Vaporization study on nonstoichiometric NbO2 ± x by mass-spectrometric method

The vapor pressures over nonstoichiometric NbO_{2 ± x}(s) (1.972?2.037) were measured by mass-spectrometric method in the temperature range 1958–2326 K. The congruently vaporizing composition in the NbO_{2 ± x} phase was determined to be stoichiometric NbO_2.000 from the composition dependence of the total vapor pressures. The partial pressures of oxygen were calculated as a function of temperature and O/Nb composition from the partial pressures of the gaseous species NbO₂(g) and NbO(g) over nonstoichiometric NbO_{2 ± x}, from which the partial molar enthalpies and entropies of oxygen were calculated as a function of O/Nb composition. The composition dependence of the partial molar enthalpy and entropy obtained suggested the existence of some kind of short-range ordering in the nonstoichiometric NbO_{2 ± x}(s) phase. The enthalpies of formation of nonstoichiometric NbO_{2 ± x}(s) were also determined as a function of composition by combining the partial molar enthalpies of oxygen with the enthalpy of formation of stoichiometric NbO_2.00(s). The phase diagram around NbO_{2 ± x} at high temperatures was determined from the vaporization study.     

Vaporization study on UO2 and (U1−yNby)O2+x by mass-spectrometric method

The vapor pressures over UO_2.000 and (U_1?yNb_y)O_2+x (y = 0.01, 0.05, x = 0.000–0.022) were measured by the mass-spectrometric method in the temperature range 2025–2343 K. The main gas species over UO_2.000 were observed to be UO₃(g) and UO₂(g) and those over (U_1?yNb_y)O_2+x were NbO₂(g), NbO(g), UO₃(g) and UO₂(g). The partial vapor pressures of almost all gas species over (U_1?yNb_y)O_2+x increased with increasing O/M (M = U + Nb) ratio. With increasing Nb content in (U_1?yNb_y)O_2.000, the partial vapor pressures of UO₂(g) and UO₃(g) decreased and those of NbO(g) and NbO₂(g) increased. The congruently vaporizing composition in the (U_1?yNb_y)O_2+x phase was estimated to be ($\text{U}{}_{\mathrm{0.985\pm 0.005}}\text{Nb}{}_{\mathrm{0.015\pm 0.005}}\text{)O}{}_{2.000}$ from the compositional dependence of the total vapor pressures. The partial molar enthalpy and entropy of oxygen of (U_1?yNb_y)O_2+x calculated from the partial pressures of gaseous species NbO₂(g) and NbO(g) were in fairly good agreement with those previously obtained by the present authors with a thermobalance.     

金属铀在CO气氛中表面反应的X射线光电子能谱研究

用Ｘ射线光电子能谱分析研究了金属铀在ＣＯ气氛中２５℃和２００℃时的表面反应，ＣＯ在金属铀表层上的吸附层导致了Ｕ４ｆ峰向低结合能方向位移，表层氧化物中氧含量减少，Ｏ／Ｕ比值随ＣＯ吸附量的增加而减少，研究结果表明ＣＯ气氛可抑制金属铀表面的进一步氧化。     

Vaporization Study on Vanadium-Oxygen Solid Solution by Mass Spectrometric Method

The vapor pressures over vanadium-oxygen solid solution (0.001≦O/V≦0.145) were measured by mass-spectrometric method in the temperature range of 1,855–2,117K. The main vapor species were observed to be V(g) and VO(g). The vapor pressure of V(g) is higher than that of VO(g) over the solid solutions with all O/V ratios except for O/V=0.145. The vapor pressure of V(g) is nearly independent of O/V ratio. The vapor pressure of VO(g) decreases with decreasing O/V ratio. The oxygen partial pressure was calculated as a function of temperature and O/V ratio from the vapor pressures of V(g) and VO(g), from which the partial molar enthalpy and entropy of oxygen in the solid solution were determined. The partial molar enthalpy of oxygen was observed to be independent of composition, suggesting the presence of very weak interaction between interstitial oxygens. The compositional dependence of the partial molar entropy of oxygen can be explained by assuming the occupation of the octahedral site in bcc vanadium lattice by the interstitial oxygens. The excess partial molar entropy of oxygen was compared with the value derived from the sum of the contributions from the volume expansion, electronic heat capacity and vibrational terms.     

Analysis of nonlinear reactor systems by forward and backwardintegration methods

In this paper, third-order nonlinear nuclear reactor systems are analyzed by plotting trajectories. The unique approach is that an accurate boundary of the asymptotic stability region can be found by first linearizing a system at an unstable singular point, such as a saddle point, and then plotting the trajectories starting from a choosing set of initial points very near the unstable singular point and on the surface spanned by the stable right eigenvector of the linearized system. In addition, the system characteristics, such as speed of response and damping, can be studied by plotting trajectories starting from a preselected sets of initial conditions. Both the forward and backward integration methods are used to calculate the trajectories with a computer. Two reactor systems are analyzed, and comparisons with the other methods in current literature are made     

Alloys based on niobium and their properties

Conclusions A number of refractory alloys based on niobium were developed, and their properties were investigated; the complex of these properties permits the recommendation of these alloys for use in various fields of technology. The alloys are characterized by good technological properties, ensuring the production of various objects: sheets, bars, tubes, and wires, under industrial conditions. The most heat-resistant alloys of the RN brand, possessing substantial short-term and long-term strength, are the alloys of tungsten, molybdenum, and zirconium (RN-6, RN-5). The alloys can be subjected to dispersion hardening.It was found that the alloy RN-6, produced by the method of centrifugal casting, possesses better mechanical properties than the alloys produced by arc and electron beam methods, as a result of its fine-grained structure. The alloying of niobium alloys with titanium, instead of zirconium, causes a smaller increase in the strength, especially at increased temperatures; however, their plasticity increases somewhat. Alloys of the RN type possess high corrosion resistance in lithium at 1000°C, as well as in solutions of hydrochloric and sulfuric acids.Translated from Atomnaya Énergiya, Vol. 23, No. 1, pp. 32–37, July, 1967.     

Vaporization Study on Vanadium Monoxide and Two-Phase Mixture of Vanadium and Vanadium Monoxide by Mass-Spectrometric Method

The vapor pressures over single phase vanadium monoxide VO_1.022(s) and the two-phase mixture of vanadium metal (β phase) and vanadium monoxide were measured by mass-spectrometric method in the temperature range of 1,803–1,990 and 1,703–1,884 K, respectively. The main gas species over both systems were found to be VO(g) and V(g). The vapor pressure of VO(g) over the two-phase mixture of V(s) and VO(s) was a little lower than that over single phase VO(s). The vapor pressure of V(g) over the two-phase mixture was nearly equal to that over single phase. From the vapor pressure data, the enthalpies of vaporization, the enthalpies of formation for VO(g) and V(g) and the dissociation energy of VO(g) were determined. The oxygen partial pressure was calculated as a function of temperature from the vapor pressures of VO(g) and V(g), from which the partial molar enthalpies and entropies of oxygen in both systems were obtained.     

Positron annihilation studies on alpha-irradiated and deformed niobium

Positron lifetime and annihilation lineshape measurements have been made to study the defect kinetics and He-vacancy interactions in alpha-irradiated Nb. A comparative study on plastically deformed Nb has also been performed. The isochronal annealing results are discussed with a brief review of previous investigations. Dislocation/vacancy loops annealing occurs above 700°C. Positron trapping rate at He-vacancy clusters is seen to increase with the addition of He atoms to the clusters. Results favour the idea of He-bubble growth by an addition of He atoms or vacancies at intermediate temperatures (350–750°C) and by bubble migration and coalescence at high temperatures (800–900 ° C). Annealing out of He-bubbles/He-vacancy complexes is seen above 900°C.     

Simulation experiments for the sputtering of niobium by 14 MeV neutrons

Simulation experiments for the sputtering of niobium by 14 MeV neutrons are conducted at the Berlin Cyclotron with protons of 11 to 20 MeV which pass through a sandwich of niobium target foils and silicon catcher disks. The stack is assembled in an UHV chamber and is irradiated to doses of 0.7 to 1.4 × 10¹⁸ p/cm². The sputtered material is detected by RBS, taking advantage of Si background reduction by the 〈111〉 channeling effect and by electronic pile-up rejection. The measured sputter ratios are in the forward direction (1.0–2.4) × 10^?4 for the first irradiation and (1.0–2.5) × 10^?5 for a second (subsequent) irradiation; in the backward direction sputter ratios are found to be considerably lower, between several 10^?6 (limit of detection) and 2.8 × 10^?5 (maximum). The emission of radioactive recoils is also observed through 7 spectrometry of targets and collectors.     

Investigation of metal matrix systems for cosmogenic Al analysis by accelerator mass spectrometry

We report experiments designed to help optimize accelerator mass spectrometry (AMS) of ²⁶Al (in the form of Al₂O₃) for geochronologic and geomorphologic applications. Analysis times are long and the precision of AMS are restricted by counting statistics for ²⁶Al, which are in turn limited by the intensity of Al⁻ beam currents. We show that ion beam currents are affected by the metal matrix in which Al₂O₃ is dispersed, by the matrix-to-Al₂O₃ mixing ratio, and for at least some matrices, such as Ag, by the depth to which the sample is packed in the AMS cathode. Typical instantaneous Al⁺⁷ currents (μA) produced by the LLNL CAMS Cs sputter ion source and measured in a Faraday cup after the accelerator are 2.26 for samples in Ag, 2.17 in Re, 2.00 in Nb, 1.92 in V and 1.73 in Mo. The AMS counting efficiency (Al⁻ ions detected per Al atom loaded in the target) for a constant analysis time (900 s) and for equimolar mixtures of Al₂O₃ and matrix is in the range of 6 × 10⁻⁵–9 × 10⁻⁵ in the order Ag > Re > Nb > V > Mo. Additionally, we observed a correlation between the ion detection efficiency (Al ions detected per Al atoms loaded) and the matrix work function and inverse vaporization enthalpy of the matrix and beam current. Typical currents (μA) obtained with elemental Al are 13.3 for samples in no matrix, 3.23 in V, 3.14 in Nb, 3.07 in Re, 2.85 in Mo, 1.46 in Ag. The ion detection efficiency for elemental Al correlates strongly with matrix electron affinity. Thus, our data indicate that the current practice of mixing Al₂O₃ with Ag is reasonable until a means is found to produce cathodes of elemental Al.     

Determination of Heats of Formation for Solid and Liquid Lithium Metasilicates by Vaporization Method

In-reactor experiments were performed in Nuclear Safety Research Reactor of Japan Atomic Energy Research Institute to study the failure behavior of stainless steel clad fuel rods under a simulated reactivity initiated accident (RIA) condition. A single test fuel rod with stainless steel cladding was contained in a capsule filled with water at room temperature and atmospheric pressure and irradiated by pulsing power simulating an RIA. It was revealed through the experiments that the failure mechanism of the stainless steel clad fuel rod was cladding melting, which was different from oxygen-induced embrittlement observed in the Zircaloy clad fuel rod in the same test condition, and the failure threshold energy was determined to be about 240cal/g·UO₂ (–1,000 kJ/kg·UO₂), which was about 20 cal/g·UO₂ (–85 kJ/kg·UO₂) lower than that of the Zircaloy clad fuel rod. It was also found that the mechanical energy was generated by explosive vaporization of coolant due to molten fuel-coolant interaction as a consequence of the fuel rod failure accompanying fuel pellet fragmentation at an energy deposition of nearly 380 cal/g·UO₂ (–1,600 kJ/kg·UO₂) or more.     

阳极氧化法制备多孔硅中的正电子湮没及扫描电子显微镜研究

用正电子湮没技术和扫描电子显微镜研究研究了阳极氧法法制备的多孔硅材料。正电以实验表明,随着阳极氧化时间的延长,平均寿命值增大,空位缺陷增多,长寿命成分较少。扫描电子显微显示,在阳极氧化过程中有尺寸为几μｍ的单晶球形成。     

Trace-element study of glass samples by using activation methods

The investigated samples were plain glasses and glassware for industrial and household purposes from different glass factories. The elemental composition of the normal quality part and the different types of anomalies in different glass products were determined, using charged-particle and neutron activation. The activating particles were protons, deuterons and fast neutrons. The anomalies can cause early and unexpected breakage of the glass product, and some types of them are visible and not aesthetic. The investigated anomalies could be sorted as follows: coloured spot on the surface caused by enrichment of the elements of the iron group and by contamination; stone-like inclusion caused by Zr enrichment coming from the furnace wall. From a comparison of the elemental constitutions of the anomalies and of the normal-quality part of the glass a conclusion could be deduced for the possible cause of anomalies.     

基于相关性分析的特征选择方法研究

讨论了特征相关性的大小与分类能力之间的联系,提出了一种以相关系数和为判据的特征自动选择方法,并将它应用到地下核爆炸与天然地震的自动识别中,实验结果表明该方法所提取的特征子集具有很好的分类能力。     

A study of the reactions between ZrC and some metal oxides

High temperature chemical reactions of ZrC powder or ZrC coating on alumina spheres with CeO₂, UO₂ and SrO were studied. CeO₂ reacts with ZrC at 1473–2073 K to give Ce₂O₃ and Ce₂Zr₂O₇. Virtually no reactions were observed in UO₂-ZrC mixtures at 1673–1973 K. SrO reacts with ZrC above 1273 K to form SrZrO₃, Sr vapor and, presumably, CO. The SrZrO₃ formation on ZrC coated spheres contained in a bed of SrO powder was rapid at 1673 K. All particles suffered serious damages on the ZrC coatings by the reaction with SrO. Though the Sr concentration in the ZrC was below the detection limit, Sr was found to be distributed within the alumina kernel.