Publicaciones
en revistas internacionales
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GOMEZ (I.), HERNANDEZ (M.), AGUILAR (J.), HINOJOSA (M.).-Comparative study
of microwave and conventional processing of MgAl2O4
based materials. Aceptado para publicación en Ceramics International,
2003.
Abstract
A comparative study of microwave and conventional processing of ceramic
materials based on MgAl2O4 is presented in this paper, in particular sinters
obtained from MgO and Al2O3 with 1 wt% of CaO as
an additive, and Al2O3-MgAl2O4
composites. Microwave processing took place under air at 800 Watts and
2.45 GHz during 4.5 minutes, conventional processing in an electrical resistance
furnace, also on air, was conducted at 1400°C for 96 hours.
The MgO:Al2O3 weight ratio employed for the synthesis
of MgAl2O4 was 1:2.45. According to semi-quantitative X-ray diffraction
analysis, approximately 90% of MgAl2O4 was produced
with both processing methods. Scanning Electron Microscope images of the
microstructure revealed a similar morphology for the two methods, nevertheless
the grain size was different. The Al2O3: MgAl2O4
weight ratios for the production of the composites were 9:1, 1:1 and 1:9
using the two methods and the conditions already described. A heterogeneous
microstructure was observed in the specimen processed by microwaves. Due
to the different nature of the processes, an extensive property was compared
against an intensive one, therefore the aim of this work was to have a
realistic comparison between the materials obtained with these processes
by taking into account energetic as well as kinetic aspects.
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AGUILAR (J.), ARATO (A.), HINOJOSA (M.), ORTIZ (U.)-Synthesis of MgAl2O4
at low temperature with CaCO3 additions. Materials Science Forum,
Vol 442 pp. 79-84, 2003.
Abstract
Ever since spinel MgAl2O4 was proposed as a substitute
material for chromium based refractories, manufacturers have been encouraged
to seek alternative forms of production. Addition of mineralizers has been
widely employed as a method for reducing processing temperatures, which
are above 1800°C without additives. Mixtures of MgO and Al2O3
(molar ratio 1:1) have been prepared in this work, together with different
additions of CaCO3 (up to 30 mol%) in a resistance furnace at
1400°C. All formed phases are identified by X-ray diffractometry and
microstructures are characterized by scanning electron microscopy. Results
show that samples contain mainly the spinel phase with a small amount of
calcium aluminates (CaAl2O4 and Ca12Al14O33).
The X-ray patterns suggest that calcium compounds as well as spinel are
present as mixtures because both, angle peak location and relative intensities
are maintained like in the mixtures of powders randomly orientated. This
assumption is confirmed by EDX analysis that shows zones in the samples
with spinel grains over calcium aluminates. The synthesized spinel has
a density of 3.19 g/cm3 after 5 hours at 1400°C.
Más texto
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AGUILAR (J.), PEARCE (J.).-Estimation of the dielectric properties of aluminum
oxide while exposed to microwaves. British Ceramics Transactions, Vol.
102, No. 2, pp 52-56, 2003
Abstract
The results of experiments are reported on aluminium oxide in a waveguide,
in order to determine its dielectric properties, by applying a method that
is a variant of the six- port technique for determining permittivity at
high power. The aiming of the work was to measure the properties of a relatively
large sample, while exposed to microwaves, as a function of temperature.
Under these conditions the thermal profile affects overall properties,
especially in the case of large samples. These aspects are important because
these are the conditions that would be present in most microwave processes.
Aluminium oxide is widely used in the refractory industry, and some reported
data are considered for comparison.
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texto.
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AGUILAR (J.), GOMEZ (I.).-Microwave processing of calcium zirconate from
CaO and ZrO2. Advances in Technology and Materials and Materials
Processing Journal, Vol. 5, No. 2, pp. 92-97, 2003.
Abstract
This paper presents the results about the production of CaZrO3
using microwaves as an energy source. The samples were obtained by mixing
CaO and ZrO2 powders in the molar ratio 1:1. Pressing, power
level and mass were the varied parameters. The obtained samples were analyzed
by means of X–Ray diffraction and observed by optical and scanning electron
microscopy. CaZrO3 was found in all the samples. The results
of temperature versus reflected power and the thermal evolution suggests
an increase in the electric conductivity of the sample. One specie that
was always found in the samples was the (CaO)0.15(ZrO2)0.85
which could be the responsible of this behavior. Despite the conductive
nature of the sample, there is evidence of volumetric heating.
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texto.
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AGUILAR (J.), RODRIGUEZ (J.), HINOJOSA (M.).-Production of B-SiC with microwaves
as an energy source. Journal of the Microwave Power and Electromagnetic
Energy, IMPI,Vol. 36, No. 3, 2001,
pp.169-177.
Abstract
This work describes the production of silicon carbide using microwaves
as the energy source, which was supplied by means of variable power, up
to 2000 Watts, magnetron operating at 2.45 GHz. The obtained samples were
analyzed by means of X-ray diffraction and observed with electron microscopy
(SEM). Temperatures achieved were around 2000°C, which is the upper
limit for the B-SiC growth regime, before getting other SiC polytypes.
Analysis of different portions of the sample showed that B-SiC was the
only formed compound, although free SiO2 and graphite were also
present. Observations made by SEM demonstrated different crystal growth
regime, meaning that thermal conditions were not totally uniform. The amount
of B-SiC found and the relative simplicity of the device prove that production
of this material from silica and graphite is possible by applying microwaves
as an energy source.
Más texto.
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ORTIZ (U.), AGUILAR (J.), KHARISSOVA (O.).-Effect of iron over the magnesia-alumina
spinel lattice. Advances in Technology and Materials and Materials Processing
Journal, Vol. 2, No. 2, 2001, pp. 107-116.
Abstract
The effect of iron over the magnesia-alumina spinel (MgAl2O4)
lattice were studied by means of observing peak positions and their intensities
in X-ray charts. Two different methods for producing magnesia-alumina spinel
(MgAl2O4) were used in this work. The first one consists
in heating up magnesia (MgO)-alumina (Al2O3)- hematite
(Fe2O3) mixtures in a resistance furnace. Temperature
was 1400°C, which is enough to produce spinel, especially when iron
was added. A second method for achieving temperatures over 2000°C was
by means of microwaves as energy source. Patterns from the samples show
that indeed there are changes in the lattice parameter and cationic distribution.
It has been observed that a spinel produced at high temperatures without
additives gives a pattern that does not correspond to the perfect spinel
structure. When hematite was added, the obtained MgAl2O4
is shows a cationic distribution that tends to correspond to the normal
spinel structure.
Más texto.
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ORTIZ (U.), AGUILAR (J.), BERRUN (J.), VIRAMONTES (R.).-Development of
iron layers on the internal walls of the direct reduction reactors, Ceramics
International, Elsevier, 1999, vol.
25, 2, pp. 165-175
Summary
Refractory bricks are the most common materials used in equipments
for carrying processes at high temperatures, such as the production of
steel, cement and glass. These bricks are exposed to severe operation conditions,
their life determines if an equipment should be stopped for reparation
or replacement of the bricks. One of the phenomena that is present inside
reactors or furnaces with an internal wall covered by refractory material
is the formation of layers. As they growth, they cause disturbs in the
product flow or at least decreases the reactor or furnace capacity, and
in the worst case it is necessary to stop the equipment for major reparations.
This work is centered in the formation of layers inside the direct reduction
reactors. These layers are formed over the firebrick (Al2O3,
SiO2) wall from the Direct Reduced Iron (DRI) that is being
processed in the reactor. The aim of this work is to describe the mechanism
of formation and growth of these layers. We conducted several test for
simulating the formation of layers by the application of shear stresses
at high temperatures and under a reductive atmosphere to the a DRI pellet-refractory
interphase. The amount of DRI adhered to the sample bricks was measured
following an experimental design of nine independent variables. Temperature,
shear stress and time were identified as important variables for the mechanism
of formation and growth of the layers. Confirmation of the importance of
these variables was determinated by means of a proposal for avoiding the
adhesion problem. This proposal consists in a treatment on the surface
of the brick that minimizes the adhesion of DRI. The successfully treatment
of more than 6000 bricks for operating plants proves that our conclusions
are correct.
Más texto.
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AGUILAR (J.), GOMEZ (I.).- Microwaves applied to carbothermic reduction
of iron ore pellets, Journal of the Microwave and Electromagnetic Energy,
IMPI,
Vol. 32, No. 2, 1997, pp. 67-73
Summary
Results of reducibility tests of reduction conducted on iron ore pellets
with carbon are presented in this work. Work done is centered on reduction
kinetics using carbon as reducing agent with conventional heat supply (heat
transfer process) compared with reduction kinetics where heat is supplied
by microwaves to the whole volume. Ore used in this work is called "Alzada"
which has reducibility characteristics well known, and is often used as
standard for comparison.
Más texto.
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AGUILAR (J.), GONZALEZ (M.), GOMEZ (I.).- Microwaves as an energy source
for producing magnesia - alumina spinel, Journal of the Microwave and Electromagnetic
Energy, IMPI, Vol. 32,
No. 2, 1997, pp. 74-79
Summary
This work describes the production of magnesia-alumina spinel using
microwaves as energy source. The microwave energy was supplied by means
of an 800 W magnetron operating at 2.45 GHz. The microstructure and the
mineral composition were studied by means of SEM and X-Ray diffraction
respectively. The resultant product shown sintered zone and incipient smelting
of the reagents meaning that microwave processing could be a practical
form for spinel production.
Más texto.
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ORTIZ (U.), AGUILAR (J.), ESPARZA (C.), GUERRERO (C.).- Production of MgO
in an electric arc furnace. Thermal analysis. Modelling and Simulation
in Materials Science and Engineering, IOP,
Vol. 5, 1997, pp. 347-356
Summary
The computer simulation that is presented here is the response of an
industrial challenge about how the electric arc furnace, where the smelting
process of magnesium oxide (MgO) is taking place, should be charged for
avoiding shell overheating. If solid MgO is charged at a very high rate,
the processing time becomes very long; on the other hand, if the feed rate
is too slow, external shell made of steel reaches temperatures above its
melting point. Thus, it is necessary to reduce the electrode current or
to charge more material for avoiding shell overheat. With the aid of this
model, a charge scheme for the furnace could be proposed, in order to have
the maximum production without shell overheat. Validation of the model
has been made with temperature measurements along the external shell while
the process was being conducted; the size and shape of the smelted zone
after the fusion were also compared with information obtained from the
graphic results predicted by the model. Results from the model are in good
agreement with the measurements done. Calculation of the specific energy
consumption can be provided with the input energy rate and the mass of
the smelted MgO.
Más texto.
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AGUILAR (J.), FUENTES (R.), VIRAMONTES (R.).-Simulation of iron ore reduction
in a fixed bed. Modelling and Simulation in Materials Engineering, IOP,
Vol. 3, 1995, pp. 135-147.
Summary
A simulation of direct reduction in a fixed bed process of iron ore
is presented. Simulation is done with a model which takes into account
bed characteristics, including reaction kinetics, thermal effects, quality
and flow of reducing gas. It is considered that reactor is a cylinder with
wall made of layers of refractory and insulator, this reactor contains
a bed of iron ore pellets which will be reduced under a flow of reducing
gas in longitudinal direction (along cylinder). Finite difference method
is used to solve simplified differential equations for description of heat
transfer gas-pellet, gas-refractory, refractory-insulator-environment,
and heat changes due to reaction inside reactor. Simulator is fitted by
using reducibility tests in laboratory and runs in a pilot plant. It is
found that due to process nature, this process is carried out almost fully
in transitory stage and that is way this simulation is necessary.
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AGUILAR (J.).-Vinculación entre Universidad e Industria; Una experiencia
provechosa. Comercio Exterior,
Vol. 44, pp. 249-252, 1994.
Resumen
En este documento se describe la manera en que el Programa de Doctorado
en Ingeniería de Materiales mantiene una estrecha vinculación
con la industria local y se muestra la importancia de que tal vinculación
haya sido considerada desde la concepción misma del Programa. Se
destacan las ventajas de contar con el acceso a los recursos financieros
y de infraestructura de la industria y se enfatizan algunos de los logros
más importantes del Programa, entre los cuales destacan la preparación
de recursos humanos de alto nivel que incidirán en los centros de
investigación y desarrollo de las empresas con las que se realizó
investigación conjunta, en centros de investigación públicos
decentralizados o en la propia Universidad.
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