Energy potential of solid composite propellants based on 1,1-diamino-2,2-dinitroethylene

To obtain new formulations for solid composite propellants for creating composites with low sensitivity to mechanical stress and improved thermal stability, the energy potential of composites based on 1,1-diamino-2,2-dinitroethylene (FOX-7) and additionally containing a hydrocarbon or active binder, aluminum, and inorganic oxidant was studied. A formulation with 60% FOX-7 and 19 vol % active binder can be created which is characterized by a specific impulse I _sp ~ 251 s, density ~1.91 g/cm³, and T _c below 3600 K. The composites containing FOX-7 have smaller specific impulse values than the same formulations with HMX: by 10 s at 60% FOX-7 and by 4 s at 30% HMX.     

Influences of pressure on methyl group,elasticity, sound velocity and sensitivity of solid nitromethane

First-principles calculations were employed to investigate the influences of pressure on methyl group, elasticity, sound velocity and sensitivity of solid nitromethane. The obtained structural parameters based on the GGA-PBE +G calculations are in good agreement with theoretical and experimental data. The rotation of methyl group appears under pressure, which influences the mechanical, thermal properties and sensitivity of solid NM. The anisotropy of elasticity, sound velocity and Debye temperature under pressure have been shown, which are related to the thermal properties of solid NM. The enhanced sensitivity with the increasing pressure has been discussed and the change of the most likely transition path is associated with methyl group.     

Electrophysical properties of composite films based on multiwalled carbon nanotubes under hydrostatic pressure

The effect hydrostatic pressure of up to 9 GPa has on the electrical behavior of polymer composites based on multiwalled carbon nanotubes (MWCNT) is investigated at room temperature. The ratio R _9GPa/R ₀ ≈ 7 for samples with resistance in the kilo-ohm range is higher than for samples in the ohm range. Pressure-induced MWCNT features at P ≈ 1.5 GPa are associated with the deformation of the circular form of nanotube walls, in agreement with theoretical predictions. Measurements of direct and reverse resistance and current voltage characteristics under pressure demonstrate the reversibility of electrophysical properties, which could find practical application in creating pressure sensors.     

Internal friction phenomena in composites based on PZT-type ferroelectric powder and ferrites

The aim of the work was to determine the phenomena of internal friction (mechanical losses) occurring in ferroelectric-ferromagnetic composites created based on PZT-type ferroelectric powder and ferrite. The composites were obtained using ceramic powders – multi-component PZT-type solid solutions with ferroelectric properties. Their magnetic component included zinc-nickel powder Ni_0.64Zn_0.36Fe₂O₄. 30 × 10 × 1 mm³ test specimens were obtained using free sintering. Temperature Q^-1(T) and amplitude Q^-1(ε) internal friction dependencies were determined. Wide high temperature maxima were observed with regard to the internal friction temperature dependencies obtained for the tested specimens. The conducted measurements of amplitude (isothermal) dependencies of internal friction Q^-1(ε) for the tested composites have allowed for interpreting the previously observed maximum on the temperature dependencies of internal friction.     

The effect of filler on the temperature coefficient of the relative permittivity of PTFE/ceramic composites

High permittivity and low-loss ceramic fillers have been prepared by means of the solid state ceramic route. Ceramic-filled composites were prepared by the Sigma Mixing, Extrusion, Calendering, which was followed by the Hot pressing (SMECH) process. The microwave dielectric properties of the composites were studied using X-band waveguide cavity perturbation technique. The temperature coefficient of the relative permittivity of the composites was investigated in the 0-100 °C temperature range using a hot and cold chamber coupled with an impedance analyzer. The temperature coefficient of the relative permittivity of the composites showed strong dependence on the temperature coefficient of the relative permittivity of the filler material. In the present study, a high-permittivity polymer/ceramic composite, having τ_εr ∼63 ppm/K, has been realized. This composite is suitable for outdoor wireless applications.     

Synthesis and characterization of MnFe2O4-BiFeO3 multiferroic composites

The mixed spinel-perovskite composites of xMnFe₂O₄-(1-x)BiFeO₃ with x=0, 0.1, 0.2, 0.3 and 0.4 were prepared by solid state reaction method. The structure and grain size were examined by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD results showed that the composites consisted of spinel MnFe₂O₄ and perovskite BiFeO₃ phases after being calcined at the temperature 950 °C for 2 h. The grain size ranged from 0.8 to 1 μm. Magnetization was found to increase with increasing concentration of ferrite content. The variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Magnetocapacitance was also observed in the prepared composites, which may be the sign of magnetoelectric coupling in the synthesized composites at room temperature.     

Electronic topological transition in metastable Al-Ge solid solutions

Al-rich Al-Ge solid solutions synthesized under high pressure demonstrate physical properties strikingly different from those of pure Al. In particular, enhanced superconductivity temperature (T_c), anomalies in the phonon spectra and decrease of the Debye temperature have been observed. We show from first-principles, based on calculations of the electronic spectra and Fermi surfaces of Al-Ge substitutional solid solutions, that an electronic topological transition (ETT) takes place in the system. We predict anomalies in transport properties to be revealed experimentally for Al-Ge solid solutions with the Ge concentration ≈10 at.%. The influence of the ETT on the thermodynamic properties of the system is discussed and, in particular, concentration dependence of the Debye temperature is reproduced in good agreement with experiment.     

Specific Heat and Thermal Expansion of Triglycine Sulfate–Porous Glass Nanocomposites

The effect of restricted geometry on specific heat capacity and thermal expansion of the triglycine sulfate (TGS)–borosilicate glass composites have been studied first. A decrease in the entropy and temperature of the P2₁ ? P2₁/m phase transition in the TGS component with decreasing the glass matrix pore diameter at the invariable specific heat and thermal expansion coefficient has been observed. The estimates are indicative of the minor effect of internal pressure on the TGS pressure coefficient dT_C/dp in the composites.     

Homogeneous He-He solid solutions in the pre-separation region

Temperature dependences of the pressure P(T) in homogeneous solid ³He-⁴He mixtures have been studied experimentally in the wide range of concentrations (35.0%, 62.0%, 68.3%, 74.1%, 75.0%, and 89.3% ³He) above and below the equilibrium phase separation temperature T_s. An anomalous behaviour of the pressure in the vicinity of T_s is found for all investigated samples. With decreasing temperature, as T_s is approached, the pressure increases instead of expected reduction due to decrease in the phonon contribution (P_ph∼T⁴). Such an increase in pressure continues in the metastable region below T_s until the mixture separates. Theoretical interpretation of the observed effects based on a rigorous thermodynamic approach is proposed. The found experimentally pressure behaviour can be described only with the consistent account for fluctuations in the impurity subsystem which near T_s dominates over phonon contribution into the pressure. The obtained theoretical results are in good quantitative agreement with the experimental data. Density fluctuations in the concentrated mixtures give rise to a spontaneous formation of impuriton nano-clusters containing several hundreds of atoms. The fluctuation can be rigorously interpreted as a nucleus of the second phase in the pre-separated homogeneous solid mixture. The estimated size of the fluctuation nano-clusters agrees with the corresponding value for second phase nuclei obtained from the Lifshits-Slesov phenomenological theory of homogeneous nucleation.     

Investigation of complex impedance and modulus properties of Nd doped 0.5BiFeO3-0.5PbTiO3 multiferroic Composites

0.5BiNd _x Fe_1?x O ₃ ? 0.5PbTiO₃ (BN _x F_1?x ? PT)(x = 0.05, 0.10, 0.15, 0.20) composites were successfully synthesized by a solid state reaction technique. At room temperature, X-ray diffraction shows tetragonal structure for all concentrations of Nd doped 0.5BiFeO₃ ? 0.5PbTiO₃ composites. The nature of Nyquist plot confirms the presence of bulk effects only for BN _x F_1?x ? PT (x = 0.05, 0.10, 0.15, 0.20) composites. The bulk resistance is found to decreases with the increasing temperature as well as Nd concentration and exhibits a typical negative temperature coefficient of resistance (NTCR) behavior. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the composites. Conductivity spectra reveal the presence of hopping mechanism in the electrical transport process of the composites. The activation energy calculated from impedance plot of the composite decreases with increasing Nd _x concentration and found to be 0.89, 0.76, 0.71 and 0.70 eV for x=0.05, 0.10, 0.15 and 0.20 respectively.     

Modeling of micromachined silicon–polymer 2-2 composite matching layers for 15 MHz ultrasound transducers

Silicon–polymer composites fabricated by micromachining technology offer attractive properties for use as matching layers in high frequency ultrasound transducers. Understanding of the acoustic behavior of such composites is essential for using them as one of the layers in a multilayered transducer structure. This paper presents analytical and finite element models of the acoustic properties of silicon–polymer composites in 2-2 connectivity. Analytical calculations based on partial wave solutions are applied to identify the resonance modes and estimate effective acoustic material properties. Finite Element Method (FEM) simulations were used to investigate the interaction between the composite and the surrounding load medium, either a fluid or a solid, with emphasis on the acoustic impedance of the composite. Composites with lateral periods of 20, 40 and 80 μm were fabricated and used as acoustic matching layers for air-backed transducers operating at 15 MHz. These composites were characterized acoustically, and the results were compared with analytical calculations. The analytical model shows that at low to medium silicon volume fraction, the first lateral resonance in the silicon–polymer 2-2 composite is defined by the composite period, and this lateral resonant frequency is at least 1.2 times higher than that of a piezo-composite with the same polymer filler. FEM simulations showed that the effective acoustic impedance of the silicon–polymer composite varies with frequency, and that it also depends on the load material, especially whether this is a fluid or a solid. The estimated longitudinal sound velocities of the 20 and 40 μm period composites match the results from analytical calculations within 2.7% and 2.6%, respectively. The effective acoustic impedances of the 20 and 40 μm period composites were found to be 10% and 26% lower than the values from the analytical calculations. This difference is explained by the shear stiffness in the solid, which tends to even out the surface displacements of the composites.     

纳米ZnO／石蜡复合相变材料的热物理性质研究

本文通过将纳米氧化锌（ZnO）颗粒加入熔融的石蜡（PW）并进行搅拌和超声制备了一种纳米ZnO／PW复合相变储能材料。为使纳米氧化锌在基体物质中分散均匀,在制备过程中使用了搅拌和超声以制备均匀的复合材料。使用扫描电镜观察其微观结构表明氧化锌在石蜡中分散良好。对所得ZnO／PW复合相变材料的相变温度、相变焓及导热系数等热物...     

State equation of condensed matter at high pressure: <Emphasis Type="Italic">D-U</Emphasis> diagram approach

For solids and liquids, an equation of state is suggested at high pressures up to a few megabars, for densities greater than that at normal conditions and for temperatures up to the melting point. Shock wave loading test data are analyzed for 40 basic chemical elements, and they prove the state equation suggested, within the limits of test error. The method is based on the analysis of D-U diagrams where D is the shock wave velocity and U is the material velocity behind the shock wave (both with respect to the material in front of the shock wave). Based on the state equation suggested the velocity of shock wave is shown to be a linear function of the material velocity behind the shock wave, the function being a specific characteristic of the material and its structure. Most significant anomaly belonging to carbon, iron, ice, and water is explained by the formation of new phases at high pressure, with two new phases of iron, and one phase in the case of water. For water, a simple nearly exact equation of state is suggested for pressures from 0.1 MPa to 150 GPa. For pressures from 0.1 to 300 MPa, it fits very well the extremely complicated state equation of the American standard obtained by static tests, and for pressures from 2 to 50 GPa it fits well the data of shock wave tests. In the pressure range from 45 to 1500 GPa liquid water becomes solid, which equation of state coincides with that of alkaline metal sodium. The model of ideal solid as contrary to ideal gas is introduced, with internal energy of ideal solid depending only on stresses or strains (and only on pressure or density, at high pressures). The equations of state for iron, diamond, pyrolithic graphite, and for several phases of ice are as well derived based on test data.     

Numerical simulation of fracture of ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic composites

The regular grid generation method was generalized for a 3D region based on the solid mechanics equations that describe deformation of a finite volume. Test calculations of fracture of ceramic composites with inclusions are represented which are based on the developed model of quasi-brittle media with regard to damage accumulation.     

Semiconductor-metal transition in selenium under shock compression

Phase transitions in selenium are studied by time-resolved measurements of the electrical conductivity under shock compression at a pressure of up to 32 GPa. The pressure dependence of the electrical conductivity (σ(P)) has two portions: a sharp increase at P < 21 GPa and a plateau at P > 21 GPa. The experimental data and the temperature estimates indicate that, at P < 21 GPa, selenium is in the semiconductor state. The energy gap of semiconducting selenium decreases substantially under compression. At P > 21 GPa, the electrical conductivity saturates at ～10⁴ Ω^?1 cm^?1. Such a high value of the electrical conductivity shows the effective semiconductor-metal transition taking place in shock-compressed selenium. Experiments with samples having different initial densities demonstrate the effect of temperature on the phase transition. For example, powdered selenium experiences the transition at a lower shock pressure than solid selenium. Comparison of the temperature estimates with the phase diagram of selenium shows that powdered selenium metallizes in a shock wave as a result of melting. The most plausible mechanism behind the shock-induced semiconductor-metal transition in solid selenium is melting or the transition in the solid phase. Under shock compression, the metallic phase arises without a noticeable time delay. After relief, the metallic phase persists for a time, delaying the reverse transition.     

Interaction between Dusty Shock Waves and Three-Dimensional Scaffolds of Carbon Nanocomposites upon the Deposition of Biocompatible Coatings

The interaction between shock waves (velocity D0 ≈ 2–2.5 km s^?1 and maximum pressure p_max ≈ 3.1–3.8 MPa) containing finely dispersed hydroxyapatite particles (with mean diameters of d_p ≈ 70 nm and 100 μm) and substrates of carbon nanostructured composites that are a periodic three-dimensional scaffold is investigated experimentally. Study of these processes is important for the development of nonconventional osteoconductive and biocompatible materials with properties of osteoinduction. Features of the interaction between dusty shock waves and these substrates are established on the basis of complex experimental studies. Optimum conditions and ways of forming high-adhesion coatings on carbon composites are determined.     

Electrode materials for potentiometric hydrogen sensors

Due to their relatively high sensitivity, improved long-term stability, possibilities for miniaturization and low cost products, mixed potential solid electrolyte sensors can be competitive for the in situ measurement of hydrogen trace concentrations in oxygen containing gases. Their response behavior in non-equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. In this work the sensitivity of electrodes made of composites (Au/MeO) has been investigated in hydrogen containing gases in the concentration range φ(H₂) = 0…800 vol.-ppm using a two-chamber setup with Pt-air reference. Electrodes made of Au/Nb₂O₅ composites show the highest sensitivities of up to 20 mV/vol.-ppm at φ(H₂) = 10 vol.-ppm and the lowest catalytic activity for hydrogen oxidation. Selected composite materials were tested additionally in self-heated solid electrolyte sensors with both electrodes exposed to the same atmosphere (gas-symmetrical sensor).     

The melting pressure and entropy of spin ordered solid 3He

We report measurements of the melting pressure of solid ³He between 0.36 mK and 1.2 mK. At 1.030 ± .005 mK we observe a first order phase transition in the solid with a loss in entropy of 0.443R ln². Below ～0.6 mK the melting pressure varies as T⁴, in agreement with antiferromagnetic spin wave theory.     

On the influence of disjoining pressure on nonlinear oscillations of a water layer on the surface of a charged melting hailstone

The influence of a disjoining pressure on the nonlinear oscillations of a thin charged liquid layer on the surface of a spherical solid core is investigated by means of second-order asymptotic calculations. With the initial deformation governed by a kth mode in the spectrum of modes excited via nonlinear interaction, the disjoining pressure causes the frequencies of modes with numbers smaller than k to decrease and the frequencies of modes with numbers larger than k to increase. In the presence of the disjoining pressure, the amplitudes of all nonlinearly excited modes grow compared with the respective amplitudes without the pressure.     

Microcellular and Solid Polylactide–Flax Fiber Composites

Polylactide–flax fiber composites with 1, 10 and 20 wt% fiber were melt-compounded and subsequently molded via the conventional and microcellular injection-molding processes. Silane was used as a coupling agent. The effects of fiber and silane content on cell morphology, static and dynamic mechanical properties, and crystallization properties have been studied. The average cell size decreased while the cell density increased with the fiber content. The degree of crystallinity increased with the fiber content. Silane treatment of fibers affected neither the cell morphology nor the degree of crystallinity. The toughness and strain-at-break of solid samples decreased with the fiber content while silane treatment increased both properties; however, neither fiber content nor silane treatment had much influence on the toughness and strain-at-break of microcellular samples. The specific modulus of both solid and microcellular samples increased with the fiber content. The specific strength of the solid and microcellular PLA–flax composites were only slightly lower than that of their solid and microcellular pure PLA counterparts. Overall, the toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than that of their solid counterparts. The storage modulus of the PLA–flax composites with 10 and 20% fiber contents was higher than that of pure PLA.