The advanced coating material TiAlN has higher corrosion resistance than TiN without Al content. TiAlN films are conventionally prepared by sputtering using a target with fixed Ti and Al composition. We prepared Ti1-xAlxN films using a dynamic ion mixing apparatus with two electron-beam evaporation sources for Ti and Al deposition. Ti and Al contents of films were changed by independently controlling the evaporation rate of the two sources at a constant N concentration of 30%. This system controls the film Ti and Al composition ratio (value x) precisely. Electrochemical film properties were measured using AC impedance and a fast Fourie transform analyzer. The measurement cell was constructed from two Ti1-xAlxN film samples coated on stainless steel used as electrodes in an HCl solution of 1mol/dm3. The equivalent circuit of the cell based on a typical parallel circuit, took film resistance Rf and capacity Cf into consideration and was determined by P-Spice simulation. Electrochemical properties were evaluated using interfacial resistance Rt, electrical double-layer capacity Cd and time constant Rt×Cd parameters. The Ti and Al composition ratio for optimum corrosion resistance was x=03.
Our study of chromium plating corrosion in oxgenated water involved three types of chromium plating on SUS 403 (13% chromium-steel): (1) conventional, (2) double-layer chromium-over-nickel plating, and (3) plating sealing with chromium oxide. Specimens were immersed in water (318K) with a 6 to 7ppm concentration of dissolved oxygen for a maximum of 180 days, during which weight changes were measured. After the test, chromium plating surface and cross section were observed. We found that conventional chromium plating corroded at microcracks, but double-layer chromium over-nickel plating and sealing chromium plating did not corrode. We therefore concluded that chromium plating corroded as follows Fe leached from the base metal due to electric potential created by the difference in concentration of dissolved oxygen inside microcracks and surface. Fe ion hydrolysis then produced acid inside microcracks. Chromium plating passivity was compromised by this acid, leaching chromium plating at microcracks.
Cobaltporphyrins having dendrimer side-chains were synthesized, and the oxygen-sensing properties of the modified electrode systems evaluated by electrochemical measurement. Such cobaltporphyrins catalyzed the twoelectron reduction of oxygen on electrodes. As oxygen sensors in modified electrode systems, (i) the current of oxygen reduction increased linearly with the concentration of dissolved oxygen, (ii) the response was reversible and rapid, and (iii) the modified electrode systems were more stable than the cobaltporphyrin monomermodified electrode under hydrodynamic conditions. These results support the potential of modified electrode systems as oxygen sensors.
Structures and its formation behavior of coating layer formed on steel by two-step hot-dipping method i e., primary dipping in a zinc bath followed by immersion in a secondary Zn-7 mass%Al bath, were studied using scanning electron microscope (SEM), electron probe micro-analysis (EPMA) and X-ray diffraction analysis (XRD). Primary dipping layers composed mainly of ζ phase and trace of η phase. The columnar structure changed to a fine acicular structure with a Fe4Al13-Znx phase at temperatures below 693K. Above 703K, it became a two-phase structure of a plate-like Fe2Al5-Znx and a fine broken acicular Fe4Al13-Znx phase. A Zn-Al coating layer over 50μm thick was obtained by secondary immersion between 683K and 733K for steel dipped into a primary bath at 763K.
Silicon powder was spread on the surfaces of CP Titanium plates and reacted with titanium by CO2 laser irradiation, forming silicide layers 600μm or thicker on the plates. Most alloy layers consisted of Ti5Si3. The highest hardness was 10GPa, and abrasion loss was 50-60% less than that of pure titanium.