Sorption of CH3131I from Steam-Gas Phase on Modified Ag-Containing Zeolites

Sorption of CH₃ ¹³¹I from the steam-gas phase on Ag-containing zeolites modified with acetylene was studied. The radioiodine adsorption in a column depends on the silver concentration in the sorbent, humidity of the steam-gas flow, and the temperature. The modified sorbents AgX-m containing 30-57% silver efficiently localize CH3I at the humidity up to 80% and sorption temperature from 120 to 195°C. Under these conditions the decontamination factor of a gas flow with respect to CH₃ ¹³¹I at 7.5-cm height of the sorbent bed and a 0.2 s gas-sorbent contact time exceeds 99.99%. The sorption properties of the modified Ag-containing sorbents are better that those of the nonmodified sorbents and known Ag-substituted zeolites.     

Sorption of Radioactive Iodine on Polymeric Sorbents from Aqueous Solutions and Gas Phase

Sorption of various species of radioactive iodine from aqueous and gas phases on polymeric sorbents Styrosorb and Polysorb-1 was studied. These sorbents do not take up ionic species of radioactive iodine (¹³¹I^- and ¹³¹IO₃ ^-) from aqueous solutions. At the same time, both sorbents take up ¹³¹I₂ from aqueous solutions at 25°C. At V/m = 500 ml g^{- 1}, the distribution factors K _d are 1350 and 590 ml g^{- 1} with Styrosorb and Polysorb-1, respectively. These sorbents efficiently recover ¹³¹I₂ from an air flow at 25°C and flow velocity of 0.33 cm s^{- 1}. The sorption capacity of Styrosorb is approximately four times higher than that of Polysorb-1 and amounts to 97.0 mg of I₂ per gram of sorbent. These data are consistent with the specific surface areas of the sorbents.     

The Effect of Hydrophobization of Ag-Containing Zeolites on Absorption of CH3131I from the Water Vapor-Air Phase

The effect of hydrophobization of Ag-containing nonmodified and acetylene-modified zeolites with poly(vinyl chloride) (PVC) on sorption characteristics of sorbents with respect to CH₃ ¹³¹I was studied. The PVC coating on the sorbent results in increased absorbtion of CH₃ ¹³¹I from a water vapor-air flow at a humidity of up to approximately 70 vol %; the decontamination factor of approximately 10⁵ is reached. The sorbent modified with PVC retains radioiodine at heating to 300°C and can be proposed for practical purposes.     

The frictional behaviour of LiF single crystals

A study has been made of the influence of initial surface roughness, renewable and non-renewable surface contaminants, and irradiation hardening on the coefficient of friction for one LiF single crystal (A) sliding on another (B) in {100}_A<010>_A{100}_B 010_B orientation at 295 K. The normal load was 1 N, the nominal contact pressure 0.1 MPa, the sliding velocity 0.2 to 0.6 mm sec^–1, and the amplitude of the (reciprocate) motion a few millimetres. Any influence of non-renewable contaminants persisted only for cumulative relative displacements 0.1 m, and that of micrometre-scale initial surface roughness only for a few metres. At steady state in the presence of renewable contaminants the coefficient of friction varied only from a high of 0.45 in ultra-high vacuum ( 7.5 × 10^–8 Pa) and dry nitrogen-rich air ( 10⁵ Pa, relative humidity 15%) to a low of 0.38 in moist nitrogen-rich air ( 10⁵ Pa, relative humidity 50%). Irradiation hardening had no effect on the coefficient of friction at steady state. The worn surfaces created by steady-state sliding always exhibited a grooved topography partly obscured by more-or-less adherent layers of variously consolidated equiaxed debris particles 100 nm in size. Owing to the action of image forces, these particles contained no dislocations. It is suggested that the coefficient of friction was determined at steady state by the stress needed to shear these tiny particles past one another as near-rigid bodies.     

Sorption of Radioactive Iodine and Fluoride Ion on Hydroxyapatite from the Aqueous Phase

Sorption of the ¹³¹I^-, ¹³¹IO₃ ^-, and F^- ions on various samples of hydroxyapatite (HAP) from aqueous solutions was studied. The HAP samples were prepared by the following reactions: Ca(OH)₂ + H₃PO₄ HAP, CACl₂ + Na₃PO₄ + NaOH HAP, and Ca(NO₃)₂ + HAP seed + (NH₄)₂HPO₄ + NH₃ HAP. None of the HAP samples sorb ionic species of radioactive iodine from aqueous solutions. As for F^-, the best sorption properties are exhibited by the HAP sample prepared by the second reaction. The degree of recovery of fluoride ion with the HAP precipitate in 5 min, 4 h, and 5 days of the contact of the solid and liquid phases is 54, 66, and >95% of the initial F^- amount, respectively. The distribution factor K _d of the fluoride ion between the HAP solid phase and solution decreases with increasing V/m ratio and pH of the initial solution.     

Structure of alkali dimers at the surface of liquid helium

Calculations are presented of the equilibrium configuration (dimple) of a Na₂ or Li₂ molecule absorbed on the surface of liquid³H e or liquid⁴He. The computed aimer binding energies are somewhat greater than those of the monomers. The lowest energy occurs when the molecule lies flat, but the energy in the erect orientation is only 1K higher (implying relatively free rotation). The center of mass lies 4Åabove the liquid surface and the dimple has a depth 3Å. An exceptional case is Li₂ on liquid³H e, for which the surface state is unstable relative to solvation in the bulk.     

Vortex imaging in superconducting films by scanning hall probe microscopy

We have used a low noise Scanning Hall Probe Microscope (SHPM) to study vortex structures in superconducting films. The microscope has high magnetic field (2.9×10^–8T/Hz at 77K) and spatial resolution, 0.85m. Magnetic field profiles of single vortices in High T_c YBa₂Cu₃O_7– thin films have been successfully measured and the microscopic penetration depth of the superconductor has been extracted as a function of temperature. Flux penetration into the superconductor has been imaged in real time (8s/frame).     

Ion-implantation technology for improved GaAs MESFETs performance

Electrical properties of Si-implanted and co-implanted with Mg or Be in semi-insulating GaAs was studied. The Si-implanted MESFETs with and without buried p-layer (formed by Mg or Be) have been fabricated and characterized by their d.c. and r.f. performance. The experimental results showed that the device with a buried p-layer can effectively suppress the substrate leakage current (thus good pinch-off characteristic) and obtained higher gain linearity than these without a buried p-layer. For 1 m×100 m MESFETs device with co-implantation of Si (8×10¹² cm^–2) and Be (6×10¹¹ cm^–2) demonstrated uniform transconductance (g_m) of 115 mS mm^–1 with the gate voltage ranging from –1 to 1 V and reduced pinch-off voltage compared to those with co-implantation of Si and Mg (6×10¹¹ cm^–2). The measured f_T and f_max of a 1 m×25 m MESFET with co-implantation of Si and Be are 10 and 39 GHz, respectively. However, FETs with increased Mg dose (from 6×10¹¹ cm^–2 to 2×10¹² cm^–2) in a buried p-layer can obtain higher transconductance and saturation current.     

Sorption of 131I2 and CH3 131I from gas-water vapor medium with porous inorganic sorbents containing d elements

Sorption of ¹³¹I₂ and CH₃ ¹³¹I from gas-water vapor medium on porous inorganic sorbents based on silica gel of the MSKG type, containing d elements, was studied. Sorbents containing Zn, Ni, Cu, and Co ammoniates show a low degree of recovery of ¹³¹I₂ and CH₃ ¹³¹I from the gas-water vapor flow (less than 30%); their calcination at a temperature above 250°C does not noticeably affect the sorption power of the sorbent. The sorbents containing Zn, Ni, and Cu nitrates, both unmodified and modified, show a low degree of recovery of CH₃ ¹³¹I from the gas-water vapor medium (less than 1%). At the same time, whereas for unmodified sorbents the degree of recovery of ¹³¹I₂ from the gas-water vapor phase does not exceed 70%, their modified analogs have higher degree of absorption of ¹³¹I₂ (more than 99%), comparable with the similar data for Ag-containing sorbents based on silica gel of the MSKG type.     

Copper electrodes multilayer ceramic capacitors Part I The dielectric composition

Several sintering aids were tested to lower the CaZrO₃ ceramic sintering temperature. Numerous additions are shown to lower the densification temperature and to promote the dielectric properties with a QF product, an insulating resistivity and a permittivity enhancement, and a lowering of the temperature coefficient . A combination of dopants was tested and optimised, resulting in a low temperature sintering ceramic based on CaZrO₃, LiNO₃, SiO₂ and TiO₂. The samples sintered at 1000°C in oxidising or reducing atmosphere exhibit very attractive properties, with a QF product of nearly 15, 28, a near zero and _i 10¹² · cm. The sintering mechanisms of this ceramic are also debated.     

Sr2YRu1?uCuuO6: Evidence for SrO-Layer Superconductivity

Sr₂YRuO₆ doped on its Ru site by Cu superconducts at the below 45 K, although its Ru and Cu are magnetically ordered at 23 K and 86 K, respectively. The SrO layers superconduct. Ba₂GdRuO₆, when doped with Cu, does not superconduct, because L = 0 Gd is not crystal-field split, and so induces Cooper pair-breaking.     

Effect of magnetic field and temperature on the voltage-current characteristics of YBCO superconductor

Voltage-current characteristics of YBCO superconductor was studied under magnetic field up to 0.4 T at different temperatures below T_c. The critical temperature decreases and the transition width broadens under magnetic field. V-I data below T_c were fitted to a power law expression V I^(T,B) in which (T,B) is found to decrease with increase of magnetic field and temperature, gradually approaching unity as T approaches T_c, being independent of magnetic field. Similarly, (T,B) approaches unity as magnetic field increases being independent of temperature.     

Sol-gel prepared Ni-alumina composite materials

The sol-gel method has been utilized for the preparation of dense, homogeneous ceramic-metal composites with up to 50% Ni in Al₂O₂. Examination by SEM and TEM shows that the materials consist of micrometre-size Al₂O₃ with metallic Ni in isolated regions from 50 m down to nanometre size. The density ranges from 97% (10% Ni) to 74% (50% Ni) of the theoretical number. The hardness decreases from 18 GPa for pure alumina to 10 GPa for alumina containing 50% Ni. The fracture toughness increases significantly from K _1c=3–4 MPa m^1/2 to K _1c=8.5 MPa m^1/2. The elastic and shear moduli decrease from E=400 GPa and G=160 GPa for pure alumina to E=320 GPa and G=135 GPa when containing 50% Ni. The electrical resistivity is 10⁶m with 10 to 40% Ni but decreases drastically at 50% Ni content.     

An investigation of shelf-life of strontium doped LaMnO3 materials

The shelf-life of Sr doped LaMnO₃ (LSM) materials of varying stoichiometric compositions prepared by wet chemical synthesis was investigated under storage conditions of low and high humidity at ambient temperature for 350 days. It has been found that the adhesion, chemical stability and stability of the electrode performance of LSM materials are critically dependent on the A-site stoichiometry (i.e., (La+Sr)/Mn ratio) of the LSM materials and much less dependent on storage conditions (humidity level and storage time) over the period investigated. In this respect, LSM materials with stoichiometric and sub-stoichiometric compositions where (La+Sr)/Mn1 are stable and LSM with A-site sub-stoichiometry ((La+Sr)/Mn0.9) is effective in achieving good adherence, high chemical stability and high stability of electrode performance.     

X-ray Photoelectron Spectroscopic Study of Hot Particles Formed by Emission from Fuel-Containing Masses Incorporating Ruthenium

X-ray photoelectron spectroscopy was applied to the study of the quantitative elemental and ionic compositions of samples of fuel-containing masses (FCMs) generated under laboratory conditions and incorporating Ru, before and after their heating in air at 1500°C for 2 min, and also of hot particles released in the process and kept in air at 700 and 900°C for 13 s. FCM samples heated under argon at 1900°C for 2 min were studied for comparison. The spectra revealed formation on the FCM sample surface of complex oxides UO_x with x varying in the range 2 >x 3. Ruthenium was detected in at least two oxidation states: Ru(IV) and Ru(VI). The relative concentrations of U and Ru in FCM (89 at. % U and 11 at. % Ru) change, respectively, to 99 and 1 at. % after heating in air and to 80 at. % U and 20 at. % Ru after heating under argon. After treatment of the sample surface with Ar⁺ ions, the carbonate groups disappeared, and the concentrations of the U(IV) and U(VI), as well as of Ru(IV) and Ru(VI) ions, changed. The condensed phase of hot particles consists mainly of ruthenium ions (80 at. %), with a lower content of uranium (20 at. %). Uranyl compounds of the type RuUO₂O₃ are probably formed on the surface of hot particles.     

Thermal expansivity of Nb3GE

X-ray powder diffraction studies as a function of temperature from 4.2 to 675 K were performed on a Nb ₃ GE sample (T _c =21.09 K) prepared by chemical vapor deposition. The cell constant varied linearly with temperature in the range 150 to 675 K and the expansion coefficient was computed to be 6.98×10^–6/K. A similar study to room temperature for sintered Nb ₃ Sn indicated an expansion coefficient similar to that of Nb ₃ Ge. No evidence was found for the occurrence of a phase change in Nb ₃ Ge over the temperature range studied.     

Crystalline transformation of Ti-B-O,Al-Ti-B-O,Si-Ti-B-O and Al-Si-Ti-B-O by thermal treatments

The thermal transformations of Ti-B-O, Al-Ti-B-O, Si-Ti-B-O and Al-Si-Ti-B-O have been investigated using the methods of thermal analysis and X-ray powder diffraction. The materials are a crystalline series of TiO₂ with partial replacement of titanium by the elements, aluminium, boron and silicon. The anatase form of the materials was transformed to the rutile form at 520680 °C for Ti-B-O, 880950 °C for Al-Ti-B-O, 10801280 °C for Si-Ti-B-O and 11801330 °C for Al-Si-Ti-B-O. The rate constant for the anatase-rutile transformation of Ti-B-O was 6.908×10^–3 min^–1 under isothermal conditions at 680 °C. Analysis of the kinetic data obtained by differential thermal analysis (DTA) gave the activation energy for transformation of anatase into rutile as 663.7 Kcal mol^–1 for Al-Ti-B-O. The lattice parameters for the compounds studied at various temperatures were calculated by least-squares fitting of the X-ray powder diffraction data.     

High-temperature X-ray structural,thermal and dielectric characteristics of ferroelectric Bi2VO5.5

The X-ray powder diffraction, dielectric and thermal studies of bismuth vanadate (Bi₂VO_5.5) ceramic have been carried out as a function of temperature (300–900 K). The hightemperature X-ray studies, supported by differential scanning calorimetry, clearly demonstrate that Bi₂VO_5.5 undergoes two major phase transitions at 730 and 835 K. It was found that the one at 730 K is associated with both the ferroelectric and the crystallographic transition, while at 835 K, Bi₂VO_5.5 undergoes only the crystallographic transition. Anomalies in both the dielectric constant and specific heat curves have been observed at 730 and 835 K. The total heat, Q, and entropy, S, associated with the transition at 730 K were found to be higher than those at 835 K.     

Critical Supersaturation of Superfluid 3He-4He Mixtures

We report the results of our systematic study of the phase separation in supersaturated ³He-⁴He liquid mixtures of the ³He-dilute phase. The amount of the critical supersaturation is determined within the wide ranges of the temperature (0.4–645mK) and the pressure (1–8.5kgf/cm²). Using the data we construct the surface of critical supersaturation, x _3,cr (T,P), which enables us to recognize almost the overall behavior of the critical supersaturation in superfluid ³He-⁴He mixtures. The main specific features observed are (i) below 10mKx _{3, cr} is almost temperature-independent, (ii) above 10mK up to 500mKx _{3, cr} increases with the temperature, and (iii) above 500mKx _{3, cr} decreases smoothly with the increase of temperature down to zero at the tricritical point. We give various discussions from the viewpoint of the quantum nucleation, the classical thermal nucleation and the crossover between them.     

Equal-channel angular pressing of an Al-6061 metal matrix composite

An Al-6061 metal matrix composite, reinforced with 10 vol % Al₂O₃ particulates, was subjected to equal-channel angular (ECA) pressing at room temperature to a total strain of 5. It is shown that the intense plastic straining introduced by ECA pressing reduces the grain size from 35 m to 1 m and this leads to an increase in the microhardness measured at room temperature. Inspection revealed some limit cracking of the larger Al₂O₃ particulates as a consequence of the ECA pressing. Tensile testing after ECA pressing gave a maximum ductility of 235% at a temperature of 853 K when testing at strain rates from 10^–4 to 10^–3 s^–1. It is suggested that high strain rate superplasticity is not achieved in this material after ECA pressing due to the presence of relatively large Al₂O₃ particulates.