Description of the electromagnetic flowmeter fluid erosion resistance of the metal electrode passivation membrane formation factors

Directly in the process of electromagnetic flowmeter measurement and measurement of key components in contact with the medium is the electrode, electrode electromagnetic flowmeter, 316 l, tantalum electrode, hartz electrodes, etc. , can be adapted to the measurement of different liquids. For different media, we have the following form to illustrate: electromagnetic flowmeter electrode material selection table used shall not apply to the 316 l life sewage water, industrial water, raw water Wells, the part of the acid, alkali, salt solution and 316 l material hartz alloy chemical reaction medium of hydrochloric acid (B Concentration & le; 10%) Non oxidizing acid sodium hydroxide ( Concentration & le; 50%) Phosphoric acid, organic acid, nitric acid hartz alloy C mixed acid such as chromic acid and sulfuric acid mixture of salt water hydrochloric acid titanium oxide ( Ti） Sodium chloride salt sodium, potassium, ammonium salt, hypochlorite seawater concentration less than 50% potassium hydroxide, ammonium hydroxide, hydrochloric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, barium hydroxide solution reduction acid tantalum ( Ta） Hydrochloric acid ( Concentration & le; 40%) Chlorine dioxide of sulfuric acid and dilute sulphuric acid, ferric chloride, hypochlorous acid, sodium nitrate, Including fuming nitric acid) Such as oxidizing acid temperature below 80 ℃ of aqua regia hydrochloric acid, fuming sulfuric acid, phosphoric acid, hydrofluoric acid reducing acid platinum-iridium alloy such as almost all of the acid, alkali, salt solution aqua regia ammonium salt corrosion resistant properties of stainless steel electrode electromagnetic flowmeter, the main reason is because the surface is covered with a layer of thin, About 1 nm thick) The density of passivation film. This is the isolation layer passivation membrane, corrosive fluid become basic stainless steel electrode protective barrier. Passivation of stainless steel electrode has the dynamic characteristic, should not be regarded as the corrosion to a full stop, but the diffusion barrier layer, the anode reaction speed is reduced greatly. Of stainless steel electrodes, usually in a reducing agent, Such as chloride ions) Cases tend to destroy the passivation film, in the oxidant ( Such as air and water) Can maintain or repair the passivation film. Stainless steel electrode placed in air and water can form oxide film, but this kind of membrane protective imperfection, speed is very slow. Figure 4 for the stainless steel electrode by XPS ( X - 雷photoelectronspectroscopy) Photoelectric spectrometry equipment to analyze the surface chemistry of quantitative graphs. Is left without the process of electromagnetic flowmeter electrode surface to the main elements in different depth of chromium ( Cr） , oxygen ( O) , iron ( Fe) The content of ratio. As you can see, in the depth of about 1 nm position of chromium content is about 20%, it indicates that the lean and chrome passivation membrane layer. Right after mechanical grinding and polishing or pickling, passivation treatment measures, chemical polishing process of iron and iron oxide ratio of chromium and chromium oxide priority to dissolve, remove the poor chromium layer, enrichment of chromium in stainless steel surface, in the depth of about 1 nm position of chromium content is about 30%. The rich chromium passivation membrane polarization potential ( SCE) Can be up to + 1. 0 v, close to the precious metals gold, platinum polarization potential, therefore, to improve the stability of the corrosion resistant stainless steel. Different passivation treatment methods also affect the composition and structure of the membrane, thus affecting stainless. Such as through electrochemical modification, can make the passivation film has a multilayer structure, formed in the barrier layer CrO3 or Cr2O3, or glassy state of oxide film formation, make the corrosion resistance of the stainless steel can play big. The corrosion resistance of stainless steel electrode relies mainly on the surface passivation membrane, if the passivation film is incomplete or flawed, and stainless steel will corrode, of course, still can appear fluid noise. Electrodes in shaping, assembly and installation tag brings in the process of surface oil dirt, rust, non-metallic, low melting point metal pollutants, paint, welding slag and splash content etc, these substances affect the surface quality of stainless steel electrode, destroyed the surface oxidation film, reducing the overall corrosion resistance of stainless steel, formation fluid noise, also affect the stability of electromagnetic flowmeter measurement. So to improve the electrode assembly processing and storage, in front of the assembly process method, protect the passivation film is one of important technology in the electromagnetic flow meter manufacturing. In this paper by embellish instrument technology co. , LTD. Arrange release.

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