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1.
Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na2O-xTiO2-50P2O5 and 45Na2O-yTiO2-(55-y)P2O5 glasses. The addition of TiO2 to the starting glasses (x=0 and y=5 mol% TiO2) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal
expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C.
The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO2 content. With increasing TiO2 content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature
towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization
were NaPO3, TiP2O7 and NaTi2(PO4)3. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na2O or P2O5 by TiO2, it increases sharply. 相似文献
2.
Thermal behaviour of the glass series (100-x)[50ZnO-10B2O3-40P2O5]·xSb2O3 (x=0-42 mol%) and (100-y)[60ZnO-10B2O3-30P2O5]·ySb2O3 (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb2O3 results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All
glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously
increases with increasing Sb2O3 content in both series and varies within the range of 6.6–11.7 ppm °C−1. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb2O3 content the ‘fragility’ of the studied glasses increases. 相似文献
3.
Specific heat measurements have been made in a-Se and a-Se90M10 (M = In, Sb, Te) alloys using differential scanning calorimetry (DSC) technique to see the effect of additives In, Sb and
Te on the specific heat in a-Se. An extremely large increase in the specific heat values has been observed at the glass transition
temperature. It has also been found that the values of C
p
below glass transition temperature (C
pg
) and after glass transition (C
pe
) are highly composition dependent. This indicates that the additives used in the present study influences the structure of
the a-Se. Specific heat and atomic mass values of the additive elements are found to be significant for the explanation of
present results. 相似文献
4.
L. Abbas L. Bih A. Nadiri Y. El Amraoui H. Khemakhem D. Mezzane 《Journal of Thermal Analysis and Calorimetry》2007,90(2):453-458
Thermal and chemical durability studies of the phosphate glasses belonging to the binary MoO3-P2O5 and the ternary K2O-MoO3-P2O5 systems are reported. The chemical resistant attack tests carried out on the free alkaline MoO3-P2O5 glasses show that the glass associated with the P/Mo ratio 2 has the high chemical durability. It shows also a high glass
transition temperature value. The above findings are interpreted in terms of the cross-link density of the glasses and the
strength of the M-O bonds (M=P, Mo).
The influence of K2O addition on the properties (density, T
g, durability) of this binary high water resistant glass is studied. It is found that the chemical durability along with the
other physical properties are reduced by the incroporation of K2O in the glass matrix. The results were explained by assuming the formation of non-bridging oxygens and weak bonds. The mechanism
of the dissolution of these glasses is proposed. 相似文献
5.
This work reports the effect of Ge, Sb, Sn additives on the thermally activated glass to crystal phase transition in binary
Se90In10 alloy. Differential scanning calorimetry (DSC) technique is used for this purpose. Different kinetic parameters of glass/crystal
transformation have been calculated. The results are explained using the chemical bond approach for the covalent network of
such glasses. 相似文献
6.
P. H. Parsania K. C. Patel R. D. Patel 《Journal of Polymer Science.Polymer Physics》1985,23(1):199-203
Thermal behavior of unfractionated poly(2-methoxy)-Cyanurate, PMCBC- film has been reported. The degradation of the polymer involved two steps. The glass transition temperature, Tg, from DSC and DMA studies is ~ 200°C. TMA study shows that the glass-rubber transition region is in the range of 157 to 199°C. The thermal stability of PMCBC has been found to be superior to commercially available polymers. 相似文献
7.
Ashmi T. Patel Heena R. Shevde Arun Pratap 《Journal of Thermal Analysis and Calorimetry》2012,107(1):167-170
Recently, multicomponent glass forming alloys have been found which exhibit extraordinary glass forming ability and cooling
rates of less than 100 K/s are sufficient to suppress nucleation of crystalline phases and consequently bulk metallic glass
(BMG) is formed. The undercooled melts of BMG systems have high thermal stability in the undercooled region. Therefore, it
is interesting to study the thermodynamics of such materials. This article investigates the thermodynamic behavior of a BMG
system namely Zr52.5Cu17.9Ni14.6Al10Ti5 by estimating the Gibbs free energy difference ΔG, entropy difference ΔS, enthalpy difference ΔH between the undercooled liquid and corresponding equilibrium crystalline solid phase, in the entire temperature range from
T
m to T
K. Glass forming ability (GFA) of this system has been investigated through various GFA parameters indicating the degree of
ease of glass formation. 相似文献
8.
Bhupendra Singh Rathore Mulayam Singh Gaur Kripa Shanker Singh 《Journal of Thermal Analysis and Calorimetry》2012,107(2):675-680
The thermally stimulated charge relaxation properties of polycarbonate (PC) filled with SiO2 nanofiller were studied by means of thermally stimulated discharge current (TSDC). The nanocomposite samples were further
characterized by UV–vis spectroscopy, scanning electron microscopy, energy dispersive X-ray spectra, and differential scanning
calorimetry (DSC) techniques to investigate the dispersion of nanofillers in polymer matrix and glass transition temperature.
All pristine and nanocomposites samples of thickness about 25 μm were prepared using solution mixing method. The suitable
weight percentage of SiO2 nanofillers has been chosen to prevent the nonuniform dispersion. TSDC measurement of PC (Pristine) and PC+ (7% SiO2) shows the single peak, while TSDC characteristic of other nanocomposites are showing two peaks. The higher temperature TSDC
peak of pristine and nanocomposites samples is originated due to the charge relaxation from shallower and deeper trapping
sites, however, low temperature peak is caused by dipolar relaxation of charge carriers. Since the position of higher temperature
TSDC peak is generally an analysis of glass transition temperature of polymer/polymer nanocomposites. The authors have observed
that the temperature of this peak is almost same as the T
g measured by DSC with 0 to ±5% variation. This article presents the deeper understanding of charge relaxation mechanism caused
by SiO2 nanofillers in polycarbonate. 相似文献
9.
S. K. Tripathi Balbir Singh Patial Nagesh Thakur 《Journal of Thermal Analysis and Calorimetry》2012,107(1):31-38
Differential scanning calorimetry data at different heating rates (5, 10, 15 and 20 °C min−1) of Se70Te15In15 chalcogenide glass is reported and discussed. The crystallization mechanism is explained in terms of recent analyses developed
for use under non-isothermal conditions. The value of Avrami exponent (n) indicates that the glassy Se70Te15In15 alloy has three-dimensional growth. The average values of the activation energy for glass transition, E
g, and crystallization process, E
c, are (154.16 ± 4.1) kJ mol−1 and (98.81 ± 18.1) kJ mol−1, respectively. The ease of glass formation has also been studied. The reduced glass transition temperature (T
rg), Hruby’ parameter (K
gl) and fragility index (F
i) indicate that the prepared glass is obtained from a strong glass forming liquid. 相似文献
10.
Jong Keun Lee Xing Liu Sung Ho Yoon Michael R. Kessler 《Journal of Polymer Science.Polymer Physics》2007,45(14):1771-1780
Dicyclopentadiene (DCPD) and 5‐ethylidene‐2‐norbornene (ENB) and their mixtures were analyzed after ring‐opening metathesis polymerization (ROMP) in the presence of Grubbs catalyst as potential candidate healing agents for self‐healing composite materials using two complementary methods, rotational dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Following isothermal DMA measurements at room temperature (RT = 25 °C) for 120 min, two consecutive dynamic temperature scan experiments were performed for each system. In the first dynamic temperature scans, there was an initial downward peak slightly above RT in the storage modulus versus temperature curve for samples with relatively slower reaction rates (i.e., DCPD and DCPD‐rich mixtures or low catalyst loadings) due to a combination of the glass transition followed by further residual reaction. However, no or negligible downward peaks were observed for the highly reactive ENB and ENB‐rich samples even at much lower catalyst loadings. Implications of the substantial decrease in storage modulus just above RT for the slowly reacting systems are discussed for healing of damage in composite materials at elevated temperatures. The maximum glass transition temperatures (Tg∞) from DMA of the fully cured samples were determined to be approximately 160 °C for DCPD and 120 °C for ENB, decreasing linearly with increased ENB in the blends. The glass transitions and further residual reactions above the glass transitions were confirmed by DSC. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1771–1780, 2007 相似文献
11.
Konstantin S. Gavrichev Mikhail A. Ryumin Alexander V. Tyurin Andrey V. Khoroshilov Larisa P. Mezentseva Alexander V. Osipov Valeriy L. Ugolkov Viktor V. Gusarov 《Journal of Thermal Analysis and Calorimetry》2010,102(2):809-811
Thermal behavior of LaPO4·nH2O and NdPO4·nH2O nanopowders from room temperature to 973 K was investigated by DSC, TA/DTG, ESM, and X-ray study. Mass loss due to the release
of adsorbed and hydrate water was found in the range from 323 to 623 K. Phase transitions from hexagonal structure nanopowders
to monoclinic one for bulk specimens were found above 873 K. 相似文献
12.
Raquel Aparecida Domingues Inez Valéria Pagotto Yoshida Teresa Dib Zambon Atvars 《Journal of Polymer Science.Polymer Physics》2010,48(1):74-81
A fluorescent silicone network was prepared by a hydrosilylation reaction using poly(dimethylsiloxane‐co‐methylhydrogensiloxane) terminated by dimethylhydrogensilyloxy groups, poly(dimethylsiloxane‐co‐methylvinylsiloxane) terminated by dimethylvinylsilyloxy groups and 9‐vinylanthracene, as the fluorescent group. These silicone‐based materials were strongly fluorescent. Steady state emission was a convenient technique to prove that reaction occurred, based on the blue‐shift of the emission from anthracenyl moieties compared with the 9‐vinylanthracene. Thermal transitions were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and by fluorescence spectroscopy, indicating that networks with and without lumophores had similar thermal properties. Networks with and without lumophores had the same swelling capability in toluene. Fluorescence spectroscopy was a more sensitive technique to the onset of the glass transition temperature (T = 145 K) than DSC or DMA. Nevertheless, the crystallization temperature at 192 K was determined more precisely by DSC, and the melting point at 237 K was indentified more clearly by both DSC and DMA. These three techniques provided complementary information about transitions in silicone networks. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 74–81, 2010 相似文献
13.
Calorimetric measurements
have been performed in glassy Se90M10
(M=In, Te, Sb) alloys to study the effect
of In, Te and Sb additives on the kinetics of glass transition and crystallization
in glassy Se90M10 system. Kinetic
parameters of glass transition and crystallization such as the activation
energy of glass transition (E
g),
the activation energy of crystallization (M
c),
the order parameter (n), the rate constant
(K), etc. have been determined using different
non-isothermal methods. The composition dependence of the activation energies
of glass transition and crystallization processes is also discussed. 相似文献
14.
Pedro Lima Forster Ademar Benevolo Lugao Hermi Felinto Brito Duclerc Fernandes Parra 《Journal of Thermal Analysis and Calorimetry》2009,97(2):497-502
Polymers doped with rare earth complexes are advantaged in film production for many applications in the luminescent field.
In this luminescent polycarbonate (PC) films doped with diaquatris(thenoyltrifluoroacetonate)europium(III) complex [Eu(TTA)3(H2O)2] were prepared and their calorimetric and luminescent properties in the solid state are reported. The thermal behavior was
investigated by utilization of differential scanning calorimetry (DSC) and thermogravimetry (TG). Due of the addition of rare
earth [Eu(TTA)3(H2O)2] into PC matrix, changes were observed in the thermal behavior concerning the glass transition and thermal stability. Characteristic
broadened narrow bands arising from the 5D0 → 7FJ transitions (J = 4−0) of Eu3+ ion indicate the incorporation of the Eu3+ ions in the polymer. The luminescent films show enhancement emission intensity with an increase of rare earth concentration
in polymeric matrix accompanied by decrease in thermal stability. 相似文献
15.
M. I. B. Bernardi E. Antonelli A. B. Lourenço C. A. C. Feitosa L. J. Q. Maia A. C. Hernandes 《Journal of Thermal Analysis and Calorimetry》2007,87(3):725-730
The results reported here based on a study
of BaTi1–xZrxO3
(x=0, 0.2 and 1) nanometric powders prepared
by the modified Pechini method. The powder samples annealed from 600 to 1000°C/2
h were characterized by thermogravimetric analysis (TG), differential scanning
calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy
(SEM) techniques. The decomposition reactions of resins were studied using
thermal analysis measurements. The barium titanate zirconate system presented
just one orthorhombic phase. Furthermore, this study produced BaTiO3
powders with a tetragonal structure using shorter heat treatments and less
expensive precursor materials than those required by the traditional methods. 相似文献
16.
A material combination that may be applied as transparent armour is glass-clad polyurethane. These are comprised of a relatively
thin glass strike face and a relatively thick (transparent) polyurethane backing layer. Three transparent polyurethane samples
were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC results identified
the glass transitions and in some cases the melting and crystallisation processes. The DMA experiments were only performed
on heating around the glass transition region to further investigate this transition. The experiments were performed at three
different frequencies (1, 10 and 100 Hz); the shift of the glass transition with the frequency was clearly observed. The method
of time–temperature superposition was used to extrapolate the results to higher frequencies as the magnitude of the strain-rate
occurring within ballistic applications is in the order of 1000 s−1 or higher. Polyurethane with a rubbery behaviour at normal (low) strain rates can be stiff and brittle when used as an armour
component (temperature below its dynamic T
g value). 相似文献
17.
A. Ananthanarayanan A. Dixit R. K. Lenka R. D. Purohit V. K. Shrikhande G. P. Kothiyal 《Journal of Thermal Analysis and Calorimetry》2011,106(3):839-844
Lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li2O–71.7SiO2–7.1Al2O3–4.9K2O–3.2B2O3–1.25P2O5–1.25TiO2 were prepared by the melt quench technique. Crystallization kinetics was investigated by the method of Kissinger and Augis–Bennett
using differential thermal analysis (DTA). Based on the DTA data, glass ceramics were prepared by single-, two-, and three-step
heat treatment schedules. The interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC)
and microhardness (MH) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical
analysis (TMA), and microhardness (MH) measurements. Crystallization kinetics revealed that Li2SiO3 is the kinetically favored phase with activation energy of 91.10 kJ/mol. An Avrami exponent of n = 3.33 indicated the dominance of bulk crystallization. Based upon the formation of phases, it was observed that the two-stage
heat treatment results in highest TEC glass ceramics. The single-step heat treatment yielded glass ceramics with the highest
MH. 相似文献
18.
Zdeněk Černošek Jana Holubová Eva Černošková 《Journal of Thermal Analysis and Calorimetry》2011,103(2):429-433
Single crystals of cycloocta-Se, unambiguously characterized by XRD were prepared and used in a study of its allotropic transformation to polycatena-Se by DSC supported by Raman spectroscopy and optical microscopy. It was found that the transformation of a Se8 single crystal to polycrystalline Se
n
proceeds progressively within the volume of the monoclinic single crystal without shape change. All the results of DSC, Raman
spectroscopy, and optical microscopy indicate that previous proposals on cycloocta-Se melting during transformation are not realistic. 相似文献
19.
Y. Akishige H. Shigematsu T. Tojo H. Kawaji T. Atake 《Journal of Thermal Analysis and Calorimetry》2005,81(3):537-540
Summary Specific heats on the single crystals of Sr2Nb2O7, Sr2Ta2O7 and (Sr1-xBax)2Nb2O7 were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of TINC (=495 K) on Sr2Nb2O7 and at the super-lattice phase transition of TSL (=443 K) on Sr2Ta2O7; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of TLOW (=95 K) on Sr2Nb2O7. The transition temperature TLOW decreases with increasing Ba content x and it vanishes for samples of x>2%. 相似文献
20.
J. D. Menczel M. Jaffe C. K. Saw T. P. Bruno 《Journal of Thermal Analysis and Calorimetry》1996,46(3-4):753-771
Poly(2-methylpentamethylene terephthalamide) (Nylon M5T) is a new high temperature aromatic polyamide developed by Hoechst Celanese. In this paper thermal properties of Nylon M5T chips, as well as as-spun and drawn fibers were studied by DSC, DMA, hot stage microscopy and WAXS.T
g of the fully amorphous Nylon M5T is 143°C when measured by DSC;T
g increases with crystallinity to 151°C. The temperature dependence of the solid and melt specific heat capacities has also been determined. The heat capacity increase at the glass transition of the amorphous polymer is 103.9 J °C–1 mol–1.T
g by DMA for the as-spun fiber is 155°C, for a drawn fiber is 180°C. Three secondary transitions were observed by DMA in addition to the glass transition. These correspond to a local mode relaxation of the methylene groups at –120°C, onset of rotation of the amide-groups at –65°C and the onset of the rotation of the phenylenegroups (at 63°C). The crystallinity of Nylon M5T strongly depends on the rate of cooling from the melt. The isothermal crystallization data are melt temperature dependent: two-dimensional crystallization takes place when the samples are crystallized from higher melt temperatures, and this phase changes into a spherulitic structure during cooling to room temperature. Spherulitic crystallization occurs when lower melt temperatures are used. This polymer has three crystal forms as indicated by DSC, DMA and WAXS data. The crystal to crystal transitions are clearly visible when amorphous samples are heated in the DSC, or the DMA curves of as-spun fibers are recorded. It is experimentally shown that a considerable melting of the lower temperature crystal forms takes place during the crystal to crystal transitions. The equilibrium melting point as measured by the Hoffman-Weeks method, has been determined to be 339°C.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthday 相似文献