Masayoshi Itoh

Fine SiC fiber synthesized from organosilicon polymers: relationship between spinning temperature and melt viscosity of precursor polymers

A very fine silicon carbide (SiC) fiber with diameter of 6 μm, about a half of that of a commercially available SiC fiber, was synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS). The fine SiC fiber was obtained by optimizing the composition and the spinning temperature of PCS-PVS polymer blends. In order to determine these optimum conditions, the relationship between temperature and melt viscosities of the polymer blends was investigated. As a result, it was found that the optimum spinning temperature range was within a temperature range where the melt viscosity is 5–10 Pa · s. Moreover, by blending PVS with PCS, the spinning temperature of the polymer blends was lowered, the spinnability of polymer system was improved, and finer polymer fiber was obtained compared with PCS. The optimum content of PVS in the polymer blend was 15–20 wt%.

Fiber reinforced plastics using a new heat-resistant silicon based polymer

Fiber reinforced plastics (FRPs), reinforced with carbon fiber, SiC fiber and glass fiber, were prepared by using a new thermosetting silicon-containing polymer, poly[(phenylsilylene) ethynylene-1,3-phenyleneethynylene](MSP), as a matrix resin. In MSP composite processing, no solvent is needed, no by-products are generated, and the curing temperature is low (150–210°C). The FRPs (MSP composite) showed high heat-, burn- and radiation-resistant properties. Bending strengths (110–140 MPa) and modulus (30 GPa) at 200°C and 400°C were almost equal with those at room temperature, and were not affected by 100 MGy of irradiation. Dynamic viscoelasticity and creep properties of MSP composite were also determined and compared with those of a polyimide composite.

Fine silicon carbide fibers synthesized from polycarbosilane-polyvinylsilane polymer blend using electron beam curing

A fine SiC fiber is synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS) with electron beam curing under vacuum. The obtained SiC fiber from the PCS-PVS blend polymer has smaller average diameter of 8.5 μm than that of 11.8 μm from PCS, and shows higher average tensile strength of 3.2 GPa than that of 2.8 GPa from PCS after heat treatment at 1673 K in Ar gas atmosphere. However, the SiC fiber from the polymer blend decreases in tensile strength after heat treatment above 1773 K due to β-SiC crystal growth near the fiber surface, because of a small amount of oxygen incorporated in the fiber.

Synthesis of amorphous carbon fiber from a new organosilicon precursor

Synthesis of amorphous carbon fiber with atomic scale dispersed silicon was investigated. An organosilicon precursor (MSP), which was developed as heat resistant plastics in recent years, was used as a precursor. Temperature control during the melt-spinning was important in order to tailor precursor fibers having thin diameters. For the fiber curing, γ-ray irradiation previous to pyrolysis in an O2 atmosphere was available. The effect of irradiation on the MSP fiber was investigated with mass change, FT-IR and SEM observation after pyrolysis. During the irradiation, oxygen was introduced in the fiber in proportion to the total dose, but the irradiation curing formed microscopic defects on the fiber surfaces at the same time which limited the resultant fiber strength.

Ceramization process of polyvinylsilane as a precursor for SiC-based material

A SiC-based material was synthesized from polyvinylsilane (PVS) by pyrolysis at 1400 K in Ar gas atmosphere. In the ceramization process of PVS, several kinds of gases such as hydrogen, silanes, and hydrocarbons were evolved in the temperature range from 500 to 800 K. The total ceramic yield from PVS was about 36%. PVS was heat-treated using several temperature programmes by reflux heat treatment with a view to increase the ceramic yield. The total ceramic yield increased to 59% by the reflux heat treatment at 600 K. The apparent SiC crystallite size and the atomic ratio of carbon to silicon (C/Si) of the SiC-based material obtained by pyrolysis at 1400 K were almost the same for the PVS reflux-treated and the PVS not heat-treated; an apparent SiC crystallite size of about 2.4 nm, and C/Si of about 1.5.

Thermal oxidation crosslinking in the blended precursors of organosilicon polymers containing polyvinylsilane with polycarbosilane

The polymer precursors containing polyvinylsilane (PVS) with polycarbosilane (PCS) in coating form were prepared. As the content of PVS increases, the onset temperature of the precursor oxidation decreases and the surfaces formed after the oxidation become smooth and hard. The role of Si–H bonds in the PCS–PVS systems during the oxidation is quantitatively analysed on the basis of the absorption of the Si–H stretching band in the precursor spectra. In the blended systems, the oxidation of the Si–H groups forms the dense crosslinked polymer layer which limits the oxygen diffusion into the precursor interior.

Synthesis of SiC Based Fibers with Continuous Pore Structure by Melt- Spinning and Controlled Curing Method

Silicon carbide (SiC) based fibers with continuous pore structures were synthesized by the precursor method using a polycarbosilane (PCS) and polymethylhydrosiloxane (PMHS) polymer blends. The pore formation process can be explained by hydrogen gas dissolution in the polymer melt and desaturation process of the dissolved gas during the fiber spinning. We investigated the effect of PMHS additives with different chemical and physical natures on the obtained pore structures, because PMHS decomposition process played a role of hydrogen gas source. The individual polymer melts were characterized by viscosity measurement, gas chromatograph analysis and thermogravimetric (TG) analysis in order to obtain details of pore structure control.

Synthesis of silicon carbide films from partially oxidized polyvinylsilane by carbon tetrachloride solution casting

Polyvinylsilane (PVS), derived from vinylsilane by radical polymerization, was partially oxidized in hot carbon tetrachloride solution by flowing air. If the air flow time is adjusted, soft gel films can be formed in a Teflon dish by casting the PVS solution. After the PVS films were peeled from the substrates, they were pyrolyzed at various temperatures. Spectroscopic studies of the pyrolyzed films up to 1273 K suggested that carbosilane (Si-CH 2 -Si) structures are formed in the films at 473-673 K. The compositions of the amorphous films obtained at 1673 K were approximately SiC 1 . 3 8 O 0 . 2 1 and SiC 1 . 4 1 O 0 . 5 1 , depending on the crosslinking conditions. The oxygen incorporated in the films was removed in the form of CO and SiO during further heating at 1673-1873 K. The compositions of the films were changed to approximately SiC 1 . 2 5 and SiC 1 . 2 6 , respectively, at 2073 K. The films obtained at 1273 K did not show degradation during the oxidation at 1273-1673 K while a protective silica layer was formed on their surfaces.