PSI - Issue 28

Nina Ogoreltceva et al. / Procedia Structural Integrity 28 (2020) 1340–1346 Nina Ogoreltceva et al. / Structural Integrity Procedia 00 (2019) 000–000

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physical and mechanical properties of baked coating the different component ratios were used (wt. %): 65-40 of TiB 2 and 35-60 of the water-soluble binder (water/binder ratio was 2:1) as it has been demonstrated in Patent RU 2724236 (2019). The coating compositions were prepared using a high-speed mixer in order to avoid the agglomeration and subsidence of the TiB 2 particles. The resulting coating composition in form of liquid suspension was applied to a 50mm x 50mm carbon cathode substrate and formed into laboratory specimens with dimensions corresponded to appropriate standards in order to characterise physical and mechanical properties of material. The TiB 2 -C composite forms during fallowing cycle: drying at room temperature (RT) during 24 hours, heating from RT over 72 hours to 950 ºС in laboratory chamber furnace, holding at this temperature for 5 hours and then cooling to room temperature. The baking at temperature which is much lower than the sintering temperature of TiB 2 is strictly related to real operating conditions of industrial cells. The thickness of coating was 1  3 mm. Prior to coating procedure the bonding layer of the thickness of 0.2-0.5 mm were applied on the surface of carbon cathode substrate to provide a stronger bond due to penetration into the pore structure of the carbon cathode blocks. The coating was protected against oxidation using a graphite powder bed with the thickness of 15-30 mm. The necessity of using the reducing atmosphere is explained by the active oxidation of TiB 2 at temperatures above 800 °C in the presence of oxygen. The physical and mechanical properties of laboratory specimens of coating were determined according to ISO standards. The methods of measuring and used equipment are listed in Table 1. Table 1. Method of determination of physical and mechanical properties of laboratory specimens of TiB 2 -based coating Parameters Method of determination/Equipment Standard Apparent density,  (g/cm 3 ) Dimensions and hydrostatic method ISO 12985-1:2014; ISO 12985-2:2014 Open porosity,  (%) Hydrostatic method ISO 12985-2:2014 Compressive strength at RT,  c (MPa) Compressive test / Instron 3369 with Bluehill 3 (Instron Corp., U.K.) ISO 18515:2014 Electrical resistivity at RT and at 950º C, ER (µ  m) ISO 11713:2000

Four-terminal method/Multimeter APPA 107(N) and MATRIX MPS– 1820L-1 DC source Dilatometry/DIL402C (NETZSCH, Germany) Pull-off test/ Instron 3369 with Bluehill 3 (Instron Corp., U.K.) Portable Hardness Tester TH130 (TIME Group Inc, China) Laboratory electrolysis cell to study corrosion and wear behavior Visual assessment after 1h of electrolysis/ Laboratory electrolysis cell

ISO 14420:2005

Coefficient of linear thermal expansion, CTE (10 -6 , К -1 )

Adhesion strength,  adh (MPa)

ISO 18515:2014

Hardness, (HB)

Wear rate, v (сm/year)

Wettability by molten aluminium

As shown in Table 1, the wear rate was measured using a laboratory electrolysis cell that has been designed previously for cathode corrosion and wear tests within the project 0.2. G25.31.0181 (Decision of the Government of the Russian Federation no. 218 of April 9, 2018). The wear rate of the coating was also monitored performing the industrial test by measuring the mass fraction of titanium and boron in aluminium as well as iron and silicon using an optical emission spectrometer ARL3560 (ThermoARL, Switzerland) according to OAO RUSAL Sayanogorsk Enterprise Standard STP-4.82.12-2012 “Primary and Deformable Aluminum. Method of Optical Atomic-Emission Spectrometry of Determining Mass Fractions of Impurities”. The control of the current distribution over blooms and the voltage drop was also performed according to the standardised procedures of OAO RUSAL Sayanogorsk.