Effect of Temperature on Scale Morphology of Fe-1.5Si Alloy

Because of the effect of silicon on the formation of oxide scale, red scale is the main surface defect of hot rolled Fe-Si plate, making the scale difficult for descaling compared with carbon steel. Thermogravimetric analyzer （TGA） is used to simulate isothermal oxidation process of Fe-1.5Si alloy for 60 min under air condition, and the temperature range is from 700 to 1 200 ℃. Electron probe microanalysis （EPMA） is used to observe cross-sectional scale morphology and analyze elemental distribution of the scale. Relational graph of temperature, scale thickness and scale structure is obtained. It is found that scale structure （outer Fe oxide layer＋inner FeO/Fe2SiO4 layer＋internal Si oxide precipitates） is almost unchanged with temperature except at 1000 and 1 200 ℃. At 1000 ℃ internal Si ox- ide precipitates cannot be found at the subsurface of the alloy, and at 1200 ℃ FeO/Fe2SiO4 not only forms a layer as usual but also penetrates into the outer Fe oxide layer deeply.

Molecular simulation of oligomer inhibitors for calcite scale

Molecular simulation was performed to study the interaction between CaCO3 crystal and several oligomer inhibitors, by using the equilibrium morphology method to calculate the growth morphology of CaCO3 without inhibitors. The calculated morphology agreed well with SEM photographs. Then, a double-layer model was built to investigate the interaction between calcite crystal and oligomer inhibitors containing maleic anhydride （MA） and acrylic acid （AA）. Interaction energy per gram of an oligomer inhibitor was introduced as a scale of inhibition efficiency of different monomers. The results indicated that, for calcite scale inhibition, acrylamide （AM） and vinyl phosphonic acid （VPA） were the most efficient monomers, while allylsulfonic acid （AS） was the poorest. Increasing proportion of AM in dimer inhibitor molecule would improve the inhibition efficiency of MA, though, for a trimer, such as MA-AA-AM, certain sequence of monomers in the inhibitor molecule was necessary besides higher proportion of AM.

Corrosion Behavior of Ferritic/Martensitic Steels CNS-Ⅰ and Modified CNS-Ⅱ in Supercritical Water

The corrosion behaviors of CNS-I and modified CNS-II were evaluated by exposing to superciritical water （SCW） at 550℃ and 25 MPa with a dissolved oxygen concentration of 200× 10 ^-9 for up to 1 000 h. Detailed corrosion results of these two alloys were provided, including the growth rate of the oxide scales, microstructure of the oxide scales, distribution of phases and alloying elements. The mass gains of CNS-I and modified CNS-II were 609.73 mg/dm2 and 459.42 mg/dm2 , respectively, after exposing to SCW for 1 000 h. A duplex oxide scale with an outer porous magnetite layer and an inner relatively dense magnetite/spinel-mixed layer was identified on CNS-I and modified CNS-II after the test. The oxide scales were rather porous at the beginning of the test but the porosity decreased with increase of the exposure duration. It was found that Fe was enriched in the outer oxide layer, Cr was enriched in the inner oxide layer and O existed at a very high concnetration in the whole oxide scale. Other alloying elements such as Mo, W, Mn were depleted from the outer oxide layer and showed slightly enrichment in the inner oxide layer. The distributution of Ni was different from other elements, it was enriched in the interface bewteen the base metal and the oxide scale and depleted in the outer and inner oxide layers.