Chemical Processes During Energy‐Saving Preparation of Lightweight Ceramics

Abstract

Lightweight glass‐ceramic material similar to foam glass was obtained at 700°C–800°C directly from alkali‐activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100–250 kg/m3 and high pore size homogeneity. Chemical processes occurring in alkali‐activated silica clay and zeolitized tuff were studied using X‐ray diffraction, thermal gravimetry, IR‐spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na2O·mSiO2·nH2O), formed during alkali activation. Additional pore‐forming gas source in alkali‐activated zeolitized tuff is trona, Na3(CO3)(HCO3)·2H2O, formed during interaction between unbound NaOH and CO2 and H2O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.

Preparation of Sound‐Insulating Lightweight Ceramics from Aluminosilicate Rocks with High CaCO3 Content

“…The similar dependence of resulting porosity on the fineness of grinded raw material was observed earlier for alkali‐activated dense zeolite‐rich rocks with cryptocrystalline zeolitization . These studies have shown that NaOH serves not as a flux only, but also reacts with zeolites giving additional pore‐forming gas source (hydrated sodium polysilicates).…”

“…It was reported that interaction of OCT‐phase with NaOH solution results in the formation of hydrated sodium polysilicates, Na 2 O· m SiO 2 · n H 2 O (liquid glass)—an important source of pore‐forming gas (water vapor). The presence of latter can be identified from amorphous halo on XRD profiles and on DTG maxima near 250°C and 350°C . Our XRD studies, however, have shown that amount of amorphous constituent after interaction of raw material with NaOH does not depend on the powder fineness (Fig.…”

“… SEM images of cellular microstructure of lightweight materials prepared from aluminosilicate rocks: (a) calcite‐zeolite rock (this study), “pseudo‐open” porosity; (b) zeolite‐rich rock without calcite, closed porosity. The scale bar is 500 μm.…”

“…(1) Chemical Processes During Alkali Activation of Calcite-Zeolite Rock The similar dependence of resulting porosity on the fineness of grinded raw material was observed earlier for alkali-activated dense zeolite-rich rocks with cryptocrystalline zeolitization. 15,16 These studies have shown that NaOH serves not as a flux only, but also reacts with zeolites giving additional pore-forming gas source (hydrated sodium polysilicates). The latter requires good accessibility of zeolite surface for NaOH solution, and so resulting porosity strongly depends on the fineness of powdered raw material.…”

“…It was reported 16 that interaction of OCT-phase with NaOH solution results in the formation of hydrated sodium polysilicates, Na 2 OÁmSiO 2 ÁnH 2 O (liquid glass)-an important source of pore-forming gas (water vapor). The presence of latter can be identified from amorphous halo on XRD profiles and on DTG maxima near 250°C and 350°C.…”