用于冲击波延时的密度梯度气凝胶飞片靶的制备及表征

本文介绍了一种用于激光状态方程实验冲击波延时的密度梯度气凝胶飞片靶的制备及表征方法。以间苯二酚和甲醛为原料,去离子水为溶剂,碳酸钠为催化剂,在溶胶-凝胶工艺的基础上采用逐层凝胶和微模具成型工艺,经过脱模、乙醇替换和真空干燥,制备了4层密度梯度渐变间苯二酚-甲醛（RF）有机气凝胶飞片靶,并使用傅里叶红外光谱仪、扫描电子显微镜、X射线相衬成像仪和比表面积及孔隙分析仪对飞片靶的成分、形貌、密度、层间界面耦合情况及微观结构进行表征。实现了总体厚度约120μm、单层厚度一致、各层均匀性良好且密度变化范围约400～1200mg/cm³的4层密度梯度RF气凝胶飞片靶的制备和表征。     

氧化锡纳米晶气凝胶制备及其表征

介绍一种低体密度、高表面积、具有纳米量级骨架和晶粒尺寸的块状多孔氧化锡(SnO2)气凝胶的制备方法。场发射扫描电子显微镜（FESEM）表明,气凝胶是由大量纳米粒子堆积而成的三维多孔材料。高分辨透射电子显微镜（HRTEM）表明,气凝胶的骨架粒子由平均粒径为2～3nm的纳米微晶构成。N2吸附表明,气凝胶具有较高的比表面积,约为355.65m2/g,通过该方法计算出的气凝胶的骨架颗粒粒径为2.4nm,与HRTEM结果吻合较好。     

微尺寸碳气凝胶的制备及其机械性能研究

以间苯二酚和甲醛为源,碳酸钠作催化剂,采用溶胶-凝胶技术和原位成型工艺制得有机气凝胶微柱、薄片.经常压下丙酮替换和后续精确温控的高温碳化工艺制备相应的微尺寸碳气凝胶.研究表明,通过控制前期反应参数,可实现碳气凝胶密度在300～1 000 mg/cm3可控、比表面积高达1 521 m2/g、具有不同内部微观结构和良好的低温力学稳定性能.所制备的微尺寸碳气凝胶是一种优秀的惯性约束聚变实验用多孔泡沫材料.     

块体气凝胶的通用制备方法进展

传统溶胶凝胶法、环氧化物法和无机分散溶胶凝胶法是3种用于制备氧化物气凝胶的通用方法,在各自适用范围内均有重要意义。对于块体气凝胶的制备,传统溶胶凝胶法的工艺和理论成熟但制备范围较窄,环氧化物法制备范围广却存在着气凝胶的密度较高、易于收缩、难以成型等缺点,且难以适用于低价态元素氧化物块体气凝胶的制备。无机分散溶胶凝胶法的制备范围则非常广,它采用金属无机盐为前驱体,低分子量聚丙烯酸为分散剂与引导剂,结合传统溶胶凝胶法与环氧化物法,辅以超临界流体干燥和热处理工艺,一步反应即可获得具有密度较低、成型性好、强度较高、杂质易去除等特点的块体气凝胶。该方法可广泛应用于多族多周期块体气凝胶的制备,在气凝胶的制备与应用领域将拥有广阔的前景。     

碳化硅气凝胶的模板限制反应法制备与特性

提出了一种酸催化制备间苯二酚 甲醛/二氧化硅复合气凝胶的方法,产物经碳化后得到碳/二氧化硅复合气凝胶。利用模板限制的镁热反应法,在低温（700 ℃）下将C/SiO₂气凝胶转化为纳米SiC气凝胶,并讨论了SiC的镁热反应机制。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、傅里叶红外光谱（FTIR）、拉曼光谱（Raman）和比表面积分析（BET）等测试技术对样品进行了表征。结果表明,产物由立方相SiC纳米晶组成,保留了与原始气凝胶模板相似的微观形貌,表观密度约为130 mg/cm³,比表面积约为230 m²/g。这种模板限制反应法适用于多种碳/过渡金属氧化物复合气凝胶向碳化物纳米泡沫材料的低温转化,将有利于激光惯性约束核聚变实验用靶的应用研究。     

β射线检测聚4-甲基-1-戊烯泡沫密度梯度

低密度多孔材料的密度均匀性及其梯度对材料性能有极其重要的影响.现有检测技术不能满足物理实验的检测需求,故新建一种β射线检测技术及相应软件,用以对低密度多孔材料的密度分布进行高灵敏定量表征.本工作叙及该系统的装置、原理和方法,通过对不同工艺制备的聚4-甲基-1-戊烯(TPX)泡沫进行测试,给出了样品密度分布的2D、3D图及密度不均匀度的统计图,并对不同样品泡沫进行对照,可明显看出泡沫密度均匀性的差异.该技术不仅满足了测量要求的空间及密度分辨率,还可实现轴向密度分布的无损检测以及径向密度分布测量.     

超低密度碳气凝胶的制备与研究

采用溶胶-凝胶技术制备了超低密度的间苯二酚-甲醛(RF)有机气凝胶(10 mg/cm³),将此气凝胶高温碳化,得到了密度只有20 mg/cm³的碳气凝胶,并用扫描电镜、透射电镜、N₂吸附法等表征了低密度碳气凝胶的微观结构、孔特征等性质。研究发现,低密度碳气凝胶是由粒径10～15 nm的碳纳米粒子以单链珍珠链状连接组成的三维网络结构;而这些纳米颗粒是由更小的石墨微晶构成,微孔主要存在于碳纳米颗粒中,比表面积达1 783.7 m²/g。氢吸附测试发现,此低密度碳气凝胶常压下在液氮温度时吸氢量可达4.4%（质量分数）。     

低密度碳气凝胶制备及其热学、力学性能研究

ICF及X光激光实验将结构和密度可调的碳气凝胶作为一种常用靶材料,其力学、热学性能和结构直接影响其应用。本文以间苯二酚（R）和甲醛（F）作为反应前驱体,通过调节反应参数和控制制备条件合成了低密度（<50mg/cm³）碳气凝胶,最低密度为36mg/cm³。利用场发射扫描电镜（FESEM）、X射线衍射仪、孔径分布及比表面积测试仪和同步热分析仪等对低密度碳气凝胶的结构进行研究;采用动态力学分析仪、电子拉伸试验机和热传导分析仪对其性能进行表征。研究表明,该低密度碳气凝胶具有明显珍珠项链状纳米网络,颗粒大小均匀,粒径约为70nm,比表面积达1217m²/g;在-120～200℃温区内,具有稳定的力学性能,杨氏模量仅为0.375MPa,是一种理想的弹性材料。常规密度碳气凝胶材料为几十MPa。在室温空气气氛下,其热导率低至0.05W/(m•K),相对于常规碳气凝胶有较大改善。     

块状氧化铁气凝胶制备初步研究

研究以氯化铁的醇溶液为前驱体、有机路易斯碱为凝胶促进剂,快速制备氧化铁的醇凝胶,再通过CO2超临界干燥工艺得到氧化铁气凝胶。用透射电镜(TEM)对氧化铁气凝胶的微观结构的表征结果表明,气凝胶主要由超细微粒堆积而成。经BET和BJH测试,气凝胶样品的密度为138 mg/cm3时,孔径为97 nm,孔体积为1.97 cm3/g,比表面积为487 m2/g。XRD研究表明,组成氧化铁气凝胶的晶形结构主要为-βFeOOH。     

无机分散溶胶-凝胶法制备块状锂基气凝胶

以无机锂盐(LiCl)的醇溶液为前驱体,聚丙烯酸(PAA)既作为分散剂又为凝胶引导剂,环氧丙烷为凝胶促进剂,采用溶胶-凝胶工艺制备了块状锂基醇凝胶,经CO2超临界流体干燥工艺,得到白色锂基气凝胶块体样品,其密度约为150 g/m3.用透射电镜(TEM)对气凝胶的微观结构进行分析表明,气凝胶样品由线性骨架构成网络结构.结合红外光谱分析及XPS测试结果分析可知,样品中主要含有锂、碳元素.由BET测试结果可知,样品比表面积达18.9 m2/g.     

等梯度行波加速管耦合器的调配方法

本文在已有的等阻抗行波加速管耦合器调配方法的基础上,根据耦合腔链的等效电路模型,推导了实验调配等梯度加速管耦合器的方法,给出定量计算该结构耦合器耦合度β的公式,并通过CST模拟计算和实验调配验证了该方法和公式的正确性。     

等梯度电子直线加速器的功率和场强

本文在沿等梯度盘荷波导的分路阻抗不为常数的情况下,对等梯度加速器的功率和场强的基本理论进行了讨论,推导了有束流负载时的功率和场强的计算公式,并分别以分路阻抗沿加速腔线性变化和二次变化为例,对功率和场强作了具体而系统的阐述,最后,给出了在分路阻抗线性变化下等梯度盘荷波导工程设计的数据图表。     

Conjugate Gradient Like Methods and Their Application to Fixed Source Neutron Diffusion Problems

This paper presents a number of fast iterative methods for solving systems of linear equations appearing in fixed source problems for neutron diffusion. We employed the conjugate gradient and conjugate residual methods. In order to accelerate the conjugate residual method, we proposed the conjugate residual squared method by transforming the residual polynomial of the conjugate residual method. Since the convergence of these methods depends on the spectrum of coefficient matrix, we employed the incomplete Choleski (IC) factorization and the modified IC (MIC) factorization as preconditioners. These methods were applied to some neutron diffusion problems and compared with the successive overtaxation (SOR) method. The results of these numerical experiments showed superior convergence characteristics of the conjugate gradient like method with MIC factorization to the SOR method, especially for a problem involving void region. The CPU time of the MICCG, MICCR and MICCRS methods showed no great difference. In order to vectorize the conjugate gradient like methods based on (M)IC factorization, the hyperplane method was used and implemented on the vector computers, the HITAC S-820/80 and ETA10-E (one processor mode). Significant decrease of the CPU times was observed on the S-820/80. Since the scaled conjugate gradient (SCG) method can be vectorized with no manipulation, it was also compared with the above methods. It turned out the SCG method was the fastest with respect to the CPU times on the ETA10-E. These results suggest that one should implement suitable algorithm for different vector computers.     

金属铁和镍中氦缺陷性质的理论研究

采用投影缀加波赝势和广义梯度近似方法分别计算了体心立方结构金属铁和面心立方结构镍中3种氦缺陷形成能及态密度分布。计算结果表明,以上两种金属的置换氦缺陷最稳定,其次是四面体间隙氦缺陷,八面体间隙氦缺陷最不稳定。分析表明,金属铁和镍中氦缺陷稳定性并不是由缺陷的弹性畸变决定的,而是由缺陷氦原子与其最邻近金属原子之间的电子相互作用决定的。     

Effect of Porous Surface Layer on Leaching Rate of Radionuclide from Cementitious Waste Form

Leach tests based on IAEA methods were carried out using three types of cementitious specimens containing ¹³⁴Cs and ¹²⁵I and an evaluation method of apparent diffusion coefficients from the leaching curves was discussed. Since the gradient of the leaching curve, i.e. the relationship between the leaching ratio and the square root of time, changes during the leach tests, it has been difficult to estimate the diffusion coefficient. The difference between the leaching rate in the early period of the leach test and that in the later period was attributed to the porous microstructure of the surface layer in the cementitious specimens. The duplicate layer model, which expressed differences in the properties between the surface layer and an inner region by different diffusion coefficients, was proposed. Its numerical solutions had good agreement with the experimental leaching curves.     

Evaluation of the correlation of the drift coefficients of random nterdiffusion processes

Random processes, specifically diffusion and wave processes, as well as the random process of crossing of two counterflows are studied. A relation is obtained for the probability distribution for the crossing process for discrete and continuous distributions of the random quantities. Examples of the density distribution of a crossing process are examined. The crossing properties of Gaussian processes are studied. A great deal of attention is devoted to wave corrections to the diffusion equation. The wave equation for the evolution of the probability density function is examined, and the wave coefficient is obtained for the particular case of random counterflow processes. A method of evaluating the drift correlation coefficients for random counterflow processes is developed. Algorithms are proposed for statistical modeling of the distribution function for the crossing process: Monte Carlo numerical modeling and an analytical-statistical method. A comparative characteristic is given for both methods.     

Computation accuracy and efficiency of a polynomial nodal method for diffusion and spatial burnup problems

The aim of this paper is to demonstrate the accuracy and computational efficiency of a polynomial nodal method (PNM) in solving multigroup neutron diffusion problems in three space dimensions, particularly the long-term burnup problems in PWRs, with their inevitable power-dependent effects. With this in mind, PNM is accurately assessed against other well-grounded nodal methods such as the analytic nodal method (ANM) and the nodal expansion method (NEM), in the case of a well-known PWR benchmark problem, and appears to be as accurate and efficient, as regards the determination of both node-average values and detailed flux distributions inside homogenized nodes. Moreover, the practical applicability of the method to the analysis of fuel cycles in actual PWRs is documented positively.     

Simulation of the effect of x-rays on the cellular structure of the chamber walls of a nuclear power facility

Computational and experimental methods are developed for simulating, by means of an explosion and shock, the wave processes occurring in the walls of the explosion chamber of pulsed nuclear power facilities under intense x-ray irradiation. The experimental measured and computed parameters of shock waves accompanying explosive and shock loading of different materials were in satisfactory agreement with one another. The methods developed are used to investigate the behavior of a liquid heat-protective film of Li₁₇Pb₈₃ on the wall of the explosion chamber when the recoil pulse produced by evaporation is the main load factor. The possibilities of decreasing the explosive loads by changing the thickness of the lead shell of the charge and by including cellular structures and porous materials in the chamber walls are examined. __________ Translated from Atomnaya énergiya, Vol. 105, No. 1, pp. 32–38, July, 2008.