The gas penetrates into the refractory bricks from the furnace space, accompanied by a series of physical and chemical processes. This depends on the gas composition, refractory brick composition and temperature. As refractory materials interact with gases, most will lose mechanical strength, thermal shock resistance, and in some cases even refractory resistance.
Chemical Reactions between Refractory Materials and Various Gases
(1) Interaction with water vapor and CO2
Calcium-containing refractory bricks are destroyed due to hydration of water vapor at normal temperatures. The hydration of CuO and MgO increases the volume almost 2 times, causing the bricks to spread out. Hydration products are decomposed at approximately 800°C. It can be seen that hydration will not occur above this temperature. Materials based on alkaline earth metal aluminates, gallates and indiums that improve the stability against water vapor and CO2. In the formula of MO-R2O3, M—Ca, Sr, Ba; R—Al, Ga, In.
(2) Interaction with alkali vapor
Alkali (K2O, Na2O) vapor combines with mullite and metakaolinite to form nepheline K2O·A12O3·2SiO2 and nepheline Na2O·Al2O3·2SiO2. As the reaction proceeds, the volume increases and some parts of the brick simultaneously peel off. The stability of refractory materials against alkali vapor increases in the following order: clay bricks (Al2O3 42%), high alumina bricks (mullite, Al2O3 70%), clay-bonded silicon carbide bricks, corundum bricks, self-bonded silicon carbide bricks, Nitride bonded silicon carbide bricks. According to the relationship between aluminum silicate refractory materials, lithium alkali corrodes the most, followed by sodium, and potassium less. This is related to the lowest melting temperature of lithium alkali and is consistent with the decreasing sequence of K2>Na>Li atomic radius.
(3) Interact with chlorine gas
Chlorine reacts with many refractory oxides to produce fusible or volatile compounds, and its vaporization causes the strength of refractory bricks to decrease. Chlorine destroys refractory materials similar to hydrogen. Perclase refractory materials are the least stable to chlorine (MgCl2 melts and volatilizes at 712°C), while high alumina bricks and corundum bricks are the most stable. It was found that at 950°C, in contact with chlorine for 72 hours, the strength of magnesite bricks and chromium magnesia bricks was reduced by 100%, clay bricks by 24%, silica bricks by 13% and high alumina bricks by 5%.
(4) Interaction with hydrocarbons
The hydrocarbons methane, ethane and natural gas, like CO, deposit carbon black in the presence of catalysts. They have a wider activation temperature range than carbon monoxide to precipitate carbon black, indicating the decomposition temperature of these hydrocarbons.
(5) “Oxidation-reduction” atmosphere
Carbon and silicon carbide refractory materials are oxidized at high temperatures in an oxidizing atmosphere. The carbon graphite brick medium has some slowdown in oxidation rate. The oxidation of silicon carbide refractory materials proceeds from the surface, and a SiO2 film is formed at the same time to prevent further oxidation. Due to the oxidation of the inner layer of carbonized carbon, the bricks will be damaged due to expansion during oxidation. Refractory bricks containing chromite are reduced at high temperatures in a reducing atmosphere. Magnesia-chromium and chromium-magnesite bricks are also reduced, and at temperatures exceeding 1600°C, there is a significant loss of strength and they become brittle.
(6)Interaction with sulfur dioxide gas
All types of magnesia bricks interact with sulfur dioxide gas SO2. MgSO4 is formed in the range of 400 to 900°C, and it decomposes at 1124°C. By further increasing the temperature, the periclase bricks are resintered by the activated form of magnesium oxide formed when the sulfide decomposes.
(7) Interaction with hydrogen
In aluminum silicate refractory materials, hydrogen is used to reduce oxides such as Na2O, TiO2, MgO, SiO2, etc. The hydrogen decomposes mullite to form corundum and silicon monoxide. In hydrogen medium, high alumina bricks and corundum bricks containing Al2O3≥85% have stable properties. Siliceous bricks are destroyed due to the rapid degradation of silica at 1200°C in a hydrogen medium.
(8) The corrosive effect of carbon monoxide
The most widespread and corrosive gas corrosive is carbon monoxide. Its corrosive effect lies in the reduction of refractory oxides and the precipitation of carbon black.
