Grain size effect on the electrical response of SnO2 thin and thick film gas sensors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Size effect on structure and dielectric properties of Nb-doped barium titanate

It is known that the dielectric properties of BaTiO3 (BT) are strongly dependent on its grain size. Coarse-grained ceramics of pure BT showed lower dielectric constant at room temperature then fine grained. Many authors considered that when the grain size is lower than 700 nm, the lattice of BT changes from tetragonal to pseudocubic, and the dielectric constant value is very low. In the doped BT this effect is more complex, because it is necessary to consider also the influence of dopants. The grain size effect on the structure and dielectric properties of niobium-doped barium titanate was investigated. Niobium-doped barium titanate was prepared from powders obtained by doping of commercial barium titanate and from organometallic complex using citrates as precursors (Pechini procedure). The crystal and microstructure of sintered niobium-doped barium titanate were determined. Dielectric constant and dissipation factor were measured. The observation confirmed that the structure and properties are strongly dependent on grain size. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Grain size effect on the structural and dielectric properties of Pb0.85La0.15TiO3 ferroelectric ceramic compound

This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 +/- 0.08 mu m and 146 +/- 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at T-m as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A Laboratory Experiment Using Nanoindentation to Demonstrate the Indentation Size Effect

A laboratory experiment using nanoindentation to demonstrate the indentation size effect is described. This laboratory introduces students to sophisticated instrumentation at low cost and low risk and utilizes recent research in the materials community as its foundation. The motivation, learning objectives, experimental details, data, and data analysis are presented. This experiment is intended for use in an upper-division materials science elective at the university level and has been successfully used in laboratory courses for senior undergraduates and first-year graduate students at Stanford University and Santa Clara University.

Latent hardening size effect in small-scale plasticity

We aim at understanding the multislip behaviour of metals subject to irreversible deformations at small-scales. By focusing on the simple shear of a constrained single-crystal strip, we show that discrete Dislocation Dynamics (DD) simulations predict a strong latent hardening size effect, with smaller being stronger in the range [1.5 µm, 6 µm] for the strip height. We attempt to represent the DD pseudo-experimental results by developing a flow theory of Strain Gradient Crystal Plasticity (SGCP), involving both energetic and dissipative higher-order terms and, as a main novelty, a strain gradient extension of the conventional latent hardening. In order to discuss the capability of the SGCP theory proposed, we implement it into a Finite Element (FE) code and set its material parameters on the basis of the DD results. The SGCP FE code is specifically developed for the boundary value problem under study so that we can implement a fully implicit (Backward Euler) consistent algorithm. Special emphasis is placed on the discussion of the role of the material length scales involved in the SGCP model, from both the mechanical and numerical points of view.

Latent hardening size effect in small-scale plasticity

We aim at understanding the multislip behaviour of metals subject to irreversible deformations at small-scales. By focusing on the simple shear of a constrained single-crystal strip, we show that discrete Dislocation Dynamics (DD) simulations predict a strong latent hardening size effect, with smaller being stronger in the range [1.5 µm, 6 µm] for the strip height. We attempt to represent the DD pseudo-experimental results by developing a flow theory of Strain Gradient Crystal Plasticity (SGCP), involving both energetic and dissipative higher-order terms and, as a main novelty, a strain gradient extension of the conventional latent hardening. In order to discuss the capability of the SGCP theory proposed, we implement it into a Finite Element (FE) code and set its material parameters on the basis of the DD results. The SGCP FE code is specifically developed for the boundary value problem under study so that we can implement a fully implicit (Backward Euler) consistent algorithm. Special emphasis is placed on the discussion of the role of the material length scales involved in the SGCP model, from both the mechanical and numerical points of view.

A survey of the literature on the size effect on material strength /

"Final report for period 1 August 1972 to 30 September 1976."

The correlation of indentation size effect experiments with pyramidal and spherical indenters

Experiments were conducted in annealed iridium using pyramidal and spherical indenters over a wide range of load. For a Berkovich pyramidal indenter, the hardness increased with decreasing depth of penetration. However, for spherical indenters, hardness increased with decreasing sphere radius. Based on the number of geometrically necessary dislocations generated during indentation, a theory that takes into account the work hardening differences between pyramidal and spherical indenters is developed to correlate the indentation size effects measured with the two indenters. The experimental results verify the theoretical correlation.

The correlation of the indentation size effect measured with indenters of various shapes

Experimental results are presented which show that the indentation size effect for pyramidal and spherical indenters can be correlated. For a pyramidal indenter, the hardness measured in crystalline materials usually increases with decreasing depth of penetration, which is known as the indentation size effect. Spherical indentation also shows an indentation size effect. However, for a spherical indenter, hardness is not affected by depth, but increases with decreasing sphere radius. The correlation for pyramidal and spherical indenter shapes is based on geometrically necessary dislocations and work-hardening. The Nix and Gao indentation size effect model (J. Mech. Phys. Solids 46 (1998) 411) for conical indenters is extended to indenters of various shapes and compared to the experimental results. © 2002 Elsevier Science Ltd. All rights reserved.

Size effect on the tensile strength of fine-grained copper

We considered the effect of the thickness of copper sheet on its tensile strength. A model in which the strength of surface grains is governed by dislocation image forces, while that of interior grains is determined by dislocation cell structure, was proposed. Using a rule of mixtures, the dependence of strength on the specimen thickness was calculated. A master curve representing the calculated dependence of normalized strength on the ratio of sheet thickness to grain size was confirmed by experiment.

Effect of body size on growth and energy budget of Nile tilapia, Oreochromis niloticus

A growth trial was conducted at 30 degrees C to investigate the effect of body size on growth and energy budget of Nile tilapia. The average initial body weights of the four size groups tested were 9.3, 34.1, 80.3 and 172.4 g, respectively. Fish were fed to satiation twice a day with a diet containing 35.6% crude protein. Food consumption (C-max: kJ/day) increased with body size (W: g) according to the relationship: Ln C-max = 1.45 + 0.42 LnW. The final body contents of dry matter, crude protein and ash per unit body weight increased with increasing body size while contents of fat and energy were independent of body size. Specific growth rates of wet weight, dry weight, protein and energy decreased as the fish increased in size. Feed efficiencies in wet weigh, dry weight and crude protein decreased with increasing body size, while that of energy remained unchanged. The proportions of energy intake allocated to the various components (faecal energy, excretory energy, heat production and recovered energy) of the energy budget were not significantly affected by body size, and the average budget was: 100IE-18.5(+/- 1.33)FE + 5.9 (+/- 3.09)(ZE + UE) + 49.3(+/- 3.77)HE + 26.3(+/- 6.23)RE, where IE, FE, (ZE + UE), HE and RE represent gross energy intake, faecal energy, excretory (non-faecal) energy loss, heat production and recovered energy (growth), respectively. It is suggested that the decrease in growth rate in larger fish is mainly due to the decrease in relative food intake. (C) 1997 Elsevier Science B.V.

Effect of parental stock size on F-1 genetic structure in the bay scallop, Argopecten irradians (Lamarck, 1819)

Three F-1 families of the bay scallop, Argopecten irradians, were produced from one, two and 10 individuals. The genetic changes in these populations, which suffered recent and different levels of bottleneck, were analysed using amplified fragment length polymorphism (AFLP) techniques. In the parental stock, a total of 330 bands were detected using seven AFLP primer pairs, and 70% of the loci were polymorphic. All F-1 groups had a significantly lower proportion of polymorphic loci when compared with the initial stock, and loss of the rare loci and reduction in heterozygosity both occurred. The progeny of the larger population (i.e., N=10) exhibited a lesser amount of genetic differentiation compared with the progeny from N=2, which showed lesser differentiation than progeny from N=1. The effective population sizes (N-e) in N=1, 2 and 10 were estimated as 1.50, 1.61 and 2.49. Based on regression analysis, we recommend that at least 340 individuals be used in hatchery populations to maintain genetic variation.

Effect of pore size on the catalytic activities of K-I 0 clay and H-zeolites for the acetalization of ketones with methanol

One-pot acetalizations of cyclohexanone. acetophenone and benzophenone were carried out using methanol over H-montmorillonite clay (a mesoporous material). silica, alumina, and different zeolites such as HFAU-Y.HBeta, H-ZSM-5, and H-mordenite. In all the cases a single product-the corresponding dimethylacetal-was obtained in high yields. Hemiacetal formation was not observed with any catalyst. A comparison of catalytic activity indicated that montmorillonite K-10 is the most active catalyst for the reaction. As evidenced by the reaction time studies, the catalyst decay is greater over the zeolite catalyst than over the clay.

Effect of grain size on the deformation and dynamic recrystallization of mg-3AI-1Zn

The influence of grain size on the deformation of extruded Mg-3Al-1Zn tested in tension at temperatures between room temperature and 300°C is investigated. The results enable estimation of the deformation conditions for the transition from slip to twinning dominated flow and for the initiation and completion of dynamic recrystallization. A map illustrating these critical parameters is constructed and it is shown that the operating conditions of the common wrought processes straddle key transitions in microstructure behaviour.