Cr Nanocomposites Research Articles

Preparation, Physical Characterization and Adsorption Properties of Synthesized Co–Ni–Cr Nanocomposites for Highly Effective Removal of Nitrate: Isotherms, Kinetics and Thermodynamic Studies

Abstract In the current effort, the Co–Ni–Cr Nanocomposites were synthesized by chemical method and characterized by means of scanning electron micrographs (SEM), X-ray diffraction (XRD), Fourier trans from infra-red (FTIR), and vibration sample magnetization (VSM). In the final step, these nanoparticles were used to study the nitrate removal efficiency from aqueous solution. The effect of important factor including pH, concentration of Nitrate (NO3 −) ion, contact time and nanoparticle dose were studied in order to find the optimum adsorption conditions. A maximum of removal of the nitrate was observed at pH 4, initial concentration of 40 mg L−1, amount of nanoparticle of 0.06 g L−1 and contact time 60 min. The adsorption isotherm values were obtained and analyzed using the Langmuir, Frenudlich, Temkin and Dubinin–Radushkevich equations, the Temkin isotherm being the one that showed the best correlation coefficient (R2 = 0.999). In addition to, the adsorption kinetics studied by the pseudo-first-order, pseudo-second-order, Elovich model, Ritchie and intraparticle diffusion models. The experimental data fitted to pseudo-second-order (R2 = 0.999).

Silica-coated nano calcium carbonate reinforced polychloroprene rubber nanocomposites: influence of silica coating on cure, mechanical and thermal properties

The main objective of the present work is to compare the influence of silica-coated nano calcium carbonate (SNCC) with uncoated nano calcium carbonate (NCC) as filler on the property enhancement of polychloroprene rubber (CR) composites. The CR nanocomposites containing SNCC exhibit superior curing, mechanical and thermal properties in comparison to NCC-filled CR nanocomposites. The fantastic enrichment in the resulting properties of CR nanocomposites containing SNCC is mainly due to better rubber–filler interaction resulting from the reasonably excellent dispersion of SNCC within the CR matrix. The more uniform distribution of SNCC in comparison to NCC within the rubber matrix is also confirmed from morphological analysis. Thus, in this article, we report SNCC as a new type of efficient filler to reinforce the ultimate properties of CR nanocomposites for the first time.

Bulk Cu–Cr nanocomposites by high-energy ball milling and spark plasma sintering

A set of nanocomposite Cu–Cr powders with the grain size of these immiscible metals below 5nm were prepared by high-energy ball milling. The powders were then consolidated by short-term (5min) spark plasma sintering at 700–900°C under pressure (50MPa) to obtain essentially pore-free pseudo-alloys. The grain sizes in the produced bulk materials remained within the ranges 5–60nm for Cr-based phase and 200–300nm for Cu-based matrix. These nanocomposites have a Vickers microhardness up to 3.9GPa and a specific electrical resistivity in the range 6–9.6μΩcm, which make them promising candidates for the application in high-voltage circuit breakers.

Influence of carbon black in polychloroprene organoclay nanocomposite with improved mechanical, electrical and morphology characteristics

The effect of carbon black on nanoclay filled polychloroprene (CR) composites has been investigated. The nanoclay loading is fixed at 5 part per hundred rubbers (phr), and carbon black loading varied from 5 to 20 phr in rubber compounds. The rubber nanocomposites are prepared in laboratory by mixing in two-roll mill. The addition of nanoclay enhances mechanical properties especially tear strength and decreases water absorption without change in electrical properties compared to gum rubber vulcanisates. Wide angle X-ray diffraction and transmission electron microscopy are used to study the microstructure of CR nanocomposites. The addition of 5 parts of nanoclay to 15 phr carbon black filled samples shows synergistic effect between the fillers and suggests that the reinforcement is due to a more developed filler network formation in hybrid filler system than that in single phase filler. Significant improvement in mechanical, electrical and low water absorption properties has been obtained with these nanoclay and carbon black filled rubber nanocomposites. The paper concludes that nanocomposites containing a mixture of organoclay and carbon black in right proportion can be a substitute for rubber components used in underwater cable and device encapsulation applications.

Fe–Co–Cr nanocomposites for application in self-regulated rf heating

Fe–Co–Cr alloys have been developed with a Curie temperature, Tc, appropriate for ferrofluid cooling and self-regulated heating applications. These alloys have low Curie temperatures, moderate magnetic moments and provide increased heat capacity in a liquid used in a thermal cycle. Amorphous powders have been synthesized by cryo-SPEX milling melt-spun ribbons at 77 K. Transmission electron microscopy reveals cryomilled magnetic nanoparticles (MNPs) with a mean diameter of 4.2 nm to form agglomerates ∼30 nm in size. Vibrating sample magnetometer and superconducting quantum interference device magnetometry of amorphous powders reveal a specific magnetization, σs, of 104 emu/g at 4 K in a 300 mT field and a Tc of 335 K. Nanoparticles were suspended in ferrofluids by ultrasonication with a Pluronic F127 surfactant to stabilize them in aqueous solution. Ferrofluids of varying MNP concentration were rf heated in a 27.2 mT field at 267 kHz. For 1.24 vol % of MNPs in the ferrofluid, a solution reached temperatures>50 °C in ∼70 s, and showed Curie-limiting temperature behavior at ∼75 °C. These results demonstrate self-limited heating of FeCoCr MNPs at 75 °C which may have application in polymer curing.

On the exclusive growth of external chromia scale on the novel electrodeposited Cu–Ni–Cr nanocomposites

Novel metal-matrix nanocomposites (MMNCs) of Cu–30Ni–20Cr and Cu–50Ni–20Cr (by wt%), having a nanocrystalline Cu–Ni solid solution matrix with the dispersion of Cr nanoparticles, were fabricated by coelectrodeposition. Both nanocomposites exclusively grew external chromia scale during oxidation at 800 °C in air. The codeposited Cr nanoparticles, together with the numerous grain boundaries in the Cu–Ni matrix, promoted the establishment of a continuous chromia scale during the initial and transient oxidation stage, and then they functioned as “a reservoir” supplying sufficient Cr flux for the exclusive growth of the scale during the steady-state stage. The theoretical treatment using a two-phase alloy oxidation model indicates that high Cr diffusivity correlated with the persistence of an ultrafine-grained structure of the Cu–Ni matrix during oxidation is crucial to the exclusive chromia growth. Ni content increase did not significantly affect the chromia scale formation. This is fundamentally different from the oxidation of conventional Cu–Ni–Cr alloys investigated for comparison.

Preparation and Oxidation of Novel Electrodeposited Cu–Ni–Cr Nanocomposites

The poor oxidation resistance of Cu-base alloys limits their applications at high temperatures, and it cannot be improved by conventional Cr alloying because that requires an extremely high Cr content. In this work a chromia scale has been formed on novel Cu-base nanocomposites which contain much less chromium. Cu-Ni-Cr nanocomposites, with the weight percentage ratio of Cu/Ni approximate to 1 and various amounts of Cr, were produced by co-electrodeposition of Cu-Ni alloy with Cr nanoparticles which subsequently acted as "seeds" for chromia formation. The results of oxidation tests in air at 800 degrees C showed that only 15 wt.% Cr in the nanocomposite was required to form an external chromia scale. Furthermore, the scale consisted only of chromia rather than the duplex scales which form on the conventional alloy even when it contains significantly more chromium.

Processing, microstructure and mechanical properties of Al 2O 3–Cr nanocomposites

Alumina–chromium composites are well known for their good mechanical properties in comparison with pure alumina or metals. The composites have high hardness, high mechanical strength and because of their strong resistance to abrupt changes of temperature within the 25–1300 °C range or high temperature resistance to oxidation, they can be used at temperatures exceeding 1000 °C. Most of earlier works tended to use particles in the micrometer range. In this work, Al 2O 3–Cr nanocomposites with 25, 50 and 75 vol.% Cr were made by pressureless sintering and hot pressing of aluminium oxide nanopowder (∼80 nm) and chromium particles in the micrometer range. The presented paper concerns the examination of the microstructure and mechanical properties (hardness, bending strength, wear resistance) of Al 2O 3–Cr nanocomposites. The microstructural examinations (optical, scanning and transmission microscopy) show that almost fully dense materials can be obtained (typically 98–99% of theoretical density), when pressureless sintering at 1600 °C or hot pressing at 1400 °C. Moreover, the sintering process did not cause any major changes in the structure of the composite, although it was stated significant growth of the Al 2O 3 nanograins.

Processing and mechanical properties of Al2O3–5 vol.% Cr nanocomposites

Abstract The use of chromium (III) acetylacetonate as a source of nanometre sized chromium particles for the production of Al 2 O 3 –5 vol.% Cr nanocomposites has been investigated. The details of the processing procedure are crucial in determining the mechanical properties of the composite. The highest strength and fracture toughness, 736±29 MPa and 4.0±0.2 MPa m 1/2 , respectively, were obtained for the nanocomposite hot pressed at 1450 °C. It is shown that the strengthening in Al 2 O 3 –5% Cr nanocomposites mainly results from microstructure refinement in that the mean alumina matrix grain size in the optimum composite was 0.68 μm compared with a grain size of 3.6 μm in the monolithic alumina hot pressed under identical conditions. Crack bridging and crack deflection by the nano-sized Cr particles did not occur to any significant extent. The slight improvement in fracture toughness may result from the observed change in fracture mode from intergranular fracture for monolithic alumina to transgranular failure for the nanocomposites.