A comparative study of the influence of trivalent and tetravalent nano-sized oxides on the performance and microstructure of dolomite refractories
Abstract Contrary to the many benefits of dolomite refractories, their usage has been limited due to poor hydration resistance. For this reason, the aim of this research work is a comparative study of the influence of trivalent and tetravalent nano-sized oxides [iron (Fe 2 O 3 ), alumina (Al 2 O 3 ), zirconia (ZrO 2 ), and titania (TiO 2 )] on the performance and microstructure of dolomite refractories with an affirmation their hydration resistance improvement. After preparation and firing the specimen's, physical properties such as bulk density, apparent porosity, and hydration resistance tests were examined. Furthermore, XRD and SEM/EDX analysis were used to evaluate the ceramic phases and their microstructure, respectively. Results revealed that specimens with trivalent and tetravalent nano-sized oxides have improved densification and hydration resistance of the specimens through the liquid phase mechanism and solid state firing mechanism, respectively. Also, the specimens with tetravalent nano-sized oxides have higher hydration resistance than the specimens with trivalent nano-sized oxides. Generally, the hydration resistance improvement trend of specimens with various nano-sized oxides presence is Al 2 O 3 2 O 3 2 2 .
Effect of BaO Addition on Densification and Mechanical Properties of Al2O3-MgO-CaO Refractories
Considering the requirement for a reduction of refractory consumption, the present work investigated the fabrication of Al2O3-MgO-CaO-based refractory with BaO addition by means of solid-state reaction sintering. The effect of BaO addition on densification and the properties of the refractory were also discussed. Results indicated that the formation of calcium hexaluminate (CaO·6Al2O3, or CA6) grains with a high aspect ratio in the alumina-rich zone depressed the densification of the sample without BaO addition, resulting in a higher apparent porosity of 21.2%. When 6 wt. % BaO was added, a new phase of Ba2Mg6Al28O50 (BAM) with a lower aspect ratio was formed and the densification of the sample with an apparent porosity of 5.52% was promoted. In addition, mechanical performance was significantly improved due to an increase in compactness and modification of the microstructure. The cold compressive strength increased from 348 MPa to 569 MPa and the flexural strength increased from 178 MPa to 243 MPa by addition of 6 wt. % BaO. Meanwhile, the breadth of the widest crack after the thermal shock test decreased from 7 μm to 1 μm in the refractory.
Description of roughness profiles by separating the random and periodic components
Abstract The probability that it is not possible to obtain a significant description of roughness profiles composed of random and periodic components by using statistical methods is discussed. It is shown that the random and periodic components can be separated by using the frequency spectrum and the autocorrelation function of the profile. The physical significance of the separate components is discussed and it is shown that it is possible to describe a long crested surface by a single profile using these components The method of separating the random and periodic components allows a parametrical description of the roughness profile to be given. It is then possible to use these parameters to calculate a synthetic signal sign with the same basic properties as the measured profile.