碳气凝胶薄片的制备及表面密度致密层去除工艺

 研究了不同密度和厚度的碳气凝胶薄片的制备及其表面致密层去除工艺。在以间苯二酚、甲醛为原料制备有机及碳气凝胶块体材料的基础上,结合自制活动式微模具成型工艺,制备了厚度在80~350 μm,密度在50~600 mg·cm^-3范围内变化的碳气凝胶薄片。采用场发射扫描电镜、X射线相衬成像和表面轮廓仪-台阶仪等手段对其表面和内部微观结构进行了表征。测试结果表明,碳气凝胶薄片与块体的内部结构相同,但薄片表面存在一层和内部结构截然不同的致密层。采用不同粗糙程度的材料对薄片进行了表面微处理,成功去除该致密“皮”层。     

密度渐变多层碳气凝胶靶型的制备

 以间苯二酚-甲醛为原料,结合自制活动式微模具成型工艺制备不同厚度和密度的碳气凝胶薄片,采用密度为10 mg·cm^-3的SiO₂溶胶为“粘合剂”,获得单元薄片厚度在100～580 μm,密度在50～400 mg·cm^-3范围内变化的5层密度渐变碳气凝胶靶型。重点研究了该特殊靶型内部C/SiO₂气凝胶层间界面情况。采用场发射扫描电镜（FESEM）,X射线相衬成像仪等对靶型整体结构及碳气凝胶单元薄片表面和内部微观结构进行了表征。结果表明：胶粘层SiO₂气凝胶厚度约为15 μm,厚度一致,远小于碳气凝胶层厚度且与碳气凝胶薄片的胶粘程度较好,界面平整,靶结构均匀。     

ICF分解实验用双介质调制靶的研制

为了研究惯性约束聚变(ICF)实验用靶丸不同密度界面的流体力学不稳定性增长,设计并制备了聚苯乙烯(CH)/碳气凝胶(CRF),CRF/硅气凝胶(SiO2)和CH/Al三种双介质调制靶。采用溶胶-凝胶工艺制备了密度分别为250和800mg/cm3的CRF气凝胶薄片;采用激光微加工工艺分别在两种不同密度的CRF薄片和工业用纯Al箔上引入调制图形;采用旋涂工艺在Al箔和CRF薄片(250mg/cm3)的调制表面制备一层CH薄膜,得到CH/Al和CH/CRF双介质调制靶,采用溶胶-凝胶工艺在CRF薄片(800mg/cm3)表面制备一层低密度SiO2气凝胶,得到CRF/SiO2双介质调制靶。采用电子天平、扫描电子显微镜、工具显微镜和台阶仪对所制备的CH/CRF,CRF/SiO2和CH/Al三种双介质调制靶进行靶参数测量。结果表明:三种双介质调制靶层与层之间结合紧密,界面清晰,调制图形为正弦,靶参数测量准确。     

碳气凝胶/聚苯乙烯双介质柱状靶的研制

 介绍了碳气凝胶/聚苯乙烯（CRF/CH）双介质柱状靶的制备方法。使用溶胶-凝胶法和微模具原位成型法制备了直径为820 μm的间苯二酚-甲醛（RF）气凝胶微柱,在氮气保护下进行高温碳化后得到直径为730 μm、密度为250 mg·cm^-3的CRF微柱;采用浸渍提拉法在CRF微柱柱面镀制一层厚度为26 μm 的CH薄膜, 形成CRF/CH双介质结构;采用机械微切割技术制备了长度为1 mm, 内径为730 μm,壁厚为26 μm的CRF/CH双介质柱状靶。实验研究了RF,CRF气凝胶微柱的制备工艺、微观形貌及CRF微柱轴向和径向的密度均匀性,探讨了影响CH薄膜厚度的主要因素,并对CH薄膜的表面形貌和两种材料之间的界面进行了表征。     

超高比表面积碳气凝胶常压干燥制备与结构分析

以间苯二酚(R)-甲醛(F)为原料,加入表面活性剂P123以增强材料的骨架强度的方法,采用常压干燥技术制备了RF碳气凝胶,并进行了二氧化碳活化以调节其孔结构。扫描电子显微镜(SEM)测试表明,常压干燥的碳气凝胶结构中具有更大的纳米颗粒,骨架结构变粗,活化使碳气凝胶骨架结构更加致密;红外吸收光谱(FTIR)表明,表面活性剂P123中的醚键与RF苯环中的羟基存在强的相互作用,碳化后P123特征峰消失;热重曲线(TG和DTG)分析说明P123在440 ℃左右分解完全,不会对碳气凝胶的成分产生影响,并能起到良好的造孔作用;氮气吸附表明常压干燥制备的碳气凝胶比表面积约为570 m2/g,活化之后的比表面积高达3 500 m2/g左右。     

间苯三酚-甲醛气凝胶及其碳气凝胶的制备与表征

 以间苯三酚(P)和甲醛(F)为原料,经溶胶-凝胶、溶剂交换、超临界干燥和碳化等过程制备出了间苯三酚-甲醛气凝胶(PF)及其碳气凝胶(CPF)。测试结果表明气凝胶具有比较高的比表面积、是一种连续nm级3维网络结构的多孔材料;碳化后密度和平均孔径增大,比表面积基本无变化,且仍然维持气凝胶的网络结构。催化剂摩尔比决定气凝胶的微观结构,反应物质量分数控制着气凝胶密度。通过优化制备条件,可以制备出能满足惯性约束聚变(ICF)靶需要的不同结构和不同密度的气凝胶。     

常压干燥法制备碳气凝胶及其电极性能研究北大核心CSCD

以间苯二酚-甲醛为前驱体,通过加入P123以增强有机气骨架的方法,采用常压干燥技术制备碳气凝胶电极材料,有机凝胶在干燥过程中收缩率极大降低。通过二氧化碳活化法对常压干燥获得的碳气凝胶孔结构进行了调控。研究了不同温度对其结构的影响,获得了最高比表面积达3544m2/g的碳气凝胶。6mol/L的KOH电解液中测试表明,常压干燥碳气凝胶具有稳定的充放电性能,随着活化温度的升高,比容量逐渐增加,最高比电容可达261F/g。常压干燥技术制备的碳气凝胶电极材料在降低生产成本的同时,仍具有理想的电化学性能。     

辐射法制备Pd掺杂碳气凝胶粉末

利用辐射还原法,在100, 200, 500 kGy辐射剂量下制备了金属Pd掺杂的碳气凝胶粉末。X射线衍射（XRD）,扫描电子显微镜（SEM）和能谱测试证实了辐射法成功地制备出Pd掺杂的碳气凝胶粉末复合物。SEM照片表明,还原生成的金属Pd相对均匀地分布在所有碳气凝胶颗粒表面。N2吸附数据分析表明:掺入金属Pd后,碳气凝胶粉末比表面积、平均孔径和总孔体积都显著减小。由于被还原金属大多沉积在碳气凝胶粉末表面,不同辐射剂量下制得的掺杂碳气凝胶粉末的比表面积等多孔特征数据相差不大。     

高密度间苯二酚-甲醛碳气凝胶ICF靶的制备与吸附性能研究

 以间苯二酚和甲醛为前驱体,通过改进传统制备技术解决了高密度间苯二酚-甲醛(CRF)碳气凝胶制备过程中的龟裂问题,制备出了符合ICF实验需要的高密度CRF碳气凝胶材料。分别对CRF碳气凝胶的元素组成和物相组成进行了鉴定,采用自动吸附仪考察了CRF碳气凝胶对N₂和H₂的吸附性能。结果表明：该碳气凝胶是一种由C元素组成的类似石墨结构的非晶固态材料,结构均匀性好,具有良好的机械加工性能,比表面积达676 m²·g^-1,平均孔径为7.16 nm;氢吸附质量分数达2.28%,相应体积密度为17.83 kg·m^-3。     

隔热材料的纳米成型与性能分析

经不同工艺和过程制备二氧化硅气凝胶,初步摸索出制备温度、溶剂、催化剂、反应时间最佳参数.在分析气凝胶干燥开裂的原因后,以三甲基氯硅烷(TMCS)为表面修饰剂,正己烷为干燥介质的表面改性工艺,一定程度控制了气凝胶的干燥收缩和开裂.在室温、常压下的通过不同的改性方案制备出四种不同气凝胶样品,揭示了改性条件、干燥温度对于气凝胶孔隙分布、微观结构的影响.     

Bi-Sr-Ca-Cu-O2212相超导单晶的定向生长

用定向凝固法已成功地生长出Bi-Sr-Ca-O2212相的超导大单晶,最大的单晶尺寸达到19×3×2mm³。定向生长的单晶(001)面平行于生长方向,[100]方向为单晶的定向生长方向。劳厄像表明大晶体确为单晶,其质量比其它方法生长的单晶要高。氧气中退火后的单晶电阻测量和交流磁化率测量表明,零电阻温度T_c(0)=81.5k。 关键词：     

Spectroscopic study of neodymium-doped potassium-lead double chloride Nd3+:KPb2Cl5 crystals

Optical spectra, radiative and nonradiative transition intensities, and luminescence kinetics of neodymium-doped potassium-lead double chloride crystals Nd³⁺:KPb₂Cl₅, (Nd³⁺:KPC) are investigated. Crystals were grown by the Stockbarger-Bridgman technique. Experimental studies of absorption and luminescence spectra are performed, intensity parameters are obtained by the Judd-Ofelt method, radiative transition probabilities and branching ratios are calculated, and nonradiative transition probabilities are estimated. Luminescence kinetics of ² K _13/2, ² P _3/2, and ⁴ D _3/2 radiative levels of neodymium under selective excitation in the 355-nm region are studied.     

Structural,optical, spectroscopic and thermal investigations on novel semi-organic nonlinear optical material - Potassium boro-oxalate single crystal

In this work, a new semi-organic nonlinear optical material of Potassium boro-oxalate (KBO) is synthesized and subsequently a single crystal of size 7 × 5 × 3 mm³ is grown from the aqueous solution by slow evaporation technique at ambient temperature. Characterizations are performed on the single crystals to study the structural, thermal, linear and nonlinear optical (NLO) properties of the as-grown single crystals. Crystal and molecular structure of KBO are solved by direct method and further refinement is performed by full-matrix least-square method employing SHELXL-2014 software. Single crystal X-ray diffraction (SXRD) studies revealed that the grown crystal associates to triclinic crystal family with non-centrosymmetric space group P1. The Fourier transform infrared (FTIR) spectrum reflected the presence of various functional groups in the title compound. The Ultraviolet-visible-near infrared (UV-VIS-NIR) absorption and transmission spectrum are recorded to capture the suitability of the grown single crystals for various optical and NLO applications. The thermal decomposition and thermal stability of the KBO single crystals up to 187°C are investigated by TGA-DTG (Thermo Gravimetric - Differential Thermo Gravimetric), TGA-DTA (Thermo Gravimetric-Differential Thermal analysis) and DSC (Differential Scanning Calorimetry) curves. Kurtz-Perry powder technique is employed to explore the SHG (Second Harmonic Generation) efficiency of the KBO single crystals. SHG efficiency of KBO is found to be comparable to KDP.     

Synthesis,growth and characterization of L-proline dimercuricchloride single crystals for frequency conversion applications

A semi-organic nonlinear optical L-proline dimercuricchloride (LPDMC) material has been synthesized. LPDMC single crystals were grown from aqueous solution by a slow cooling method. Good quality single crystals of size 19×6×3 mm³ have been grown over a period of 3 weeks. The grown crystals have been subjected to single crystal X-ray diffraction analysis to determine the cell parameters. The title compound crystallizes in the triclinic system with a noncentrosymmetric space group P1 and with unit-cell parameters a=7.2742(4) Å, b=9.4472(5) Å, c=10.4767(6) Å, α=108.621(3)^°, β=107.260(2)^°, γ=97.353(2)^° and volume=631.51(6) Å³. Optical and dielectric properties of the crystals have been studied. The thermal stability of the crystals was determined by thermogravimetric analysis/differential thermal analysis. The second harmonic generation efficiency of the crystals was obtained by the classical powder technique using a Nd:YAG laser and it is found to be 2.5 times that of potassium dihydrogen phosphate.     

Modification of structural,optical, thermal and mechanical properties of KDP crystals on the addition of Ni

Nonlinear optical materials are acquiring a new significance day by day with the advent of a large number of devices utilizing solid state laser sources. Owing to this technological application KDP having superior nonlinear optical property has been exploited for various applications. KDP crystals were grown from aqueous solutions added with Ni²⁺. SHG studies confirm that the title exhibits NLO property. The influence of doping Ni²⁺ on the structural, optical, thermal, NLO and mechanical properties has been studied in this present investigation. It is observed that addition of Ni²⁺ improves the optical, thermal and mechanical properties of the crystal.     

Thermal conductivity of <Emphasis Type="Italic">n</Emphasis>-type Ge monocrystals

The pyroelectric method is used to demonstrate the dependence of the thermal conductivity and thermal diffusivity coefficients of n-type germanium monocrystals on the concentration of antimony impurities (6 × 10¹³, 1.3 × 10¹⁴, 1.7 × 10¹⁴, 3.7 × 10¹⁴, 6 × 10¹⁴ cm^?3). The investigated samples are cut from germanium crystals grown from a melt using the Czochralski method with crystallographic orientation [111].     

Spectroscopic Study of Neodymium-Doped Sodium–Yttrium Double Fluoride Nd<Superscript>3+</Superscript>:Na<Subscript>0.4</Subscript>Y<Subscript>0.6</Subscript>F<Subscript>2.2</Subscript> crystals

Nd³⁺:Na_0.4Y_0.6F_2.2 (Nd³⁺:NYF) crystals are grown by the Stockbarger–Bridgman method for a stoichiometric mixture prepared by the solid-phase method and containing neodymium up to 20 at. %. The absorption spectrum of Nd³⁺:NYF crystals exhibits bands located in the emission region of laser diodes. The peak absorption cross section of the 796.8-nm band is σ _a = 0.96 × 10^–20 cm² and the bandwidth is Δλ = 17.5 nm. The most intense luminescence band is located at 1.05 μ m and the radiative time of the ⁴F_3/2 level is τ₀ = τ_exp ~ 960 μ s. It is shown that the ²P_3/2 and ⁴D_3/2 levels of Nd³⁺:NYF crystals are also radiative with lifetimes τ exp equal to ~110 and 9.5 μ s, respectively. However, these radiative transitions are partially quenched due to nonradiative relaxation. The intensity parameters Ω t are determined by the Judd–Ofelt method to be Ω₂ = 1.18 × 10^–20, Ω₄ = 1.55 × 10^–20, and Ω 6 = 2.85 × 10–20 cm 2. Using these parameters, the probabilities of radiative transitions and branching ratios are calculated, and the probabilities of nonradiative transitions are estimated. A conclusion is made that Nd³⁺:NYF crystals are promising as active media for diode-pumped tunable lasers, in particular, up-conversion-pumped lasers.     

Structural, optical and electrical studies on amino acid based new GBC crystals having non linear optical response

Transparent crystals of α-glycine with barium nitrate and calcium nitrate (GBC) have been grown from aqueous solution by slow evaporation technique at room temperature. Crystals of size 22 × 25 × 4 mm³ have been obtained in 3-4 weeks time. The solubility of GBC has been determined in water. The grown crystal belongs to orthorhombic system with cell parameters a = 12.7321 A.U, b = 13.7752 A.U and c = 8.6002 A.U with unit cell volume of 1508.36 (A.U)³. Comparative IR and Raman studies indicate a molecule with a lack of center of symmetry. A wide transparency window useful for optoelectronic applications is indicated by the UV Studies. Using Nd:YAG laser (1064 nm), the optical second harmonic generation (SHG) conversion efficiency of GBC is found to be 0.702 times than that of standard KDP. On exposure to light the GBC crystals exhibit positive photoconductivity. I-V characteristics, dielectrics studies, electrical and Vickers micro hardness measurement have been carried out. The GBC crystal exhibits more mechanical strength compared to the reported GSN crystals.     

Growth, structural and optical studies on amino acid based new GSB crystals having non-linear optical characteristics

Transparent crystals of α-glycine with sodium nitrate and barium nitrate (GSB) have been grown from aqueous solution by slow evaporation technique at room temperature. Crystals of size 11 × 7 × 4 mm³ have been obtained in 3-4 weeks time. The solubility of GSB has been determined in water. The grown crystal belongs to orthorhombic system with cell parameters a = 4.684 a.u., b = 12.184 a.u. and c = 10.969 a.u. with unit cell volume of 625.99 (a.u.)³. Comparative IR and Raman studies indicate a molecule with a lack of centre of symmetry. A wide transparency window useful for optoelectronic applications is indicated by the UV studies. Using Nd-YAG laser (1064 nm), the optical second harmonic generation (SHG) conversion efficiency of GSB is found to be 0.648 times that of standard KDP. On exposure to light the GSB crystals exhibit positive photoconductivity. I-V characteristics, dielectrics studies and Vickers micro hardness measurement have been carried out. The GSB crystal exhibits more mechanical strength compared to the reported GSN crystals.     

Luminescence properties of “relatively” trap-free crystals of anhydrous salts containing divalent manganese

Crystals of RbMnCl₃, Rb₂MnCl₄, CsMnCl₃, RbMnBr₃, CsMnBr₃ and CsMnI₃ which are grown from melts in contact with elemental manganese luminescence strongly throughout the 10K to 300K range. At room temperature the emission intensities from these crystals are larger by orders of magnitude than those observed from crystals of the same salts prepared without metallic manganese. Emission lifetime and intensity measurements made as a function of temperature are consistent with the view that the contact of the molten salt with metallic manganese during crystal growth yields materials which are relatively free of quenching traps. The effect appears to be quite general.