Antonio Díaz-Parralejo

Use of cork agglomerates as acoustic absorbents

Abstract Black agglomerate (BA) and composite agglomerate (CA) of cork were tested as acoustic absorbents. The energy absorption coefficient was studied as a function of the specimen thickness. For CA, the effects on the acoustic absorption of the particle size and the resin dosage used in its preparation were also analysed. The wave ratio n, the coefficient of acoustic absorption α and the coefficient of noise reduction (CNR) were calculated using an ASTM norm (C-384-56). Usually, regardless of the specimen thickness, for both BA and CA, α first increased with frequency and then decreased. The maximum of α shifted to a higher frequency with decreasing specimen thickness. In general, BA was the best acoustic absorbent at low and high frequencies, whereas CA was at intermediate frequencies. Particle size and resin dosage had a less important influence on the absorbent behaviour of CA.

Influence of ion nitriding process on the properties of zirconia coating deposited on stainless steel

ZrO2-3 mol % Y2O3-coated AISI 310 stainless steel was nitrided using plasma produced by dc pulsed discharge in a mixture of N2 and H2 at an equilibrium temperature of 450oC. Profile chemical analyses with GDOS (glow discharge optical spectroscopy) and XRD showed the formation of Nitrogen/Y-ZrO2 solid solution. Nitrogen atoms enter in the zirconia substituting to the oxygen atoms in the network. Although, the nitrogen content measured in zirconia coating is greater than the allowed maximum nitrogen content in doped-zirconia solid solution, the formation of oxynitrides could not be detected. The phase structure was investigated by X-ray diffractometry The mechanical properties were studied by means ultramicrohardness indentation tests. The nitruration improves the mechanical responses of the ZrO2-3 mol% Y2O3 -coated AISI 310 stainless steel.

The Excellent Mechanical Properties of Cork: A Novel Approach through the Analysis of Contact Stress

In many technological applications of cork, this biomaterial is under strongly localized contact stresses, which largely differ from the homogeneous distribution of stresses of the typical uniaxial compression tests. Indentation tests constitute an excellent form of determining the behavior of the materials under localized stresses. In the present study, the applicability of Hertzian and Brinell indentation tests to the evaluation of the mechanical properties of cork is tested. One of the main conclusions of the study is that the elastic anisotropy of the material is related to the anisotropic structure of the different sections cut from a cork sample, a clear difference between the back tangential section and the other sections being observed.

Interdiffusion Phenomena of Zirconia-Nitride Layers on Coated AISI 310 Steel

Duplex coatings on stainless steel American Iron and Steel Institute (AISI) 310 were prepared by a double process consisting of a plasma nitriding treatment and a multilayer ZrO2-3 mol % Y2O3 coating grown by chemical solution deposition. In this paper we investigate the interdiffusion phenomena between the elements and the deposited phases. The zirconia coating process over the nitrided steel initiated strong diffusion events. Hydrogen diffuses easily throughout the coating and acts as a reducing agent. The layer of zirconia works as a sieve, retaining nitrogen and allowing the passage of hydrogen. The contribution of this study show the interdiffusion at the interfaces of elements in samples subjected to treatments known as duplex coatings.