Silicon nitride Si3N4 is a non-oxide high temperature ceramic structural material. Powdered Si3N4 can be prepared by reacting a mixture of SiCl4 vapor and NH3 gas. Powdered Si3N4 is unstable to air and water. Powdered Si3N4 can form a pungent odor, a gas commonly used as a refrigerant and a poorly soluble acid when it is in contact with water. Powdered Si3N4 can generate N2 and contact with air. a substance. However, heat treatment of powdered Si3N4 and appropriate amount of MgO (refractory) in a closed vessel at 230 ° C, 1.01 × 105 Pa and 185 ° C, can obtain a solid material with a very tight structure and relatively stable air and water.
(1) Write the reaction equation for the preparation of Si3N4 from SiCl4 and NH3: ______.
The mixture of vapor of SiCl4 and NH3 reacts to form Si3N4, and its chemical equation is: 3SiCl4+4NH3═Si3N4+12HCl; so the answer is: 3SiCl4+4NH3═Si3N4+12HCl;
(2) Write the equation for the reaction of powdered Si3N4 and H2O and O2 respectively: ______; ______.
Powdered Si3N4 can form a pungent odor when exposed to water. The gas commonly used as a refrigerant is ammonia and a poorly soluble acid is silicic acid. The reaction equation is: Si3N4+9H2O═3H2SiO3+4NH3; powdered Si3N4 Contact with air can produce N2 and another substance, which is known as silicon dioxide according to the conservation of atoms, and its reaction equation is Si3N4+3O2═3SiO2+2N2;
Therefore, the answer is: Si3N4+9H2O═3H2SiO3+4NH3; Si3N4+3O2═3SiO2+2N2;
(3) Why is the tightly structured solid Si3N4 no longer attacked by H2O and O2?
Therefore, the answer is: Si3N4+9H2O═3H2SiO3+4NH3; Si3N4+3O2═3SiO2+2N2;
(3) Why is the tightly structured solid Si3N4 no longer attacked by H2O and O2?
Because SiO2 is formed on the surface of Si3N4 particles under pressure and heating conditions, together with MgO, a dense oxide protective film is formed, so that solid Si3N4 is no longer attacked by H2O and O2;
Therefore, the answer is: SiO2 is formed on the surface of Si3N4 particles under pressure and heating conditions, together with MgO to form a dense oxide protective film.
Therefore, the answer is: SiO2 is formed on the surface of Si3N4 particles under pressure and heating conditions, together with MgO to form a dense oxide protective film.
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