trapped between two layers of glass. The electricity is conducted to the liquid film via a conductive material that is used to coat the panes of glass. A rival to SPD is polymer dispersed liquid crystals. They work in a similar way to liquid crystals. Liquid crystals are hardly cutting edge; they are used in calculators, mobile phones and laptops. In these applications when electricity is applied to the crystals they change shape and allow light to pass through. The non-scientific term for polymer dispersed liquid crystals is switchable windows. ...read more.

Conclusion

This wasn't the end of the argument though. There is the debate that glass is actually a super-cooled liquid. The theory is that if you get a liquid and cool it very quickly before the molecules have time to align themselves into regular patterns then you will get a glass. The most suitable liquids for turning into a glass are liquids that are very viscous at their freezing point. The more viscous the liquid, the greater the difficulty the particles have forming a crystalline structure. Glass is constantly (but very slowly) trying to crystallise, people don't actually know what would happen if a window were left for millions of years, there are theories that it might become opaque, unchanged or a rigid puddle on the floor. No one can know for certain which theory is correct; you just have to weigh up the differences between the theories and see which one seems to be based mostly on fact. You could say that glass is a super-cooled liquid or an amorphous solid or even a state that is somehow in-between solid and liquid. Terminology specific to glass 17 There are many words that I have used which are specific to glass. In this section I will explain what they mean. * Anneal: To remove stresses in glass by controlled cooling. * Annealing point: The temperature at which the internal strains in glass are reduced to an acceptable level. * Blister: An imperfection in the glass, usually a bubble. * Check: A crack on the surface of glass. * Cullet: Waste glass, usually recycled. * Dice: Tempered glass's fracture. * Softening point: The temperature at which a uniform fibre 0.5 or 1 mm in diameter and length elongates under its own weight at a rate of 1mm per minute when the upper 10cm of its length is heated in a furnace which temperature increases by 5 degrees every minute. * Tempered glass: Glass that has been cooled quickly from its softening point to increase certain properties. * Transition point: The temperature at which molten glass turns into glass. ...read more.

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