ELECTRODE MATERIAL FOR GLASS MELTING FURNACE

Abstract: An electrode material for glass melting furnaces, having a composition comprising 25 to 40 wt% of chromium, 10 to 45 wt% of cobalt, optionally 0.1 to 1.5 wt% of titanium, optionally 0.01 to 0.50 wt% of one or a plurality of REMs, and the balance of nickel and unavoidable impurities.

Description: Technical Field The present invention relates to an electrode material of a glass melting furnace having an excellent corrosion resistance in molten glass in an energized state and utilizable as an electrode material of glass melting furnace. Background Art The composition of the ternary alloy Ni-40%Cr-10%Co is known from Chem. Abs., 79 , (1973), 151, 10 74 50e, for example. Moreover, the ternary phase diagram of Ni-Cr-Co is generally known from Fig. 21, Cobalt and its alloys, W. Betteridge, John Wiley & Sons, (1982), 52-53. Also, Nickel und Nickellegierungen, K.E. Volk, Springer Verlag, (1970), 253-254, discloses an alloy consisting of Ni-20%Cr-18%Co-Ti. Examples of electrode material of a glass melting furnace which have hitherto been used include a molybdenum-base alloy comprising 10 to 60% of copper and 0.5 to 5% of barium (see Japanese Patent Laid-Open No. 88739/1974), a platinum-base alloy comprising 1 to 20% of rhodium and 0.5 to 5% of tungsten (see Japanese Patent Laid-Open No. 51124/1978), and further those using tin oxide and those using a nickel-base alloy. Examples of the nickel-base alloy include Inconel 690 which is a nickel-base alloy comprising about 30% of chromium and about 9% of iron. Since this type of electrode of a glass melting furnace is used in molten glass in an energized state, it must have not only an excellent corrosion resistance in molten glass in an energized state but also a high melting point for the purpose of improving the operability of the melting furnace. Conventional electrode materials, however, had problems such as poor corrosion resistance in molten glass and low melting point. For example, Inconel 690 which is a nickel-base alloy comprising the above-described ingredients is not always excellent in the corrosion resistance in molten glass and has also a drawback that the melting point is as low as about 1350°C. The present invention has been made in view of the problem accompanying conventional electrodes particularly comprising a nickel-base alloy. An object of the present invention is to provide a nickel-base electrode material of a glass melting furnace which has an excellent corrosion resistance in molten glass ln an energized state and a melting point above 1350°C, i.e., the melting point of the above-described conventional nickel-base Inconel, and is suitable as an electrode material of a glass melting furnace. Disclosure of the Invention The electrode material of a glass melting furnace excellent in the corrosion resistance in molten glass in an energized state according to the present invention is characterized by having a chemical composition comprising by weight 25 to 40% of chromium, 10 to 45% of cobalt, optionally 0.1 to 1.5% of titanium and optionally 0.01 to 0.50% of at least one element selected from among REMs (rare earth metals) with the balance consisting of nickel and unavoidable impurities. More particular, in a first embodiment, the present invention provides the use of an alloy consisting of (in wt %): 25 to 40% chromium, 10 to 45% cobalt, optionally: 0.1 to 1.5% titanium, 0.01 to 0.5% of at least one element selected from the rare earth metals, the balance being nickel and unavoidable impurities, for an electrode of a glass melting furnace, the said electrode having excellent corrosion resistance in molten glass in an energized state and, in a second embodiment, it provides a glass melting furnace characterised in that it comprises an electrode comprising such an alloy. The reason for the limitation of the chemical composition (% by weight) of the electrode material of a glass melting furnace excellent in the corrosion reisstance in molten glass in an energized state according to the present invention will now be described. Chromium: 25 - 40% Chromium is added for ensuring the corrosion resistance of an electrode used for electric melting of glass in a glass melting furnace and is limited to 25% or more for the purpose of ensuring the corrosion resistance of such an electrode. The upper limit of the chromium content is set to 40% or less because the addition of an excessive amount of chromium not only causes the effect to be saturated but also lowers the melting point and deteriorates the toughness of the electrode. Cobalt: 10 - 45% Cobalt is an element useful for improving the operability of the glass melting furnace through a rise of the melting point of the electrode and, at the same time, improving the corrosion resistance of the electrode in molten glass in an energized state. The cobalt content is limited to 10% or more for the purpose of attaining the effect of raising the melting point and improving the corrosion resistance of the electrode. The upper limit of the cobalt content is set to 45% or less because the addition of an excessive amount of cobalt not only causes the effect to be saturated but also deteriorates the toughness of the electrode. Titanium: 0.1 - 1.5% Titanium is an element useful for improving the resistance Of the electrode to molten glass in an energized state and, at the same time, attaining an improvement in the releasability of scale and may be optionally added in amount of 0.1% or more for attaining the effect of improving the above-described corrosion resistance and releasability of scale. The addition of an excessive amount of titanium, however, not only causes the effect to be saturated but also unfavorably lowers the melting point of the electrode. Therefore, when the titanium is added, the content should be 1.5% or less. At least one member selected from among REMs: 0.01 - 0.50% REM is an element useful for improving the corrosion resistance of the electrode in molten glass in an energized state and may be optionally added in an amount of 0.01% or more for the purpose of attaining such an effect. The addition of an excessive amount of REM, however, not only causes the effect to be saturated but also unfavorably deteriorates the toughness of the electrode. Therefore, when REM is added, the content should be 0.50% or less. Nickel: the balance Nickel is effective in ensuring the corrosion resistance of the electrode in molten glass as well as in improving the operability of a glass melting furnace by virtue of its high melting point. Therefore, nickel is usd as the balance. The electrode material of a glass melting furnace according to the present invention has the above-described chemical composition and comprises nickel having a high melting point and an excellent corrosion resistance as a matrix, and a suitable amount of chromium added for the purpose of ensuring the resistance of the electrode to corrosion by molten galss, a suitable amount of cobalt added for the purpose of improving the melting point of the electrode and the resistance to corrosion by molten glass, a suitable amount of titanium optionally added for the purpose of further improving the corrosion resistance and also the releasability of scale, and a suitable amount of at least one REM optionally added for allowing voides to stay inside the alloy to further improve the corrosion resistance. By virture of this constitution, the electrode material of the present invention has an excellent corrosion resistance in molten glass in an energized state, and the high melting point thereof serves to improve the operability of the melting furnace. Best Mode for Carrying out the Invention Nickel-base alloys comprising various chemical ingredients listed in Tabale 1 were molten by vacuum, induction melting to prepare ingots each having a weight of 30Kg. In Table 1, Mm represents mischmetal (La + Ce) among REMs and Inconel 690 was used in Comparative Example 1. Subsequently, each ingot was hot-forged to make a round bar having a diameter of 20 mm and a current was allowed to flow at a density of 0.8 A/cm² through the round bar at 1250°C in a molten borosilicate glass to determine the extent of corrosion (the extent of wearing out) under immersion for 100 hr in an energized state to thereby evaluate the resistance of the electrode to corrosion by molten glass. The results are given in Table 1. The solidus temperature of each nickel-base alloy was determined with a differential thermal analyzer. The results are also in Table 1. Division No. Chemical ingredients (wt.%) 1250°C/100 hr 0.8 A/cm² Extent of corrosion (µm) Solidus (°C) Cr Co Ti REM Ni Example 1 33.5 10.2 - - the balance 183 1393 2 33.6 18.0 - - the balance 196 1401 3 32.2 31.3 - - the balance 175 1408 4 27.5 15.6 - - the balance 194 1414 5 25.8 30.9 - - the balance 188 1433 6 37.1 31.5 - - the balance 189 1399 7 26.5 44.7 - - the balance 190 1436 8 37.1 44.2 - - the balance 199 1413 9 32.2 41.8 1.1 - the balance 177 1417 10 32.2 31.3 0.3 - the balance 164 1402 11 31.5 30.8 1.3 Y:0.09 the balance 185 1381 12 33.1 30.9 - Y:0.34 the balance 132 1380 13 30.9 34.2 0.2 Mm:0.15 the balance 146 1387 14 29.1 28.2 1.3 Mm:0.03 the balance 167 1362 Comp. Example 1 28.6 Fe:9.0 0.32 Al:0.28 the balance 356 1341 2 33.6 <0.01 - - the balance 216 1378 3 32.2 52.2 - - the balance 254 1414 4 42.0 <0.01 - - the balance 209 1356 5 42.0 15.9 - - the balance 207 1363 6 20.2 40.3 - - the balance 211 1430 As is apparent from the results given in Table 1, the electrode materials comprising nickel-base alloys of Examples 1 to 14 according to the present invention exhibited a less extent of corrosion in a molten borosilicate glass in an energized state, i.e., were found to have a superior resistance to corrosion by molten glass in an energized state. Further, they had a melting point above that of Inconel 690 (Comparative Example 1) which is a conventional nickel-base alloy, i.e., have been confirmed to be able to improve the operability of a glass melting furnace. By contrast, the nickel-base alloys of Comparative Examples 1 to 6 exhibited a larger extent of corrosion in molten glass in an energized state. This brings about a problem of durability when then are used as an electrode material. Further, some of them has a low melting point. The electrode material of a glass melting furnace according to the present invention has a composition comprising by weight 25 to 40% of chromium, 10to45% of cobalt, optionally 0.1 to 1.5% of titanium and optionally 0.01 to 0.50% of at least one element selected from among REMs with the balance consisting of nickel and unavoidable impurities and, by virture of this constitution, brings about such a remarkably excellent effect that it exhibits an excellent resistance to corrosion by molten glass in an energized state when used as an electrode material of a glass melting furnace and, at the same time, improves the operability of the glass melting furnace because of its higher melting point than that of Inconel 690, i.e., the conventional nickle-base alloy.

Claims: Use of an alloy consisting of (in wt %): 25 to 40% chromium, 10 to 45% cobalt, optionally: 0.1 to 1.5% titanium, 0.01 to 0.5% of at least one element selected from the rare earth metals, the balance being nickel and unavoidable impurities, for an electrode of a glass melting furnace, the said electrode having excellent corrosion resistance in molten glass in an energized state. A glass making furnace characterised in that it comprises an electrode comprising an alloy as defined in claim 1.

Inventors: IGARASHI HIROSHI - - USHIRONO, IIKUBO TOMOHITO - - ICHIBAN AT, MASAKI TOSHIO - - TAJIRI-CHO, SASAKI NORIAKI - MAWATARI, SHIMIZU TETSUYA - UBAKOYAMA KA, TORATA SHIN-ICHIRO C- AZA-TSUK, IGARASHI, HIROSHI, 1-4-11, USHIRONO, IIKUBO, TOMOHITO, 1-20-34, ICHIBAN ATSUTA-KU, MASAKI, TOSHIO, 3-48-11, TAJIRI-CHO, SASAKI, NORIAKI, 2774-20, MAWATARI, SHIMIZU, TETSUYA, 15-7, UBAKOYAMA KASADERA-CHO, TORATA, SHIN-ICHIRO, C-301, AZA-TSUKANOUE TAKABA
Applicants: DORYOKURO KAKUNENRYO, DORYOKURO KAKUNENRYO KAIHATSU JIGYODAN
Application year: 1990
Main classification: C22C19
IPC codes: C22C19, H05B3, C03B5, C22C30, C22C27