共查询到20条相似文献,搜索用时 15 毫秒
1.
P. S. Thomas P. Šimon A. Smallwood A. S. Ray 《Journal of Thermal Analysis and Calorimetry》2007,88(1):231-235
The dehydration of an opal specimen was investigated
by thermogravimetric analysis (TG) in powder and bulk forms. The change in
geometry resulted in a significant difference in the temperature range in
which dehydration occurred with peak temperatures in the differential TG (DTG)
curve for the hand ground opal at 203°C and for the bulk opal at 340°C.
This difference was attributed to time taken for diffusion of free water in
the bulk opal to the specimen surface prior to evolution as a registered mass
loss. A model was proposed to account for the diffusion of water and was used
to estimate the diffusion coefficient. 相似文献
2.
Brown L. D. Ray A. S. Thomas P. S. Guerbois J. P. 《Journal of Thermal Analysis and Calorimetry》2002,68(1):31-36
Naturally occurring opals from three different regions in Australia were studied for their thermal characteristics. All the
opals showed initial expansion followed by contraction in thermomechanical analysis (TMA) although the temperature at which
the change from expansion to contraction occurred depended on their provenance. Thermogravimetric analysis (TG) revealed different
rates and temperatures of dehydration for these opals. A general correlation between the temperature at which there was a
zero thermal expansion and that of the maximum rate of dehydration was observed. A dehydration–sintering mechanism is proposed
with the effect of sintering being more pronounced following total dehydration.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Cerium-doped barium titanate inverted opal was synthesized from barium acetate contained cerous acetate and tetrabutyl titanate in the interstitial spaces of a polystyrene (PS) opal. This procedure involves infiltration of precursors into the interstices of the PS opal template followed by hydrolytic polycondensation of the precursors to amorphous barium titanate and removal of the PS opal by calcination. The morphologies of opal and inverse opal were characterized by scanning electron microscope (SEM). The pores were characterized by mercury intrusion porosimetry (MIP). X-ray photoelectron spectroscopy (XPS) investigation showed the doping structure of cerium, barium and titanium. And powder X-ray diffraction allows one to observe the influence of doping degree on the grain size. The lattice parameters, crystal size and lattice strain were calculated by the Rietveld refinement method. The synthesis of cerium-doped barium titanate inverted opals provides an opportunity to electrically and optically engineer the photonic band structure and the possibility of developing tunable three-dimensional photonic crystal devices. 相似文献
4.
Implantable materials have broad applications in tissue engineering and in vivo sensors.It is essential to know the detailed information of the implantable materials during their degradation.In this paper,we developed a method to monitor the degradation process of a well-used biomaterial,poly(lactide-coglycolide) (PLGA) by taking advantage of inverse opal structure.We found that mass loss,molecular weight and glass transition temperature of PLGA during the degradation process in Hank’s artificial body fluid can be in situ monitored by measuring the optical properties of PLGA inverse opal. 相似文献
5.
6.
AbstractPervaporative ethanol dehydration was studied using some chitosan-boehmite nanocomposite membranes. Nanocomposite membranes were prepared by incorporation of 1 and 2?Wt. % loading of the boehmite nanoparticles synthesized by the low temperature sol-gel process. The prepared samples were characterized by FTIR, FESEM and XRD analysis. The results showed the filler particles uniform distribution within the chitosan matrix. Pervaporation performance of the prepared pristine and the nanocomposite membranes were evaluated for ethanol dehydration. The 2?Wt. % loaded boehmite nanocomposite membrane exhibited highest ethanol dehydration performance for 20?Wt. % water content feed at 50?°C as 0.513?kg/m2 h and 676 as permeation flux and separation factor revealed ~50% and 2 times increments, respectively. 相似文献
7.
从测试角度出发,主要以聚丙烯材料为研究对象,研究样品和方法两大方面各因素对静态热机械试验仪(TMA)测试材料线性热膨胀系数(CLTE)的影响。结果表明:样品方面各因素注塑工艺、样条类型、材料热历史、改性填充及裁样位置对材料的CLTE结果有较大影响,测试方法方面各因素升温速率、施加负荷、放置位置及谱图处理方式对材料的CLTE结果有不同程度的影响。研究结果对深入研究CLTE测试、辅助开发低CLTE材料具有重要指导意义。 相似文献
8.
The kinetics of the thermal dehydration of yttrium formate dihydrate was studied by means of isothermal gravimetry under various water vapour pressures from 5×10–4 to 8 torr. On the whole, the dehydration was described as the three dimensional phase boundary reaction, R3. An unusual dependence of the rate of dehydration on the atmospheric water vapour pressure was observed: with increasing water vapour pressure, the rate increased at first, passed through a maximum, and then decreased gradually to a constant value. These phenomena were similar to the Smith-Topley effect. The mechanism of the phenomena can be described on the basis of the crystallinity of the dehydrated product phase.The authors wish to thank Mr. H. Minagawa of the Analytical Instrument Laboratory of Niigata University, for the X-ray diffraction measurements at high temperatures, and Mr. K. Hirata for help in the experimental work. 相似文献
9.
10.
Müge Sarı Yılmaz Sibel Kasap Sabriye Pişkin 《Journal of Thermal Analysis and Calorimetry》2013,112(3):1325-1333
Titanate nanotubes were synthesized utilizing the hydrothermal method using titanium dioxide nanoparticles. The experiments were carried out considering the process as a function of reaction temperature, time, NaOH concentration and the acidity of the washing solution. The formation of titanate nanotubes was shown to be affected strongly by variations in any parameter. The optimum conditions for the synthesis of titanate nanotubes were determined to be a reaction temperature of 190 °C, and a reaction time of 12 h, using 10 M NaOH concentration and the washing solution to have a pH of 5.5. In addition, thermogravimetric analysis (TG/DTG) was used to investigate the thermal behaviour and dehydration kinetics of titanate nanotubes. In order to better understand their thermal behaviour, the thermal analysis of bulk hydrogen trititanate was performed. The values of the apparent activation energies of the first and second dehydration stages for titanate nanotubes were 81.44 ± 15.85 and 82.69 ± 7.46 kJ mol?1, respectively. The values of the apparent activation energies of the first, second and third dehydration stages for bulk hydrogen trititanate were 115.93 ± 5.40, 137.58 ± 6.47 and 138.97 ± 8.47 kJ mol?1, respectively. 相似文献
11.
Andrew K. Galwey 《Journal of Thermal Analysis and Calorimetry》1992,38(1-2):99-110
Thermal Analysis, the central topic of this conference, is a technique that is widely used for the measurement of reaction rates and from which deductions can be made concerning the identity of the bond redistribution steps contributing to the chemical change being investigated. The mechanistic insights obtained from such studies enable us to identify the factors that determine reactivity and to understand theoretically the controls operating in chemical reactions. The present article points out, however, that kinetic data alone do not usually provide sufficient information to enable detailed identification of the sequence of steps through which reactants are converted into products.This review discusses recent research concerned with characterizing mechanisms within a group of solid state processes that has been the subject of extensive kinetic investigations (including thermal analyses): the dehydrations of crystalline hydrates. Conclusions from previous studies of reactions of this type have contributed extensively to the more general understanding of solid-state reactions. Here we discuss some mechanistic conclusions from a number of recent studies in the field and emphasize the value of complementing rate measurements with other relevant observations, including microscopic examinations of the textural modifications that accompany chemical changes.The sincere thanks of the author to all his collaborators cited in the reference list and to M. E. Brady for his helpful contributions during the preparation of this review. 相似文献
12.
The effect of the water vapor pressure on the thermal dehydration of manganese(II) formate dihydrate was studied by means
of isothermal gravimetry under various water vapor pressure, ranging from 4.6 to 24.4 torr.
The kinetics of dehydration was described by a two-dimensional phase-boundary model,R
2. The rate of dehydration decreased with increasing atmospheric water vapor pressure, but the Smith-Topley phenomenon was
not observed for the present dehydration. The activation energy and the frequency factor for the dehydration were 110–170
kJ·mol−1 and 1010–1016 cm·s−1, respectively. These values increased with increasing water vapor pressure, and were much larger than those reported for
the dehydration in vacuum. 相似文献
13.
A. Smallwood P. S. Thomas A. S. Ray P. ?imon 《Journal of Thermal Analysis and Calorimetry》2009,97(2):685-688
A model developed for the estimation of the diffusion coefficient based on Fickian diffusion is applied to the dehydration
of a Coober Pedy white play of colour (precious) opal using thermogravimetric analysis (TG). The model was originally applied
to bulk and powdered opal (opal with no bulk). In this paper the opal was graded prior to TG analysis. The diffusion coefficient
was calculated and is reported up to the critical point of water. 相似文献
14.
A novel coordination polymer nickel 1,3,5-benzenetricarboxylate (TMA) Ni3(H2O)6(TMA)3-(TMA)23-·2H2O with two-dimensional porous structure was synthesized and characterized. It crystallizes in the hexagonal system, space group P6522, with a=1.665 2(10) nm, c=2.045 4(11) nm, V=4.912(5) nm3, Z=6, Dc=1.916 g·cm-3, μ(Mo Kα)=0.181 8 mm-1, F(000)=2 892. The final R1=0.066 4, wR2=0.175 6 for 2 710 observed reflections [I>2σ(I)] out of 2 904 unique reflections . This coordination polymer reveals not only two-dimensional porous structure but also particular magnetic properties. CCDC: 274177. 相似文献
15.
Summary As one of the typical examples of producing an amorphous dehydration product, the thermal dehydration process of K2B4O7·4H2O was subjected to thermoanalytical and morphological studies. An anhydrous glass was formed via three distinguished dehydration stages. The overall thermal dehydration process was characterized as a self-induced sol-gel process to form anhydrous glass. The as produced anhydrous glass exhibited glass transition at around 700 K and subsequently crystallized via two consecutive exothermic peaks at around 770 and 900 K. The final crystallization product, triclinic K2B4O7, melted at 1072 K. 相似文献
16.
Application of thermal analysis methods for characterization of polymer/montmorillonite nanocomposites 总被引:2,自引:2,他引:0
Agnieszka Leszczynska Krzysztof Pielichowski 《Journal of Thermal Analysis and Calorimetry》2008,93(3):677-687
Thermal analysis is a useful tool for investigating the properties of polymer/clay nanocomposites and mechanisms of improvement
of thermal properties. This review work presents examples of applications of differential scanning calorimetry (DSC), modulated
temperature differential scanning calorimetry (MT-DSC), dynamic mechanical thermal analysis (DMA), thermal mechanical analysis
(TMA), thermogravimeric analysis (TG) and thermoanalytical methods i.e. TG coupled with Fourier transformation infrared spectroscopy
(TG-FTIR) and mass spectroscopy (TG-MS) in characterization of nanocomposite materials. Complex behavior of different polymeric
matrices upon modification with montmorillonite is briefly discussed. 相似文献
17.
Mojumdar S. C. Chowdhury B. Varshney K. G. Mazanec K. 《Journal of Thermal Analysis and Calorimetry》2004,78(1):135-144
The results, presented here discusses the Macro-Defect-Free (MDF) cements prepared from the blends of sulfoaluminate ferrite
belite (SAFB) clinkers, ordinary Portland cement (OPC), Al2O3 and poly(butyl acrylate) (PBA), styrene/acrylonitrile co-polymer (SACP) or sodium polyphosphate (poly-P). Though MDF cements
have several attractive properties, their utilization has been limited due to the insufficient moisture resistance. It is
a very challenging task for scientists and technologist to improve the moisture resistance of MDF cements. Therefore, the
new MDF cements were subjected to various moist atmospheres to investigate their moisture resistance. The most significance
of this work is the improvement of moisture resistance of the studied MDF cements. The aim of this work was to understand
the effects of polymers, Al2O3, OPC and SAFB clinkers in the raw mix and delayed drying on MDF cements and also on their subsequent moisture resistance
and thermal stability as well as to discover the new properties of these materials. Their chemical, thermal and scanning electron
microscopic (SEM) analysis was also carried out before and after exposure to moisture. PBA was found to be the most suitable
polymer for MDF cement synthesis, since the samples containing PBA showed the highest resistance to moisture. There are three
main temperature regions on TG curves of both series of MDF cement samples. The significant differences in SEM of MDF cements
before and after moisture attack and with different polymers were observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Conventional thermogravimetric analysis (TG) uses constant heating rates to determine decomposition rates of a material and
compositional analysis. Often, the decomposition steps can not be separated clearly enough due to parallel or consecutive
reactions. If the reaction rates and the respective activation energies are enough different the TG resolution can be much
enhanced by lowering the heating rate during the decomposition steps. The automated discrete adjustment of the heating rate
is controlled by a set of parameters, such as threshold values, waiting times and rate factors. This technique, called MaxRes,
allows for faster compositional analysis without loss of resolution. The same technique is also applicable to thermomechanical
analysis (TMA) if time/temperature dependent events such as softening are to be separated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
C. D. Wingard 《Journal of Thermal Analysis and Calorimetry》1997,49(1):393-398
During the recent processing of a forward segment of the Reusable Solid Rocket Motor (RSRM) for the Space Shuttle, the topcoat white paint turned light brown after autoclave cure of the case insulation. Thermomechanical analysis (TMA) in the film tension mode produced modulusvs. temperature data that helped to explain why a certain insulation vacuum bagging material contributed to the brown paint color. TMA film tension data was also obtained on lab-created white and brown topcoat paint samples (with and without primer). The brown/white ratios of moduli were about 2/1 and 4/1 for topcoat/primer and topcoat only samples, respectively, from 25 to 55C. 相似文献
20.
Atsushi Asano Masaru Eguchi Takuzo Kurotu 《Journal of Polymer Science.Polymer Physics》1999,37(16):2007-2012
Thermal dehydration process of PMAA was investigated by solid‐state 13C NMR. For heat‐treated PMAA at 150°C, at which the dehydration goes very slowly, we observed three 13C peaks at 172, 178, and 187 ppm in the carboxyl group region. The peak at 172 ppm is due to the intramolecular cyclic anhydrides by comparing the reported value of 13C chemical shift. The peaks at 178 and 187 ppm were assigned to regularly aligned free carboxylic acids and intermolecular acid dimers, respectively, from the 2D‐exchange 13C NMR spectra, 13C chemical shift values and IR spectra. We concluded that by heat‐treatment the rearrangement of intermolecular hydrogen bonding of the carboxylic acids in PMAA occurs firstly to form the regularly aligned acid dimers, and the dimers dissociated to be the regularly aligned free carboxylic acids at high temperatures. The adjacent free carboxyl acids dehydrate with each other, resulting in the formation of intramolecular anhydrides. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2007–2012, 1999 相似文献