A. Martínez-Villafañe

Erosion of alumina and silicon carbide at low-impact velocities

Abstract The erosion performance of two commercial ceramics, alumina (Al 2 O 3 ) and silicon carbide (SiC), has been studied in a laboratory fluidized-bed (FB) facility in the temperature range from 250 to 560 °C. Tests were carried out in air using angular alumina particles with an average size of 100 μm as erodent material at an impact velocity of 5 m/s. The SiC ceramic revealed a better erosion resistance than Al 2 O 3 , irrespective of temperature. It is assumed that, at testing temperatures, oxidation plays no transcendental role in the extent of damage. Instead, under present conditions, the high hardness value conferred into the ceramics through higher densifications might lead to a better erosion resistance. At temperatures above 250 °C, SEM analysis on the surface of both ceramics disclosed ripple formation, i.e. a plastic deformation process occurring under particle impaction. This was less evident at the lowest testing temperature. Reasons to explain the behavior found are discussed.

Corrosion behavior of engineering alloys in synthetic wastewater

The corrosion behavior of 1018, 410, and 800 steels exposed to synthetic wastewater have been studied using linear polarization resistance, cyclic potentiodynamic curves (CPCs), electrochemical noise (EN), and electrochemical impedance spectroscopy (EIS) tests. The conditions were: a biochemical oxygen demand of 776 ppm; a chemical oxygen demand of 1293 ppm; a pH of 8; and a cell temperature of 25 °C. From the CPC and EN results, no localized corrosion was found for the stainless steels. However, small indications of a possible localized corrosion process were detected for the 1018 steel. The EIS results revealed that different corrosion mechanisms occurred in the carbon steel compared with the stainless steels. The results show that the corrosion mechanism strongly depends on the type of steel. Overall, the 1018 steel exhibited the highest corrosion rate, followed by the 410 alloy. The highest corrosion resistance was achieved by the 800 alloy. In addition, scanning electron microscopy analyses were carried out to explain the experimental findings.

Synthesis and Characterization of Porous Polyurethane- Chitosan Blends

In this work the synthesis and characterization of polyurethane (PU)-chitosan(CH) porous prepared by thermal induced phase separation (TIPS) is described, the obtained products were characterized by thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC), evidence of the interaction between both polymers was acquired from infrared spectroscopy. The morphology of the scaffolds was studied by scanning electron microscopy also the mechanical properties were acquired. The results showed that the TIPS technique is appropriate for the production of PU-CH porous materials.

Low Impact Velocity Wastage in FBCs - Experimental Results and Comparison Between Abrasion and Erosion Theories

The use of technologies related to combustion of coal in fluidized bed combustors (FBCs) present attractive advantages over conventional pulverized coal units. Some of the outstanding characteristics are: excellent heat transfer, low emission of contaminants, good combustion efficiencies and good fuel flexibility. However, FBC units can suffer materials deterioration due to particle interaction of solid particles with the heat transfer tubes immersed on the bed (Hou, 2004, Oka, 2004, Rademarkers et al., 1990). Among other issues, some of the most important factors believed to cause wear problems are: the motion of slowly but relatively coarse particles, particles loaded onto the surface by other particles, erosion by relatively fast-moving particles associated with bubbles, and abrasion by blocks of particles thrown into the surface by bubble collapse. Thus, erosion or abrasion processes can occur by a variety of causes. For the case of particle movement against in-bed surfaces, it has been suggested that there is no difference in the ability to cause degradation between solid particle erosion and low stress three body abrasion, and distinctions between the two forms of wear should not to be made (Levy, 1987).

Modeling of Volatiles Combustion and Alkali Deposition in a Fluidized Bed Coal Combustor

A simplified kinetic model, coupled with the bed hydrodynamics and a volatile evolution region within the bed, was formulated to predict the extent of gas-phase combustion in a laboratory-scale fluidized bed coal combustor (FBC). A close examination has also been made to highlight the relevance of the reducing/oxidizing environment (computed with the present theoretical model) in relation to FBC materials exposed to fireside corrosion at high temperature, under various operating conditions. The model results revealed that, for high-volatile coals with particle diameters (d c ) of 1-3 mm and sand particle size (d s ) of 0.674 mm, over one third of the original coal volatiles may burn in the freeboard region at bed temperature (T b ) ≤ 850 °C and excess air (XSA) ≤ 10 %. These values, together with the computed equilibrium conversion of alkali chlorides to sulfates, may suggest that sodium and potassium salts present in the vapor phase are likely to accelerate hot corrosion of heat exchange tubes above the bed when an FBC operates at T b ≤ 840 °C, XSA ≤ 20 %, d c 890 °C and XSA > 30 %, high oxidation rates may be present for the in-bed tubes. At these higher T b values and XSA < 10 %, a sulfidation mechanism presumably influences the extent of corrosion on the metallic components within the bed.