| Mesoporous material has high specific surface area and rich pore structure,and the pore size range of 2-50nm,it is mainly applied to the fields of catalytic separation,ion adsorption,drug release.At present,mesoporous material is mainly synthesized by chemical reagents,but mesoporous material prepared by this method has poor hydrothermal stability and mechanical strength.In recent years,more and more attention has been paid to composites that mesoporous material as supporter encapsulated nano-magnetic material.Nano-NiZn ferrite is a kind of nanomagnetic materials with ferromagnetic and dielectric properties.The ferrite has fine grains,strong chemical activity and low density,it is widely applied to the fields aeronautics and spaceflight and electromagnetic shielding because of its good absorbing properties at high frequency.This thesis is supported by the National Natural Science Foundation of China "based on outer template to preparation of mesoporous materials and absorbing properties of natural zeolite(51372108)".In this paper,the preparation and characterization of mesoporous material using natural mordenite as raw material,nano-NiZn ferrite and composite material were studied,and the formation mechanism of mesoporous material prepared by natural morde-nite and the absorbing properties,preparation and absorbing mechanism of nanocomposites were determined.(1)Preparation of mesoporous material:MCM-41 and SBA-15 mesoporous materials were prepared by hydrothermal method using natural mordenite as raw material,hexadecyl trimethyl ammonium bromide(CTAB)and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)triblock copolymer(P123)as template.The samples were characterized by X-ray diffraction(XRD),specific surface and porosity analyzer,scanning electron microscope(SEM),transmission electron microscope(TEM),and vector network analyzer(VNA).The effects of template type,template concentration,reaction temperature,crystallization time and pore expanding agent on the phase structure,specific surface area,pore diameter,pore volume and micro-morphology of mesoporous material were systematically studied.Results showed that the concentration of CTAB as template agent is 3.6 g/L,pH value is 10.5,crystallization temperature is 100℃,crystallization time is 60h,then MCM-41 ordered mesoporous material of which specific surface area is 1016.723 m2/g,the average pore size is 3.716 nm,pore volume is 1.087 cm3/g can be prepared.And with the concentration of P123 as template agent is 6g/L,reaction temperature is 35℃,crystallization temperature is 110℃,crystallization time is 48h,then SBA-15 ordered mesoporous material of which specific surface area is 560.276 m2/g,the average pore size is 8.802 nm,pore volume is 1.167cm3/g can be prepared,and the average pore size expand to 23.529nm and the pore volume increases to 1.46 cm3/g by adding the swelling agent of sym-trimethylbenzene.The mechanism of calcining-acid/base treatment of natural mordenite and the formation mechanism of mesoporous materials are proposed.(2)Preparation of nano-NiZn ferrite:by hydrothermal method,the nano-NiZn ferrite with fine grain size,uniform particle size distribution and good dispersion was prepared.The effects of nickel zinc ratio,iron salt concentration,crystallization temperature and crystallization time on phase structure,micro-morphology and microwave absorbing properties of nano-NiZn ferrite were studied and characterized by XRD,SEM,TEM,VNA.Results showed that the polyethylene glycol is adopted as surface active agent,nickel zinc ratio is Ni0.6Zn0.4Fe2O4,iron salt concentration is 0.40mol/L,crystallization temperature is 180℃,crystallization time is 8h under the conditions,the prepared nano-NiZn ferrite is spherecal,particle size is 15nm.The loss factor of the nano-NiZn ferrite reached the maximum value of 1.15 at 3.21 GHz,the minimum value of the absorption reflectance in the frequency range of 1-6GHz was-10.69dB,and microwave absorbing properties are better in the high frequency L(1-2 GHz),S(2-4 GHz)and C(4-8 GHz)bands.(3)Mesoporous material encapsulates nano-NiZn ferrite:the thesis was realized mesoporous material dispersed nano-NiZn ferrite to solve the agglomeration problem of nano-NiZn ferrite in utilization process.By methods of chemical coprecipitation and suspension polymerization,the preparation of nano-NiZn ferrite composites encapsulated in mesoporous material was completed.The phase structure,pore structure parameters,micro-morphology and microwave absorbing properties of nano-composites were characterized by XRD,specific surface and porosity analyzer,SEM,TEM,VNA.The results showed that the specific surface area of the composite prepared by suspension polymerization was 330.385m2/g,while the specific surface area of the raw mesoporous material was 530.739m2/g,the specific surface area decreased 200.354m2/g,and the average pore size decreased from 23.529nm to 9.725nm,the average pore size reduced 13.804nm.The nano-NiZn ferrite of the composites prepared by suspension polymerization has a relatively complete grain size and a higher relative crystallinity.Nano-NiZn ferrite encapsulated by suspension polymerization is better than coprecipitation.Microwave absorbing properties of composite materials prepared by suspension polymerization method were enhanced in L,S,C band,while it also has a certain microwave absorbing properties in X and Ku band,and the effective absorbing frequency band of less than-10dB was increased from 1.19GHz to 2.89GHz.The composite of mesoporous materials and nano-NiZn ferrite has synergistic effect,which widened the frequency range of absorbing microwave and enhanced the absorbing property,and microwave absorbing properties of nanometer composite materials were improved.The absorbing properties of nanometer composite materials are mainly derived from nano-NiZn ferrite,and the resonance loss caused by microstructure is the key to the absorbing properties of nano-NiZn ferrite encapsulated in mesoporous materials,which the periodic dielectric loss conforms to the law of intrinsic vibration,and the eigenvibration frequency formula was calculated.In the dissertation there are 113 figures,22 tables,181 references. |
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