Structure and dielectric properties of a new series of pyrochlores in the Ca–Sm–Ti–M–O (M = Nb and Ta) system

The present work investigates the dielectric properties of pyrochlore type oxides, Ca–Sm–Ti–M–O (M = Nb and Ta) in the low frequency region (100 Hz–1 MHz) over the temperature range 30–100 °C. The 1 MHz dielectric constants (K) of these oxides are in the range 23–108 and show low variation with frequency (1 kHz–1 MHz). The temperature coefficient of dielectric constant (TCK) over the temperature range varies from positive to negative values in the range 48 to −107 ppm/°C. Rietveld analysis of the X-ray diffraction data establishes a cubic pyrochlore-type phase in the space group Fd3 m (no. 227).The grain morphology observation by scanning electron microscope shows well sintered grains.     

Characterization of dynamic recrystallisation in as-homogenized Mg–Zn–Y–Zr alloy using processing map

The hot working behavior of a as-homogenized Mg–Zn–Y–Zr alloy has been investigated in the temperature range 200–400°C and strain rate range 0.0015–7.5 s⁻¹ using processing map. The power dissipation map reveals that a domain of dynamic recrystallisation (DRX) in the temperature range 300–400°C and strain rate range 0.0015–0.15 s⁻¹, with its peak efficiency of 38% at 350°C and 0.0015 s⁻¹, which are the optimum hot working parameters. The apparent activation energy in the hot deformation process is 148 ± 3 KJ/mol that is larger than that of ZK60 alloy because of the obstruction of Y atoms for diffusion. DRX model indicates that DRX of Mg–Zn–Y–Zr alloy is controlled by the rate of nucleation, which is lower one order of magnitude than growth. And the rate of nucleation depends on the process of mechanical recovery by cross-slip of screw dislocations.     

Synthesis of SrCrO<Subscript>4</Subscript> nanostructures by onion inner-coat template and their optical properties

This paper describes a bio-template method of the squama inner coat of onion for preparing the SrCrO₄ nanostructures including nanospheres, nanorods and dumbbell-shaped superstructure. The method is able to make SrCrO₄ nanoparticles with average diameters in the range of 90–170 nm, SrCrO₄ nanorods with length in the range 0·70–2 μm, width in the range of 80–180 nm, and SrCrO₄ dumbbell-shaped superstructure with length in the range 10–14 μm. The dumbbell-shaped superstructures are assembled by many SrCrO₄ nanowires with length in the range 10–14 μm and width in the range 30–50 nm. The products were characterized by transmission electron microscope, powder X-ray diffraction, UV-Vis spectroscopy and luminescence spectrophotometer. A possible formation mechanism was also proposed. In the preparation, the SrCrO₄ nanostructures were synthesized at room temperature without any surfactants. This new bio-template method will have potential applications in preparation of the nanoscale materials with different morphologies.     

Waveguide-dielectric resonator method for accurate measurement of parameters of materials at high frequencies

The theory is given, with an analysis and various examples, of the practical implementation of a method for measuring the relative permittivity ɛ^*=ɛ′−iɛ″ of materials in the 0.5–26-GHz frequency range. The results and experimental errors are given of measurements of ε′ in the range 2–200 and of tanδ in the range from 5·10⁻⁵ to 2·10⁻². Translated from Izmeritel'naya Tekhnika, No. 6, pp. 62–66, June, 1999.     

Electrical and optical properties of InSbSe<Subscript>3</Subscript> amorphous thin films

Electrical conductivity, I–V characteristics and optical properties are investigated for InSbSe₃ amorphous thin films of different thicknesses prepared by thermal evaporation at room temperature. The composition of both the synthesized material and thin films were checked by energy dispersive X-ray spectroscopy (EDX). X-ray analysis indicated that all samples under investigation have amorphous structure. The dc electrical conductivity was measured in the temperature range (303–393 K) and thickness range (149–691 nm). The activation energy ΔE _σ was found to be independent of film thickness in the investigated range. The obtained I–V characteristic curves for the investigated samples are typical for memory switches. The switching voltage increases linearly with film thickness in the range (113–750 nm), while it decreases exponentially with temperature in the range (303–393 K). The switching process can be explained according to an electrothermal process initiated by Joule-heating of the current channel. Measurements of transmittance and reflectance in the spectral range (400–2,500 nm) are used to calculate optical constants (refractive index n and absorption index k). Both n and k are practically independent of film thickness in the investigated range (149–691 nm). By analysis of the refractive index n the high frequency dielectric constant ε_∞ was determined via two procedures and was found to have the values of 9.3 and 9.15. Beyond the absorption edge, the absorption is due to allowed indirect transitions with energy gap of 1.46 eV independent on film thickness in the investigated range.     

Investigation of TiC–C Eutectic and WC–C Peritectic High-Temperature Fixed Points

TiC–C eutectic (2,761°C) and WC–C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC–C and three WC–C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC–C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC–C peritectic within 1 day was 17 mK with a melting range of ∼70 mK. The repeatability of the freezing temperature of the WC–C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC–C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC–C cells were easily constructed, like metal–carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC–C peritectic has more potential than the TiC–C eutectic as a high-temperature reference point. The investigation of the purification of the TiC–C cell during filling and the plateau observation are also reported.     

Characteristics of ZnS films pulse plated using non-aqueous electrolytes

Thin films of ZnS were deposited by the pulse electrodeposition technique employing zinc sulphate and sodium thiosulphate in diethylene glycol solution at 80°C and at different duty cycles in the range 6–50%. The films were polycrystalline exhibiting cubic structure. The intensity of the peaks increased with duty cycle. Transmission measurements indicated interference fringes from which the refractive index fo the films were calculated to be in the range of 2.30–2.70. The band gap of the films was in the range of 3.66–3.62 eV with increase of duty cycle. The films exhibited resistivities in the range of 400–50 ohm cm with increase of duty cycle. The films exhibited higher Photoelectrochemical cell output compared to earlier reports.     

Hot deformation behavior of Ti-15-3 titanium alloy: a study using processing maps,activation energy map,and Zener–Hollomon parameter map

The hot deformation behavior of Ti-15-3 titanium alloy was investigated by hot compression tests conducted in the temperature range 850–1150 °C and strain rate range 0.001–10 s⁻¹. Using the flow stress data corrected for deformation heating, the activation energy map, processing maps and Zener–Hollomon parameter map were developed to determine the optimum hot-working parameters and to investigate the effects of strain rate and temperature on microstructural evolution of this material. The results show that the safe region for hot deformation occurs in the strain rate range 0.001–0.1 s⁻¹ over the entire temperature range investigated. In this region, the activation energy is ~240 ± 5 kJ/mol and the ln Z values vary in range of 13.9–21 s⁻¹. Stable flow is associated with dynamic recovery and dynamic recrystallization. Also, flow instabilities are observed in the form of localized slip bands and flow localization at strain rates higher than 0.1 s⁻¹ over a wide temperature range. The corresponding ln Z values are larger than 21 s⁻¹. The hot deformation characteristic of Ti-15-3 alloy predicted from the processing maps, activation energy map, and Zener–Hollomon parameter map agrees well with the results of microstructural observations.     

Equipment for the Spectral Characterization of High-Temperature Particles

The spectral radiant characteristics of plume particles of a solid rocket engine are important in the design of the engine specific impulse, ablative material, and plume flame hiding. These parameters are measured from tests of the engine. Some equipment has been established to realize particle heating, uniform particle distribution, and measurements based on an FTIR spectral instrument. The equipment is based on SiC heating and is divided into a warm-up chamber and a measurement chamber to improve the particle temperature stability. A special design of uniform particle distribution combined with an acoustic levitation device is used to determine the particle falling speed. The spectral characteristics and the transmission rate of the particles have been measured by using the system including a standard blackbody, an assembled optical system, and an FTIR spectrometer. The measurements of particle concentration and temperature are given in detail. The instrument specifications are as follows: temperature range – 60–1500 °C; spectral range – 0.60–25 μm; and particle dimension range – 10–500 μm. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Processing of sucrose to low density carbon foams

A novel process for preparation low density carbon foams from sucrose has been demonstrated. A resin prepared by heating aqueous acidic sucrose solution when heated in an open Teflon mould at 120 °C undergoes foaming and then setting in to a solid organic foam. The solid organic foam undergoes carbonization in air by dehydration at 250 °C under isothermal condition. Carbon foams thus obtained sintered at temperature in the range 600–1,400 °C showed density in the range 115–145 mg/cc and electrical conductivity in the range 1.5 × 10⁻⁵ to 0.2 ohm⁻¹ cm⁻¹, respectively. The carbon foams contain spherical cells of size in the range 450–850 μm and the cells are interconnected through circular or oval shape windows of size in the range 80–300 μm. The carbon foam samples sintered at 1,400 °C showed compressive strength of 0.89 MPa.     

Determination of the thermodynamic properties of liquid <Emphasis Type="Italic">n</Emphasis>-hexadecane from the measurements of the velocity of sound

The density, the isobaric expansion coefficient, the specific heats at constant pressure and constant volume, and the isothermal compressibility coefficient of liquid n-hexadecane have been calculated in the range of temperatures 298–433 K and pressures 0.1–140 MPa from the data on the velocity of sound. The coefficients of the Tate equation in the above parametric range have been determined. The table of the thermodynamic properties of n-hexadecane has been presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 150–156, January–February, 2009.     

The VNIIFTRI magnetic temperature scale in the 0.3–3 K range

A thermodynamic temperature scale in the range 0.3–3 K is established by a magnetic method. The results of investigations enable the range of the State Standard of temperature to be extended from 0.8 K to 0.3 K with a simultaneous increase in its accuracy by a factor of 2–3. __________ Translated from Izmeritel’naya Tekhnika, No. 8, pp. 47–53, August, 2007.     

Hot deformation behavior of an 8% Cr cold roller steel

An 8% Cr cold roller steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s⁻¹. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the microstructure evolution and the mechanism of flow instability. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 8% Cr steel; the efficiency of power dissipation decreased with increasing Z value; flow instability was observed at higher Z-value conditions and manifested as flow localization near the grain boundary. The hot deformation equation and the dependences of critical stress for dynamic recrystallization and dynamic recrystallization grain size on Z value were obtained. The suggested processing window is in the temperature range 1050–1200 °C and strain rate range 0.1–1 s⁻¹ in the hot processing of 8% Cr steel.     

Effect of rare earth element additions on the impression creep of Sn–9Zn solder alloy

Creep behavior of the Sn–9Zn–RE alloys containing 0.1, 0.25 and 0.5 wt.% rare earth (RE) elements was studied by impression testing and compared to that of the eutectic Sn–9Zn alloy. The tests were carried out under constant punching stress in the range 40–135 MPa and at temperatures in the range 298–420 K. Results showed that for all loads and temperatures, Sn–9Zn–0.25RE had the lowest creep rate, and thus the highest creep resistance among all materials tested. This was attributed to the formation of Sn–RE second phase precipitates which act as the main strengthening agent in the RE-containing Sn–Zn alloys. RE contents higher than 0.25 wt.%, resulted in a lower creep resistance due to a reduction in the volume fraction of Zn-rich phase caused by the formation of Sn–Zn–RE intermetallics. The average stress exponents of 6.8, 6.9, 7.1, 6.8 and activation energies of 42.6, 40.6, 43.0 and 44.9 kJ mol⁻¹ were obtained for Sn–9Zn, Sn–9Zn–0.1RE, Sn–9Zn–0.25RE, and Sn–9Zn–0.5RE, respectively. These activation energies were close to 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about seven suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.     

Fatigue of VT20 titanium alloy with vacuum-plasma coatings at high temperatures

We study the influence of vacuum–plasma TiN, (TiAl)N, and (TiC)N coatings on the high-cycle fatigue of VT20 titanium alloy in the temperature range 350–640°C for a loading frequency of 10 kHz. It is shown that, in this temperature range, the fatigue limits of VT20 alloy with the indicated coatings 6 μm in thickness become 15–25% higher than for the material without coating. The possibility of replacement of steel blades with titanium blades with vacuum-plasma coatings is demonstrated. Translated from Problemy Prochnosti, No. 4, pp. 101–107, July–August, 2009.     

Temperature dependences of the mechanical properties of austenitic and martensitic steels in hydrogen

The influence of gaseous and preliminarily dissolved hydrogen on the characteristics of short-term static strength, crack resistance, and low-cycle durability of martensitic and austenitic steels is studied within the temperatures range 293–1073°K, under pressures of hydrogen varying within the range 0–35 MPa, for the strain rates of 0.01–100 mm/min, and the strain amplitudes of 0.8–1.6%. We determine the loading rates and the conditions of action of hydrogen leading the maximum possible hydrogen degradation of each material. The influence of the chemical composition and structural state on the degree of embrittlement and fractographic features of the fracture of steels in the presence of hydrogen is analyzed. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 53–64, September–October, 2007.     

Spark plasma sintering synthesis and mechanical spectroscopy of the ω-Al0.7Cu0.2Fe0.1 phase

Starting from a mixture of Al–Cu–Fe quasicrystalline (QC) particles and Al powder, a fully dense and almost Al–Cu–Fe ω single-phase alloy was produced by spark plasma sintering. This technique allows synthesising large samples with sizes suitable for mechanical spectroscopy experiments. Mechanical spectroscopy was selected because it is a relevant tool for detecting the presence of structural defects at both nano and microscopic scales. Young’s moduli were measured in the 15 kHz range as a function of temperature by the resonant frequency method. Young’s moduli behave similarly for typical metals and exhibit values that are comparable to those of the Al–Cu–Fe QC phase. The damping coefficient Q ⁻¹ was determined at various temperatures between room temperature and 840 K over a large frequency range, i.e. between 10⁻³ and 10 Hz. The results suggest that solid friction effects do occur. In addition, a relaxation peak is observed in the intermediate temperature range.     

Electrical conductivity,thermoelectric power and dielectric constant of a Gd2Ti2O7 single crystal

Electrical conductivity, thermoelectric power and dielectric constant of a Gd₂Ti₂O₇ single crystal have been studied in the temperature range 300–1000 K. Gd₂Ti₂O₇ is found to be an-type semiconductor with energy band gap 1.5 eV. It exhibits an extrinsic nature up to 675 K and an intrinsic nature above 675 K. The thermoelectric power increases with temperature in the region 300–675 K whereas it decreases with temperature in the region 675–1000 K. The dielectric constant increases slowly in the temperature range 300–675 K but this increase becomes fast in the temperature range 675–1000 K.     

The applicability of the ITS-90 method to platinum resistance thermometers of different purity

The static characteristics of platinum resistance thermometers with different platinum purities were measured. It is shown that in the 0–420°C range the ITS-90 method gives an error of less than 0.01°C, while in the 0–230°C range the error is less than 0.006°C. __________ Translated from Izmeritel’naya Tekhnika, No. 12, pp. 33–36, December, 2006.     

Synthesis and laser-excited IR luminescence of Y<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Yb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> solid solutions

We have determined the composition range of solid solutions in the binary system YPO₄-YbPO₄ and identified the key trends in the composition dependence of their IR Stokes luminescence intensity and decay time in the range 0.96–1.1 μm. The results were used to develop a new narrow-band IR phosphor, YPO₄:Yb³⁺. Under 0.940-μm laser excitation, this phosphor offers an increased IR Stokes luminescence intensity in the range 0.96–1.1 μm (about twice as high as that of the well-known commercially available phosphors L-54 and FSD-546-2), with an afterglow time of 1700–1800 μs.