Foaming of Recyclable Clays into Energy-Efficient Low-Cost Thermal Insulators

Abstract

Thermal insulators are crucial to reduce the high energy demands and greenhouse emissions in the construction sector. However, the fabrication of insulating materials that are cost-effective, fire resistant, and environmental-friendly remains a major challenge. In this work, we present a room-temperature processing route to fabricate porous insulators using foams made from recyclable clays that can be locally resourced at very low costs. Foams containing either pure Kaolin or a Kaolin-based clay mixture are produced through mechanical frothing or an in-situ gas-generating reaction. Surface modification of the clay particles using a cationic amphiphilic molecule leads to particle-stabilized foams that are sufficiently strong to withstand the high capillary stresses developed during water evaporation. Self-supporting insulators with up to 90% porosity and thermal conductivities as low as 0.13 W/mK can thus be obtained by simple casting and drying at ambient temperature in an ultralow energy process. Such materials can be recycled by crushing, redispersion in water, and subsequent foaming. Porous structures with higher compressive strength are optionally created by sintering the dried foams at 1000 °C. The obtained porous materials perform comparably well with existing fire-resistant insulators while offering the possibility of closed-loop processing and wide availability from local resources as well as ultralow cost and embodied energy.

3D Printing of Hierarchical Porous Ceramics for Thermal Insulation and Evaporative Cooling

“…This air content compares well with that of mechanically frothed foams studied in previous research. [ 3,11 ] In contrast to the constant air content, the size of the incorporated air bubbles was found to steadily decrease from 109 to 70 µm as the mixing time increased from 30 sec to 6 min (Figure 2B). This microstructural change was accompanied by a strong shift in the rheological properties of the system, which transformed from a fluid suspension to a viscoelastic foam.…”

Structure of Industrial Sacrificial Fragile Cementitious Foams

“…Figure b shows the SFCF blocks that were readily prepared for installation, and Figure c shows the well-installed EMAS in Nyingchi Mainling Airport, Tibet, China. As a type of foamed composites with high collapse deformations under relatively low loads, most of the volume of SFCFs should be occupied by the air voids (over 80%), while the skeleton occupies the rest of the volume. − The porous structure of foam composites possesses some special properties, such as high thermal resistance, excellent sound absorption, and a high potential for energy storage, enabling wide applications in the energy system as well as in our daily life. − …”

3D Printing of Hierarchical Porous Steel and Iron‐Based Materials

“…Despite the unique biocompatibility, mechanical properties, and electrochemical response demonstrated so far, [9b,10] the potential of direct ink writing as a tool to manufacture metals with tunable hierarchical porous architectures has not yet been fully exploited.An enticing strategy to control the porosity of materials across multiple length scales is to print inks or resins containing building blocks that generate porosity through programmable self-assembly processes. [11] In this approach, the large pores created through the tool path are combined with the small pores arising from the self-assembling ink to create structural features below the printer's resolution. Air bubbles, liquid droplets, or organic particles have been used as self-assembling building blocks to print ceramics and polymers with programmable hierarchical porosity.…”