236 research outputs found
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Novel Binders and Methods for Agglomeration of Ore
Many metal extraction operations, such as leaching of copper, leaching of precious metals, and reduction of metal oxides to metal in high-temperature furnaces, require agglomeration of ore to ensure that reactive liquids or gases are evenly distributed throughout the ore being processed. Agglomeration of ore into coarse, porous masses achieves this even distribution of fluids by preventing fine particles from migrating and clogging the spaces and channels between the larger ore particles. Binders are critically necessary to produce agglomerates that will not break down during processing. However, for many important metal extraction processes there are no binders known that will work satisfactorily. A primary example of this is copper heap leaching, where there are no binders that will work in the acidic environment encountered in this process. As a result, operators of acidic heap-leach facilities see a large loss of process efficiency due to their inability to take advantage of agglomeration. The large quantities of ore that must be handled in metal extraction processes also means that the binder must be inexpensive and useful at low dosages to be economical. The acid-resistant binders and agglomeration procedures developed in this project will also be adapted for use in improving the energy efficiency and performance of other agglomeration applications, particularly advanced primary ironmaking
Cavitation Damage During Flexural Creep of SiAlONâYAG Ceramics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65505/1/j.1151-2916.1991.tb07156.x.pd
Recommended from our members
NOVEL BINDERS AND METHODS FOR AGGLOMERATION OF ORE
Many metal extraction operations, such as leaching of copper, leaching of precious metals, and reduction of metal oxides to metal in high-temperature furnaces, require agglomeration of ore to ensure that reactive liquids or gases are evenly distributed throughout the ore being processed. Agglomeration of ore into coarse, porous masses achieves this even distribution of fluids by preventing fine particles from migrating and clogging the spaces and channels between the larger ore particles. Binders are critically necessary to produce agglomerates that will not breakdown during processing. However, for many important metal extraction processes there are no binders known that will work satisfactorily. Primary examples of this are copper heap leaching, where there are no binders that will work in the acidic environment encountered in this process. As a result, operators of many facilities see large loss of process efficiency due to their inability to take advantage of agglomeration. The large quantities of ore that must be handled in metal extraction processes also means that the binder must be inexpensive and useful at low dosages to be economical. The acid-resistant binders and agglomeration procedures developed in this project will also be adapted for use in improving the energy efficiency and performance of a broad range of mineral agglomeration applications, particularly heap leaching
Electroweak Bubble Nucleation, Nonperturbatively
We present a lattice method to compute bubble nucleation rates at radiatively
induced first order phase transitions, in high temperature, weakly coupled
field theories, nonperturbatively. A generalization of Langer's approach, it
makes no recourse to saddle point expansions and includes completely the
dynamical prefactor. We test the technique by applying it to the electroweak
phase transition in the minimal standard model, at an unphysically small Higgs
mass which gives a reasonably strong phase transition (lambda/g^2 =0.036, which
corresponds to m(Higgs)/m(W) = 0.54 at tree level but does not correspond to a
positive physical Higgs mass when radiative effects of the top quark are
included), and compare the results to older perturbative and other estimates.
While two loop perturbation theory slightly under-estimates the strength of the
transition measured by the latent heat, it over-estimates the amount of
supercooling by a factor of 2.Comment: 48 pages, including 16 figures. Minor revisions and typo fixes,
nothing substantial, conclusions essentially unchange
Baryogenesis from Primordial Blackholes after Electroweak Phase Transition
Incorporating a realistic model for accretion of ultra-relativistic particles
by primordial blackholes (PBHs), we study the evolution of an Einstein-de
Sitter universe consisting of PBHs embedded in a thermal bath from the epoch
sec to sec. In this paper we use Barrow
et al's ansatz to model blackhole evaporation in which the modified Hawking
temperature goes to zero in the limit of the blackhole attaining a relic state
with mass . Both single mass PBH case as well as the case in which
blackhole masses are distributed in the range gm
have been considered in our analysis. Blackholes with mass larger than gm appear to survive beyond the electroweak phase transition and,
therefore, successfully manage to create baryon excess via
emissions, averting the baryon number wash-out due to sphalerons. In this
scenario, we find that the contribution to the baryon-to-entropy ratio by PBHs
of initial mass is given by , where
and are the CP-violating parameter and the initial mass
fraction of the PBHs, respectively. For larger than ,
the observed matter-antimatter asymmetry in the universe can be attributed to
the evaporation of PBHs.Comment: Latex2e file with seven figures included as postscript file
The order of the quantum chromodynamics transition predicted by the standard model of particle physics
We determine the nature of the QCD transition using lattice calculations for
physical quark masses. Susceptibilities are extrapolated to vanishing lattice
spacing for three physical volumes, the smallest and largest of which differ by
a factor of five. This ensures that a true transition should result in a
dramatic increase of the susceptibilities.No such behaviour is observed: our
finite-size scaling analysis shows that the finite-temperature QCD transition
in the hot early Universe was not a real phase transition, but an analytic
crossover (involving a rapid change, as opposed to a jump, as the temperature
varied). As such, it will be difficult to find experimental evidence of this
transition from astronomical observations.Comment: 7 pages, 4 figure
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