Aluminosilicophosphate geoceramics as matrices for the immobilization of partitioned 90Sr and 137Cs wastes

Immobilization of ⁹⁰Sr and ¹³⁷Cs in geoceramic matrices synthesized on the basis of phosphatized calcinate of simulated radioactive wastes and apatite ore dressing tailings is studied. The samples were sintered at 950–1150°C for 1 h. Leaching tests were carried out at 90°C with double-distilled water in the quasiflow and accumulative modes. The leaching was monitored by the conductivity of the liquid phase. To estimate the leaching rates R, the Na, Cs, and Sr concentrations were measured by flame photometry. The best samples of geoceramics are characterized by R of (5–15) × 10^?6 and <0.3 × 10^?6 g cm^?2 day^?1 with respect to Cs and Sr, respectively. Aluminosilicophosphate geoceramics show promise as materials for immobilization of partitioned ⁹⁰Sr and ¹³⁷Cs radioactive wastes.     

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.     

Geopolymeric Agent for Immobilization of Radioactive Ashes after Biomass Burning

Solidification of low-level radioactive wastes obtained after biomass burning was studied. Two solidification modes using Portland cement and geopolymeric binder were tested experimentally. The strength at various hardening times, compacting efficiency, and leaching rate of the resulting monolithic concretes were analyzed. The compacting efficiency in concretes prepared by two different modes is similar. At the same time, geopolymeric binder is solidified in significantly shorter period and its compression strength is several times higher, but its main advantage is chemical immobilization of strontium cations. The leaching rate under the static conditions after 28-day hardening is nearly 10^{- 6} g cm^{- 2} day^{- 1}. Thus, substitution of geopolymerization of the clay component (in general case, aluminosilicate material) for common solidification of low-level wastes using Portland cement is economically promising due to significant energy and resource saving. The geosynthesis can be easily realized as an environmentally safe process, yielding no liquid waste and involving no high-temperature stages with radioactive materials.     

Titanate Ceramics with Pyrochlore Structure as a Matrix for Immobilization of Excess Weapons-Grade Plutonium: II. Hydrolytic Resistance

Hydrolytic resistance of titanate ceramics of a complex cationic composition with the pyrochlore structure is studied from the standpoint of its use for immobilization of excess weapons-grade plutonium. Data are obtained for both as-prepared ceramics and that transferred into the metamict state under the action of self-irradiation due to the presence of ²³⁸Pu (accumulated dose 160 ×10^{2 3} -events m^{- 3}). As-prepared ceramics demonstrate high chemical resistance (low leaching of environmentally significant U and Pu radionuclides). Metamictization results in increasing normalized weight loss (modified MCC-1 test at 90°C in distilled water) in a three-day leaching experiment: by about two orders of magnitude with respect to U and by over two orders, to Pu. The features of hydrolytic behavior of the complex ceramics studied are discussed.     

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.     

CO/pH2: A Molecular Thermometer

We utilize reversible temperature dependent changes in the IR absorption spectrum of CO molecules isolated in solid parahydrogen (pH₂) to probe bulk temperature changes during rapid vapor deposition. The intensity of a well resolved feature near 2135 cm^–1 increases monotonically with temperature over the 2 to 5 K range. The thermally populated initial state of this transition lies 12 K above the CO/pH₂ ground state. During the deposition of 100 ppm CO/pH₂ samples, we detect temperature gradients 10 K/cm in 0.1 cm-thick samples subjected to heat loads 10 mW/cm². The resulting estimated thermal conductivity (TC) is 3(±2) mW/cm-K, averaged over the 2 to 5 K region. This value is 1000 times lower than the TC of single crystal solid pH₂, and 10 times lower than previously measured for pH₂ solids doped with 100 ppm concentrations of heavy impurities [Manzhelii, Gorodilov, and Krivchikov, Low Temp. Phys. 22, 131 (1996)]. We attribute this abnormally low TC to the known mixed fcc/hcp structure of the rapid vapor deposited solids.     

Polymeric matrices promising for immobilization of tritium radioactive wastes

The resistance of polymeric matrices to leaching of tritium water incorporated in oil microcapsules or in chemisorbent particles was studied. The phenol-formaldehyde matrix with tritium and cesium in oil microcapsules ensures highly reliable radionuclide immobilization: The half-decile leaching rate, g cm^?2 day^?1, is 9 × 10^?5 for ³H and 2 × 10^?5 for ¹³⁷Cs. A borate chemisorbent in combination with a polyurethane matrix was suggested for immobilization of highly radioactive tritium water vapor.     

Pyrosol deposition of fluorine-doped tin dioxide thin films

Fluorine-doped tin dioxide (SnO₂F) films were deposited from a tin tetrachloride solution in methanol utilizing a pyrosol deposition process. It is shown from thermodynamic calculations that the atmosphere during deposition is oxygen-rich and also suggested that chlorine and hydrogen chloride, which are produced during the deposition reaction, influence crystal growth. Detailed electrical, optical and structural properties of the material with respect to varying film thickness and substrate temperature are presented and discussed. Resistivity of the films deposited at 450 °C decreased from 6×10^–4 to 2×10^–4 cm, while the mobility increased from 14 to 45 cm²V^–1s^–1, respectively, when the film thickness was varied from 100 to 1650 nm. The carrier concentration was relatively unchanged for film thicknesses higher than 200 nm. Optimized SnO₂F films (600 nm) having a resistivity of 6×10^–4 cm, a carrier mobility of 20 cm²V^–1s^–1, a carrier concentration of 8×10²⁰ cm^–3 and a transmittance in excess of 80% are quite suitable as electrodes for amorphous silicon solar cells.     

High Critical Current Density of c-Axis-Oriented MgB2 Thin Films

From the magnetic hysteresis loops (M-H) and the current-voltage (I-V) relations, we obtained the critical current density (J _c) for c-axis-oriented MgB₂ thin films with a transition temperature of 39 K. The temperature dependence of J _c obtained from the M-H and the I-V curves coincide, which indicates the strongly linked nature of the intergrains in these thin films. And, the high value of J _c was estimated to be 4×10⁷ A/cm² at 5 K and 1×10⁵ A/cm² at 37 K under a self field, indicating a promising candidate for technological applications.     

Phonon Modes in CMR Manganites at Elevated Temperatures

Phonon modes of the colossal magnetoresistance manganites La_0.7Ca_0.3MnO₃ and La_0.8Li_0.2MnO₃ have been investigated by far-infrared (100–700 cm^–1) reflectivity spectroscopy at elevated temperatures (300–800 K). The three principal optical phonons all move systematically to lower frequency as temperature increases, in accordance with a Grüneisen relationship. The La(Ca,Li)–(MnO₃) vibration (170 cm^–1) varies with cation mass as expected. The Mn–O stretching mode (580 cm^–1) has a higher frequency in the Li-doped compound than in the Ca-doped, whereas the O–Mn–O bending mode )340 cm^–1) occurs at the same frequency in each, demonstrating that the cation strongly influences the Mn–O– length but not the bond angle.     

Mechanical property changes in sapphire by nickel ion implantation and their dependence on implantation temperature

Sapphire plates, cut parallel to an {0001} plane, have been implanted with 300 keV nickel ions to doses ranging from 5×10¹² to 1×10¹⁷ Ni cm^–2 at specimen temperatures of 100, 300 and 523 K, in order to investigate the effect of implantation temperature on the mechanical property changes in sapphire caused by ion implantation. The measured changes in surface hardness, surface fracture toughness and bulk flexural strength were found to depend strongly on the implantation temperature, and were largely correlated with the residual surface compressive stress measured by using a cantilever beam technique. The surface amorphization that occurred only by the implantation at 100 K and at doses larger than 2×10s15 Ni cm^–2 reduced the hardness to 0.6 relative to the value of the unimplanted sapphire, and considerably increased the surface plasticity. Furthermore, the amorphization was found to involve a large volume expansion of 30% and to change drastically the apparent shape and size of a Knoop indentation flaw made prior to implantation. This effect was suggested to reduce stress concentrations at surface flaws and hence to increase the flexural strength.     

Chemically resistant alloys for immobilization of radioactive wastes

The possibility of using intermetallic compounds or alloys of actinides with nickel for preparing matrices incorporating radioactive wastes was examined. Such intermetallic compounds or alloys are prepared by electrolytic deposition of a lanthanide or actinide from a melt of its salt in eutectic mixtures of alkali metal chlorides. The process is performed under the conditions when an actinide being reduced reacts with the cathode material to form a layer of an intermetallic compound. Based on the results of the physicochemical studies performed, an electrochemical process was developed for compacting highly radioactive toxic nuclides of Am, Pu, and REE in environmentally safe forms with high chemical, thermal, and radiation resistance: (a) in the form of alloys or intermetallic compounds containing up to 90 wt % radionuclide, with the leaching rate in water of 10^?5–10^?6 g cm^?2 day^?1; (b) in the form of layers of alloys or intermetallic compounds of the radionuclides on metal supports, with the radionuclide content of up to 80 wt % and leaching rate in water of ～10^?6–10^?7 g cm^?2 day^?1.     

Some natural carbonates for magnetic cooling below 1°K

The natural minerals calcite, magnesite, and dolomite containing 0.1% Mn ²⁺ ions have been investigated to determine their usefulness as cooling agents for adiabatic demagnetization. Cooling curves below 1°K, obtained by a series of adiabatic demagnetizations, gave characteristic temperatures: 0.05°K for the pink and the white calcites and the magnesite, and 0.1°K for the dolomite, in fair agreement with the values predictable from the ESR data for Mn ²⁺ . As for the specific heat constant,cT ²/R, the agreement with the ESR was good below 0.4° K with values of 6×10 ^–3 (°K) ² for the pink and the white calcites and the magnesite, and 22×10 ^–3 (°K) ² for the dolomite. The static magnetic susceptibility was measured from 4.2 to 0.06° K and gave the values of Curie constant: 0.44×10 ^–3 , 0.27×10 ^–3 , and 0.05×10 ^–3 emu/cm ³ at high temperature, for the polycrystalline samples of pink calcite, magnesite, and dolomite, respectively. The pink calcite and the dolomite obey Curie's law down to 0.8°K and the magnesite to 0.3°K. The ordering temperatures for these samples are deduced to be lower than 0.06°K. Measurement of the thermal conductivityK(T) is reported for several types of samples between 4 and 0.2°K.K(T) of the Iceland spar is 15 times better than that of CrK alum as reported elsewhere, whereas that of the single crystal of white calcite is about two times higher. The polycrystalline samples are poor from this point of view.Work supported by a grant from the National Research Council of Canada.     

The effects of various hydrothermal treatments on magnesium-aluminium hydrotalcites

Mg/Al hydrotalcites were synthesised by coprecipitation followed by hydrothermal treatment. The materials were characterised by XRD, infrared and Raman spectroscopy, electron microscopy and thermal analysis. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO₃ ^2–, with a basal distance of 23.5 Å. All possible CO₃ ^2– modes were observed in the infrared and Raman spectra, at 1068 cm^–1, 844 cm^–1, 1380 cm^–1, and 680 cm^–1. XRD, Infrared and Raman spectroscopy complimented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity and that treatment in water rather than in the mother liquid resulted in a more crystalline material. TEM showed that crystal size increased with aging, such that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. Thermal analysis showed 3 major weight losses corresponding to the loss of interparticle water, interlayer water, and dehydroxylation of the hydroxide layers and decarbonation of the interlayer region.     

Diffusional penetration of silver from electrodes into PZT ceramics

Diffusion of silver was studied in a ceramic based on lead zirconate-titanate, Pb_0.95Sr_0.05(Zr_0.53Ti_0.47)O₃+1 wt%. Nb₂O₅ (PZT), by means of a radio-tracer method. Parameters of silver diffusion and silver content in PZT after continuous diffusion saturation of the ceramic by this impurity were determined in the temperature range 500–850 °C. Concentration-depth profiles and silver content in the ceramic were obtained as a result of metal diffusion from the electrode during ceramic silvering. Our results show that silver has a high diffusivity. No evaporation of silver during metallization (T _max=750 °C) was found, but part of it ( 0.1 mg cm^–2) penetrates into the ceramic from the electrode to a depth of more than 1000 m, and the silver concentration varies from 2×10¹⁹ to 2×10¹⁸ at cm^–3. The silver concentration does not exceed 0.2 at% at diffusion saturation of the ceramic during 100–120 h over the temperature range 650–850 °C.     

Preparation and properties of TaC/C/TaC∼TaC composite micro-tubes by vapor phase tantalizing of the regular carbon micro-coils/micro-tubes

TaC/C/TaCTaC composite micro-tubes were prepared by the vapor phase tantalizing of the regular carbon micro-coils/micro-tubes, and the preparation conditions and some properties were examined. The carbon micro-coils with a tube-like morphology were tantalized from the surface to the core of the carbon fibers with full preservation of the tube-like morphology to form TaC/C/TaCTaC composite micro-tubes. The bulk electrical resistivity and specific surface area of the TaC/C/TaCTaC composite micro-tubes were 4 × 10^–3 to 5 × 10^–4 ·m and 5 × 10³ to 2 × 10⁴ m²/kg, respectively, depending on the tantalized ratio and the bulk density.     

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.     

Deactivation of Process Solutions from Nuclear Power Units with NaA(4A), NaX(13X), and Zk-5 Zeolites of Enhanced Adsorption Capacity and Their Cement Grouting

Treatment of spent coolant and other liquid radioactive wastes from ship nuclear power units with NaA(4A), NaX(13X), and Zk-5 zeolites (no binders) and their immobilization by cementation are studied. All the three types of zeolites demonstrate high sorption capacity for ¹³⁷Cs. Cement blocks with incorporated zeolites are characterized by high strength (above 5 MPa) and low leachability of radionuclides (below 10^{- 3} g cm^{- 2} day^{- 1}), providing safe disposal.     

Hydrolysis of Np(IV)

Hydrolysis of Np(IV) at p[H⁺] from 0 to 2.7 and ionic strength I = 0.1-1.0 was studied spectrophotometrically. In the p[H⁺] range from 0 to 2.2 and Np(IV) concentrations of 4.5 ×10^{- 5}-1.75 ×10^{- 4} M, polymerization and formation of colloids are negligible and do not noticeably affect the hydrolysis constant measurements. The hydrolysis is completely reversible. With increasing p[H⁺] to 2, only the NpOH^{3 +} complex is formed; the spectrum of this hydroxy complex was calculated. The typical narrow band of Np(IV) aqua ion occurs at 732.2 nm; in hydroxy complex, it is shifted to 729.5 nm and its intensity decreases by a factor of about 2.7. The average constant of Np(IV) hydrolysis equilibrium [Np^{4 +} + H₂O NpOH^{3 +} + H⁺] recalculated to the ionic strength I = 0 was determined as logK ₁ ⁰ = -1.23±0.06, which corresponds to the stability constant of the complex NpOH^{3 +} log₁ ⁰ = 12.77±0.06. The stability constant of the complex Np(OH)₂ ^{2 +} was calculated to be log₂ ⁰ = 24.3.