Synthesis and morphological control of europium doped cadmium sulphide nanocrystals

Europium doped cadmium sulphide (Cd(0.98)Eu(0.2)S) nanostructures were synthesised by chemical co-precipitation method using ethylene glycol (EG) and deionized water (Eu:CdS-1), and isopropyl alcohol (IPA) and deionized water (Eu:CdS-2) as mixed solvents. It has been found that the nanostructure of the europium doped CdS can be controlled by simply varying the mixed solvent system. Powder XRD pattern reveals the formation of hexagonal (wurtzite) and cubic (zinc blende) structure for Eu:CdS-1, and Eu:CdS-2, respectively. The crystallite size of the sample prepared using IPA and deionized water was measured to be 2.64 nm which is much smaller than that of the sample prepared using EG and deionized water as mixed solvent (3.65 nm). Morphology of the materials can also be changed from flower shaped crystals to paddy like structures by varying the mixed solvents. Band gap values of Eu3+ doped CdS nanocrystals synthesized from two different solvents were estimated using UV-reflectance spectra. The size and crystallinity of the samples were confirmed by HRTEM and SAED analysis. A significant change in the PL emission of the CdS nanocrystals was observed for the europium doped CdS which is mainly due to the presence of EU3+ ions which also play a significant role in the energy transfer process. It was also observed that the shift in the emission and efficiency depends on size and shape of the synthesised nanoparticles.     

Photothermal Characterization of Nanocomposites Based on High Density Polyethylene (HDPE) Filled with Expanded Graphite

The effective thermophysical and optical properties of high density polyethylene (HDPE) filled with 50???m and 5???m particle sizes of expanded graphite (EG50, EG5) are characterized. The methods used were front- and back-detection modulated photothermal radiometry (FD-, BD-PTR) and BD-flash IR thermography. Results were interpreted according to one-dimensional heat diffusion models. The absolute thermal diffusivity was determined at low frequency from FD- and BD-PTR spectra, while the volumetric heat capacity, the thermal effusivity, and the optical absorption coefficient were determined from broad-band FD-PTR spectra. The directly obtained diffusivity values compare well with those calculated from the heat capacity and thermal effusivity, and with BD-flash results. The errors caused by the finite absorption coefficient of diluted samples are also evaluated and corrected for. A particle-size effect with the opposite influence on thermal and optical properties has been observed. Heat transport parameters of HDPE/EG composites are significantly enhanced (factor of 3 to 4 in thermal diffusivity) at low particle charge before reaching saturation above a 0.10 particle volume fraction. These features are explained in the framework of effective medium models by strongly non-spherical EG particles.     

Preparation and properties of electrically conductive PPS/expanded graphite nanocomposites

Nanocomposites based on poly (phenylene sulfide) (PPS) and expanded graphite (EG) or ultrasonicated EG (S-EG) were prepared by melt blending. Morphologies of the nanocomposites were examined using both SEM and TEM. Electrical conductivity and thermal stability of PPS were notably enhanced by the introduction of EG. The percolation threshold values are 1 wt% (S-EG) and 2 wt% (EG) for PPS/S-EG and PPS/EG nanocomposites, respectively. The variation of mechanical strength with the weight fraction of EG and S-EG in the nanocomposites showed somewhat correlation with the threshold filler concentration. The crystallization behavior of PPS matrix in the nanocomposites was investigated using DSC, and the results indicated that the crystallization process was significantly accelerated, leading to an increase in crystallinity.     

Energy transfer and thermal studies of Pr3+ doped cerium oxalate crystals

Energy transfer process at room temperature for cerium (sensitizer) oxalate single crystals doped with different concentrations (10, 13, 15, 17 and 20%) of praseodymium ions (activator) grown by hydro silica gel method has been evaluated. The analysis of energy level diagrams of cerium and praseodymium ions indicates that the energy gap between the sensitizer and the activator ions varies in a small range suggesting a possible energy transfer from the Ce³⁺ to Pr³⁺. The emission and absorption spectra of these crystals were recorded. The overlapping of the absorption spectra of Pr³⁺ and emission spectra of Ce³⁺ at wavelengths 484 and 478 nm, respectively, strongly supports the possible energy transfer process in this system. From the absorption spectra, oscillator strength, electric dipole moment, branching ratio and Judd-Ofelt parameters of this system were evaluated by least square programming. The quantum efficiency, energy transfer probabilities and thermal properties have been studied.     

Comparison of fluorescence spectra of Yb:Y3Al5O12 and Yb:YAlO3 single crystals

Yb:Y₃Al₅O₁₂ (Yb:YAG) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 25 at.%, 50 at.%, 100 at.% and Yb:YAlO₃ (Yb:YAP) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 30 at.% were grown by the Czochralski process. The fluorescence spectra of these crystals and the effects of self-absorption on the shape of the fluorescence spectra were studied. Through comparing the fluorescence spectra of Yb:YAG and Yb:YAP, all results indicate that the effects of self-absorption on the fluorescence spectra of Yb:YAP are remarkably stronger than that of Yb:YAG at the same Yb concentration.     

多元醇方法制备SnO2包覆碳纳米管复合材料

本文采用SnC2O4.2H2O为Sn源和乙二醇(ethylene glycol,EG)为反应介质的多元醇法,制备得到SnO2包覆多壁碳纳米管复合材料(SnO2/MWNTs),其中SnO2是通过EG中溶解的O2氧化Sn2+反应生成的.没有加入MWNTs的情况下,SnC2O4.2H2O的水解反应生成Sn6O4(OH)4,SnC2O4.2H2O与EG之间的聚合反应生成聚羟基乙酸锡,由于水解反应降低了EG中Sn2+的浓度,使得聚羟基乙酸锡产量较低.加入MWNTs后,仅有少量聚羟基乙酸锡生成,且没有Sn6O4(OH)4生成,主要产物为包覆在MWNTs表面的SnO2.这是由于SnO2在EG中的溶解度极低,随O2氧化Sn2+反应进行,EG中的Sn2+浓度不断降低,Sn6O4(OH)4的溶解结晶平衡不断向溶解的方向进行,并最终转化为SnO2.以上对多元醇法制备SnO2/MWNTs合成机理的理解,将有助于采用类似的方法设计合理条件制备得到其他种类金属氧化物包覆碳纳米管的复合材料.     

Production of graphene layer by liquid-phase exfoliation with low sonication power and sonication time from synthesized expanded graphite

Multi-layer graphene was produced through synthesized expanded graphite (EG) liquid exfoliation using organic solvent. Hexagonal graphite (HG) was used as a starting material. HG was mixed with an acidic mixture, dried, rand subjected to thermal treatment. After this process, EG was obtained. This obtained EG was sonicated for 1 h via an ultrasonic homogenizer by blending an organic solvent. Samples were subjected to SEM, TEM, FTIR, and UV-Vis/NIR spectroscopy investigations. After the investigations, it was shown that nano-size graphene sheets were obtained.     

Electrical and mechanical properties of expanded graphite/high density polyethylene nanocomposites

High density polyethylene (HDPE) were filled with expanded graphite particles that have different particle sizes, 5–7 μm (EG5) and 40–55 μm (EG50) in diameter. Nanocomposites were prepared by the melt-mixing technique using EG5 and EG50 at different weight ratios. Transmission Electron Microscopy (TEM) was used to observe the morphology of the nanocomposites. X-ray diffraction patterns of EG5-HDPE and EG50-HDPE nanocomposites were investigated. Tensile tests were carried out to determine tensile strength, Young’s modulus and elongation at break values. The storage modulus and loss modulus were evaluated by Dynamic Mechanical Analysis (DMA). The effect of EG5 and EG50 on electrical conductivity of HDPE was also determined. The tensile strength of HDPE increased 18.7% and 8.5% when 40 wt% EG5 and EG50 was added into HDPE, respectively. The storage modulus of EG5-HDPE and EG50-HDPE is higher compared to that of HDPE. Incorporation of EG5 and EG10 into HDPE also increased the relaxation transition peak of HDPE. The values of electrical conductivity for EG50-HDPE nanocomposites under the same filler content obtained higher in comparison with those for EG5-HDPE nanocomposites.     

Dispersion of nanoplatelets of graphite on PMMA matrix by in situ polymerisation technique

Poly(methyl methacrylate)/expanded graphite (PMMA/EG) composites were prepared by the incorporation of EG in various proportions (1%, 2%, 3%, 4% and 5%) with PMMA by in situ polymerisation technique. The polymer composites were characterised by ultraviolet–visible (UV–vis) and Fourier transform infra-red spectroscopies. The structural property of PMMA/EG nanocomposites was studied by X-ray diffraction. The scanning electron microscopy and transmission electron microscopy of synthesised composites were taken in order to study their morphological properties. The conductivity of composites was measured as function of EG concentration. It was found that conductivity of composites gradually increased with the increase in EG loading. Oxygen permeability of PMMA/EG nanocomposites was calculated and it was found that the property was reduced substantially with rise of EG proportion. The thermal stability of PMMA/EG nanocomposites was improved by dispersion of EG with PMMA matrix.     

Unidirectional growth of pure and L-lysine added ADP crystals from aqueous solution

Pure and L-lysine added ammonium dihydrogen phosphate (ADP) crystals were grown in the 〈001〉 direction by Sankaranarayanan-Ramasamy (S-R) method. The grown crystals were characterized by X-Ray diffractometry (XRD), UV-Vis spectroscopy, Fourier Transform Infrared (FT-IR) and Vicker’s Microhardness analysis. XRD spectrum of each of the grown crystals proved its crystallinity. The crystals showed good transparency in the entire visible region. FT-IR spectra of the specimens revealed the presence of functional groups in them. The hardness of the pure and L-lysine added ADP crystals were measured and that of the added one was found higher. Meanwhile, it was found that the ADP crystals (pure and L-lysine added) grown by S-R method had higher hardness compared to ADP crystal grown by conventional method.     

氘代聚苯乙烯胶体晶体的制备及光学性质研究

以水作为介质合成了高度单分散的氘代聚苯乙烯微球,并利用垂直沉积法制备了高质量的氘代聚苯乙烯胶体晶体.傅立叶变换红外光谱清楚地表明氘代苯乙烯单体发生了聚合反应;扫描电镜表面分析展示出胶体微球的高度有序排列,断面分析表明氘代聚苯乙烯胶体晶体为面心立方结构;光学透射谱显示出氘代聚苯乙烯胶体晶体的高次布拉格衍射特征,通过和理论计算的能带结构对比,进一步证实了氘代聚苯乙烯胶体晶体为面心立方结构;变角度光学透射谱测量显示,随着入射角的增大,(111)面的衍射峰蓝移,而(200)和(220)面的衍射峰发生红移.     

Mn^5＋：Ba3（VO4）2可调谐激光晶体的生长

报导了用中频感应引上法生长Ｍｎ＾５＋；Ｂａ３（ＶＯ４）２晶体的实验呼结果，晶体主要解理面为（０００１）面，常见缺陷是沿生长中心轴的散射颗粒“芯”，指出了生长高质量高浓度Ｍｎ＾５＋：Ｂａ３（ＶＯ４）２单晶的有效途径、优质尺寸大于直径３０ｍｍ×４５ｍｍ测定了该晶体的吸收光谱和荧光光谱。     

聚对二甲苯 /SiO2复合薄膜的制备及光学性能研究

聚对二甲苯是一种可应用于光学器件和晶体保护的新型高分子材料。采用真空化学气相沉积法制备聚对二甲苯薄膜,并通过提拉镀膜法在其表面镀制一层SiO2增透膜,可提高薄膜的透射率至90％以上。用FT-IR、紫外一近红外分光光度计和XPS对聚对二甲苯／SiO2复合薄膜结构和光学性能进行了表征和测试,并初步研究了薄膜受紫外光辐照而产生光氧化现象的机理。     

Chemical effects of DCCA to the sol-gel reaction process

The effects of drying control chemical additives (DCCA) on the growth of silica particles, gelation time and physical properties of the dry gel were examined in a two-step silica sol-gel process.N,N-dimethylformamide,N,N-dimethylacetamide and ethylene glycol (EG) were applied as DCCAs. The shapes of growing silica particles were distorted spheres on addition of DCCA. EG accelerated the gelation process. Despite the use of DCCA, crack-free, dry gels were obtained only under limited conditions.     

可膨胀石墨改性APP/PER/EN防火涂料热降解行为

采用可膨胀石墨 (EG) 对APP/PER/EN防火体系进行改性,制备成一种新型EG改性APP/PER/EN防火涂料。运用示差热分析 (DTA) 、热重分析 (TG) 、扫描电镜分析 (SEM) 、能谱分析 (EDS) 和隔热性能试验分析研究APP/PER/EN防火涂料和EG改性防火涂料的热降解行为、残余炭体元素含量、成炭率和隔热性能。EG改性防火涂料的APP-PER-EN之间的化学反应膨胀过程与可膨胀石墨物理膨胀过程作用温度范围接近,能产生很好的协同配合作用。膨胀石墨提高了APP/PER/EN防火涂料炭质层的成炭率、抗氧化性和热稳定性。EG添加量过高 (≥15%) 会造成燃烧后期炭质层脱离基材。10% EG (质量分数) 添加量能有效提高APP/PER/EN防火涂料的隔热防火性能。      

可膨胀石墨/环氧树脂体系的固化动力学

采用非等温差示扫描量热(DSC)法分别对环氧树脂(EP)及可膨胀石墨/环氧树脂(EG/EP)体系的固化过程进行了研究。利用Kissinger和Crane法计算得到两种体系固化反应的表观活化能Ea、指前因子A、固化反应级数n等动力学参数,建立了固化反应动力学方程,并用T-β外推法确定了固化工艺温度。结果表明,EG的加入,降低了EP体系固化反应的完全程度,对固化反应时间的影响不大,体系的Ea由63.15 kJ/mol升高到65.89 kJ/mol,A由2.02×107提升到4.5×107,两种体系的反应级数基本一致,同时,EG的加入对体系固化工艺温度影响不大。     

Paraffin core-polymer shell micro-encapsulated phase change materials and expanded graphite particles as an enhanced energy storage medium in heat exchangers

The Micro-Encapsulated Phase Change Materials (MEPCMs) with the melting point temperature of 28 °C was used as an energy storage medium to control the thermal behaviour of a heat exchanger. The NEPCM particles were mixed with Expanded Graphite (EG) microparticles to improve the heat transfer rate in the heat exchanger. The MEPCM particles are made of paraffin cores with a particle average size of 45 μm. The paraffin core of the particles can undergo a solid/liquid phase change and store a tremendous amount of thermal energy due to the latent heat of phase change. The heat exchanger is a copper pipe radiator with aluminium fins confined in either a bed of MEPCMs or a composite mixture of MEPCMs + Expanded Graphite (EG) microparticles. The thermophysical properties of MEPCMs and MEPCM + EG were measured. The outcomes show 132% enhancement in thermal conductivity and a 28% decrease in the sensible specific heat of the MEPCM + EG composite with the weight ratio of 70% MEPCM and 30% EG compared to pure MEPCM. The charging and discharging behaviour of heat exchanger for various flow rates and two cases of MEPCM and MEPCM + EG were studied experimentally. The results reveal that using EG notably enhances the heat transfer and capability of the heat exchanger during the charging and discharging process. Using MEPCM + EG reduces the temperature drop at the heat exchanger outlet about 15 °C compared to the case of pure MEPCM.     

磷杂菲反应型阻燃多元醇制备聚异氰脲酸酯硬泡及性能

以9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)、顺丁烯二酸、丙三醇、乙二醇为原料,合成出一种基于磷杂菲基团的新型无卤阻燃多元醇。通过傅里叶变换红外光谱、核磁共振氢谱表征了目标化合物的基本结构,热失重测试表明硬泡的残炭量也随阻燃多元醇的增加而升高,锥形量热测试表明阻燃多元醇的加入,使热释放速率和总热释放量大幅下降,阻燃多元醇制备的硬泡极限氧指数为26.7,达到UL-94V0级,压缩强度测试结果表明阻燃泡沫能满足建筑用聚氨酯硬泡保温材料高承载使用要求。     

Growth and optical property of Mg,Fe co-doped near-stoichiometric LiNbO3 crystal

The Mg-doped and undoped, Fe near-stoichiometric LiNbO₃ crystals were grown from the Li-rich melt by Czochralski technique. The UV-Vis absorption spectra and infrared transmittance spectra were measured to study the structure and defects of the crystals. The photo-damage resistance ability of the crystals was characterized by observing transmission facula distortion directly. The photo-damage resistance ability of Mg (3.0 mol%):Fe (0.01 wt.%):SLN is higher than that of Fe (0.01 wt.%):SLN and Fe (0.01 wt.%):CLN. This difference is attributed to the photoconductivity increase.     

Controllable synthesis of nickel dendritic crystals induced by magnetic field

We demonstrated in this paper a simple and easy method for the preparation of dendritic nickel crystals in an external magnetic field in boiling ethylene glycol (EG) solution. The structural features and morphology of the sample were investigated using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The values of saturation magnetization (M_s) and coercivity (H_c) of the dendritic crystals characterized by using a vibrating sample magnetometer (VSM) are 170.3 emu g^?1 and 50.7 Oe, respectively. It was clear that the external magnetic field was the most important factor for controlling the morphology of the product.