Effect of Reaction Time on Microwave Absorption Properties of Fe3O4 Hollow Spheres Synthesized via Ostwald Ripening

Hollow magnetic structures have great potential to be used in the microwave absorbing field. Herein, Fe3O4 hollow spheres with different levels of hollowness were synthesized by the hydrothermal method under Ostwald ripening effect. In addition to their microstructures, the microwave absorption properties of such spheres were investigated. The results show that the grain size and hollowness of Fe3O4 hollow spheres both increase as the reaction time increases. With increasing hollowness, the attenuation ability of electromagnetic wave of Fe3O4 spheres increases first and then decreases, finally increases sharply after the spheres break down. Samples with strong attenuation ability can achieve good impedance matching, which it does preferentially as the absorber thickness increases. Fe3O4 hollow spheres show the best microwave absorption performance when the reaction time is 24 h. The minimum reflection loss (RL (min)) can reach −40 dB, while the thickness is only 3.2 mm

Microstructure and anti-corrosion properties of supersonic plasma sprayed Al-coating with Nano-Ti polymer sealing on AZ91-Magnesium alloy

Supersonic plasma spray was used to deposit Al-coating on AZ91-alloy. Nano-Ti polymer was then employed to seal the pores on the as-sprayed Al-coating. The microstructures and corrosion resistances of the as-obtained Al-coating and Al+nano-Ti polymer composite-coating were examined by field scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), micro computed tomography (micro-CT), potentiodynamic polarization, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and neutral salt spray testing (NSS). For comparative purposes, AZ91-alloy was used as reference and tested under the same conditions. The as-sprayed Al-coating exhibited excellent properties with porosity of 1.5 ± 0.58% and bonding strength of 30 ± 2.68 MPa. By comparison, the composite-coating depicted a porosity of only about 0.05 ± 0.01% and bonding strength of 10.05 ± 1.72 MPa. The long-term anti-corrosion properties of Al-coating and composite-coating were better than that of AZ91-alloy, and composite coating possessed better protective effect with its Ecorr and Icorr of about −0.807 V and 1.4137 × 10−8 A·cm−2, respectively. Meanwhile, composite-coating surface without the formation of blisters, pulverization or macro-defects even after 720 h of accelerated corrosion using neutral salt spray experiments. The Al-coating displayed slight pitting corrosion on its surface, much milder than of AZ91-alloy. The composite coating exhibited superior corrosion resistance by forming wrapped pathways of nano-Ti polymer coating and excellent passivation layer of dense Al-coating

Effect of Sn Addition on Microstructure and Corrosion Behavior of As-Extruded Mg–5Zn–4Al Alloy

The effect of Sn addition on the microstructure and corrosion behavior of extruded Mg–5Zn–4Al–xSn (0, 0.5, 1, 2, and 3 wt %) alloys was investigated by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemical measurements, and immersion tests. Microstructural results showed that the average grain size decreased to some degree and the amount of precipitates increased with the increasing amount of Sn. The extruded Mg–5Zn–4Al–xSn alloy mainly consisted of α-Mg, Mg32(Al,Zn)49, and Mg2Sn phases as the content of Sn was above 1 wt %. Electrochemical measurements indicated that the extruded Mg–5Zn–4Al–1Sn (ZAT541) alloy presented the best corrosion performances, with corrosion potential (Ecorr) and corrosion current density (Icorr) values of −1.3309 V and 6.707 × 10−6 A·cm−2, respectively. Furthermore, the corrosion mechanism of Sn is discussed in detail

High-resolution relaxometry-based calibrated fMRI in murine brain: Metabolic differences between awake and anesthetized states

International audienceFunctional magnetic resonance imaging (fMRI) techniques using the blood-oxygen level-dependent (BOLD) signal have shown great potential as clinical biomarkers of disease. Thus, using these techniques in preclinical rodent models is an urgent need. Calibrated fMRI is a promising technique that can provide high-resolution mapping of cerebral oxygen metabolism (CMR O2 ). However, calibrated fMRI is difficult to use in rodent models for several reasons: rodents are anesthetized, stimulation-induced changes are small, and gas challenges induce noisy CMR O2 predictions. We used, in mice, a relaxometry-based calibrated fMRI method which uses cerebral blood flow (CBF) and the BOLD-sensitive magnetic relaxation component, R 2 0 , the same parameter derived in the deoxyhemoglobin-dilution model of calibrated fMRI. This method does not use any gas challenges, which we tested on mice in both awake and anesthetized states. As anesthesia induces a whole-brain change, our protocol allowed us to overcome the former limitations of rodent studies using calibrated fMRI. We revealed 1.5-2 times higher CMR O2 , dependent upon brain region, in the awake state versus the anesthetized state. Our results agree with alternative measurements of whole-brain CMR O2 in the same mice and previous human anesthesia studies. The use of calibrated fMRI in rodents has much potential for preclinical fMRI