Procedia Chemistry 10 ( 2014 ) 349 – 357

1876-6196 © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Peer-review under responsibility of Tomsk Polytechnic Universitydoi: 10.1016/j.proche.2014.10.059

Available online at www.sciencedirect.com

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XV International Scientific Conference “Chemistry and Chemical Engineering in XXI century” dedicated to Professor L.P. Kulyov

Laminated Composition Coatings

Konstantinova T.A.a,b*, Mamaev A.I.a,b, Chubenko A.K.b, Mamaeva V.A.b, Beletskaya E.Yu.a,b

aTomsk State University, 36 Lenina ave., Tomsk, 634050, Russia b Sibspark Ltd, 8/8 Akademichesky ave., Tomsk, 634021, Russia

Abstract

The present paper discusses the results of research into production of thermally stable composition coatings that have nanostructured inorganic non-metallic coating (NIN coating) of different compositions on zirconium alloy substrate as their part, as well as metals introduced into coating pores. Researchers identified optimal conditions of microplasma treatment, as well as composition of electrolyte solutions for each stage of composition material production. Was used to construct and analyze current-voltage characteristics obtained in the course of electrical impact upon samples. Phase and element composition of NIN coatings, surface morphology of NIN coatings and coatings with metal injected into were studied. © 2014 The Authors. Published by Elsevier B.V. Peer-review under responsibility of Tomsk Polytechnic University.

Keywords: Thermally stable coating, composition coating, laminated coating, nanostructured inorganic non-metallic coating, in situ diagnostics, current-voltage dependencies, metal-ceramic coating, microplasma oxidation, items made of zirconium.

1. Introduction

It was earlier established in papers by A.I. Mamaev and research team of Sibspark Ltd1-3 that at the initial stage of oxide film formation on the metal or alloy under certain microplasma regime conditions voltage-current dependencies are the measurement system response and they reflect the element composition of valve metal alloys, their crystalline structure and presence of defects. Properties and characteristics of the coating formed in the

* Corresponding author. Tel.: +7-382-248-8550 E-mail address: konstantinova.ta9@gmail.com

© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Peer-review under responsibility of Tomsk Polytechnic University

350 T.A. Konstantinova et al. / Procedia Chemistry 10 ( 2014 ) 349 – 357

microplasma regime depend on the process mode, electrolyte composition and concentration of components. That is why this method allows producing new materials with preset properties and carrying out direct non-destructive in-situ4 diagnostics of the product quality.

At present there is a pressing need to develop new construction materials suitable for non-destructive operation under high-temperature conditions5. They find application in heavy and light industries, automotive industry, aircraft engineering etc.

Laminated materials possess a unique complex of physical and mechanical properties significantly exceeding the properties of monolithic materials. After deposition of the oxide ceramics layer on the metal or alloy surface, material will acquire new surface properties inherent to ceramics, such as hardness, wear-resistance, heat resistance etc.; furthermore, it is characterized by bulk properties of the material itself (structural strength).

The goal of the present research is to design a thermally stable composition coating.

Nomenclature

NIN coating nanostructured inorganic non-metallic coating

2. Idea of thermally stable coating design

The idea of producing a thermally stable composition coating lies in the need to form layers, where each subsequent layer has higher boiling heat than the previous one.

On the basis of literature review6-9 zirconium E110 alloy was chosen as the main material. Parameters of the metal and its oxide10-12 are presented in Table 1.

Table 1. Physical properties of zirconium and zirconium oxide

Material

Den-sity, g/cm3

Melting tempera-ture, °С

Boiling temperature, °С

Specific melting heat, kJ/kg

Specific boiling heat, kJ/kg

Specific heat capacity (25-100°С), kJ/(kg·K)

Specific electrical resistivity(20°С), microhm·cm

Linear thermal expansion coefficient ∙10-6, °С-1

Zr 6.506 1862 4409 210.47 6.215 0.291 44.1 5.7 ZrO2 5.68 2715 4273 730 - - - 10-11

Scheme of the laminated thermally stable material is presented in Fig. 1.

Fig. 1. Cross-section of laminated material structure.

1 – base material; 2 – porous nanostructured inorganic non-metallic coating; 3 – metal in pores; 4 – coating made of metal injected into pores or metal of other nature; 5 – through pores of the nanostructured inorganic non-metallic coating.

Thickness, structure and porosity of the nanostructured inorganic non-metallic coating (NIN coating) are

regulated by deposition time, driving voltage and pulse duration, while nature of the deposited material is regulated by electrolyte composition.

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During high-temperature impact on hardware in the course of operation, as well as in case of continued stay

under such conditions, parts of hardware might break down, which will result in disruption of the whole system operation. In order to remove heat and balance the temperature field10-12, researchers used an opportunity to inject functional thermal conductivity materials into NIN coating pores, for instance, copper with properties10-12 listed in table 2. Quasiuniform pores and possibility of quasiuniform filling of pores with metallic materials, such as copper, allow avoiding heat accumulation.

Table 2. Copper properties

Ma-terial

Den-sity, g/cm3

Melting tempe-rature, °С

Boiling temperature, °С

Specific melting heat, kJ/kg

Specific boiling heat, kJ/kg

Specific heat capacity (25-100°С), kJ/(kg·K)

Specific electrical resistivety (20°С), microhm ·cm

Thermal conducti-vity (20°С), W/(m·K)

Linear thermal expansion coefficient ∙10-6, °С-1

Cu 8.96 1083 2600 213 4.790 385.48 1.68·10-8 394.279 16.7 3. Experimental 3.1. Zirconium alloy oxidation

On the basis of literature review2, 13-15 researchers considered the following electrolyte solution options when

studying formation of functional coatings on zirconium alloys using microplasma oxidation method: acid14, silicate and silicate-alkaline15.

Silicate and silicate-alkaline electrolytes primarily consist of alkali metal silicates and alkali silicates or silicates of salt giving alkaline medium and working as a buffer to prevent hydrolysis. Coatings resistant to corrosion and abrasive wear are formed in this type of electrolytes. Coatings primarily consist of zirconium oxides and silicates, as well as oxides and silicates of alloy components. They are formed on the basis of the following mechanism1, 2:

eOHZrOHZr 44 4 ;

24322 223 HNaOHZrSiOSiONaOHZr ; OHZrOOHZr t

224 2 . (1)

Acid electrolyte contains soluble organic acids (ethane, acetic, citric acid etc.). Coatings produced in the acid electrolyte consist of zirconium oxides and are formed on the basis of the following mechanism1:

eOHZrOHZr 44 4

OHZrOOHZr t224 2 . (2)

Zirconium alloy was treated with microplasma at driving anode voltage of 300 V and pulse duration of 100 mcs for 5 minutes for each electrolyte.

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The treated sample of zirconium alloy served as anode. Electrolyte temperature in the bath did not exceed 40ºС.

Dense uniform coatings having brown, grey and light blue-grey color are formed as a result (Fig. 2).

a b c

Fig. 2. Coatings formed on zirconium electrolyte (E110) by microplasma oxidation method: (а) in silicate electrolyte; (b) in silicate-alkaline electrolyte; (c) in acid electrolyte.

3.1.1. Testing of nanostructured inorganic non-metallic coatings produced on zirconium E110 alloy

Coating thickness was determined using QuaNix 1500 eddy current thickness gauge. It was found out that thickness of coatings formed under the same microplasma treatment conditions depends on the nature of electrolyte. Coating with 32 mcm thickness was produced in the silicate electrolyte, with 20 mcm thickness – in silicate-alkaline electrolyte, with 5 mcm – in acid electrolyte.

When forming the coating in the course of microplasma oxidation, information and measurement complex developed under the leadership of A.I. Mamaev1, 2 was used to put current-voltage characteristics on the graph and analyze them (Fig. 3).

a)

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b)

c)

Fig. 3. Current-voltage characteristics obtained in the course of coating formation on zirconium in different electrolytes: (а) silicate; (b) silicate-alkaline; (c) acid.

Based on variation in active (Ia) and capacitive (Ic) current components, one can make a conclusion about the rate

of coating formation depending on electrolyte composition. The shape of current-voltage curves indicates that in silicate electrolyte the rate of coating formation is higher than in silicate-alkaline and acid electrolytes. The lowest rate of formation is seen in acid electrolyte. One can suggest that in silicate electrolyte a thick dense coating is formed within 5 minutes. In case of silicate-alkaline electrolyte a less thick uniform coating is formed, and a thin coating is formed in acid electrolyte. Information obtained on the basis of current-voltage curves conforms well to experimental data on coating thickness.

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One can see that when coating was formed in silicate electrolyte, the value of active current component went down 10 times in the course of the process and by the time the process was complete it was 2 A, while capacitive current value was 22.5 A. In silicate-alkaline electrolyte the value of active current component underwent a practically twofold reduction, and by the time the process was complete it was 12 A, while value of capacitive current was 12.5 A. In case of process in acid electrolyte the values of active and capacitive components were practically unchanged in the course of 5 minutes and were 25 A and 2.5 A respectively. 3.1.2. Morphology of the coating surface, pore size, porosity

Sample surface morphology was studied using scanning electron microscope SEM 515. Photos obtained indicate

that fine-pored coating was deposited on zirconium alloy in silicate electrolyte, the average size of pores is 1 mcm, and there are some pores with size up to 3 mcm. Coating porosity is 5% (Fig. 4). Surface morphology of the coating produced in silicate-alkaline electrolyte is presented in Fig. 5. Average size of pores is 0.5 mcm; general porosity is approximately 15-20%.

Coating produced in acid electrolyte is thin and dense. There are practically no pores in the coating. Average size of pores is visible at 10000 magnification, it is 0.2 mcm, and general porosity of the coating is approximately 0.5% (Fig. 6).

a b c

Fig. 4. Morphology of nanostructured inorganic non-metallic coating on zirconium alloy formed by method of microplasma oxidation in silicate electrolyte: (а) magnification 500; (b) magnification 2 000; (c) magnification 10 000.

a b c

Fig. 5. Morphology of the nanostructured inorganic non-metallic coating on zirconium alloy formed by method of microplasma oxidation in silicate-alkaline electrolyte: (а) magnification 500; (b) magnification 2 000; (c) magnification 10 000.

a b c

Fig. 6. Morphology of the nanostructured inorganic non-metallic coating on zirconium alloy formed by method of microplasma oxidation on acid electrolyte: (а) magnification 500; (b) magnification 2 000; (c) magnification 10 000.

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Microphotographs obtained conform well to current-voltage dependencies. One can see that the size of pores

changes as a result of variation in electrolyte composition. 3.1.3. Phase and element composition of NIN coating

Phase composition of NIN coatings was studied using XRD-6000 diffractometer. Data were obtained for coating formed in silicate-alkaline and acid electrolytes (Table 3). It was confirmed that electrolyte composition has an impact upon oxide composition of the coating. Nanocrystalline and amorphous phase is present in coatings on zirconium. Size of coherent-scattering regions of coatings is within the range of 15-30 nm, i.e. coatings are nanostructured and have a sufficiently developed surface, which can explain the presence of unique properties.

Table 3. Phase analysis of NIN coatings on zirconium E110 alloy

Electrolyte Phases identified Phase content, volume %

Grid parameters, Ǻ

Size of coherent-scattering regions, nm

∆d/d*10-3

Acid

ZrO2 86.5 а=5.169 16 8.856 Zr3O 13.1 а=5.612

c=5.162 26 3.728

Traces of ZrC, ZrC0.47O0.15 phases, as well as X-ray amorphous phase are present in the sample

Silicate-alkaline

ZrO2 92.3 а=5.169 27 1.335 ZrSiO4 7.6 а=5.612

c=5.162 14 2.61

Traces of Zr, Zr5P3, ZrB2O5, ZrSi phases, as well as X-ray amorphous phase are present in the sample

Semiquantative estimation of the sample element composition was carried out using EDAX Genesis microanalyzer. Data are presented in table 4.

Table 4. Element composition of NIN coatings on zirconium alloy E110

Element Electrolyte C, % mass O, % mass Zr, % mass Si, % mass

Silicate 7.3 29.6 60.9 2.2

Silicate-alkaline 5.2 23.1 56.3 15.4

Acid 15.3 16.4 68.3 -

These data demonstrate that oxygen prevails in the composition of coatings obtained on zirconium alloy in

silicate and silicate-alkaline electrolyte, base element is zirconium, there is also significant quantity of silicon and carbon from electrolyte. Oxygen prevails in the composition of coatings obtained in acid electrolyte, base element is zirconium, there is also significant amount of carbon.

Results of phase and element analysis indicate that change in coating composition occurs as a result of change in electrolyte composition.

At the first stage silicate electrolyte was selected for thermally stable composition coatings. This choice is explained by the fact that corrosion-resistant thermally stable coatings are formed in silicate electrolyte16 and have quasiuniform position of pores.

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3.2. Metallization of nanostructured inorganic non-metallic coating Copper-plating was the next stage. Introduction of copper into NIN coatings was carried out by electrochemical

method in pyrophosphate electrolyte17. The process was carried out on the basis of the following scheme18:

62722726 6 OPCuKOPCuK ;

7222

726272 2)( OPHOPCuHOPCu ;

472

272 )(2 OPCueOPCu . (3)

As a result copper is deposited in the pores of NIN coating (Fig. 7).

a b

Fig. 7. Surface microphotographs of the E110 zirconium alloy sample at different stages of treatment, 2000 and 5000 magnification respectively: (а) porous NIN coating produced by method of microplasma oxidation; (b) NIN coating, into the pores of which functional material (copper) was

introduced. Relying on the method described, one can produce composition coatings consisting of inorganic material (NIN

coatings) and metal of different nature (silver, copper, nickel) depending on the application field. Presence of metal in the pores of NIN coating does not exclude the possibility of depositing additional layers of different nature on it, according to the scheme given in Fig. 1.

The obtained laminated metal-ceramic coatings are currently on research of thermophysical properties.

4. Conclusions:

1. Thermally stable composition coating was designed for structural parts operated at high temperatures. Composition coating is a nanostructured inorganic non-metallic coating on the part surface, into the pores of which a certain material was injected – in this case copper.

2. Properties of NIN coatings are determined by microplasma regime and composition of electrolyte solution and are controlled in the course of formation relying on current-voltage curves produced using information and measurement complex.

3. Presence of metallic surface layer does not exclude the possibility of depositing additional layers of different nature.

Acknowledgement

This work was financially supported by the Ministry of Education and Science of Russian Federation, Assignment № 16.461.2014 / K for performing research work in the framework of project of the state assignment in the field of scientific activity.

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