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1.
The thermal conductivity of bio-SiC, a heavily defected material with specific cellular pores (channels), was studied in the temperature range 5–300 K. The bio-SiC sample was prepared from the SiC/Si biomorphic composite through the chemical removal of silicon. The thermal conductivity of silicon embedded in cellular pores of the SiC/Si biomorphic composite was determined.  相似文献   

2.
The thermal conductivity κ and electrical resistivity ρ of a cellular ecoceramic, namely, the SiC/Si biomorphic composite, are measured in the temperature range 5–300 K. The SiC/Si biomorphic composite is fabricated using a cellular biocarbon template prepared from white eucalyptus wood by pyrolysis in an argon atmosphere with subsequent infiltration of molten silicon into empty through cellular channels of the template. The temperature dependences κ(T) and ρ(T) of the 3C-SiC/Si biomorphic composite at a silicon content of ~30 vol % are measured for samples cut out parallel and perpendicular to the direction of tree growth. Data on the anisotropy of the thermal conductivity κ are presented. The behavior of the dependences κ(T) and ρ(T) of the SiC/Si biomorphic composite at different silicon contents is discussed in terms of the results obtained and data available in the literature.  相似文献   

3.
The thermal conductivity κ and electrical resistivity ρ of a SiC/Si biomorphic composite were measured at temperatures T = 5–300 K. The composite is a cellular ecoceramic fabricated by infiltrating molten Si into the channels of a cellular carbon matrix prepared via pyrolysis of wood (white eucalyptus) in an argon ambient. The κ(T) and ρ(T) relations were measured on a sample cut along the direction of tree growth. The experimental results obtained are analyzed.  相似文献   

4.
The electrical resistivity ρ and the thermopower coefficient α of a SiC/Si biomorphic composite fabricated from a porous carbon matrix [prepared through pyrolysis of wood (white eucalyptus)] by infiltrating molten Si into the empty channels of the matrix were measured in the temperature ranges 100–950 and 100–750 K, respectively. Silicon reacts chemically with the carbon of the matrix to produce 3C-SiC, which, in combination with the excess Si unreacted with carbon, forms the SiC/Si biomorphic composite. The SiC/Si samples studied had a concentration of “excess” Si of ~30 vol % and a porosity of ~13–15 vol %. Measurements of ρ were carried out on samples cut either along (ρ) or across (ρ) the tree growth direction, and α was measured on a sample cut along the tree growth direction.  相似文献   

5.
The thermal conductivity κ and electrical resistivity ρ of a white-eucalyptus cellular carbon preform used to fabricate silicon-carbide-based (SiC/Si) biomorphic ceramics have been measured in the 5-to 300-K temperature interval. The carbon preform was obtained by pyrolysis (carbonization) of white-eucalyptus wood at 1000°C in an argon ambient. The κ(T) and ρ(T) relations were measured on samples cut along the tree growth direction. The experimental data obtained were processed.  相似文献   

6.
A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature and magnetic field for the SiC/Si composite fabricated from spanish beech wood and bio-SiC, a high-porosity material formed by chemical extraction of silicon from this composite. The main charge transport parameters of these materials have been determined and analyzed. It has been shown that electric transport in bio-SiC is effected by n-type carriers with a high concentration of ~1019 cm?3 and a low mobility of ~1 cm2 V?1 s?1. The relations obtained have been analyzed by invoking the theory of quantum corrections to conductivity.  相似文献   

7.
The effect of the vibrational strain amplitude on the Young’s modulus and ultrasound absorption (internal friction) of a SiC/Si biomorphic composite prepared by pyrolysis of sapele wood followed by infiltration of silicon were investigated. The studies were conducted in air and in vacuum by the acoustic resonance method with the use of a composite vibrator in longitudinal vibrations at frequencies of about 100 kHz. Measurements performed on sapele wood-based bio-SiC/Si samples revealed a substantial effect of adsorption-desorption of molecules contained in air on the effective elasticity modulus and elastic vibration decrement. Microplastic characteristics of the SiC/Si composites prepared from wood of different tree species were compared.  相似文献   

8.
The heat capacity of biomorphic silicon carbide, a high-porosity material with specific cellular pores, is measured in the temperature range 3.5–60 K. Biomorphic silicon carbide is prepared by the chemical removal of excess silicon from the SiC/Si biomorphic composite, a product of eucalyptus wood. It is shown that the major contribution to the heat capacity of biomorphic SiC comes from surface vibrational modes.  相似文献   

9.
The thermopower coefficients of bio-SiC and SiC/Si ecoceramics prepared from sapele tree wood have been measured in the temperature interval 5–300 K. The measurements have been performed both along and perpendicular to empty (bio-SiC), as well as empty and partially silicon-filled (SiC/Si) channels in the samples. In bio-SiC, a contribution to thermopower associated with electron drag by phonons has been shown to exist within the temperature interval 5–200 (250) K. No such effect is realized in SiC/Si. This is assumed to derive from the presence in this material of heavily doped silicon embedded in SiC channels and the dominant part it plays in the behavior of the thermopower of this ceramics. The results obtained for the thermopower are compared with the available data for bio-SiC prepared from white eucalyptus tree wood and heavily doped bismuth.  相似文献   

10.
The electrical resistivity of Sapele-based biomorphic SiC/Si materials was measured in a wide temperature range from 10 K to room temperature. The samples were fabricated by the reactive infiltration of molten silicon into a carbonized Sapele (African Entandrophragma Cylindricum) wood preform. All the samples studied contained residual Si (10–35 wt %). It was found that the resistivity-temperature (ρ(T)) dependences have semimetallic behavior which becomes very close to linear metallic behavior at 100 < T < 300 K. The obtained values of resistivity were quite low (ρ ≈ 0.002–0.02 Ω cm) and showed strong anisotropy: the resistivity along the wood growth axis was several times lower than that in the perpendicular direction. The extent of this anisotropy was in correlation with the amount of residual Si (and, hence, with the amount of residual porosity) in a sample. The resistivity perpendicular to the wood growth axis drastically increased with the Si content, whereas the resistivity parallel to it was practically independent of the Si content. It is suggested that the presence of residual carbon in the samples and carrier scattering at SiC/Si interphases could determine the observed character of ρ(T) dependences.  相似文献   

11.
This paper reports on the results of a comparative investigation into the elastic and microplastic properties of biomorphic SiC/Si composites and biomorphic SiC prepared by pyrolysis of oak and eucalyptus with subsequent infiltration of molten silicon into a carbon matrix and additional chemical treatment to remove excess silicon. The acoustic studies were performed by the composite oscillator technique using resonant longitudinal vibrations at frequencies of about 100 kHz. It is shown that, in biomorphic SiC (as in biomorphic SiC/Si) at small-amplitude strains ε, adsorption and desorption of the environmental (air) molecules determine to a considerable extent the Young’s modulus E and the internal friction (decrement of acoustic vibrations δ) and that the changes in E and δ at these amplitudes are irreversible. The stress-microplastic strain curves are constructed from the acoustic data for the materials under study at temperatures of 100 and 290 K.  相似文献   

12.
In the temperature range 100–650 K, the linear expansion coefficient β was measured for the SiC/Si biomorphic composite, a new cellular ecoceramic fabricated from a porous cellular carbon matrix prepared through pyrolysis of wood (white eucalyptus) in an argon ambient with subsequent infiltration of molten Si into the channels of the matrix and the formation of 3C-SiC. The SiC/Si samples studied had an “excess” ~30% volume concentration of Si and a porosity of ~13–15%. The measurements were conducted on samples cut along (β) and across (β) the tree growth direction. The measured values of β(T) of SiC/Si are compared with literature data available for the linear expansion coefficients of Si and 3C-SiC.  相似文献   

13.
This paper reports on measurement of the heat capacity at constant pressure C p of silicon bio-carbide prepared within the 5–300 K temperature interval from beech tree wood (bio-SiC(BE)), and within 80–300 K, from tree wood of sapele (bio-SiC(SA)), as well as SiC/Si ecoceramics of beech, sapele, and white eucalyptus wood. It has been shown that in bio-SiC(BE) the measured heat capacity contains a significant contribution of surface heat capacity, whose magnitude decreases with increasing temperature. Of the ecoceramics, only SiC/Si(SA) characterized by a high enough porosity has revealed a small contribution to the heat capacity coming from its surface component. The experimental results obtained are discussed.  相似文献   

14.
The specific heat at constant pressure and the velocity of sound in the SiC/Si biomorphic composite prepared from white eucalyptus wood are measured in the range 3.5–65 K and at 77 K, respectively. The heat capacity of the SiC/Si sample under investigation is calculated within three proposed models according to the Kopp-Neumann additivity rule.  相似文献   

15.
The electrical resistivity and thermal conductivity of high-porosity (~52 vol %, channel-type pores) bio-SiC samples prepared from sapele wood biocarbon templates have been measured in the temperature range 5–300 K. An analysis has been made of the obtained results in comparison with the data for bio-SiC samples based on beech and eucalyptus, as well as for polycrystalline β-SiC. The conclusion has been drawn that the electrical resistivity and thermal conductivity of bio-SiC samples based on natural wood are typical of heavily doped polycrystalline β-SiC.  相似文献   

16.
The amplitude and temperature dependences of the Young’s modulus and the internal friction (ultrasonic absorption) of biomorphic carbon, silicon carbide, and SiC/Si composite produced from medium density fiberboard (MDF) by pyrolysis (carbonization), followed by infiltration of molten silicon into the prepared carbon preform have been studied in the temperature range 100–293 K in air and under vacuum. The measurements have been performed by the acoustic resonance method with the use of a composite vibrator for longitudinal vibrations at frequencies of approximately 100 kHz. The data obtained by acoustic measurements of the amplitude dependences of the elastic modulus have been used for evaluating the microplastic properties of samples under study. It has been shown that the Young’s modulus, the decrement of elastic vibrations, and the conventional microyield strength of the MDF samples differ from the corresponding data for previously studied similar materials produced from natural eucalyptus, beech, sapele, and pine woods. In particular, the desorption of environmental molecules at small amplitudes of vibrations, which is typical of biomorphic materials based on natural wood, is almost absent for the MDF samples. The results obtained have been explained by different structures and the influence of pores and other defects, which, to a large extent, determine the mechanical characteristics of the biomaterials under investigation.  相似文献   

17.
傅春寅  鲁永令  曾树荣 《物理学报》1989,38(9):1534-1539
利用真空淀积和真空热处理(1050℃,20h)向Si单晶中引入了稀土元素Ce,热处理过程中Ce首先与Si形成合金,然后向Si中扩散,于是在Si中形成Ce的扩散层。用二次离子质谱(SIMS)技术测定了Ce的纵向相对浓度分布,并据此分析了Ce在Si中的扩散系数。并在77—450K范围内测量了扩散层的平均电导率。 关键词:  相似文献   

18.
The dielectric properties of nano Si/C/N composite powder and nano SiC powder at high frequencies have been studied. The nano Si/C/N composite powder and nano SiC powder were synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) and SiH4–C2H2, respectively, by a laser-induced gas-phase reaction. The complex permittivities of the nano Si/C/N composite powder and nano SiC powder were measured at a frequency range of 8.2–12.4 GHz. The real part (′) and imaginary part (″) of the complex permittivity, and dissipation factor (tg δ=″/′) of nano Si/C/N composite powder are much higher than those of nano SiC powder and bulk SiC, Si3N4, SiO2, and Si, especially the tg δ. The promising features of nano Si/C/N composite powder would be due to more complicated Si, C, and N atomic chemical environment than in a mixture of pure SiC and Si3N4 phase. The charged defects and quasi-free electrons moved in response to the electric field, diffusion or polarization current resulted from the field propagation. Because there exists graphite in the nano Si/C/N composite powder, some charge carries are related to the sp3 dangling bonds (of silicon and carbon) and unsaturated sp2 carbons. The high ″ and tg δ of nano Si/C/N composite powder were due to the dielectric relaxation. The nano Si/C/N composite powder would be a good candidate for electromagnetic interface shielding material.  相似文献   

19.
Yamada S  Song BS  Asano T  Noda S 《Optics letters》2011,36(20):3981-3983
We experimentally investigate and compare the thermo-optic effects of silicon carbide (SiC) and silicon (Si) photonic crystal nanocavities on their resonant wavelengths over a temperature range of 25?°C to nearly 200?°C by using a laser source with a wavelength close to the telecommunication wavelength range of 1550?nm. The measured results clearly show that the shift in the resonant wavelength of the SiC cavity is significantly (by a factor of 3) less than that of the Si cavity for the same ambient temperature changes. In addition, the measured results provide direct estimates of the thermo-optic coefficients (dn/dT) for thin SiC and Si as 3.87×10(-5)/°C and 1.60×10(-4)/°C, respectively, for this temperature range.  相似文献   

20.
采用半固态搅拌铸造法制备Al Si7-Si C复合材料,并利用真空压铸工艺实现了其近净成形,结合第一性原理计算方法研究了共晶Si对Si C颗粒和基体界面结合强度的影响.结果显示,在Al Si7-Si C复合材料中,发现较为严重的共晶Si偏析现象,当Si C颗粒同时处于共晶Si和α-Al边界时,形成了少量的共晶Si夹杂、被大量共晶Si包裹、完全被共晶Si包裹三种典型的界面.第一性原理计算结果显示,在C端和Si端的Si/Si C界面中,弛豫后top Si1配位方式具有最大的粘附功,与Al/Si C界面相比,Si/Si C界面具有更高的结合强度.Si偏析相提高了界面处的电荷密度,因而具有更好的界面结构稳定性.  相似文献   

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