Refractories Review: Seek and You Shall Find
One excellent source of information is the annual Ceramic Industry Data Book and Buyers’ Guide. Each year the CI Data Book is revised and updated to provide more and better information. In addition, the Data Book is also featured and continually updated on CI’s website at www.ceramicindustry.com. To enhance this process, readers are invited to provide feedback about needed updates and any other information that should be included in the print edition and on the website.
The Data Book includes eight sections, one of which is devoted to refractories. In addition, pertinent information is offered in the master product index, trade (brand) name listing, trade association directory and the alphabetical buyers’ guide address index (which includes contact information). More than 1500 products and 1000+ companies are listed.
The Master Product IndexThe master product index lists items under eight headings: raw and manufactured materials, batching and materials handling, forming and finishing, decorating, firing and drying, refractories, instrumentation and professional services, and reference. The index includes over 500 entries for raw materials and more than 100 for refractories. Raw materials choices range from traditional (more than a dozen categories of clay and nine of sand) to exotic—with items like fullerenes, praseodymium oxide and zirconia mullite. The refractories entries likewise cover a wide range, from alumina to zirconia.
For each entry in the index, a page reference points readers to suppliers of each item for contact as needed. For example, raw materials suppliers can be found for making all kinds of refractories from relatively simple 70% alumina bricks, to a complex advanced composite like magnesia carbon bricks. These are widely used in basic oxygen (BOF) and electric arc furnaces (EAF) worldwide, and contain magnesia, carbon/graphite, inorganic and organic additives, and powdered metal (Al, Si, etc.). And based on the increasing popularity and use of castables and other monolithic refractories, sources of the needed raw materials, binders and other special additives are available.
The Professional Services SectionThe professional services section offers the opportunity to locate technical assistance of various types. For example, some of the headings include hot repair of refractory linings by ceramic welding, custom grinding and particle sizing, environmental protection, dryout/heatup of monolithic linings, lab testing of refractories, technology transfer and licensing, and plant construction.
The Reference SectionThe reference section includes assorted technical data—properties, forming/finishing, drying/firing, testing, and conversion factors. A table of melting points of selected compounds and minerals shows that the refractory oxides with highest melting point are CaO, 2570°C (4658°F); dolomite, 2570-2800°C (4658-5072°F); and MgO, 2825°C (5117°F).
It is interesting that a new castable refractory, which allows increased slag-line life in steelmaking ladles without a mid-campaign repair, has been developed using a custom-made magnesia-lime raw material (79% MgO and 21% CaO). This is yet another example where refractory advancement has provided users a more durable and cost-effective lining. Because the refractory lasts longer in service and requires less material, the manufacturer’s market for the product is reduced. And although the user gains an effective reduction in refractory cost and maintenance, plus increased productivity, the manufacturer does not receive a value that is commensurate with the benefit(s) that was provided to the customer. There are many examples of this scenario over the last 20 years, and it will continue.
A table of room temperature strengths provides generic entries for fireclay and magnesite bricks, showing 5.2 MPa (754 psi) and 28 MPa (4060 psi), respectively. These strengths indicate single point values for each of the products, but it must be noted that multiple fireclay and magnesite brick products, made by various manufacturers, are available in the marketplace. And the properties of refractory products from various manufacturers can vary significantly, which means that a low-to-high range of strength values would better represent any type of refractory.
Refractories differ from metals/alloys in this regard, because metals/alloys from any manufacturer have a consistent composition and uniform properties. Problems have been known to occur when engineers or designers, who had experience with metals and alloys but not refractories, were involved in designing a refractory lining and erroneously assumed that a refractory product of a given type from any manufacturer would have the same properties.
A graph of representative thermal expansion data is provided for a range of refractory products. Vitreous silica is a very low expansion material, with excellent thermal shock resistance given its very small dimensional change with changing temperature. 98% magnesia is a high expansion material with an associated higher susceptibility to damage by thermal cycling. While most of the refractories exhibit linear thermal expansion behavior, the silica curve is different with very high expansion up to about 400°C (750°F), due to the silica polymorphism. So thermal shock is a major concern for silica bricks in the lower temperature range, for both heatup and cooldown. But at higher temperatures there is little expansion, so there is minimal effect of changing temperature. And it is clear that for high alumina refractories, the higher the alumina content, the higher the thermal expansion.
Reader input on the Data Book is always welcome. Please call Kristi Grahl, editor, at (248) 244-1294, fax (248) 244-6429 or e-mail firstname.lastname@example.org with your comments.