Study on Influence of Silicate Modulus and Cation Type on Tensile Strength for Sand Core.

In this research, it was explored how the strength of sand core would be affected by the silicate binder with varying modulus and different cation types (Na and K) and micro-silica powder. To be specific, the microscopic morphology of the bonding bridge was examined by scanning electron microscope (SEM), while the changes in internal structure were revealed through Fourier transform infrared spectrum (FT-IR) analysis. It was discovered that with the modulus reduced from 2.3 to 1.3, there was a progressive increase from 20% to 50% in the amount of micro-silica powder as required for the sand cores to reach the maximum bonded strengths. Under the same conditions, the strength of sand cores bonded by potassium silicate was improved compared to sodium silicate. According to FT-IR analysis, the decline in modulus improved not only the concentration of OH– but also the density of active groups inside silicate solution, which is conducive to the formation of Si–O–Si bonds through reaction with micro-silica powder. Meanwhile, the results of the EDS and FT-IR analysis suggest a higher concentration of Si–O–Si bonds in the mixture of potassium silicate and micro-silica powder. Consequently, the sand core bonded by potassium silicate outperformed that with sodium silicate in both tensile strength and storage performance. [ABSTRACT FROM AUTHOR]