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91.
Sirirat Wacharawichanant Angsumon Sangkhaphan Niramon Sa‐Nguanwong Vitsarut Khamnonwat Supakanok Thongyai Piyasan Praserthdam 《应用聚合物科学杂志》2012,123(6):3217-3224
The effects of particle size of titanium dioxide (TiO2) on mechanical, thermal, and morphological properties of pure polyoxymethylene (POM) and POM/TiO2 nanocomposites were investigated and compared with the results for nanoparticle ZnO in the same matrix, reported in a previous paper. POM/TiO2 nanocomposites with varying concentration of TiO2 were prepared by the melt mixing technique in a twin screw extruder, the same method that used for blending the homogeneous ZnO nanocomposites. The dispersion of TiO2 particles in POM nanocomposites was studied by scanning electron microscopy (SEM). The agglomeration, as observed by the mechanical properties of TiO2 particles in the polymer matrix, increased with increasing TiO2 content, a result not found for ZnO even at lower particle sizes. Increasing the filler content of POM/TD32.4 and POM/TD130 (130 nm) nanocomposites resulted in a decrease in tensile strength. The Young modulus, stress at break and impact strength of TiO2 nanocomposite did not improve with increasing filler contents, in opposition to the better agglomeration conditions of ZnO nanocomposite even at lower particle sizes. Because of agglomeration, the POM/TD32.4 nanocomposites had lower mechanical properties and lower degradation temperature than the POM/TD130 ones. The sizes of nanoparticles determined the agglomeration, but however, the agglomeration also depended on the type of nanoparticles, even when using the same matrix (POM) and the same mixing method. TiO2 nanoparticles were more difficult to mix and were more agglomerated in the POM matrix as compared to ZnO nanoparticles, regardless of the size of the nanoparticles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
92.
Suphot Phatanasri Piyasan Praserthdam Thana Punsupsawat 《Korean Journal of Chemical Engineering》2000,17(4):414-419
Toluene methylation with methanol was investigated on MFI-type zeolite catalysts containing Fe or Zn within the range of 0-2% by weight as an active component. The catalytic performances were compared on catalysts to which Fe or Zn was introduced by different methods, i.e., ion-exchanged and incorporation methods. The prepared catalysts were characterized by XRD, XRF, BET, FTIR and pyridine adsorption technique on in-situ FTIR. The results showed that the incorporated samples, H-Fe, Al-silicate (Si/Fe=150) and H-Zn, Al-silicate (Si/Zn=150), exhibited catalytic activity and xylene selectivities approximately equivalent to those from the ion-exchanged samples, Fe(0.8)/H-MFI and Zn(1.0)/H-MFI, containing nearly the same amount of Fe or Zn. The higherp-xylene selectivity was achieved with H-Fe, Al-silicate (Si/Fe=150) and H-Zn, Al-silicate (Si/Zn=150) because of Brönsted acid strengths weaker than Fe(0.8)/H-MFI and Zn(1.0)/H-MFI. Therefore, the isomerization ofp-isomer produced primarily was suppressed on the incorporated catalysts better than the ion-exchanged ones. 相似文献
93.
Eakkapon Promaros Suttichai Assabumrungrat Navadol Laosiripojana Piyasan Praserthdam Tomohiko Tagawa Shigeo Goto 《Korean Journal of Chemical Engineering》2007,24(1):44-50
The carbon dioxide reforming of methane under periodic operation over a commercial Ni/SiO2·MgO catalyst was investigated at two different temperatures, 923 and 1,023 K. According to this operation, pure methane and
carbon dioxide were alternately fed to the catalyst bed where methane cracking and the reverse Boudouard reaction took place,
respectively. Therefore, hydrogen and carbon monoxide products appeared separately in different product streams. The performance
of this operation was compared to that of the steady state operation with simultaneous feed of both carbon dioxide and methane.
At 1,023 K, the methane conversion and hydrogen yield from the periodic operation initially decreased with time on stream
and eventually leveled off at values about half of those obtained in the steady state operation with co-feed of both reactants.
The decreased catalytic activity was due to the accumulation of carbonaceous deposit and loss of metal active sites. However,
a different trend was observed at 923 K. The methane conversion and hydrogen yield were almost constant over the time on stream,
although more carbonaceous deposit was progressively accumulated on the catalyst bed during the reaction course. At this temperature,
the periodic operation offered the equivalent hydrogen yield to the steady state operation. The observed behavior could be
due to the different mechanisms of carbon formation over the catalyst. Finally, it was found that cycle period and cycle split
did not influence the reaction performance within the ranges of this study. 相似文献
94.
95.
Jantana Wiwattanapongpan Okorn Mekasuwandumrong Choowong Chaisuk Piyasan Praserthdam 《Ceramics International》2007,33(8):1469-1473
The effects of dopants on zirconia prepared via the glycothermal method were investigated by XRD to determine the crystal structure and crystallite size. Morphologies of products were observed by SEM. The basic sites of zirconia were studied by CO2-temperature programmed desorption (CO2-TPD). The functional group in the samples was determined using IR. The intensity of Zr3+, characterized by ESR, could be described as the oxygen coordinatively unsaturated Zr sites. The results suggest that doping elements can modify the surface chemistry of ZrO2 to form hydroxyl groups and surface energies depending on the structure (cubic, tetragonal) in different dense phase. ESR peaks of Pb- and Bi-doped zirconia are different from the others, which showed high intensity of Zr3+. 相似文献
96.
Patta Soisuwan Dean C. Chambers David L. Trimm Okorn Mekasuwandumrong Joongjai Panpranot Piyasan Praserthdam 《Catalysis Letters》2005,103(1-2):63-68
A modified Pechini method was used to prepare alumina–zirconia mixed oxides at three different molar ratios. For comparison, pure alumina and pure zirconia were prepared using the same method. The mixed oxides were characterised by the BET method for surface area, X-ray diffraction, CO2 and NH3 temperature-programmed desorption. Elimination of 2-propanol was used as a probe reaction to characterise the surface of the mixed oxides. The modified Pechini preparation resulted in a poor acid–base strength of alumina surface resulting in high acetone selectivity where imperfect crystal structure of the tetragonal zirconia favoured high propylene production in 2-propanol elimination at 200 °C. 相似文献
97.
Boron modification on MCM-41-supported cobalt (Co) catalysts was found to decrease the catalyst activity during CO hydrogenation.
The decreased activities were due to stronger support interaction between Co oxide species and the support with the presence
of boron resulting in lower reducibility. However, based on methanation the selectivity to C2–C4 products slightly increased with low loading of boron. 相似文献
98.
Piyasan?PraserthdamEmail author Jirathana?Phungphadung Waraporn?Tanakulrungsank 《Materials Research Innovations》2003,7(2):118-123
The thermal reaction of chromium acetylacetonate in various organic solvents at 300 °C for 2 h yielded an amorphous product.
Single nanocrystalline chromium oxide was obtained after being calcined at 300 °C for 1 h. The crystallite size of product
is in the range of 16–26 nm. In this work, the thermal stability of product was given by BET/BET0. It was found that the crystals of large crystallite size show higher thermal stability than the crystals of small crystallite
size. Thermal stability of chromium oxide can be presented by the correlation of the BET surface area after calcination, crystallite
size of as-synthesized product and calcination temperature (500–900 °C) as shown below.
where
BET = surface area of product after calcination (m2/g)BET0 = surface area of as-synthesized product (m2/g)T = calcination
temperature (K)d0 = crystallite size of as-synthesized product (nm)n = arbitrary constant
Electronic Publication 相似文献