Purpose

This study aims to optimise the effect of pre-oxidation on hot corrosion behaviour of Tribaloy T-900 at 900 °C in mixed Na₂SO₄ and K₂SO₄.

Design/methodology/approach

Prior to hot corrosion experiment, pre-oxidation treatments were carried in ambient air at 900 °C for 1, 5 and 10 h, respectively. The hot corrosion experiments were performed in a box type furnace at 900 °C. Both surfaces of specimens were brushed with saturated salt solution of 75 wt.% Na₂SO₄ + 25 wt.% K₂SO₄. After brushing, the salt-coated specimens were placed in electric stove to ensure drying of salt. After drying, presence of 3 mg/cm² salt on specimen’s surface was ensured through weighting.

Findings

The 1-h pre-oxidation treatment prior to hot corrosion showed superior hot corrosion resistance against molten salt attack. An optimum pre-oxidation time of 1 h helped timely formation of protective Cr₂O₃ layer and inhibited the formation of less stable and porous surface oxides of Ni and Mo during hot corrosion.

Originality/value

Pre-oxidation effect on hot corrosion behaviour of refractory metal (such as Mo in investigated alloy) containing alloy has never been reported previously. Refractory metals oxide (e.g. MoO3) could transform the corrosion phenomena to catastrophic failure through acidic fluxing.

中文翻译：

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混合硫酸盐中钴基涂层合金耐腐蚀预氧化时间的优化

目的

本研究旨在优化预氧化对900°C的Na ₂ SO ₄和K ₂ SO ₄混合条件下Tribaloy T-900热腐蚀行为的影响。

设计/方法/方法

在进行热腐蚀实验之前，先在900°C的环境空气中分别进行1、5和10 h的预氧化处理。热腐蚀实验是在900°C的箱式炉中进行的。用75重量％的Na ₂ SO ₄  +25重量％的K ₂ SO _4的饱和盐溶液刷洗样品的两个表面。刷牙后，将涂有盐的标本放在电炉中以确保盐干燥。干燥后，通过称重确保在样品表面上存在3 mg / cm ^2的盐。

发现

热腐蚀之前的1小时预氧化处理显示出优异的抗熔融盐侵蚀的抗热腐蚀性能。最佳的预氧化时间为1 h，有助于及时形成保护性Cr ₂ O ₃层，并抑制了热腐蚀过程中不稳定的Ni和Mo多孔表面氧化物的形成。

创意/价值

以前从未报道过预氧化对含合金的难熔金属（如研究合金中的Mo）的热腐蚀行为的影响。难熔金属氧化物（例如MoO3）可通过酸性助熔剂将腐蚀现象转化为灾难性破坏。