Papers by Author: S.D. De la Torre

Abstract: The corrosion rate (Cr) of commercially available ball bearings made of silicon nitride (Si3N4) of high degree (HD) and standard quality (S) was measured at hydrothermal conditions in different aqueous concentrations of sulphuric acid (H2SO4) and sodium hydroxide (NaOH). The Cr magnitude for the materials diminished when increasing the acid concentration. At higher concentrations of H2SO4 (98%) the formation of SiO2 on the surface of the balls inhibited the progress of corrosion. The corrosion rate of the materials was increased when the sodium hydroxide solution concentration was increased. The surface of the materials was analyzed by means of scanning electron microscopy (SEM), while the corrosion rate was determined based on weight losses.

Abstract: The high temperature oxidation resistance of Cr-ZrO2-Al2O3 composites fabricated by mechanical alloying and spark plasma sintering (SPS) has been evaluated. Composite powders were prepared by ball milling Cr-5vol%ZrO2-50vol%Al2O3 powder mixtures. Powders were compacted by SPS in less than 5 min, so that a particular metal-ceramic interpenetrating network is obtained. High temperature oxidation tests (900-1100 0C) in air have revealed good oxidation resistance (1.8, 2.6 and 15.3 mg/cm2 at 900, 1000 and 1100 °C, respectively) due to a protective Cr2O3 layer. EDX analysis revealed that Cr diffusion takes place at 1100 oC from the bulk towards the composite surface leading to Cr depletion at near-surface zones. Chromium contained in the bulk tends to oxidize through oxygen diffusion apparently occurring along the grain boundaries.