Ceramics

Introduction

  • Ceramics are a wide range of materials, most of which are a combination of metals and non-metals.
  • They're usually semi-metals which can be found from Earthen materials such as sand, lime etc.
  • Ceramics are typically hard, brittle and have good temperal stability, compressive strength and insulation.
  • Yet they are extremely prone to failure by cracking, have a porous
  • Most common ceramics are clays, glasses and cement.
  • In Civil structures we look at Glasses and Cement.

Glasses

  • Glass is an amorphous (non-crystalline) material.
  • Its structure is typically brittle and optically transparent.
  • The most common type of glass is soda-lime glass, which is the type used in drinking glasses.
    • It consists of silica, sodium oxide and calcium oxide.
  • To make glass:
    • The materials above are mixed in ratio and then heated in a furnace until it is in a liquid state
    • This is then homogenised and removed of any bubbles (known as refining)
    • The glass is then formed.
    • This is can be done through blowing in which air is forced into the molten glass against a mould.
    • To make flat sheet glass (known as float glass):
      • A layer of the molten glass is floated on a bath of liquid tin
      • The depth of the layer is then controlled by toothed wheel rollers and a device forces it to flow to the desired end.
      • This stream then passes through a "shoulder" to again limit its depth
      • It is then cooled and passed to the cutting area on rollers.
      • It is cut through the use of snap-rolling, in which a roller acts as a fulcrum to snap off dents made by cutters.
  • Once glass is formed, it is usually annealed to remove internal stresses.
  • It can be toughened through tempering
    • This is when the surface is cooled down faster than the inside.
    • This causes the surface to be in compression, which is good since it prevents cracking.
    • In fact, when toughened glass is shattered, it does so into small, safe pieces.
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  • Some uses of glass can be in:
    • Flat glass (such as windshields, windows etc.)
    • Glass containers (such as cups, bottles)
    • Glass wool (Insulation)
    • Glass fibres (To transmit information or to be a strong matrix for composites, optic fibres/ fibreglass)

Cement

  • Not to be confused with concrete.
    • Cement is the binding agent for concrete.
    • Concrete is a composite mixture of cement, aggregate and water that is often used in bridges and beams.
    • It is explained in detail later.
  • Cement comes in two flavours:
    • Hydraulic cement, which hardens underwater.
      • A famous cement of this type is Portland cement
      • This type of hardening occurs due to complex chemical reactions which turn the cement to silicate gel.
      • Hardening and curing then involves the removal of this gel and the water.
      • The process emits heat.
    • Non-Hydraulic cement, which hardens through other methods.
  • Cement comes in a powder form, which is created through the following process.
    • Limestone and Shale are crushed, grinded and then mixed together.
    • This mixture then goes into a kiln.
    • Inside the kiln, the mixture is heated up to almost 1500 degrees, and forms clinker.
    • The clinker is then ground up again, and mixed with gypsum.
    • It is continually ground up and refined, and this powder is known as cement.