Cement-based Composite Materials For Microwave Absorbing

The research and application of radar absorbing materials have been carried out since thirties of the twenty-century. Some of the achievements have been applied in military since then. Absorbing materials are mostly been used in motion military targets as coating materials or structure materials. There are few reports on the structure type materials of the fixed targets, such as aerodrome, martial blindage and military command post and a little the cement-based as electromagnetic shielding materials. It would have great military significant and academic values to study the absorbing materials of cement-based composites and to improve the ability disturbing radar detecting of the ground military target due to cement was the main building material for fixed ground military target and military construction. With the rapidly development of economic, electromagnetic radiation has become to be the fourthly pollution following the atmospheric pollution, water pollution and noise pollution and imperil the health of human beings seriously. Using cement-based absorbing composites would be one of the effective methods to protect the electromagnetic radiation according to the defend requirement of civil construction. Therefore it would have great significant to study the cement-based absorbing composites materials both in military and civil utilization.Both the cement-based absorbing composites materials and the ordinarily absorbing materials are based on the same design principle that is the absorbing capability of cement-based absorbing composites depend greatly on the absorbing agents. Some of the materials that have been proved to have the absorbing ability such as carboxide iron powder, ferrite, some nanometer materials and carbon fibers had been used as the absorbing agents in cement-based material in the application study, the compatibility of the absorbing agent with cement component and the absorbing capability of the cement-based absorbing composites been measured and discussed in this paper. The results show that nano-TiO2 and ferrite as the absorbing agent not onlyhave the perfect compatibility with cement component but also have good absorbing capability in 8-18 GHz frequency range.Effect of dispersed technology, the content of absorbing agent, thickness of sample and kinds of cementitious materials on the absorbing capability of cement-based materials composites had been studied when nano-TiO2 and ferrite had been used as absorbing agent. The mechanical properties of the cement added nano-TiO2 or ferrite as absorbing agent had been tested. The absorbing capability and compatibility and the absorbing capability over a long age were investigated respectively to the cement-based composite with nano-TiO2 as absorbing materials in the frequency range of 2-26.5 GHz (S, C, X, KU and K) and to that with ferrite in the range of 8~18 GHz (X and KU). It is revealed that cement-based absorbing composites with 5% nano-TiC>2 had the minimum reflectivity of - 16.26dB, the continuous bandwidth reaches 4.5GHz when reflectivity is less than - lOdB, the continuous bandwidth reaches 21.1 GHz when reflectivity is less than- 5 dB, and have good capability of absorbing compatibility in X, KU and K wave band and have a good stability of absorbing capability for a long period of time also. The flexure strength and compressive strength of 28d of this cement-based absorbing composites improved by 12.6% and 19.1% respectively compared with cement paste. Cement-based absorbing composites with 35% JH10 ferrite had the minimum reflectivity of - 9.13dB, the continuous bandwidth reaches all the test wave band when reflectivity is less than - 5dB, and had good capability of absorbing compatibility in X and KU wave band and a good stability of absorbing capability for a long period of time. The flexure strengths and compressive strengths of 28d of this cement-based absorbing composites decreased by 50% and 50% respectively compared with cement paste.Comparing the physical properties of the nano-TiC>2 with ordinary TiC?2 and comparing the absorbing capability and electromagnetic parameter of the cement-based absorbing materials composites with nano-TiO2 and ordinary TiO2, it could be proposed that the cement-based absorbing materials composites with nano-TiC>2absorbing mechanism of was due to the nano-TiO2 had higher transmittancefor electromagnetic wave compared that of the ordinary TiC>2, which decrease the reflect of electromagnetic wave greatly, and the surface area is four magnitude larger than ordinary TiO2 which improved the activity and accelerative the movement of atom and electron, and then improved the magnetization, polarization and conduction, made the electromagnetic energy transform into the heat. The matching characteristic of the electromagnetic parameter of cement-based absorbing materials composites could have been improved with the incorporation of nano-TiO2. The quantum dimension effect of the nanometer materials resulted in the abruption of electronic level of nano-TiCh particle, and the interval of the abruption level was in the energy range of the electromagnetic wave (l0"2eV~10"5eV) which bring out the new absorbing channels and improved the absorbing capability of nano-TiCh and the cement-based absorbing materials composites.Some research were carried out on the manufacture and the absorbing capability of two-member absorbing agent, and cement-based double layers absorbing materials had been investigated as well. Single layer and double layers of cement-based composite added compound magnetism ferrite and resistance type of graphite had better absorbing capability. Some problems which should be taken into account in the manufacture of the composite absorbing agent and double layers absorbing material have been discussed, further study engaged in the future have been proposed.