Case Of Nanocomposites Research Articles

Roles of Size, Shape, Amount, and Functionalization of Nanoparticles of Titania in Controlling the Tribo-Performance of UHMWPE Composites

AThe present research is based on development and performance evaluation of UHMWPE composites with Titania particles in various amounts and two sizes including nano-size. It also included functionalization of nano-particles (NPs) with siloxane group to enhance the adhesion with the matrix, which would help to reduce wear. Thus, the work had objectives such as; to investigate size effect (nano vs micro) and optimise the amount for best performance from the series with varying amounts (0-8 % in case of micro-composites (MCs) and 0-4 % case of nano-composites (NCs)). It was also of interest to examine effect of siloxane-functionalization of NPs (since they performed significantly better than micro-particles (MPs)) on the performance of nano-composites. It was observed that for adhesive and erosive wear modes, both types of particles (MPs and NPs) proved detrimental in spite of enhanced hardness of the composites basically because of irregular shape of particles, which altered wear mechanisms adversely. NPs proved less detrimental while F-NPs (functionalized NPs) proved marginally detrimental. In abrasive wear mode, both proved beneficial, NPs being more effective than MPs and F-NPs proved the best. The studies revealed how shape of particle influence the performance of composites in various wear modes.

Time-resolved rheology as a tool to monitor the progress of polymer degradation in the melt state – Part II: Thermal and thermo-oxidative degradation of polyamide 11/organo-clay nanocomposites

Thermal and thermo-oxidative degradation of nanocomposites based on polyamide 11 (PA11) and organo-modified clay (Cloisite® 30B) are studied in the melt state (T = 215 °C) via time-resolved mechanical spectroscopy (TRMS). The goal is assessing the potentiality of rheological analysis for studying polymer degradation in complex systems such as polymer nanocomposites, whose rheological response stems from the combination of the contributions of polymer and nanoparticles. We prove that a thorough analysis grounded on TRMS allows to isolate the effect of degradation of the polymer matrix, whose progress can be hence profitably monitored. Essentially the same degradation mechanisms as in neat PA11 are identified for the nanocomposite, but the kinetics of the thermo-oxidation processes are much faster in the presence of organo-clay. In particular, rheology promptly identifies cross-linking reactions since the early stage of the treatment in air. Matrix-assisted laser desorption/ionization and oxidative induction time measurements corroborate the conclusions drawn on the basis of rheological analyses, shedding light on the chemical aspects of PA11 degradation. Overall, rheological analysis confirms to be a valuable tool for monitoring polymer degradation even in case of inherently complex systems such as nanocomposites. In this case, however, the analysis can be difficult if the dynamics of the nanoparticles prevail over those of the polymer matrix, which is the case of nanocomposites at high filler contents.

GRAIN REFINEMENT OF ALUMINUM-BASED NANOCOMPOSITES

ABSTRACTGrain refinement of an aluminum alloy was carried out by adding 0.6 wt.% Al-Ti5-B1master alloy to the aluminum alloy melt at 720 °C for a holding time of 10 minutes. 2wt.% Al2O3 nanoparticles were added to the base melt and mechanically stirred toproduce the nanocomposite. The two types of additions were used in case of thecombined treatment. A considerable grain refinement of the aluminum alloy wasobtained by the addition of Al-Ti5-B1 to its melt. A nanocomposite of fine matrixgrains was also produced. A modified nanocomposite of more refined matrix grainsand homogeneous microstructure was produced by application of the combinedtreatment. Both hardness and wear resistance of the aluminum alloy were increasedby grain refinement. Greater increases in these properties were obtained in case ofnanocomposite. Remarkable improvements in these properties were achieved in thecase of grain refined nanocomposite.

Nanoparticles prepared by the sol–gel method and their use in the formation ofnanocomposites with polypropylene

Hybrid layered aluminosilicate nanoparticles (HLNP) containing octadecylamine (ODA) asthe organic part, and silica nanoparticles with spherical morphology containing ODA(HSNP) or without ODA (SNP) were prepared by the sol–gel method and used for theformation of nanocomposites with polypropylene. The polypropylene matrices, of differentmolecular weight and polydispersity, were prepared using polymers obtained viaZiegler–Natta or metallocene catalysts. A strong influence of the morphologyand the presence of ODA on the surface of the nanoparticles was found on theformation and characteristics of the nanocomposites. The mechanical properties andthermal stability of these materials were determined and compared with those ofnanocomposites prepared with 2:1 phylosilicate clays such as montmorillonite andhectorite in similar polymer matrices. X-ray diffraction, transmission electronmicroscopy, and the study of mechanical properties showed that the use of HLNPallows nanocomposites with considerably improved mechanical properties to beobtained, compared with nanocomposites prepared with exfoliated clays. In the caseof nanocomposites prepared with spherical particles functionalized with ODA(HSNP), materials with high specific strength combined with high elongationbefore rupture were obtained. The thermal stabilization of polypropylene matricescontaining the synthesized nanoparticles (HLNP, HSNP or SNP) occurs about50 °C higher than that attained with clays.

Zirconia/nickel interfaces in micro- and nanocomposites

Abstract Experimental tests for zirconia/nickel composites determined lower toughness than expected. In this regard, the combination of ab initio density functional theory calculations and high-resolution transmission electron microscopy observations allowed to describe the nature of the zirconia/nickel interface and to justify the absence of any toughening mechanism by grain bridging of the metal particles. In the particular case of nanocomposites, enhanced values of hardness were found. Hardness increases have been justified by a novel model which takes into account the Hall — Petch effect and mean particle size according to the percolation theory. It has been found that this model is not exclusive to zirconia/nickel but can be extended to several other superhard composites.

Nanocrystalline functional materials and nanocomposites synthesis through aerosol routes

This paper represents the results of the design of functional nanocrystalline powders and nanocomposites using chemical reactions in aerosols. The process involves ultrasonic aerosol formation (mist generators with the resonant frequencies of 800 kHz, 1.7 and 2.5 MHz) from precursor salt solutions and control over the aerosol decomposition in a high-temperature tubular flow reactor. During decomposition, the aerosol droplets undergo evaporation/drying, precipitation and thermolysis in a single-step process. Consequently, spherical, solid, agglomerate-free submicronic particles are obtained. The particle morphology, revealed as a composite structure consisting of primary crystallites smaller than 20 nm was analysed by several methods (XRD, DSC/DTA, SEM, TEM) and discussed in terms of precursor chemistry and process parameters. Following the initial attempts, a more detailed aspect of nanocrystalline particle synthesis was demonstrated for the case of nanocomposites based on ZnO-MeO (MeO=Bi Cr+), suitable for electronic applications, as well as an yttrium-aluminum base complex system, suitable for phosphorus applications. The results imply that parts of the material structure responsible for different functional behaviour appear through in situ aerosol synthesis by processes of intraparticle agglomeration, reaction and sintering in the last synthesis stage.