| The aim of this work is to develop an effective and practicable method to evaluate the coatability of cement clinker on basic refractory bricks, susceptible to be translated in numbers. Determinations of the dominant influential factors, and assessment of reliability, as well as of coating mechanisms on different basic bricks, are to be tackled.; Raw meal has been investigated in terms of chemical and phase compositions, particle size distribution, using DTA and TGA, as well as x-ray diffraction and microstructural analysis after heating at different temperatures. Raw meal calcinated at 1000°C for 4 hours contains plenty of free lime. Over 1350°C, most of liquid phases and belite C2S have formed. At 1450°C, there are still some clusters of free lime in clinker. Alite C 3S becomes dominant phase in clinker fired at temperature of 1550°C, with reduction of belite C2S and depletion of free lime.; Samples of 50 x 50 x 60 mm are directly cut dry from available bricks (without water-cooling) and the sandwich is prepared using the cut surfaces. At least six pieces are needed to have three sandwiches for all tested brands of basic refractories.; Mean value of the modulus of rupture obtained from three replicates is considered as representative of the adherence strength of the coating.; Statistical process analysis was also used to plan and carry out experiments carefully so as to confirm repeatability and reproducibility of the sandwich protocol. Variability of ±0.5 MPa is considered to be acceptable on a 5 MPa measured value.; The following conclusions can be derived from the results: (1) The most significant effects on adherence strength are the compressive loads, the nature of the raw meal, the heating temperature and the holding time, ranked in the order of importance. (2) A ruggedness test indicates that the sandwich test is insensitive to minor changes, in holding time, paste thickness and mixing mode of the paste. (3) Adherence mechanism of cement clinker on doloma brick is due to participation of lime from doloma brick in clinkerization of raw meal and formation of alite phase rich zone at the brick/clinker interface. (4) Fine, crystalline spinel easily reacts with lime containing phases from clinker to form low-melting phases and belite zone at the clinker/brick interface; this explains adherence on magnesia spinel brick. (Abstract shortened by UMI.)... |
