We found particles consisting of silicon and oxygen in primary phase alpha in AlSi7Mg cast by rheocasting.
At high temperature Al can be expected to react with SiO2, perhaps accordingly: 4 Al + 5 SiO2 → 3 Si + 2 Al2O3·SiO2. I would hence expect Al to be detectable, besides Si and O, if such germs can somehow precipitate within the alloy matrix.
I don't think so! Oxides generally have a weak wetability with alpha-aluminum.
Thank you, yes, there was also Al deceted besides Si and O. Could you (Carlos Araújo Queiroz) please more specify the temperature you mentioned in you answer?
It is known that aluminium caps, that may contaminate cullet if not entirely removed, can cause silicon inclusions on container (soda-lime) glass. The following reaction, supported by X-ray diffraction data, was proposed to explain this kind of inclusions: 4 Al + 3 SiO2 → 3 Si + 2 Al2O3 (*). This reaction seemingly can be thought to occur between the Al melting point (660 ºC) and the melting point of the glass, about 1400 ºC; while it should also play a significant role by the working point of this type of glass, around 1000 ºC. Silicon inclusions may possibly be globular shaped owing to high interface tension.
(*) José María Fernández Navarro, "El Vidrio", 3rd ed., CSIC / Sociedad Española de Cerámica y Vidrio, Madrid, 2003, pp. 285-286; in Spanish.
I have briefly discussed other glass defects ― concerning float glass ― elsewhere at this forum: https://www.researchgate.net/post/What_causes_Striae_in_float_glass
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