The rejection of Si3N4,Mg3N2, AlN and Si particles from different slurries consisting of molten aluminum and magnesium alloy with 10% of silicon or pure molten metals was experimentally investigated by measuring changes in the electrical resistance of the slurries before and after rejection occurred. In stirring experiments, only individual powder fractions which passed through a 45 µm sieve screen and remained on a 30 µm screenwere applied. The experiments showed that the rejection of Si3N4 particles from Al-10%Si and Mg-10%Si melts occurs when more than 17-18 vol.% of the ceramic phase is dispersed into the melt, while in pure Al and Mg molten metals spontaneous rejection occurs at 7-8 vol.% of the introduced ceramic phase. A similar tendency of rejection (at 16-18 vol.% of particulate in slurry) was also observed during the introduction of silicon particles into Al-10%Si and Mg-10%Si melts.Preučevali smo stabilnost suspenzij ▫Si3N4▫, ▫Mg3N2▫, AlN in Si delcev (sejalna frakcija med 30 in 45 ▫mu▫m), dispergiranih v raztaljenem aluminiju in maagneziju ter v talinah iz Al in Mg zlitin z 10% silicija. Izločanje delcev iz talin smo eksperimentalno ugotavljali s pomočjo sprememb električne prevodnosti taline. Ugotovili smo, da prihaja do izločanja ▫Si3N4▫ in Si delcev iz raztaljenih Al in Mg zlitin z 10 vol.% silicija šele, ko koncentracija delcev v obeh talinah doseže 16-18 vol.%. V primeru talin iz čistega aluminija in magnezija se ▫Si3N4▫ delci večinoma izločijo, ko njihova koncentracija doseže 7-8 vol.% Za razliko od tega se delci AlN in ▫Mg3N2▫, ne glede na to, ali so dispergirani v raztaljeni Al in Mg zlitini z 10% silicija ali v čisti kovini, spontano izločijo pri koncentraciji keramične faze, ki praviloma ne presega 4 vol.%. Različno stabilnost suspenzij keramičnih delcev v Al in Mg talini smo skušali pojasniti z reaktivnostjo med raztaljeno kovino in dispergiranimi delci oz. s kemijskimi reakcijami do katerih prihaja na meji med keramično fazo in talino
