INFLUENCE OF INPUT RAW MATERIALS SIZE ON THE RESULTING BRITTLE-FRACTURE PROPERTIES OF VITREOUS ENAMEL COATINGS

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1 INFLUENCE OF INPUT RAW MATERIALS SIZE ON THE RESULTING BRITTLE-FRACTURE PROPERTIES OF VITREOUS ENAMEL COATINGS Sylvie KOPA ÁKOVÁ a, Jitka PODJUKLOVÁ b, Vratislav BÁRTEK c, Kamila HRABOVSKÁ d, Kate ina SUCHÁNKOVÁ e, Petr RUBA f, Tomá LANÍK g a V B TU Ostrava,7. listopadu 5, Ostrava-Poruba, R, sylvie.kopanakova.st@vsb.cz b V B TU Ostrava, 7. listopadu 5, Ostrava-Poruba, R, jitka.podjuklova@vsb.cz c V B TU Ostrava, 7. listopadu 5, Ostrava-Poruba, R, vratislav.bartek.st@vsb.cz d V B TU Ostrava, 7. listopadu 5, Ostrava-Poruba, R, kamila.hrabovska@vsb.cz e V B TU Ostrava, 7. listopadu 5, Ostrava-Poruba, R, katerina.suchankova.st@vsb.cz f V B TU Ostrava, 7. listopadu 5, Ostrava-Poruba, R, petr.srubar.st4@vsb.cz g V B TU Ostrava, 7. listopadu 5, Ostrava-Poruba, R, tomas.lanik.st@vsb.cz Abstract Vitreous enamel coatings are surface treatments which occur on metallic substrates by burning at a temperature above 800 C. These coatings provide good protection for metal materials against corrosion, aggressive environments and also significantly improve the surface properties of basic material. The resistance of the enamel coating to cracking and fracture can significantly reduce the risk of defects such as fish scales, chipping, cracking, etc. Vitreous coatings are widely used in many technology sectors (construction, engineering, architecture, medicine, food industry, chemical industry, etc). The most important inorganic components in the manufacture of these coatings are glassy frit, pigments and clay. Usage of different sizes of inorganic components has a large influence on the quality of the final coating. The size of the input components of inorganic nano-sized particles positively impacts the brittle-fracture properties of the vitreous enamel coating compared to conventional particle size. The experimental works focused on the comparison of particle sizes of clay on the resulting brittle-fracture properties and mechanical properties of vitreous enamel coatings. The raw materials input used a clay component of a conventional size in microns and the new nano scale. The fracture properties of enamel coatings are important for understanding the causes of defects in vitreous enamel coatings and their dissemination. The tests were focused on the testing of vitreous enamel coatings in contact with the biological environment and its influence on the brittle-fracture properties and mechanical properties of enamel coating. The current test results show the positive effect of the nano size of the input components on the properties of these coatings. Key words: vitreous enamel coat, brittle fracture, clay, break toughness

. INTRODUCTION Vitreous enamel coating is a method of surface protection. Enamel can be characterized as glass with a complex chemical composition which is applied on a metal substrate.

2 . INTRODUCTION Vitreous enamel coating is a method of surface protection. Enamel can be characterized as glass with a complex chemical composition which is applied on a metal substrate. The system metal enamel joins the plastic properties of metals and the anticorrosive properties of glasses. Continuous enamel coating is the basic prerequisite for its convenient functional properties, thus guaranteeing good resistance to highly aggressive environments and corrosion. The advantages of vitreous enamel coatings are its health wholesomeness, resistance to acids and abrasion resistance. On the other hand, its low value of fracture toughness causes low resistance to cracking and the emergence of cracks in enamel coating.. EXPERIMENTAL MATERIAL Steel with the trade mark of KOSMALT E300T (samples sizes mm) was used as substrate material for experimental tests. The samples were blasted to the substrate purity of Sa ½ according to ISO 850- by means of a cut wire. The experimental material was degreased in a solution of water and the degreasing agent SIMPLE GREEN in the ratio of 0:. The samples were being degreased at a temperature of 5.0 C and ph 9.44 for 5 minutes. Rinse was carried out by submersion into a water bath with a temperature of.7 C and ph 8.9 for the period of minute. The samples were being dried at 00 C for 5 minutes. Further, the enamelling slurry of ground enamel was applied onto the samples by means of manual spraying with a pressure spraying gun, and the samples were dried at 00 C for 5 minutes. Subsequent burning of the enamel coating was carried out at 850 C for 8 minutes. Cooling of the burned enamel coating was carried out in the air. Cover-coat enamelling slurry was applied onto samples with enamel cover-coat by means of manual spraying with a pressure spraying gun. The samples were dried at 00 C for 5 minutes, and burning of enamel coating was carried out at 850 C for 8 minutes. Ground and cover coat enamels with a nano-sized clay component in the contents of 3 and 6% were applied onto the samples A and A. Ground and cover coat enamels with a micro-sized component in the contents of 6 and 8% were applied onto the samples B and B. The samples were divided into two sets. The first set was intended for comparison and it was not exposed to the biological environment, while the other set was exposed to the biological environment (swine blood) at a temperature of 35 for 40 hours 3. Results of the Experimental Tests Within the frame of the experimental tests, the microhardness of the vitreous enamel coating according to SN ISO 456 was carried out and fracture toughness of the vitreous enamel coating was calculated.

3 It follows from graph that the ground (A, B) and cover (A, B) enamel coatings containing nano-sized clay components which had not been exposed to the biological environment did not show any significant differences in microhardness values. During exposure to the biological environment, a significant drop in the microhardness values occurred in the enamel coating containing fine clay components. The enamel coatings 3

4 containing common-sized components (A3, B3, A4, B4), increased in microhardness values after exposure to the biological environment occurred. 3.. Fracture Toughness Calculation for the Enamel Coating Fracture toughness value K IC was set by means of calculation based on the formula of Palmquist crack []: 5 r K IC c = 0,035 r E k Hv 0, Hv0, k [MPa.m ½ ] c Palmquist crack length [m] r half the length of the indentation diagonal [m] E tensile elasticity module E = 90 [MPa] H v0, Vickers hardness k dimensionless constant, for which k = 3 applies 4

$differences in the values of fracture toughness. For cover enamel coating containing nano-sized clay components (A, B), significant increases in the fracture toughness values occurred.$

5 It follows from the graph that the ground (A, B) enamel coatings containing nano-sized clay components which had not been exposed to the biological environment did not show any significant differences in the values of fracture toughness. For cover enamel coating containing nano-sized clay components (A, B), significant increases in the fracture toughness values occurred. While exposed to the biological environment, a significant drop in fracture toughness values in ground (A3, B3) and cover (A4, B4) enamel coating containing micro-sized clay components occurred. 4. CONCLUSION The experimental tests showed that the biological environment affects the brittle-fracture properties of vitreous enamel coatings based on enamel coatings. Better results of fracture toughness were obtained with the coatings with the nano-sized clay components. The size of clay in nanometers, compared to the common size in microns, favourably influences coating plasticity and its resistance to cracks and cracking occurrence. It also favourably influences the properties of the coating for the contact with the biological environment..literature USED AND CITED [] MEN IK, J.: Pevnost a lom skla a keramiky. Prague: SNTL, 990. [] KVOR, P.: Studium sklovitého smaltového povlaku v kontaktu s biologickým prost edím. Ostrava: V B Technical University Ostrava. Faculty of Mechanical Engineering. Department of Mechanical technology, p. Diploma thesis supervisor Assoc. Prof. habil. Ing. Ph.D. Prof. h. c. Jitka Podjuklová 5

23 rd International Enamel Congress Monday May 25 th 2015

23 rd International Enamel Congress Monday May 25 th 2015 New coatings for the functionalization of enamelled surfaces Giovanni Baldi Enamel is an extremely heat and abrasion resistant coating, able to