A study of internal friction in polypropylene (PP) filled with nanometer-scale CaCO3 particles

The internal friction and relative elastic modulus of polypropylene (PP) filled with nanometer-scale calcium carbonate (nm-CaCO₃) particles in different contents (0, 4, 7, and 15 vol.%) are measured in the temperature range 150–400 K with a torsion pendulum. The peak associated with the glass transition and a small peak (′ peak) associated with the pre-melting process in crystalline parts of PP was observed around 290 and 370 K, respectively. At temperatures lower than 270 K, no peaks were observed. With increasing content of nm-CaCO₃ particles, the apparent activation energy of the peak decreases, and after passing a minimum of 4.7 eV at 4 vol.% of nm-CaCO₃, it increases. In contrary to this behavior, the peak temperature has a maximum of 289 K at the same filler fraction. Correspondingly, the highest tensile and flexural strength of PP were obtained around this content. These observations may be understood through the influences of fillers on the degree of crystallization of PP and on the mobility of molecules of PP.     

Gamma double prime precipitation kinetic in Alloy 718

Gamma double prime (γ′′), precipitation was studied in Alloy 718 using isothermal and isochronal aging heat treatments applied between 943 and 1003 K. It is shown, that the coarsening behavior of γ′′ precipitates follows the coarsening kinetic predictions of the Lifshitz–Slyozov–Wagner (LSW) theory. The activation energy for γ′′ growth has been determined as equal to 272 kJ mol⁻¹ and seems to be controlled by volume diffusion of niobium in the matrix. The energy of the γ′′/matrix interface, Γ, has been found to be 95 ± 17 mJ m⁻² by assuming that the γ′′ precipitates adopt a disk shape which minimizes the total energy. This energy includes a volume distortion term calculated from the Eshelby inclusion theory and a surface component which is assumed to be isotropic. This interfacial energy is discussed and compared with the energy of γ′/matrix and γ′′/matrix interfaces in other superalloys. The constant K′′ of the LSW law time dependence has been calculated using the value of interfacial energy and the activation energy of γ′′ precipitates coarsening and is found to be in good agreement with our experimental values.     

Separation of CO2 and CH4 through two types of polyimide membrane

Two asymmetric polyimide membranes that have a thermal stability up to 550 K and good resistance to solvents were prepared. Some membrane-forming conditions such as coagulation solution, evaporation and immersion time were examined. Regarding the coagulation solution, a water–methanol mixture gives good membranes in eleven solutions tested. The permeabilities of two asymmetric polyimide membranes for CO₂ and CH₄ pure gases were determined at 25°C and at applied pressures up to 0.25 MPa. The prepared polyimide membranes, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)-4,4′-diaminodiphenyl ether (ODA) and 1,2,3,4-butanetetracarboxylic dianhydride (BDA)-4,4′-diaminodiphenyl ether (ODA) exhibited higher selectivity and permeability for CO₂/CH₄.     

Microstructural changes inside the lamellar structures of alloy ZA27

The microstructural changes inside the lamellar structure of the cast and aged alloy ZA27 were studied using TEM, XRD and SEM techniques. Using TEM, the network of transitional phase η_m^′ was determined to be of an fcc crystal structure inside the lamellae η phase during ageing at 150 °C. The mechanism of the decomposition of the η phase lamellae can be summarized as follows: η → η_m^′ + η′ →  + η. The adjacent co-existence of the ε phase and the T′ phase inside the phase lamellae confirmed that a four phase transformation,  + ε → T′ + η, had occurred during the prolonged ageing.     

Experimental investigation of the viscoelastic deformation of PC, ABS and PC/ABS alloys

Dynamic Mechanical Analysis (DMA) tests are carried out to investigate the viscoelastic deformation of PC, ABS and PC/ABS alloys with ratio of PC to ABS being 80/20, 60/40, 50/50, 40/60, respectively. Storage and loss moduli and loss angle of PC, ABS and PC/ABS alloys are measured from DMA tests from 30 °C in 160 °C at 1 Hz. Glassy temperature of PC/ABS alloys is determined with loss modulus and loss angle curves. Also, static tests are carried out to measure the relaxation moduli of PC, ABS and PC/ABS alloys. Effect of ABS fraction on the glassy transition temperatures and relaxation moduli of PC/ABS alloys is discussed.     

First principles calculations of thermal equations of state and thermodynamical properties of MgH2 at finite temperatures

We present the first principles calculations of the thermodynamical properties of magnesium hydride (MgH₂) over a temperature range of 0–1000 K. The phonon dispersions are determined within the density functional framework and are used to calculate the free energy of MgH₂ within the quasiharmonic approximation (QHA) at each cell volume and temperature T. Using the free energies the thermal equation of state (EOS) is derived at several temperatures. From the thermal EOS structural parameters such as the equilibrium cell volume (V₀) and elastic properties, namely, bulk modulus (K₀) and its pressure derivative are computed. The free energies are also used to calculate various thermodynamical properties within QHA. These include internal energy E, entropy S, specific heat capacity at constant pressure C_P, thermal pressure P_thermal(V, T) and volume thermal expansion ΔV/V (%). The good agreement of calculated values of S and C_P with experimental data exhibits that QHA can be used as a tool for calculating the thermodynamical properties of MgH₂ over a wide temperature range. P_thermal(V,T) increases strongly with T at all the volumes but it is a slowly varying function of volume for T = 298–500 K. According to Karki [B.B. Karki, Am. Miner. 85 (2000) 1447] such volume based variations can be neglected and so it is possible to estimate the thermal EOS only with the knowledge of the measured P_thermal(V, T) versus temperature at ambient pressure and isothermal compression data at ambient temperature. Temperature dependence of ΔV/V(%) shows that V₀ increased with increase in temperature. However, the percentage decrease in K₀ superseded this percentage increase in V₀ even at temperatures moderately higher than 298 K. Therefore, we suggest application of temperature (T > 298 K) as an approach to enhance the hydrogen storage capacity of MgH₂ because of its better compressibility at these temperatures.     

High performance very low frequency forced pendulum

A forced torsion pendulum has been constructed for the measurement of mechanical loss angle (tan δ) and elastic shear modulus in three different modes: (a) as a function of temperature (80–1250 K), at imposed frequency, during heating or cooling at imposed heating or cooling rate (0.1–5 K/min); (b) as a function of frequency (10–10⁻⁴ Hz) in isothermal conditions, and (c) as a function of amplitude (5×10⁻⁶ to 5×10⁻⁵) at imposed frequency and under isothermal conditions. The mechanical part of the pendulum has been designed in such a way that torsional plastic deformation of the specimen can be performed in situ, i.e., at low temperatures to generate fresh dislocations in metals, and at high temperatures to enhance grain boundary sliding, for instance. The whole installation is computer controlled and exhibits not only outstanding performances but also a very high capability of working in different conditions, being a useful tool for studying a large variety of mechanisms in different materials.     

Temperature dependence of fracture toughness of silica/epoxy composites: Related to microstructure of nano- and micro-particles packing

Temperature dependence of the fracture toughness of epoxy composites reinforced with nano- and micro-silica particles was evaluated. Epoxy composites containing varied composition ratios Φ_SP of spherical nano- and micro-silica particles, 240 nm and 1.56 μm, were prepared at a fixed volume fraction (V_P = 0.30). The thermo-viscoelasticity and fracture toughness of the composites and neat epoxy were measured at 143 K, 185 K, 228 K, 296 K, 363 K, and 399 K. Experimental results revealed that fracture toughness strongly depended on the microstructure of nano- and micro-particles bidispersion as well as its interactions with the matrix at all temperature, but depended on toughened matrix due to increase in mobility of matrix at the relaxation temperatures.     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Effect of ferroic domain pattern changes on the Raman spectra of some ferroic crystals

The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH₄SO₄ and (NH₄)₃H(SO₄)₂ single crystals were studied. It was shown that the Raman spectra of β-LiNH₄SO₄ passed from the ferroelastic phase differ from those of “as-grown” crystal and those of the crystal, which was in the paraelectric phase. Significant changes could be observed in the Raman bands related to triply degenerated ν₃ and ν₄ vibrations of the SO₄ tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH₄SO₄ close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO₄ in the temperature range where a regular large-scale structure is observed. Different types of evolution of the ferroelastic domain structure and temperature behaviour of the donor and acceptor vibrations were shown while heating and cooling the (NH₄)₃H(SO₄)₂ crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (ΔT_S  3–5 K) and in Raman spectra studies (ΔT_S  12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature T_II–III  265 K, at which C2/c → P2/n structural phase transition takes place. On the other hand, at T_III–IV  135 K additional domains with W′-type of domain wall orientation were found.     

Structural, dielectric and electrical conducting properties of CsB′B′′O6 (B′=Nb, Ta; B′′=W, Mo) ceramics

Polycrystalline samples of the defect pyrochlore-type CsB′B′′O₆ (B′=Nb, Ta; B′′=W, Mo) compounds were prepared by solid-state reaction technique. The formation of the compounds was checked by X-ray diffraction (XRD) method. All the compounds were found to have a cubic crystal structure at room temperature. Dielectric studies of the tungstate compounds, CsNbWO₆ and CsTaWO₆ indicated a small dielectric anomaly at (183±2) and (328±2) K, respectively, whereas the molybdate compounds, CsNbMoO₆ and CsTaMoO₆ did not exhibit such anomaly. The conductivity measurements indicated ionic transports (t_ion≥0.80) in the high temperature region (≥573 K).     

Effects of aging on martensitic transformation of Ti50Ni25Cu25 shape memory alloy

Martensitic transformation has been studied in Ti₅₀Ni₂₅Cu₂₅ shape memory alloy by internal friction (IF) measurement and X-ray diffraction. It shows that the martensitic transformation proceeds from B2 to B19 for the solution-treated Ti₅₀Ni₂₅Cu₂₅ alloy. B2 phase is stabilized, and aging the alloy at 723–923 K decreases internal friction values. Part of the remaining B2 parent phase transform to B19′ monoclinic martensite at much lower temperatures.     

Anelastic relaxation in high purity molybdenum single crystals at medium temperatures

The internal friction of deformed molybdenum single crystals with two different orientations has been measured in the 300–1300 K temperature range. After annealing to 950 K, a relaxation peak is seen in the 880–840 K range, with a hysteresis between the warming and cooling runs. For higher annealing temperatures, the peak position change to 970 K for the 1 1 0 and 1040 K for the 1 4 9 sample. The influence of a bias stress on the sample relaxation was studied. Possible mechanisms for this relaxation have been considered, and an interaction of dislocations with vacancy type point defects has been proposed.     

Effect of deposition temperature on the structural and thermoelectric properties of bismuth telluride thin films grown by co-sputtering

Thermoelectric bismuth telluride thin films were prepared on SiO₂/Si substrates by radio-frequency (RF) magnetron sputtering. Co-sputtering method with Bi and Te targets was adopted to control films' composition. Bi_xTe_y thin films were elaborated at various deposition temperatures with fixed RF powers, which yielded the stoichiometric Bi₂Te₃ film deposition without intentional substrate heating. The effects of deposition temperature on surface morphology, crystallinity and electrical transport properties were investigated. Hexagonal crystallites were clearly visible at the surface of films deposited above 290 °C. Change of dominant phase from rhombohedral Bi₂Te₃ to hexagonal BiTe was confirmed with X-ray diffraction analyses. Seebeck coefficients of all samples have negative value, indicating the prepared Bi_xTe_y films are n-type conduction. Optimum of Seebeck coefficient and power factor were obtained at the deposition temperature of 225 °C (about − 55 μV/K and 3 × 10^− 4 W/K²·m, respectively). Deterioration of thermoelectric properties at higher temperature could be explained with Te deficiency and resultant BiTe phase evolution due to the evaporation of Te elements from the film surface.     

Viscoelastic interlaminar shear modulus of fibre reinforced composites

An inverse parameter identification technique using a modified Iosipescu shear test (MIST) has been developed for determining the viscoelastic interlaminar shear modulus of composite laminates. The main component of the technique involves minimising the difference between an experimentally measured and a numerically determined creep response at various elevated temperatures by varying the interlaminar shear modulus terms in the numerical model. Consequently, the ‘optimum’ model for the viscoelastic interlaminar shear modulus can be found at each temperature. These individual models are then combined to form a single ‘master curve’ for which a time-shift function and a Prony-series is fitted. In the present studies, Hexcel F593–18 plain weave pre-preg laminates were investigated. Experimental creep tests were conducted at various temperatures between 40 °C and 150 °C. Through the application of the inverse parameter identification technique, it was determined that the viscoelastic interlaminar shear moduli of the composite material can be effectively modelled by a nine-term Prony series and a third-order polynomial time-shift function.     

Relaxation processes in a glassy polymer containing methanol molecules

The interaction of small guest molecules with the molecular degrees of freedom of a glassy polymer matrix is investigated, i.e. (i) the dynamics of these guest molecules and (ii) their effect on the secondary ‘β’ and main ‘’ relaxations of the host polymeric matrix. The system considered here is the glassy poly(methyl metacrylate) modified by introduction and desorption of methanol. The dynamics of the system is observed by means of low-frequency mechanical and wide band dielectric spectroscopies. The presence of small molecules in the PMMA glassy matrix induces several effects, namely (i) a strong relaxation peak develops at low temperature (near 120 K at 1 Hz and called _m in the following), (ii) the strength of the β relaxation is increased while the temperature of the maximum shifts towards the low temperatures, (iii) a sharp peak appears superimposed on the β peak, and finally (iv) the relaxation shifts towards the low temperatures. Dielectric and mechanical spectroscopies results are in agreement and make it possible to capture the dynamical behavior in a wide frequency range (eight decades). The experimental results are explained on the basis of physical concepts recently introduced in the physics of glassy matter: cooperativity and nanoheterogeneity. In particular, the low-temperature relaxation process _m is attributed to cooperative motions in methanol clusters which form in the nanoheterogeneous polymeric matrix, in agreement with small angle X-rays scattering and low-frequency Raman scattering observations recently reported.     

Synthesis and physical characterization of magnetite nanoparticles for biomedical applications

Iron oxide nanoparticles for biomedical applications in the size range of 15–130 nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous/ferric chloride solutions. The magnetite particle size is controlled by variation of pH and temperature. The synthesized magnetite nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24 wt% Fe²⁺ and lattice parameters of a₀ ≤ 8.39 Å which are smaller compared to 8.39 Å for stoichiometric magnetite. The extend of oxidation increases with decreasing particle size. Heating at 150–350 °C topotactically transforms the magnetite nanoparticles into stoichiometric tetragonal maghemite (ferrous ion concentration c_Fe²⁺=0 and a₀ = 8.34 Å) without significant particle growth. The magnetite–maghemite transformation is studied with thermal analysis, XRD and IR spectroscopy. The saturation magnetizations of the magnetite and maghemite particles decrease with decreasing particle size. The variation of M_s with particle size is interpreted using a magnetic core–shell particle model. Magnetite particles with d ≤ 16 nm show superparamagnetic behavior at room temperature whereas particles with diameter >16 nm display hysteresis behavior. These particles are candidates for biomedical applications, e.g. controlled drug release or hyperthermia.     

The Dislocation Structure of a Single-Crystal γ + γ′ Two-Phase Alloy After Tensile Deformation

The dislocation structures of an industrial single-crystal γ + γ′ two-phase alloy DD3 after tensile deformation from room temperature to 1273K were studied by transmission electron microscopy. The strength of this alloy decreased with an increase in the temperature, and showed a strength peak at 1033K. At room temperature, the dislocations shearing the γ′ particles were found to be 1/3<112> partial dislocations on the dodecahedral slip system <112>{111}. Some dislocation pairs on the cubic <110>{100} system that blocked the glide of dislocations were found at a medium temperature of 873K. As a result, dislocation bands were formed. Shearing of γ′ particles by 1/3<112> partial dislocations on the dodecahedral slip system <112>{111} was also found at this temperature. At the peak temperature of 1033K, because of the strong interaction between dislocations on the {111} and {100} planes, the extent of dislocation bands with high dislocation densities was extensive. The 1/3<112> partial dislocations on the dodecahedral slip system <112>{111} also existed. When the temperature reached the high temperature of 1133K, the range of dislocation bands was limited. The γ′ particles were sheared by <110> dislocation pairs on the octagonal <110>{111} system and the cubic <110>{100} system. At 1273K, the regular hexagonal dislocation networks were formed in the γ matrix and at the γ/γ′ interface. The Burgers vectors of the network were found to be b₁ = 1/2[110], b₂ = 1/2[1–10], b₃ = [100], and the last one was formed by the reaction of b₁ + b₂ → b₃. Dislocations shearing the γ′ particles were found to be <110> dislocation pairs on the octagonal system <110>{111} and cubic slip system <110>{100} at 1273K.     

Hydriding effects on negative cell electrode

Internal friction (IF) and modulus measurements have been carried out on a composite material taken from the negative electrode of a commercial Ni–metal-hydride (Ni–MH) battery, both in the as-received condition and after in situ gaseous hydrogen exposure, using a sub-resonant torsion pendulum at fixed frequencies between 0.1 and 10 Hz in the temperature range 90–450 K. In both cases the IF spectrum is composed by two peaks: P1 at 190 K and P2 at 290 K, with corresponding modulus variations. The P1 data are detected to be due to a thermally activated process which frequency shift activation energy is (0.175±0.004) eV and fitted to a relaxation peak with a larger wide respect to a Debye peak, being β equal to 2.2. It is interpreted to be due to the movement of misfit dislocations within the AB₅ intermetallic-type alloy particles in the presence of nearby H atoms, acting as a Cottrell atmosphere. Peak P2 is ascribed to the decomposition and formation of hydride phase in the alloy particles upon heating and cooling, respectively. The peak heights are shown to increase in the hydrided samples, supporting the above interpretation. These results are also discussed in connection with previous measurements on an electrode material prepared at the laboratory.     

Structure–morphology–mechanical properties relationship of some polypropylene/lignocellulosic composites

Natural lignocellulosic materials have an outstanding potential as thermoplastic reinforcement. Polypropylene composites were prepared using different types of lignocellulosic materials by melt blending of 70 wt% polypropylene (PP) and 30 wt% biomasses. The specimens were firstly evaluated for structural and morphological properties by infrared spectroscopy, X-ray diffraction, scanning electron and polarized optical microscopy. Depending on the biomass type, there were evidenced some particular shifts of the infrared bands and also crystallinity changes. An increase in crystallinity is explained by nucleating agent role of biomass. The morphological changes are directly related to variation in mechanical and rheological properties, an increase in Young modulus, melt viscosity and storage and loss moduli being recorded.