A Novel Approach to Prepare CaCO3/Polyvinylpyrrolidone (PVP) Composite Nanofibers

A new route to prepare CaCO₃ nanoparticles/polyvinylpyrrolidone (PVP) nanofibers is reported. An aqueous solution of K₂CO₃ was added to a solution of CaCl₂/PVP, resulting in in-situ preparation of CaCO₃ nanoparticles. Then composite nanofibers containing CaCO₃ nanoparticles were successfully prepared by electrospinning. The morphology of the resulting composite nanofibers was characterized by field-emission scanning electron microscopy. In addition, the products were characterized by thermogravimetry analysis and Fourier transform infrared spectra.     

Crystallization and Thermal Conductivity of CaCO3 Nanoparticle Filled Polypropylene

Isotactic polypropylene (IPP) and calcium carbonate (CaCO₃) nanocomposites were prepared by melt extrusion in a twinscrew extruder. The effect of CaCO₃ nanoparticles on the crystallization and thermal conductivity (TC) of PP was studied by thermal analysis (DSC) and thermal conductivity analysis (TCA). The introduction of CaCO₃ nanoparticles resulted in an increase in crystallinity. The incorporation of this nanoparticle (up to 15 phr) caused a significant increase of TC of PP, especially for larger filler content. Several models were used for prediction of TC of the nanocomposites. The experimental results had a good correlation with the Ce Wen Nan Model.     

Biosynthesis of different morphologies of CaCO3 nanomaterial assisted by thermophilic strains HEN-Qn1

Thermophilic bacterial strains HEN-Qn1 were incubated at 60 °C in a solution containing calcium chloride. With slow release of CO₂ metabolic end products from the bacteria, CaCO₃ nanomaterials were found after 12 h through a transmission electron microscope (TEM). CaCO₃ nanorods were obtained extracellularly, whereas a unique morphology of nanosphere was observed intracelluarly. A single crystal was further characterized by electron pattern (ED) and X-ray powder diffraction (XRD). Moreover, a putative mechanism has been proposed based on theoretical analyses and experimental evidences. These results indicated that thermophilic bacteria had a well-controlled effect during the crystal growth of inorganic materials, which provided us a promising application of bacteria in biosynthesis of nanomaterials.     

Mechanochemical Activation of Magnetite Nanoparticles

Using Mössbauer spectroscopy as a function of ball milling time, it was found that nanomagnetite behaves differently than magnetite during mechanochemical activation. The phase sequence is determined by the original particle size of the powder. Magnetite suffers a phase transformation to hematite, while nanomagnetite (d = 19nm) gives rise to superparamagnetism as effect of prolonged milling.     

Aggregation,fracture initiation,and strength of PP/CaCO3 composites

Polypropylene/CaCO₃ composites were homogenized in a twin-screw compounder and then injection molded into tensile bars. Six different fillers were used in a wide range of average particle sizes between 0.08 and 12 μm. Tensile and flexural properties were measured by standard techniques, while impact resistance was determined by instrumented impact testing. Structure was characterized by light and electron microscopy, while failure initiation and propagation was studied with in situ high-voltage electron microscopy. The results showed that aggregation of particulate fillers occurs when their particle size is smaller than a critical value. This critical size depends on component properties and processing conditions. Strength and impact resistance usually decrease with increasing number of aggregates. The presence of aggregation can be detected by the use of a simple semiempirical model. Comparison of samples prepared by two different technologies showed that twin-screw extrusion and injection molding leads to relatively homogeneous composites, which was indicated by smaller deviations of the properties from theoretical predictions. In spite of the acceptable dispersion, impact resistance showed a large standard deviation, probably determined by the local variation of structure. In composites containing relatively large particles, the dominating micromechanical deformation process is debonding, while in the presence of extensive aggregation of small particles, cracks are initiated inside and propagate through aggregates. Mixed-mode failure may also occur at certain intermediate panicle sizes.     

Mechanochemical Synthesis and Characterization of GaN Nanocrystals

A solid-state displacement reaction of Ga₂O₃ with Mg₃N₂ has been used to synthesize GaN nanocrystals by mechanochemical processing. X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) measurements indicated that the nanocrystals had a hexagonal structure and sizes ranging from 4 to 20nm. Optical absorption and transmission measurement showed the bandgap of the nanocrystals was consistent with that of bulk GaN samples (3.43eV). This study demonstrates that mechanochemical processing has significant potential for the synthesis of GaN nanocrystals in a simple and efficient way.     

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.     

利用聚乙烯亚胺修饰的CaCO3仿生模板合成3D花朵型二氧化硅微球

利用聚乙烯亚胺(PEI)修饰的碳酸钙仿生模板合成了具有3D花朵型形貌的SiO₂微球.通过调整碳酸钙微粒表面不同浓度PEI的吸附量实现SiO₂微球的形貌控制呈现花朵或刀锋的形状. 用XPS和SEM对制备的SiO₂微粒进行表征. 结果表明,不用浓度的PEI修饰可以较好地控制3花朵型DSiO₂微球的形貌.     

Characteristics of Fe2O3 Nanoparticles from Doped Low-pressure H2/O2/Ar Flames

A burner stabilized premixed low-pressure flame has been used to generate iron-oxide (Fe₂O₃) nanoparticles with sizes in the range 7–20nm. The H₂/O₂/Ar flames were doped with different amounts of iron-pentacarbonyl (Fe(CO)₅) with concentrations in the range 524–2096ppm. The influence of precursor concentration on composition, structure, morphology, and size have been studied utilizing transmission electron microscopy (TEM), X-ray powder diffraction (XRD), measurements of the specific surface area (BET), and infrared spectroscopy (FT-IR). The product particles consist of both, the - and the -phase of Fe₂O₃. Average particle sizes were measured in the range 7.4–16nm depending on precursor concentration and flame conditions.     

In situ preparation of hydrophobic CaCO3 in the presence of sodium oleate

Hydrophobic CaCO₃ particles were directly prepared via carbonation of Ca(OH)₂ slurry in the presence of sodium oleate at room temperature. Sodium oleate was used to modify the surface property of CaCO₃ particles. The measurement of relative contact angle and active ratio indicated that CaCO₃ samples were hydrophobic. DTG, FT-IR and TEM analysis of the obtained product indicated that the hydrophobic property was attributed to the deposition of calcium oleate, produced in the reaction mixture, onto the surface of calcium carbonate particles. They were covered on the CaCO₃ crystals surface and modified their surface property; at the same time they own CC bonds and could be polymerized or copolymerized later to give a polymeric monolayer.     

Synthesis of Single Crystalline ZnO Nanoparticles by Salt-Assisted Spray Pyrolysis

LiNO₃ was used as a shield in the preparation of single crystalline ZnO particles by a spray pyrolysis process in order to prevent agglomeration and enhance the crystallinity of the ZnO. LiNO₃ was added to a precursor solution of zinc acetate dihydrate prior to its atomization by means of an ultrasonic transducer. Agglomerate-free particles having a mean particle size of 26 nm were successfully obtained after washing the product. X-ray diffractometry, field-emission scanning electron micrograph and transmission electron micrograph data indicate that the size and morphology of ZnO were strongly influenced by the operating temperature used and the residence time of the particle in the reactor.     

Surface Modification of Al2O3 Fiber with Binary Nanoparticles using a Dry-Mechanical Coating Technique

Integrating materials with different functionalities into a composite material to obtain synergetic properties has generated considerable interest in various scientific and technical fields. In this study, a dry-mechanical coating process was used to fix nanosized Al₂O₃ and CuO particles directly onto the surface of Al₂O₃ fiber substrates by employing high shear and compression forces. The resulting composite materials showed good dispersion and homogeneous distribution of Al₂O₃ and CuO nanoparticles. Important coating parameters, including initial particle loadings and processing times were investigated for their effects on coating characteristics and product properties. The experimental results showed that the product surface area increased with higher nanoparticle loadings. The degree of dispersion and homogenous distribution of Al₂O₃ nanoparticles with CuO nanoparticles increased with the processing time. Additionally, the crystalline phase of raw materials was preserved during the coating process under the conditions studied in this work.     

Synthesis and Rapid Densification of Nanoparticles of Barium Praseodymium Hafnium Oxide: A New Complex Perovskite

Nanoparticles (25–100 nm) of barium praseodymium hafnate (Ba₂PrHfO_5.5), a new substrate material for high temperature superconducting YBa₂Cu₃O_7- and Bi-cuprate films has been synthesized through an exothermic chemical reaction for the first time. The Ba, Hf and Pr ions required for the formation of Ba₂PrHfO_5.5 were obtained in solution by dissolving a stoichiometric mixture of BaCO₃, Pr₆O₁₁ and HfO₂ heated at 1200°C for 4 h in boiling nitric acid. By complexing the ions with citric acid and adjusting the oxidant/fuel ratio, it was possible to obtain Ba₂PrHfO_5.5 as nanoparticles in a single step chemical process. The nanoparticles thus obtained were characterized by powder X-ray diffraction, thermogravimetric analysis, differential thermal analysis, infrared spectroscopy, and surface area analysis. The Ba₂PrHfO_5.5 synthesized through the present exothermic chemical process, because of its nanoparticulate nature, could be sintered to a density of 98% in a period of just 9 min at a temperature of 1435°C in air. Scanning electron microscopic studies on the sintered Ba₂PrHfO_5.5 samples showed that densification has occurred without significant microstructural coarsening up to a sintered density of 98% of its theoretical value in a short duration.     

Synthesis of spherical LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was successfully prepared by controlled crystallization. The preparation started with the spherical coprecipitate of Ni_1/3Co_1/3Mn_1/3CO₃ from NiSO₄, CoSO₄, MnSO₄, NH₄HCO₃, and NH₃·H₂O, followed by pyrolysis of Ni_1/3Co_1/3Mn_1/3CO₃ at 600°C for 3 h. The X-ray diffraction analysis showed that the homogeneous cubic (Ni_1/3Co_1/3Mn_1/3)₃O₄ was obtained after the pyrolysis. Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was obtained by sintering of the mixture of as-obtained (Ni_1/3Co_1/3Mn_1/3)₃O₄ and LiOH·H₂O at 900°C for 6 h in air. As-prepared spherical LiNi_1/3Co_1/3Mn_1/3O₂ presented initial discharge capacity of 162.9 mA h g⁻¹ and capacity retention of 98% at 50th cycle.     

Effect of Mechanochemical Processing on Illite Particles

Dry grinding of illite particles has been investigated by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption techniques. Prolonged grinding results in an amorphous illite structure and the mechanochemical effect markedly promotes a reduction in reflection intensities with increased grinding time. It is confirmed that illite is very susceptible to alteration by grinding. The illite crystal size (d₀₀₆) appears to reach a limit after 2 h of grinding. N₂ adsorption studies indicate that illite ground for 8 h shows a larger average pore diameter than a sample after 4 h grinding or the original illite. It is inferred that grinding is good for the formation of macrostructural pores. Illite grinding results in a decrease in the Brunauer‐Emmet‐Teller (BET) surface area and total pore volume. IR spectroscopy shows a slight alteration in the illite bands after mechanochemical processing and some new bands were detected after 4 or more hours of grinding.     

Synthesis and properties of Au-Fe3O4 and Ag-Fe3O4 heterodimeric nanoparticles

Monodisperse Au-Fe 3 O 4 heterodimeric nanoparticles (NPs) were prepared by injecting precursors into a hot reaction solution.The size of Au and Fe 3 O 4 particles can be controlled by changing the injection temperature.UV-Vis spectra show that the surface plasma resonance band of Au-Fe 3 O 4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size.The as-prepared heterodimeric Au-Fe 3 O 4 NPs exhibited superparamagnetic properties at room temperature.The Ag-Fe 3 O 4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO 3 as precursor instead of HAuCl 4.It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs.     

Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.     

Structural, electrical and gas-sensing properties of In2O3 : Ag composite nanoparticle layers

The central objective of this study is to investigate (i) size-dependent properties of In₂O₃ nanoparticles and (ii) the role of metal additives in enhancing the gas sensing response. For this purpose, In₂O₃ : Ag composite nanoparticle layers having welldefined individual nanoparticle size and composition have been grown by a two step synthesis method. Thermogravimetric analysis, X-ray diffraction and transmission electron microscopy have been used to study the effect of post-synthesis heat treatment on the size and structure of the nanoparticles. A first-time unambiguous observation of sizedependent lowering of transformation temperature has been explained in terms of lower cohesive energy of surface atoms and increase in surface-to-volume ratio with decrease in nanoparticle size. The gas sensing studies of In₂O₃ as well as the In₂O₃ : Ag composite nanoparticle layers have been studied as a function of size and composition. In₂O₃: Ag composite nanoparticle layers with 15% silver show a sensitivity of 436 and response time of 6 s for 1000 ppm of ethanol in air. Ag additives form a p-type Ag₂O, which interact with n-type In₂O₃ to produce an electron-deficient space-charge layer. In the presence of ethanol, interfacial Ag₂O reduces to Ag, creating an accumulation layer in In₂O₃ resulting in increased sensitivity     

Synthesis and structural properties of polypyrrole/nano-Y2O3 conducting composite

In this work, polypyrrole/nano-Y₂O₃ conducting composite was synthesized by chemical oxidative polymerization. The composite was characterized using transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectra, UV-vis absorption spectra, X-ray photoelectron spectroscopy and electrical conductivity measurements. The results indicate that Y₂O₃ nanoparticles are almost enwrapped by polypyrrole. The addition of Y₂O₃ nanoparticles results in changes in the surface structure and conductivity of the composite. Thermogravimetric analysis shows that composite has better thermal stability than that of pure polypyrrole.     

Morphology Control of Platinum Nanoparticles and their Catalytic Properties

Platinum nanoparticles with different morphology were prepared by reduction of K₂PtCl₄ solution in the presence of different capping polymers. It was found that the shapes and the sizes of the Pt nanocrystals resulted were related to the kind of capping polymer used. When poly(vinylpyrrolidon) (PVP), poly(N-isopropylacrylamide) (NIPA) and sodium poly(acrylate) (SPA) were used as capping agents, the dominant shapes of the Pt nanocrystals observed by transmission electron microscopy were hexagonal (62%), square (67%) and triangular (41%), respectively. The average sizes of Pt nanocrystals were 6.9, 13.6 and 14.6 nm for capping polymers of PVP, NIPA and SPA, respectively. The colloidal Pt nanoparticles with different morphologies were supported on -Al₂O₃ (1 wt.% Pt) and then their catalytic activity for NO reduction by CH₄ was tested in the 350–600°C temperature range. Additionally, the catalytic activities of these alumina-supported Pt nanocrystals were compared with a conventional catalyst having the average size of Pt particles of 2.4 nm. Over the alumina-supported Pt nanocrystals as compared with the conventional Pt/Al₂O₃, it was observed that the NO/CH₄ reaction yields to NH₃ and CO decreased significantly and on the other hand, the yield to N₂O increased. The experimental results are suggesting that the catalytic behavior can be tuned in a convenient way through the morphological control of the metal nanoparticles.