The recently proposed technique of excess infrared spectroscopy was extended for the first time to a solid system to explore the host–guest interactions between the framework of zeolite Y and the encapsulated lanthanum species. By employing infrared, excess infrared and Raman spectroscopies, the physical insights into the band shifts/intensity variations of asymmetric TO4 (T = Si, Al) stretching and T–O–T bending were revealed. In the ion-exchange process, the ring distortions were sensitively distinguished by the red shift of the T–O–T bending bands. Upon dehydration, the strengthening effect on the T–O bond was demonstrated by the absorption of the interaction pair between the zeolite framework and dehydrated lanthanum species ([La(OH)n](3−n)+ (n = 1, 2) and La3+), revealing the mechanism of the stabilization effect of lanthanum species on the zeolite framework. Also, the Raman band located at 362 cm−1 was found to be directly related to the 6-membered rings in the hexagonal prisms of zeolite Y. Moreover, Raman spectroscopy showed the capability to describe the distinction between rare earth oxides within and outside the microporous zeolites. XPS, 27Al and 29Si MAS NMR were also performed for further validations.

Hollow silicon boron nitride (Si-B-N) ceramic fibers with composition of Si0.3BN1.4 were prepared by melt-spinning, partial curing with trichlorosilane (HSiCl3), and pyrolysis of a novel polyborosilazane under NH3 up to 1000°C. The polyborosilazane fibers with low ceramic yield were partially cured to make sure the hollow Si-B-N ceramic fibers could be fabricated after pyrolysis. The hollow Si-B-N ceramic fibers were ~16μm in diameter with inner hollow pore diameter of ~4μm, and showed good average tensile strength of 1.03GPa and elastic modulus of 106GPa. Moreover, the hollow Si-B-N ceramic fibers also exhibited excellent dielectric properties with the average dielectric constant real part and loss tangent about 3.06 and 0.0032 at 2–18GHz, respectively, making them to be promising microwave-transparent materials.

We report a metamaterial absorber (MA) with a broad absorption band in the frequency region of 2–4 GHz, whose thickness is not limited to the quarter-wavelength. Theoretical and experimental results show that the absorber has two adjacent absorption apexes at 2.24 and 3.46 GHz, respectively, which are both related to the electric and magnetic resonances of the metamaterial. The absorption is over 68% in the whole wave band of 2–4 GHz provided the thickness of 4 mm. The distributions of the surface currents and the power loss density indicate that the surface currents produced by the electric and magnetic resonances are strongly consumed by the resistive patches. This low-frequency absorber has potential applications in many scientific and martial fields.

A polyferrocarbosilane(PFCS) is synthesized from liquid polysilane and ferrocene.Continuous Fe-containing silicon carbide(SiC(Fe)) fibers are prepared with the following process: The PFCS is porous melt-spinning,the resulted green fibers are cured by heating in air,and the cured fibers are continuously sintered under an inert atmosphere at 1 320 ℃.The fibers are characterized by chemical element analysis、Raman、XRD、29Si-NMR、HRTEM and XPS et al.The results show that the fibers are composed of free carbon、β-SiC and small amount of Fe3Si-like crystalline,amorphous SiC2O2、SiCO3、SiO4 and SiC3O and so on. A carbon-enriched layer of about 120 nm is formed on the surface of the fibers,the atomic concentration of element carbon decreases from edge to inner.

SiC fibers are a kind of anisotropic microwave absorbing materials due to their fiber-shaped semi-conductive properties. In this paper, oriented SiC short fiber sheets were prepared and their anisotropic electromagnetic parameters and microwave absorbing properties were measured and analyzed. It is found that axial permittivity of SiC fibers was several times larger than their radial permittivity. With increasing volume content, both real part and imaginary part of permittivity increased obviously. Simulated microwave absorbing properties based on measured anisotropic electromagnetic parameters coincide well with those measured results. Both the orientation angle and the number of layers, as well as the fiber direction of the top layer, affect the anisotropic property greatly. The higher the orientation angle and the number of layers, the more isotropic microwave absorbing properties the multilayer sheets have.

Continuous Fe-containing silicon carbide (SiC(Fe)) fibers were prepared for the first time from a precursor polyferrocarbosilane (PFCS), which was synthesized from polydimethylsilane and ferrocene, followed by melt-spinning, curing in air, and continuous pyrolysis at 1320°C in N2 atmosphere. The structural materials prepared with the fibers and resin show good radar-wave absorbing property in the frequency region of 2 to 18GHz. PFCS was analysized with elemental analysis, IR, NMR, XPS and the other characterizations. As a result, element iron was inducted to the PFCS; the structure of PFCS is established, the backbone of PFCS is made up of -Si-CH2-, with -CH3, -CH2Si, or -H connected to atom Si of the main chains; ferrocene exists as that the cyclopentadienyl rings connect with atoms Si of the chains, and therefore ferrocene acts as crosslinker of the chains. The continuous SiC(Fe) fibers were composed of free carbon, β-SiC and amorphous SiCxO4-x by HRTEM analysis.

Tensile strength of SiC fibers are determined by the flaw size, so the dispersion of tensile strength is the reflection of the defect types and the dispersion of flaw size. The relationship between tensile strength and diameter was firstly deduced using Weibull theory, and then was compared with experimental results of KD-SiC fibers (fabricated by authors). It is concluded that the critical defects of KD-SiC fibers are internal defects. In addition, mirror constant of KD-SiC fibers is about 2.4 MPa.m(0.5) as calculated from the fracture mirror analysis. Surface defects usually lead to lower tensile strength while internal defects usually have higher thensile strength.

In order to prepare carbide silicon radar-wave absorbing fibers,the continuous carbide silicon(SiC(Fe)) fibers containing Fe were prepared for the first time from a precursor polyferrocarbosilane(PFCS),which was synthesized from polydimethylsilane and ferrocene,followed by melt-spinning,curing in air,and continuous pyrolysis at 1320℃ in N2 atmosphere.The structural materials prepared with this fibers and resin show good radar-wave absorbing properties.XPS depth analysis shows that a carbon-enriched layer of about 100nm is formed on the surface of the fiber and the atomic concentration of element Fe increases a little from edge to inner.The free carbon arranges gradually in order with increasing the temperature by Raman spectra analysis.The effect of the free carbon on the properties of the continuous SiC(Fe) fibers was studied.The results show that the free carbon is of benefit to decreasing the specific resistance but increasing the complex permittivity(e′ and e″) and relative complex permittivity(er) of the fibers.

Using polydimethylsilane as silica source, silica aerogels were synthesized via a polymer supercritical method. The silica aerogels, with an average pore diameter of 15 nm before carbon removal, are hydrophobic, and their specific surface area and pore volume are 27.68 m2/g and 0.1037 cm3/g respectively. After carbon removal, the silica aerogels, which have an average pore diameter of 3.23 nm, become hydrophilic. Their specific surface area and pore volume are 500.6 m2/g and 0.4043 cm3/g respectively. Moreover, the reaction mechanism of silica aerogels prepared by this processing method was discussed.

Silicon carbide fiber reinforced siliconoxycarbide(Si-O-C) composites were fabricated via precursor infiltration and pyrolysis using polysiloxane. Flexural strength, tensile strengths, shear strength, dentsity, thermal expansion coefficient, thermal conduction coefficient, ablative properties of SiCf/Si-O-C composites were tested . The results indicated that SiCf/Si-O-C composites had fairly excellent properties. Microstructure and properties of SiCf/Si-O-C composites was discussed, the high properties were mainly attributed to ideal interface structure and density.

Silicon carbide(SiC) fibers were directly synthesized by chemical vapor growth(CVG). Methyltrichlorosilane(MTS) was selected as the Sic gaseous source and, ferrocence and thiophene as the catalyst and the cocatalyst, respectively. The influences of pyrolysis temperature, the contents of catalyst and the cocatalyst, and the molar ratio of H-2 to MTS on the morphologies of the pyrolysis products were investigated, respectively. The products were identified by X-ray diffraction (XRD), scanning electron microscopy(SEM) coupled with energy-dispersive X-ray (EDX), respectively. The results show that, the products are composed of beta-SiC. The growing of Sic fibers suggests a conditions-dependent process. Sic fibers with different diameters (20 nm-1.5 mu m) and length (10 mu m to several micrometers), therefore, can be synthesized directly by CVG under various conditions without the help of laser, high or reduced pressure.

Polyferrocarbosilane(PFCS) was synthesized from polydimethylsilane and ferrocene. Low specific resistance Si-Fe-C-O fibers were prepared with the following process: The PFCS was melt-spun, the resulted green fibers were cured by heating in air, and the cured fibers were sintered under an inert atmosphere. The preparation techniques of continuous Si-Fe-C-O fibers were investigated. The results show that the specific resistance of the Si-Fe-C-O fibers is reduced to 10(-2)Omega.cm, when the amount of ferrocene in feed is 2%. The tensile strength of the fibers is about 2.0GPa, and the length of the fibers is more than 500 meters. The element iron contained in the fiber accelerates the growth of beta-SiC crystalline grain. XPS depth analysis shows a carbon-enriched layer of about 120nm on the surface of fiber, the atomic concentration of element Fe increasing a little from edge to inner.

Polymethylsilane is sensitive to oxygen and pyrophoric sometimes. Si-Si bond and Si-H bond are not stable and can be oxidized into Si-O-Si under the condition of higher temperature and humidity. Because of the existence of plenty of the bonds of Si-H, polymethylsilane can be crosslinked from dehydrogenation above 120°C and the rate of dehydrogenation is increased with the increase of temperatures. Its ceramic yield is not high because low-molecular-mass volatile species are escaped from the system during pyrolysis. The pyrolytic products mostly are β-SiC microcrystalline, and the mole ratio of Si to C is 1.23 with a small amount of oxygen.

Thermal Curing process was adopted to improve the traditional air-process to lower the oxygen content of continuous silican carbide fibers by leading oxygen as little as possible to the fibers during their curing treatment. The influence of the thermal curing process on the oxygen content of the fibers, the structure and properties of fibers were systematically studied by means of IR, EA (Element Analyse), SEM and XRD.

Ceramic fibers with the Si-C-O-Al composition were prepared by melt-spinning of polyaluminocarbosilane (PACS), initial curing in air and then thermal curing, before finally being pyrolyzed at 1300degreesC. The ceramic fibers so-obtained were sintered at 1800degreesC in argon to produce Si-C-Al ceramic fibers as a super high temperature-resistant reinforcement. When the Si-C-O-Al fibers were sintered to the Si-C-Al ceramic fibers, the structural evolution and the associated properties were studied in comparison to PCS-derived Si-C-O ceramic fibers with respect to tensile strength, creep resistance, electrical resistivity, morphology, and crystalline grain size using Si-29 MAS NMR, C-13 MAS NMR, AES, XRD and SEM. The Si-C-O-Al ceramic fibers had low creep resistance because they contained high levels of silicon oxycarbide, poorly organized SiC crystalline grains at the nanometer level and high levels of free carbon. The electrical resistivity of the Si-C-O-Al ceramic fibers was high due to the high level of silicon oxycarbide. However, the Si-C-Al ceramic fibers were strongly resistant to creep due to a silicon oxycarbide free structure, a well-organized and crystallized SiC content and a lower content of free carbon. The absence of silicon oxycarbide in the Si-C-Al ceramic fibers is responsible for their low electrical resistivity and high tensile strength retention at high temperature.

Trilobal polycarbosilane(PCS) fibers were prepared by melt spinning PCS precursor through Y-shaped spinneret. Then, after curing in air and heat treatment under N2 atmosphere, trilobal silicon carbide fibers were manufactured. The effect of spinning temperature and velocity on the fibers degree of profile was analyzed. Preparation conditions such as curing, heat-treatment and microwave-absorbing properties were also studied. Compared with circular SiC fibers, the fiber exhibits higher mechanical properties and microwave-absorbing properties. The structural radar absorbing materials, composed of the fibers with resin, exhibit a reflection attenuation amount of 10～20 dB in the range of 8～18 GHz.

Nano-nickel particles were dispersed into polycarbosilane (PCS) homogeneously and subsequently the silicon carbide (SiC) fibers containing nickel were prepared by melt spinning, curing treatment and sintering. It was discovered that the melt spinning temperature of PCS and the diameter of PCS fibers increased after adding nano-nickel particles. When the weight-gain of PCS fibers caused by the curing treatment reaches to 9%-11% at optimum the pyrolytic temperature was 1250°C, the ultimate SiC fibers possessed the highest tensile strength. The forming Ni was intermetallics in ceramic fibers and adding nano-Ni particles accelerated grain growing of β-SiC during pyrolytic process.