How Not to Transfer Heat

How Not to Transfer Heat

Since the advent of fire, which means nearly time immemorial, we have been using heat for all kinds of applications in our lives, at the same time trying to find solutions for retarding transfer of heat. We have always required heat as a source of energy, but we had to simultaneously innovate the means to manage or control the heat. Clay must be one of the earliest examples of such insulating material, and there have been many more to follow. The most recent instance that comes readily to my mind is the case of disintegration of Columbia Space Shuttle, causing untimely death of all astronauts aboard, including our own, Kalpana Chawla. We all know that the spacecraft was burnt and annihilated on re-entry into Earth´s atmosphere as one or more of its ceramic heat shields fell away. Similar was the suspected reason of the last accident involving Concorde Aircraft. It all goes to underline the huge importance of heat insulation or thermal protection in maintaining integrity of materials.

This issue of INDIAN CEMENT REVIEW covers the interesting topic of Refractories, which form a very crucial part of not only in cement plants, but also most process/metal industries like steel, aluminium, etc. Being no expert on refractories myself, I can only deal with this in a broader way, like a semi-layman, and express hope that the cover story meets your expectations. To a person belonging to cement industry, refractories are a very critical part of his professional life, and therefore, I presume that this issue will be read with interest, and will be actively critiqued also.

Refractory is simply defined as something that retains its physical shape and chemical identity, when exposed to high temperatures. This definition fails to do justice to the fact that refractory materials have contributed immensely to the field of material science, by simply extending thermal protection to conventional materials of construction and enabling them to withstand higher and higher operating temperatures, effectively extending the range of their usability. Steel, the strongest among common materials, would not be able to melt and hold liquid iron or steel, but for the remarkable shield of refractories. This is why I feel that refractories, insulating materials and ceramics have collectively done more to further the cause of materials science, than materials science itself.

Lastly, even good and cool things like refractories have their own share of downsides and controversies. Disposal of used refractory materials, be they bricks, castable or inserts, [sometimes] pose a problem, particularly when they contain chromium, or are contaminated with hazardous materials from the process (like in case of spent pot linings of a smelter) like fluorides. Chromium can also get into cement clinker due to wear and tear of refractory lining of a cement kiln, and then leach into groundwater during concrete mixing. It is to prevent such possibilities that Mag-Chrome bricks, which were once the favourite of cement kiln designers, have now fallen out of favour, even as state-of-the-art and more environment-friendly refractory materials like Magnesite, Dolomite, etc. have emerged. Every problem has a solution which can be found in the fullness of time.

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