Search results for "Expansion"
showing 10 items of 630 documents
Electrostatic model and NMR results for EFG tensors in tetragonal BaTiO3
1990
Abstract We present 47,49Ti and 135,137Ba NMR second-order quadrupolar rotation patterns in a tetragonal single domain crystal of BaTiO3. These data will be analysed in terms of a ionic polarizable point multipole model.
CNT and Graphene Growth: Growing, Quality Control, Thermal Expansion and Chiral Dispersion
2017
The chapter presents and discusses the production of graphene sheets of carbon nanotubes (CNT) of various types. The Iijima arc discharge method, following the purification methods, is described identifying advantages and disadvantages. Several types of non-regularities such as the Stone–Wales defect and corner effect, which locally increases reactivity, are described from the structural point of view. The laser ablation method is presented as one of the most prominent methods in the production of CNTs. The catalytic chemical vapour deposition (CVD) method is a very effective tool for the controlled production of different carbon shells. The sporadic and simulated growth of CNTs depends on …
Mechanical, thermal and electrical properties of monolayer and bilayer graded Al/SiC/rice husk ash (RHA) composite
2017
Abstract The mechanical, electrical and thermal properties as well as thermal expansion of Al/SiC/RHA (rice husk ash) monolayer and bilayer composite have been studied using the Taguchi method and analysis of variance (ANOVA). The parameter that most significantly affects the modulus of elasticity of Al/SiC/RHA bilayer composites is processing time, with contribution percentages of 68 and 27% calculated from stress-strain graphs and ultrasonic method, respectively. However, the factor which mostly affects bending strength, CTE value and electrical resistivity of composites is process temperature with contribution percentages of 32, 28, and 22%, respectively. The projected values for modulus…
Preparation and structural study of sodium germanium phosphate-sodium titanium phosphate solid solutions. I. Evolution of structure with composition
1993
Compounds NaM2IV(PO4)3 with M = Ge, Ti present the [NZP]-type structure, with a low thermal expansion. The space group at room temperature for the compound NaGe2(PO4)3 is R3, whereas for the compound NaTi2(PO4)3 is R3c. Evolution of the structure with composition in NaGe2(PO4)3 NaTi2(PO4)3 system is discussed. The space group and lattice parameters were determined for NaGe2−xTix(PO4)3 (0 < x < 2) solid solutions, prepared by ceramic method. Compositions rich in Ge(IV) (0 ≤ x ≤ 1) show the R3 space group, whereas for those rich in Ti(IV) (1.2 ≤ x ≤ 2) the space group is R3c. The variation of the lattice parameters with composition agreed with these results since it showed a change in its t…
Melting and multipole deformation of sodium clusters
1999
Melting and multipole deformations of sodium clusters with up to 55 atoms are studied using an ab initio molecular dynamics method. The melting temperature regions for Na20, Na40, and Na 55 + are estimated. The melting temperature region determined here for Na 55 + agrees with the one determined experimentally. The dominating deformation type observed at the liquid phase for Na20 and Na40 is octupole deformation and for Na14 and Na 55 + quadrupole deformation.
Particle size and morphology control of the negative thermal expansion material cubic zirconium tungstate
2009
Cubic ZrW2O8 is a negative thermal expansion (NTE) material that is of interest as filler in controlled thermal expansion composites. It is easily accessible from a hydrated precursor, ZrW2O7(OH)2·2H2O, which can be obtained by hydrothermal synthesis. Different reaction conditions were investigated to gain control over the morphology, and to minimize the particle size. Optimized procedures resulted in rod-shaped particles with widths of 10–30 nm and lengths of 200–500 nm, which showed little agglomeration. The particle size and morphology of the precursor are preserved during conversion to the NTE phase at 600–650 °C.
Multifunctional properties of nanocomposites made by 1D and 2D graphene based fillers
2015
High aspect ratio graphene based fillers with different dimensionalities showed the ability to greatly modify rheological, mechanical, thermal and electrical properties of polymers at very low content. In this work, the effect of filler dimensionality on the multifunctional properties of an epoxy matrix reinforced by both carbon nanotubes (1D) and graphite nanoplatelets (2D) have been investigated across the percolation region. Keywords-- Carbon nanotube, Graphite nanoplatelet, nanocomposites, mechanical properties, ...
X-ray micro-tomography based FEM modelling of hygroexpansion in PLA composites reinforced with birch pulp fibres
2017
This article presents a microscale modelling approach coupled with X-ray computed micro-tomography for the evaluation of material properties of polylactic acid (PLA) reinforced by birch pulp fibers under the effect of moisture. The results in terms of elastic moduli and hygroexpansion deformation were found in good agreement with the measurements taken at different levels of water uptake.
Structural study, thermal expansion and electrical conductivity of the composition NaSnZr(PO4)3
1993
Abstract The structure of the composition NaSnZr(PO4)3 and its evolution with temperature has been studied. The structure presents the space group R 3 c. The refinement of the structure shows that the Sn and Zr atoms are statistically distributed over the same crystallographic position. The unit cell expands in the c direction and contracts in the a direction, remaining the space group R 3 c at temperatures between 26 and 1000°C. The low value of the electrical conductivity at 400°C, 5.729×10−7S/cm and the low density of the pellets limited the use as electrical conductor.
Capacitive scanning dilatometry and frequency-dependent thermal expansion of polymer films
2000
The dilatometric properties of polymer films near and above their glass-transition temperatures were explored using capacitive high-frequency detection in temperature ramping as well as in harmonic temperature cycling experiments. The broad applicability of capacitive scanning dilatometry is demonstrated by the investigation of macromolecular systems of vastly different polarity such as polystyrene, polybutadiene, and polyvinylacetate. From temperature cycling experiments the real and imaginary parts of the frequency-dependent thermal-expansion coefficient are determined in the sub-Hz regime.