Journal of Metastable and Nanocrystalline Materials 

About: Journal of Metastable and Nanocrystalline Materials is an academic journal. The journal publishes majorly in the area(s): Nanocrystalline material & Amorphous metal. It has an ISSN identifier of 1422-6375. Over the lifetime, 828 publications have been published receiving 3995 citations.

Ductility in Nanostructured and Ultra Fine-Grained Materials: Recent Evidence for Optimism

Abstract: This paper reviews the present data on tensile ductility of nanostructured and ultra finegrained materials and discusses the various phenomena believed relevant to deformation and therefore ductility in these materials. While most nanostructured materials are “brittle” in tension (<5% elongation) there are now a few examples of ductile behavior. There are a number of instances of ductile ultra fine-grained materials. The recent evidence for both increased strength and ductility in certain nanostructured and ultra fine-grained materials is cause for much optimism.

Growth of Zinc Oxide nanowires and nanobelts for gas sensing applications

Abstract: Zinc Oxide (ZnO) is a very useful as a solid state gas sensor material. In chemical sensing the surface and interface interactions between the analyte molecules and the sensing material is all but important that is read through the changes in electrical conductance. In that sense, nano-objects with a large surface atom/bulk atom ratio, like nanoparticles and nanowires, are potentially the best chemical sensors. The mechanism envisioned involves the adsorption (and eventually diffusion) of the analyte molecule at the surface that induces a change in the electrical resistance of the nano-object. The most convenient way to measure changes in electrical resistance in such devices is to obtain the specific material as nanowires or as connected nanoparticles. Here, we will discuss about a low-temperature wet-chemical process of synthesizing ZnO nanoparticles, nanowires and nanobelts for application as gas sensors.

Field Dependence of Blocking Temperature in Magnetite Nanoparticles

Abstract: Spherical magnetite nanoparticles having average particle size = 5 nm have been synthesized by coprecipitation of Fe(II) and Fe(III) salts in KOH with Polyvinylalcohol (PVA). The resulting dry powder displayed superparamgnetic (SPM) behaviour at room temperature, with a transition to a blocked state at TB ~ 45 K for applied field Happ = 500 Oe. The effect of dipolar interactions was investigated by measuring the dependence of TB on the applied field Hap and driven ac field in susceptibility data. A thermally activated model has been used to fit the dynamic data to obtain the single-particle energy barriers Ea = KeffV, allowing us to estimate the contributions of dipolar interactions to the single-particle effective magnetic anisotropy Keff. We have measured the dependence of TB with Hap in order to draw the transition contours of a H-T diagram. Two different regimes are found for the (TB-T0) ~H dependence at low and high fields, that can be understood within a pure SPM relaxation-time (Neel-Brown) landscape. The TB(H) data shows a crossover from λ = 2/3 to λ ~2 for applied magnetic fields of ≈ 550 Oe. Introduction. Along the last two decades we have witnessed considerable achievements related to the design of magnetic nanostructures, aiming both basic research and technological applications. [1,2] These genuine improvements of fabrication techniques have not been accompanied by a detailed comprehension of the relationships between structural and magnetic properties in fine particle systems, even those composed of ‘simple’ materials whose bulk properties are well understood. One of the oldest magnetic materials known, magnetite, has been revisited in recent years since it turned out that the magnetic and spin structures in this material are appealing for applications in magnetoelectronic and spin-valve devices. Magnetite Fe3O4 is a ferrimagnet (TC=860 K) with a cubic spinel structure. The Fe and Fe ions occupy the tetrahedral (A) and octahedral (B) sites, with a formal ionic distribution that can be represented by (Fe)A(FeFe)BO4 i.e. there is a mixed valence of Fe on the octahedral sublattice. The firstorder magnetocrystalline anisotropy constant has a negative value (at room temperature) of K1 = 13.5 kJ/m. This material undergoes a magnetic transition at the Verwey temperaure TV = 120 K, which is related to structural changes from cubic to triclinic symmetry, yielding to uniaxial magnetic anisotropy with easy axis. In this work we report on the magnetic properties of Fe3O4 nanoparticles with average linear dimensions = 5 nm, in order to study the effect of temperature and external field on the transition to the ordered state. Experimental Procedure Magnetite particles of around 5 nm were obtained following Lee et al. method [3]. The iron salt mixture (Fe(II) and Fe(III) was added to 1M K(OH) solution with 1wt.% of Polyvinylalcohol (PVA) at room temperature, and afterwards dried in air. X-ray diffraction (XRD) measurements 1 Corresponding author. E-mail: goya@macbeth.if.usp.br

XRD and FTIR Studies of Nanocrystalline Cellulose from Water Hyacinth ( Eichornia crassipes ) Fiber

Abstract: The isolation and characterization of nanocrystalline cellulose (NCC) from water hyacinth (WH) fibers were carried out. There are two treatments to obtain NCC from WH fibers by chemical and mechanical treatments. The chemical treatment involved alkalization with NaOH 25% in a highly-pressured tube, acid hydrolysis with 5M HCl, and bleaching with (NaClO2:CH3COOH) in ratio 5:2. The mechanical treatment was performed by using ultrasonic homogenizing at 12000 Rpm for 2 h. The morphological surface was observed by Transmission Electron Microscopy (TEM). TEM reported that the size of NCC was 10–40 nm. Crystallinity index and functional group analysis of the NCC WH fibers were also examined using X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. XRD reported that the crystallinity index increased significantly after chemical and mechanical treatment due to the presents of crystalline area in the WH fibers. The crystallinity index of raw fiber, digester, bleaching, and ultrasonic homogenizing were 7%, 68%, 69%, and 73% respectively. The content cellulose of final product was 68% as measured by the chemical composition test. Meanwhile, FTIR reported that WH fibers after being given chemical treatment lead the functional group change due to removal hemicellulose and lignin. The result of XRD and FTIR were indicated that the sample of NCC WH fibers presents the structure of cellulose crystal type I.