Meisetsu Kajiwara

Synthesis of silicon carbide fibers by sol-gel processing

Silica-phenolic resin hybrid fibers with carbon-to-silicon atomic ratios of 2.6 to 5.4 have been prepared from ethanol solutions of tetraethoxysilane, phenolic resins, water, and hydrochloric acid with a tetraethoxysilane-H2O−HCl molar ratio of 1:2:0.01 by sol-gel processing. The hybrid fibers have been heated at 1500°C in Ar for carbothermal reduction to convert them into silicon carbide fibers. The effects of the holding time at 1500°C and the carbon-to-silicon atomic ratio of the hybrid fibers on the free carbon content in the silicon carbide fibers have been investigated. It has been found that the conversion is complete by the heat-treatment for more than 2 h. The silicon carbide fibers with a free carbon content of ca. 2 wt% have been obtained from the hybrid fibers with the ratios of 2.6 to 4.3.

Silica gel-phenolic resin hybrid fibres: new precursors for continuous β-silicon carbide fibres

Silica gel-phenolic resin hybrid fibres have been synthesized by hydrolysis and polycondensation of tetraethoxysilane [Si(OC2H5)4, TEOS] in the presence of phenolic resins in ethanol under acidic conditions. The fibres had C : Si atomic ratios of 2.6–5.4 and could be converted into β-silicon carbide (SiC) fibres by carbothermal reduction at 1500 °C under an argon atmosphere.

Electrical properties of poly(n-butylamino) (di-allylamino) phosphazene

A new organic–inorganic hybrid polymer, poly(n-butylamino) (di-allylamino) phosphazene, is synthesized and electrical properties of the polymer are reported. From the results of Fourier transform infrared (FTIR), 1H-nuclear magnetic resonance (NMR) and 31P-NMR measurements, it was confirmed that the synthesized polymer was poly(n-butylamino) (di-allylamino) phosphazene. From an Arrhenius plot of d.c. conduction it was found that experimental points fit to two straight lines, that the discontinuous point could be the glass transition (Tg=268.9 K) and that the activation energies are 0.74 and 1.5 eV at temperatures higher and lower than Tg, respectively. Dielectric constant and dielectric loss factors were measured over the temperature range from −20°C to 70°C with frequency 100 Hz∼100 kHz, and a dielectric loss contour was obtained. A relaxation process with the activation energy of 1.44 eV was found from the dielectric loss contour, which can be attributed to α relaxation. A comparison was made between the present results and those of other phosphazene polymers. Because the polymer was non-flammable and shows high resistance and low dielectric constant, it could be used as an insulator in the field of electronics.

The formation of potassium titanate fibre with flux methods

The formation of potassium titanate fibre was tried with fluxes such as PbO, Bi2O3, K2CO3-K4P2O7, K2CO3-V2O5 and PbO-K4P2O7. Also, the reaction was carried out with changing the cooling rate and the weight ratio of the flux to K2Ti6O13 crystal powder. However, only needle-like crystals or a milky gel were formed and potassium titanate fibre was not formed under the experimental conditions.

Gas permeability of poly(organophosphazenes)

The gas permeability and oxygen-to-nitrogen selectivity were determined for some poly-(organophosphazenes). It was found from the data that the membrane having the highest gas permeability was [NP(NHPrn)(NEt2)]n, which had 1.5 x 10−6cm3 (cm cm−2) s−1 (cm Hg)−1 to oxygen or 2.2 x 10−6cm3 (cm cm−2) s−1 (cm Hg)−1 to nitrogen. On the other hand, the membrane having the highest oxygen-to-nitrogen selectivity of about 3 had the formula [NP(OC6H4Cl-p)2]n Also, the selectivity did not depend on the glass transition temperature of the membranes. The membrane prepared from [NP(OC6H4CH3-p)2]n had a negative activation energy for oxygen and nitrogen permeability.

Phosphonitrilic chloride: 21. Synthesis of chelating polymers with cyclophosphazene thiocarbamate and the properties of chelating polymers

Abstract Chelating polymers containing copper, nickel and cobalt have been formed from cyclophosphazene thiocarbamate trimer and copper, nickel or cobalt ions. These polymers obtained from the reaction are amorphous and the values of electron conductivity are 2·7 × 10 11 Ω- cm , 3·6 × 10 13 Ω- cm and 1·5 × 10 13 Ω- cm for the Cu, Ni and Co polymers respectively. The Cu polymer is the most thermally stable on heating to 500°C in air.

An improved procedure for fabricating SiO2-TiO2-phenolic resin hybrid fibers as precursors for long Si-Ti-C fibers by sol-gel processing

Abstract Synthesis conditions for producing SiO 2 -TiO 2 -phenolic resin hybrid fibers with a wide range of Si-to-Ti atomic ratios from tetraethoxysilane, titanium tetrakis(2,4-pentanedionate) and novolak-type phenolic resins by sol-gel processing have been investigated. It was found that 2,4-pentanedione was an effective solvent for the sol-gel reaction in order to produce the hybrid fibers. For favorable spinn-ability of the hybrid fibers from the solutions it was necessary to adjust critically the amounts of H 2 O and of acid, which were added to promote hydrolysis and polycondensation of the Si and Ti compounds in the solutions, according to their Si-to-Ti ratios. The amounts found to be optimal for spinning the hybrid fibers were in proportion to the Si-to-Ti ratio of the solutions. Using these combinations, SiO 2 -TiO 2 -phenolic resin hybrid fibers with various Si-to-Ti ratios could then be produced, which could then be converted into Si-Ti-C fibers by carbothermal reduction at 1500 °C in Ar.

Synthesis of continuous silicon carbide-titanium carbide hybrid fibers through sol-gel processing

Abstract Silica-titania-phenolic resin hybrid fibers have been prepared from ethanol solutions of tetraethoxysilane (TEOS), titanium tetrakis(2,4-pentanedionate) (TTP), and novolac-type phenolic resins, where water and HCl have been added at a (TEOS + TTP):water:HCl molar ratio of 1:2:0.01, by sol-gel processing. The Si-to-Ti atomic ratio of the hybrid fibers was varied down to 10.4 by changing the amounts of TEOS and TTP in the starting solutions. Carbothermal reduction of both silica and titania components of the hybrid fibers has taken place at 1500 °C in an Ar flow, resulting in the formation of continuous β-silicon carbide-titanium carbide hybrid fibers with Si-to-Ti atomic ratios varied down to 9.9.

Liquid crystalline phase transitions in hexakis(4-(4′-heptyloxy)biphenoxy)cyclotriphosphazene

Abstract Hexakis(4-(4′-heptyloxy)biphenoxy)cyclotriphosphazene (HHCP) was synthesized from hexachlorocyclotriphosphazene and 4-heptyloxy-4′-hydroxybiphenyl. The mesogenicity of HHCP was studied by DSC, FTIR spectroscopy and polarizing microscopy. Enantiotropic smectic C and nematic phases were observed between 450 and 455 K and 455 and 456 K, respectively, on heating, and between 456 and 455 K (nematic) and 455 and 440 K (smectic C) on cooling from the isotropic liquid phase. The introduction of the heptyloxybiphenoxy groups as side chains into cyclotriphosphazene has generated the liquid crystalline phase. FTIR spectroscopy showed that the P=N and P-O-(C) stretching vibrations converted to lower frequencies from 1224 to 1210 cm−1 and from 920 to 910cm−1, respectively, at the crystalline (C)-Sc phase transition. This result suggests that the state of the cyclotriphosphazene ring dramatically changes near the C-Sc phase transition.

The liquid crystalline state in organophosphazenes with biphenyl mesogenic groups

Hexakis[4-(4′-decyloxy)biphenoxy]cyclotriphosphazene (HDBCTP), hexakis [4-(4′-cyano)biphenoxy]cyclotriphosphazene (HCBCTP), poly{bis[4-(4′-decyloxy) biphenoxy]phosphazene} (PDBP), and poly{bis[4-(4′-cyano)biphenoxy] phosphazene} (PCBP) were synthesized from hexachlorocyclotriphosphazene or polydichlorophosphazene and the corresponding sodium alkoxide. Their phase transition and liquid crystalline state were then studied by differential scanning calorimetry (DSC) measurements and polarizing microscope observation. We found enantiotropic smectic C in HDBCTP between 431 and 457 K and monotropic nematic between 529 and 488 K in HCBCTP only in the cooling process. No mesomorphic state was found in PDBP and PCBP.