Digitalfire Test Procedure Database

Co-efficient of Linear Expansion - COLE

Notes

Most solids expand as they are heated. This expansion occurs in microscopically small amounts and can be observed along a line (linear), across an area and volumetrically. Since ceramics are brittle materials uneven changes in expansion across a cross section or incompatible expansions across joints or between body and glaze can cause ware failure.

In ceramics thermal expansion is a measure of how much a thin fired ceramic bar increases in length as it is heated from room temperature until the melting point of the glaze. It is measured by a dilatometer and yields a curve that can be graphed. This graph is typically distilled down to an average value (which is less than representative if the graph line is very curved) in the 10-6 range. Thus a value of 7.5 is 7.5 x 10-6 in/in/degree C (some data sheets would quote this number as 75 x 10-7). Actually, the units of length do not matter. If this specimen was 1 inch long, it would increase in length an average of 7.5x10-6 inches for each degree increase in temperature.

To be most meaningful this value should be presented like this example:
(25-500C) Pre-fired at 1200C
In this example the range of heating over which the average has been taken is shown and the degree of vitrification of the body being measured is also indicated.

Expansion numbers are typically comparative, thus the units are not specified.

Variables

VAL - Value (V)

Out Bound Links

• (URLs) More Information
  http://216.239.33.104/search?q=cache:Ai8sbYmKGqEJ:...
• (URLs) Linear vs. Area vs. Volume expansion
  http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/...
• (Glossary) COE, Co-efficient of Thermal Expansion

  A measure of the reversible volume or length chang...

• (Typecodes) 5: BDT - Body Tests
• (Typecodes) 5: MTT - Material Tests
• (URLs) ASTM-C372 Thermal Expansion
  http://www.astm.org/Standards/C372.htm

In Bound Links

• (Articles)

  Bringing Out the Big Guns in Craze Control: MgO (G1215U)

  MgO is the secret weapon of craze control. If your application can tolerate it you can create a cone...

• (Articles)

  Crazing in Stoneware Glazes: Treating the Causes, Not the Symptoms

  Band-aid solutions to crazing are often recommended by authors, but these do not get at the root cau...

• (Articles)

  Understanding Thermal Expansion in Ceramic Glazes

  The way to deal with crazing or shivering is to understand what thermal expansion is, how it relates...

• (Articles)

  Adjusting Glaze Expansion by Calculation to Solve Shivering

  This page demonstrates how you might use INSIGHT software to do calculations that will help you incr...

• (Tests) CIGF - Boiling Water:Ice Water Glaze Fit Test