RESUMO
Porous ceramics are good candidates for thermal-insulating materials. Glass is a low-cost material that possesses low intrinsic thermal conductivity of less than 10 W·m-1·K-1. However, the mechanical strength of a homogeneous glass material is fairly low. We, in this work, have fabricated Al2O3-hollow glass sphere (HGS) foam ceramics with a facile particle-stabilized foaming method. The obtained foam ceramic presents a hierarchical microstructure that is rare to be seen elsewhere using this foaming technique. The foaming system contains two types of particles having opposite charges, and the particle-stabilized foaming mechanism is hence discussed. The optimal sample possesses a porosity above 94% with a thermal conductivity as low as 0.0244 W/m·K, which reaches the level of superinsulating materials. The compressive strengths of the foam ceramics range from 0.07 to 0.83 MPa. The effective medium theory model is used to calculate the thermal conductivities as reference. The deviation of the theoretical values from the experimental ones are derived from the effect of the hierarchical microstructure of the foams. The results of this work may deepen one's understanding and pave new ways for the particle-stabilized foaming technique. The unique microstructure of the ceramic may also shed some light on fabricating superior thermal-insulating ceramic materials.
RESUMO
Nanofibrous aerogels constructed solely by ceramic components with temperature-invariant hyperelasticity could have broad technological implications in extreme environments. However, creating such materials has proven to be extremely challenging. Despite the results from laboratory, those aerogels are, unfortunately, still plagued with issues that would retard their further application: inferior structural integrity, failure at large compressive deformation, high production cost, and inability to withstand rigorous working conditions. To tackle these challenges, we report a facile strategy combining the chemical vapor deposition process and layer-by-layer self-assembly to construct hyperelastic SiC nanofibrous aerogels with three-dimensional porous architecture and improved structural integrity. The resultant aerogels outperform their natural counterparts and most state-of-the-art ceramic nanofibrous aerogels in their capability to quickly recover from large compressive deformation (50% strain), function in a wide range of temperatures, from -196 °C to 1100 °C in air, maintain high particle matter removal efficiency of >99.96%, and rapidly absorb various organic solvents and oils with high capacity and robust recoverability. Nanofibrous aerogels constructed by such a versatile method could provide fresh insights into the exploration of multifunctional nanofibrous aerogels for a variety of applications in extreme environments.
RESUMO
In this paper, hollow gangue microspheres (GM) were introduced into a geopolymer matrix through a geopolymeric method; our aim was to synthesize a green and low-cost adsorbent (GM/KGP) for the removal of heavy metal ions (Cu2+, Cd2+, Zn2+, and Pb2+) from aqueous solutions. We investigated the microstructure of the GM/KGP adsorbent, as well as the effects of adsorbent dose, time, and temperature on adsorption behavior; moreover, an adsorption mechanism was proposed. The GM/KGP adsorbent possessed a typical broad amorphous structure and abundant O-containing functional groups on its surface. The adsorption of Cu2+, Cd2+, Zn2+, and Pb2+ onto the GM/KGP adsorbent fitted well to the pseudo-second-order kinetic model, while the equilibrium isotherm adsorption data were fitted well to the Langmuir equation. The adsorption mechanism GM/KGP was attributed to physical, chemical, and electrostatic attractions, as well as to ion exchange. We conclude that this novel adsorbent has great potential in removing heavy metal ions from contaminated wastewater.