Facile Synthesis and Properties of Highly Porous Quartz Fiber-Reinforced Phenolic Resin Composites with High Strength.

Lightweight and high-strength insulation materials have important application prospects in the aerospace, metallurgical, and nuclear industries. In this study, a highly porous silica fiber reinforced phenolic resin matrix composite was prepared by vacuum impregnation and atmospheric drying using quartz fiber needled felt as reinforcement and anhydrous ethanol as a pore-making agent. The effects of curing agent content on the structure, composition, density, and thermal conductivity of the composite were studied. The mechanical properties of the composite in the xy direction and z direction were analyzed. The results showed that this process can also produce porous phenolic resin (PR) with a density as low as 0.291 g/cm3, where spherical phenolic resin particles are interconnected to form a porous network structure with a particle size of about 5.43 µm. The fiber-reinforced porous PR had low density (0.372~0.397 g/cm3) and low thermal conductivity (0.085~0.095 W/m·K). The spherical phenolic resin particles inside the composite were well combined with the fiber at the interface and uniformly distributed in the fiber lap network. The composite possessed enhanced mechanical properties with compressive strength of 3.5-5.1 MPa in the xy direction and appeared as gradual compaction rather than destruction as the strain reached 30% in the z direction. This research provides a lightweight and high-strength insulation material with a simple preparation process and excellent performance.

The Effect of Different Diluents and Curing Agents on the Performance of Epoxy Resin-Based Intumescent Flame-Retardant Coatings.

The epoxy resin-based (ESB) intumescent flame-retardant coatings were modified with 1,4-butanediol diglycidyl ether (14BDDE) and butyl glycidyl ether (BGE) as diluents and T403 and 4,4'-diaminodiphenylmethane (DDM) as curing agents, respectively. The effects of different diluents and curing agents on the flame-retardant and mechanical properties, as well as the composition evolution of the coatings, were investigated by using large-plate combustion, the limiting oxygen index (LOI), vertical combustion, a cone calorimeter, X-ray diffraction, FTIR analysis, a N2 adsorption and desorption test, a scanning electron microscope (SEM), a tensile strength test, and a viscosity test. The results showed that the addition of 14BBDE and T403 promoted the oxidation of B4C and the formation of boron-containing glass or ceramics, increased the residual mass of char, densified the surface char layer, and increased the specific surface area of porous residual char. When their dosage was 30%, ESB-1T-3 coating exhibited the most excellent flame-retardant properties. During the 2 h large-plate combustion test, the backside temperature was only 138.72 °C, without any melting pits. In addition, the peak heat release rate (PHRR), total heat release rate (THR), total smoke production (TSP), and peak smoke production (PSPR) were reduced by 13.15%, 13.9%, 5.48%, and 17.45%, respectively, compared to the blank ESB coating. The LOI value reached 33.4%, and the vertical combustion grade was V-0. In addition, the tensile strength of the ESB-1T-3 sample was increased by 10.94% compared to ESB. In contrast, the addition of BGE and DDM promoted the combustion of the coating, affected the ceramic process of the coating, seriously affected the formation of borosilicate glass, and exhibited poor flame retardancy. The backside temperature reached 190.93 °C after 2 h combustion. A unified rule is that as the amount of diluent and curing agent increases, the flame retardancy improves while the mechanical properties decrease. This work provides data support for the preparation and process optimization of resin-based coatings.

A Novel Inorganic Aluminum Phosphate-Based Flame Retardant and Thermal Insulation Coating and Performance Analysis.

Currently, most thin-layer expandable coatings are polymer-based, with very few inorganic expandable coatings. Due to the high environmental friendliness of inorganic coatings, studying new types of inorganic coatings is of great significance. A novel amorphous aluminum phosphate-based flame-retardant coating was prepared by modifying it with nano-silica, hollow silica beads, hollow glass microspheres, and boron carbide. A comprehensive study was conducted on the flame retardancy and thermal insulation performance, composition and structural evolution under flame and physical and chemical properties, and the mechanisms of flame retardancy and thermal insulation were elucidated. Large-plate combustion testing, bonding strength testing, XRD, IR, TG-DSC, and SEM testing were all applied in this work. The synergistic effect of the four fillers was very obvious, and a series of AP22XY (nano-silica/silica beads/hollow glass microspheres/boron carbide = 2:2:0:4, 2:2:1:3, 2:2:2:2, 2:2:3:1, 2:2:4:0) coatings were prepared. The change in the ratio of glass microspheres to boron carbide had a significant impact on the composition and structural evolution of the coating, thus reflecting its effectiveness as a flame retardant and thermal insulation. Although decreasing the ratio would promote the formation of borosilicate glass and Al18B4O33 and improve the thermal stability of coatings, the structure inside of the coating, especially the skeleton, would be dense, which is not conducive to thermal insulation. When the ratio of glass microspheres to boron carbide is 3:1, AP2231 shows the best fire resistance. Under the combustion of butane flame at about 1200-1300 °C, the backside temperature reaches a maximum of 226 °C at 10 min, and then the temperature gradually decreases to 175 °C at 60 min. This excellent performance is mainly attributed to three aspects: (1) the foaming and expandability of coatings when exposed to fire, (2) the multiple endothermic reactions the coating undergoes, and (3) the improvement effect of boron carbide. Additionally, AP2231 shows the best bonding performance with a strength of close to 4.5 MPa after combustion, because of the appropriate content matching between borosilicate glass, Al18B4O33, and hollow glass microspheres. The coating has potential application prospects in the construction and transportation fields, such as the protection of structural steel, fire prevention in subways and tunnels, and the prevention of lithium battery fires.

High Emissivity MoSi2-SiC-Al2O3 Coating on Rigid Insulation Tiles with Enhanced Thermal Protection Performance.

High emissivity coatings with sol as the binder have the advantages of room temperature curing, good thermal shock resistance, and high emissivity; however, only silica sol has been used in the current systems. In this study, aluminum sol was used as the binder for the first time, and MoSi2 and SiC were used as emittance agents to prepare a high emissivity MoSi2-SiC-Al2O3 coating on mullite insulation tiles. The evolution of structure and composition at 1000-1400 °C, the spectral emissivity from 200 nm to 25 µm, and the insulation performance were studied. Compared with the coating with silica sol as a binder, the MoSi2-SiC-Al2O3 coating has better structural uniformity and greater surface roughness and can generate mullite whiskers at lower temperatures. The total emissivity is 0.922 and 0.897, respectively, at the wavelength range of 200-2500 nm and 2.5-25 µm, and the superior emissivity at a low wavelength (<10 µm) is related to a higher surface roughness and reduced feature absorption. The emissivity reduction related to the oxidation of emittance agents at a high temperature (-10.2%) is smaller than that of the silica-sol-bonded coating (-18.6%). The cold surface temperature of the coated substrate is 215 °C lower than the bare substrate, suggesting excellent thermal insulation performance of the coating.