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

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.