Kanichi Kamiya

The sol-gel transition in the hydrolysis of metal alkoxides in relation to the formation of glass fibers and films

Abstract The sol-gel transition of Si(OC 2 H 5 ) 4 was investigated by measuring the volume, the density, the SiO 2 content, the viscosity and the specific and intrinsic viscosities of the solution. The transition behavior of Si(OC 2 H 5 ) 4 solutions with different amounts of water and different catalysts was compared. The measurements indicated that solutions with a small water content were comprised of linear polymer when catalyzed by HCl. Fibers could be easily drawn from such solutions immediately before gelation. Solutions catalyzed by HCl and containing a large amount of water behaved similarly to solutions catalyzed by NH 4 OH, suggesting that a high water content causes the formation of non-linear or network colloidal polymers in hydrolysis-polycondensation. Such solutions did not exhibit spinnability but gelled into elastic bulk masses which were easily converted to bulk glasses.

Glasses from metal alcoholates

Abstract Developments in the technique of preparing oxide glasses from metal alcoholates through hydrolysis, gelling and heating at low temperatures have been reviewed. This technique makes it possible to produce (1) glasses of very high purity and (2) glasses of compositions which the conventional melting technique could not give because of immiscibility, crystallization and high melting temperatures. This technique can provide glasses having various shapes such as fibers, thin coating films, isolated films and bulk glasses. Discussion was made on the microscopic processes leading to fibers and bulk glasses.

IR study on the structural evolution of sol-gel derived SiO2 gels in the early stage of conversion to glasses

Abstract The structure of alkoxysilane-derived SiO 2 gels which were prepared under the partial hydrolysis condition and contained a considerable amount of unhydrolyzed alkoxy groups, and the structure change of the gels in the early stage of gel to glass conversion were investigated as a function of the behavior of a small IR band peaking at 550–600 cm −1 . The 550–600 cm −1 peak was assigned to the skeletal vibration of the 4-fold siloxane rings by reference to various cyclic siloxanes and silicate minerals. The presence of unhydrolyzed alkoxy groups was important for the formation or retention of 4-fold rings in the gels. On heating the gels in air, it was found that the 4-fold siloxane rings were broken to form SiOH bonds with release of alkoxy groups around 200°C, at which temperature the siloxane network was degraded, followed by healing through the condensation of SiOH at a higher temperature.

Preparation of glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems from metal alkoxides and their resistance to alkaline solution

Glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems containing up to 33 wt% ZrO2 were prepared by a non-melting technique using zirconium n-propoxide, sodium methoxide and silicon tetraethoxide as raw materials. The mixed alkoxide solutions were exposed to moist air for hydrolysis. The fibrous gels were drawn from these solutions in the course of hydrolysis, and converted to the corresponding oxide glass fibres by heating at 500 to 700° C. It was found that chemical durability of the fibres toward alkaline solution increased with ZrO2 content. The weight loss due to the corrosion by 2 N NaOH solution at 96° C for 4 h was around 14 mg dm−2 for the fibres containing 17 to 26 wt% ZrO2, which was comparable to the alkali-resistant glasses so far obtained by the conventional melting technique. The glass fibres containing 33 wt% ZrO2 showed higher resistance.

Third harmonic generation from Li2OTiO2TeO2 glasses

Abstract Third harmonic generation from high refractive index Li 2 OTiO 2 TeO 2 glasses was investigated. The maximum content of TiO 2 in the glass forming region was 10 mol% by conventional melt-quenching technique, and gc (3) was dependent on TiO 2 /(Li 2 O+TiO 2 ). The highest χ (3) , 8.0 × 10 −13 esu, was observed in 10Li 2 O·10TiO 2 ·80TeO 2 (mol%). In these glasses, χ (3) is 40 times larger than that of SiO 2 glass.

Structure of alkali germanate glasses studied by spectroscopic techniques

Abstract EXAFS spectra and X-ray radial distribution curves were determined for Li2OGeO2, Na2OGeO2 and K2OGeO2 glasses to elucidate the glass structure. The formation of 6-coordinated Ge atoms on the addition of an alkali oxide R2O to GeO2 glass was confirmed. The concentration of 6-coordinated Ge atoms N6 increased with an increase of the R2O content, exhibited a maximum around 20 mol% R2O and decreased again with a further increase of the R2O content. No essential dicrepancies between the techniques employed and between the glass systems investigated were found in the N6 value and the R2O content of glass at the maximum. The small discrepancies were attributed to the different assumptions made for the calculations. It was concluded that the concentration of 6-coordinated Ge atoms N6 follows the formula N6=x/(100-x), where x is mol% R2O. The maximum value of N6 was about 25% for the composition of about 20 mol% R2O.

Thermal evolution of gels derived from CH3Si(OC2H5)3 by the sol-gel method

Abstract The structure change of CH3Si(OC2H5)3 (MTES)-derived gels on heating in N2 and NH3 to form C- and N-containing SiO2 glasses, respectively, was examined by IR spectroscopy and thermal analysis. The gel was considered to consist of siloxane polymers containing strained 4-fold siloxane ring structure. The SiCH3 and 4-fold rings were thermally cleaved around 700°C to form SiH, SiOH and carbonous matter in N2, and SiNH2 as well as SiH and SiOH bonds in NH3. The SiNH2 was condensed at higher temperatures, resulting in N-containing SiO2 glass.

Preparation of multiple oxide BaTiO3 fibres by the sol-gel method

Multiple oxide BaTiO3 gel fibres were prepared by the sol-gel method from Ba(OC2H5)2-Ti(O-isoC3H7)4-H2O-C2H5OH-CH3COOH and Ba(CH3COO)2-Ti(O-isoC3H7)4-H2O-CH3COOH solutions. Relatively long gel fibres of 10cm length were obtained from both solutions in the limited composition region. The latter solution in particular showed a spinnability even when it contained no water. Therefore, the occurrence of spinnability of the solution was considered to be due to the formation of linear polymers composed of bridging acetate groups such as Ti←O-C(CH3)-O-Ti rather than metalloxane bonding as Ti-O-Ti. Addition of water to the solutions seems to break the bridging acetate bonds and replace some of them by bridging oxygen bonds. The as-drawn gel fibres which were X-ray amorphous crystallized into BaTiO3 ceramic fibres of 5mm average length upon heating above 600 ° C. However, the gel fibres drawn from the sols without water became powdery on heating because of the lack of Ti-O-Ti metalloxane bonds. The crystallization behaviour of the BaTiO3 gel fibres is discussed based on the infrared spectroscopy, X-ray diffraction analysis and thermogravimetric-differential thermal analysis.

Preparation of TiO2 fibres by hydrolysis and polycondensation of Ti(O—i-C3H7)4

Preparation de fibres TiO 2 par la methode de polymerisation chimique a partir de Ti(O−iC 3 H 7 ) 4 . Les proprietes et la structure des fibres obtenues dependent de la temperature et de la duree du traitement thermique

Structure and ionic conductivity of LiClLi2OTeO2 glasses

Abstract The structure and the ionic conductivity of the ternary LiClLi 2 OTeO 2 glasses were investigated. The structure was studied mainly by means of IR spectroscopy. It was observed that the TeO ax bond, where ax stands axial position of the TeO 4 trigonal bipyramid, became weaker with increasing the LiCl content in binary LiClTeO 2 glasses, indicating that LiCl works as a network modifier. On the other hand, the gradual increase in the wave number of the peak due to the TeO ax bond was observed when Li 2 O was replaced with LiCl. This was explained in terms of a difference in bonding characteristics between TeO eq and TeCl eq bonds, where eq denotes the equatorial position. The electrical conductivity of the glasses with a high concentration of Li + ion reached an order of 10 −6 S cm −1 at 25° C. This value was comparable to those of the other fast Li + ion conducting glasses such as LiClLi 2 OB 2 O 3 and LiPO 3 LiCl systems. The composition dependence of the electrical conductivity was discussed in relation to the glass structure, especially in terms of bonding characteristics of TeCl and TeO.