Study Of Low Cast And Environmental Corrosion Inhibitors Of AZ91D Magnesium Alloy

Since the concept of light metal has been put forward, the metal of aluminum, magnesium, sodium, potassium, calcium, strontium and barium whose density are less than4.5g/cm3have attracted the people’s attention. Compared with heavy metals, the toxicity of light metals is relatively low, and they show certain toxicity only in a large number of cumulative. These advantages of light metals composite people requirements on environmental protection. Thereinto, the magnesium alloy which is composed of the magnesium element and other metal elements, has high specific strength, high specific stiffness, high elastic modulus, good heat dissipation and machinability. These features make it one kind of the most practical light metal material. Compared with the aluminum alloy which has large-scale production applications, the magnesium alloy have better performance in high impact load and the corrosion resistance to organic matter and alkali will be more perfect. So the magnesium alloy is very likely to replace aluminum alloy used in different fields in the near future.As a kind of alkaline earth metals, the chemical property of magnesium is very lively. In the acidic solution at25℃, the standard electrode potential of magnesium is-2.372V, just above the barium showing strong reducibility. While in the internal of magnesium alloy, due to the addition of different metal elements, it appears obvious potential difference among the heterogeneous structures which are composed by magnesium and different metal element, resulted the corrosion of magnesium alloy. And this limits the application of magnesium alloy materials which has become the bottleneck for the development of it. At present, there are many ways to protect magnesium alloy, and adding corrosion inhibitors to medium is one of the most effective surface treatment methods.One kind of that is organic compounds containing N, O and S atoms, N, O and S have stronger electronegativity than C, which show negative electricity in organic molecules, and the metal surface takes a positive charge as the corrosion of metal surfaces. Under the electrostatic interaction, the negatively charged N, O, S which are the adsorption sites adsorb on the magnesium alloy surface, and-CH3hydrophobic groups are repel on the outside for positive charge electrostatic. At last, adsorption layer is formed on the surface of magnesium alloy. And then, hydrophobic groups will prevent the attack of corrosive ions in aqueous solution. Another kind is inorganic salts, which often combined with magnesium ions and formed sediment layer to prevent the occurrence of corrosion.Most corrosion inhibitors of magnesium alloy are heavy metal salts and heterocyclic compounds. These substances has certain inhibitory effect to the corrosion of magnesium alloy, but its high toxicity and high cost are largely prevented the large-scale production and application. In the day of increasingly serious environmental pollution, the requirements of people to environmental protection are increasingly high, and the application of high toxic compounds is limitted. Therefore, it is a very meaningful work which is study the type of environmental corrosion inhibitor of magnesium alloy.This paper studies the synergistic inhibition effect of sodium alginate and sodium silicate on the AZ91D magnesium alloy in the3.5wt.%NaC1corrosion medium. The surface chemistry of magnesium alloy is analysised by solid fluorescence spectroscopy and fourier transform infrared spectroscopy. The spectral tests show that sodium alginate adsorption on the surface of the magnesium alloy sample. Based on electrochemical test, corrosion inhibition efficiency of sodium silicate and sodium alginate were calculated, and the index of cooperation indicates that sodium silicate and sodium alginate have a relationship of synergistic reaction. When they are use together, the inhibition efficiency reached98.56%, and the corrosion of AZ91D magnesium alloy in3.5wt.%NaCl solution can be suppressed effectively. The author thinks this environment-friendly synergistic agent of alginate sodium and sodium silicate has very important significance to study.Due to adsorption inhibitors have the advantages of low cost, low toxicity, easy to industrialized production, these paper studies four kinds of adsorption inhibitors which are sodium dodecylsulphate, sodium dodecyl benzene sulfonate, sodium alginate and i-carrageenan. The highest inhibition efficiencies the corrosion inhibitors to AZ91D magnesium alloy in3.5wt.%NaC1corrosion mediumin a certain concentration range (0～1600ppm) are calculated by the electrochemical method. The electronegativities and optimal spatial structures of four corrosion inhibitors are calculated by Gaussian and NBO computational chemistry software. Through discussion of the relationship between corrosion inhibition efficiency and the possible adsorption sites, steric, and it proves that the space configuration of inhibitors is the key factor to inhibition efficiency. At last, through adding pefloxacin mesylate to the corrosive medium, the adsorption of the inhibitors to the surface of samples is enhanced, which takes further inhibiting corrosion. The author considers that the main factors to adsorption of the type corrosion adsorption inhibitors are discussed by computational chemistry methods and this provide powerful guidance for the design of new corrosion inhibitors...