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1.
Cordierite porous ceramics Z, X, and K were prepared using three mixtures of clay minerals: Z from kaolinite, talc, and aluminum
hydroxide, X from kaolinite, talc, vermiculite, and aluminum hydroxide, and K from kaolinite, talc, and magnesium oxide. Ceramics
were different in porosity, specific surface area, cordierite polymorphs, and secondary crystalline phases. Vermiculite influenced
textural architecture of calcined cordierite ceramics X and predestinated crystallization of the high-temperature hexagonal
α-cordierite with secondary minerals enstatite, spinel and corundum. Ceramics Z contained low-temperature orthorhombic β-cordierite,
enstatite, and corundum, K was diphase of β-cordierite and forsterite. Total pore area (TPA) and specific surface area (SSA)
of X, in spite of the higher porosity and the pore size distribution in the range of 300–1000 nm, were smaller in comparison
with TPA and SSA of Z. Ceramics K retained high porosity, two maxima at 300–1000 nm and 50–200 nm in the pores size distribution,
and the highest TPA and SSA compared to those observed in ceramics Z and X.
Presented at the 8th Conference on Solid State Chemistry, 6-11 July 2008, Bratislava, Slovak Republic. 相似文献
2.
3.
The channelling of 3 MeV protons in the 〈110〉 direction of silicon has been simulated using Vineyard model taking into account
thermally vibrating nuclei and energy loss due to ion-electron interactions. A beam made up of constant energy particles but
with spatial divergence has been simulated for the purpose. The values of the minimum scattering yield and half width of the
channelling dip are shown to be depth sensitive and agree well with the measured values. The dependence of yield on the angle
of incidence has been found to give information of all three types of channelling. The critical angles for the three types
of channelling and wavelength of planar oscillations are consistent with the previous calculations. 相似文献
4.
Free volume quantities proposed earlier by Boyer and Simha in connection with the glass transition are reformulated by taking into account the temperature dependence of the thermal expansivities α l and αg for the liquid and the glass, respectively. This necessitates an extrapolation of the liquid to temperatures below Tg which is performed by means of the reduced volume-temperature function established and given a theoretical foundation previously. For the glass, low temperature experimental data, encompassing all relaxations occuring below Tg, are required. Two polymer series are examined in detail, namely, poly(methacrylates) and poly(vinyl) alkyl ethers, where αg has been measured between at least 30°K and Tg. Results for poly(methylacrylate) and poly(styrene) are also given. The systematic decrease in the product (αl - αg) · T|T=Tg with increasing length of the side chain noted previously is considerably reduced but not eliminated when the appropriately corrected expression is substituted instead. However, the free volume fraction related to the quantity αlT|T=Tg remains more nearly invariant in the polymers analyzed. An alternative treatment is discussed which considers an occupied volume expanding below Tg by a mechanism of thermal vibrations solely. Experimental and theoretical means of obtaining this quantity arc suggested. 相似文献
5.
We continue the comparison of the results of an interlayer model, based on the theory of elastic continua, and a molecular model, derived from a theory of mixtures, previously presented in terms of bulk moduli K. We now derive expressions for the dependence of the thermal expansivity
c
on the volume fraction
f
of the filler, at low and elevated values of
f
. Correspondencies between the characteristic parameters, viz. adhesion and repulsion ratios on the one hand, and interlayer content and thermal properties of matrix, filler, and layer, on the other, are examined. Since in the molecular theory both andK are derived from an equation of state, the identical set of parameters determines both functions and suggests correlations between them. 相似文献
6.
The pressure—volume—temperature properties of a series of copolymers ranging in content from 18 to 40 wt % of vinyl acetate, and up to a maximum pressure of 1800 kg/cm2 are studied. The results for the melt state can be satisfactorily fitted by the scaled equation of state, developed previously and applied to single-component systems and to mixtures. The dependence of the scaling parameters for the copolymers on composition deviates from that expected for a mixture, where volumes at elevated pressures can be predicted without further recourse to experiment. These differences are discussed in terms of the sequential structure of the copolymer chain and its series of interfaces between the two species. 相似文献
7.
E. Plevová A. Kožušníková L. Vaculíková G. Simha Martynková 《Journal of Thermal Analysis and Calorimetry》2010,101(2):657-664
The definition as well as prediction of rock thermal behavior seems to be a quite difficult problem significantly effected
by rock composition and structure. Temperature increase causes various changes of rock material (such as decomposition, oxidation,
phase and polymorphic transformation, etc.). These changes are connected to thermal expansion with following appearance of
tensions and cracks in minerals and rock structure. After consequential temperature decrease, developed tensions and cracks
still influence the process. This study presents the application of thermogravimetric analysis, differential thermal analysis
and thermomechanical analysis in characterization of selected marble thermal behavior. The texture and morphological orientation
of calcite grains for marble samples was determined by optical microscopy. FTIR spectroscopy application along with X-ray
diffraction (XRD) extended data about mineralogical composition. According to optical microscopy, the calcite grains show
marked morphological anisotropy in one direction for some samples. Therefore, the thermal expansion had to be measured in
three different (perpendicular to each other) directions. It is evident, that the effect of temperature on the final marble
properties depends not only on mineralogical composition, but also on structure, texture and morphological orientation of
grains. All these facts significantly influence the interpretation of differences in various marble thermal behavior. 相似文献
8.
N.K Simha F.D Fischer O Kolednik C.R Chen 《Journal of the mechanics and physics of solids》2003,51(1):209-240
This article evaluates the effect of material inhomogeneities on the crack-tip driving force in general inhomogeneous bodies and reports results for bimaterial composites. The theoretical model, based on Eshelby material forces, makes no assumptions about the distribution of the inhomogeneities or the constitutive properties of the materials. Inhomogeneities are modeled by making the stored energy have an explicit dependence on the reference coordinates. Then the material inhomogeneity effect on the crack-tip driving force is quantified by the term Cinh, which is the integral of the gradient of the stored energy in the direction of crack growth. The model is demonstrated by two model problems: (i) bimaterial elastic composite using asymptotic solutions and (ii) graded elastic and elastic-plastic compact tension specimen using numerical methods for stress analysis. 相似文献
9.
F. D. Fischer J. Predan O. Kolednik N. K. Simha 《Archive of Applied Mechanics (Ingenieur Archiv)》2007,77(2-3):95-112
The material forces concept has become an elegant tool in continuum mechanics for the calculation of the thermodynamic driving
force of a defect. Based on this concept, we have recently shown that inhomogeneities essentially shield or anti-shield crack
tips from applied far-field stresses. The goal of this paper is to illustrate this by considering the model example of a crack
in a CT-type specimen that contains a bimaterial interface. The crack driving force is calculated as the sum of the far-field
driving force and the crack-tip shielding or anti-shielding. Several cases of inhomogeneity in either thermal or elastic properties
are considered. Rather simple hand calculations are provided in addition to numerical results to illustrate the advantages
of using the material forces concept. 相似文献
10.
Z. Yu U. Yahsi J. D. McGervey A. M. Jamieson R. Simha 《Journal of Polymer Science.Polymer Physics》1994,32(16):2637-2644
Positron annihilation lifetime measurements are reported for four monodisperse polystyrenes with molar mass M = 4,000, 9,200, 25,000, and 400,000. The temperature dependences of orthopositronium (o-Ps) lifetime (τ3) and intensity (I3) were measured from 5°C to Tg + 30°C for each sample. From these data, the free volume hole size, 〈vf(τ3)〉, and fractional free volume hps=CI3〈vf(τ3)〉 were calculated. The temperature dependences of τ3, 〈vf(τ3)〉 and hps show a discrete change in slope at an effective glass transition temperature, Tg,ps, which is measurably below the conventional bulk Tg. This suggests that τ3 is sensitive to large holes which retain their liquid-like mobility in the glassy state. Good agreement was found for T > hg,ps between hps and the theoretical free volume fraction hth deduced from experimental P-V-T data for polystyrene using the statistical mechanical theory of Simha and Somcynsky. Below Tg,ps, deviations between hps and hth are observed, hps falling increasingly below hth as temperature decreases. Whereas hps and hth depend strongly on M in the melt, each essentially independent of M in the glass. A free volume quantity, computed from the bulk volume, which is in good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with hps in the glassy state. © 1994 John Wiley & Sons, Inc. 相似文献