Abstract
In cement processing, which involves the production of clinker in rotary kilns, the main refractories used in the transition and burning zones are magnesia–spinel bricks. These bricks present suitable chemical and thermomechanical properties, not to mention that they can be easily landfilled. Among the main wear mechanisms of these bricks in the kiln, the infiltration of alkaline salts is noteworthy and occurs through the open pores of the refractory. In this way, the coating—a clinker layer adhered to the brick surface—appears as a protection mechanism of the lining against infiltration. Thus, the objective of this investigation is to run a qualitative coating test based on the contact method, and quantitative coating test based on the sandwich method to check the suitability of the methodologies and to evaluate the coating adherence on two different magnesia–spinel bricks. It was possible to distinguish the superior adherence ability of brick B in both coatings due to the higher porosity and the presence of nonreacted ZrO2. Despite the similarity between the test results, the quantitative sandwich-coating test is preferable because it does not depend on subjective analysis.
Highlights
The magnesia–spinel bricks are the major chrome-free refractories used in the transition and burning zones of cement rotary kilns
The coating is a clinker layer adhered to the brick surface and has become one of the main requirements for basic bricks in cement rotary kiln
The bricks were previously characterized in relation to bulk density (BD) and apparent porosity (AP) according to ISO 5017: 2015 standard; cold crushing strength (CCS) according to ISO 10059—Part 2: 2014 standard; hot modulus of rupture (HMOR) at 1200 ◦ C for 3 h according to ISO 5013: 2012 standard; permeability according to ASTM C577 standard; chemical analysis by
Summary
The magnesia–spinel bricks are the major chrome-free refractories used in the transition and burning zones of cement rotary kilns. They are composed of magnesia (MgO) as a primary phase and spinel (MgO.Al2 O3 or MA) as a secondary phase. During a campaign in a cement kiln, these bricks are exposed to thermal, mechanical and chemical wear mechanisms but infiltration of alkaline salts is the predominant cause of wear [1,2,3]. The increased use of alternative fuels by cement producers, due to the low cost of this energy source and as a safe route for waste disposal, aggravates wear by exposure to alkaline salts
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