Anelastic relaxation processes due oxygen in Nb-3.1 at.% Ti alloys

In the last 50 years several studies have been made to understand the relaxation mechanisms of the heavy interstitial atoms present in transition metals and their alloys. Internal friction measurements have been carried out in a Nb-Ti alloy containing 3.1 at.% of Ti produced by the Materials Department of Chemical Engineering Faculty of Lorena (Brazil), with several quantities of oxygen in solid solution using a torsion pendulum. These measurements have been performed by a torsion pendulum in the temperature range from 300 to 700 K with an oscillation frequency between 0.5 and 10 Hz. The experimental results show complex internal friction spectra that have been resolved, into a series of Debye peaks corresponding to different interactions. For each relaxation process it was possible to obtain the height and temperature of the peak, the activation energy and the relaxation time of the process. (C) 2003 Elsevier B.V. All rights reserved.

Influence of the network former on the properties of magnesium spinels

Undoped and/or doped with 1 mol% of Co2+ Mg2TiO4 and Mg2SnO4 powders were synthesized by the polymeric precursor method. The influence of the network former (Sn4+ or Ti4+) on the thermal, structural and optical properties was investigated. The recorded mass losses are due to the escape of water and adsorbed gases and to the elimination of the organic matter. Mg2TiO4 crystallizes at lower temperatures and also presents more ordered structure with a smaller unit call and having more intense green color than Mg2SnO4 has.

Thermal behavior of alpha-(Cu-Al-Ag) alloys

Thermal behavior of alpha-(Cu-Al-Ag) alloys, i.e. alloys with composition less than about 8.5 mass% Al, was studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that the presence of silver introduces new thermal events ascribed to the formation of a silver-rich phase and, after addition higher amounts than 8 mass% Ag to the Cu-8 mass% Al alloy it is possible to observe the formation of the gamma(1) phase (Al4Cu9), which is only observed in alloys containing minimum of 9 mass% Al. These results may be attributed to some Ag characteristics and its interaction with Cu and Al.

Preparation of Fe-Cr-P-Co amorphous alloys by electrodeposition

The effects of bath composition and electroplating conditions on structure, morphology, and composition of amorphous Fe-Cr-P-Co deposits on AISI 1020 steel substrate, priorly plated with a thin Cu deposit, were investigated. The increase of charge density activates the inclusion of Cr in the deposit. However, above specific values of the charge density, which depend on the deposition current density, the Cr content in the deposit decreases. This Cr content decreasing is probably due to the significant hydrogen evolution with the increasing of deposition cur-rent and charge density. The effect of charge density on the content of Fe and Co is not clear. However, there is a tendency of increasing of Fe content and decreasing of Co content with the raising of current density. The Co is more easily deposited than the P, and its presence results in a more intense inhibition effect on the Cr deposition than the inhibition effect caused by P presence. Scanning electron microscope (SEM) analysis showed that Co increasing in the Fe-Cr-P-Co alloys analyzed does not promote the susceptibility to microcracks, which led to a good quality deposit. The passive film of the Fe-Cr-P-Co alloy shows a high ability formation and high protective capacity, and the results obtained by current density of corrosion, j(cor), show that the deposit with addition of Co, Fe31Cr11P28Co30, presents a higher corrosion resistance than the deposit with addition of Ni, Fe54Cr21P20Ni5. (C) 2004 Published by Elsevier B.V.

Stress-induced ordering due heavy interstitial atoms in Nb-0.3 wt.% Ti alloys

The mechanical properties of metals with bee structure, such as niobium and their alloys, are changed of a significant way by the introduction of heavy interstitial elements. These interstitial elements (oxygen, for example) present in the metallic matrix occupy octahedral sites and constitute an elastic dipole of tetragonal symmetry and might produce anelastic relaxation. Polycrystalline samples of Nb-0.3 wt.% Ti (Nb-Ti) alloy with oxygen in solid solution were analysed. The anelastic spectroscopy measurements had been made in a torsion pendulum, with frequencies in the Hz range, in a temperature range between 300 and 700 K. The results showed thermally activated relaxation structures were identified four relaxation process attributed to stress-induced ordering of single oxygen, nitrogen and carbon atoms around niobium and stress-induced ordering of single oxygen atoms around titanium atoms. (c) 2005 Elsevier B.V. All rights reserved.

Magnesium sulphate given topically by iontophoresis for viability of random skin flaps in rats

Our aim was to assess the effects of magnesium sulphate given by iontophoresis on the viability of random skin flaps in rats. Endovenous magnesium sulphate is used to treat pre-eclampsia and diseases of blood vessels. Iontophoresis is an electrotherapeutic method which has shown satisfactory results in controlling ischaemia within the boundaries of the area in which it was given. Forty-five adult male Wistar rats, weighing 300 to 440 g were randomly divided into three groups of 15 animals each: random skin flap (control); random skin flap treated with magnesium sulphate without electrical stimulation; and random skin flap treated with magnesium sulphate with electrical stimulation of 4 mA for 20 minutes. The treatments were applied immediately after the operation and repeated on the following two days. The percentage of necrotic area was measured on the seventh postoperative day using a paper template. For each group, the mean percentage of flap necrosis was as follows: control, 46%; magnesium sulphate without electrical stimulation, 34%; and magnesium sulphate with electrical stimulation, 42%. There was no significant difference among the groups (p=0.18). Magnesium sulphate given by iontophoresis does not increase the viability of random skin flaps in rats.

Effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys

In this work the effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys with additions of 4, 6, 8 and 10 mass% Ag was studied using differential scanning calorimetry (DSC), in situ X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that for the Cu-10 mass% Al alloy Ag addition induce the beta'(1) phase formation and for the Cu-11 mass% Al alloy these additions increase the amount of martensite formed on quenching and decrease the stability range of this phase on heating.

Completeness of beta-phase decomposition reaction in Cu-Al-Ag alloys

The completeness of beta-phase decomposition reaction in the Cu-11wt%Al-xwt%Ag alloys (x = 0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that beta-phase transformations are highly dependent on cooling rate and on the presence of Ag. on slow cooling, the silver presence prevents the beta- and beta(1)-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures.

Magnesium-enriched hydroxyapatite at immediate implants: a histomorphometric study in dogs

AimTo evaluate the influence of magnesium-enriched hydroxyapatite (MHA) (SintLife (R)) on bone contour preservation and osseointegration at implants placed immediately into extraction sockets.Material and methodsIn the mandibular pre-molar region, implants were installed immediately into extraction sockets of six Labrador dogs. MHA was placed at test sites, while the control sites did not receive augmentation materials. Implants were intended to heal in a submerged mode. After 4 months of healing, the animals were sacrificed, and ground sections were obtained for histomorphometric evaluation.ResultsAfter 4 months of healing, one control implant was not integrated leaving n=5 test and control implants for evaluation. Both at the test and the control sites, bone resorption occurred. While the most coronal bone-to-implant contact was similar between test and control sites, the alveolar bony crest outline was maintained to a higher degree at the buccal aspect of the test sites (loss: 0.7 mm) compared with the control sites (loss: 1.2 mm), even though this difference did not reach statistical significance.ConclusionsThe use of MHA to fill the defect around implants placed into the alveolus immediately after tooth extraction did not contribute significantly to the maintenance of the contours of the buccal alveolar bone crest.To cite this article:Caneva M, Botticelli D, Stellini E, Souza SLS, Salata LA, Lang NP. Magnesium-enriched hydroxyapatite at immediate implants: a histomorphometric study in dogs.Clin. Oral Impl. Res. 22, 2011; 512-517doi: 10.1111/j.1600-0501.2010.02040.x.

Mechanochemical synthesis of lead magnesium niobate ceramics in iron media

The possibility of mechanochemical synthesis of the lead magnesium niobate (PMN) powders of the composition Pb(Mg(1/3)Nb(2/3))O(3) in iron vials was investigated. According to X-ray and energy-dispersive spectroscopy (EDS) analysis of the obtained powder mixtures, milling in iron vials resulted in incorporation of Fe and formation of PFN of composition Pb(Fe(1/2)Nb(1/2))O(3) simultaneously with formation of PMN. Relative amounts of PMN and PFN were determined based on values of Curie temperature and lattice constant of perovskite phase. Although only 1 wt pct of Fe was incorporated, a stoichiometry of the system was significantly changed, resulting in formation of pyrochlore phase and excess MgO. Single-phase perovskite was obtained when the excess of PbO and Nb(2)O(5) was added during mechanochemical synthesis. Because the dielectric properties were worse than expected, the alternative ways for improvement of dielectric properties were tried and discussed.

Effect of calcium and magnesium silicate on the growth of the castor oil plant subjected to salinity levels

Salt stress decreases the osmotic potential of soil solution causing water stress, causing toxic effects in the plants resulting in injuries on the metabolism and nutritional disorders, thus compromising the plant growth, resulting in lower production. The calcium silicate and magnesium can perform the same function as limestone, besides providing silicon to plants, may also contribute to the resistance of plants to salt stress. Thus, the objective of this study was to evaluate the effect of calcium and magnesium silicate on the growth of the castor oil plant BRS Energia cultivated under saline conditions. This study evaluated plant height, stem diameter, number of leaves, leaf area, dry weight of shoot and root, and soil chemical characteristics. There was no interaction between factors of salinity level and of silicate level regarding the evaluated variables. There was a direct relationship between salinity levels and plant growth in height and stem diameter. The K concentration in soil were affected by salinity levels.