Science, Part 12
Question 1: Define amorphous solids.
Answer 1: Amorphous solids have no definite melting point nor do they have regular repeating units. These are solids with no long-range order in positioning of the atoms. This is unlike atoms in crystalline solids. Window glass is an example of amorphous solids. Many polymers such as polystyrene are also amorphous. These solids may exist in two separate states. One is a “rubbery” state. The other is a “glassy” state. The transition temperature between the rubbery and glassy states is known as their glass transition temperature (Tg). More specifically, it is a temperature at which a loss of flexibility becomes lost in adhesives. Adhesives will become hard and inflexible. Adhesives which reach the Tg may fail if they are flexed. The actual temperature widely varies. From 105 degrees C to less than 0 degrees C.
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Question 2: Explain the properties of a liquid.
Answer 2: Liquids have definite volumes, however, they are unable to change shape by flowing. Liquids and solids have similarities in that in each the particles touch but they can move around. This means the density of liquids will be near that of a solid. Because liquid molecules can move, they assume the shape of their container. Specific liquid properties include viscosity, or the resistance of a liquid to flow. Surface tension, when there is an attraction between the molecules of the liquid that causes the surface to act as a thin and elastic film that is under tension, is another property. This property is what causes the formation of water into spherical drops. Vapor pressure is the pressure a solid or liquid exerts when at equilibrium with its vapor at a particular temperature. Boiling point is when atmospheric pressure equals the boiling point.
Question 3: Explain how a boiling liquid expanding vapor explosion occurs.
Answer 3: A boiling liquid expanding vapor explosion (BLEVE) is a danger in many railroad accidents in which flammable chemicals are involved. It is an explosion that happens when a vessel, such as a railroad tank car, fails and inside the vessel is a liquid at a temperature well above its boiling point at normal atmospheric pressure. With such a failure, boiling can occur instantly depending on the particular boiling point of the liquid. This causes the vaporization of a large amount of the liquid to occur. If the liquid's temperature is higher than the superheat limit, then boiling of an instantaneous nature happens. If the temperature is below that limit, the energy for blast and fragmentation generation is released. This mainly comes from vapor expanding in the space above the liquid. In either instance, if the container is burning the metal is heated and this causes a loss of mechanical strength.
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