Ultrasonic study of the temperature and pressure dependences of the elastic properties of β-silicon nitride ceramic

Ultrasonic wave velocity measurements have been used to determine the elastic stiffness moduli and related elastic properties of high-purity, dense -Si₃N₄ ceramic samples as functions of temperature in the range 150–295 K and hydrostatic pressure up to 0.2 GPa at room temperature. Due to its covalently bonded, rigid structural framework -Si₃N₄ is an elastically stiff material; the elastic stiffness moduli of the ceramic at 295 K are: C _L = 396 GPa, = 119 GPa, B ^S = 238 GPa, E = 306 GPa, Poisson's ratio = 0.285. The longitudinal elastic stiffness C _L increases with decreasing temperature and shows a knee at about 235 K; the decrease in slope below the knee indicates mode softening. The shear elastic stiffness shows mode softening which results in a plateau centred at about 235 K and an anomalous decrease with further reduction in temperature. The hydrostatic-pressure derivatives of elastic stiffnesses at 295 K are (C _L/P) _P=0 = 4.5 ± 0.1, (B ^S/P) _P=0 = 4.3 ± 0.1 and (/P) _P=0 = 0.17 ± 0.02 (pressure < 0.12 GPa). An interesting feature of the nonlinear acoustic behaviour of this ceramic is that, in the pressure range above 0.12 GPa, the values obtained for (/P) _P=0 and the shear mode Grüneisen parameter (_S) are small and negative, indicating acoustic-mode softening under these higher pressures. Both the anomalous temperature and pressure dependences of the shear elastic stiffness indicate incipient lattice shear instability. The shear _S(=0.005) is much smaller than the longitudinal _L(=1.18) accounting for the thermal Grüneisen parameter ^th(=1.09): since the acoustic Debye temperature _D(=923 ± 5 K) is so high, the shear modes play an important role in acoustic phonon population at room temperature. Hence knowledge of the elastic and nonlinear acoustic properties sheds light on the thermal properties of ceramic -Si₃N₄.     

Sintering and mechanical properties of β-wollastonite

Detailed microstructural studies have been carried out on porous -wollastonite (CaSiO₃) ceramics with 40–60% of the theoretical density. Xonotlite (Ca₆Si₆O₁₇(OH)₂) was used as starting material, and the reaction and sintering behaviour were systematically examined in the range 800–1200 °C in air. Analysis of the mechanical properties showed that the strength degradation of -wollastonite ceramics was certainly induced by the change of microstructure. Isothermal annealing at 1100 °C, however, did not preferentially affect the microstructure or the mechanical properties of sintered -wollastonite. These observations lead to the conclusion that the measured bending strength and Vickers hardness of porous -wollastonite ceramics can be substantially modified and improved by controlling the microstructure, in particular due to the shape of randomly oriented grains in the matrix.     

Change in the Rheological Properties of High‐Paraffin Petroleums under the Action of Vibrojet Magnetic Activation

The influence of the method of vibrojet magnetic activation on the rheological properties of highparaffin petroleums has been investigated. The maximum decrease in the rheological characteristics of the petroleums was obtained in 20min vibrojet treatment. It has been noted that the maximum effect of vibroaction is observed for petroleums with a higherthanaverage content of paraffins. The role of the magnetic component contributing to the decrease in the congelation point and the amount of the basic sediment in the petroleums under study has been shown.     

Caloric and acoustic properties of β-cyanopropionic aldehyde

The results of an experimental determination of the specific heat at constant pressure of -cyanopropionic aldehyde are given; calculated values of the specific heats at constant pressure and constant volume, and of the velocity of sound, are also given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 898–900, May, 1981.     

Structure,properties and production of β-alumina

The crystal structures of the -alumina compositions have been described and used to explain the fast ion transport for which these materials are renowned. Measured values of both the single crystal and polycrystalline ionic conductivity show a wide variation; this is explained in terms of the range of chemical compositions of the -alumina system and also the variety of measuring techniques used. Dopants or impurity ions can have a significant effect on the physical properties of the -aluminas. The ionic conductivity, the stability of the material and the densification during sintering have been considered in relation to the nature and level of a range of dopants described in the literature. The optimization of the ionic and mechanical properties has been achieved by development of the fabrication techniques and it is this which accounts for much of the present research. Thus the many different methods of producing both single and polycrystalline material have been described, including the range of sintering routes currently available. The advantages and disadvantages of each production route in terms of the resulting properties have also been discussed.     

Change of the Sign of the Effect with Increase in the Intensity of High‐Frequency Acoustic Excitation of a Turbulent Jet

Results of an experimental investigation of highfrequency acoustic excitation of turbulent jets for different intensities of the acoustic field are presented. It is shown that upon reaching a certain limiting level of excitation at high frequencies, the sign of the effect changes, i.e., at this level, highfrequency excitation leads to generation of turbulence in the jet rather than its suppression. Hence it follows that the highfrequency acoustic effect that suppresses turbulence is most efficient within an optimum range of frequencies and at an optimum level of excitation.     

EPMA Study of the Interface of β-Tricalcium Phosphate Ceramies in Vivo

Electron probe and X-ray energy spectrum were used to investigate the chemical composition of the interface between material and new bone after porous tricalcium phosphate ceramie implanted in tibia of rabbits. The element changes of the interface, the materials transformation and the situation of new bone formation at different implantation period were observed. The results showed that the carbon element content decreased gradually in new bone tissue, and the content of calcium and phosphor element increased by degrees with the implantation time. At the same time, calcium-phosphor ratio in the new bone kept a higher Ievel. New bone grew into the materials interior, material dispersed and degraded simultaneously. Both composition of materials and new bone tended to be consentient. Finally, the materials were substituted by new bone. After implantation, not only the materials itself dissolved and degraded partially, but also new bone formed on the outer and pore surface of β-TCP porous bioceramics, which     

EPMA Study of the Interface of β-Tricalcium Phosphate Ceramics in Vivo

Electron probe and X-ray energy spectrum were used to investigate the chemical composition of the interface between material and new bone after porous tricalcium phosphate ceramic implanted in tibia of rabbits. The element changes of the interface, the materials transformation and the situation of new bone formation at different implantation period were observed. The results showed that the carbon element content decreased gradually in new bone tissue, and the content of calcium and phosphor element increased by degrees with the implantation time. At the same time, calcium-phosphor ratio in the new bone kept a higher level. New bone grew into the materials interior, material dispersed and degraded simultaneously. Both composition of materials and new bone tended to be consentient. Finally, the materials were substituted by new bone. After implantation, not only the materials itself dissolved and degraded partially, but also new bone formed on the outer and pore surface of β-TCP porous bioceramics, which showed that the degradation products of lifeless calcium phosphate inorganic materials took part in constituting of new bone tissue.     

Effect of drawing on the dielectric properties and polarization of pressed solution cast β-PVDF films

Poly(vinylidene fluoride), PVDF, samples containing exclusively the polar β phase were obtained by crystallization from N,N-dimethylformamide (DMF) solution at 60 °C and subsequent pressing. Some of these samples were uniaxially drawn at 120 °C at draw ratio of 4, resulting in oriented films. Oriented and unoriented samples were characterized as to relative fraction of β phase, degree of crystallinity and orientation by infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The dependence on frequency of the real ( e_\textr^￠ \varepsilon_{\text{r}}^{\prime} ) and imaginary ( e_\textr^￠￠ \varepsilon_{\text{r}}^{\prime\prime} ) components of the relative permittivity of the samples was determined between 10⁴ and 1.7 × 10⁷ Hz. The coercive field and stable and metastable remanent ferroelectric polarization were determined from the hysteresis loop obtained by the ramp voltage technique, described in detail in this work. The results allowed verification of the effect of drawing on structure and of the resulting structure on the dielectric properties, remanent polarization, and coercive field of β-PVDF. A possible effect of the crystal–amorphous interphase region on the metastable remanent polarization is suggested. The results obtained with the oriented and unoriented samples were compared with those obtained for films commercialized by Piezotech S.A.     

Critical properties of4He in aerogel near the λ-line

We measured the superfluid fraction _s/ and the isobaric thermal expansion coefficient _P of⁴He confined in an aerogel. Data were obtained near the -line along several isobars. Powerlaw fits to the results for _s/ as a function of tT/T_c–1 (T_c is the transition temperature) give a pressure—independent exponent =0.755 when a confluent singular term is included. Fits to the _P data of power laws yield the specific-heat exponents –0.6 and –1.0 above and below T_c respectively. When an analytic background term a×t is included in the fit, the pressure-independent value =–0.59 is permitted, but the amplitude ratio A/A is found to be near zero and the coefficient of the analytic term is large. The measured values for and or are inconsistent with hyperscaling in three dimensions.     

Dielectric properties of apples in the range 0.1–100 kHz

Capacitance and conductance spectra are measured between 100 Hz and 100 kHz for three varieties of apple. Analysis of the spectra for several types of electrode material indicates that electrode effects may be neglected for frequencies above 1 kHz. Power-law responses are observed withCf ^–0.3 for the capacitance andG _a.c.f ^+0.9 for the a.c. conductance. Activation energies were found to be of the order of 0.05–0.15 eV for the three apple varieties and found to be frequency dependent. Comparison is made with an apple in which the cellular structure has been damaged by freezing. Freezing produced a significant increase in the high-frequency activation energy for conductance and a decrease in the power-law exponent to +0.3 for a.c. conductance. It is suggested that the dielectric properties result from a combination of relatively free ionic diffusion in the extracellular medium and the hopping of counterions along trap sites on the cell wall.     

Characterization of the tableting properties of β-cyclodextrin and the effects of processing variables on inclusion complex formation,compactibility and dissolution

Abstract

The tableting properties of a number of commercially available β-cyclodextrins were characterized. Fluidity was insufficient for routine direct compression. Compactibility varied by source but was excellent. Lubrication requirements were minimal. An inclusion complex of β-cyclodextrin/Progesterone was formed and the tableting properties of the complex were compared to those of a physical mixture in both directly compressed and wet granulated products. Inclusion complexes spontaneously formed during wet granulation processing. Substantial differences in tableting properties were found as processing variables were changed. β-cyclodextrin exhibits considerable promise as a standard filler binder in tableting.     

A Monte Carlo simulation for the study of the influence of the thickness of the source in 3H β-ray spectroscopy

A Monte Carlo simulation for the study of the influence of the thickness of the radioactive source in β-ray spectroscopy is presented in this paper. We make use of the Bethe-Bloch formula for ionization loss and Rutherford scattering cross section to trace the tracks of the β particles from a randomly sampled point source of given energy, which has been implanted in an aluminum coating with copper backing. We have studied seven groups of β rays with momenta from 119.14262 to 139.12328 keV/c. There are the peak shift, the broadening of the line width and the low energy tail. Their momentum dependences have been found. The program can be applied to similar cases with minor modification.     

Effects of the anion in glycine-containing electrolytes on the mechanical properties of electrodeposited Co–Ni films

Tailoring of the mechanical properties (e.g., hardness, Young's modulus or wear characteristics) of Co–Ni electrodeposits has been accomplished by changing the anion (sulphate versus chloride ions) in glycine-containing solutions at 80 °C, while maintaining all the other electroplating conditions unaltered. Galvanostatic deposition on metalized silicon substrates at 5–40 mA cm⁻² produced well adherent Co–Ni films with varying surface finish, chemical composition (50–83 wt% Co), morphology and structure. The deposition from chloride salts yielded matte grey, cobalt-rich Co–Ni films with hexagonal close-packed structure and crystallite sizes around 65–85 nm. Films obtained under the same electrodeposition conditions from sulphate salts were Ni-rich, displayed smoother surfaces and smaller crystallite sizes (30–40 nm) belonging mainly to the face-centered cubic phase. The crystallite size played a key role on the mechanical properties of the films, while the composition and the phase percentage had little effect. It is thus demonstrated that the nature of the anion induces a large tunability both in the microstructure and mechanical properties of the deposits. In particular, the nanoindentation hardness could be varied between 1.6 and 7.1 GPa, while the Young's modulus ranged between 122 and 181 GPa.     

Investigation of the effect of composition on microhardness and determination of thermo-physical properties in the Zn–Cu alloys

Zinc–copper of (99.99%) high purity alloys were directionally solidified upward with different compositions, C_o, Zn–(0.7,1.5, 2.4 and 7.37) wt.% Cu under two different solidification conditions (G = 3.85 K/mm, V = 0.0083 mm/s and G = 8.70 K/mm, V = 0.436 mm/s) using a Bridgman type directional solidification apparatus. The measurements of microhardness of directionally solidified samples were made by using a microhardness test device. The dependence of microhardness (HV) on composition was analyzed. According to these results, it has been found that the values of HV increase with the increasing Cu content (C_o). Variation of electrical resistivity (ρ) and electrical conductivity (σ) with the temperature were also measured by using a standard d.c. four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (Cp) of the Zn–Cu alloys were determined from heating curve during the transformation from solid to liquid phase by using differential scanning calorimeter (DSC).     

Optical properties of tin in the 2.5 to 40μm region

The optical constantsn andk of evaporated tin deposited on different substrates (potassium bromide and mica-sheet discs) were determined in the 2.5 to 40m region by measuring its transmittance. From these values a second step vveacarried out to determine other physical parameters of tin films. These were the density of conduction electrons,N, the effective collision frequency of the electrons ₀ the plasma frequency, ₀, the velocity on the Fermi surface,V ₀ the effective area of the Fermi surface,A _eff, and the absorption coefficient,A. The energy-loss functions for surface and volume plasmons show sharp peak at 7.69m. These values are compared with those found in earlier work.