CN101186474A - Cement-based composite wave-absorbing material doped with nano-titanium oxide and its preparation method - Google Patents

Abstract

A cement-based composite wave-absorbing material doped with nano-titanium oxide and a preparation method thereof, the composite wave-absorbing material is composed of nano-titanium oxide, a dispersant, Portland cement, and water, and the dispersion system includes the dispersant sodium hexametaphosphate and water The mass percentage of the dispersant sodium hexametaphosphate to the weight of the dispersion system is 0.3%-0.7%, and the ratio of water to dry material, that is, the water-cement ratio is between 0.32-0.38. The preparation steps are: a. preparing nano titanium oxide suspension by ultrasonic wave; b. preparation method of cement-based composite wave-absorbing material mixed with nano titanium oxide. The invention mixes a small amount of nano-titanium oxide wave-absorbing agent into the traditional cement material, so that the cement-based composite material has better wave-absorbing performance and mechanical performance, the economic cost is not much increased, and the preparation process is simple and feasible.

Description

Cement-based composite wave-absorbing material doped with nano-titanium oxide and its preparation method

technical field

The invention belongs to the technical field of building functional materials.

Background technique

Cement-based composite wave-absorbing material is a new type of material that has the function of absorbing electromagnetic waves by mixing wave-absorbing agents into cement or concrete. In terms of civilian use, it can be used to shield the radiation of electromagnetic waves on the human body to achieve the purpose of purifying the environment polluted by electromagnetic waves; it can also be used to prevent data leakage in the computer center and play a role in keeping secrets. In the military, cement-based composite absorbing materials can interfere with radar detection targets and weaken echo signals, so that radars cannot detect fixed targets on the ground or the detection accuracy is significantly reduced, avoiding enemy military strikes. Cement-based absorbing materials used for civil buildings have practical value for electromagnetic waves with a reflectivity of more than 5dB, and cement-based absorbing materials for ground military targets with a reflectivity of more than 7dB for radar waves also have engineering application value.

Foreign countries began to study electromagnetic shielding cement concrete in the early 1990s. Among them, the scientific research group headed by D.D.L. Chung studied the mixing of fine carbon wire, steel paper clip, colloidal graphite, coke powder and stainless steel fiber into cement. The cement-based composite material, the shielding effectiveness of this cement-based composite material within 1.5GHz can generally reach about 40dB, but the reflection attenuation is only 2-4dB. In recent years, some domestic scholars have also carried out research work in this area. For example, Yang Haiyan and others have studied cement mortar mixed with steel fibers. In the frequency range of 2-18GHz, the absorption rate of the cement mortar sample is 4dB and the bandwidth can reach 15.28 GHz, the maximum absorption rate is 9.8dB; Zhao Yanbo and others studied the cement-based porous composite absorbing material mixed with expanded polystyrene (EPS). When the filling rate (volume fraction) of EPS is 60% and the sample thickness is At 20mm, the bandwidth with a reflectivity less than -10dB reaches 6GHz, and the minimum reflectivity reaches -15.27dB at 18GHz; When the amount is 33% (mass fraction) and the thickness is 3mm, the maximum reflectance is about 7dB and the minimum reflectance is 15dB in the 8-12GHz frequency band, indicating that ferrite mixed into cement mortar can improve the absorbing performance of the material.

The frequency of electromagnetic waves shielded by the cement-based shielding materials studied above is almost in the tens of Hz to 1-2GHz. These cement-based shielding materials are mainly used to prevent the leakage of electromagnetic signals and external electromagnetic interference, and their shielding effect on electromagnetic waves is relatively low. Good, but the absorption attenuation and reflection attenuation of electromagnetic waves are poor; the absorbing properties of the cement-based absorbing materials studied are not ideal, and the mechanical properties of the cement-based composite materials mixed with ferrite absorbers are different. Reduced to a certain extent, affecting practical applications.

Contents of the invention

In view of the above-mentioned problems, the object of the present invention is to use nano-titanium oxide as a wave-absorbing agent to form a uniform suspension of nano-titanium oxide through ultrasonic dispersion, and then mix the suspension of nano-titanium oxide with cement evenly under mechanical stirring. The cement-based composite wave-absorbing material is obtained through vibration molding and curing.

The present invention and concrete technical scheme are as follows:

The cement-based composite wave-absorbing material doped with nano-titanium oxide was prepared by ultrasonic dispersion technology and mechanical stirring method. Its composition features are: the composite wave-absorbing material is composed of nano-titanium oxide, dispersant, Portland cement, and water, the dry material is nano-titanium oxide and Portland cement, and the weight percentage of nano-titanium oxide in the dry material is 3 %-7%, and the weight percentage of cement in dry materials is 93%-97%. The dispersion system includes dispersant sodium hexametaphosphate and water, the mass percentage of the dispersant sodium hexametaphosphate to the dispersion system weight is 0.3%-0.7%, and the ratio of water to dry material, that is, the water-cement ratio is between 0.32-0.38.

The preparation steps and necessary process parameters of the composite wave-absorbing material are as follows:

1. Ultrasonic preparation of nano-titanium oxide suspension,

Weigh a certain amount of sodium hexametaphosphate dispersant, dissolve it in a certain amount of water according to the mass percentage of the dispersion system weight of 0.3%-0.7%, keep the concentration of the dispersion system between 7.0%-10%, and then weigh Take 3%-7% nano-titanium oxide, pour it into the above solution, place it in an ultrasonic disperser, and ultrasonically disperse for 20-30 minutes to prepare a uniform nano-titanium oxide suspension.

2. Preparation method of cement-based composite wave-absorbing material doped with nano-titanium oxide

Weigh 93%-97% of 42.5 ^# or 32.5 ^# , 52.5 ^# Portland cement and a certain amount of water, so that the ratio of water to dry material, that is, the water-cement ratio, is kept between 0.32-0.38; put the cement in the stirring Irrigate, start stirring, slowly add the suspension of nano-titanium oxide and water, stir for 3-5 minutes, pour the mixture into the steel mold, then place it on a vibration table and vibrate for 1-2 minutes, smooth the surface, Curing for 1 day under the conditions of 20°C-25°C and humidity of 85-90%, and continuing to cure under the above conditions for 28 days after removing the formwork, to obtain a cement-based composite wave-absorbing material doped with nano-titanium oxide.

The invention mixes a small amount of nano-titanium oxide wave-absorbing agent into the traditional cement material, so that the cement-based composite material has better wave-absorbing performance and mechanical performance, the economic cost is not much increased, and the preparation process is simple and feasible. The reflectivity of the cement-based composite wave-absorbing material in the frequency range of 8-26.5GHz is basically less than 7dB, the minimum reflectivity reaches 17.37dB, and the continuous bandwidth with the reflectivity less than 10dB reaches 11GHz. It shows that the cement-based composite absorbing material has good compatible absorbing performance in the three bands of X (8-12.5GHz), KU (12.5-18GHz) and K (18-26.5GHz), and realizes the effect of broadband absorbing ; At the same time, its mechanical properties are increased by 12.6% and 19.1% compared with the cement slurry, and the mechanical properties are obviously improved.

Description of drawings

The reflectance test figure of Fig. 1 embodiment sample;

The mechanical performance test diagram of the sample of Fig. 2 embodiment.

specific embodiment

Example 1:

1. Ultrasonic preparation of nano-titanium oxide suspension,

Take by weighing a certain amount of sodium hexametaphosphate dispersant according to the mass percentage of the dispersion system weight of 0.5%, dissolve it in a certain amount of water, keep the concentration of the dispersion system at 9.0%, then take by weighing 5% nano titanium oxide, pour into the above solution, placed in an ultrasonic disperser with an ultrasonic power of 150W and an ultrasonic frequency of 40KHz, and ultrasonically dispersed for 25 minutes to obtain a uniform nano-titanium oxide suspension.

2. Preparation method of cement-based composite wave-absorbing material doped with nano-titanium oxide

Weigh 95% of 42.5 ^# Portland cement and a certain amount of water, so that the ratio of water to dry material, that is, the water-cement ratio, is kept between 0.35; put the cement in the mixing tank, start stirring, and slowly add nano-titanium oxide After stirring for 3 minutes, pour the mixture into a steel mold with a cross-section of 180mm×180mm and a thickness of 5-30mm, then place it on a vibrating table and vibrate for 1 minute, and smooth the surface. It was cured for 1 day under the condition of 90% humidity, and continued to be cured under the above conditions for 28 days after removing the formwork to prepare a cement-based composite wave-absorbing material doped with nano-titanium oxide.

3. Test the reflectivity and flexural and compressive strength of the sample after curing for 28 days in the frequency range of 8=26.5GHz. The results are shown in Figure 1 and Figure 2.

From the reflectance of the sample in Figure 1, it can be seen that the reflectance of the cement slurry sample is above 6dB, while the reflectance of the cement-based composite absorbing material doped with nano-titanium oxide is basically below 7dB. The continuous bandwidth of less than 10dB covers 13-24GHz, and the minimum reflectivity appears at 16.2GHz, with a value of 17.37dB, reflecting better broadband absorbing performance.

From the mechanical properties of the samples in Figure 2, it can be seen that the flexural and compressive strengths of the samples after curing for 28 days are improved to varying degrees compared with the cement slurry.

Claims (2)

1. A cement-based composite wave-absorbing material mixed with nano-titanium oxide, its composition characteristics are: the composite wave-absorbing material is composed of nano-titanium oxide, dispersant, Portland cement, and water, and the dry material is nano-titanium oxide and Portland cement, the weight percentage of nano-titanium oxide in dry materials is 3%-7%, and the weight percentage of cement in dry materials is 93%-97%. The dispersion system includes dispersant sodium hexametaphosphate and water, the mass percentage of the dispersant sodium hexametaphosphate to the dispersion system weight is 0.3%-0.7%, and the ratio of water to dry material, that is, the water-cement ratio is between 0.32-0.38. 2. A preparation method of a cement-based composite wave-absorbing material mixed with nano-titanium oxide, characterized in that the preparation steps and process parameters of the composite wave-absorbing material are as follows: a. Ultrasonic preparation of a suspension of nano-titanium oxide, Weigh a certain amount of sodium hexametaphosphate dispersant, dissolve it in a certain amount of water according to the mass percentage of the dispersion system weight of 0.3%-0.7%, keep the concentration of the dispersion system between 7.0%-10%, and then weigh Take 3%-7% nano-titanium oxide, pour it into the above solution, place it in an ultrasonic disperser, and ultrasonically disperse for 20-30 minutes to prepare a uniform nano-titanium oxide suspension. b, preparation method of cement-based composite wave-absorbing material doped with nano-titanium oxide Weigh 93%-97% of 42.5 ^# or 32.5 ^# , 52.5 ^# Portland cement and a certain amount of water, so that the ratio of water to dry material, that is, the water-cement ratio, is kept between 0.32-0.38; put the cement in the stirring Irrigate, start stirring, add nano-titanium oxide suspension and water, stir for 3-5 minutes, pour the mixture into the steel mold, then place it on a vibration table and vibrate for 1-2 minutes, smooth the surface, ℃-25 ℃, humidity of 85-90% under the conditions of curing for 1 day, after removal of the formwork, continue to cure under the above conditions for 28 days, to prepare the cement-based composite wave-absorbing material doped with nano-titanium oxide.