Metal-matrix nanocomposites

According to the matrix, nanocomposites may be classified into three categories i) Ceramic matrix nanocomposite, ii) metal matrix nanocomposites, and iii) polymer matrix nanocomposite. In the first group of composites the matrix is a ceramic material, i.e., a chemical compoxmd from the group of oxides, nitrides, borides, silicides, etc. In most cases of ceramic-matrix nanocomposites the dispersed phase is a metal, and ideally both components, the metallic one and the ceramic one, are finely dispersed in each other in order to elicit the particular nanoscopic properties. Nanocomposites from these combinations were demonstrated to improve their optical, electrical and magnetic properties [5,4], as well as tribological, corrosion-resistance and other protective properties [6,5]. Thus the safest measure is to carefully choose immiscible metal and... 

Metal matrix nanocomposites are those having metal as the continuous phase or matrix and other nanoparticles like carbon nanotube as the reinforced materials. These types of composites can be classified as continuous and noncontinuous. One of the more important nanocomposites is Carbon nanotube reinforced metal matrix composite, which is an emerging new material with the high tensile strength and electrical conductivity of carbon nanotube materials. In addition to carbon nanotube metal matrix composites, boron nitride reinforced metal matrix composites and carbon nitride metal matrix composites are the new research areas on metal matrix nanocomposites [9,10]. 

Nanocomposites in orthopedic tissue engineering mimic the complex nanoarchitecture of natural bone, muscle, cartilage, and tendon tissue, providing a novel and practical approach to tissue regeneration. All ceramic, polymer, and metallic matrix nanocomposites offer a wide range of properties with different chemical and mechanical features they also exhibit indispensable bioactivity. There is a great potential to improve current biomaterials and nanocomposite scaffolds for musculoskeletal tissue regeneration. However, the variety of different chemical elements and structures of nanocomposites make it difficult to predict unknown outcomes of exposure to musculoskeletal tissue. More research is clearly needed to fully understand favorable nanocomposite chemistries for musculoskeletal tissue. 

Sanaty-Zadeh, A., 2012. Comparison between current models for the strength of particulate-reinforced metal matrix nanocomposites with emphasis on consideration of HaU-Petch effect. Materials Science Engineering A 531, 112-118. 

Buhro, W.E., Haber, J.A., Waller, B.E., Trentler, T.J., Suryanarayanan, R., Frey, C.A. and Sastry, S.M.L. (1995) Nanocrystalline metals, intermetallics, and a metal-matrix nanocomposite by solution-based chemical reductions. Polymer Materials Science and Engineering, 73, 39. ... 

Processing and microstructural control of metal-reinforced ceramic matrix nanocomposites... 

For most metal-reinforced nanocomposites the thermal expansion coefficient of the metal phase will be larger than that of the matrix, reversing the expected stress fields compared to SiC-reinforced alumina. Thus while the tensile radial stresses surrounding occluded particles may induce transgranular cracking, the compressive hoop stresses may inhibit crack propagation if the particles are located at grain boundaries. Macrostresses in sub-micron Ni... 

The initial interest in ceramic matrix nanocomposites arose from reports by Niihara and co-workers indicating enhanced mechanical properties due to the presence of ceramic (SiC) particles.53 With the development of various processing routes to introduce nanometer-sized metal particles in a ceramic matrix, variations in functional (i.e. magnetic) properties are possible. In the following we briefly review the microstructurally dependent properties, with emphasis on the possible mechanisms leading to improved properties and using SiC-reinforced alumina as a point of comparison. 

In metal-reinforced ceramic matrix nanocomposites, matrix grain refinement has also been demonstrated by Niihara and co-workers.12 At the same time, as mentioned in the previous section, significant residual stress fields have been measured for Ni-reinforced alumina nanocomposites,23 although with reversed compression-tension fields compared to SiC-reinforced alumina. Thus for metal particles below the critical size for intrinsic cracking11 and... 

Abstract. IR pyrolysis of PAN and PAN based composites yields ordered graphitelike structure as well as several carbon nanostructures. Metal-carbon nanocomposites, in which the nanosized metal particles were introduced into the structure of carbon matrix in the course of IR pyrolysis of composite-precursor on the basis of PAN and metal (Gd, Pt, Ru, Re) compounds were prepared. The carbon phase of metal-carbon nanocomposites was shown to include different types of nano structured carbon particles. Bamboo-like CNT were observed in the structure of pyrolized at 910 and 1000°C composite-precursor based on PAN and GdCl3. At T=1200°C the solid carbon spheres with diameter in the range of 50-360 nm and octahedral carbon particles with the size in the range of 300-350 nm were observed. These nanostructured particles consist of carbon only or they include Gd nanoparticles incapsulated in carbon shell. IR pyrolysis of composite-precursor based on PAN as well as H2PtCl6 and RuC13 or NH4Re04 (Pt Ru(Re)=10 l) allows the preparation of Pt-Ru and Pt-Re alloys nanoparticles with 2[Pg.577]

Including into initial PAN solution metal compounds provides the formation of metal-carbon nanocomposites. The nanosized metal particles were introduced into the structured carbon matrix in the course of IR pyrolysis of composite-precursor on the basis of PAN and compounds of corresponding metals. In this way carbon composites containing nanosized Gd particles (4Efficient reduction of metal takes place in the course of IR pyrolysis of composite-precursor with participation of hydrogen, which is released in dehydrogenation of main polymeric chain of PAN. 

Figure 7 depicts histograms of size distribution of bimetallic nanoparticles in carbon matrix. Nanoparticles finely disperced in carbon matrix based on IRPAN are sized as 280% Pt-Re nanoparticles have the size as 6-7 nm. This metal-carbon nanocomposites can be used as possible catalyst materials in fuel cells. 

IR-pyrolysis of composite-precursor based on PAN as well as H2PtCl6 and RuC13 or NH4ReC>4 (Pt Ru(Re)=10 l) allows the preparation of Pt-Ru and Pt-Re alloys nanoparticles with 2carbon matrix. Such metal-carbon nanocomposites can se used as the possible catalyst material in fuel cells. 

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