Escuela de Ingeniería Química

The effect of ferric iron on the properties of Mg-silicate post-perovskite (PPv) were studied up to 138 GPa using synchrotron X-ray diffraction and Mössbauer spectroscopy. Our diffraction measurements revealed that the incorporation of Fe 3+ has virtually no effect on the volume of PPv, in contrast to Fe 2+ , which increases the volume. Therefore, incorporation of Fe 3+ increases the density of PPv much more effectively than Fe 2+ . Mössbauer spectroscopy suggests that Fe 3+ enters PPv through chargecoupled substitution and is high spin in the bipolar prismatic site and low spin in the octahedral site (i.e., mixed spin state). Our results may have important implications for the gravitational stability of lower-mantle heterogeneities.

FINEMET type ribbons (Fe 73.5 Si 13.5 Nb 3−x Mo x B 9 Cu 1 , x = 1.5, 2 at.%) were produced by the planar flow casting technique and subsequently heat treated at 823 K to induce nanocrystallization and to optimize its soft magnetic properties. The coercivity, measured by conventional fluxmetric method, resulted in H C = 0.53 ± 0.10 and 0.41 ± 0.05 A/m for x = 1.5 and 2 respectively. A correlation between magnetic properties and the amorphous and nanocrystalline phases when Nb was partially substituted with Mo was studied by means of Mössbauer spectroscopy and X-ray diffraction.

Recently, bulk amorphous alloys were produced in the Fe-B-Si-P-C system with high glass forming ability, excellent magnetic properties and the advantage of containing no expensive glass-forming elements, such as Ga, Y, Cr or Nb, having, therefore, a good perspective of commercial applications. In the present work, the Fe 76 P 5 (Si 0.3 B 0.5 C 0.2 ) 19 amorphous alloy prepared by two quenching techniques has been studied. Amorphous ribbons of about 40 m thick were obtained by planar-flow casting together with cylinders having 1 and 2 mm diameter produced by copper mold injection casting. All the samples appear fully amorphous after X-ray diffraction analysis. A comprehensive set of thermal data (glass, crystallization, melting and liquidus temperatures) were obtained as well as a description of the melting and solidification processes. Mechanical microhardness tests showed that the samples have a hardness of 9.7 ± 0.3 GPa. Good soft-magnetic properties were obtained, including a high magnetization of 1.44 T and a low coercivity (4.5 A/m for ribbons and 7.5 A/m in the case of 1 mm rod samples, both in as-cast state). Thermomagnetic studies showed a Curie temperature around 665 K and the precipitation of new magnetic phases upon temperatures of 1000 K. Furthermore, the frequency dependence of magnetic losses at a fixed peak induction was studied. The results suggest the occurrence of a fine magnetic domain structure in bulk samples. The good soft magnetic properties of the bulk metallic glass obtained by copper mold casting for this particular Fe-based composition suggests possible applications in transformer cores, inductive sensors and other devices.

Two simple models were developed in order to determine the chemical composition of both nanocrystals and intergranular amorphous phases in nanocrystallized Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 containing Ge using data from X-ray diffraction and Mössbauer spectroscopy techniques. Saturation magnetization of the amorphous intergranular matrix (M s am ) was calculated considering the contribution of the a-Fe(Si,Ge) nanocrystals and saturation magnetization of the alloys. The behavior of M s am with the iron content of the matrix was obtained and discussed. The exchange stiffness constant for the nanograins and for the amorphous phases was determined. The increment in the coercive field (H c ) with increasing Ge content was evaluated using two theoretical models for the random magnetocrystalline anisotropy constant (/K 1 S). Results show that the magnetic hardening observed could not be attributed to an increase in /K 1 S but mainly to an important increment of the magnetostriction constant of the a-Fe(Si,Ge) nanocrystals (l s cr ). Values for l s cr are proposed.

The magnetic and mechanical properties of amorphous ribbons heat treated in a conventional furnace are compared with those observed in current-annealed samples (in which the heating is produced by a #ow of an electric current through the sample). To perform this comparison, a current-to-temperature semiempirical function is used, and di!erent parameters are "tted. The current-annealed samples present less brittleness when annealed near the nanocrystallization temperature, while maintaining the well-known excellent soft magnetic properties.

Two series of Fe}Si}B}Cu}Nb-based ribbons with partial substitution of aluminium were investigated with respect to their magnetoimpedance and the in#uence of heat treatments on it. Although the original Finemet composition (f"s"b"0) showed a much higher magnetoimpedance ratio, substitution of Si by Al improves the "eld sensitivity of the GMI response. 0304-8853/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 9 9 ) 0 0 2 0 7 -3

The magnetization properties of granular bimetallic systems are discussed in detail. These systems can never be described as simple superparamagnets, because of the presence of non-negligible dipolar interactions among nanoparticle moments. Their anhysteretic magnetization can be well represented over a wide temperature range by a superposition of Langevin functions whose argument must be properly modified to account for interactions. Granular systems are therefore described as being in a particular regime, called the interacting superparamagnetic regime, and features of these are briefly discussed. Dipolar magnetic interactions are also responsible for the hysteretic behavior of these materials. A recent mean-field model for the hysteresis loops is shown to perfectly describe the temperature behavior of their shape and the hysteretic properties of the simulated magnetic response of an assembly of interacting equal moments. r

Three metastable materials of compositions Cu 80−x Fe 20 Ni x (x = 0, 5, 20 at.%) have been obtained by rapid solidification. Magnetization and magnetoresistance measurements have been performed at different temperatures on as cast samples of all alloys and on annealed samples of the alloy with x = 20. A measurable magnetoresistance is observed only for the latter material, a frustrated ferromagnet with short magnetic coherence length. This effect is related to the action of the magnetic field destroying the locally canted arrangement of magnetic spins in the ordered phase.

The influence on mechanical and magnetic properties of adding different proportions of Ge and Al to the well-known FeSiBNbCu system is analyzed in ribbons obtained by the melt-spinning technique and heat treated at several temperatures. These results and the changes observed in the internal structure are compared with those obtained in similar studies performed on the Fe 73.5 Si 22.5Àx B x Nb 3 Cu 1 alloy. r

Amorphous alloys with composition (at%) Fe 48 Cr 15 Mo 14 C 15 B 6 Gd 2 (alloy A) and Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 (alloy B) were prepared either using pure elements (A and B1) and a commercial AISI430 steel as a base material (B2). When prepared from pure elements both alloys (A and B1) could be cast in plate form with a fixed thickness of 2 mm and variable lengths between 10 and 20 mm by means of copper-mold injection in air atmosphere. In the case of alloy B2, prepared using commercial grade raw materials, rods of 2 mm diameter were obtained.

We studied the relationship between the saturation magnetization (M S ) of the Fe 73.5 Si 3.5 Ge 10 Nb 3 B 9 Cu 1 alloy and its nanocrystalline structure. Amorphous ribbons obtained by the melt spinning technique were heat-treated for 1 h at different temperatures. The optimal treatment to obtain a homogeneous structure of Fe 3 (Si,Ge) nanocrystals with a grain size of around 10 nm embedded in an amorphous matrix involved heating at 540 1C for 1 h. We calculated the magnetic contribution of the nanocrystals to the heat treated alloy using a linear model and measured the M S of the Fe 73.5 Si 3.5 Ge 10 Nb 3 B 9 Cu 1 nanocrystalline and of an amorphous alloy of the same composition of the amorphous matrix: Fe 58 Si 0.5 Ge 3.5 Cu 3 Nb 9 B 26 . Using experimental data and theoretical calculations, we obtained the amorphous and crystalline fraction of the heat-treated ribbons. r

By a combined use of Mössbauer spectroscopy and polarised small angle neutron scattering, we investigated the structure and magnetic properties of iron nanoparticles obtained by inert gas condensation techniques. The detailed local information on the intrinsic magnetic properties derived from the Mössbauer data have been used in order to build up an appropriate model for the analysis of the magnetic

Objective: To validate a questionnaire to identify psychosocial repercussions of the lipodystrophy syndrome (LD) in HIV-infected patients. Methods: A questionnaire containing 35 items in 6 subscales [body image, anxiety, depression, social support, social distress, quality of life (QoL)] was consecutively administered to 128 patients with LD, 25 naı¨ve patients or on therapy without LD, and to 15 HIV negative patients from January to July '04. Reliability was assessed using Cronbach's alpha and the intraclass correlation coefficient (ICC). The area under the curve (AUC) was used for discrimination between patients and control groups, and the scores were compared according to the severity of the LD. Results: In all the subscales, the relationship between higher scores and LD severity was statistically significant (0.37-0.64, p<0.01), whereas the control groups had significantly lower scores. The internal consistency showed Cronbach's alpha coefficients ranging from 0.64 to 0.93. Test-retest reliability after 15 days in 30 patients showed ICC values of 0.8-0.94. AUC values for the different subscales were higher than 0.7 with the exception of QoL score, and construct validity showed a significant correlation with the Beck Depression Inventory and the MOS-HIV scores (0.49 and 0.51, respectively, p<0.01). Conclusions: Our questionnaire shows satisfactory psychometric properties for identifying psychosocial repercussions of the LD in HIV-infected patients.

Development of thermal energy storage (TES) systems for concentrated solar power (CSP) is essential in order to match a variable electricity demand with an intermittent energy source supply, enhancing energy generation dispatchability. The high energy storage densities and the possibility of working at higher temperature ranges make thermochemical heat storage (TCS) via reduction-oxidation (redox) cycles of metal oxides a promising concept for energy storage. For this purpose, manganese and cobalt oxides have been selected as feasible candidates due to their favourable thermodynamic properties. In order to explore the potential of these materials, the capacity of both pure (Mn 2 O 3 and Co 3 O 4 ) and mixed oxides (Mn 3 À x Co x O 4 ) to withstand several charge-discharge cycles was evaluated by thermogravimetrical analysis. Results showed better cyclability for the mixed oxides with low Mn content (x Z2.94) and, specially, for the corresponding pure oxides, confirming that these materials may be a viable option for TCS.

Prosthetic heart valve thrombosis is a serious complication with a high mortality. We report the case of a thrombosed St Jude Medical valve placed in the pulmonary position, in a patient who had undergone repair of tetralogy of Fallot, which was successfully treated with intravenous thrombolytic therapy with streptokinase.