104
Remanufacturing and Advanced Machining
• Magnesium oxide (MgO) is a stronger flux than CaO. It increases hardness,
luster, strength, and elasticity of a glaze coating. It is introduced in the form
of opoka, talc, magnesite, and dolomite.
• Barium oxide (BaO) is a flux introduced in the form of barium carbonate.
It decreases the TCLE and, when introduced in a small amount, improves
luster and mechanical properties of a glaze.
• Zinc oxide (ZnO) is a good flux. It decreases the TCLE and facilitates crystallization and opacification of a glaze. It is added in the form of zinc white.
• Zirconium oxide (ZrO 2 ) is an opacifier that increases hardness and chemical resistance. It is introduced in its pure form or as zircon, which is itself
an opacifier.
• Tin oxide (SnO 2 ) is a better opacifier, increasing chemical resistance, especially alkali resistance.
As raw materials for technological temporary coatings, volcano glass and wastes
from glass production can be used. Addition of broken, used-up glass appears to be
very effective since it avoids melting of frits. Application of frits mixed with broken
EoL glass, volcanic ashes, and metallurgical slag seems to gain in popularity.
It should be noted that heat-resistant vitreous coatings of finished products may
be single-component or complex with a higher softening temperature than normal enamels. Crystalline coatings may be either entirely crystalline, composite,
or glassy-crystalline. Composite high-temperature coatings are a combination of a
glass matrix and refractory filler. They exhibit good operating and physicochemical properties as a result of combining the composition of multicomponent silicate
enamels and refractory or chemically stable fillers, and they are used to protect lowcarbon, unalloyed, and alloy steels, nickel, chromium–nickel, and titanium alloys
from high-temperature gas corrosion in aviation, rocket building, power generation,
metallurgy, and engineering (Kazak and Didenko, 2016).
Ceramic coatings can be divided into three groups, namely oxide, silicon-based,
and oxygen-free ceramics. Oxide ceramics consist of pure refractory and chemically
inert oxides, mainly Аl 2 O 3 , ZrO 2 , and MgО.
Alumina (Аl 2 O 3 ) can be considered one of the most chemically inert and heatresistant compounds. At 1705–1815 °С, Аl 2 O 3 is resistant to any gas, stable both
in oxidizing and highly reducing atmospheres (Gevorkyan and Nerubatskyi, 2009).
Thus, alumina is able to create a thermal diffusive barrier on the surface of a protected alloy. Content of alumina in a coating can often reach 80 and even 90%.
Zirconia (ZrO 2 ) at ca. 1000°С transforms its monolithic crystalline to a tetragonal
structure (Gevorkyan et al., 2010). Since the transition is accompanied by substantial
volume change of ca. 10%, zirconia can be successfully applied as a self-removable
technological coating. In addition, its relatively low thermal conductivity promotes
destruction of such a temporary coating.
Zircon (ZrO 2 ·SiO 2 or ZrSiO 4 ) is a silicate mineral with a strong bond between
zirconia (ZrO 2 ) and silica (SiO 2 ), which makes zircon an exceptionally stable compound with low thermal expansion and thermal conductivity, excellent corrosion
resistance even at temperatures as high as 1285–1700°C (Kaiser et al., 2008).
Remanufacturing and Advanced Machining
• Magnesium oxide (MgO) is a stronger flux than CaO. It increases hardness,
luster, strength, and elasticity of a glaze coating. It is introduced in the form
of opoka, talc, magnesite, and dolomite.
• Barium oxide (BaO) is a flux introduced in the form of barium carbonate.
It decreases the TCLE and, when introduced in a small amount, improves
luster and mechanical properties of a glaze.
• Zinc oxide (ZnO) is a good flux. It decreases the TCLE and facilitates crystallization and opacification of a glaze. It is added in the form of zinc white.
• Zirconium oxide (ZrO 2 ) is an opacifier that increases hardness and chemical resistance. It is introduced in its pure form or as zircon, which is itself
an opacifier.
• Tin oxide (SnO 2 ) is a better opacifier, increasing chemical resistance, especially alkali resistance.
As raw materials for technological temporary coatings, volcano glass and wastes
from glass production can be used. Addition of broken, used-up glass appears to be
very effective since it avoids melting of frits. Application of frits mixed with broken
EoL glass, volcanic ashes, and metallurgical slag seems to gain in popularity.
It should be noted that heat-resistant vitreous coatings of finished products may
be single-component or complex with a higher softening temperature than normal enamels. Crystalline coatings may be either entirely crystalline, composite,
or glassy-crystalline. Composite high-temperature coatings are a combination of a
glass matrix and refractory filler. They exhibit good operating and physicochemical properties as a result of combining the composition of multicomponent silicate
enamels and refractory or chemically stable fillers, and they are used to protect lowcarbon, unalloyed, and alloy steels, nickel, chromium–nickel, and titanium alloys
from high-temperature gas corrosion in aviation, rocket building, power generation,
metallurgy, and engineering (Kazak and Didenko, 2016).
Ceramic coatings can be divided into three groups, namely oxide, silicon-based,
and oxygen-free ceramics. Oxide ceramics consist of pure refractory and chemically
inert oxides, mainly Аl 2 O 3 , ZrO 2 , and MgО.
Alumina (Аl 2 O 3 ) can be considered one of the most chemically inert and heatresistant compounds. At 1705–1815 °С, Аl 2 O 3 is resistant to any gas, stable both
in oxidizing and highly reducing atmospheres (Gevorkyan and Nerubatskyi, 2009).
Thus, alumina is able to create a thermal diffusive barrier on the surface of a protected alloy. Content of alumina in a coating can often reach 80 and even 90%.
Zirconia (ZrO 2 ) at ca. 1000°С transforms its monolithic crystalline to a tetragonal
structure (Gevorkyan et al., 2010). Since the transition is accompanied by substantial
volume change of ca. 10%, zirconia can be successfully applied as a self-removable
technological coating. In addition, its relatively low thermal conductivity promotes
destruction of such a temporary coating.
Zircon (ZrO 2 ·SiO 2 or ZrSiO 4 ) is a silicate mineral with a strong bond between
zirconia (ZrO 2 ) and silica (SiO 2 ), which makes zircon an exceptionally stable compound with low thermal expansion and thermal conductivity, excellent corrosion
resistance even at temperatures as high as 1285–1700°C (Kaiser et al., 2008).