| Dinitrogen tetroxide,molecular formula N2O4,a gaseous mixture blended with nitrogen dioxide at normal temperature and pressure,has strong oxidizing and toxicity,and is often used as a propellant in aerospace applications;pure tetraoxide dinitrogen is not corrosive,But industrially produced finished products often contain small amounts of water(0.1%～0.4%),which reacts to form nitric acid and nitrous acid.It is corrosive to storage tanks made of metal materials,which is easy to cause corrosion and damage of the tank body,bring about safety problems.For the corrosion of metal materials by nitrous oxide,most scholars are studying in a closed environment under real conditions,and the corrosion behavior is studied by means of corrosion morphology,mechanical properties and electrochemical corrosion current.However,these research methods usually require a research cycle of 5-10 years,and there are many problems such as long research time,high cost,and low safety factor.In this paper,based on the principle of mutual conversion of nitrous oxide and nitrogen dioxide,nitric acid is formed by the neutralization reaction of nitric acid and sodium nitrite,and establish the nitric acid-nitrous acid-sodium nitrate-water simulation system similar to the corrosion mechanism of the tetraoxide dinitrogen/water mixture system in a closed environment,and further study the corrosion behavior of alloy material aluminum alloy 5A06,stainless steel 0Cr18Ni9,aluminum lithium alloy 1420.The method not only has simple operation and high safety factor,but also can accelerate the corrosion behavior by changing the concentration of the corrosion system,shortening the experimental period.In this paper,the corrosion of metal materials was studied by setting different simulated corrosion system concentrations.By analyzing the mass change of the sample before and after treatment,the corrosion rate curve was drawn and data regression analysis was carried out to establish the accelerated corrosion curve at the corresponding concentration.The apparent morphology of the samples before and after corrosion was observed by means of 3D video microscopy,characterized the degree of corrosion by surface roughness.Quantitative analysis of metal ions in corrosive liquid by inductively coupled plasma atomic emission spectrometry(ICP),summarizing the corrosion law.Comparing the base material and the weld material of the tank,and observe the mechanical properties change of the weld material in the simulated corrosion system.Finally,the corrosion products generated on the surface of the material were qualitatively analyzed by scanning electron microscopy and energy dispersive X-ray spectrometry to explore the corrosion mechanism.The results show that sodium nitrate in the nitric acid-nitrous acid-sodium nitrate-water system has no obvious acceleration effect on metal corrosion,and its effect can be neglected,the simulation system can be approximated to the real system from the corrosion mechanism.The corrosion resistance of stainless steel is far better than that of aluminum alloy and aluminum-lithium alloy materials under different corrosion concentration systems.It appears obvious corrosion stains and potholes on the surface of aluminum alloy and aluminum-lithium alloy samples with the prolongation of corrosion time.If different metal materials exist in the same corrosion system,it will constitute electrochemical corrosion:Metal materials with high chemical reactivity and high reactivity are preferentially corroded as anodes,and materials with lower reactivity are protected as cathodes.SEM detected that aluminum alloy 5A06,aluminum-lithium alloy 1420 sample will produce obvious corrosion products on the surface after corrosion,those are mainly composed of H-Al-O.For the weld material of butt surfacing,the corrosion resistance is better than that of the base material at the initial stage.As the corrosion time prolongs,the mechanical properties of the weld material decrease significantly,from plastic fracture of the raw material to brittle fracture.Under certain corrosive liquid concentration(0.008 mol/L≤c≤0.167 mol/L),aluminum alloy 5A06 and aluminum-lithium alloy 1420 meet certain linear accelerated corrosion laws in the simulated corrosion system. |
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