On the dependence of the nonlinearity coefficient of marine silica sands on grain size, shape, and packing density

2016 ◽  
Vol 140 (4) ◽  
pp. 3233-3233
Author(s):  
William Sanders ◽  
Allen Reed ◽  
Warren Wood
Keyword(s):  
Grain Size ◽  
Packing Density ◽  
Nonlinearity Coefficient

Reactive Milling and Mechanical Alloying in Electroceramics

2010 ◽  
Vol 63 ◽  
pp. 420-424
Author(s):  
Riva Rivas-Marquez ◽  
Carlos Gomez-Yanez ◽  
Ivan Velasco-Davalos ◽  
Jesus Cruz-Rivera
Keyword(s):  
Grain Size ◽  
Mechanical Activation ◽  
Raw Materials ◽  
Planetary Mill ◽  
Fabrication Technique ◽  
Nonlinearity Coefficient ◽  
Grain Sizes ◽  
Zno Varistor ◽  
Reactive Milling ◽  
Good Homogeneity

Using Mechanical Activation it is possible to obtain small grain size and good homogeneity in a ceramic piece. For ZnO varistor devices Mechanical Activation appears to be a good fabrication technique, since good homogeneity and small grain sizes are advantageous microstructural features. The typical formulation is composed by ZnO, Bi2O3, Sb2O3, CoO, MnO2 and Cr2O3 as raw materials, and during sintering, several dissolutions and reactions to form pyrochlore and spinel phases occur. When Mechanical Activation is applied to the entire formulation, it is difficult to know what processes are being mechanically activated due to the complexity of the system. The aim of the present work was to clarify how the mechanical activation is taking place in a typical ZnO varistor formulation. The methodology consisted in the formation of all possible combinations of two out of the five oxides above mentioned and to apply mechanical activation on the mixture of each pair of powders. The results showed that systems containing Bi2O3 are prone to react during mechanical activation. Also, reduction reactions were observed in MnO2. In addition, the powder mixture corresponding to the whole formulation was milled in a planetary mill, pressed and sintered, and varistor devices were fabricated. Improvement in the nonlinearity coefficient and breakdown voltage was observed.

scholarly journals Packing density of bi-disperse mixtures under one-dimensional compression

2021 ◽  
Vol 249 ◽  
pp. 07012
Author(s):  
Giulia Guida ◽  
Francesca Casini
Keyword(s):  
Grain Size ◽  
Packing Density ◽  
High Pressures ◽  
Maximum Density ◽  
Size Distributions ◽  
Compression Tests ◽  
One Dimensional ◽  
Grain Crushing ◽  
Granular Microstructure ◽  
Grain Size Distributions

This work aims to investigate the effect of fines in different type of bi-disperse grain size distributions in terms of minimum/maximum density, compressibility and crushing. The material adopted is the Light Expanded Clay Aggregate (LECA), an artificial granular material characterized by light, porous and crushable grains. The bi-disperse grading are firstly analysed in terms of packing density, measuring experimentally the minimum and the maximum porosity for different combination of sizes and volume proportions. Then, some selected mixtures are subjected to one-dimensional compression tests up to high pressures. Evolution of grain size due to grain crushing phenomena and compressibility are therefore measured and interpreted. Finally a theoretical model is adopted in order to predict the mechanical material response accounting grain crushing and granular microstructure.

scholarly journals Scattering Properties of Cometary Grains

1996 ◽  
Vol 150 ◽  
pp. 433-436
Author(s):  
D. B. Vaidya ◽  
J. N. Desai
Keyword(s):  
Grain Size ◽  
Angular Distribution ◽  
Linear Polarization ◽  
Packing Density ◽  
Phase Function ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Scattered Intensity ◽  
Porous Grains

AbstractHalley probes (Giotto, Vega) have shown that cometary grains can be extremely dark and might have fluffy structures. These probes have also detected submicron sized particles in the coma of the comet. In view of these observations and to interpret the observed data on several other comets we calculate the angular distribution of the scattered intensity, polarization and albedo for porous and compact particles. For these calculations, we apply discrete dipole approximation (DDA) first to the spheroidal particles, assumed to be made of small scattering elements (dipoles). Then we reduce the number of dipoles systematically to model the porous grains. We study the phase function, linear polarization, and albedo as a function of grain size and packing density.

Effect of Shock Loading on the Microstructure of Uniloy 326

1974 ◽  
Vol 32 ◽  
pp. 504-505
Author(s):  
K. P. Staudhammer ◽  
L. E. Murr
Keyword(s):  
Grain Size ◽  
Shock Loading ◽  
Current Investigation ◽  
Two Phase ◽  
05 C ◽  
Shock Deformation ◽  
Heat Treated

The effect of shock loading on a variety of steels has been reviewed recently by Leslie. It is generally observed that significant changes in microstructure and microhardness are produced by explosive shock deformation. While the effect of shock loading on austenitic, ferritic, martensitic, and pearlitic structures has been investigated, there have been no systematic studies of the shock-loading of microduplex structures.In the current investigation, the shock-loading response of millrolled and heat-treated Uniloy 326 (thickness 60 mil) having a residual grain size of 1 to 2μ before shock loading was studied. Uniloy 326 is a two phase (microduplex) alloy consisting of 30% austenite (γ) in a ferrite (α) matrix; with the composition.3% Ti, 1% Mn, .6% Si,.05% C, 6% Ni, 26% Cr, balance Fe.

Aspects of microanalysis in a transmission electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 510-511
Author(s):  
R. Sinclair ◽  
B.E. Jacobson
Keyword(s):  
Grain Size ◽  
Electron Beam ◽  
Electron Microscope ◽  
Chemical Analysis ◽  
Transmission Electron Microscope ◽  
Vapor Deposition ◽  
Critical Currents ◽  
X Ray ◽  
Fine Grain ◽  
Transmission Electron

INTRODUCTIONThe prospect of performing chemical analysis of thin specimens at any desired level of resolution is particularly appealing to the materials scientist. Commercial TEM-based systems are now available which virtually provide this capability. The purpose of this contribution is to illustrate its application to problems which would have been intractable until recently, pointing out some current limitations.X-RAY ANALYSISIn an attempt to fabricate superconducting materials with high critical currents and temperature, thin Nb3Sn films have been prepared by electron beam vapor deposition [1]. Fine-grain size material is desirable which may be achieved by codeposition with small amounts of Al2O3 . Figure 1 shows the STEM microstructure, with large (∽ 200 Å dia) voids present at the grain boundaries. Higher quality TEM micrographs (e.g. fig. 2) reveal the presence of small voids within the grains which are absent in pure Nb3Sn prepared under identical conditions. The X-ray spectrum from large (∽ lμ dia) or small (∽100 Ǻ dia) areas within the grains indicates only small amounts of A1 (fig.3).

Novel magneto-optical recording materials: Bi-substituted garnet films

1991 ◽  
Vol 49 ◽  
pp. 776-777
Author(s):  
Takao Suzuki ◽  
Hossein Nuri
Keyword(s):  
Grain Size ◽  
Amorphous Film ◽  
Nitrogen Atmosphere ◽  
Optical Recording ◽  
Garnet Film ◽  
Media Noise ◽  
Garnet Films ◽  
Order Of Magnitude ◽  
A New Technique ◽  
A Current

For future high density magneto-optical recording materials, a Bi-substituted garnet film ((BiDy)3(FeGa)5O12) is an attractive candidate since it has strong magneto-optic effect at short wavelengths less than 600 nm. The signal in read back performance at 500 nm using a garnet film can be an order of magnitude higher than a current rare earth-transition metal amorphous film. However, the granularity and surface roughness of such crystalline garnet films are the key to control for minimizing media noise.We have demonstrated a new technique to fabricate a garnet film which has much smaller grain size and smoother surfaces than those annealed in a conventional oven. This method employs a high ramp-up rate annealing (Γ = 50 ~ 100 C/s) in nitrogen atmosphere. Fig.1 shows a typical microstruture of a Bi-susbtituted garnet film deposited by r.f. sputtering and then subsequently crystallized by a rapid thermal annealing technique at Γ = 50 C/s at 650 °C for 2 min. The structure is a single phase of garnet, and a grain size is about 300A.

Structure of second phases in TiAl alloys containing Cr and B

1991 ◽  
Vol 49 ◽  
pp. 576-577
Author(s):  
Ernest L. Hall ◽  
Shyh-Chin Huang
Keyword(s):  
Grain Size ◽  
Second Phase ◽  
Structure And Properties ◽  
Tial Alloys ◽  
Second Phases ◽  
Interstitial Elements

Addition of interstitial elements to γ-TiAl alloys is currently being explored as a method for improving the properties of these alloys. Previous work in which a number of interstitial elements were studied showed that boron was particularly effective in refining the grain size in castings, and led to enhanced strength while maintaining reasonable ductility. Other investigators have shown that B in γ-TiAl alloys tends to promote the formation of TiB2 as a second phase. In this study, the microstructure of Bcontaining TiAl alloys was examined in detail in order to describe the mechanism by which B alters the structure and properties of these alloys.

Interfacial studies in Nb3Sn superconductors

1991 ◽  
Vol 49 ◽  
pp. 590-591
Author(s):  
Ernest L. Hall ◽  
Lee E. Rumaner ◽  
Mark G. Benz
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Flux Pinning ◽  
Size Control ◽  
High Magnetic Fields ◽  
Type Ii ◽  
Reaction Interface ◽  
Liquid Diffusion ◽  
Type Ii Superconductor ◽  
Grain Size Control

The intermetallic compound Nb3Sn is a type-II superconductor of interest because it has high values of critical current density Jc in high magnetic fields. One method of forming this compound involves diffusion of Sn into Nb foil containing small amounts of Zr and O. In order to maintain high values of Jc, it is important to keep the grain size in the Nb3Sn as small as possible, since the grain boundaries act as flux-pinning sites. It has been known for many years that Zr and O were essential to grain size control in this process. In previous work, we have shown that (a) the Sn is transported to the Nb3Sn/Nb interface by liquid diffusion along grain boundaries; (b) the Zr and O form small ZrO2 particles in the Nb3Sn grains; and (c) many very small Nb3Sn grains nucleate from a single Nb grain at the reaction interface. In this paper we report the results of detailed studies of the Nb3Sn/Nb3Sn, Nb3Sn/Nb, and Nb3Sn/ZrO2 interfaces.

The crystallization of thin-film ceramics

1992 ◽  
Vol 50 (1) ◽  
pp. 338-339
Author(s):  
J.M. Schwartz ◽  
L.F. Francis ◽  
L.D. Schmidt ◽  
P.S. Schabes-Retchkiman
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Sol Gel ◽  
Processing Route ◽  
Small Areas ◽  
Ceramic Thin Films ◽  
Complex Shapes ◽  
Sol Gel Process ◽  
Ceramic Precursors ◽  
Crystalline Ceramic

Ceramic thin films and coatings are of interest for electrical, optical, magnetic and thermal barrier applications. Critical for improved properties in thin films is the development of specific microstructures during processing. To this end, the sol-gel method is advantageous as a versatile processing route. The sol-gel process involves depositing a solution containing metalorganic or colloidal ceramic precursors onto a substrate and heating the deposited layer to form a crystalline or non-crystalline ceramic coating. This route has several advantages, including the ability to create tailored microstructures and properties, to coat large or small areas, simple or complex shapes, and to more easily prepare multicomponent ceramics. Sol-gel derived coatings are amorphous in the as-deposited state and develop their crystalline structure and microstructure during heat-treatment. We are particularly interested in studying the amorphous to crystalline transformation, because many key features of the microstructure such as grain size and grain size distribution may be linked to this transformation.

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