glass

Examples of glass in the following topics:

• Properties of Quartz and Glass

  • Glass is an amorphous (non-crystalline) solid material.
  • Glass is in widespread use largely due to the production of glass compositions that are transparent to visible wavelengths of light.
  • These properties, which give glass its clearness, can be retained even if glass is partially light-absorbing or colored.
  • Common glass has a refractive index of 1.5.
  • When used in art glass or studio glass, glass is colored using closely guarded recipes that involve specific combinations of metal oxides, melting temperatures, and 'cook' times.

• Capillary Action

  • The molecules in a sample of water in contact with a glass surface experience attractive forces toward the glass molecules.
  • By comparison, for a 4 m diameter glass tube in the lab conditions given above (radius 2 m, or 6.6 ft), the water would rise an unnoticeable 0.007 mm (0.00028 in).
  • When the lower end of a vertical glass tube is placed in a liquid, a concave meniscus forms.
  • This may be seen between mercury and glass in barometers and thermometers.
  • This can be seen in a glass of water.

• Amorphous Solids

  • The most frequently cited example of an amorphous solid is glass.
  • Additional examples include thin film lubricants, metallic glasses, polymers, and gels.
  • Samples of amorphous metallic glass are shown below.

• Silver

  • Silver nitrate is used as the starting point for the synthesis of many other silver compounds, as an antiseptic, and as a yellow stain for glass in stained glass.
  • Silver chloride is used in glass electrodes for pH testing and potentiometric measurement and as a transparent cement for glass.
  • This reaction is used to silver glass mirrors and the interior of glass Christmas ornaments.

• Cathode Rays

  • If an evacuated glass tube is equipped with two electrodes and a voltage is applied, the glass opposite the negative electrode is observed to glow from electrons emitted from the cathode.
  • Cathode rays are invisible, but their presence was first detected in early vacuum tubes when they struck the glass wall of the tube, exciting the atoms of the glass and causing them to emit light—a glow called fluorescence.
  • In 1838, Michael Faraday passed a current through a rarefied air-filled glass tube and noticed a strange light arc with its beginning at the cathode (negative electrode) and its end almost at the anode (positive electrode).
  • But at the anode (positive) end of the tube, the glass of the tube itself began to glow.
  • When they struck atoms in the glass wall, they excited their orbital electrons to higher energy levels, causing them to fluoresce.

• Changes in Energy

  • For example, consider ice water in a glass.
  • The difference in temperature between a warm room (the surroundings) and a cold glass of ice and water (the system and not part of the room) begins to equalize.
  • Over time, the temperature of the glass and its contents and the temperature of the room become equal.

• The Third Law of Thermodynamics and Absolute Energy

  • A more general form of the third law applies to systems such as glasses that may have more than one minimum energy state: the entropy of a system approaches a constant value as the temperature approaches zero.
  • In addition, glasses and solid solutions retain large entropy at absolute zero, because they are large collections of nearly degenerate states, in which they become trapped out of equilibrium.
  • Materials that remain paramagnetic at absolute zero, by contrast, may have many nearly-degenerate ground states, as in a spin glass, or may retain dynamic disorder, as is the case in a spin liquid.

• Changes in the Entropy of Surroundings

  • Consider a glass of ice water in a room.

• The Halogens (Group 17)

  • Fluorine is one of the most reactive elements in existence, attacking otherwise inert materials, such as glass, and forming compounds with the heavier noble gases.
  • The reactivity of fluorine is such that if it is used or stored in laboratory glassware, it can react with glass in the presence of small amounts of water to form silicon tetrafluoride (SiF4).
  • Therefore, fluorine must be handled with substances such as Teflon (which is itself an organofluorine compound), extremely dry glass, or metals such as copper or steel that form a protective layer of fluoride on their surface.

• Mechanistic Background

  • Care must also be taken to construct lamps and reaction vessels from glass that is transparent to the desired wavelength range.
  • The low wavelength cut-off for some common glass types are given in the table below.