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1.
A. Marotta P. Pernice A. Aronne M. Catauro 《Journal of Thermal Analysis and Calorimetry》1993,40(1):181-188
The non-isothermal devitrification of lithium germanate glasses, examined by DTA and XRD, is reported and discussed. The glass compositions are expressed by the general formula:xLi2O(1?x)GeO2 withx=0.050, 0.125, 0.167, 0.200 and 0.250. All the glasses studied, unlike GeO2 glass, exhibit internal crystal nucleation without the addition of any nucleating agent. The devitrification processes occur in one or more steps. Phases which crystallized at each step are identified and crystallization mechanisms proposed. These crystallization mechanisms are related to structures of the crystallizing phases. Activation energy values as well as those for glass transition temperatures, do not vary linearly with increase in Li2O content but pass through a maximum atx=0.200. 相似文献
2.
D. N. Sorensen A. P. Quebral E. E. Baroody W. B. Sanborn 《Journal of Thermal Analysis and Calorimetry》2006,85(1):151-156
In previous
works, the effects on the devitrification mechanism of a certain composition
calcium phosphate with additives of TiO2, SiO2,
Al2O3, CeO2
have been studied. It was found that some metal oxide additives played a key
role as the nucleation agent in calcium phosphate glass-ceramics, and the
devitrification mechanism of calcium phosphate glass system was changed drastically
by addition such as metal oxide. Hydroxyapatite (HAp), tricalcium phosphate
(TCP) and β-calcium phosphate (β-CaP2O6)
whisker are the three most biologically compatible materials to human bone
in bio-ceramics field. In this work, the effect on devitrification mechanism
and the physical properties of certain composition calcium phosphate glass
with three above additives were investigated, and the result shown that although
no fine crystalline was induced in the certain composition of calcium phosphate
glass when a large amount of additive was added, but such additives play a
catalyst role by lowering the activation energies of devitrification. It would
supplement the mechanical properties and the biocompatibility for the calcium
phosphate glasses. 相似文献
3.
J. V. Dubrawski 《Journal of Thermal Analysis and Calorimetry》1997,48(1):63-72
A series of aged granulated blast furnace slags were investigated by DTA. Devitrification characteristics were found to change as a function of age, and regular trends could be established. XRD showed the devitrification process to result predominantly in melilite formation and minor amounts of merwinite, depending on slag age.Hydration of fresh slags resulted in the gradual formation of hydrated species and calcite. DTA indicated that the devitrification profile also changed with the extent of hydration.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthdayThe author acknowledges the assistance of Ms S. Bell and M. Venour (BHP) in this study. 相似文献
4.
5.
HA纳米微粒对PEG-600低温保护剂反玻璃化结晶的影响 总被引:1,自引:0,他引:1
为了研究羟基磷灰石HA纳米微粒对低温保护剂反玻璃化结晶的影响,本文利用DSC和低温显微镜研究了含有不同粒径(20nm、40nm、60nm)和不同质量浓度(0.1%、0.2%、0.4%、0.8%)HA纳米微粒的PEG-600(50%,w/w)溶液反玻璃化过程中的结晶现象.试验结果表明:与未添加纳米微粒的PEG-600溶液相比,加入40nm、0.4%纳米微粒的HA-PEG600溶液的反玻璃化温度升高了7℃;加入20nm、0.4%和40nm、0.8%纳米微粒的HA-PEG600溶液的冰晶生长速率分别降低了35%和提高了50%;纳米低温保护剂溶液的冰晶形貌从大圆形变成了小圆形、枝晶或小圆形中夹带枝晶. 相似文献
6.
Tomasi C. Scavini M. Speghini A. Bettinelli M. Riccardi M. P. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):151-164
The devitrification of glassy PbGeO3 was studied and interpreted by means of isothermal and non-isothermal Johnson-Mehl-Avrami equations. In the case of the non-isothermal
approach, several approximated equations proposed by various authors were considered in order to obtain both the activation
energy E
a and the Avrami morphological coefficient n of the crystallisation process. A critical discussion of the Avrami coefficient on the basis of experimental morphological
evidence is also presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Lee Jinn-Shing Hsu C.-K. Huang Chin-Wang 《Journal of Thermal Analysis and Calorimetry》1999,56(1):137-142
The effects of Al2O3 and SiO2 additives on the crystallization of calcium phosphate glasses were studied. When the Al2O3 content was higher than 7 mol%, surface devitrification occurred in the glasses. However, for glasses with Al2O3 contents higher than 10 mol%, bulk devitrification predominanted. For the glasses with SiO2, a surface devitrification mechanism predominanted. Non-isothermal DTA techniques were applied in order to establish the
devitrification mechanism, and the kinetic parameters of crystal growth were obtained. The parameter m depends on the mechanism
and morphology of devitrification of calcium phosphate, glass containing SiO2 as additive, the values of m being lower than 1.2. These results indicate that the devitrification is controlled by the reaction
at the glass-crystal interface, or occurs from surface nuclei.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
F. Branda A. Costantini A. Buri A. Tomasi 《Journal of Thermal Analysis and Calorimetry》1994,41(6):1479-1487
In this paper a thermoanalytical study of the kinetic parameters and mechanism of the devitrification process of CaO·SiO2, 1.6CaO·0.4MgO·2SiO2 and 1.4CaO·(0.6/3)Y2O3·2SiO2 is reported. The experimental results suggest that, in the studied glasses, a surface nucleation process is operative; however, in finely powdered samples, that soften and efficiently sinter before devitrifying, surface nuclei behave as bulk nuclei. In this case lamellar crystalline structures are obtained. 相似文献
9.
The effect of replacing SrO by BaO on the glass transition temperature and on devitrification behaviour in a series of glasses in the strontium tetragermanate — barium tetragermanate composition range has been studied by differential thermal analysis, X-ray diffraction and Fourier-transform infrared spectra. All glasses studied exhibit internal crystal nucleation. The progressive replacing of SrO by BaO causes the decrease of the glass transition temperature. Solid solutions between SrGe4O9 and BaGe4O9 were found to crystallize in glass containing both SrO and BaO. The effect of the specific surface of the glass samples on devitrification processes has been also pointed out.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
10.
Lee Jinn-Shing Hsu Chung-King Lin Li-Kuo Chang Chih-Long Borjinn Shich Huang Chin-Wang 《Journal of Thermal Analysis and Calorimetry》1999,56(1):131-136
Vitreous solder glasses, such as Mansol #40 and FEG-2002, are commercialized solder glasses, which are compression sealing
glasses that can be used to solder materials with expansions between 55-68⊙10-7°C-1, such as Al2O3.
In order to understand and tailor the thermal behaviour of solder glasses, cylindrical-like glasses were first carefully ground
with a stainless steel mortar and pestle. Initially, no exothermic or endothermic data were obtained from the DTA/DSC curves
except those relating to melting. However, exothermic peaks appeared after the glass samples were re-melted. In this work,
kinetic parameters such as the activation energy, and the morphology of the devitrification mechanisms for two kinds of solder
glasses were also investigated, using non-isothermal DTA techniques. The activation energies ranged from 220 to 235 kJ mol-1 and the devitrification mechanism parameters were close to 1. This indicates that the devitrification mechanisms of the two
kinds of solder glasses involve surface nuclei.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献