多晶钇铝石榴石纤维的制备工艺研究

采用溶胶-凝胶法制备了钇铝石榴石(YAG)纤维,并研究了YAG溶胶的粘度和纺丝性、红外吸收特征和热分解特性,分析了YAG纤维的物相结构和微观形貌。结果表明:当YAG溶胶的固含量为26%~28%、纺丝温度为20℃时,YAG溶胶纺丝性最佳;YAG溶胶中存在大量的Al—OH和Y—OH基团,二者之间失水可缩聚成大分子链,宏观表现出纺丝性;YAG溶胶热处理中失重主要发生在600℃之前。采用溶胶-凝胶法可获得单一相的YAG纤维;随着煅烧温度的升高、时间的延长,YAG纤维晶粒不断长大,晶粒之间的孔洞也逐渐增多、增大,导致纤维性能下降。     

添加ZrO2对YAG纤维物相和形貌的影响

以氯化铝、金属铝粉、氧化钇、氧氯化锆、醋酸为原料,采用溶胶-凝胶法制备了钇铝石榴石(YAG)纤维,并研究添加ZrO2对YAG纤维的物相和形貌的影响.结果表明,添加ZrO2的YAG纤维物相仍为钇铝石榴石相,纤维表面光滑且直径均匀;ZrO2可作为YAG纤维的增韧相.     

溶胶—凝胶法微晶氧化锆纤维的研究

溶胶—凝胶法制备氧化锆纤维其结构的均与微晶化对使用性能至为重要,近年来,对此研究报道较多。通常以Y_2O_3为稳定剂的Y-PSZ纤维经过一定热处理过程可获得≤0.5 μm晶粒度的微晶结构。 采用溶胶—凝胶法制备氧化锆陶瓷材料,当进行热处理时锆质凝胶无机高分子转化成的无定形ZrO2将逐步晶化。本文对3.6 mol％Y_2O_3-ZrO_2纤维的制备及热处理中晶化现象进行了研究,并初步探讨了晶核剂的加入对晶化的影响。所制Y-PSZ纤维直径5～1μm,1400 ℃处理2h后,晶相为t-ZrO_2。和极少量m-ZrO2,晶粒度均小于0.1 μm。     

在多孔不锈钢表面制备多孔氧化钛膜的研究

利用溶胶凝胶相分离方法成功地在多孔不锈钢表面获得了多孔氧化钛薄膜。对比不同溶胶浓度和干燥抑制剂量对溶胶粘度的影响,对比结果表明,溶胶的浓度对粘度的影响具有决定性的作用,溶胶浓度高会造成后续添加剂加入时粘度升高过快;干燥抑制剂的量不宜超过1.5 g/L,过高的干燥抑制剂量也会造成溶胶粘度的快速增加。用扫描电镜(SEM)和X射线衍射仪(XRD)分别对650℃以上烧结得到的膜层微观结构和相组成进行分析,得到膜层主要成分由金红石型Ti O2组成,另有部分Ti Ox;氧化钛膜层平整、均匀,与基体界面结合良好。用自制的泡点压力测试设备对实验室级别的20 mm样品以及工业化的600 mm样品进行了透气量测试,结果表明两种样品具有相同的透气量,说明该工艺具有良好的稳定性,可用于批量化工业生产。     

加张烧结下连续氧化铝纤维的组织结构演变规律

采用溶胶凝胶干法纺丝-高温烧结的方法制备连续氧化铝纤维,在对前驱体纤维进行预烧结和高温烧结时,利用自行设计搭建的加张烧结装置对纤维施加轴向张力,通过对氧化铝纤维的形貌、成分及组织结构进行表征,并与自由烧结(不加张力)的纤维进行对比,研究张力对烧结过程中氧化铝纤维的热分解、相变、组织结构演变以及性能的影响。结果表明：施加张力可显著提高预烧结纤维和烧结纤维的平直度,促进前驱体纤维中残留物质的分解和脱除;加张烧结可抑制纤维的轴向收缩,加大径向收缩,并促进 γ-Al₂O₃向 α-Al₂O₃转变;加张烧结还能改善纤维的晶粒形貌与孔洞分布,促进晶粒生长与晶间孔洞的收缩脱除,促进纤维致密化。相对于自由烧结,施加 0.9 MPa 轴向张力使得 1 500 ℃烧结 3 min 的氧化铝纤维平均抗拉强度从 0.35 GPa 提高到 1.16 GPa,提高231%。     

气电纺丝法制备硅铝增强氧化铈纳微纤维

通过在聚乙烯吡咯烷酮/硝酸铈(PVP/Ce(NO_3)_3)纺丝液中添加一定比例硅铝溶胶,结合气电纺丝法和高温煅烧工艺成功制备出硅铝增强氧化铈(CeO_2)纳微纤维。采用SEM、XPS、XRD等手段研究了添加比例、电压、风压、煅烧温度等对纤维形貌与结构的影响。结果表明,适量硅铝溶胶的加入,有助于提高PVP/Ce(NO_3)_3纺丝液的粘度;当PVP/Ce(NO_3)_3纺丝液与硅铝溶胶比为6∶1(纺丝液粘度为2.85 Pa·s),纺丝电压为38 kV,风压0.08 MPa时,纺丝效果最佳,制得初生纤维连续、光滑,经高温煅烧后得到纤维材料蓬松、柔软,纤维直径约为1μm~2μm,长度可在10 mm以上;其晶型结构为CeO_2的立方晶系,Si/Al存在一定程度上抑制了CeO_2晶粒的生长,有利于改善纤维的柔韧性。     

温度和晶粒尺寸及分布影响下的氧化铝纤维烧结晶粒长大的相场模拟

采用相场法对溶胶凝胶法制备氧化铝纤维的高温烧结中α-Al_2O_3晶粒的生长进行仿真模拟,并结合实验,研究不同烧结温度和不同初始尺寸的α-Al_2O_3晶粒长大行为及动力学规律。相场模拟和实验结果均表明,在1 200～1 500℃烧结温度范围内,晶粒生长速率随烧结温度升高而明显增大,其中1 400～1 500℃温度区间内晶粒生长速率最快;初始晶粒尺寸越细小,晶粒生长速率越快。模拟结果显示,初始α-Al_2O_3晶粒尺寸不均匀性增加也会促进晶粒长大。     

溶胶黏度、氧化铝含量和旋转盘转速对凝胶纤维直径的影响

采用溶胶凝胶法制备多晶氧化铝纤维,在聚合氯化铝先驱体溶胶中加入5%的硅溶胶和一定的聚乙烯醇及表面活性剂等,真空浓缩制得具有可成纤性的溶胶;在高速旋转盘的离心力作用下甩制成纤维坯体。在固定其他工艺参数的条件下,讨论了在离心力成纤过程中溶胶的黏度、氧化铝含量和旋转盘的转速对凝胶纤维直径的影响。当溶胶内的氧化铝含量在24%左右,黏度为0.2～0.35 Pa.s时,溶胶呈现为牛顿型流体,具有较好的成纤性,制得的纤维坯体细而均匀;而对于黏度为0.35 Pa.s的溶胶,当旋转盘的旋转速率达到300 r/s时,凝胶纤维被再次细化,直径减小至4.4μm。     

微波诱导溶胶-凝胶燃烧法制备YAG:Ce荧光粉

以EDTA为络合剂,采用微波诱导溶胶-凝胶燃烧法制备黄色YAG:Ce荧光粉。研究煅烧温度、EDTA与阳离子的摩尔比、pH值等工艺条件对荧光粉结构和发光性能的影响规律。结果表明:干凝胶分解主要在286.7℃左右,质量损失率达63.85%;干凝胶于900℃煅烧后可以看到明显的YAG晶相峰,1 000℃煅烧后获得分散性好的近球形纯相YAG颗粒,随煅烧温度的升高,荧光粉的结晶度提高,颗粒长大;当EDTA与阳离子的摩尔比为1.0时,荧光粉获得最大的发光强度,并且峰的位置随EDTA浓度的增大发生蓝移;发光强度随pH值的增加先减小后增大,当pH=8.0时,发光强度最大并趋于稳定;YAG:Ce荧光粉的发光强度与粉体颗粒尺寸成正比;以EDTA络合剂,微波诱导使得荧光粉的发光强度提高6.1%,微波诱导溶胶-凝胶燃烧法比溶胶-凝胶法所得荧光粉的发光强度增大56.2%。     

以软模板法从过氧化钛酸制备双晶结构的介孔TiO_2

以TiOSO_4为初始原料、H_2O_2为络合剂制备过氧化钛酸(peroxo-titanic acid,PTA)溶胶;再以PTA溶胶为前驱体、以P123为软模板剂组成水基自组装体系,可以制备一系列具有较高比表面积的锐钛矿-金红石双晶结构介孔二氧化钛(TiO_2).实验采用广角XRD、TEM和HR-TEM等测试对介孔二氧化钛晶体结构进行了表征.结果表明:不同的制备路径、P123的用量、H_2O_2的用量和焙烧温度对介孔TiO_2的双晶结构都有影响.本工作为从过氧化钛酸采用软模板法制备具有可调双晶结构的介孔TiO_2提供了新的依据.     

溶胶-凝胶法制备95多品氧化铝纤维

以结晶氯化铝、铝粉和硅溶胶为主要原料,用溶胶-凝胶法制备95多晶氧化铝纤维.研究了PEG的加入量和胶体黏度对纤维平均直径和单丝拉伸强度的影响,并对不同温度烧成的纤维单丝拉伸强度和比表面积进行了对比.结果表明:当PEG加入质量分数为4%、胶体黏度为30 Pa·s时,纤维平均直径为3.7 μm,且拥有较好的强度;纤维的比表...     

Effect of Additive on Microstructure of Transparent YAG Ceramics

Crystallineyttriumaluminumgarnet (Y3 Al5O12 )isanimportantlasermaterialduetoitssuperioropti calandmechanicalproperties[1,2 ] .NeodymiumdopedYAGisusedwidelyaslaserhostmaterialinvarioussolidstatelasers .SingleYAGcrystalsaregenerallysynthesizedbyCzochralskim…     

Synthesis and characterization of YAG:Ce³⁺ fluorescence powders by co-precipitation method

YAG:Ce3+(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate,yttrium nitrate,cerous nitrate as the starting materials and ammonium carbonate as precipitant.The products were characterized by X-ray powder diffraction,luminescence spectrometer,transmission electron microscope(TEM).The XRD results showed that the obtained YAG:Ce3+ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 oC and the TEM results showed that the grain diameters were about 100 nm.The YAG:Ce3+ fluorescence powders,synthesized by co-precipitation method,had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y3-xCexAl5O12,the calcinations time was 2 h and the calcinations temperature was 1000 °C.     

Sintering of transparent Nd:YAG ceramics in oxygen atmosphere

Yttrium aluminum garnet (YAG) transparent ceramics were fabricated by sintering at oxygen atmosphere. Tetraethyl orthosilicate (TEOS) was added as the sintering additive to control the grain growth and densification. Pores were eliminated clearly at temperature lower than 1700oC, while grain size was around 3 μm. The in-line transmittance was 80% at 1064 nm when samples were sintered at 1710oC. The effect of TEOS was studied in oxygen atmosphere sintering for Nd:YAG transparent ceramics. At higher temperature like 1710oC, the grain growth mechanism was solute drag, while at 1630 and 1550 oC the grain growth was controlled by liquid phase sintering mechanism. And 0.5 wt.% TEOS was the best adding content for Nd:YAG sintered in oxygen atmosphere.     

Synthesis of monodispersed nanometer-sized YAG powders by a modified coprecipitation method

Nanometer-sized yttrium aluminum garnet （YAG） powders were synthesized by using the coprecipitation method with ammo- nium hydrogen carbonate as a precipitant. The results indicated that an extremely loose YAG precursor was obtained when iodine was intro- duced in the coprecipitation process on the condition that the initial concentrations of Y^3＋ and Al^3＋ in the solution were set at 0.018 and 0.03 mol/L, respectively, and pH=8. Consequently, the resulting YAG powders after calcination at 1173 K for 2 h were composed of monodispersed particles with an average grain size of 30 nm and better sinterability. The present results indicated that the modified coprecipitation method, with iodine as an additive, was superior to the conventional coprecipitation method, to synthesize ultrafine YAG powders.     

Effects of various laser types and beam transmission methods on female organ tissue in the pig: an in vitro study

The purpose of this in vitro study was to investigate and compare effects of various laser types (CO2, Argon, Erbium:YAG, Erbium:YSGG, and Holmium:YAG) and laser beam transmission methods (optical lens and flexible fiber) on ovarian and uterine tissue of the pig. The Erbium laser radiation was transmitted through Zirconium fluoride fibers (ZrF4). To circumvent the low mechanical stability of these fibers, we developed a special microlens system, which refocuses the radiation and protects the distal end from damage. Tissue lesions were performed with 1 and 5 joule. Histologic analysis of acute Er:YAG laser lesions reveal precise cutting effects with a minimal thermal damage zone of 40 microns and a high damage resistance of the fiber microlens systems. The extent of thermal damage caused by the Erbium:YSGG and CO2 laser is about two times larger, whereas the Argon and Holmium laser tissue lesions show a damage of the surrounding tissue of 200-300 microns. This study suggests that for precise cutting and coagulation, Erbium and Holmium lasers transmitted via our modified fiber tip may render the use of these lasers possible in a wide range of laparoscopic surgery applications.     

Ballistic Impact of Braided Composites with a Soft Projectile

Impact tests using a soft gelatin projectile were performed to identify failure modes that occur at high strain energy density during impact loading. Failure modes were identified for aluminum plates and for composites plates and half-rings made from triaxial carbon fiber braid having a 0/±60° architecture. For aluminum plates, a large hole formed as a result of crack propagation from the initiation site at the center of the plate. For composite plates, fiber tensile failure occurred in the back ply at the center of the plate. Cracks then propagated from this site along the ±60° fiber directions until triangular flaps opened to form a hole. For composite half-rings fabricated with 0° fibers aligned circumferentially, fiber tensile failure also occurred in the back ply. Cracks first propagated from this site perpendicular the 0° fibers. The cracks then turned to follow the ±60° fibers and 0° fibers until rectangular flaps opened to form a hole. Damage in the composites was localized near the impact site, while cracks in the aluminum extended to the boundaries.     

Mechanical property and fracture behavior of squeeze-cast Mg matrix composites

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-casting technique, with variations in the reinforcement material and applied pressure. Microstructural and fractographic observations, along with in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process. Two of them are reinforced with two different short fibers and the other is a whisker-reinforced composite. From the in situ fracture observation of Kaowool-reinforced composites, the effect of the applied pressure on mechanical properties is explained using a competing mechanism: the detrimental effects of fiber breakage act to impair the beneficial effects of the grain refinement and improved densification as the applied pressure increases. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at considerably higher stress intensity factor levels, while the degradation of fibers was not observed even in the case of the highest applied pressure. This finding indicates that the higher applied pressure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropriate applied pressure in the short fiber-reinforced composites, their mechanical properties were far below those of conventional A1 matrix composites. In this regard, the Alborex aluminum borate whisker is suggested as a replacement for the short fibers used in the present investigation, to achieve better mechanical properties and fracture toughness.     

Synthesis and characterization of YAG: Ce3+ fluorescence powders by co-precipitation method

YAG:Ce³⁺(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate, yttrium nitrate, cerous nitrate as the starting materials and ammonium carbonate as precipitant. The products were characterized by X-ray powder diffraction, luminescence spectrometer, transmission electron microscope (TEM). The XRD results showed that the obtained YAG:Ce³⁺ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 °C and the TEM results showed that the grain diameters were about 100 nm. The YAG:Ce³⁺ fluorescence powders, synthesized by co-precipitation method, had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y_3-xCe_xAl₅O₁₂, the calcinations time was 2 h and the calcinations temperature was 1000 °C.