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1.
Ken’ichiro Kita Masaki Narisawa Atsushi Nakahira Hiroshi Mabuchi Masaki Sugimoto Masahito Yoshikawa 《Journal of Materials Science》2010,45(13):3397-3404
We synthesized ceramic fibers based on silicon carbide (SiC) from polymer blends of polycarbosilane (PCS) and polymethylphenylsiloxane
(PMPhS) by melt-spinning and radiation curing. PMPhS was compatible with PCS up to 30 mass%, and formed a transparent melt
at temperatures higher than 513 K. The softening point was also lowered by adding PMPhS and 15 mass% of PMPhS to PCS was the
most suitable condition for obtaining thin fibers with an average diameter of 14.4 μm. Due to the lowered softening point
of the PCS–PMPhS fibers, γ-ray curing in air was adopted. The ceramic yield of the cured fiber was 85.5% after pyrolysis at
1273 K. In spite of the small diameter, the resulting tensile strength at 1273 K was rather limited at 0.78 GPa. Blooming
of the PMPhS component during pyrolysis may have caused surface defects. After high-temperature pyrolysis at 1673–1773 K,
a porous nanocrystalline SiC fiber with a unique microstructure was obtained with surface area of 70–150 m2/g. When the fiber was pyrolyzed at the same temperature under a highly reductive atmosphere, wire bundle-shaped fibers were
obtained by gas evolution and reactions. 相似文献
2.
Polycarbosilane (PCS) ceramic precursor fibers are irradiated in a nuclear reactor and pyrolyzed under inert atmosphere. Bridge
structure of Si–CH2–Si is formed in the irradiated products by the rupture of Si–H bonds and succeeding cross-linking. When irradiated at the
neutron fluence of 2.2 × 1017 cm−2 under N2 atmosphere, the gel content and ceramic yield at 1,273 K of PCS fibers are up to 80% and 94.3%, respectively, and their pyrolysis
products are still fibrous, which illuminates that the infusibility of PCS fibers has been achieved. FT-IR spectra indicate
that the chemical structure of pyrolysis products is very similar to that of pure SiC, while X-ray diffraction curves suggest
that β-SiC microcrystals are formed in the fibers, and their mean grain size is about 7.5 nm. The oxygen content (1.69–3.77 wt%)
is much lower than that of conventional SiC fibers by oxidation curing method (about 15 wt%). Tensile strength of the SiC
fibers is up to 2.72 GPa, which demonstrates that their mechanical properties are excellent. After heat-treated at 1,673 K
in air for an hour or at 1,873 K under Ar gas atmosphere for 0.5 h, their external appearance is still undamaged and dense,
and their tensile strength decreases to a small extent, which verifies that heat resistance of the SiC fibers is eximious. 相似文献
3.
Shigeru Hanzawa 《Journal of Materials Science》2012,47(2):833-844
The following technique is known to synthesize C/C (carbon fiber-reinforced carbon) composites. The organic matter in the
preformed yarn (plastic straw covered yarn including bundles of long carbon fibers, carbon powder, and organic binder) is
pyrolyzed at 500 °C and concurrently hot-pressed. Then, the carbon ingredient is graphitized in an atmosphere of nitrogen
at 2000 °C. The authors used the above mentioned C/C composites as a starting material and developed a dense Si–SiC matrix
C/C composites in which most long carbon fibers remain without reacting with Si which is infiltrated in argon at 1600 °C and
100 Pa. As a result, production of 1 × 2 m large size plates free from warps and cracks was attained in NGK Insulators, Ltd.
This mechanism consists of three steps. First, a trunk-shaped Si–SiC matrix is synthesized between yarn and yarn. Then a trunk-shaped
Si–SiC matrix extends a yarn by force. Only differential gap is made in a yarn surface. Finally, branch-shaped Si–SiC matrix
is synthesized so that a trunk-shaped Si–SiC matrix leads to the yarn inside. 相似文献
4.
Oxidation behavior of a refractory NbCrMo0.5Ta0.5TiZr alloy 总被引:1,自引:0,他引:1
O. N. Senkov S. V. Senkova D. M. Dimiduk C. Woodward D. B. Miracle 《Journal of Materials Science》2012,47(18):6522-6534
Isothermal oxidation behavior of a refractory high-entropy NbCrMo0.5Ta0.5TiZr alloy was studied during heating at 1273 K for 100 h in flowing air. Continuous weight gain occurred during oxidation, and the time dependence of the weight gain per unit surface area was described by a parabolic dependence with the time exponent n = 0.6. X-ray diffraction and scanning electron microscopy accompanied by energy-dispersive X-ray spectroscopy showed that the continuous oxide scale was made of complex oxides and only local (on the submicron levels) redistribution of the alloying elements occurred during oxidation. The alloy has a better combination of mechanical properties and oxidation resistance than commercial Nb alloys and earlier reported developmental Nb–Si–Al–Ti and Nb–Si–Mo alloys. 相似文献
5.
Takahiro Namazu Tomohiro Ishikawa Yoshio Hasegawa 《Journal of Materials Science》2011,46(9):3046-3051
In this article, strength evaluation of silicon carbide (Si–C) ceramics fabricated from polycarbosilane (PCS) precursor is
described. Si–C ceramics was prepared by firing a green body made of the mixture of Si–C nano-powders and a PCS solution at
1,273 K in N2 gas for an hour. To obtain dense Si–C, the solution was infiltrated into the produced body, and then it was fired again.
The polymer infiltration and pyrolysis (PIP) process was conducted up to 12 cycles. Si–C ceramics was diced to be rectangle
shape measuring 1.0 mm × 3.0 mm × 0.5 mm, and was subjected to the three-point bending test for measurement of the Young’s
modulus and bending strength. Si–C specimens fabricated through PIP processes less than 2 cycles showed non-linear force–displacement
curves like a polymer, whereas those through the processes more than 3 cycles showed linear relations and fractured in a brittle
manner. The Young’s modulus of 12-cycles-PIPs specimen was found to be 56 GPa on average, which was approximately 22-fold
of non-PIP specimen. The bending strength was also increased with an increase in the number of PIP process. The maximum value
was found to be 157 MPa. The cause of the influence of PIP process on the mechanical characteristics is discussed using a
PCS-derived Si–C model. 相似文献
6.
Askwar Hilonga Jong-Kil Kim Pradip B. Sarawade Hee Taik Kim 《Journal of Materials Science》2010,45(5):1255-1263
In this study, we report a versatile method for designing a titania–silica composite using relatively inexpensive precursors.
The composite was synthesized by grafting (impregnating) a precursor of a guest component into the preformed host’s solid
network. The latter was prepared using sodium silicate as a silica precursor in the presence of cetyltrimethylammonium bromide
(CTAB). A freshly prepared solution of titanium oxychloride (TiOCl2, titania precursor that is relatively stable) was introduced into the host’s network to develop a titania–silica composite
with initial ratio of Ti:Si = 1. The final product has the overall ratio of Ti:Si = 7:3 and was obtained after calcination
for 5 h at 600–1000 °C. The XRD patterns for the calcined samples indicate the presence of TiO2, and there was a significant increase in peak intensity as the calcination temperature increased. EDS, XRF, and FT-IR analyses
indicated the formation of a highly pure composite rich in Ti, Si, and O. A Si–O–Ti band at 954 cm−1 was observed, confirming the formation of a titania–silica composite. A composite with optimum properties (homogenous dispersion
of the composite and less individual oxide phase separation) was obtained at 600 °C. A similar experiment was also conducted
in the absence of CTAB. In this case, the final product was microporous, rendering it unsuitable for some applications. 相似文献
7.
Ken’ichiro Kita Masaki Narisawa Atsushi Nakahira Hiroshi Mabuchi Masayoshi Itoh Masaki Sugimoto Masahito Yoshikawa 《Journal of Materials Science》2010,45(1):139-145
The polymer blends of PCS (polycarbosilane) and PMHS-h (polymethylohydrosiloxane with high molecular weight) were prepared
by freeze-drying process of mixed benzene solution. Melt viscosity, mass loss, and gas evolution from prepared polymer blends
were analyzed. A polymer blend of HSah15 (15 mass% PMHS-h to PCS) was melt-spun to fiber form, curing by thermal oxidation
and pyrolyzed at various temperatures up to 1773 K. The obtained fibers were investigated by tensile tests, FE-SEM (field
emission scanning electron microscope) observation, and XRD (X-ray diffraction) analysis. After pyrolysis at 1273 K, there
were no pores in the cross section of the fiber derived from pure PCS; however, there were amounts of pores in the cross sections
of the fiber derived from HSah15. After pyrolysis at 1773 K, the coarse β-SiC (silicon carbide) crystals were formed on the
outside surface of the fiber derived from pure PCS; however, no remarkable β-SiC crystal were formed on the outside surface
of the fiber derived from HSah15. 相似文献
8.
George Stiubianu Carmen Racles Maria Cazacu Bogdan C. Simionescu 《Journal of Materials Science》2010,45(15):4141-4150
Cellulose acetate was reacted in different ratios with poly[dimethyl(methyl-H)siloxane] containing 25 mol% Si–H side groups
along the chain. A dehydrocoupling reaction between Si–H and C–OH groups occurred in presence of Karstedt’s catalyst, leading
to the formation of Si–O–C bond, as proved by FTIR spectra, thus crosslinking the cellulose derivative. The networks were
processed as films by casting before the end of the reaction and were investigated by different techniques to emphasize the
morphology, thermal, dielectric and surface properties developed in correlation with the ratio between the two involved components
(cellulose and siloxane derivatives). A decrease of the dielectric constant values of cellulose acetate was noticed throughout
the studied frequency and temperature range as a result of crosslinking. 相似文献
9.
The carbon fiber/Si–O–C glass composite was prepared from the silicone and carbon fiber by pre-oxidation and spark plasma sintering (sintered composite). The mass loss of the sintered composite oxidized at 1200 °C for 90 min was 5%, which was lower than that of same dimension for similar composites, although the mass loss at 600 °C was still high. This indicated its excellent oxidation resistance at elevated temperature. No cracks and pores were found in the sintered composite, indicating that the combination of pre-oxidation and spark plasma sintering was better than the pyrolysis for manufacturing dense composites. Compared with the flexural strength of about 60 MPa for carbonaceous composites, the flexural strength of the sintered composite was obviously improved to 220 MPa. Moreover, microstructures of the specimen before and after sintering as well as after oxidation were investigated. 相似文献
10.
Ali Sharafat Bertil Forslund Jekabs Grins Saeid Esmaeilzadeh 《Journal of Materials Science》2009,44(2):664-670
Glass formation in the system Sr–Si–O–N was investigated and properties of obtained glasses evaluated. The glass-forming region
was determined for glasses prepared by melting mixtures of Sr metal, SiO2 and Si3N4 powders in Nb crucibles at 1600–1750 °C in nitrogen atmosphere using a radio frequency furnace. The glasses were found to
be homogenous, translucent gray to opaque black, and to contain high contents of N (up to 45 e/o) and Sr (up to 36 e/o). The
glass transition temperature (790–973 °C), density (2.99–4.07 g/cm3), microhardness (8.10–10.50 GPa), and refractive index (1.65–1.93) are strongly correlated with the amounts of Sr and N.
The properties are compared with findings in other oxynitride silicate glass systems. 相似文献
11.
The curing and pyrolysis of hydrogen-containing polysiloxane (PSO) and divinylbenzene (DVB) were investigated in this paper. It was found that H2PtCl6 was an effective catalyst for the curing of DVB/PSO. The mass ratio of DVB/PSO had great effect on ceramic yield. The cured DVB/PSO with a mass ratio of 0.5:1 had the highest ceramic yield (76%) at temperature up to 1000°C, and its pyrolysates consisted of 38.3 wt% silicon, 27.4 wt% oxygen, and 34.3 wt% carbon of which 26.3 wt% was free carbon. The composition and structure of pyrolysates of DVB/PSO were changed with increasing pyrolysis temperature. The pyrolysis behavior of DVB/PSO was characterized by thermal analysis. DVB/PSO-derived Si–O–C composites reinforced with carbon fiber cloth (Cf/Si–O–C) were fabricated. The results showed that the flexural strength of Cf/Si–O–C composites could be increased from 118.00 ± 5.00 MPa to 139.78 ± 7.68 MPa if the pyrolysis temperature was elevated from 1000 to 1400°C, which was ascribed to the weakened interfacial bonding. 相似文献
12.
Protective coatings (Al–O–N and Al–O–B–N) on Si–O–C fibers (Tyranno ZMI) were applied in order to enhance oxidation resistance under severe thermo-mechanical conditions in the 400–600 °C temperature range. The coating process consisted in three steps: (i) the transformation of the Si–O–C fiber surface into microporous carbon; (ii) the impregnation of these carbon microporous layers by an aluminium trichloride (AlCl3) solution and then, (iii) a final heat treatment under ammonia. Processing parameters were studied in order to select the best conditions. Using these conditions, obtained results have shown that coatings were present around each fiber, with a controlled thickness, and that the mechanical properties of the fibers were preserved. Although, these coatings did not entirely stop the oxygen ingress, it has been shown that they strongly reduced the oxidation of the fiber. 相似文献
13.
Fawad Tariq Nausheen Naz Rasheed Ahmed Baloch Ashraf Ali 《Journal of Materials Science》2010,45(6):1695-1708
Effects of quenching and tempering treatments on the development of microstructure and mechanical properties of ultrahigh
strength 0.3C Si–Mn–Cr–Mo low alloy steel were investigated. Samples were austenitized at 1123–1323 K for 2400 s and oil quenched
(OQ) to produce mixed microstructures. Tempering was carried out at 473–773 K for 2–3 h. Phase transformation temperatures
were measured using dilatometer. The microstructures were characterized using optical and scanning electron microscope. SEM–EDS
analysis was carried out to determine the type and size of non-metallic inclusions. Volume percent of retained austenite was
measured by X-ray diffraction technique. Hardness, tensile properties, and impact energies were also determined for all heat
treated conditions. Fractography of impact specimens were done using stereomicroscope and SEM. The results showed that newly
developed steel exhibited peak hardness, yield strength, and tensile strength of about 600 HV, 1760 MPa, and 1900 MPa, respectively,
when OQ from 1203 K and tempered in between 473 and 573 K, combined with adequate ductility and impact toughness. Decrease
in hardness and strength was observed with increasing tempering temperature whereas the impact energy was stable up to 623 K,
however, impact energy was found to decrease above 632 K due to temper martensite embrittlement. 相似文献
14.
The subcritical crack growth resistance in water of a Y–Si–Al–O and Y–Si–Al–O–N glasses has been investigated with three point bending experiments. It has been shown that the SCG behaviour of the Y–Si–Al–O–N glass is superior to that of the Y–Si–Al–O glass. This is reflected by the power law exponent n which is 21 for the Y–Si–Al–O glass and 63 for the Y–Si–Al–O–N glass. Mechanistic implications of these observations are discussed. 相似文献
15.
Computer modelling techniques were employed to investigate the effect of surface silanol groups on the strength of adhesion
of apatite thin films to silica surfaces. To this end, we have studied a series of silica surfaces with different silanol
densities and calculated their interaction with apatite thin films. Our findings indicate that apatite does not attach strongly
to surface hydroxy groups, but that apatite should deposit at dehydrated silica surfaces, especially when the surface silicon
and oxygen species rearrange to form O–Si–O links. Any dangling silicon and oxygen bonds at the silica surfaces are saturated
by coordination to oxygen and calcium atoms in the apatite layer, but the extra reactivity afforded by these under-coordinated
surface species does not necessarily lead to more favourable substrate/film interactions. The lowest energy silica/apatite
interfaces are those where an undistorted apatite layer can be deposited on a regular, stable substrate surface. Our simulations
support the suggestion, that in vivo surface hydroxy groups are first condensed to form O–Si–O bridges before deposition and
growth of apatite. 相似文献
16.
Cumulative work over the last twenty years has defined the glass-forming regions in several M–Si–Al–O–N systems (M = Mg, Ca,
Y, Ln) with the resulting crystalline products identified after heat treatment. Glass-forming regions in nitrogen-rich sialon
glasses have been recently reported and heat treatment of some of these glasses in the Y–Si–Al–O–N system has been performed.
The crystallization of yttrium-containing glasses is particularly sensitive to small variations in composition and heat treatment
temperature and in the current work the results of three series are discussed: (1) a single composition, Y15.2Si14.6Al8.7O54.6N6.9
(16 e/oN), treated at 30 °C intervals between 875–1410 °C; (2) compositions of a constant Y: Si:Al ratio of 3:3:2 and up to
32 e/oN and (3) selected compositions lying on the 28 e/o N plane. Two different sets of crystalline products are found to
form above and below 1200 °C.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
17.
Decarbonization mechanisms of polycarbosilane during pyrolysis in hydrogen for preparation of silicon carbide fibers 总被引:1,自引:0,他引:1
Xueyuan Tang Li Zhang Huibin Tu Hui Gu Lifu Chen 《Journal of Materials Science》2010,45(21):5749-5755
Polycarbosilane (PCS) fibers are cured by electron beam irradiation in helium. Then, the cured fibers are pyrolyzed under
hydrogen. The mechanisms of carbon removal during pyrolysis are investigated using chemical elemental analysis, FTIR, Raman,
and AES analysis. The development of microstructure and phase is examined by SEM, TEM, and XRD. The results show that the
thermal cleavage of relatively weak Si–H and Si–CH3 bonds takes place first during pyrolysis in hydrogen, generating free radicals. The free radicals then react with C–H bonds
or with each other to form Si–CH2–Si groups, releasing hydrogen and methane. As temperature increases, the Si–CH2–CH2–Si groups in PCS begin to dissociate and react with hydrogen to form methane, resulting in the further removal of carbon
and giving silicon-rich silicon carbide fibers (i.e. C/Si <1). 相似文献
18.
Powder and pellets composed mainly of indialite (α-Mg2Al4Si5O18) with 2.1 wt% added B2O3 were prepared by a sol–gel process
using metal salts as raw materials. When heated at 900°C for 6 h, the pellets showed a relative density of 91.4% of ideal
cordierite (β-Mg2Al4Si5O18), a Vickers hardness of 1080 and a relative dielectric constant of 5.0 (at 1 MHz), which was the
same value as that of cordierite. Magic angle spinning nuclear magnetic resonance measurements of 29Si, 27Al and 11B showed
that boron disturbed the formation of the Si–O–Al network below 300°C and broke the network between 700 and 800°C. The high
homogeneity and fluidity caused by the melting helped indialite to crystallize directly from the amorphous state between 800
and 850°C.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
19.
C. C. Fu J. S. C. Jang L. J. Chang T. Y. Lin C. M. Kuo 《Journal of Materials Science》2007,42(14):5327-5334
The effect of strain rate and environment on the mechanical behavior at different temperatures of the Ni–19Si–3Nb–0.15B–0.1C
alloy is investigated by atmosphere-controlled tensile testing under various conditions at different strain rates and different
temperatures). The results reveal that the Ni–19Si–3Nb–0.15B–0.1C alloy exhibits ductile mechanical behavior (UTS ∼ 1250 MPa,
ε ~ 14%) at temperatures below 873 K under different atmosphere conditions. However, the alloy without boron and carbon addition
shows ductile mechanical behavior only when the sample is tested in vacuum. This indicates that the microalloying of boron
and carbon does overcome the environmental embrittlement from water vapor at test temperatures below 873 K for the Ni–19Si–3Nb
base alloy. However, the boron and carbon doped alloy still suffers from embrittlement associated with oxygen at a medium
high temperature (i.e. 973 K). In parallel, both of the ultimate tensile strength and elongation exhibit quite insensitive
response with respect to the loading strain rate when tests are held at temperatures below 873 K. However, the ultimate tensile
strength exhibits high dependence on the strain rate in air at temperatures above 873 K, decreasing the ultimate tensile strength
with decreasing strain rate. 相似文献
20.
Thermal degradation behaviors of the poly(p-phenylene benzobisoxazole) (PBO) fiber and phenolic resin matrix were investigated. The unidirectional PBO fiber reinforced phenolic resin composite material laminates were fabricated and exposed in a muffle furnace of 300 °C, 550 °C, 700 °C, and 800 °C for 5 min, respectively, to study the effects of thermal treatment on mechanical properties of the composites. After undergone thermal treatments at 300 °C, 550 °C and 700 °C for 5 min, the flexural strength was reduced by 17%, 37% and 80%, respectively, the flexural modulus was decreased by 5%, 14% and 48%, respectively, and the interlaminar shear strength (ILSS) was lowered by 12%, 48% and 80%, respectively. Thermal treatment at 300 °C, the phenolic resin began to pyrolyze and shrink resulted in the irreversible damage of the composites. After 550 °C thermal treatment, the phenolic resin pyrolyzed mostly but the PBO fiber had no obvious pyrolyze, the interface had sever broken. After 700 °C thermal treatment, the phenolic resin formed amorphous carbonaceous and PBO fiber pyrolyzed mostly so the mechanical properties dropped dramatically. At being heated at 800 °C for 5 min, the fiber was nearly totally pyrolyzed and and kept fibrous carbonaceous although the specimen became too brittle to stand any load thereon. 相似文献