No abstract

The waste chromium-oxide rods from thermal spray processes contained the valuable components of high chromium. The carbothermic reduction with graphite powders can be used to recover the chromium from the chromium-oxide rod. The waste rods were prepared into small pieces with a half-dimensions of 6.3 mm diameter and 5 mm length, and heated under the reducing atmosphere at 1150 – 1350 °C. Besides, the effect of different types and sizes of reducing agent on the reduction was observed. During the heating and cooling period, argon gas was fed into the atmosphere. Chromium carbide formation was promoted when the temperature and time were increased. Cr-O and Cr-O-Al-Si were observed in the microstructures before and after the reduction. The outermost part of the waste rod can be reduced to chromium because of the interphase zone. Consequently, the carbothermic reduction is one possible recycling method for utilizing ceramic rod wastes from the thermal spray process.

Biomass fuel is effective renewable energy and being used for replacing fossil fuel energy. It can be produced from synthesis gas containing a high percentage of carbon monoxide (CO) and hydrogen (H2) in biomass-to-liquid plants. Austenitic stainless steel AISI 316L (Cr17% Ni 10% Mo 2%) is used for equipment parts in chemical and petrochemical industries due to good corrosion resistance at various operating conditions. The corrosion resistance of stainless steel may be degraded by the reduction reaction of the passive film and carbide formation from carbon diffusion, which leads to the intergranular corrosion on the steel surface. This research aims to study the degradation of stainless steel AISI 316L in a simulated carbon monoxide containing atmosphere at 15-45%CO and a sensitizing temperature of 800 °C. Before the test, the samples were preoxidized in the air at 800 °C for 6 hours. An electrochemical reactivation (EPR) technique was used to analyze for detecting sensitization. The mass change of AISI 316L slightly increased after the reduction test. Besides, the high carbon diffusion was shown on the steel surfaces as chromium carbides at the high percentage of carbon monoxide.

AISI 304 austenitic stainless steel specimens are oxidised in laboratory air at 750 °C for 48 h. They are further subjected to the reduction test in carbon at 1350 °C for 30 and 60 min. The results show that the mass gain of the oxidised AISI 304 slighter increases to be 0.08 mg cm–2 after the reduction for 30 min and is unchanged at the longer reduction period up to 60 min. The oxide on AISI 304 is deteriorated after the reduction but its morphology tends to be unchanged when the reduction period is longer from 30 to 60 min. The results then indicate the superior performance of the AISI 304 to combat the corrosion under carbon at this high temperature.

No abstract