Impact of adding Na₂SiF₆ on the crystal phase and copper valence state in glass ceramics made from leftover granite for use as architectural ornamentation

Abstract The accumulation of granite waste can result in the occupation of a considerable amount of land resources. Using granite waste as glass ceramics for architectural decoration represents a potential solution to this issue. The microstructure, valence state, and crystalline phase of copper ions were examined by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The findings demonstrated that the concentration of Na 2 SiF 6 affects the valence condition of Cu ions in crystallized glass. The crystalline phases of the sample containing 1.84 wt% Na 2 SiF 6 consisted of forsterite (MgSiO 3 ) and diopside (CaMgSi 2 O 6 ), and the Cu + accounted for 39.9% of the total Cu ions in the sample which showed a grey-black color. For the sample containing 3.67 wt% Na 2 SiF 6 , the crystalline phases consisted of richterite (Na, F) syn (Na (Na, Ca) Mg 5 Si 8 O 22 F 2 ), cuprite (Cu 2 O), and forsterite, its Cu + accounted for 39.9%, and the sample appeared orange-red. With the increase of Na 2 SiF 6 content, the percentage of Cu + in the total Cu ions showed an increasing trend, and the corresponding red color of the samples gradually deepened.