流化床-化学气相沉积技术在先进核燃料制备中的应用进展

流化床-化学气相沉积（FB-CVD）技术是化工流化床技术和材料化学气相沉积制备技术的交叉耦合,兼有流化床处理量大、传热快、温度均匀以及化学气相沉积温度调节范围广、产物丰富多样等优点,其在先进核燃料制备中有着重要的应用,但随着先进核燃料“质”和“量”的不断发展要求,现有的FB-CVD技术有许多方面亟待完善。本文回顾了作者课题组利用流化床-化学气相沉积在高温气冷堆TRISO核燃料颗粒、先进核燃料包覆颗粒、核燃料示踪颗粒、基体SiC纳米颗粒、SiC@Al₂O₃复合纳米颗粒等方面的研究进展,阐述了基本方法、实验过程和典型研究结果,并分析了流化床-化学气相沉积过程中遇到的实际问题。指出了FB-CVD技术未来发展方向,主要涉及反应器规模化放大和连续性生产、孔口沉积消除及温区控制、粉体制备中的纳米颗粒连续收集、新型反应器及工艺设计等方面,具体包括高密度颗粒稳定流化放大准则、床层局部温区控制以及分区流化床结构设计等。     

流化床化学气相沉积法激发粉煤灰水化活性及流动性

设计流化床-气相沉积(FB-VD)试验装置,并以NaOH为化学激发剂预激发粉煤灰(FA),与传统在搅拌过程中直接加入化学激发剂的方式进行对比试验与分析.通过水泥净浆抗压强度、水泥胶砂强度、水泥胶砂流动度等性能指标,评价了FB-VD方法对FA活性的改善作用.结果显示,采用等量的NaOH,FB-VD方法比直接外掺的传统方法更提高了FA水化活性的作用的比较、分析,不会产生传统方法中的后期强度倒缩现象,但会对水泥浆体的流动性产生一定的降低作用.     

化学气相沉积法制备碳纳米管的研究进展

从催化剂、碳源气体及反应器的选择等方面综述了化学气相沉积法制备碳纳米管的研究进展 ,讨论了碳纳米管的合成机理。指出催化合成碳纳米管的研究难点在于管径的有效调控和大批量生产 ,今后的研究方向应为单层碳纳米管的有效合成     

非化学计量比镁铝尖晶石粉体的制备及性能

将异丙醇镁铝双金属醇盐滴加到含有5%(质量分数)EDTA分散剂的水解液中,制得镁铝氢氧化物无色透明溶胶,后经干燥、高温焙烧得到非化学计量比的铝镁尖晶石粉体。研究了Mg/Al摩尔比、焙烧温度、干燥工艺流程以及助溶剂的添加对粉体材料性能影响。结果表明:Mg/Al摩尔比在1.0:(2.5～4.0)范围内,1 200℃焙烧后对应粉体为纯相镁铝尖晶石结构,随铝含量增加,衍射峰向大角度方向偏移,且粉体颗粒粒径逐渐增大,Mg O·1.25Al_2O_3粉体红外透过率较高,可潜在应用于红外隐身等材料。     

流化床-化学气相沉积技术的应用及研究进展

流化床-化学气相沉积(FB-CVD)技术是一种多学科交叉的材料制备技术,兼有流化床传热传质性能良好以及化学气相沉积均匀、产物单一等优点,在工业生产中有着广泛的应用,但因其属于交叉学科,散见于各种研究,没有进行专门的进展评述。本文拟对FB-CVD的工业应用进行专题综述,分析其发展和研究趋势。首先探讨了FB-CVD的基本原理,分别综述了其在颗粒包覆、一维纳米材料、多晶硅制备、颗粒表面改性及粉体制备等方面的应用,介绍了FB-CVD的过程模拟及反应器结构优化方面的研究进展。通过以上讨论,梳理了FB-CVD研究的科学内涵。可以看出,该过程具有明显的多尺度特征,即材料制备的微观层次、颗粒流化均匀性的介观层次以及反应器结构设计的宏观尺度。总结得出:FB-CVD技术的未来发展取决于3个尺度的耦合分析,其研究重点也应关注尺度间的相互影响效应,如材料制备的均相成核、非均相成核和颗粒流化及运动规律的相互耦合等。     

基于流化床化学气相沉积的碳化硅材料制备、性能及其在核领域的应用（英文）

采用流化床化学气相沉积法(FB-CVD)制备了碳化硅包覆层,利用多尺度耦合模型对包覆过程进行了模拟,以提高包覆层的均匀性。开发了可应用在核能领域的碳化硅材料,如致密碳化硅层、细晶粒碳化硅包覆层、碳化硅/碳/硅混合包覆层、多孔碳化硅包覆层、碳化硅纳米线、碳化硅纳米粒子等。为了评估碳化硅包覆层的可靠性,进行了极端条件下的模拟事故氧化考验。对于以碳化硅为主要包覆层的燃料元件,在高通量核反应堆中进行了辐照试验,结果表明:该碳化硅包覆层材料在核应用中的表现优异。     

化学气相沉积法制备碳化硅纤维

一、前言 现代宇航、航空等尖端科学技术的迅速发展,对高比强、高比模、耐高温、抗氧化及易加工的新型材料要求越来越迫切。碳纤维增强金属基复合材料固然有很优异的性能,但需在接近或高于金属熔点的高温下制造,金属与碳纤维之间会发生界面反应,从而产生浸润性差、粘结强度不高及高温抗氧化性能差等问题,导致复合材料性能下降,难以满足高温氧化等苛刻条件的使用要求。     

等离子体化学气相沉积法合成石英玻璃

用高频等离子体作为热源,采用化学气相沉积法合成了石英玻璃样品.实验分别使用02和空气作为等离子体电离气体和冷却保护气体,改变等离子体电离工作气体种类时,等离子体火焰长度和石英玻璃沉积温度变化较大,而灯具冷却保护气体的改变对等离子火焰长度和石英玻璃沉积温度的影响不大.当等离子体电离气体和灯具保护气体均为O2时,等离子体火焰长度为12cm,石英基体温度为1 300℃,当等离子体电离气体和灯具保护气体均为空气时,等离子体火焰长度可达24cm,石英基体温度升高到l 840℃,可确保气相沉积过程进行,合成的石英玻璃在波长190nm处光透过率达84%,羟基含量3.5×10-6,可达到全光谱透过的要求.     

近化学计量比SiC陶瓷纤维先驱体制备方法

近几年来，近化学计量比SiC陶瓷纤维的制备已成为SiC陶瓷纤维领域中的热点．PMS和PSE是制备近化学计量比SiC陶瓷纤维的两种先驱体，其制备是得到近化学计量比SiC陶瓷纤维的关键．因此本文综述了近化学计量比SiC陶瓷先驱体的制备方法，包括脱卤合成、MeSiH3的催化脱氢偶合、H3SiH2SiCH3的脱氢偶合、Bu4PCl催化氯硅烷重分配反应等，同时也简评了国内的发展。     

TiN粉末的制备方法

简要介绍了TiN的性能及主要用途,分析和阐述了TiN粉末制备的研究现状及发展趋势,重点讨论了碳热还原氮化合成TiN粉末存在的问题和前景。     

化学气相沉积工艺制备绳状纳米碳管的研究

用硝酸铁作催化剂,乙炔作碳源气体,高纯氮气作稀释气体,在750℃下化学气相沉积生长了绳状纳米碳管,用高分辨扫描电镜观察了所得绳状纳米碳管的形貌.纳米碳管的直径为100～200nm,长度为10～20 μm.文中还提出了绳状纳米碳管的生长机理.     

化学气相催化热解法制备螺旋纳米碳纤维

采用酒石酸铜前驱体热分解得到纳米铜粒子作为催化剂,分别对250℃、280℃、310℃分解产生的纳米铜粒子进行测试分析,在3个温度下用化学气相沉积法生长螺旋纳米碳纤维并进行综合热分析。采用X-射线衍射(XRD)分析其物相组成,晶粒大小;用扫描电子显微镜(SEM)观察螺旋纳米纤维的外观形貌。结果表明,310℃生长出的螺旋纳米碳纤维纯度高、外观形貌清晰,热分析质量损失少。     

High-speed deposition of silicon nitride thick films via halide laser chemical vapor deposition

Silicon nitride shows significant potential in the field of surface protection for electronic devices owing to its excellent insulation performance and mechanical properties. In this study, silicon nitride films were fabricated via halide laser chemical vapor deposition (LCVD). The effects of deposition parameters on the crystallinity, microstructure, deposition rate (R_dep), Vickers microhardness, nano-hardness and electrical resistivity were investigated. The maximum R_dep of the silicon nitride thick films was 972 µm/h at T_dep of 1573 K and P_tot of 10 kPa, which is the highest value compared with those obtained via conventional CVD. As T_dep increased, the Vickers microhardness and nano-hardness of the films increased to the highest value of 25.1 GPa and 34.8 GPa at 1573 K, respectively. The electrical resistivity of the films decreased with increasing T_dep and showed a maximum value of 1.49 × 10¹⁴ Ω·cm at T_dep of 1273 K.     

Structure of copolymer films created by plasma enhanced chemical vapor deposition

The interface structure in copolymer films made using plasma enhanced chemical vapor deposition (PECVD) has been probed for the first time using X-ray reflectivity. Copolymer films made from comonomers benzene (B), octafluorocyclobutane (OFCB), and hexamethyldisiloxane (HMDS) show extremely sharp interfaces and scattering length density depth profiles that are uniform with depth, making them useful for optical applications. The polymer/air interface has an rms roughness (∼5 Å) that is only slightly larger than that of the supporting substrate (∼3 Å). Addition of either benzene or HMDS as a comonomer in the deposition of OFCB alters a transient deposition behavior at the silicon oxide interface that occurs when using only OFCB. For the B-OFCB copolymer films, a facile control of refractive index with monomer feed composition is achieved. A nonlinear variation in the X-ray scattering length density with composition for the HMDS-OFCB copolymer films is consistent with the nonlinear visible light refractive index (632.8 nm) variation reported earlier.     

Growth of vertically aligned BN nanosheets via Fe-catalyzed thermal chemical vapor deposition

Hexagonal boron nitride nanosheets (BNNSs) demonstrated potential applications for ultraviolet (UV) nanoelectronics, catalytic support, electron field emission, and many other areas. However, their extensive industrial application is limited by the complicated conventional procedures for scalable preparations. In this study, vertically aligned BNNSs were directly synthesized without any substrates using Fe-catalyzed thermal chemical vapor deposition (CVD) method under a NH₃ gas flow at 1200 °C via the catalytic pyrolysis of the inorganic hybrid precursor. BNNSs grew via an Oswald ripening process assisted by oriented attachment mechanism under Fe catalyzed by analyzing the evolution process. Most nanosheets are <10 nm thick, and the number of constituent layers is typically between 10 and 20 nm. BNNSs improved crystallinity, had high UV light emission, and had excellent anti-oxidation behavior because of their unique structures. The development of a simple, high yield and environmentally friendly synthesis method for BNNSs allows for the exploration of industrial upscaling applications.     

Fabrication of SiC/diamond composite coatings by electrophoretic deposition and chemical vapor deposition

In this research, SiC/diamond composite coatings were fabricated by a novel procedure that consisted of the electrophoretic deposition (EPD) of diamond particles onto graphite substrates followed by chemical vapor deposition (CVD) of SiC. Various concentrations of MgCl₂ were employed to increase the deposition rate and uniformity of the deposits during the EPD process by giving a positive charge to diamond particles. The CVD of SiC was found to have a tightly connected diamond‐graphite interface and spherical texture. With higher weight fraction of diamond particles deposits, the wear of steel ball increased, while the wear of SiC coating decreased.     

Effect of catalyst on carbon nanotubes synthesis on titanium diboride via chemical vapor deposition

Carbon nanotubes (CNTs) were in situ synthesized on titanium diboride (TiB₂) substrates using different catalysts (Fe, Co, and Ni) via ethylene chemical vapor deposition (CVD). The effects of various catalysts on the quality and quantity of grown CNTs were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman characterization techniques. Next, as-received powders were sintered by spark plasma sintering to obtain compact bulk composites. The effects of the metallic catalysts as sintering aids on the microstructural and mechanical properties of TiB₂-based composites were also studied. Results show that metal Ni not only plays a significant role in the catalyst to produce larger numbers of CNTs but also promotes the densification of TiB₂ ceramics in sintering and has been shown to provide good reinforcement. Maximum values of flexural strength (1093 ± 19 MPa) and toughness (13.9 ± 0.3 MPa ·m^1/2) were obtained using the Ni catalyst, which were significantly higher than the same values for Fe and Co catalysts.     

High-speed epitaxial growth of SrTiO3 films on MgO substrates by laser chemical vapor deposition

Epitaxial (100) and (111) SrTiO₃ films were prepared on (100) and (111) MgO single-crystal substrates, respectively, using laser chemical vapor deposition. The effect of deposition temperature (T_dep) on the orientation and microstructure of the SrTiO₃ films was investigated. On the (100) MgO substrates, SrTiO₃ films showed a (111) orientation at a low T_dep of 1023 K. (100) SrTiO₃ films, which were epitaxially grown at T_dep=1123–1203 K, had dense cross sections and flat surfaces with rectangular-shaped terraces. On the (111) MgO substrates, (111) SrTiO₃ films were epitaxially grown at T_dep=983–1063 K; however, these films' orientations became random at high T_dep of 1063–1113 K. The (111) SrTiO₃ films consisted of columnar grains with triangular pyramidal caps. The deposition rates of the epitaxial (100) and (111) SrTiO₃ films were 13–25 and 18–32 μm h⁻¹, respectively, which is 5–530 times higher than those obtained by MOCVD.     

化学气相沉积的过程监测

介绍了化学气相沉积(CVD)过程监测的内容。根据CVD过程的特点和薄膜生长的要求,在CVD中需要被实时监测的主要过程参数是温度、化学物种和流体流动。对现有监测方法的原理和优缺点进行分析对比。重点介绍了常用监测方法以及原位实验监测的研究进展。