What Are the Uses of Advanced Composite Ceramic Substrates in Missiles?

In the mid-1980s, the United States developed an aerospace aircraft program that required both high-temperature tolerance and light mass. For this purpose, a variety of new high-temperature materials were developed, including advanced resin matrix composites, metal matrix composites, ceramic matrix composites, and carbon/carbon composites. Ceramic material is the preferred material for missile radome because of its excellent mechanical, thermal and electrical properties. The radome is the most widely used ceramic matrix composite material in missile structure.

Missile radome

The missile radome is located at the front end of the missile. Its function is to protect the navigation antenna from damage so that the missile can effectively hit the target. It is not only an important part of the aerodynamic shape of the missile but also the protection device of the antenna. During the flight of the missile, the radome should not only withstand aerodynamic heating and mechanical overload, resist the erosion of rain, sand, and other adverse working conditions, but also meet the stringent requirements of electrical performance proposed by the missile control loop. Therefore, the missile radome material should have the following properties:

Missile-radome

  • Excellent dielectric properties

In the guidance system, the transmission efficiency and aiming error of the radome are very sensitive to the dielectric properties of the material and its relationship with temperature and frequency. It is required that the material has low dielectric constant (10) and dielectric loss, and the dielectric properties do not change obviously with temperature and frequency.

  • Good heat resistance and thermal shock resistance

The high Mach number of missile can make the radome of instantaneous heating rate is as high as above 120 ℃ / s, so the material is required to have good thermal shock resistance, and the molecular structure of the material is required to be stable when the temperature is raised, and the material properties (such as dielectric properties and mechanical properties) change little to ensure that the radome can work normally when the temperature is raised.

  • High strength structural properties

The strength of the radome material should be high and rigid enough to satisfy the mechanical stress and bending moment caused by the longitudinal or transverse acceleration of the aerodynamic forces in the spacetime of the missile flying at high speed.

  • Resistance to rain erosion

It plays a decisive role in the design allowable range of impact Angle and the sensitivity of aircraft in rain erosion.

  • Low-temperature sensitivity

The dielectric properties and strength properties of general materials change obviously when they work at high temperature. Therefore, the properties of the radome material, especially the dielectric properties and strength, are affected by the temperature change as little as possible.

Ceramic-based missile radome

Ceramic-based missile radome materials mainly include silicon nitride based, a silicon oxide based and phosphate-based materials. Silicon nitride ceramics have not only excellent mechanical properties and high thermal stability but also low dielectric constant. Its decomposition temperature is 1900 ℃, and its erosion resistance is better than fused silica, and it can withstand 6 ~ 7 Ma rating of flight conditions. Silicon nitride ceramic composite radome is one of the main research targets in various countries, which has been identified as the most promising radome material by the test of the Georgia Institute of Technology. Yttria Stabilized Zirconia (YTZ), also known as yttria-zirconia, is the strongest ceramic material. This material offers the highest flexural strength of all zirconia-based materials, and the research on zirconia-based materials as missile radome is in progress.

Ceramic-based-missile-radome

  • Silica-based material

Because of the high flying Mach number of the missile and the relatively long heating time, if the radome of the medium-range missile is made of a single quartz ceramic material, it cannot meet the bearing requirement of thermal stress. In order to meet the requirements of medium and long-range ground-to-ground tactical and strategic missile radome, quartz glass, high-silica puncture fabric and orthogonal tri-directional quartz fabric reinforced silica matrix composites have been developed and successfully applied.

  • Phosphate-based materials

Phosphate matrix composite material is a kind of Russian characteristic permeable material, which is made by impregnating cloth or fabric with a phosphate solution and then curing under pressure. Aluminum phosphate has stable performance in 1500 ~ 1800 ℃. At present, such materials have been used in cruise missiles, anti-missile missiles, tactical missiles and space shuttles. The most obvious disadvantage of phosphate is that it is highly hygroscopic, so the surface of the composite material needs to be coated with an organic coating for moisture-proof treatment.

  • Silicon carbide ceramic matrix composites

Silicon carbide ceramic matrix composites have a series of excellent properties, such as low density, high-temperature resistance, ablation resistance, erosion resistance, and oxidation resistance, and it has a wide application prospect in the field of aerospace. Since the late 1980s, the United States has successfully developed a series of C/SiC, SiC/SiC ceramic matrix composites, which can be applied to the re-entry nose cone of missiles, the front end of wings and other heat-resistant structures.

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What Are the Nano Zirconia Composite Ceramic Powders?

Zirconia is a new structural ceramic material developed in the 1970s. It is widely used in metallurgy, electronics, chemical industry, machinery and other fields due to its abrasion resistance, corrosion resistance, high strength, and high melting point.

Zirconia ceramic material, as the most important material in advanced ceramics, is an important basic material for the development of modern high-tech industry. In particular, nano-oxide ceramics with its special structure and performance has become the focus of the industry. The following is a brief introduction of the powder materials needed to prepare nano zirconia ceramics.

Ni-P coated nano zirconia composite powders

The preparation process of Ni-P coated nano zirconia (ZrO2) composite powders is firstly to prepare nano-ZrO2 powders by the chemical precipitation method, and then to prepare Ni-P nano-ZrO2 powders by an electroless plating method. Since ZrO2 has no autocatalytic activity in the electroless nickel plating solution, it is necessary to pretreat ZrO2 nanoparticles. Generally, Pd2+ is directly adsorbed on the surface of ZrO2 powder by one-step palladium catalysis method, and then Pd2+ is reduced to palladium in reducing solution so that the surface of nanopowder has the catalytic activity of electroless nickel plating. The two-step sensitization-activation method is usually used in the pretreatment of non – conductive powders. However, it is difficult to remove the residual nickel ions in the powder after two-step treatment, which often brings adverse effects on the activity of the powder. At present, one-step palladium catalysis and in-situ palladium pretreatment are used.

At present, Ni-P coated nano zirconia composite powders have been widely used and studied in semiconductor nanomaterials.

SEM images of Ni-P coated nano zirconia composite powders
SEM images of Ni-P coated nano zirconia composite powders

Zirconia toughened alumina ceramic composite powder

Zirconia toughened alumina ceramic is one of the most widely studied structural ceramic materials. The toughening mechanism of zirconia toughening alumina ceramics is the refinement of matrix grain, the toughening of phase change, the toughening of microcrack, the turning and bifurcation of crack. The properties of zirconia toughened alumina ceramics are mainly determined by the microstructure formed during sintering, and the microstructure is mainly determined by the powder state of raw materials. Therefore, the preparation of high-quality Al2O3/ZrO2 nanocomposite ceramic powders is the prerequisite for the preparation of zirconia toughened alumina ceramics with excellent properties. The preparation methods of Al2O3/ZrO2 nanocomposite ceramic powders mainly include mechanical mixing method, multi-phase suspension mixing method, the sol-gel method, chemical precipitation method, etc.

Alumina is a kind of high-strength matrix in the composite ceramic system of zirconia toughening alumina, and the zirconia in the intercalation provides a phase change toughening mechanism. The use of ZrO2 phase change properties to toughen ceramic materials is still one of the main research topics of ceramic toughening in the future.

Zirconia toughened alumina composite ceramics have excellent corrosion resistance, thermal shock resistance, high strength, and toughness, as well as wide application prospects. Zirconia toughened alumina composite ceramics can be used to make ceramic cutters for the processing of cast iron and alloy, and the interface structure of engineering ceramics can be made to extend the service life of engineering materials. Alumina toughened with zirconia can be used to make wear-resistant ceramic balls. Due to its good biocompatibility, alumina can also be used as a biomedical material for the reconstruction and repair of hard tissues (teeth).

Boron nitride-zirconia composite powder

Boron nitride-zirconia composite powders were prepared by mechanical mixing method. Boron nitride, zirconia, and additives were used as the main raw materials. After mixing, the powders were ball-ground and mixed in an alcohol medium, and then the zirconia composite ceramics were sintered in a hot press sintering furnace. Due to the poor sintering capacity of pure boron nitride and its difficulty in sintering densification, CaO, B2O3, Al2O3, and ZnO are generally added as sintering AIDS.

Boron nitride-zirconia composite ceramics are characterized by high strength, high toughness, high thermal conductivity, low expansion, and excellent physical and chemical properties, such as chemical inertness and chemical corrosion, which are present in molten metals. In addition, it also has excellent thermal shock resistance, erosion resistance, wear resistance and easy processing and other properties, which make the material suitable for thin strip continuous casting side seal plate, jet forming liquid guide pipe, the nozzle for metal spinneret, continuous casting functional refractories and other fields.

Boron nitride - zirconia composite powder
Boron nitride-zirconia composite powder

Nano cerium-zirconium composite oxide powder

The preparation methods of nano cerium-zirconium composite oxide powders include high-temperature roasting, the sol-gel method, coprecipitation method, hydrothermal method, and solid phase reaction method. High-temperature roasting was carried out in a water-ethanol solvent, and the suspension consisting of dry Al (NO3) 3•9H2 O•Ce (NO3) 3•6H2O and monocline phase zirconia nano-powder was pyrolyzed by high-temperature, Al2O3 doped CeO2 coated monoclinal zirconia powders with a particle size less than 100 m were prepared.

Nano cerium - zirconium composite oxide powder
Nano cerium-zirconium composite oxide powder

Nano cerium-zirconium composite oxide materials are used as auxiliary catalysts, mainly used in automobile exhaust treatment, with good high-temperature stability, high REDOX ability, high oxygen storage, and release capacity.

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