Study of Transparent Nanocoating Based on Acrylic Specified for Short-term Corrosion Protection Materials

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1 Study of Transparent Nanocoating Based on Acrylic Specified for Short-term Corrosion Protection Materials PODJUKLOVÁ a, Kateřina SUCHÁNKOVÁ b Tomáš LANÍK c, Vratislav BÁRTEK d, Sylvie KOPAŇÁKOVÁ e, Petr ŠRUBAŘ f Kamila HRABOVSKÁ g a VŠB TU Ostrava, 17. listopadu 15, Ostrava-Poruba, ČR, jitka.podjuklova@vsb.cz b VŠB TU Ostrava,17. listopadu 15, Ostrava-Poruba, ČR, katerina.suchankova@vsb.cz c VŠB TU Ostrava, 17. listopadu 15, Ostrava-Poruba, ČR, tomas.lanik@vsb.cz d VŠB TU Ostrava, 17. listopadu 15, Ostrava-Poruba, ČR, vratislav.bartek@vsb.cz e VŠB TU Ostrava, 17. listopadu 15, Ostrava-Poruba, ČR, sylvie.kopanakova@vsb.cz f VŠB TU Ostrava, 17. listopadu 15, Ostrava-Poruba, ČR, petr.srubar@vsb.cz g VŠB TU Ostrava, 17. listopadu 15, Ostrava-Poruba, ČR, kamila.hrabovska@vsb.cz Abstract Nowadays nano-technology is one of the most extensive fields of scientific activities. As far as finishing is concerned, the field of nanotechnology mainly focuses on the sizes of individual ingredients and reduction in the thickness of the applied nano-coating. In other industrial sectors, such as metallurgical production of materials, it has been proved that application of nano-coatings influences corrosion resistance of metal substrate at a lower applied thickness. Pre-finishing of the substrate surface before application of nanocoating is also very important. Therefore, the coatings which are tolerant to the surface of the metal substrate are topical these days. Further development in this area will lead to a reduction in coating thickness, by means of which financial costs as well as environmental impact will be reduced. The contribution is focused on short-term anticorrosion protection of materials from metallurgical production, such as pipes intended for oil recovery. The finishing must meet the required lifetime of up to 6 months as for transportation and placement in the site, taking into account a corrosive environment with the corrosion category C5. Further, it is necessary to limit the pre-finishing of materials from metallurgical production to the lowest possible value. Two kinds of undercoat materials underwent experimental tests a rolled seamless pipe and Standard sheet samples. The STANDARD samples had been supplied with the specified finishing and roughness, which are used for laboratory testing and for development of paint systems. The samples of the rolled pipe were free of finishing after rolling. Transparent nano-coating was applied using pneumatic spraying to these base materials substrates. The transparent nano-coating had been modified in co-operation with the Russian Federation. The 60μm-thick nano-coating containing nano-particles on the basis of the corrosion inhibitors met the requirements for anticorrosion protection in the C5-environment for 3 to 6 months in these experimental tests. Key words: metallurgic production, paint system, corrosion resistance 1. INTRODUCTION Surface pre-finishing before application of protective coatings is a more and more topical issue these days. In practice, various kinds and qualities of steel are used. They vary in processing technology. The final surface quality and its suitability for the current type of protective coating and anticorrosion protection are derived from this technology. As far as short-term anticorrosion protection of materials from metallurgical production, such as pipes intended for oil recovery, which should be protected during transportation to the destination by means of transparent conservation, is concerned, pre-finishing of the surface needs to be

2 limited to the lowest possible value. There is an effort to modify the coating in order to meet the operating conditions and requirements needed by the practice. 2. EXPERIMENTAL MATERIAL Two types of undercoat materials were used for experimental work. The first one was a steel sheet, STANDARD type, and the other one was hot-rolled seamless pipe. The STANDARD samples are low-carbon cold-rolled seamless steel sheets sized mm, supplied cleaned and degreased. The samples of the steel pipes are made of low-alloy steel sized TR Ø mm. a) b) Fig. 1 a) Surface of the substrate material STANDARD, b) Surface of the substrate material PIPE (both photographed on electron microscope EDAX PHILIPS XL 30, magnification 500x) 2.1. Nano-Coating Specifications The nano-coating used, which was supplied in co-operation with the Russian Federation, is intended for short-term protection of steel substrate. It is a water-borne system with low contents of volatile organic compounds. The nano-coating contains additives, volatile compounds, film-forming compounds, reducers and phosphate corrosion inhibitors based on sodium and drying salts with an admixture of manganese. The anticorrosion pigment, together with the corrosion inhibitors, forms a several-nano-meter thin protective layer on the metal surface of the substrate. The inhibitor is adsorbed during nano-coating application to the steel substrate surface and the reaction between the substrate and the nano-coating causes formation of a 50- nm-thick passivating layer. 3. EXPERIMENTAL WORK Before application of the two types of water-borne transparent nano-coating, the PIPE samples were preheated to 40 C due to simulation of operating conditions. The STANDARD samples were not pre-heated. The nano-coating was applied to the steel substrate by means of the pneumatic spraying method in one 150 μm-thick wet layer. For one type of the nano-coating, pipeline water was used, whereas for the other type of the nano-coating, distilled water was used. The thickness of the transparent nano-coating after drying ranged about 60 μm.

3 3.1. Determination ph for Nano-Coating Solution Measuring was carried out using the potentiometer method. The principle consists in the measuring of the potential of a couple consisting of a measuring glass and a reference calomel electrode in a measured environment. The acidity of the measured solution is determined by the potential of the measuring glass electrode. The ph-value is expressed by a negative common logarithm of hydrogen-ion activity. ph-value measuring was carried out three times for each type of the nano-coating the one thinned by pipeline water and the one thinned by distilled water. Tab. 1 The measured ph-values of the paint system kind of nano-coating ph-values measured average phvalue RUS N (pipeline water) RUS D (distilled water) The measured ph-values show alkalinity of the nano-coating solution in both cases. The differences in the ph-values of the nano-coating thinned by pipeline water and the one thinned by distilled water are not significant Determination of Volatile Organic Compounds In order to determine the contents of volatile organic compounds (VOC), the gravimetric method, whose measuring principle is based on the measuring of the nano-coating weight loss during hardening, was used. The weight loss is measured in specific time intervals. The measuring of the loss was carried out using the PIONEER PA214C analytic scales. Each measured value of the weight loss was included into a graph and separately interspaced by logarithmic regression curves. Graph 1 Comparison of weight-loss dependencies on time It follows from graph 1 that the weight loss is similar for both the types of nano-coating. The position of the weight-loss curve for the RUS N nano-coating is caused by inaccuracy when including the input weights. The RUS N nano-coating weighed 8.96 g and the RUS D nano-coating weighed 7.55 g.

4 3.4. Nano-Indentation of the Nano-Coating Surface According to ČSN EN ISO The nano-indentation test is intended for the determination of the properties of the nano-coating under consideration, above all for the determination of the hardness. The principle consists in the penetration of a test body (indenter) into the tested substrate within the range of nano-meters up to micrometers. The nanoindentation test was carried out under dynamic activity of the indenter on the Triboindenter Ti950 apparatus. The shape of the used indenter was spherical. The test was carried out on the STANDARD metal testing panels with applied RUS N and RUS D nanocoatings. The PIPE-type sample did not undergo the test because of the roundness of the pipe surface, where the surface hardness is impossible to monitor. The maximum force of the indetation appartus in the Z axis (indexation axis) was 10 nm, and in the X axis (the scratch axis) the force was 2 mn. The maximus shift was 0.04 nm in the Z axis and 4 nm in the X axis. Graph 2 Upper layer hardness of the experimental nano-coatings It follows from graph 2 that the deeper the impression, the lower the hardness value. This applies to both monitored samples, i.e. RUS D and RUS N. Based on the depth of the impression, the surface hardness values are almost the same in both instances. Generally speaking, both of the nano-coatings are comparable as to their hardness Phase Interface Micrographs of the substrate nano-coating interface were taken by the EDAX electron microscope in the Nano-Technology Centre at VŠB TU Ostrava. RUS D RUS N a) b) Fig. 2 a) Phase interface of the STANDARD sample with the nano-coating thinned by distilled water, b) Phase interface of the STANDARD sample with the nano-coating thinned by pipeline water (both zoomed 1000 )

5 It is evident from the micrographs that the STANDARD samples show even phase interface. On both micrographs, a thin white strip over the whole phase interface on the undercoat substrate surface can be seen. This is the passivation layer of the corrosion phosphate inhibitors. Neither of the micrographs shows any defects between the undercoat substrate and nano-coating. Even and integral layers of nano-coatings on the substrate were formed and, as to their adhesiveness, both types of nano-coatings adhered to the undercoat substrate surfaces well. RUS D RUS N a) b) Fig. 3 a) Phase interface of the PIPE sample with the nano-coating thinned by distilled water, b) Phase interface of the PIPE sample with the nano-coating thinned by pipeline water (both zoomed 1000 ) The micrographs show the phase interface between the nano-coatings and undercoat substrates. The phase interface on the PIPE samples is more jagged compared to the STANDARD samples. This jaggedness is caused by uneven thickness of the nano-coatings, above all by the character of oxides occurring on the surface of the undercoat substrates. The micrographs also show that both nano-coatings pour into individual pores and profiles of the undercoat substrates, and there are no defects in the phase interface and the integral layer of nano-coatings formed Corrosion Test in Salt Spray According to ČSN ISO 9227 Within the experimental work, a corrosion resistance test in the LIEBISCH S400 M-TR salt corrosion chamber was conducted. Exposure of the samples in the salt chamber is, if converted, comparable to exposure of the samples in the C5 corrosion environment. The exposure time of the samples in the corrosion chamber was 48 hours. The assessment of the samples was carried out in accordance with the ČSN EN ISO 4628 standard. Tab. 2 The resultant classification of blistering and degradation of the STANDARD and PIPE samples Exposure time [hrs] Blistering classification Delamination/corrosion STANDARD PIPE STANDARD PIPE RUS D RUS N RUS D RUS N RUS D RUS N RUS D RUS N 0 0 (S0) 0 (S0) 0 (S0) 0 (S0) 0/0 0/0 0/0 0/0 8 3 (S2) 0 (S0) 0 (S0) 0 (S0) 1/0 0/0 1/0 0/ (S2) 0 (S0) 2 (S2) 0 (S0) 2/1 1/0 3/1 1/ (S2) 3 (S2) 4 (S2) 2 (S2) 3/2 2/1 3/1 2/ (S3) 5 (S2) 5 (S3) 4 (S3) 4/2 3/2 4/2 4/2

6 The PIPE-type samples with applied nano-coatings show better assessment of blistering compared to the STANDARD-type samples, which tended to blistering more. The assessment, as far as the type of paint systems more resistant to blistering effects is concerned, brought the result that the RUS N paint system is more suitable. As to degradation of nano-coatings, the STANDARD-type samples showed worsened corrosion resistance compared to the PIPE-type samples, which was caused by the application of pre-heating, which was used only for the PIPE samples. Substrate pre-heating influences reduction in water content in the nano-coating during its application to a certain limit. Thus, it reduces the tendency of the substrate surface towards formation of flash corrosion. 4. CONCLUSION The ph-value of both the nano-coating solutions before their actual application showed alkalinity of the solutions. Further, measuring of volatile organic compounds was carried out with the nano-coatings. The results showed that both nano-coatings contain a reduced amount of these volatile organic compounds. The nano-indentation test of nano-coatings showed that the hardness value decreases from the coating surface towards the substrate. Thus, it can be assessed that both nano-coatings are comparable as far as hardness is concerned. It is evident from the micrographs of the phase interface that the formed coatings are even, integral, free from defects for both types of nano-coatings and that the coatings adhered perfectly. The STANDARD-type samples showed worse corrosion properties compared to the PIPE-type samples. The corrosion resistance was better for the RUS N-type nano-coating compared to the RUS-D type nano-coating, which had been thinned by distilled water. One of the features of distilled water is that it returns to a balanced state. This means that it binds the substances which it misses, and it has a stronger tendency to corrosion attack if it is in contact with the surface material. Therefore, thinning with pipeline water is more suitable for nano-coating application. It can be assessed that both nano-coatings are suitable for application to the PIPE-type unfinished metal substrate. As to corrosion resistance, both nano-coatings are suitable for short-term anticorrosion protection for a period of 3 to 6 months in an environment with the C5 corrosion category. The contribution was prepared with the support of the Ministry of Education project KONTAKT ME LITERATURE [1] POLANSKÝ, L. Study of Influence Relief Surface Steel Substrate on Adhesion of Protective Coatings. Department of Mechanical Technology, Faculty of Mechanical Engineering - Technical University of Ostrava, 2012, 96 pp. Diploma thesis, Supervisor: Podjuklová, J.