Spinnability silicate

It should be noted that based on Si NMR results, there is no evidence for strictly linear or ladder polymers in spinnable silicate sols prepared with r = 1.5 or 1.67 [150]. By analogy, claims that linear polymers form in spinnable titanate systems may be unjustified. 

A) Slit-smeared Porod plot for spinnable silicate precursor (W2) measured by SAXS. K=iniX(sm0/2). (B) Corresponding SiNMR spectrum. From Drinker and Assink [32]. 

The precursor of a similar fiber was prepared by polycondensation of an organoaluminum compound, such as monoisopropoxydiethyl aluminum, dissolved in ethylether [60]. Some isopropoxy groups were presumably replaced by a phenoxy group, such as ethyl 0-hydroxybenzoate, in order to improve the spinnability of the final dope. The polyaluminoxane was dissolved in benzene, the ether was distilled off and ethyl silicate was added. After concentration, the dope was dry spun and the green fibers were aged in a humid atmosphere and calcined. The fibers (Table II) had a glassy appearance and were composed of a nanocrystalline Al-Si spinel phase (or r /y-transition alumina) in an amorphous silica based matrix [33] [53]. After mullitization that starts at 1150 C and is complete after 2 min at 1400 C, the fibers were composed of mullite and corundum [33]. 

If ladder polymers were the primary product of the tetrafunctional silicate systems that exhibit spinnability, Si NMR investigations would reveal... 

Sakka and coworkers [28,29,31,146] and Kamiya et al. [147] have investigated the rheology of silicate systems prepared from TEOS (see Table 17) in conjunction with fiber formation (spinnability). Acid- and... 

Refractive index of films prepared from the two-step acid-catalyzed precursor (Wl) as a function of normalized times from gelation (defined in Fig. 13). The silicate species were grown under more concentrated conditions (undiluted) and then diluted with solvent immediately before dip coating. X denotes the refractive index of a film made from the spinnable precursor (W2). From Brinker el ai. [20]. 

Polarized FTIR spectra of spun films prepared from (a) unaggregaled, spherical, silicate particles and (b) spinnable polysilicate precursors at 8000 rpm. Spectra collected near edge (side) are vertically offset for clarity. From Drinker et ai. 120). 

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