- Mar 31, 2018 -
Three organic phosphine agents PBTCA (2-phosphonobutane-1,2,4-tricarboxylic acid), HEDP (hydroxyethylene diphosphonic acid), ATMP (amino trimethylene) were selected from commonly used water treatment agents. Phosphonic acid) was compounded with ClO2 and ZnSO4, and the best formula was determined by orthogonal test. The formula was calculated by ab initio calculation. The relationship between corrosion inhibition performance and molecular structure was analyzed. The results showed that: P atom The net charge QP, charge density, and molecular minimum orbital energy ELUMO have a good correlation with the inhibition rate. At the same time, the highest occupied orbital energy EHOMO and the lowest empty orbital energy E LUMO of Fe and ClO2 and the difference between the two are calculated. The value ?E indicates that the tendency of corrosion inhibitor electrons and Fe to act is greater than the tendency of accepting electrons and Fe, and the ability of PBTCA, HEDP and ATMP to withstand oxidation of chlorine dioxide and the lowest empty orbital energy of the corrosion inhibitor and chlorine dioxide The difference in the maximum occupied orbital energy (LUMOinhib? HOMOC?O2 value) has a good correlation. The experimental data also shows the correctness of the corrosion inhibition mechanism.
Key words: Chlorine dioxide; 2-phosphonobutane-1,2,4-tricarboxylic acid; hydroxyethylidene diphosphonic acid; aminotrimethylenephosphonic acid
The structure of organic corrosion inhibitors has a decisive influence on their corrosion inhibition performance. The use of quantum chemistry methods for the quantitative or semi-quantitative study of corrosion inhibition performance of corrosion inhibitors has important theoretical and practical significance. Since Vosta 1971 After studying organic corrosion inhibitors with HMO molecular orbital approximation method, the quantum chemistry calculation method has become an effective method to study the relationship between corrosion inhibitor molecular structure and corrosion inhibition performance. Many scholars at home and abroad have studied various methods using various quantum chemical calculation methods. The quantitative relationship between the molecular structure of corrosion inhibitors and corrosion inhibition efficiency was studied according to the characteristics of the charge distribution , and it has been studied in quantum chemical studies with N and S corrosion inhibitors. Active exploration was made , but reports on the quantum chemistry of P-containing organic corrosion inhibitors have rarely been reported, and organophosphorus corrosion inhibitors are one of the most important inhibitors currently used. Therefore, It is a meaningful work to carry out theoretical exploration in this area. This paper studied the corrosion inhibition mechanism of PBTCA, HEDP and ATMP from the molecular and atomic level to evaluate the corrosion inhibition of organic phosphine corrosion inhibitors. Energy and to further the development of new low-phosphorus or phosphorus-free green corrosion inhibitors provide theoretical information.
One type of scale inhibitor that is currently particularly effective is a non-chemical ratio scale inhibitor. This type of scale inhibitor can achieve a significant scale inhibition effect when the concentration of the scale inhibitor is only a fraction or even a few percent of the concentration of calcium ions in the solution. On the contrary, natural phosphate ions and magnesium and zinc ions inhibit the growth of calcite crystals, the effect of which is directly proportional to the concentration . Over a long period of time, various theoretical models have been proposed for the scale inhibition effect of non-chemical inhibitors such as crystal nucleation suppression , growth position adsorption , surface charge change  and other models. However, the experimental facts verifying the above theoretical model are still lacking, especially the lack of experimental images that can directly reflect the micromorphological changes of the scale inhibition process.
1? corrosion inhibitor corrosion test
1?1? Corrosion Inhibition of Organic Phosphine Agents
The test solution is a mixture of standard water, C l O 2 and corrosion inhibitor. The concentration of PBTCA, HEDP and ATMP is changed to study the effect of the concentration change on the corrosion inhibition effect. The concentration of C l O 2 added is 7 0 mg/L. (40?0 ? 1?0) ?, p H value is 9?0, rotation time is 72 h
Experiments have shown that HEDP has a very good scale inhibition effect on flake-shaped rhombohedral crystals; however, the inhibition of rhombohedral crystal growth is not ideal.
1 ? Experimental The calcium carbonate crystal sample used for the experiment was artificially grown with a calcium carbonate supersaturated solution. The supersaturated solution of calcium carbonate is prepared by adding calcium hydroxide dropwise to carbonic acid, and the degree of supersaturation is about 3-4. Calcium carbonate seed crystals are generated by the spontaneous precipitation of an excess of calcium hydroxide in a solution of calcium carbonate. The seed crystals were introduced into a calcium carbonate supersaturated solution and incubated in a constant temperature water bath. The experimental temperature is controlled at (35 ? 1) ?. The cup solution used as a control was not supplemented with any drug. Another cup was added with HEDP of about 2 -10 4 kg/m3 after 0?5 h. After the calcium carbonate crystals were allowed to grow for 12 h, they were removed and observed by AFM.
The AFM experiment was conducted using a contact mode using an atomic force microscopy mirrored by Digital Instruments' Nano Scope ®a.
2 ? Discussion
(1) Under the light microscope, the crystal morphology grown with and without HEDP is indistinguishable. The AFM can obtain a clear image of the three-dimensional surface of the calcium carbonate crystal on the sub-micrometer scale, which can greatly deepen the understanding of the scale inhibition mechanism.
(2) A lot of AFM experiments have studied the step growth of calcite cleavage surface in supersaturated calcium carbonate solution.
(3) The AFM image shows that after the addition of HEDP, the morphology of rhombohedral crystals has undergone a fundamental change (Figures 4, 5). Figure 4 shows the appearance of a crystal with a refined structure, whereas in Figure 5 the crystal no longer has a flat crystal face, forming a polycrystalline surface structure. It can be inferred that HEDP cannot prevent the growth of this rhombohedral crystal; however, HEDP greatly affects the atomic arrangement and surface energy on the surface of calcium carbonate crystal and changes its original orderly growth.
(4) In order to further understand the change in crystal growth after the addition of HEDP, the surface topography of calcium carbonate rhombohedral crystals after approximately 1 h of addition of HEDP was also scanned.
(5) Sundara Rajam and Stephen Mann used SEM to study the crystal morphology of the presence of Li
(6) The different scale inhibition results of HEDP for different crystal forms also indirectly explain why the combination of different scale inhibitors will have better scale inhibition effect, and thus will also provide important help in designing scale inhibitors using molecular simulation methods.
3 Conclusions The use of AFM technology gives an intuitive and clear physical picture of the crystal growth process. From the experimental results, it can be inferred that the adsorption of the scale inhibitor on the surface of the crystal disrupts the normal growth process of the crystal, causing crystal distortion or even stopping the growth. The effect of scale inhibitors on different growth planes is of great significance for artificially designed scale inhibitor molecules for different applications.