氧化层对钛吸附与解吸氘的动力学影响研究(Ⅱ)--氧化层对氘化钛热解吸动力学的影响

测定了3种不同氧化层厚度的氘化钛在873～1073K范围内的热解吸反应速率常数,得到673K下氧化5、2h的氘化钛和未经氧化处理的氘化钛热解吸氘的活化能分别为(29.0±1.0)、(27.6±1.0)和(24.9±1.4)kJ/mol。实验表明:氘化钛表面氧化层具有阻氘性能,氘化钛表面氧化层越厚,表观活化能越大。     

Ti—Mo合金氘化物热解吸过程研究

采用非零初压热解吸法研究了不同钼含量的钛钼合金TiMo_x(x=0.03、0.13、0.25、0.50、1.00,Mo与Ti原子数之比)氘化物的热解吸动力学,测试了氘解吸量与解吸时间的关系,应用反应速率分析方法得到了其热解吸速率常数k_d和热解吸表观活化能E_d;并与氕化物的热解吸动力学行为进行了比较。结果显示,x=0.03时,合金氕化物E_d小于氘合金化物E_d,与钛放氢动力学同位素效应一致;x=0.13、0.25时,氕化物E_d大于氘化物E_d;x=0.50、1.00时,氕化物与氘化物的E_d差别不大。通过初始解吸时合金中氕、氘含量的比较,结合室温下合金吸氕、氘量及物相结构,对合金放氢动力学同位素效应的本质进行了探讨。     

载钯硅藻土吸氕/氘动力学同位素效应

恒温等容条件下,通过p-t曲线测量,研究在223~393K范围内载钯硅藻土(Pd/K)吸氕、氘动力学特性。应用反应速率分析方法计算了反应速率常数,得到了Pd/K吸氕、氘反应活化能。动力学计算结果显示:在整个温度范围内,载钯硅藻土与氕、氘反应明显分为两个温度段。低温段(223~313K),载钯硅藻土吸氕、氘反应速率常数随温度升高而增大且吸氕反应速率大于吸氘反应速率,吸氕、氘反应活化能分别为19.5、19.2kJ/mol;高温段(313~393K),载钯硅藻土吸氕、氘反应速率则随温度升高而减小,氕、氘反应活化能分别为:-18.6、-12.1kJ/mol。测试结果表明,载钯硅藻土吸氕、氘反应存在显著的动力学同位素效应且同位素效应依赖于温度的变化。     

TiD_(1.92)热解析的动力学行为研究

采用热分析和理论计算的方法对TiD1.92粉末的解析行为进行了研究。计算的TiD1.92粉末有3类解析峰,均与TiD1.92解析中发生相变导致的氘扩散速率变化有关。球形颗粒模型的解析与平板颗粒模型的解析因其相变和扩散机制不同导致β→α相变解析峰表现出一定的差异。TiD1.92粉末的热分析结果与平板颗粒模型的计算结果完全一致,其中δ相和β相钛氘化物的解析由表面反应控制,β→α相变阶段的解析由氘在α相的扩散控制,实验获得氘在钛表面的解析活化能为152.8kJ/mol以及氘在α相中的扩散活化能为68.6kJ/mol。     

Ti87.5Hf12.5合金的贮氢性能

测定了Ti87.5Hf12.5合金的吸氢体膨胀率和氢化物热稳定性,并与Ti及TiZr、TiV和TiNb等a相合金的相应特性进行了对比.TiHf合金具有最小的吸氢体膨胀率和最高的氢化物共析转变温度.Hf的添加显著长大了TiH2的晶格常数.测试了TiHf合金的吸放氢动力学特性和吸氢PCT曲线,Hf的添加未显著改变Ti的吸氢热力学特性,外推室温吸氢平衡压与Ti的相当.     

Ti-Mo合金吸氢动力学的同位素效应

为寻找一种价格低廉、分离性能优良的氢同位素分离材料来替代金属Pd,对Ti-Mo合金的氢同位素效应进行研究。采用磁悬浮熔炼方法制备5种不同组成的TiMox（x=0.03、0.13、0.25、0.50、1.00,Mo/Ti原子比）固溶体合金,用定容变压法测试了250～650℃范围内的吸氘动力学性能。结合前期吸氕动力学的研究结果可知,在250～650℃范围内,合金的平衡吸氕量略大于合金的平衡吸氘量。Mo含量小于1.00,在低温（250～450℃）下,合金的吸氘表观活化能均为负值。高温（450～650℃）下,合金的吸氘表观活化能大于吸氕表观活化能,与钛吸氢同位素动力学效应保持一致。     

模拟乏燃料短段673～873 K下的氧化行为

氧化挥发是一种具有良好应用前景的后处理首端技术,该技术不仅能有效实现氚的管控还可简化后续处理流程。为预测乏燃料的氧化行为并为氧化挥发技术提供参考,本文利用旋转式氧化挥发装置,对模拟乏燃料短段在673～873 K下的氧化行为进行了研究。结果表明,673~823 K范围内,随着温度的升高,模拟乏燃料短段氧化速率、氧化产物（小于200 μm）粒径均会增加。823 K下,由于包壳内部分芯块未能完全反应,所得转化率只有86%。此外,当温度低于773 K时,模拟乏燃料短段氧化不够充分。因此,673~873 K范围内,乏燃料短段最佳氧化挥发温度为773 K。     

模拟乏燃料短段673～873 K下的氧化行为

氧化挥发是一种具有良好应用前景的后处理首端技术，该技术不仅能有效实现氚的管控还可简化后续处理流程。为预测乏燃料的氧化行为并为氧化挥发技术提供参考，本文利用旋转式氧化挥发装置，对模拟乏燃料短段在673～873 K下的氧化行为进行了研究。结果表明，673～823 K范围内，随着温度的升高，模拟乏燃料短段氧化速率、氧化产物(小于200μm)粒径均会增加。823 K下，由于包壳内部分芯块未能完全反应，所得转化率只有86%。此外，当温度低于773 K时，模拟乏燃料短段氧化不够充分。因此，673～873 K范围内，乏燃料短段最佳氧化挥发温度为773 K。     

Ti-Mo合金氢化物放氢动力学同位素效应研究

在高真空金属系统中,采用非零初压热解析方法研究了钛钼合金TiMox（x=0.03, 0.13, 0.25, 0.50, 1.00, 原子比）氘化物的热解析动力学,测试了氘解析量c随时间t的变化关系,应用反应速率分析方法得到了热解析速率常数kd和热解析表观活化能Ed ,合金氘化物Ed依次为46.6, 22.4, 13.7, 17.1, 10.4kJ.mol-1。比较氕化物的热解析动力学行为,Mo含量小于0.03时,合金氕化物Ed小于氘合金化物Ed,与钛放氢动力学同位素效应保持一致。Mo含量在0.13 ~ 0.25时,氕化物Ed大于氘化物Ed,Mo含量大于0.50时,氕,氘化物Ed 差别不大。通过初始解析时合金中氕,氘含量的比较,结合室温下合金吸氕,氘量,对合金放氢动力学同位素效应的本质进行了探讨。     

纯Ti吸放氢过程研究

对纯Ti在500和580℃下的吸氢速率常数进行了测定。500℃时,纯Ti吸氢速率随循环测试次数增多而变小,且吸氢动力学曲线出现拐点,吸氢时发生α→β和β→δ2次相变。580℃下的吸氢速率较500℃下的明显变快,吸氢动力学曲线为直线,吸氢时未发生β→δ相变。研究了表面及晶粒度对磁控溅射和球磨制备的TiH2放氢过程的影响。结果表明,在相同升温速率下,由磁控溅射和球磨制备的纳米晶氢化物的放氢曲线与块体材料的放氢曲线存在显著差异。此现象与样品中的缺陷结构有关。     

High temperature oxidation of some zirconium alloys in flowing oxygen

The oxidation behavior of three zirconium alloys, Zr-2.2wt%Hf, Zr-2.5wt%Nb and Zr-3wt%Nb-1wt%Sn, has been studied in flowing oxygen in the temperature range 873–1173 K to 120 ks (2000 min). Zr-2.5Nb and Zr-3Nb-1Sn showed a transition to rapid linear kinetics after initial parabolic oxidation at all temperatures. Zr-2.2Hf, on the other hand, showed this transition at temperatures in the range 973–1173 K; no transition was observed at 873 K within the oxidation times reported. Zr-2.2Hf showed the smallest weight gains, followed by Zr-2.5Nb and Zr-3Nb-1Sn. Increased oxidation rates and shorter time-to-rate transition of Zr-2.5Nb and Zr-3Nb-1Sn as compared with Zr-2.2Hf are attributed to the presence of the alloying elements Nb, Sn and Hf. Based on the Nomura-Akutsu model, Hf should delay the rate transition, while Nb and Sn lead to shorter transition times. The scale on Zr-2.2Hf was identified as monoclinic zirconia, while the tetragonal phase, 6ZrO₂ · Nb₂O₅, was contained in the monoclinic zirconia scales on both other alloys.     

立方烧绿石Gd_2Zr_2O_7的高温高压合成

为探索高温高压固相反应法合成Gd2Zr2O7烧绿石的可能性,以Gd2O3和ZrO2的混合粉体为原料,在5.2GPa压力、1473～1873K温度范围内进行了实验研究。通过XRD对合成样品进行了结构表征,结果证实,在5.2GPa和1873K条件下,保温保压30min,成功地合成出单一物相的、具有立方烧绿石结构的Gd2Zr2O7化合物。这种新的合成方法对于开展武器级多余钚和含钚高放废物固化具有重要的科学价值和实际意义。     

Thermal stability of hydrostatically extruded EUROFER 97 steel

EUROFER 97 steel is a candidate structural material for the future fusion power reactors, as well as for the European Test Blanket Modules (TBMs) to be tested in ITER. In the reported study, the microstructure of EUROFER 97 was modified by hydrostatic extrusion (HE) which reduced the grain size from 400 to 86 nm and that of the carbide particles from 111 to 75 nm. The changes in the microstructure significantly improved the strength of the extruded samples. However, it is important that the enhanced properties of nanostructured materials are stable over the required range of intended service temperature. The thermal stability of the nanostructured EUROFER steel was evaluated by subjecting the hydrostatically extruded samples to annealing at temperatures ranging from 473 to 1073 K (200–800 °C) for 1 h. Tensile tests and microhardness measurements with a 200 g load were carried out on the annealed samples to determine the effect of the heat treatment. The results show that the highest microhardness (403 HV_0.2) was achieved for samples annealed at 673 K. However, the tensile and yield strength decreased at the higher temperature of 873 K and the total elongation increased to 15%, compared to only 3% for as-extruded samples. The changes in the mechanical properties were rationalized by the examination of the microstructural changes. During heating the initial grain size remains virtually unchanged below a temperature of 873 K. However, above 873 K the grain size increased and it is very likely that growth will be very rapid at higher temperatures.     

Heat capacity of hydrogenated Zircaloy-2 and high Fe Zircaloy

Heat capacities (C_p) of non-hydrogenated and hydrogenated Zircaloy-2 and high Fe Zircaloy were measured in the temperature range from 350 to 873 K, using a differential scanning calorimeter. The hydrogen concentrations in the two types of alloys ranged from 26 to 1004 ppm. The C_p values of the as-received alloys with 26-29 ppm hydrogen were in good agreement with literature data for low hydrogen Zircaloys. From this finding and observation of almost the same enthalpy changes for hydride dissolution for both alloys, it was concluded that there was no difference in C_p values between the two types of hydrogenated Zircaloys. The dissolution enthalpy of hydrides calculated from C_p data was 41.0 kJ/g-atom H. For Zircaloy-2 samples with higher hydrogen concentrations than 700 ppm, the phase transition from α+δ to α+β was observed at the eutectoid temperature of 824-827 K. Two types of models describing an additional heat capacity due to the hydride dissolution were presented based on the present C_p data and previously derived terminal solid solubility of hydrogen.     

Deuterium retention and release in tungsten co-deposited layers

A systematic study of the influence of the deposition conditions on the deuterium retention in co-deposited tungsten layers formed both by magnetron sputtering and in the PISCES-B linear device has been carried out. Experimental parameters such as the tungsten deposition rate, the incident particle energy and the substrate temperature are shown to affect the level of deuterium retention in the layers. A decreased retention for increased substrate temperature and deposition rates, and an increased retention for increasing incident deuterium particle energy are observed. A scaling equation is proposed to describe the influence of the conditions during the co-deposition process (surface temperature, incident particle energy and deposition flux) on the deuterium retention. In addition, the desorption kinetics of deuterium has been studied by TDS. Two desorption stages at 473-573 K and at 1073 K have been observed.     

LaNi_(4.25)Al_(0.75)吸氕、氘、氚热力学同位素效应

采用自制的全金属氢化物吸放氢实验装置,恒温等容条件下测定LaNi_(4.25)Al_(0.75)材料吸氕、氘、氚单质气体的压力-组成等温线(P-C-T曲线),并根据Van’t Hoff(范特霍夫)方程得到LaNi_(4.25)Al_(0.75)吸氕、氘、氚形成氢化物相的热力学参数焓变ΔH分别为:-44.5、-45.0、-47.1kJ·mol-1,熵变ΔS分别为:-118.0、-121.8、-127.5J·mol~(-1)·K~(-1)。结果表明:LaNi_(4.25)Al_(0.75)材料吸收氕、氘、氚单质气体,在温度较低时,同位素效应不明显;温度高于100℃时,热力学同位素效应显著。相同温度、吸气容量条件下,吸气平衡压力从低到高依次是氕、氘和氚,其反应焓变和熵变从小到大依次是氚、氘和氕。结果表明,LaNiAl合金吸氢的热力学同位素效应依赖于温度的变化。     

Preparation of Zn/TiO2 powder and its photocatalytic performance for oxidation of P-nitrophenol

Zn-doped TiO2 catalysts were prepared using a sol-gel method and characterized by XPS,UV-Vis, BET, XRD in this study. Under the irradiation of simulant sunlight, the photocatalytic activity for the degradation of p-nitrophenol was studied too. After irradiation for 2.5 h, the degradation percentage of p-nitrophenol could rise to more than 80 %. The results showed that the spectrum absorption band edge of Zn/TiO2 powder does not broaden obviously comparing with pure TiO2 powder. Zinc exists as Zn （11）. When calcined at 973 K, there is a new phase as ZnTiO3 in Zn/TiO2 catalyst. The order of photocatalytic activity of Zn/TiO2 catalysts calcined at different temperatures for p-nitrophenol is 773 K 〉 673 K 〉 873 K 〉 573 K 〉 973 K and the photocatalytic activity of Zn/TiO2 catalyst calcined at 773 K is better than TiO2 catalysts heated at the same temperature, and outclasses that of commercial TiO2 catalyst. It also showed that the photocatalytic degradation of p-nitrophenol follows first-order kinetics under the irradiation of simulant sunlight.     

Reorientation of Hydrides and Its Effect on the Mechanical Properties of Zr-Nb-Sn-Fe Cladding Tubes

The reorientation of hydrides and its effect on the fracture of Zr—Nb—Sn—Fe cladding tubes were investigated. The reorientation of hydrides along the radial direction was most pronounced if the tube was cooled from 573 to 473 K under circumferential loading. Reorientation occurred much less frequently at either higher (from 673 to 573 K) or lower (from 473 to 373 K) temperature range. The strength decreased to 250 MPa and the ductility decreased to zero in the tube which was reorientation-treated from 573 to 473 K (RS32AC). Fracture surface of RS32AC sample exhibited flat cleavage fracture along the radial hydride platelet. The reorientation of hydrides was also found to increase with increase of loading time, suggesting time dependent stress-aided dissolution of circumferential hydrides and re-precipitation of radial hydrides.