Thermal stability and deformation of poly(acrylic acid)–metal oxides

In this work, we investigated the thermal stability and deformation of the compound of poly(acrylic acid) (PAA) and metal oxides (ZnO, CaO, CuO, Al₂O₃, and Cr₂O₃). The kinetic parameters of the desorption of water from PAA–metal oxide were calculated. The activation energies of the water desorption of PAA–metal oxide were less than 5 kcal/mol. The order of bonding capability of oxygen (PAA–O–metal) and water was PAA–CaO > PAA–ZnO > PAA–CuO > PAA–Cr₂O ₃ > PAA–Al₂O₃. The reaction types of the composites were clarified. Incorporating metal oxide into PAA increased the thermal stability. The factors which influence the mechanical properties of the composites, e.g., the chemical compositions, curing environment, and curing time, were also studied. The various curing environments (pure water, 0.1N HCl, 0.1N NaOH, and methanol) decreased the compressive strength of PAA—metal oxide. Moreover, the thermal stability and compressive strength of PAA–ZnO and PAA–CuO reached an optimum because of their crosslinking nature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2021–2027, 1997     

Comparison between the effects of alcohols and diols on polymethyl‐methacrylate and polyacrylamide with positron annihilation lifetime and electric conductivity measurements

Comparison between the effect of alcohols and diols on poly(methylmethacrylate) (PMMA) and polyacrylamide (PAA) was investigated by positron annihilation lifetime (PAL) spectroscopy and electric conductivity measurements. The samples were prepared by adding alcohols, such as ethanol (E), isopropyl alcohol (P), and butyl alcohol (B), and diols, such as ethanediol (E_1,2), isoproponendiol (P_1,2), and butanediol (B_1,2, B_1,3, B_1,4). The o‐Ps lifetime values (τ₃) of PMMA–alcohol or PMMA–diol composites are shorter than the τ₃ value of the virgin PMMA, whereas the τ₃ values of PAA–alcohol or PPA–diol composites fluctuate above and blow the corresponding value of virgin PAA. On the other hand, a significant increased was observed in the o‐Ps intensities (I₃) of both PMMA and PAA composites with added alcohols and diols compared with pure PMMA and PAA. The electric conductivity (σ) also increased for both PMMA and PAA composites with added alcohols and diols compared with the virgin PMMA or PAA polymer. A correlation was found between positron annihilation lifetime parameters and electric conductivity of PAA composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3078–3083, 2003     

Facile synthesis of amorphous Cr2O3/N‐doped carbon nanosheets and its excellent lithium storage property

The Cr₂O₃ with high‐energy density and relatively low lithium insertion potential is a promising anode candidate for LIBs. However, the intrinsic poor electroconductivity and side effects like volume expansion of Cr₂O₃ severely limit its capacity and cyclability at high charge/discharge rates. To address the problem, the amorphous Cr₂O₃/N‐doped carbon nanosheets (denoted as a‐Cr₂O₃/NC) have been designed and prepared by an easy one‐step solution combustion synthesis method from a uniform solution of chromium nitrate, glucose, and glycine. The as‐synthesized a‐Cr₂O₃/NC consist of amorphous Cr₂O₃ particles and N‐doped carbon sheet, where the amorphous Cr₂O₃ is evenly encapsulated in the carbon sheet support. An anode prepared from the synthesized a‐Cr₂O₃/NC demonstrates much higher specific capacity and better cycling performance than the crystalline Cr₂O₃ anode. Upon extended cycling, the a‐Cr₂O₃/NC anode exhibits good long‐term stability and its reversible capacity retains as high as 782.4 mAh g^?1 after 500 cycles at 1 A g^?1. Such good performance stems from its unique structure. The amorphous structure of Cr₂O₃ can furnish a mass of enterable active sites which can favor the lithium ions insertion/extraction, whereas the sheet‐like N‐doped carbon support can increase the electroconductivity and facilitate the transportation of lithium ions and electrons.     

Near-infrared long-lasting phosphorescence in transparent glass ceramics embedding Cr3+-doped LiGa5O8 nanocrystals

Cr³⁺ doped transparent glass ceramics of SiO₂–Ga₂O₃–Li₂O were fabricated by melt-quenching and subsequent crystallization. X-ray diffraction and transmission electron microscopy analyses evidenced that cubic LiGa₅O₈ nanocrystals were homogeneously precipitated among the silicate glass matrix. The incorporation of Cr³⁺ ions into LiGa₅O₈ nanocrystals was evidenced by absorption, emission and time-resolved luminescence spectra. Impressively, the present Cr³⁺ doped glass ceramics were demonstrated to be a new near-infrared (∼720 nm) long-lasting bulk phosphor whose luminescence can last for more than 2 h after stoppage of UV (250–350 nm) irradiation. The occurring of Cr³⁺ long-lasting phosphorescence in the glass ceramics was confirmed to be mainly due to the precipitation of Cr³⁺:LiGa₅O₈ nanocrystals from glass matrix. The filling/releasing of electrons into/from the intrinsic traps of LiGa₅O₈ nanocrystals through the conduction band of host were proposed to be responsible for the realization of the long-lasting phosphorescence of the investigated Cr³⁺ doped glass ceramics.     

Infrared spectroscopy and electrical properties of ternary poly(acrylic acid)–metal–poly(acrylamide) complexes

Fourier transform infrared spectroscopy (FTIR) and electrical measurements were used for the characterization of the interpolymer complexation between poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) and also the ternary PAA–metal–PAAm complexes. The interpolymer complexes were prepared by adjusting the pH value of the mixture solutions at different PAA weight fractions (W_PAA). The ternary complexes were prepared by mixing metal chloride solutions (such as ErCl₃ and LaCl₃) with different concentrations to PAA–PAAm mixtures and adjusting the pH value for different W_PAA. It was found that the IR spectra of the interpolymer complexes showed absorption bands at shifted positions and of intensities different from those of the parent polymers. Also, the examination of the spectra of the ternary metal–polymer complexes revealed that they depend on the nature, lency, ionic radius, and concentration of the added metal chlorides. Analysis of the electrical results showed that the electrical conductivity of the interpolymer complexes are always lower than those of PAA and PAAm, which was attributed to the decrease in the mobility of the polymer chains as a result of the complexation. Also, the conductivity of the ternary metal complexes showed a dependence on the properties of the additives and were found to decrease with increasing their concentrations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2699–2705, 2002     

Poly(o-toluidine dihydrochloride): Spectral Characterization and Synthesis of Eskolite Nanoparticles

Poly(o-toluidine?·?2HCl) and its doped polymers with Mn and Cr ions have been synthesized and characterized by FT-IR, UV–Vis. and thermogravimetrical analyses. Potassium dichromate has been used as an initiator and a dopant of chromium in CrPOT preparation. The effect of doping on thermal and optical properties of Poly(o-toluidine dihydrochloride) has been discussed.

CrPOT has been used as a precursor of Cr₂O₃ nanoparticles through thermal decomposition rout. The obtained nanoparticles have been characterized by X-ray diffraction and high resolution transmission electron microscope. The results indicated that Cr₂O₃ exists in hexagonal structure as mesoporous Eskolit with average particle size of 48?nm. Optical band gap measurements indicated that Eskolite nanoparticles have wider band gap than the bulk.     

Fe3O4–carbon black nanocomposite as a highly efficient counter electrode material for dye-sensitized solar cell

Iron oxide–carbon black (Fe₃O₄–CB) nanocomposite has been proposed as a cost–effective alternative counter electrode (CE) to the conventional Pt in a dye sensitized solar cell (DSSC). The Fe₃O₄–CB nanocomposite at three different weight ratio (1:1, 1:2 and 2:1) was prepared by a simple solution mixing process and the material was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy techniques. The performance of the three Fe₃O₄–CB nanocomposite CEs was assessed with respect to Fe₃O₄, CB and Pt in a conventional DSSC consisting of N719 dye sensitized TiO₂ (P25) photoanode in contact with an electrolyte containing the I⁻/I₃⁻ redox couple. The electrocatalytic activities of the various CEs towards triiodide (I₃⁻) reduction were analyzed by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization analysis. The photocurrent voltage (J–V) characteristics of the DSSCs assembled with various counter electrodes were assessed at a light intensity of 80 mW cm⁻². The DSSC assembled with Fe₃O₄–CB nanocomposite (1:2) CE showed the best photovoltaic performance in terms of a high power conversion efficiency of 6.1% which is superior to that of sputtered Pt (4.1%). The simple preparation, excellent electrocatalytic activity and low-cost nature allow the Fe₃O₄–CB nanocomposite to be a promising alternative CE to Pt for use in DSSCs.     

Effects of Cr content and morphology on the luminescence properties of the Cr-doped alpha-Al2O3 powders

Al₂O₃:Cr³⁺ samples were synthesized via hydrothermal and microwave solvothermal methods and thermal decomposition of Cr³⁺ doped precursors. The sample characterizations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD results indicated that Cr³⁺ doped samples were pure α-Al₂O₃ phase after being calcined at 1573 K. SEM results showed that the length and diameter of these Cr³⁺ doped alumina microfibers by hydrothermal route were about 2–5 μm and 100–300 nm, respectively; the obtained α-Al₂O₃ based powders via the microwave solvothermal method were microspheres with an average diameter about 1–2 μm. PL spectra showed that the Al₂O₃:Cr³⁺ samples presented a broad R band at 696 nm. It is shown that the 0.3 mol% of doping concentration of Cr³⁺ ions in α-Al₂O₃:Cr³⁺ is optimum. According to Dexter's theory, the critical distance between Cr³⁺ ions for energy transfer was determined to be 24 Å. It is found that the curve followed the single-exponential decay. Furthermore, the luminescence properties of the samples are also dependent on the morphology.     

532 nm laser damage and nonlinear absorption of Cr2O72− doped KDP crystals

Potassium dihydrogen phosphate (KDP) single crystals doped with a series of trace dichromate (Cr₂O₇^2?) were prepared using “point seed” technique. The IR spectra suggest that the KDP crystal network becomes compact with trace of Cr₂O₇^2? while the lattice of crystal also can be destroyed by excessive doping. The UV–Vis spectra show that the transmittance percentage is descended of the doped KDP crystals. Z-scan analysis demonstrates that with increasing of Cr₂O₇^2? concentration, a gradual raise has been observed for the nonlinear absorption coefficient (β). The laser-induced damage threshold (LIDT) at 532 nm of the KDP crystal doped with 3000 ppm Cr₂O₇^2? is found to be 28.29 J/cm² which is higher than that of pure one under the R-on-1 model. However, as the doping concentration continues to increase, the LIDT decreases significantly. The variation of photoluminescence (PL) results is also consisted with the trend of LIDT for the doped samples. The LIDT of pyramidal sample is higher than that of prismatic one with the same doping concentration. The results suggest that the laser damage of doped crystal may be due to a synergistic effect of the concentration of micro defects and nonlinear absorption.     

Sliding wear characteristics of plasma-sprayed Cr2O3 coatings with incorporation of metals and ceramics

Different additives (metals, ceramics, and metal/ceramic assembles) were incorporated into chromium oxide (Cr₂O₃) coatings to improve its wear resistance. The doping or co-doping effects were compared in terms of the microstructure, phase composition, microhardness and sliding wear properties of plasma-sprayed Cr₂O₃-7wt.% Mo, Cr₂O₃-7wt.% Nb₂O₅, Cr₂O₃-4wt.% MoO₃-3wt.% Mo, and Cr₂O₃-4wt.% Nb₂O₅-3wt.% Mo coatings. Under the low sliding loads, the composite coatings mated with WC-Co counterparts have lower friction coefficients than those against Si₃N₄, which are inverse with their microhardnesses, but more obvious fatigue wear characteristics. Under the high sliding loads, Mo/Nb₂O₅ co-doped Cr₂O₃ coating (CNM) has the best wear resistance than other coatings, due to the delaying co-effects of crack formation and propagation on basis of the crack deflection and the toughening effects of Mo additives and the high hardness of Nb₂O₅ additives. As the reciprocating sliding loads exceed the critical stress of brittle Cr₂O₃-based coatings, the coating detachments occur, displaying obvious fatigue wear characteristics.     

Significantly Enhanced Infrared Emissivity of LaAlO3 by Co‐Doping with Ca2+ and Cr3+ for Energy‐Saving Applications

In this study, Ca²⁺–Cr³⁺ co‐doped LaAlO₃, a novel energy‐saving material with significantly enhanced infrared emissivity, was synthesized by solid‐state reaction. The experimental results demonstrated that 20 mol% Ca²⁺ and 10 mol% Cr³⁺‐doped LaAlO₃, namely La_0.8Ca_0.2Al_0.9Cr_0.1O₃, had an infrared emissivity as high as 0.92 in the spectral region of 1–5 μm, which was 12 times higher than that of pure LaAlO₃. The first‐principles electronic structure calculations revealed that the Ca²⁺–Cr³⁺ co‐doping results in the occurrence of impurity energy levels in the forbidden band of LaAlO₃, which were mainly composed of the Cr 3d orbitals. Electrons partly occupied these impurity donor states and significantly reduced the energy bandgap, thus the infrared radiation property of LaAlO₃ was enhanced. This novel material with high infrared emissivity shows promising applications for energy‐saving in the field of thermal process equipment.     

Er2O3 Doping Effect on Varistor Properties and Multiimpulse Stress Behavior of ZnO–PrO1.83–CoO–Cr2O3–Dy2O3 Ceramics

The Er₂O₃ doping effects on varistor properties and impulse aging behavior of the ZnO–PrO_1.83–CoO–Cr₂O₃–Dy₂O₃ ceramics were investigated in the range of 0–2.0 mol%. The nonlinear coefficient increased from 42 to 56 with an increase in the amount of Er₂O₃. The clamp voltage ratio (K) decreased with an increase in the amount of Er₂O₃. The varistors doped with 2.0 mol% in the amount of Er₂O₃ exhibited the best clamping characteristics, with K = 1.43–1.83 at an impulse current of 1–50 A. The varistors doped with 0.25 mol% in the amount of Er₂O₃ exhibited the strongest electrical stability, with the variation rate of the breakdown field of ?0.5%, the variation rate of the nonlinear coefficient of ?5.5%, and the variation rate of the leakage current of ?1.5% after applying 400 times at an impulse current of 400 A     

Infrared luminescence in Er3+:Yb3Al5O12 bulk ceramics prepared by sol–gel method

Erbium doped and pure ytterbium aluminium garnet (YbAG, Yb₃Al₅O₁₂) bulk ceramics were successfully prepared by a chelating sol–gel route based on the polyesterification of ethylenediaminetetraacetic acid (EDTA) with triethanolamine (TEA). The gel decomposition and phase formation in precursor powders were studied using XRD and TG/DTA. Amorphous precursor was directly converted to YbAG phase after calcinations at 800 °C. The influence of intermediate grinding on microstructure and luminescent properties was investigated. The discrete luminescence bands of the ⁴I_13/2 → ⁴I_15/2 transition were observed in the infrared emission spectra of erbium doped samples. The lifetime of luminescence at 1530 nm was 2.82 ms and 1.82 ms for the doped samples. This may be attributed to the different efficiency of surface recombination channel, caused by different grain size distribution. Prepared samples are suitable as a standard for photoluminescence measuring of Er-doped YbAG thin films.     

Energy transfer to Eu(III) in the solid‐state low‐density polyethylene–poly(acrylic acid) and low‐density polyethylene–Fe2O3–poly(acrylic acid) matrices

Ion exchange between H⁺ and Eu³⁺ and/or Tb³⁺ was studied in the material modified by in situ sorption and thermal polymerization of acrylic acid in low‐density polyethylene (LDPE–PAA) and in the composite system LDPE–Fe₂O₃–PAA. Fluorescence spectroscopy showed evidence of Eu³⁺ and/or Tb³⁺ ion exchanges in these materials. The matrix LDPE–PAA after Eu(III) ion exchange presented luminescence (excitation 265 nm). This was explained by an energy‐transfer process from the matrix LDPE–PAA to Eu³⁺ ions. The LDPE–PAA matrix after simultaneous Eu³⁺/Tb³⁺ ion exchange exhibited Eu³⁺ and Tb³⁺ ion luminescence (excitation 265 nm), confirming an energy‐transfer process from LDPE–PAA to Eu³⁺ ions in LDPE–PAA–Eu³⁺–Tb³⁺ matrix. Fe₂O₃ in LDPE–Fe₂O₃–PAA quenched the matrix for excitation at 265 nm and no emission at the region 400 nm was observed. The luminescence of Tb³⁺ ions in the matrix LDPE–Fe₂O₃–PAA–Tb³⁺ (excitation 265 nm) was partially quenched by Fe₂O₃. However, a weak emission of Eu³⁺ ions was observed (excitation 265 nm) in the matrix LDPE–Fe₂O₃–PAA after simultaneous Eu³⁺ and Tb³⁺ ion exchanges, suggesting an energy transfer from Tb³⁺ to Eu³⁺ ions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 919–931, 2000     

Free volume‐related microstructural properties of lithium perchlorate/sodium alginate polymer composites

The effect of salt (LiClO₄) on free volume‐related microstructural, optical, and dielectric properties of lithium perchlorate (LiClO₄)‐doped sodium alginate (NaC₆H₇O₆)_n solid polymer electrolyte were studied using Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), UV–Visible, dielectric measurements, and positron annihilation lifetime spectroscopy (PALS) techniques. The FTIR study reveal that the LiClO₄ interact with the O H groups of sodium alginate (NaAlg) and forms charge transfer complex (CTC). These formed CTC within the composite film affect the optical property of the polymer composite, which was reflected from UV–Visible study. The free volume was probed by the PALS technique, which uses the o‐Ps pickup lifetime τ _3, as an indication of local electron density and mean free volume radius. The o‐Ps pickup intensity I₃, reflects the probability of o‐Ps formation. The o‐Ps components τ₃ and I₃ increases with salt concentration, which shows microstructural modifications due to the decrease in the crystallinity of the NaAlg as observed from XRD studies. Therefore, electrical studies on the doped NaAlg reveal that the ionic movement in the composites is mainly due to the segmental motion of the polymer backbone. So, the complex formation due to doping affects the free volume‐related microstructure and hence the dielectric properties including the AC conductivity of the polymer composites. POLYM. COMPOS., 35:1267–1274, 2014. © 2013 Society of Plastics Engineers     

Effect of Alumina Reactivity on the Densification and Properties of Al2O3–Cr2O3 Refractories

Alumina‐chrome (Al₂O₃–Cr₂O₃) refractories with Al₂O₃:Cr₂O₃ molar ratio 1:1 were synthesized in the temperature range of 1400–1700°C by conventional solid–oxide reaction route. The effect of different aluminas (viz., hydrated and calcined) on the densification, microstructure, and properties of Al₂O₃–Cr₂O₃ refractories was investigated without changing the Cr₂O₃ source. The starting materials were analyzed to determine the chemical composition, mineralogy, density, surface area, and particle size. Sintered materials were characterized in terms of densification, phase assemblage, and mechanical strength at room temperature and at higher temperatures. Microstructural evolution at different sintering temperature was correlated with sintering characteristics. It can be concluded that the Al₂O₃–Cr₂O₃ refractories prepared with hydrated alumina as Al₂O₃ source show better densification and hot mechanical strength than corresponding calcined variety.     

Dielectric behaviors of Nb2O5–Co2O3 doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics

Nb₂O₅ and Nb–Co doped 0.85BaTiO₃–0.15Bi(Mg_1/2Ti_1/2)O₃ (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb₂O₅/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb₂O₅ was found to possess a moderate dielectric constant (? ～ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from ?55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.     

Reaction of polyacrylic acid and metal oxides: Infrared spectroscopic kinetic study and solvent effect

In this work, we performed infrared spectroscopic studies of the reaction of poly(acrylic acid) (PAA) and metal oxides (ZnO, CaO, CuO, Cr₂O₃, and Al₂O₃). Factors such as the amount of metal oxide, reaction time, solvents, the kind of metal oxides, and temperature were also evaluated to derive the optimum condition for this reaction. The reactions of Cr₂O₃ and Al₂O₃ were far from complete. An extra solvent added to the reaction system could increase the solubility of PAA and metal oxide in the solution so as to completely react. The reactivity of the reaction was increased by using the hydrophilic solvent, particularly H₂O and CH₃OH. Moreover, the reaction rate increased when temperature decreased. The reactivity of the reaction was proportional to the pH value of the metal oxide in the aqueous solution. © 1997 John Wiley & Sons, Inc.     

Thermal evolution of Al2O3–CaO–Cr2O3 castables in different atmospheres

Al₂O₃–CaO–Cr₂O₃ castables are required for various furnaces linings due to their excellent corrosion resistance. However, toxic and water-soluble Cr(VI) could be generated in these linings during service. In this study Al₂O₃–CaO–Cr₂O₃ castables were prepared and heated at 300–1500 °C in air and coke bed to simulate actual service conditions. The formations of various phases were investigated by XRD and SEM-EDS. The Cr(VI) compounds CaCrO₄ and Ca₄Al₆CrO₁₆ formed in air at 300–900 °C and 900–1300 °C respectively, while C₁₂A₇ and CA₂ were generated rather than forming Cr(VI) compounds in coke bed at 700–1300 °C. However, at 1500 °C, nearly all the chromium existed in the form of (Al_1-xCr_x)₂O₃ solid solution in both atmosphere. As a result, the specimens treated in air contained 185.0–1697.8 mg/kg of Cr(VI) at 500–1300 °C but only 17.2 mg/kg of Cr(VI) at 1500 °C, whereas specimens treated in coke bed exhibited extremely low Cr(VI) concentration in the whole temperature range studied. Moreover, in coke bed, the mutual diffusion between Cr₂O₃ and Al₂O₃ was suppressed and a trace of Cr₂O₃ would even be reduced to form chromium-containing carbides on its surface, which would hindered the sintering process and hence lower the density as well as strength of the castables.     

Effects of Sintering Aids on the Transparency and Conversion Efficiency of Cr4+ Ions in Cr: YAG Transparent Ceramics

Tetravalent chromium‐doped Y₃Al₅O₁₂ ceramics were fabricated by solid‐state reactive sintering method using high‐purity Y₂O₃, α‐ Al₂O₃, and Cr₂O₃ powders as the starting materials. CaO and MgO were co‐doped as the sintering aids. The effects of TEOS and divalent dopants (CaO and MgO) on the optical qualities, the conversion efficiency of Cr⁴⁺ ions, and the microstructure evolutions of 0.1 at.% Cr⁴⁺: YAG ceramics were investigated. Fully dense, dark brown colored Cr⁴⁺: YAG ceramics with an average grain size of 3.1 μm were achieved. The in‐line transmittance of the as‐prepared ceramic at 2000 nm was 85.3% (4 mm thick), and the absorption coefficient at 1030 nm (the characteristic absorption peak of Cr⁴⁺ ions) was as high as 3.7 cm^?1, which was higher than that of corresponding single crystals fabricated by Czochralski method.