铝的电位-pH图及铝腐蚀曲线的测定

测定了在 pH =2～ 1 6范围内 ,铝的腐蚀电位 pH图 ,对铝腐蚀电位 pH图中的各临界线上的反应进行了分析 ,得到了铝在水溶液中腐蚀的钝化pH值范围 ,并建立了在不同 pH值范围内 ,铝的腐蚀电位方程 ;还测定了在 pH =7时 ,纯水及人造海水中铝的腐蚀极化曲线·

温度对轻烃回收装置换热器腐蚀行为的研究

通过模拟再生气换热器E-303在现场使用时的工况和环境,研究了不同温度下换热器常用材料Q345钢的腐蚀行为。结果表明:当温度为180℃时,腐蚀电流密度Icorr最大,为501.5μA/cm^(2);当温度为120℃时,腐蚀速率明显下降,腐蚀电流密度Icorr为357.5μA/cm^(2);当温度为240℃时,Icorr为77.62μA/cm^(2),Q345的腐蚀速率最小。结合微观形貌分析可知温度为180℃时,Q345钢的腐蚀程度最严重,120℃时次之,而240℃时腐蚀程度较小。腐蚀模拟实验结果与现场出现腐蚀情况吻合。

Electrochemical corrosion behavior of arc sprayed Al-Zn-Si-RE coatings on mild steel in 3.5% NaCl solution

Al-Zn-Si-RE coating with high Al content was deposited on mild steel by arc spraying. The electrochemical behavior of Al-Zn-Si-RE coating in 3.5%NaCl solution was systematically studied by potentiodynamic polarization, corrosion potential (φcor ) and electrochemical impedance spectroscopy techniques (EIS). The impedance data were fitted to appropriate equivalent circuits to explain the different electrochemical processes occurring at the electrode-electrolyte interface. The results indicate that Al-Zn-Si-RE coating reveals the similar polarization behavior as Zn-15Al coating. The coating has no passive region in the anodic polarization, but far lower corrosion current and much higher corrosion potential. Al-Zn-Si-RE coating provides effective sacrificial protection for steel substrate and the sacrificial anodic protection plays dominant role during the immersion process. In addition, theφcor evolution and EIS plots indicate that the corrosion process can be divided into five stages: pitting-dissolution-redeposition, activation corrosion, cathodic protection, physical barriers and the coating failure.

Effect of purification treatment on corrosion resistance of Mg-Gd-Y-Zr alloy

Mg-Gd-Y-Zr alloys were purified by filtering purification with and without vacuum. The type, morphology, size distribution and volume fraction of inclusion were analyzed with OM and SEM. The effect of inclusion in Mg-Gd-Y-Zr alloys on anticorrosion ability was investigated with salt spray test and electrochemical test. The results show that the inclusions in the alloy can be removed effectively by filtering purification. The average size of inclusions in the alloys is decreased from 12.7 μm to 2.0 μm and the volume fraction of inclusions is reduced from 0.30% to 0.04%. With the decrease of the size of inclusions in the alloys, the corrosion rate of the alloys decreases dramatically from 38.8 g/（m 2 ·d） to 2.4 g/（m 2 ·d） in the salt spray test. The corrosion potential increases while the corrosion current decreases and the polarization resistance increases in the electrochemical tests, which indicates that the anticorrosion ability is improved.

Comparative study on corrosion behavior of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr alloy in 5% NaCl aqueous solution

The corrosion behaviours of Mg-5Y-7Gd-1Nd-0.5Zr magnesium alloys prepared by as-casting and extrusion were investigated in 5% NaCl aqueous solution by immersion and electrochemical tests. The microstructure indicates the mean grain size of 15 μm for the extruded and 100 μm for the as-cast Mg-5Y-7Gd-1Nd-0.5Zr magnesium alloys. The corrosion morphology of as-cast sample shows pitting corrosion and little filiform corrosion, but that of the extruded sample shows pitting corrosion at the initial stage. The corrosion rate of extruded sample is higher than that of as-cast Mg-5Y-7Gd-1Nd-0.5Zr alloy according to the immersion test. The second phases containing RE acting as cathodes improve the corrosion properties. The corrosion potentials of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr alloys are -1.658 V and -1.591 V, respectively. The origins of the distinctive corrosion behavior of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr Mg alloys were discussed.

Corrosion and electrochemical behavior of Mg-Y alloys in 3.5% NaCl solution

The corrosion mechanism of Mg-Y alloys in 3.5% NaCl solution was investigated by electrochemical testing and SEM observation. The electrochemical results indicated that the corrosion potential of Mg-Y alloys in 3.5% NaCl solution increased with the increase of Y addition. The corrosion rate increased with the increase of Y addition because of the increase of Mg24Y5 intermetallic amounts. The corrosion gradually deteriorated with the increase of immersion time. The corrosion morphologies of the alloys were general corrosion for Mg-0.25Y and pitting corrosion for Mg-8Y and Mg-15Y, respectively. The main solid corrosion products were Mg（OH）2 and Mg2（OH）3C1·4H2O.

Effect of Mo_2C on electrochemical corrosion behavior of Ti(C,N)-based cermets

The electrochemical corrosion behavior of Ti（C,N）-based cermets with different Mo2C additions was investigated in freely aerated 10% H2SO4 and potentiodynamic polarization of all the materials was conducted from -0.5 to 1.5 V. There are two passive regions for all polarization curves. The first should be attributed to passive film formation due to Ti（C,N）, while the second may be due to the presence of Ni. Corrosion current density increases with M02C content increasing, from 2.06×10^-3 to 6.70×10^-3 mA/cm2. It is indicated that the corrosion resistance of Ti（C,N）-based cermets decreases with the increase of Mo2C addition. A skeleton of Ti（C,N） gains is observed after dissolution of Ni. The inner rim of cermets, rich in Mo2C, is corroded along with Ni binder and is more serious with the increase of Mo2C content. The secondary carbide Mo2C can be oxidized and dissolved in sulphuric acid.

Effect of coal slurry on the corrosion of coal-mine equipment

The corrosion of coal mine equipment immersed in coal slurry is addressed. The corrosion of low carbon steel samples immersed in coal slurries of different concentrations （80, 130, and 180g/L） prepared from coals of different rank （long-flame coal, meager lean coal, and anthracite） and different granularity （0.25-0.5 ram, 0.074-0.25 mm, and less than 0.074 mm particle size） was studied by the electrochemical method of polarization curve measurement, controlled potential sweeping, and continuous scanning. The results show that the corrosion rate in an anthracite slurry, where the coal has high coalification, is far greater than corrosion in a long-flame or a meager lean coal slurry. Furthermore the corrosion current, polarization current, and corrosion rate of low carbon steel become larger, and the polarizability becomes smaller, as the coal particle size decreases. The same trend is seen as the concentration of the coal slurry increases.