Thermal Stabilities of Poly(Vinyl Chloride)/Calcium Carbonate (PVC/CaCO3) Composites

Poly(vinyl chloride)/calcium carbonate (PVC/CaCO₃) composites with micrometer or nanometer CaCO₃ as fillers were prepared by the solution blending method. The thermogravimetric analysis (TGA) of the composite films conducted in N₂ atmosphere showed that the addition of the CaCO₃ fillers could improve their thermal stabilities. It was also found that the nanometer CaCO₃ filler provided better thermal stabilities than the micrometer fillers even with a smaller amount. The mechanism of the improvements was investigated by a facile chemical analysis developed to examine the thermal stabilizing effect of calcium carbonate particles with different sizes in PVC/CaCO₃ composites after the pyrolysis of the samples in an air atmosphere in an oven.     

Effect of Surface Structure of Nano-CaCO3 Particles on Mechanical and Rheological Properties of PVC Composites

To study the effect of different surface structures on resultant mechanical and rheological properties, nano-CaCO₃ particles were treated with isopropyl tri-stearyl titanate (H928), isopropyl tri-(dodecylbenz-enesulfonyl) titanate (JN198), and isopropyl tri-(dioctylpyrophosphato) titanate (JN114). Scanning electron microscopy (SEM) and dynamic mechanic analysis (DMA), carried out to characterize the effective interfacial interaction between the nano-CaCO₃ particles and a poly(vinyl chloride) (PVC) matrix, indicated that JN114 treated nano-CaCO₃ particles had the strongest interfacial interaction with a PVC matrix, while H928 treated nano-CaCO₃ had the weakest. The rheological and mechanical properties of PVC/nano-CaCO₃ composites were investigated as a function of surface structure and filler volume fraction. The tensile yield stress and elongation at break decreased with the increasing of calcium carbonate content while tensile modulus increased. PVC filled with JN114 treated nano-CaCO₃ had the highest tensile modulus and tensile yield stress, while those filled with H928 treated nano-CaCO₃ had the highest elongation at break at the same filler content. The impact strength of PVC/nano-CaCO₃ composites increased with the increasing of CaCO₃ content, and PVC composites filled with JN198 treated nano-CaCO₃ particle had a higher impact strength than those with JN114 or H928 treated, with the value reaching 23.9 ± 0.7 kJ/m² at 11 vol% CaCO₃, four times as high as that of pure PVC. Rheological properties indicated that a suitable interfacial interaction and a good dispersion of inorganic filler in a PVC matrix could reduce the viscosity of PVC/nano-CaCO₃ composites. The interfacial interaction was quantitatively characterized by semiempirical parameters calculated from the tensile strength of PVC/nano-CaCO₃ composites to confirm the results from the SEM and DMA experiments.     

Nanocomposites of Poly(vinyl alcohol) Reinforced with Chemically Modified AL2O3: Synthesis and Characterization

The surface of α-alumina (Al₂O₃) nanoparticles was first modified with γ-aminopropyltriethoxy silane as a coupling agent. Then a series of poly(vinyl alcohol)/ surface modified Al₂O₃ nanocomposite suspensions were prepared in ethanol by a simple ultrasonic irradiation process. Composite films with 5, 10, and 15 wt % of inorganic Al₂O₃ nanoparticles were achieved after solvent evaporation. The formation of the composite materials were confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and optical transparencies. The FE-SEM and TEM results showed a homogenous dispersion of nanoscale inorganic particles in the poly(vinyl alcohol) matrix. TGA thermographs showed that the thermal stability of the prepared Al₂O₃-reinforced nanocomposites was improved, increasing with increasing content of the nanoparticles. According to the optical transparencies, the optical clarity of poly(vinyl alcohol)/Al₂O₃ nanocomposite films was only slightly affected by the presence of the Al₂O₃ content.     

Morphology and Properties of Poly(vinyl alcohol)/MMT Nanocomposite Prepared by Solid-state Shear Milling (S3M)

Poly(vinyl alcohol) (PVA)/montmorillonite (MMT) nanocomposites were prepared by combining solid-state shear milling (S³M) technology with melt intercalation. Compared with the composite obtained by simple melt intercalation, more MMT layers were exfoliated and apparently oriented along the injection molding direction in the nanocomposite prepared by combining S³M technology and melt intercalation, which greatly increased the orientation degree of MMT, resulting in the greater interactions between PVA and MMT layers. Simultaneously, this also promoted the orientation of PVA molecules and produced effective nucleation of the crystallization of PVA. Consequently, the thermal stability and mechanical properties of PVA were obviously improved. For instance, when the MMT content was 3 wt%, the tensile strength and modulus of the nanocomposite with MMT prepared by S³M were 98.9 MPa and 3.1 GPa, respectively, increasing by 52% and 63.2% compared with PVA.     

Properties and Morphology of Poly(Lactic Acid)/Calcium Carbonate Whiskers Composites Prepared by a Vane Mixer based on an Extensional Flow Field

Binary composites of poly(lactic acid) (PLA)/calcium carbonate whiskers (CCW) with different weight fractions were prepared with a vane mixer based on extensional rheology. The mechanical properties, thermostability, crystallization behavior, rheology behaviors and micromorphology of the composites were analysed to study the effect of the CCW fibers on the composite's properties; a pure PLA sample was also prepared for comparison. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed that the CCW fibers had excellent compatibility with the PLA matrix and the CCW fibers were dispersed and distributed evenly in the PLA matrix under the action of the extensional flow field produced by the vane mixer. Differential scanning calorimetric (DSC) analysis showed that introducing a vane mixer into the PLA processing could increase the degree of crystallization (χ_c) of the composites significantly, and moderate CCW fibers adding could further increase its χ_c value. Thermogravimetric analysis (TGA) revealed that adding the CCW fibers reduced the thermostability of the composites. The G′, G″, η* and the torque, T_N, of the composites, obtained from rheology analyses, declined obviously, because of the hydrolysis and chains scission induced by residual water and fatty acid when the CCW content less than 4%. Tensile tests proved that filling moderate amounts of CCW fibers into PLA could increase its tensile strength and strain at break, increasing by 5% and 29.6%, respectively.     

Comparison of the Morphological,Mechanical, and UV Protection Properties of TiO2/Polyamide 6 (PA6), and ZnO/PA6 Nanocomposite Multifilament Yarns

The properties of TiO₂/polyamide 6 (PA6) and ZnO/PA6 nanocomposite filament yarns produced on a pilot-plant melt spinning machine were compared. Concentrated masterbatches were prepared using a twin screw extruder. Then continuous multifilament yarns were produced by blending nylon 6 chips and various amounts of the prepared masterbatches. Melt spinning was carried out at the spinning temperature of 265°C and take-up speed of 4000 m/min. As-spun multifilament yarns were then drawn and textured. Morphological properties of the produced yarns were studied. Thermal behavior and physical properties, including shrinkage and tensile properties, were measured. Weft-knitted fabrics were evaluated for their ultraviolet protection properties. Although both kinds of the nanoparticles had a positive effect on the ultraviolet protection properties of their nanocomposite fabrics as compared to pure PA6 fabric, the efficiency of the TiO₂ nanoparticles was more than that of the ZnO ones for the same concentrations. The differences between the different properties of the two kinds of nanocomposites are discussed based on their interaction with the polymeric matrix, specific surface area, steric hindrance effect, and band gap energies.     

高温无铅BaTiO_3-(Bi_(1/2)Na_(1/2))TiO_3正温度系数电阻陶瓷阻抗和介电谱分析

采用固相反应法制备了Y2O3施主掺杂的92 mol%BaTiO3-8 mol%(Bi1/2Na1/2)TiO3(BBNT8)高温无铅正温度系数电阻(positive temperature coe?cient resistivity,PTCR)陶瓷.利用透射电镜观察材料的显微结构,发现陶瓷的显微结构主要包括晶粒和晶界两部分,观察不到明显的壳层结构.进一步利用交流阻抗谱研究了陶瓷的宏观电学性能,发现陶瓷的总电阻是晶粒和晶界两部分的贡献,而晶粒电阻很小,在居里温度以上变化不大,材料的PTCR效应主要是晶界部分的贡献.当温度高于居里温度时,随着温度的升高,晶界介电常数逐渐减小,导致势垒增加,晶界电阻增大,从而产生正温度系数效应.最后,通过测试材料的介电频谱特性,研究计算了陶瓷的室温电阻率.     

Mixed alkali metal selenate proton conductors: Phase transitions and crystal structure of [Rb0.54(Nh4)0.46]3H(SeO4)2

Optical birefringence, calorimetric, thermal expansion, powder and single crystal X-ray diffraction investigations of mixed proton conductors [Rb_1-x(NH₄)_x]₃H(SeO₄)₂ were performed with the aim of studying the influence of partial substitution of cations on the superprotonic phase transition, on the atomic structure and on other characteristic features of this type of crystals.     

Photooxidation of different organic dyes (RB, MO, TB, and BG) using Fe(III)-doped TiO2 nanophotocatalyst prepared by novel chemical method

The nano-structured Fe(III)-doped TiO₂ photocatalysts with anatase phase have been developed for the oxidation of non-biodegradable different organic dyes like methyl orange (MO), rhodamine B (RB), thymol blue (TB) and bromocresol green (BG) using UV-Hg-lamp. The different compositions of Fe_xTi_1−xO₂ (x = 0.005, 0.01, 0.05, and 0.1) nanocatalysts synthesized by chemical method (CM), have been characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra, specific surface area (BET), transmission electronic microscopy (TEM) analysis, XPS, ESR and zeta potential. From XRD analysis, the results indicate that all the compositions of Fe(III) doped in TiO₂ catalysts gives only anatase phase not rutile phase. For complete degradation of all the solutions of the dyes (MO, RB, TB, and BG), the composition with x = 0.005 is more photoactive compared all other compositions of Fe_xTi_1−xO₂, and degussa P25. The decolorization rate of different dyes decreases as Fe(III) concentration in TiO₂ increases. The energy band gap of Fe(III)-doped TiO₂ is found to be 2.38 eV. The oxidation state of iron has been found to be 3+ from XPS and ESR show that Fe³⁺ is in low spin state.     

Perovskite Pb(Sc1/2Nb1/2)O3 nanopowders synthesized by surfactant-modulated precipitation

A novel surfactant-modulated precipitation method is proposed to produce pure perovskite Pb(Sc_1/2Nb_1/2)O₃ (PSN) nanopowders at a low temperature of 700 °C. The samples were characterized by XRD, SEM, TEM, and HRTEM, respectively. The results indicate that the powders exhibit a granular shape of 80 nm in diameter. It is believed that the nanosize of as-prepared PSN powders is dependent on the well-dispersed performance, which arouse from the combined effects of both precipitant TMAH and surfactant CTAB. The mechanism of the formation of the pure perovskite PSN nanopowders is discussed in detail. Our method is expected to create a new, low-cost route to produce the promising nanopowders of multi-component perovskite systems.     

Growth and spectroscopic characterization of Er: Sr3Y(BO3)3 crystal

This paper reports the growth and spectroscopic characterization of Er³⁺:Sr₃Y(BO₃)₃ crystal. Er³⁺:Sr₃Y(BO₃)₃ crystal with dimensions up to ∅20×35 mm³ has been grown by Czochralski method. The polarized spectroscopic properties of Er³⁺:Sr₃Y(BO₃)₃ crystal were investigated. Based on the Judd-Ofelt theory, the effective intensity parameters Ω_t were obtained: Ω₂=1.71×10⁻²⁰ cm², Ω₄=1.39×10⁻²⁰ cm², Ω₆=0.74×10⁻²⁰ cm² for π-polarization, and Ω₂=1.77×10⁻²⁰ cm², Ω₄=1.44×10⁻²⁰ cm², Ω₆=0.65×10⁻²⁰ cm² for σ-polarization. The emission cross-section σ_em was calculated to be 4.75×10⁻²¹ cm² for π-polarization at 1536 nm and 6.30×10⁻²¹ cm² for σ-polarization at 1537 nm. The investigated results showed that Er³⁺:Sr₃Y(BO₃)₃ crystal may be regarded as a potential laser host material for 1.55 μm IR solid-state lasers.     

Effect of temperature on the conductivity, structural, and morphology of PVA-based alkaline solid polymer electrolyte

Alkaline polymer electrolytes (ASPE) have been prepared by using poly(vinyl alcohol) (PVA) polymer and which different weight percentages of potassium hydroxide (KOH), ceramic filler (α-Al₂O₃), and propylene carbonate (PC) have been added. The pure PVA/H₂O weight ratio (1.00:1.49), the PVA/KOH/H₂O (1.00:0.67:2.22), the PVA/KOH/α-Al₂O₃/H₂O (1.00:0.67:0.09:7.56), and PVA/KOH/α-Al₂O₃/PC/H₂O (1.00:0.67:0.09:2.64:1.32) were studied. The hysteresis phenomena in the conductivity temperature of ASPE were investigated. The polymer electrolytes prepared were characterized using X-ray diffraction and scanning electron microscopy.     

Luminescence of Ca(NbO3)2:Pr at ambient and high hydrostatic pressure

In this contribution, photoluminescence and time-resolved photoluminescence spectra of Ca(NbO₃)₂ doped with Pr³⁺ obtained at high hydrostatic pressure up to 72 kbar applied in a diamond anvil cell are presented. At ambient conditions, the emission spectrum obtained in the time interval 0-1 μs is dominated by spin-allowed transitions from the ³P₀ state. On the other hand, transitions from ¹D₂, characterized by a decay time equal to 30 μs dominate the steady-state luminescence.At pressures lower than 60 kbar, the continuous wave emission spectrum consists of sharp lines peaking between 600 and 625 nm, related to the ¹D₂→³H₄ transition and three lines at 500, 550 and 650 nm related to emission transitions originating from the ³P₀ level of Pr³⁺. The emission from the ¹D₂ excited state depends weakly on the pressure. Its decay time decreases from 33 μs at ambient pressure to less than 22 μs at 68 kbar. On the other hand, the ³P₀ emission is strongly pressure dependent. At pressures of 60 kbar and higher, the Pr³⁺ emission intensity from the ³P₀ state decreases. This is accompanied by a strong shortening of the luminescence decay time.The observed pressure quenching of the f-f emission transitions and the concomitant lifetime shortening have been attributed to increasing crossover from the ³P₀ state of Pr³⁺ to a Pr³⁺-trapped exciton state.     

(Bi1-x Agx)2(Te1-ySey)3粉体的机械合金化制备及其放电等离子烧结体的热电输运特性

采用机械合金化制备了n型(Bi_1-xAg_x)₂(Te_1-ySe_y)₃合金粉体,对其进行XRD分析表明Bi,Te,Ag,Se单质粉末,经2h球磨后实现了合金化;SEM分析表明随着机械合金化时间延长粉体颗粒变得均匀、细小,颗粒尺寸在微米至亚微米数量级.采用放电等离子烧结制备了块体样品,研究了合金成分和球磨时间对热电性能的影响.结果表明材料的热电性能与掺杂元素有密切关系,Ag有利于提高功率因子和降低晶格热导率,球磨10h的(Bi_0.99Ag_0.01)₂(Te_0.96Se_0.04)₃合金粉末的烧结块体具有最大的功率因子和最低的晶格热导率,并在323K取得最高ZT值0.52. 关键词： 1-xAg_x)₂(Te_1-ySe_y)₃合金')" href="#">(Bi_1-xAg_x)₂(Te_1-ySe_y)₃合金 机械合金化 放电等离子烧结 热电性能     

Microstructure and properties of Ni-Co/nano-Al2O3 composite coatings by pulse reversal current electrodeposition

Ni-Co/nano-Al₂O₃ (Ni-Co/Al₂O₃) composite coatings were prepared under pulse reversal current (PRC) and direct current (dc) methods respectively. The microstructure of coatings was characterized by means of XRD, SEM and TEM. Both the Ni-Co alloy and composite coatings exhibit single phase of Ni matrix with face-centered cubic (fcc) crystal structure, and the crystal orientation of the Ni-Co/Al₂O₃ composite coating was transformed from crystal face (2 0 0) to (1 1 1) compared with alloy coatings. The hardness, anti-wear property and macro-residual stress were also investigated. The results showed that the microstructure and performance of the coatings were greatly affected by Al₂O₃ content and the electrodeposition methods. With the increasing of Al₂O₃ content, the hardness and wear resistance of the composite coatings enhanced. The PRC composite coatings exhibited compact surface, high hardness, better wear resistance and lower macro-residual stress compared with that of the dc composite coatings.     

Z-scan measurements of nonlinear refraction and Kerr-lens mode-locking with Yb3+:KY(WO4)2

The nonlinear refractive index n₂ of Yb³⁺:KY(WO₄)₂ crystal has been measured using picosecond Z-scan technique. The magnitude of n₂ was found to be 8.7 × 10^–16 cm²/W at wavelength of 1.08 m. The numerical modeling based on fluctuation model showed a great potential of this crystal as active medium for Kerr-lens mode-locking.     

Spectroscopic Properties and Conformational Features of Short Linear Peptides in Solution: A Fluorescence and Molecular Mechanics Investigation

The ground- and excited-state properties of two conformationally constrained hexapeptides of general formula Boc-Bin-A₁-A₂-T-A₁-A₂-OtBu, where A₁ and A₂ are -aminoisobutyric acid (Aib) or L-alanine (Ala), Bin is an optically pure, axially chiral 1,1-binaphthyl-substituted Aib, and T (Toac) is a stable nitroxide free radical-containing Ac6c analog, were investigated in methanol solution. These peptides are denoted as (R)-Bin/Toac and (S)-Bin/Toac, depending on the chirality of the binaphthyl moiety. Electronic spectra in methanol indicate the occurrence of intramolecular exciton interaction between the naphthyl moieties of Bin, and time-resolved fluorescence measurements show a biexponential decay for both peptides examined. According to infrared (IR) absorption data in the NH stretching frequency region, and to earlier X-ray diffraction results on (S)-Bin/Toac in the crystal state, both (R)-Bin/Toac and (S)-Bin/Toac populate a 3₁₀-helix in solution with opposite screw sense, the helical handedness being determined by the chirality of binaphthyl and not by that of the Ala residues in the main chain. The combination of molecular mechanics calculations with fluorescence decay data indicate that the two observed lifetimes for each peptide arise from two conformations having different interprobe distance and orientation, in which electronic energy transfer from excited Bin to Toac takes place.     

White light generation through the zinc metaphosphate glass activated by Ce, Tb and Mn ions

The photoluminescence of Ce³⁺, Tb³⁺ and Mn²⁺ ions was investigated in the Zn(PO₃)₂ glass. The blue and green emissions of Tb³⁺ ions and the red emission of Mn²⁺ ions are enhanced upon UV excitation through a non-radiative energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions. The efficiency of this transfer was estimated in at least 62%. It is demonstrated that this glass activated with three ions (Ce³⁺, Tb³⁺ and Mn²⁺) can generate white light emission (x=0.420 and y=0.423 chromaticity coordinates and 3440 K colour temperature) under excitation at 254 nm, i.e., using an AlGaN-based LED as excitation source.     

Vibrational Study of the Complexes Pentamethyl Cyclopenta-Dienyldicarbonyl Rhenium Phosphine and Phosphite : (n5-C5Me5)Re(CO)2(PR3) R= Me,OMe, OPh

Abstract

A complete vibrationalassignment of the title compounds is performed from their IR and Raman Spectra. A normal coordinate treatment of these molecules based on a simplified model allow us to confirm most of the experimental assignments.

A comparison of some structural aspects of these complexes with Cp?Re(CO)₃ are also discussed. Additionally, the preparation and characterization of the trimethylphosphite derivative is reported.