Formation of Mg-silicates by reaction of perhydropolysilazane with MgO during pyrolysis in air

Abstract

The present study deals with the synthesis of Mg 2 SiO 4 (Forsterite) applying the route of polymer derived ceramics (PDCs). The liquid, inorganic perhydropolysilazane (PHPS) was used because it is very reactive during pyrolysis in air and forms amorphous SiNO ceramic containing a tremendous amount of SiO 2 . Both facts are crucial for the reaction with MgO in order to synthesize Mg-silicates. The results of this study demonstrate, that the Mg-orthosilicate phase is formed at the MgO/SiNO interface via solid state reaction at comparably low temperatures of 1100°C during pyrolysis in air for 2 h. Furthermore the high reactivity of the polysilazane leads to an almost full conversion of the MgO to Mg 2 SiO 4 under the used conditions.

Tailored Oxidation Barrier Coatings for Mo-Hf-B and Mo-Zr-B Alloys

“…Due to the presence of hydroxyl groups on the filler’s surface [14], and the high reactivity and sensitivity of PHPS to moisture and –OH groups, siloxane bonds ( Si – O – Si ) form according to chemical reactions (3) and (4), [10]:≡Si–OH + H–Si≡ → ≡Si–O–Si≡ + H 2 (g)…”

“…Polysiloxanes, polycarbosilanes or polysilazanes are silicon containing precursors, which can be converted into polymer-derived ceramic coatings on steel to provide thermal shock resistance, creep resistance and thermal stability [12,13]. The use of fillers reduces the shrinkage of precursor coatings during ceramics formation, which leads to an in-crease of the coating thickness and prevention of cracks [14,15]. There is limited data in the literature of polymer ceramic coatings on molybdenum substrate.…”

Polysilazane‐Type Coatings on Mo–Si–B Alloys: A Thermodynamic Assessment of the Phase Composition

“…From Equation 20, it becomes obvious, that a steady thickness oxide layer will develop when the rate of a parabolic oxide growth is equal to a linear oxide recession (i.e., dx/dt ¼ 0). The contribution of the SiO 2 layer to the parabolic constituent in the equation may enhance the probability of oxidation deceleration in Mo-Mo 3 Si(A15)-Mo 5 SiB 2 (T2) alloys.…”