A Study on the Action of Ozone and on the Thermal Stability of Nanodiamond

Ultradisperse detonation diamond (UDD), a nanodiamond having particle size around 4 nm has been treated with ozone in an aqueous slurry. The reaction kinetics appeared to be relatively slow and long ozonation times were needed in order to functionalize the surface of a special nanodiamond sample with a very low degree of oxidation and foreign groups. The resulting ozonated nanodiamond has been studied by FT-IR and electronic spectroscopy. It has been shown that the ozonation of cyclohexane and adamantane can be taken as a model reaction for the ozonation of diamond. Together with ketonic groups of various nature formed on the surface of nanodiamond, the ozonation leads also to the formation of simple molecules like for instance HCOOH and HCHO which remain in the water solution and which have been detected by HPLC analysis using a diode-array detector. The thermal stability of the nanodiamond sample has been studied by thermogravimetric analysis (TGA-DTG) combined with differential thermal analysis (DTA) both under inert atmosphere and in air flow. The studies on thermal stability have been conducted in comparison to a sample of bulk diamond. It appears that the behavior of nanodiamond is completely different than the bulk diamond sample. For instance, under inert atmosphere and at 900°C the weight loss undergone by the nanodiamond is 11.5% while it is negligible in the case of bulk diamond under the same conditions. Similarly, in air flow the nanodiamond burns abruptly above 450°C while bulk diamond starts to burn only above 850°C. These differences have been explained in terms of different particle size and surface functionalization.     

Study on the Modification of Nanodiamond with DN-10

Fourier transform infrared spectroscopy (FT-IR) and ζ-potential were introduced to study the effect of different modification parameters on the surface properties of nanodiamond (NO). Results showed that under stirring grinding conditions, ND hard aggregates were smashed and some active spots on them reacted with surfactant molecules, which led to the increase in its ζ-potential and stability. Different models of surface modification were also given in this study.     

Study on the Modification of Nanodiamond with DN-IO

Fourier transform infrared spectroscopy （FT-IR） and ζ-potential were introduced to study the effect of different modification parameters on the surface properties of nanodiamond （ND）. Results showed that under stirring grinding grinding conditions, ND hard aggregates were smashed and some active spots on them reacted with surfactant molecules, which led to the increase in its ζ-potential and stability. Different models of surface modification were also given in this study.     

Comparison of Mechanical Properties of Acid and UV Ozone Treated Nanodiamond Epoxy Nanocomposites

Nanodiamond（ND） powder was successfully activated by wet chemical method and by exposure of UV/O3 in a chamber followed by mixing in triethylenetetramine（TETA） solution.The reinforcement role of activated ND in the mechanical properties of epoxy matrix was studied.Both treatments,i.e.acid and UV/O3 provide ND surface with chemical functionalities for adhesion with epoxy resin.Fourier transform infrared spectroscopy was utilized to confirm the attachment of surface groups to the ND particles.The low content of acid and UV/O3 activated ND was dispersed ultrasonically in the epoxy matrix separately to make nanocomposites.The mechanical properties of the nanocomposites were investigated under three point bending.The strong interactions among activated ND particles and the epoxy resin provide efficient load transfer interfaces,which enhances the mechanical properties of the composites.It was found that the flexural strength,modulus,and toughness of 0.1 wt%ND loaded nanocomposites have been enhanced up to 85%,57%,and 39%,respectively for UV/O3 treated ND powder.It is also found that the optimum ND concentration to achieve maximum reinforcement is 0.1 wt%while higher concentrations lead to decrease in mechanical properties.The significant improvement of the mechanical properties of the ND/epoxy nanocomposites is attributed to the good dispersion of the functionalized ND in epoxy matrix.     

Oxyfluorotellurite glasses doped by dysprosium ions. Thermal and optical properties

The paper shows results of investigation of thermal and optical properties of oxyfluorotellurite (65 − x)TeO₂–20ZnF₂–12Pb₂O₅–3Nb₂O₅–xDy₂O₃ (x = 0.5, 2 and 5) glass systems. Thermal stability and the onset of crystallization of the materials were monitored by differential thermal analysis (DTA). It was found that characteristic parameters, namely glass transition temperatures (T_g), onset of crystallization temperatures (T_c) and thermal stability criteria ΔT and H’ increased with increasing Dy₂O₃ content indicating that the incorporation of dysprosium ions improves substantially thermal stability of glass system under study.Optical absorption and emission spectra of Dy³⁺ ions in oxyfluorotellurite glass were investigated at room temperature in the visible (VIS) and near-infrared (NIR) region. Oscillator strengths, phenomenological Judd–Ofelt (JO) intensity parameters Ω_2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were determined. Decay curves of the ⁴F_9/2 luminescence of incorporated Dy³⁺ ions were recorded and analysed. Lifetimes and the luminescence dynamics were studied as a function of the Dy₂O₃ concentration. It was concluded that good thermal stability combined with desirable spectroscopic parameters of investigated dysprosium-doped oxyfluorotellurite glass point at the suitability of this material for the design of UV-excited visible phosphors.     

Thermal and optical properties of the Ga-Ge-Sb-Se glasses

A selected glass composition from the Ga-Ge-Sb-Se has been studied in detail for potential applications in the 8-12 μm region. The Ga₅Sb₁₀Ge₂₅Se₆₀ glass has a high enough glass transition temperature (283 °C), a relatively high refractive index (2.63 at 10 μm) and is very stable towards crystallization. An original purification method is developed to produce high purity glass with good transmission up to 15 μm. This glass is very resistant in normal environmental conditions and even in hot water (60 °C) during 24 h. It may be a good candidate for producing infrared components operating in the mid and far infrared region.     

Thermodynamic Properties of Nanograin Boundary and Thermal Stability of Nanograin Structure

The thermal features of the nanograin boundary were described by a developed thermodynamic model.Using the nanocrystalline Cu as an example,the pressure,the bulk modulus,and the volume thermal expansion coefficient were calculated to characterize the thermodynamic properties of the grain boundaries on the nanoscale.Based on the parabolatype relationship between the excess free energy and the excess volume of the nanograin boundary,the thermal stability,as well as its evolution characteristics,was analyzed.T...     

Si_(1-x-y)Ge_xC_y合金的热氧化物的生长动力学及光学特性

利用椭偏仪、荧光光谱和X光电子谱研究了Si1-x -yGexCy合金在 90 0℃干O2 气氛下所形成的氧化物的生长动力学及其光学特性。结果表明 :随着合金中碳含量的增加 ,氧化速率逐渐下降 ;而氧化物中 383nm附近的发光带是由于氧化薄膜中与 (SixGe1-x)O2 有关的缺陷引起的     

Thermal stability of indium tin oxide thin films co-sputtered with zinc oxide

The thermal stability of indium tin oxide (ITO) films and ITO co-sputtered with zinc oxide (ZnO) films at different zinc atomic ratios in various atmospheres are investigated. The resistivity of the annealed ITO films decreased with increased annealing temperatures. The improved electrical properties were attributed mainly to the increase in carrier concentration originating from the significant formation of oxygen vacancies in the ITO films. In contrast, due to the lower oxidation potential of zinc ions, the resistivity of the annealed co-sputtered films showed no significant reduction and an increase with annealing temperatures. The film decomposition due to the high degree outdiffusion of oxygen atoms and aggregation of In atoms observed from the metal-like In phase in the diffraction patterns was responsible for the drastic thermal degradation in the electrical and optical properties of the samples annealed at elevated temperatures in reducing gas atmosphere. In contrast, the superior thermal stability of the co-sputtered films, at an atomic ratio of 60% annealed in reducing gas atmospheres, was ascribed to the stable Zn₃In₂O₆ crystalline structure that appeared in the diffraction pattern. The absorption edge observed from the optical transmittance of these annealed films also showed evidence of carrier concentration evolution in various annealing atmospheres. The lower oxidation potential of the zinc atoms introduced into the ITO films was concluded to be efficient in compensating for the formation of oxygen vacancies resulting in the alleviated decomposition behavior during thermal annealing.     

Preparation,Thermal Stability and Electrochemical Properties of LiODFB

Lithium oxalyldifluoroborate (LiODFB) was synthesized in dimethyl carbonate solvent and purified by the method of solvent-out crystallization. The structure characterization and thermal stability of LiODFB were performed by Fourier transform infrared (FTIR) spectrometry, nuclear magnetic resonance (NMR) spectrometry and thermogravimetric analyzer (TGA). LiODFB was exposed to 50% humid air at 25 C for different time, then dried at 80 C for 12 h, and the electrochemical properties of the cells using 1 mol/L dried LiODFB in ethylene carbonate + dimethyl carbonate + ethyl(methyl)carbonate were investigated. The results showed that, pure crystallization LiODFB was obtained; it had good thermal stability with a thermal decomposition temperature of 248 C; when it was exposed to humid air, it was firstly converted into LiODFB·H2O; with increasing exposure time, more and stronger impurity peaks in the X-ray diffraction (XRD) patterns of LiODFB were observed, and both the discharge specific capacity and the capacity retention decreased gradually.     

A Study on the Action of Ozone on Multiwall Carbon Nanotubes

The functionalization of the surface of multiwall nanotubes (MWNTs) is the first step for the synthesis of more complex supramolecular structures and for their application by attaching molecules, macromolecules and biologically active molecules. Here we show in detail a couple of methods for introducing oxygenated surface groups on MWNTs by room temperature ozonization.

The reaction kinetics between MWNTs and O₃ has been studied in static conditions inside an IR gas cell. The pseudofirst order rate constant has been determined and compared with those of other carbon materials. MWNTs appear as the most reactive carbon materials with ozone, producing CO₂ and even CO in certain special conditions when treated with a stream of ozonized oxygen. The ozonization reaction is strongly exothermic and conforms to the Elovich equation, an equation normally employed for the gas-solid oxidation kinetics and the chemisorption of gases over solid surfaces. The ozonized MWNTs have been characterized qualitatively by FT-IR spectroscopy and different types of ketonic groups have been detected although the most common has been found the carboxyl moiety. The quantitative analysis of ozonized MWNTs has been made by thermogravimetric analysis under N₂ flow.     

Spectroscopic properties of Sm-containing yttrium-aluminoborate glasses and analogous huntite-like polycrystals

Sm_xY_1–xAl₃(BO₃)₄ polycrystals with huntite structure and glasses of system (mol %) 12.5 (Sm_xY_1–x)₂O₃–37.5Al₂O₃–50B₂O₃ with identical composition have been synthesized by solid state reaction and by melting process, respectively in order to compare light-emission and nonradiative energy transfer mechanisms in the two systems. The data have been analyzed to determine the concentration-dependent quantum yield of the Sm³⁺ luminescence as well as multipolarity and macro- and microparameters of the Sm–Sm interaction. The results show that the structure of the huntite cation lattice is preserved by passing from polycrystals to glasses, with an increase in the Sm–Sm minimum distance from 0.59 to 0.67 nm. At activator concentration ≤1 × 10²⁰ cm⁻³, the luminescence quantum yield in glass is higher than in polycrystals. The result turns out to be related to the partial substitution in glass by BO₄ groups of the trigonal BO₃ groups, which are responsible in crystalline Sm_xY_1–xAl₃(BO₃)₄ for efficient intracenter non-radiative energy exchange from the metastable excited ⁴G_5/2 state to phonon excitations.     

Infrared emission properties of RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn co-doped Co0.6Zn0.4Fe2O4 ferrites

The RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn ions co-doped Co-Zn ferrites were prepared by solid-state reaction method. X-ray diffraction, infrared spectra, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and infrared emission measurement (IRE-2) were employed to investigate the effect of the substitution RE³⁺ and Mn ions for Fe³⁺ ones on the spinel structure, the chemical homogeneity, and the infrared emission properties of the Co-Zn ferrites. The substitution leads to non-monotonous change of the lattice parameters and infrared emissivity properties, which is mainly attributed to the partial cation exchange among the spinel structure of Co-Zn ferrites. The infrared emission properties of Co-Zn ferrites seem to be greatly influenced by the co-doped of RE³⁺ and Mn ions—maxima values were 0.96-0.97, found for LaF, NdF and GdF, respectively.     

Effect of thermal neutron irradiation on Gd ions doped in oxyfluoroborate glass: an infra-red study

Infrared spectra of oxyfluoroborate glasses of composition (70−x)H₃BO₃+20Li₂CO₃+xGd₂O₃, where x=0, 0.5, 1.0, 3.0 and 5.0 mol%, have been recorded to explore the role of Gd³⁺ ions in the structure of the glasses. We concluded that Gd³⁺ ion behaves as a glass modifier. The effect of thermal neutron irradiation on the structure of these glasses also has been explored and the changes compared with earlier results on γ-irradiation.     

Optimized infrared switching properties in thermochromic vanadium dioxide thin films: role of deposition process and microstructure

This work deals with high efficient optical switching properties at 68 °C of thermochromic vanadium dioxide (VO₂) thin films deposited on amorphous silica substrates. VO₂ thin films were deposited by radio frequency reactive sputtering process. Conditions of deposition were optimized making use of parameters such as film thickness, gas ratio and substrate temperature. Process was optimized adjusting the distance between target and substrate, and dimensions of target and substrates, to obtain a good uniformity and reproducibility of the layers. X-Ray diffraction patterns and scanning electron microscopy convincingly illustrated that VO₂ thin films could grow on amorphous silica substrates with a specific preferential crystal orientation: the [001]_M crystallographic direction of oxygen octahedral chains is parallel to the substrate plane and corresponds with vanadium-vanadium links (insulating state) or with a maximum of electron delocalization (metal state). Optical switching properties in the mid-infrared range are discussed: transmittance, reflectance and emissivity values are strongly modified at the thermochromic transition temperature (Tc=68 °C). A maximum of optical transmittance contrast is observed for a thickness of 120-nm, then interpreted in terms of absorption law. Using a specific software, the n and k optical indices are determined and used to simulate the variation of transmittance vs. film thickness.     

Energy transfer between lead sulfide quantum dots in the liquid phase

Förster resonant energy transfer (FRET) from smaller sized PbS Quantum Dots (QDs) to larger sized ones occurs in the liquid phase when adjacent QDs are brought in close proximity by the bridging action of the two SH groups in aromatic or aliphatic dithiols. Signatures of FRET were observed by the lowering of the fluorescence peak corresponding to the smaller particle group and intensification of the peak corresponding to the larger particle group in a mixture of the two in the liquid phase. The suspensions of the two QDs size distributions were mixed in a ratio such that total surface area of the smaller QDs was equal to that of the larger QDs. A 10–13% size deviation in each PbS QDs group also allows this phenomenon to be observed in these samples and is manifested by red-shift and broadening of the fluorescence peak. The ratio of the absorption peak intensity corresponding to the two groups of PbS QDs in the mixture remains the same.     

Influence of Small Cr Addition on Thermal Stability and Magnetic Properties of Fe-Co-Zr-Nb-B Glassy Alloys

Fe62Cos-xCrxZr6Nb4B20 （x=0-4 at. pct） metallic glasses show high thermal stability with a maximum supercooled liquid region of about 84.8 K. The addition of 2 at. pct Cr causes the extension of the supercooled liquid region remarkably, leading to the enhancement of thermal stability and glass-forming ability. The crystallization of the Fe-based glassy alloys takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The long-range atomic rearrangements required for the precipitation of the multiple crystalline phases seem to play an important role in the appearance of the large supercooled liquid region through the retardation of the crystallization reactions. The Fe-based alloys exhibit soft ferromagnetic properties. The saturation magnetization decreases with increasing Cr content while the saturated magnetostriction increases as a function of Cr content. There is no distinct change in the saturation magnetization and coercive force with annealing temperature below the crystallization temperature. The devitrification gives rise to a considerable enhancement in both as and He.     

Deposition and optical studies of silicon carbide nitride thin films

Thin films of silicon carbide nitride (SiCN) have been prepared by reactive radioactive frequency (r.f.) sputtering using SiC target and nitrogen as the reactant gas. Deposition rates are studied as a function of deposition pressures and argon-nitrogen flow ratios. The optical absorption studies indicated the band edge shifting of the films when the nitrogen ratios are increased during deposition. Fourier transform infrared spectroscopy (FTIR) analysis on the films indicated several stretching modes corresponding to SiC, SiN and CN compositions.     

Effect of Pd on GFA and Thermal Stability of Zr-based Bulk Amorphous Alloy

The effect of Pd addition on the glass-forming ability and thermal stability of the Zr55Al10Cu30Ni5-xPdx (x=0, 1, 3, 5 at. pct) alloys upon copper-mold casting has been investigated. The structure, thermal stability and microstructure were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), respectively. It was identified that a new bulk amorphous alloy with the larger supercooled liquid region Tx of 100 K is obtained with substituting Ni by 1 at. pct Pd. Furthermore, the origins that thermal stability and GFA change with increasing of Pd have also beer discussed.     

Parafilm的结构及热稳定性研究

目的采用红外光谱法研究Parafilm的分子结构。方法采用变温傅里叶变换衰减全反射红外光谱(ATR-FTIR)技术,分别研究Parafilm的一维变温光谱、二阶导数变温光谱、四阶导数变温光谱及去卷积变温光谱。结果 Parafilm主要存在着CH_3不对称伸缩振动模式、CH_2不对称伸缩振动模式、CH_2对称伸缩振动模式、CH_2变角振动模式、CH_3不对称变角振动模式、CH_3对称变角振动模式、C—C骨架伸缩振动模式和CH_2面内摇摆振动模式等8种红外吸收模式,最终确定Parafilm的主要分子结构为聚异丁烯。采用变温ATR-FTIR技术(293~393 K)进一步开展Parafilm热稳定性研究,研究发现Parafilm的热稳定较差,而其临界使用温度为313 K。结论该研究拓展了变温ATR-FTIR技术在高分子包装材料的结构及热稳定性方面的研究范围。