According to the Refractory Institute, "Refractories are heat-resistant materials that constitute the linings for high-temperature furnaces and reactors and other processing units. In addition to being resistant to thermal stress and other physical phenomena induced by heat, refractories must also withstand physical wear and corrosion by chemical agents. Refractories are more heat resistant than metals and are required for heating applications above 1000°F (538°C)."

In a boiler the refractory protects the metal surfaces at critical points such as the rear door and in the furnace. This refractory should be inspected periodically to insure protection. Here is a list of what to look for and possible maintenance solutions:

***Visually inspect refractory. Look for large cracks or broken pieces. Small hairline cracks are to be expected.
***Wash coat the refractory with a high temperature bonding, air dry mortar.
***Face all cracks and joints with hi-temp bonding cement.
***If any bricks have fallen out or show signs of excessive wear, replace them.
***Remember, once the repair is complete it is important to follow the manufacturers recommendation for curing the refractory.

We also suggest that you inspect the refractory of your brand new boilers when they arrive on site. Check to be sure that the refractory has not been damaged in shipment. Report any defects to your boiler supplier immediately.

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The Clay As Refractory Materials

To assess their use as refractory materials, the geo-chemical characteristics of the clays were compared with these industrial specifications namely, Grimshaw (1975), Brick Clay (Murray, 1960), and Refractory Bricks (Parker, 1967). Based on comparison with the Plasticity Fire Clay (Huber, 1985), as seen in Table 15, the silica oxide, alumina and iron oxide contents of the studied clays are generally not comparable.

The silica oxide values (57.14-73.14 %) are higher in value, while the alumina oxide value is lower than the values of the industrial standards in Refractory Materials. According to (Chukwudi, 2008), the clays cannot be classified as fire clays since the alumina content of fire clays range from 25-45%. The iron oxide content is higher and not comparable. Except for the alkali metal oxide content, all other values of titanium oxide content and LOI values are not comparable with the industrial standards in Refractory Materials. It can be deduced that the clays are not fire clays.

Grimshaw (1975) stated that clay is a good refractory material when its range of chemical composition is similar to the values listed in Table 14. Based on comparison between the studied clays and Grimshaw (1975) values, it can be deduced that the studied clays are not similar in chemical compositions (see Table 13).

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