Huang Zhengren

Effect of Density and Surface Roughness on Optical Properties of Silicon Carbide Optical Components

The effect of density and surface roughness on the optical properties of silicon carbide optical components is investigated. The density is the major factor of the total reflectance while the surface roughness is the major factor of the diffuse reflectance. The specular reflectance of silicon carbide optical components can be improved by increasing the density and decreasing the surface roughness, in the form of reducing bulk absorption and surface-related scattering, respectively. The contribution of the surface roughness to the specular reflectance is much greater than that of the density. When the rms surface roughness decreases to 2.228 nm, the specular reflectance decreases to less than 0.7% accordingly.

Microstructure and Thermal Shock Resistance of ZrB 2 and ZrB 2 -20vol% SiC Composites from Aqueous Tape Casting: Microstructure and Thermal Shock Resistance of ZrB 2 and ZrB 2 -20vol% SiC Composites from Aqueous Tape Casting

The microstructure and thermal shock resistance of ZrB2 and ZrB2-20vol% SiC (ZS20) composites prepared by aqueous tape casting and hot-pressing were investigated. Zr-B-C and Zr-B-W solid solution phases were formed in ZS20 composites, but not formed in ZrB2 samples. The diffraction peaks for ZrB2 of ZS20 composites shifted to higher 2 theta values possibly due to the formation of solid solution phases which resulted in a decrease in lattice parameters. The critical thermal shock values for ZrB2 and ZS20 were measured to be 298 degrees C and 306 degrees C respectively using water quench tests. The thermal shock resistance of ZrB2 and ZS20 were also calculated and compared with the experimental data. The results revealed that the measured thermal shock resistance of ZS20 composites was lower than the calculated ones, which might be due to the thermal residual stress in the samples resulted from the difference in thermal expansion coefficient of ZrB2 matrix and SiC second phase as well as the solid solutions phases.

Facile Synthesis of Au/Pd Nano-dumbells for Catalytic Reduction of p-Nitrophenol

Au nanorods (Au NRs) with good monodispersity and uniform aspect ratio were prepared via seed-meditated method. Au/Pd nano-dumbbells (Au/Pd NDs) were synthesized by using H2PdCl4\ as precursor, hexadecyl trimethyl ammonium chloride (CTAC) as soft template, Ag+ as structure-directing agent and ascorbic acid as reduction agent to modify Au NRs. Structure and morphology of the samples were characterized by transmission electron microscope (TEM), energy dispersive spectrometer (EDS) and ultraviolet-visible-near infrared spectrophotometry (UV-Vis-NIR). The formation mechanism of Au/Pd NDs were discussed. The results of Au/Pd NDs samples demonstrated that lots of poly-crystalline Pd particles were deposited onto two ends of Au nanorods selectively to form dumbbell-like structure. The dumbbell size can be continuously tuned by adjusting the molar ratio of AA and H2PdCl4. The experiments of reduction of p-nitrophenol by NaBH4 to p-aminophenol indicate that the sample with good dispersibility and large number of total catalytic active sites of Pd nanoparticles has high catalytic performance. Adding 0.04 mg/mL Au/Pd NDs with suitable Pd particles size (20.7 nm) show excellent catalytic activity (rate constant 0.44 min(-1)), indicating it is useful for reducing p-nitrophenol.

水基浆料涂覆结合原位反应制备C f /SiC复合材料表面光学涂层

A novel surface modification method for C-f/SiC composites is proposed with aqueous slurry painting together with reaction bonding. Stable slurries were obtained by dispersing SiC to carbon black in aqueous solution, under centain binder content and solid loading conditions. The results show that porous carbonaceous C/SiC tape with porosity of 49% could be obtained by aqueous slurry painting. Si/SiC coating with high density and strong bonding onto the substrate is realized by infiltrating liquid silicon into the as-prepared tape. A reaction layer of similar to 15 um in thickness is formed between the coating and the substrate. This Si/SiC coating exhibits excellent mechanical properties, with HV hardness of (14.19 +/- 0.46) GPa and fracture toughness of (3.02 +/- 0.30) MPa.m(1/2). The coating is achieved fine surface of 2.97 nm RMS in roughness after precision grinding and polishing.本研究提出一种C f /SiC复合材料表面改性新方法为水基浆料涂覆结合原位反应烧结工艺。系统研究了SiC和炭黑在水基浆料中的共分散、粘结剂的量和浆料固含量对浆料流变性能的影响、涂层的微观结构和性能等。研究结果表明: 采用水基浆料涂覆工艺可在基材表面制备一层气孔率达49%的多孔C/SiC预涂层; 通过液相渗硅原位反应工艺, 多孔预涂层转变为高致密、与基材强结合的光学涂层, 并且在涂层与基材间形成了~ 15 μm的化学反应过渡层; Si/SiC涂层的维氏硬度为(14.19 ± 0.46) GPa, 断裂韧性为(3.02 ± 0.30) MPa·m 1/2 ; 经过精细研磨抛光, 涂层的表面粗糙度可达2.97 nm RMS。

Optical Coating on C

A novel surface modification method for C-f/SiC composites is proposed with aqueous slurry painting together with reaction bonding. Stable slurries were obtained by dispersing SiC to carbon black in aqueous solution, under centain binder content and solid loading conditions. The results show that porous carbonaceous C/SiC tape with porosity of 49% could be obtained by aqueous slurry painting. Si/SiC coating with high density and strong bonding onto the substrate is realized by infiltrating liquid silicon into the as-prepared tape. A reaction layer of similar to 15 um in thickness is formed between the coating and the substrate. This Si/SiC coating exhibits excellent mechanical properties, with HV hardness of (14.19 +/- 0.46) GPa and fracture toughness of (3.02 +/- 0.30) MPa.m(1/2). The coating is achieved fine surface of 2.97 nm RMS in roughness after precision grinding and polishing.本研究提出一种C f /SiC复合材料表面改性新方法为水基浆料涂覆结合原位反应烧结工艺。系统研究了SiC和炭黑在水基浆料中的共分散、粘结剂的量和浆料固含量对浆料流变性能的影响、涂层的微观结构和性能等。研究结果表明: 采用水基浆料涂覆工艺可在基材表面制备一层气孔率达49%的多孔C/SiC预涂层; 通过液相渗硅原位反应工艺, 多孔预涂层转变为高致密、与基材强结合的光学涂层, 并且在涂层与基材间形成了~ 15 μm的化学反应过渡层; Si/SiC涂层的维氏硬度为(14.19 ± 0.46) GPa, 断裂韧性为(3.02 ± 0.30) MPa·m 1/2 ; 经过精细研磨抛光, 涂层的表面粗糙度可达2.97 nm RMS。

lt;inf

采用碳热还原氮化法合成了Eu 2+ /Tb 3+ 掺杂的Sr 2 Si 5 N 8 基荧光粉, 并重点研究了Tb 3+ -Eu 2+ 共掺时Sr 2 Si 5 N 8 基荧光粉的发光性能。研究结果表明: 由于Tb 3+ 的f → d间的跃迁是自旋允许的, Sr 2 Si 5 N 8 :Tb 3+ 在330 nm激发光下, 在490、543、585和623 nm四处各有一发射峰, 它们分别来源于Tb 3+ 的 5 D 4 → 7 F j ( j = 6、5、4、3)能级跃迁; 掺入Tb 3+ 对Sr 1.96 Si 5 N 8 :0.04Eu 2+ 的激发谱和发射谱的形状及峰位无明显影响, 当共掺离子Tb 3+ 浓度为 x = 0.01时, 样品发射强度比未共掺的Sr1.96Si5N8:0.04Eu2+提高了约20%, Tb 3+ 主要通过电多极能量传递的方式转向Eu 2+ 。

gt;f

采用碳热还原氮化法合成了Eu 2+ /Tb 3+ 掺杂的Sr 2 Si 5 N 8 基荧光粉, 并重点研究了Tb 3+ -Eu 2+ 共掺时Sr 2 Si 5 N 8 基荧光粉的发光性能。研究结果表明: 由于Tb 3+ 的f → d间的跃迁是自旋允许的, Sr 2 Si 5 N 8 :Tb 3+ 在330 nm激发光下, 在490、543、585和623 nm四处各有一发射峰, 它们分别来源于Tb 3+ 的 5 D 4 → 7 F j ( j = 6、5、4、3)能级跃迁; 掺入Tb 3+ 对Sr 1.96 Si 5 N 8 :0.04Eu 2+ 的激发谱和发射谱的形状及峰位无明显影响, 当共掺离子Tb 3+ 浓度为 x = 0.01时, 样品发射强度比未共掺的Sr1.96Si5N8:0.04Eu2+提高了约20%, Tb 3+ 主要通过电多极能量传递的方式转向Eu 2+ 。

lt;/inf

以Sr2CO3、Si3N4和Eu2O3为原料,以C为主要还原剂,采用碳热还原氮化工艺合成Sr2Si5N8：Eu2＋荧光粉,着重研究了C、Sr2CO3添加量及Eu2＋浓度对产物物相及发光性能的影响。研究结果表明：当C与Si3N4的摩尔比nc/3 4Si Nn=9/5时,合成出Sr2Si5N8：Eu2＋单相荧光粉,添加适当过量的Sr2CO3可提高合成产物的N含量,且荧光粉的发光强度与其N含量呈现正相关关系。在450 nm蓝光激发下,受Eu2＋的4f^6 5d^1→4f^7跃迁作用,Sr2Si5N8：Eu2＋荧光粉在550~700 nm波段范围产生非对称宽带发射。随着Eu2＋掺杂浓度由1.5mol%增加到20mol%,荧光粉的发光强度先增强后减弱,达到2mol%时发生浓度淬灭现象;发射主峰由608 nm逐步红移至641 nm;CIE色坐标从（0.606,0.393）位移至（0.656,0.343）,是一种可用于白光LED的优质红色荧光粉。以Sr 2 CO 3 、Si 3 N 4 和Eu 2 O 3 为原料, 以C为主要还原剂, 采用碳热还原氮化工艺合成Sr 2 Si 5 N 8 :Eu 2+ 荧光粉, 着重研究了C、Sr 2 CO 3 添加量及Eu 2+ 浓度对产物物相及发光性能的影响。研究结果表明: 当C与Si 3 N 4 的摩尔比 n c / n Si 3 N 4 =9/5时,合成出Sr 2 Si 5 N 8 :Eu 2+ 单相荧光粉, 添加适当过量的Sr2CO3可提高合成产物的N含量, 且荧光粉的发光强度与其N含量呈现正相关关系。在450 nm蓝光激发下, 受Eu 2+ 的4f 6 5d 1 → 4f 7 跃迁作用, Sr 2 Si 5 N 8 :Eu 2+ 荧光粉在550~700 nm波段范围产生非对称宽带发射。随着Eu 2+ 掺杂浓度由1.5mol%增加到20mol%, 荧光粉的发光强度先增强后减弱, 达到2mol%时发生浓度淬灭现象; 发射主峰由608 nm逐步红移至641 nm; CIE色坐标从(0.606, 0.393)位移至(0.656, 0.343), 是一种可用于白光LED的优质红色荧光粉。以Sr 2 CO 3 、Si 3 N 4 和Eu 2 O 3 为原料, 以C为主要还原剂, 采用碳热还原氮化工艺合成Sr 2 Si 5 N 8 :Eu 2+ 荧光粉, 着重研究了C、Sr 2 CO 3 添加量及Eu 2+ 浓度对产物物相及发光性能的影响。研究结果表明: 当C与Si 3 N 4 的摩尔比 n c / n Si 3 N 4 =9/5时,合成出Sr 2 Si 5 N 8 :Eu 2+ 单相荧光粉, 添加适当过量的Sr2CO3可提高合成产物的N含量, 且荧光粉的发光强度与其N含量呈现正相关关系。在450 nm蓝光激发下, 受Eu 2+ 的4f 6 5d 1 → 4f 7 跃迁作用, Sr 2 Si 5 N 8 :Eu 2+ 荧光粉在550~700 nm波段范围产生非对称宽带发射。随着Eu 2+ 掺杂浓度由1.5mol%增加到20mol%, 荧光粉的发光强度先增强后减弱, 达到2mol%时发生浓度淬灭现象; 发射主峰由608 nm逐步红移至641 nm; CIE色坐标从(0.606, 0.393)位移至(0.656, 0.343), 是一种可用于白光LED的优质红色荧光粉。

gt;/SiC Composites via Aqueous Slurry Painting and Reaction Bonding

以Sr2CO3、Si3N4和Eu2O3为原料,以C为主要还原剂,采用碳热还原氮化工艺合成Sr2Si5N8：Eu2＋荧光粉,着重研究了C、Sr2CO3添加量及Eu2＋浓度对产物物相及发光性能的影响。研究结果表明：当C与Si3N4的摩尔比nc/3 4Si Nn=9/5时,合成出Sr2Si5N8：Eu2＋单相荧光粉,添加适当过量的Sr2CO3可提高合成产物的N含量,且荧光粉的发光强度与其N含量呈现正相关关系。在450 nm蓝光激发下,受Eu2＋的4f^6 5d^1→4f^7跃迁作用,Sr2Si5N8：Eu2＋荧光粉在550~700 nm波段范围产生非对称宽带发射。随着Eu2＋掺杂浓度由1.5mol%增加到20mol%,荧光粉的发光强度先增强后减弱,达到2mol%时发生浓度淬灭现象;发射主峰由608 nm逐步红移至641 nm;CIE色坐标从（0.606,0.393）位移至（0.656,0.343）,是一种可用于白光LED的优质红色荧光粉。以Sr 2 CO 3 、Si 3 N 4 和Eu 2 O 3 为原料, 以C为主要还原剂, 采用碳热还原氮化工艺合成Sr 2 Si 5 N 8 :Eu 2+ 荧光粉, 着重研究了C、Sr 2 CO 3 添加量及Eu 2+ 浓度对产物物相及发光性能的影响。研究结果表明: 当C与Si 3 N 4 的摩尔比 n c / n Si 3 N 4 =9/5时,合成出Sr 2 Si 5 N 8 :Eu 2+ 单相荧光粉, 添加适当过量的Sr2CO3可提高合成产物的N含量, 且荧光粉的发光强度与其N含量呈现正相关关系。在450 nm蓝光激发下, 受Eu 2+ 的4f 6 5d 1 → 4f 7 跃迁作用, Sr 2 Si 5 N 8 :Eu 2+ 荧光粉在550~700 nm波段范围产生非对称宽带发射。随着Eu 2+ 掺杂浓度由1.5mol%增加到20mol%, 荧光粉的发光强度先增强后减弱, 达到2mol%时发生浓度淬灭现象; 发射主峰由608 nm逐步红移至641 nm; CIE色坐标从(0.606, 0.393)位移至(0.656, 0.343), 是一种可用于白光LED的优质红色荧光粉。以Sr 2 CO 3 、Si 3 N 4 和Eu 2 O 3 为原料, 以C为主要还原剂, 采用碳热还原氮化工艺合成Sr 2 Si 5 N 8 :Eu 2+ 荧光粉, 着重研究了C、Sr 2 CO 3 添加量及Eu 2+ 浓度对产物物相及发光性能的影响。研究结果表明: 当C与Si 3 N 4 的摩尔比 n c / n Si 3 N 4 =9/5时,合成出Sr 2 Si 5 N 8 :Eu 2+ 单相荧光粉, 添加适当过量的Sr2CO3可提高合成产物的N含量, 且荧光粉的发光强度与其N含量呈现正相关关系。在450 nm蓝光激发下, 受Eu 2+ 的4f 6 5d 1 → 4f 7 跃迁作用, Sr 2 Si 5 N 8 :Eu 2+ 荧光粉在550~700 nm波段范围产生非对称宽带发射。随着Eu 2+ 掺杂浓度由1.5mol%增加到20mol%, 荧光粉的发光强度先增强后减弱, 达到2mol%时发生浓度淬灭现象; 发射主峰由608 nm逐步红移至641 nm; CIE色坐标从(0.606, 0.393)位移至(0.656, 0.343), 是一种可用于白光LED的优质红色荧光粉。

Eu 2+ /Tb 3+ 掺杂的Sr 2 Si 5 N 8 基荧光粉的制备与发光性能

为制备高性能SiC-ZrB 2 网眼多孔陶瓷, 对SiC-ZrB 2 复合浆料的流动性质进行了初步研究。分析SiC和ZrB 2 粉体在水溶液中的流动性质, 并对分散剂硅溶胶和粘结剂羧甲基纤维素(CMC)的添加量进行了优化。基于以上优化结果, 重点探索了固含量和ZrB 2 添加量对浆料流动性质的影响。固含量为65wt%的浆料可作为有机泡沫浸渍过程的最佳条件, 而ZrB 2 添加量不可超过25wt%。