Application of Quartz New Materials in Aerospace Field

2023-02-13

Quartz ceramic materials have excellent comprehensive properties such as dielectric, thermal and mechanical properties. Quartz ceramics can be used in aerospace vehicle heat insulation materials, rocket engine nozzles, heads and front chambers, missile radomes, and substrates in nuclear fuel (SiO2 -UO system) and radiation shielding ceramic materials. Quartz ceramic radome needs to have good wave-transmitting properties to ensure the correct transmission of electromagnetic signals, and also needs properties such as heat resistance and corrosion resistance.

In recent years, the continuous development of my country’s aerospace industry has also provided new important and key applications for new quartz materials. One of the representative ones is the model material for casting high-temperature alloy parts that has only been greatly developed in recent years. In order to improve the temperature bearing performance of the engine inlet, many developed countries in the world have improved the structure of engine blades from solid blades to hollow blades, from the original multi-grain blades to the current single-grain blades. Various types of ceramic auxiliary materials have been invented and widely used to ensure that the inner surface of the cast hollow blade is very smooth, with high dimensional accuracy and low probability of defects, which improves the quality level and reduces unnecessary losses. In the field of precision casting, fused silica can be used as auxiliary materials to make ceramic cores, shells and various ceramic auxiliary materials. Fused silica has the characteristics of strong creep resistance, easy filling and removal, and the price of fused silica is cheaper than zircon, with low density and low impurities, so the quality of raw materials used for the same volume of shell is small and the cost is lower .

In 2001, the American Refractory Company made a shell formula containing a large amount of quartz, specifically (mass fraction): 55% aluminum-silicon refractory material, 30% fused silica, 9% corundum, and 6% zircon. 90% of the hollow blades in developed countries in Europe and the United States use silicon-based ceramic cores, which can be used to manufacture single crystal hollow blades, and the operating temperature can reach 1650 °C.

In the preparation process of silica-based ceramic core, attention should be paid to its volume change, and it is most appropriate to control it below 1%. Otherwise, the gap between the shape and specifications required by the mold and the core is too large, which will reduce the yield, affect the shape and size of the blade, and increase the difficulty of subsequent mechanical grinding. From the following four angles to control the performance of silicon-based ceramic core:

(1) The influence of the purity and particle size gradation of raw materials on the performance of the core. The raw material of the silica-based ceramic core is quartz glass, and its purity and particle size gradation have a great influence on the high-temperature flexural resistance, room temperature strength, shrinkage and other properties of the core. The content of impurities in quartz (such as potassium, sodium, calcium, iron, etc.) needs to be controlled to a certain extent, otherwise too much glass phase will be produced, which will greatly reduce the high temperature performance of the core;

(2) The influence of mineralizers and high-temperature additives on product performance. The mineralizer can form a certain high-temperature stable phase while promoting sintering. In addition, adding some high-temperature-resistant materials (such as mullite, zirconium silicate, zirconia, etc.) can also significantly improve high-temperature performance;

(3) The sintering system mainly includes four stages: draining steam at 100-200°C, wax discharge at about 300-400°C, crystal transformation at 600 and 900°C, and final firing at 1100-1200°C. The main research work on the optimization of the firing system is focused on the fourth temperature stage, by adjusting the final firing temperature and time to adjust high temperature flexural resistance, room temperature strength, shrinkage and other properties. This is because the content of cristobalite in the sintering process can improve high-temperature performance, and its content is mainly affected by the final sintering system. The melting point of cristobalite is about 1700°C, and it has good high-temperature resistance, but at about 300°C, cristobalite will crystallize. Type transformation, the volume changes, so too much cristobalite will reduce the room temperature strength of the product;

(4) The influence of the strengthening process on the comprehensive performance of the product. Excessive cristobalite content will cause a significant decrease in the room temperature strength of the product, and it needs to be strengthened at room temperature to increase the room temperature strength. Room temperature strengthening refers to mixing suitable resins (such as phenolic resin, epoxy resin, etc.) Can be doubled.