Aerogels for Thermal Protection and Their Application in Aerospace.

With the continuous development of the world's aerospace industry, countries have put forward higher requirements for thermal protection materials for aerospace vehicles. As a nano porous material with ultra-low thermal conductivity, aerogel has attracted more and more attention in the thermal insulation application of aerospace vehicles. At present, the summary of aerogel used in aerospace thermal protection applications is not comprehensive. Therefore, this paper summarizes the research status of various types of aerogels for thermal protection (oxide aerogels, organic aerogels, etc.), summarizes the hot issues in the current research of various types of aerogels for thermal protection, and puts forward suggestions for the future development of various aerogels. For oxide aerogels, it is necessary to further increase their use temperature and inhibit the sintering of high-temperature resistant components. For organic aerogels, it is necessary to focus on improving the anti-ablation, thermal insulation, and mechanical properties in long-term aerobic high-temperature environments, and on this basis, find cheap raw materials to reduce costs. For carbon aerogels, it is necessary to further explore the balanced relationship between oxidation resistance, mechanics, and thermal insulation properties of materials. The purpose of this paper is to provide a reference for the further development of more efficient and reliable aerogel materials for aerospace applications in the future.

Preparation and Properties of Highly Transparent SiO2 Aerogels for Thermal Insulation.

SiO2 aerogels have attracted extensive attention due to their unique structural characteristics, which exhibit many special properties, especially good optical transparency. As far as we know, the sol-gel stage during the synthesis of aerogel plays an important role in the construction of the gel skeleton. In this study, we adjusted the amount of silicon source and catalyst to explore the best scheme for preparing highly transparent SiO2 aerogels, and further clarify the effects of both on the properties of SiO2 aerogels. Results indicated that the pore size distribution was between 10 and 20 nm, the thermal conductivity was between 0.0135 and 0.021 W/(m·K), and the transmittance reached 97.78% at 800 nm of the aerogels, better than most studies. Therefore, it has the potential to be used in aerogel glass for thermal insulation.

Liquid Oxygen Compatibility and Ultra-Low-Temperature Mechanical Properties of Modified epoxy Resin Containing Phosphorus and Nitrogen.

Endowing epoxy resin (EP) with prospective liquid oxygen compatibility (LOC) as well as enhanced ultra-low-temperature mechanical properties is urgently required in order to broaden its applications in aerospace engineering. In this study, a reactive phosphorus/nitrogen-containing aromatic ethylenediamine (BSEA) was introduced as a reactive component to enhance the LOC and ultra-low-temperature mechanical properties of an EP/biscitraconimide resin (BCI) system. The resultant EP thermosets showed no sensitivity reactions in the 98J liquid oxygen impact test (LOT) when the BSEA content reached 4 wt% or 5 wt%, indicating that they were compatible with liquid oxygen. Moreover, the bending properties, fracture toughness and impact strength of BSEA-modified EP were greatly enhanced at RT and cryogenic temperatures (77 K) at an appropriate level of BSEA content. The bending strength (251.64 MPa) increased by 113.67%, the fracture toughness (2.97 MPa·m1/2) increased by 81.10%, and the impact strength (31.85 kJ·m-2) increased by 128.81% compared with that of pure EP at 77 K. All the above results demonstrate that the BSEA exhibits broad application potential in liquid oxygen tanks and in the cryogenic field.

[Molecular Mechanism of Ventilator-associated Lung Injury Based on Keap1/Nfr2/ARE Signaling Pathway].

OBJECTIVE: To explore the molecular mechanism of ventilation induced lung injury (VILI) formation based on Keap1/Nfr2/ARE signaling pathway. METHODS: The VILI model was established by excessive mechanical ventilation in SD rats. HE staining was used to detect the pathological changes of lung tissue in the control group, normal tidal volume (VT) group and large VT group (VT 40 mL/kg). The wet weight of lung tissue was detected in each group. Dry weight (W/D) ratio change; BCA method was used to detect the changes of total protein in bronchoalveolar lavage fluid (BALF) of each group; ELISA was used to detect interleukin-1ß (IL-1ß) and leukocyte in BALF and serum of each group. The content of 8-OHdG in the lung tissue was detected by IL-8 and the content of malondialdehyde (MDA) in the lung tissue was detected by TBA method. The NLRP3, ASC and caspase-1 proteins in macrophages were detected by Western blot. The changes of Keap1 and Nrf2 proteins in lung tissues were detected by RT-PCR. The expressions of SOD mRNA and HO-1 mRNA in lung tissues of each group were detected by RT-PCR. RESULTS: Excessive mechanical ventilation could damage lung tissue, leading to alveolar rupture, inflammatory cell infiltration and erythrocytosis. Compared with the control group and normal VT group, the W/D value, 8-OHdG and MDA content in the large VT group, and total BALF, the contents of IL-1ß and IL-18 in protein, IL-1ß, IL-18 in serum increased significantly ( P<0.05). Compared with the control group and normal VT group, NLRP3, ASC, in macrophage of large VT group, the content of Keap1 protein in caspase-1 protein and lung tissue increased significantly ( P<0.05). The expression of Nrf2 protein, SOD mRNA and HO-1 mRNA in lung tissue decreased significantly. CONCLUSIONS: Large VT ventilation can cause acute inflammatory injury in lung tissue and lead to the occurrence of VILI. Inflammatory bodies of NLRP3 in alveolar macrophages are involved in this process, and the mechanism of NLRP3 inflammatory bodies is caused by hyperventilation in addition to mechanical injury. Decreased Keap1/Nrf2-ARE pathway inhibition and ROS clearance may also cause macrophage production of NLRP3 inflammatory bodies.

An elevated-temperature depth-sensing instrumented indentation apparatus for investigating thermo-mechanical behaviour of thermal barrier coatings.

In our study, an elevated-temperature depth-sensing instrumented indentation apparatus was designed and developed to investigate thermo-mechanical response of thermal barrier coatings (TBCs). A furnace was used to heat the test region up to 1600 °C and a heat protection design was proposed to protect electronic devices from high temperature environment. Load was applied by a precise loading motor and a piezoelectric actuator in high (0-440 N) and low (0-40 N) load ranges, respectively. A loading shielding scheme was designed to protect the low load sensor during the high loading process. In order to obtain reliable test data, the as-developed apparatus was calibrated at room and elevated temperatures. It is found that the developed apparatus was suitable to obtain the intended data. After that, two typical TBCs were tested from 600 to 1500 °C, and the load-depth curves were presented to show the main functions and usability of the measuring system.