Physicochemical Mechanisms Of Glazes Derived From Granite Waste

With the development of stone processing industry,the waste generated due to the processing has been detrimental to our ecological environment.Granite waste(GW),a high-potential resource with high productivity for reutilization,is mainly utilized to substitute raw materials in the fabrication of low-added-value building components.The use of glaze and pigment is the main factor that leads to a high cost in the ceramic manufacturing industry.It is an efficient and costeffective method of recycling low-quality GW to fabricate iron-based colored glazes due to their similar chemical composition and high iron concentration.Insufficient attention has been given to systematic research on the practical application of these materials and the high-temperature melting behavior and controlled manufacturing of iron-based colored glazes.Moreover,most of the research on high-temperature behavior was based on analysing the fired samples.Poor understanding of the transient state of glaze samples during heating and cooling processes leads to a lack of clarity and comprehensive comprehension of high-temperature physicochemical mechanisms and coloring mechanisms.Furthermore,analyzing the types of crystalline phases and their formation mechanisms in iron-based crystalline glazes is significant for investigating and manufacturing current ferromagnetic materials.Two artistic glazes with different iron content—iron-crystalline glaze and celadon glaze—were prepared using GW as an iron source.The study investigated the evolution of phase,morphology,and microstructure of glazes derived from granite waste,as well as the formation mechanism and crystal growth process of crystalline phases.The following are the main findings of the research:(1)An iron-rich glaze was prepared from GW.The evolution of the crystalline phases and the microstructure of this material during heating at different temperatures was investigated through a set of quenched samples to probe the thermal behavior of the glaze.The findings revealed that alternating reactions of crystallization and melting occurred simultaneously during the thermal glaze process.The thermal decomposition of mica led to the crystallization of Mg-Fe spinel and Ti-substituted hematite at about 1030℃.At 1170℃,the melting of the glaze caused the formation of bubbles that facilitated the precipitation of iron-rich crystals.The subsequent rise of the bubbles then transported the crystals from the interior of the glaze to its surface.Upon reaching 1350℃,an unmelted hematite layer with crystal formation was observed.(2)The phase composition and microstructure change of the quenched samples obtained at different temperatures during cooling were investigated to explore the crystallization behavior of the iron-rich glaze derived from GW.The results showed that surface crystallization due to the oxidation of Fe2+ occurred firstly at the glaze surface where magnetite precipitated,followed by ε-Fe2O3 and Mg-Fe spinel.Formation of cubic iron-rich spinel,tetragonal γ-Fe2O3 and orthorhombic ε-Fe2O3 particles were identified by transmission electron microscopy(TEM)in the quenched sample obtained at 1100℃.This confirmed that the magnetite precipitated from the glass matrix would transfer to ε-Fe2O3 or Mg-Fe spinel depending on the concentration of Mg2+in the spinel structure.(3)Red-brown,brown,and black glazes were prepared from GW with the addition of calcite.The effect of calcite content on the crystallization and color performance of the glazes was investigated.The results showed crystallization of iron-rich crystals was suppressed with increased calcite content.Crystallization and diffusion capacities of Mg2+ were improved by the increase of Ca2+,which promoted the crystallization of augite.It was indicated that the phase composition and thickness of the iron-rich crystalline layer had an essential impact on the coloring performance of the glazes.(4)Imitation Jun celadon glazes were prepared from GW by fir-ing under an air atmosphere.The influence of GW content on the color performance of the glazes was investigated.The results showed that the glazes with sky-green and sky-blue colors were obtained by firing at 1280℃ when the addition of GW was 40 wt.%and 50 wt.%respectively.The Jun glazes’ composition from GW lay in the metastable liquid-liquid immiscibility region.The phase separation occurred in the glass matrix,forming a spherical and inter-connected structure.The disappearance of the blue hue of the glaze with GW addition up to 60 wt.%was due to the decrease of the tendency towards liquid-liquid immiscibility as the composition shifted away from the immiscibility gap.(5)By analyzing the evolution of microstructure in quenched samples obtained during cooling,the coloring mechanism of Jun artistic glazes derived from GW was investigated using techniques,such as TEM and ultra-violet and visible spectrophotometry(UV-VIS).The results showed that the transition of glaze color from brown to blue occurred at about 900℃ during cooling.During the color shift,phase separation occurred,and the array of phase-separative structures in the glazes changed from entirely disordered to short-range.The findings suggested that the blue hue in the glaze resulted from the coupling effects of amorphous structural color and chemical color from the absorption of Fe ions.In addition,the formation of blue and white patterns was attributed to the uneven distribution of Ca,Mg,and Si composition caused by the liquid-liquid phase separation and the crystallization of augite and cristobalite on residual quartz.