• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2762-2764
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• 2009

• Journal of the Korean Applied Science and Technology
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• v.25 no.2
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• pp.144-150
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• 2008

The polyamide-amide-imide (PAAI) was synthesized by reacting 4,4'-diaminobenzanilide (DBA) with trimellitic anhydride chloride using a two-stage heating. The precursor of polyamide-acids was formed at first stage and followed by the formation of imide of PAAI. Two polyamide-imides (PAIs) were prepared from benzidine (BZ) or 4,4'-diaminodiphenylether (DPE) with trimellitic anhydride chloride. These three polymers had glass transition temperature in the temperature range of $240-250^{\circ}C$. X-ray data were obtained on thin film specimens cured at $250^{\circ}C$. There was a minimal kind of short-range order consisting of the most probable distances between neighboring chains. The average segmental spacing of short-range order decreased in the order of polymers obtained from 4,4'-diaminobenzanilide (DBA), polyamide-imide, and 4,4'-diaminodiphenylether (DPE). The imidization of three polyamide-imides was confirmed by $^{15}N$ MAS NMR and FT-IR spectroscopy. $^{15}N$ NMR spectrum of cured polyamide-imide showed imide $^{15}N$ peak, thereby providing an evidence for the imidization of three polyamide-imides.

• Bulletin of the Korean Chemical Society
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• v.25 no.1
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• pp.51-54
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• 2004

Gallium nitride (GaN) powders were prepared by calcining a gallium(III) nitrate salt in flowing ammonia in the temperature ranging from 500 to 1050 $^{\circ}C$. The process of conversion of the salt to GaN was monitored by X-ray diffraction and $^{71}Ga$ MAS (magic-angle spinning) NMR spectroscopy. The salt decomposed to ${\gamma}-Ga_2O_3$ and then converted to GaN without ${\gamma}-{\beta}Ga_2O_3$ phase transition. It is most likely that the conversion of ${\gamma}-Ga_2O_3$ to GaN does not proceed through $Ga_2O$ but stepwise via amorphous gallium oxynitride ($GaO_xN_y$) as intermediates. The GaN nanowires and microcrystals were obtained by calcining the pellet containing a mixture of ${\gamma}-Ga_2O_3$ and carbon in flowing ammonia at 900 $^{\circ}C$ for 15 h. The growth of the nanowire might be explained by the vapor-solid (VS) mechanism in a confined reactor. Room-temperature photoluminescence spectra of as-synthesized GaN powders obtained showed the emission peak at 363 nm.

• Journal of the Mineralogical Society of Korea
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• v.31 no.4
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• pp.295-306
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• 2018

Despite the utility of solid-state NMR, NMR studies of iron-bearing silicate glasses remain a challenge because the variations in the peak position and width with increasing iron content reflect both paramagnetic effect and iron-induced structural changes. Therefore, it is essential to elucidate the effect of temperature on the NMR signal for iron-bearing silicate glasses. Here, we report the $^{29}Si$ and $^{27}Al$ MAS NMR spectra for $(Mg_{0.95}Fe_{0.05})SiO_3$ and $Fe_2O_3$-bearing $CaAl_2Si_2O_8$ (anorthite) glasses with varying spinning speed to interpret the NMR spectra for iron-bearing silicate glasses. The increase in the spinning speed results in an increase in the sample temperature. The current NMR results allow us to understand the origins of the changes in NMR signal with increasing iron content and to provide information on the dipolar interaction between nuclear spins. The $^{29}Si$ NMR spectra for $(Mg_{0.95}Fe_{0.05})SiO_3$ glass and $^{27}Al$ NMR spectra for $Fe_2O_3$-bearing $CaAl_2Si_2O_8$ glasses show that the peak shape and position of iron-bearing glasses do not change with increasing spinning speed up to 30 kHz. These results suggest that the NMR signal in the Fe-bearing glasses may stem from the 'survived nuclear spins' beyond the cutoff radius from the Fe, not from the paramagnetic shift. Based on the current results, the observed apparent shifts toward lower frequency of Al peak for $Fe_2O_3$-bearing $CaAl_2Si_2O_8$ glasses with increasing $Fe_2O_3$ at all spinning speed (15 kHz to 30 kHz) indicate the increase in the fraction of ${Q^4}_{Al}$(nSi) with lower n (i.e., 1 or 2) with increasing $Fe_2O_3$ and the spatial proximity between Fe and ${Q^4}_{Al}$(nSi) with higher n (i.e., 3 or 4). The present results show that changes in the NMR signal for iron-bearing silicate glasses reflect the actual iron-induced structural changes. Thus, it is clear that the applications of solid-state NMR for iron-bearing silicate glasses hold strong promise for unraveling the atomic structure of natural silicate glasses.

• Clean Technology
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• v.15 no.2
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• pp.122-129
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• 2009

The effect of calcination temperature or hydrothermal treatment of commercial Fe-beta zeolites in the range of $450{\sim}900^{\circ}C$ were examined in the direct decomposition of $N_2O$. Fe-beta zeolites used were characterized using XRD, $N_2$ sorption, $^{27}Al$ MAS NMR and XPS. Although the surface area and micropore volume of Fe-beta zeolite after calcination at $900^{\circ}C$ and hydrothermal treatment at $750^{\circ}C$ decreased ca. 30%, a larger decrease in the surface area and micropore volume by hydrothermal treatment was observed than by calcination treatment alone. However, the Al sites in frameworks of zeolite were conserved in stable tetrahedral form resulting from low degree of dealumination which was related to the adjacent Fe ions on the Al sites. This could likely be correlated with the conservation of high surface area and micropore volume of Fe-beta zeolites. The increase in the calcination or hydrothermal treatment temperature caused the increase of decomposition temperature of $N_2O$ and the severe deactivation was observed after hydrothermal treatment than calcination treatment.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.5
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• pp.563-569
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• 2001

In order to utilize the processing wastes of squid, chitosan was prepared by intermittent deacetylation treaoent of $\beta-chitin$ contained richly in the pen of squid. Acetylchitosan also was synthesized from squid pen chitosan with anhydrous acetic acid and their characteristics were investigated. The amounts of nitrogen and ash of squid pen chitosan were $5.80.2\% and 0.2\pm0.03\%$ respectively, the yield of squid pen chitosan was $25\pm3\%$, the degree of deacetylation was $92\%$, and the molecular weight was $1.15\times10^6$, Acetyl contents of N-acetylchitosan powder, acetylchitosan bead, N-ACF-1 (N-acetylchitosan film-1) and N-ACF-2 (N-acetylchitosan film-2) were $55.9\%, 63.2\%, 56\% and 58.7\%$ respectively. Two major peaks, amide I ($1,653 cm^{-1}$) and II ($1,558 cm^{-1}$) bent, on FT-IR spectra of the N-acetylchitosan from squid pen were almost similar to these of $\beta-chitin$, While there was a broad single peak at $1,601 cm^{-1}$assigned to be an amide I bend in squid pen chitosan. The CP/MAS NMR spectra of $\beta-chitin$, squid pen chitosan and N-acetylchitosan from squid pen showed a relative broad and single peak at 74 ppm assigned to fifth carbon (C-5) and third carbon (C-3). In case of $\beta-chitin$ and N-acetylchitosan from squid pen, single peak at 74 ppm was showed as the same of $\beta-chitin$ type.