Controllable Fabrication of CuO/Ammonium Perchlorate (AP) Nanocomposites through Ceramic Membrane Anti‐Solvent Recrystallization

To improve the dispersion of CuO nanoparticles in ammonium perchlorate (AP), CuO/AP nanocomposites are designed and the novel ceramic membrane anti‐solvent crystallization (CMASC) method is applied to the nanocomposites synthesis. Typical experimental results demonstrate that nanocomposites with a size of less than 20 μm exhibit well‐defined hexahedral‐like structure and that the CuO nanoparticles are physically coated by AP crystals. The well‐dispersion of CuO nanoparticles and preparation of superfine AP crystals can be achieved at one step. The nucleation and growth mechanism of nanocomposites is discussed. To explore the actual formation process of the nanocomposites, relevant experiments are designed and carried out. The results are well consistent with previous assumptions and verify that several parameters, including feeding rate, volume ratio of matched solvent and anti‐solvent, can be employed to manipulate the size and morphology of the nanocomposites. The catalytic activity of CuO nanoparticles in the nanocomposites exhibits superior performance.     

Facile Preparation of AP/Cu(OH)2 Core‐Shell Nanocomposites and Its Thermal Decomposition Behavior

Ammonium perchlorate (AP)/Cu(OH)₂ core‐shell nanocomposites were successfully synthesized using a facile ultrasonic assisted‐coprecipitation synthesis route. The obtained AP/Cu(OH)₂ nanocomposites were characterized by means of powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Its thermal decomposition was studied under the non‐isothermal conditions with thermogravimetric analysis and differential scanning calorimeter (TG‐DSC) techniques. In this procedure, SEM and TEM observations revealed that Cu(OH)₂ nanoparticles with an average size of 10–15 nm were uniformly deposited on the surface of AP particles. Detailed characterization results indicated that the existence of evidence of Cu(OH)₂. As expected, it was found that the AP/Cu(OH)₂ nanocomposites with mass fraction of 2 wt % Cu(OH)₂ remarkably decreased the peak temperature of high temperature decomposition of AP by 80.2 °C from approximately 441.3 °C to 361.1 °C. As compared with pure AP, the AP/Cu(OH)₂ nanocomposites show lower impact and friction sensitivity. These results may lead to potential applications of the AP/Cu(OH)₂ nanocomposites in the composite solid propellants for accelerating the thermal decomposition of AP.     

Efficient Sensitivity Reducing and Hygroscopicity Preventing of Ultra‐Fine Ammonium Perchlorate for High Burning‐Rate Propellants

In this research, several inert materials, including some functional carbon materials, paraffin wax and the well‐known insensitive energetic material 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) were selected to reduce the undesirable high sensitivity and hygroscopicity of ultra‐fine ammonium perchlorate (UF‐AP) via polymer modified coating. Structure, sensitivity, thermal and hygroscopicity performances of the UF‐AP based composites were systematically studied by scanning electron microscopy, sensitivity tests, thermal experiments, contact angle, and hygroscopicity analysis. The results showed that both the impact and friction sensitivity of UF‐AP can be remarkably reduced, respectively, with only a small amount of 2 % (in mass) desensitization agents. Meanwhile, improved thermal decomposition was gained, and the hygroscopicity can also be reduced to a large extent. Propellants containing 10 % coated UF‐AP in mass were processed and tested, the burning rate reached 45.7 mm s⁻¹, 50 % higher compared with that of normal AP, with remarkably reduced impact sensitivity from 11.5 J to 29.6 J and friction sensitivity from 76 % to 28 %.     

Preparation of Nano‐Sized Copper β‐Resorcylate (β‐Cu) and its Excellent Catalytic Activity for the Thermal Decomposition of Ammonium Perchlorate

Copper β‐resorcylate (cupric 2,4‐dihydroxy‐benzoate, β‐Cu) nanoparticles were prepared at a large‐scale via a facile wet mechanical grinding method and vacuum freeze‐drying process. The as‐prepared β‐Cu nanoparticles were characterized by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier‐transform infrared spectroscopy (FT‐IR). The results revealed that the nano‐sized β‐Cu is of semi‐spherical shape and of homogeneous distribution, with a fairly uniform size of 100 nm. The formation mechanism of β‐Cu nanoparticles in the whole process was discussed in detail. Furthermore, the catalytic properties of as‐obtained β‐Cu were investigated. The TG/DSC study showed that nano‐sized β‐Cu could be a promising additive for accelerating the thermal decomposition of ammonium perchlorate (AP).     

Preparation of Magnesium‐based Hydrogen Storage Materials and Their Effect on the Thermal Decomposition of Ammonium Perchlorate

Magnesium‐based hydrogen storage materials (MgH₂, Mg₂NiH₄, and Mg₂Cu‐H) were prepared and their structures were determined by XRD and ICP investigations. Mg₂NiH₄ has a monoclinic crystal structure and Mg₂Cu‐H is a mixture of MgCu₂ and MgH₂. The effects of magnesium‐based hydrogen storage materials on the thermal decomposition of ammonium perchlorate (AP) were studied by thermal analysis (DSC). It was found that magnesium‐based hydrogen storage materials show obvious boosting effects on the thermal decomposition of AP. The thermal decomposition peak temperature of AP was decreased, while the heat release of the decomposition of AP was increased. It was revealed that the effects of magnesium‐based hydrogen storage materials on the decomposition of AP become stronger with increasing content. The influence mechanism on the thermal decomposition of AP is suggested as follows: hydrogen released from magnesium‐based hydrogen storage materials and Mg, Ni, or Cu react with the decomposed products of AP.     

Al2O3/Yttria‐Stabilized Zirconia Hollow‐Fiber Membrane Incorporated with Iron Oxide for Pb(II) Removal

Removal by absorptive ceramic membranes can simultaneously absorb and separate metal ions from water. Alumina/yttria‐stabilized zirconia (Al₂O₃/YSZ) hollow‐fiber membranes, fabricated using phase inversion and sintering process, were deposited with iron oxide by an in‐situ hydrothermal process. The results showed that α‐Fe₂O₃ was produced and incorporated across the membranes. A reduction in flux was recorded with the deposition of α‐Fe₂O_3. However, it improved the adsorption capacity for heavy metal adsorption. The adsorption‐separation test demonstrated that the optimized membrane is able to completely remove Pb(II) ions after two hours.     

Preparation and Properties of Fe3O4/Polypyrrole/Poly(Pyrrole-Co-Acrylamide) Nanocomposites

Polypyrrole (PPy)/poly(pyrrole-co-acrylamide) (Poly(Py-co-AAm)/nanocomposite was prepared by a simple and inexpensive in-situ co-polymerization of pyrrole and acrylamide in the presence of Fe₃O₄ nanoparticles. The nanocomposites were characterized by FTIR, SEM, XRD, TGA, and conductivity measurements. The FTIR spectra ascertain the chemical interlinking of polypyrrole and copolymer with magnetite nanoparticles. The XRD revealed that crystallinity of the copolymer was increased with weight percentage of the magnetite nanoparticles. SEM analysis showed that the nanoparticles were well shaped and uniformly dispersed in the nanocomposites. Thermal stability and the electrical conductivity of the nanocomposite were higher than that of polypyrrole and the copolymer.     

Highly Efficient Solvent‐Free Condensation of Carboxylic Acids with Alcohols Catalysed by Zinc Perchlorate Hexahydrate,Zn(ClO4)2⋅6 H2O

Zinc perchlorate hexahydrate, Zn(ClO₄)₂⋅6 H₂O, efficiently catalyses the esterification between nearly equimolar amounts of carboxylic acids and alcohols. The reaction works under solvent‐free conditions at relatively low temperatures. Excellent results were obtained with a wide range of substrates.     

Characterization of Solution‐Processed Double‐Walled Carbon Nanotube/Poly(vinylidene fluoride) Nanocomposites

Dispersion of CNTs in polymers can yield impressive property enhancements at low volume fractions, thus maintaining the inherent processability of the polymer. In particular, they can improve the electromechanical response of piezoelectric polymers by lowering the actuation voltage and increasing strain and stress response. In this work, piezoelectric PVDF and DWNTs are solution‐cast into films. SEM of fracture surfaces confirms good dispersion, and electrical conductivity measurements reveal a low percolation threshold (0.23 vol.‐%). The effect of CNTs on storage modulus, T_c, T_m and T_g of PVDF is studied. Electromechanical strain is observed at low actuation voltages, possibly due to enhanced local electric field in the presence of DWNTs.

     

Synthesis and Characterization of New Poly(ether-amide-imide)/Amino-Functionalized Fe3O4 Nanocomposites

New poly(amide-imide)/amino functionalized Fe₃O₄ nanocomposites were successfully fabricated through solution intercalation technique. A poly(amide-imide) derived from an imide-containing diacid and ether linkage diamine was synthesized and characterized. Aiming to have better compatibility, the hydrophilic nature of Fe₃O₄@SiO₂ was changed into organophilic using N-[3-(trimethoxysilyl)propyl]ethylenediamine. The amino-functionalized Fe₃O₄ showed well dispersion in the poly(amide-imide) matrix. Thermal gravimetric analysis results indicated that char yields of the nanocomposites were improved. Microscale combustion calorimetry results showed that poly(amide-imide) had good flame retardancy and amino-functionalized Fe₃O₄ has further improved this property of poly(amide-imide).     

Propylene/1‐Hexene Copolymer as a Tailor‐Made Poly(propylene) for Membrane Preparation via the Thermally Induced Phase Separation (TIPS) Process

Summary: Poly[propylene‐co‐(1‐hexene)], one example of a “tailor‐made poly(propylene)”, was synthesized using an iso‐specific metallocene catalyst in order to study the influence of copolymer composition on the pore size of isotactic poly(propylene) (iPP) membranes prepared by the TIPS process. The structure of the copolymers and their properties in solution were analyzed and discussed in relation to the polymer‐diluent phase diagram, the droplet growth kinetics during the TIPS process, the viscosity of the system and the final pore size of the membranes. The crystallization curve in the phase diagram was found to shift significantly as comonomer content increased and thus the droplet growth period was drastically increased. The resulting increase of the characteristic pore size in the membranes demonstrated that it is possible to use tailor‐made poly(propylene)s to control the pore size in porous membranes prepared via the TIPS process (under otherwise constant conditions).

Porous size is controlled by the polymer and the TIPS process.     

Crystallization and melting behavior of blends comprising poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) and poly(ethylene oxide)

Blends of poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) (PHBV) and poly(ethylene oxide) (PEO) were prepared by casting from chloroform solutions. Crystallization kinetics and melting behavior of blends have been studied by differential scanning calorimetry and optical polarizing microscopy. Experimental results reveal that the constituents are miscible in the amorphous state. They form separated crystal structures in the solid state. Crystallization behavior of the blends was studied under isothermal and nonisothermal conditions. Owing to the large difference in melting temperatures, the constituents crystallize consecutively in blends; however, the process is affected by the respective second component. PHBV crystallizes from the amorphous mixture of the constituents, at temperatures where the PEO remains in the molten state. PEO, on the other hand, is surrounded during its crystallization process by crystalline PHBV regions. The degree of crystallinity in the blends stays constant for PHBV and decreases slightly for PEO, with ascending PHBV content. The rate of crystallization of PHBV decreases in blends as compared to the neat polymer. The opposite behavior is observed for PEO. Nonisothermal crystallization is discussed in terms of a quasi‐isothermal approach. Qualitatively, the results show the same tendencies as under isothermal conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2776–2783, 2006     

Synthesis of the Ammonium Salt of 6‐Amino‐2‐hydroxy‐ 3,5‐dinitropyrazine and a Comparison of its Properties with those of Ammonium 3,5‐Diaminopicrate (ADAP)

The ammonium salt of 6‐amino‐2‐hydroxy‐3,5‐dinitropyrazine has been synthesised from 2,6‐dimethoxy‐3,5‐dinitropyrazine and its properties (DSC, crystal structure, impact sensitiveness and thermochemical properties) are compared with the analogous benzene derivative, ammonium 3,5‐diaminopicrate.     

Interfacial and mechanical properties of γ‐Fe2O3/segmented polyurethane/poly(vinyl chloride) composites

Segmented polyurethane (SPU)/poly(vinyl chloride) (PVC) blends were particulated with γ‐Fe₂O₃. Interfacial properties of the composite were studied through the adsorption behaviors of SPU and PVC and their blends on γ‐Fe₂O₃ particles surface. Mechanical properties of the composite were measured with dynamic mechanical analysis and tensile test measurements. PVC with functional groups (FPVC), because of strong interactions, showed preferential adsorption on γ‐Fe₂O₃ compared with SPU and PVC. Moreover, the γ‐Fe₂O₃ particles were covered by FPVC in the γ‐Fe₂O₃/SPU/FPVC composite. The adsorption layer of FPVC protected SPU from catalytic degradation by γ‐Fe₂O₃, resulting in increasing hydrolytic stability for SPU. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3030–3035, 2001     

Preparation of nanostructured Gd2Zr2O7-LaPO4 thermal barrier coatings and their calcium-magnesium-alumina-silicate (CMAS) resistance

Nanostructured 30 mol% LaPO₄ doped Gd₂Zr₂O₇ (Gd₂Zr₂O₇-LaPO₄) thermal barrier coatings (TBCs) were produced by air plasma spraying (APS). The coatings consist of Gd₂Zr₂O₇ and LaPO₄ phases, with desirable chemical composition and obvious nanozones embedded in the coating microstructure. Calcium-magnesium-alumina- silicate (CMAS) corrosion tests were carried out at 1250 °C for 1–8 h to study the corrosion resistance of the coatings. Results indicated that the nanostructured Gd₂Zr₂O₇-LaPO₄ TBCs reveals high resistance to penetration by the CMAS melt. During corrosion tests, an impervious crystalline reaction layer consisting of Gd-La-P apatite, anorthite, spinel and tetragonal ZrO₂ phases forms on the coating surfaces. The layer is stable at high temperatures and has significant effect on preventing further infiltration of the molten CMAS into the coatings. Furthermore, the porous nanozones could gather the penetrated molten CMAS like as an absorbent, which benefits the CMAS resistance of the coatings.     

Synthesis and Characterization of Poly(ethylene glycol) Methacrylate Based Hydrogel Networks for Anti‐Biofouling Applications

A series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid‐state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA‐based hydrogels could be highly beneficial for uses as fouling‐resistant materials, for instance, as protective coatings for desalination membranes.

     

逆向热致相分离法(RTIPS)制备PES/DMAc/DEG体系微孔膜及其性能表征

以PES/DMAc/DEG低临界共溶温度(LCST)体系为铸膜液,利用低临界共溶温度(LCST)的热致相分离(LCST-TIPS,简称RTIPS)法制备PES微孔膜.探究影响PES微孔膜理化性能及其结构的2个主要因素:凝胶浴温度、非溶剂(DEG)/溶剂(DMAc)的质量比.运用扫描电镜(SEM)﹑纯水通量﹑BSA截留率...     

Electric Field‐Enhanced Solid‐State Conversion of Ceramic Sr5(PO4)3F to Crystals

The single crystal solid‐state conversion of fluorapatite‐type Sr₅(PO₄)₃F (Sr‐FAP) has been achieved by spark plasma sintering with the assistance of NaF additive. NaF was determined to act as both a sintering aid and impurity solute along the grain boundaries (GBs), controlling both the space charge and GB migration rate. Postsintering isothermal annealing was performed to examine the effect of DC electric field on grain growth. From the space charge potential determined from impedance spectra measurements, in combination with the theoretical contribution of space charge to grain‐boundary energy reduction, it was concluded that the magnitude of the space charge in Sr‐FAP is temperature dependent. As such, a moderate decrease in polycrystalline GB driving force is the main cause for the increased single crystal migration length that was observed in this study.     

Thermogravimetric analysis of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T_o) was derived by T_o = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (T_p) was T_p = 1.07B + 273, and the final temperature (T_f) at which degradation was completed was T_f = 1.10B + 280. The percentage of the weight loss at temperature T_p (C_p) was 69 ± 1% whereas the percentage of the weight loss at temperature T_f (C_f) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), T_o = 0.98B + 262, T_p = 1.00B + 278, and T_f = 1.12B + 285. The values of C_p and C_f were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T_o, T_p, andT_f) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001