Influence of TiHX Addition on SHS Porous Shape Memory Alloy

Abstract Porous NiTi alloys are receiving considerable attention as they can be used as scaffold for bone replacement. Most production routes presented in the literature use metal powders as raw material (pure Ni and Ti or prealloyed NiTi powders): among these processes, Self propagating High temperature Synthesis (SHS) is investigated as a possible energy saving, quick and easy method of production. To obtain porous NiTi, compacted Ti and Ni powders are preheated and then ignited, avoiding high reaction temperatures at which the compound melts and consequently pores collapse. A drawback of low reaction temperatures is the formation of secondary phases. In this paper the addition of hydrided titanium (TiHX, x=1.5-1.9) powder is considered. During the reaction, hydrided titanium endothermically decomposes and can act as process controlling media. Reference Ni-Ti and Ni-TiHx mixed powders were reacted and the temperature evolution monitored. Differential Scanning Calorimetry was used to verify the presence of transforming phases (austenite, martensite). Microstructure characterization was performed with X-ray diffraction analysis and scanning electron microscope, equipped with EDX and EBSD detectors. The results confirmed that decomposition of hydrided titanium is the controlling process of the reaction, limiting the availability of Ti and absorbing reaction heat. The presence of TiHx can suppress SHS reaction, leaving un-reacted Ni and Ti powders and high amount of other intermetallic phases. If partial or complete decomposition of TiHx is allowed during preheating of reactants, NiTi production can occur: secondary phases content decreases for increased decomposition of TiHx before SHS reaction

A importância da abordagem teórica de agroecossistemas para formação de professores na área de ciências da Natureza

O presente trabalho de conclusão de curso tem como finalidade apresentar os resultados obtidos através da pesquisa, realizada com professores formados em licenciatura em Educação do Campo - Ciências da Natureza e professores formados em licenciatura em Biologia. O principal objetivo do trabalho é investigar como estes professores, que trabalham em escolas do meio rural e que são formados em Educação do Campo e formados em Biologia, entendem e percebem as questões teóricas e práticas dos conceitos de agroecossistemas. Esse trabalho aborda o conceito de agroecossistemas, sendo eles conhecidos por serem ecossistemas sustentáveis ou não-sustentáveis, transformados pela ação humana em sistemas agrícolas. Esta temática é presente no projeto político pedagógico do curso. Dentro do curso de Educação do Campo é proporcionado um método de se fazer a formação diferenciada e de maneira interdisciplinar. Por essa razão, que o curso promove desenvolvimento crítico do educador, pois procura sempre contextualizar com o mundo e a vida rural e também o curso sempre busca valorizar os saberes dos povos do campo. . A metodologia utilizada para a realização da pesquisa foi um questionário online, com perguntas fechadas, evidenciando os tópicos relacionados sobre os conceitos de agroecossistemas e se cada professor (a) sabe o que são os conceitos, como que foi abordado na formação de cada um deles (as), e qual importância que cada professor (a) observa que tem este conceito para a formação dos alunos do campo. O trabalho está dividido entre a descrição do tema a Educação do Campo, os conceitos de agroecossistemas segundo os autores que embasam o trabalho, e a análise dos resultados obtidos com a aplicação do questionário. As repercussões do questionário e as reflexões construídas a partir das análises, nos permitiram apresentar os dados de que os professores formados em Educação do Campo - Ciências da Natureza têm um vínculo mais próximo aos conceitos de agroecossistemas, pois, segundo eles(as), foram conceitos abordados durante as suas formações no ensino superior

Performance-based Re-use of Tunnel Muck as Granular Material for Subgrade and Sub-base Formation in Road Construction

Large volumes of muck are produced in the Alpine Region and bordering areas as a result of new road and railway construction. For example, in Austria every year approximately 32*10^6 Mg of muck are produced from tunnelling activities. In the near future, many other initiatives along the European corridors will lead to further construction activity, with an inevitable increase in the environmental problems related to the use or disposal of the muck generated. Therefore, there is a clear opportunity for the extensive re-use of muck due to the high demand for granular materials (about 3 billion tonnes in Europe, only 5% of which comes from recycling), the depletion of existing quarries (approximately 24,000 in Europe), and the environmental constraints preventing or delaying the opening of new quarries. In this scenario, a new approach to the re-use of muck is both necessary and timely. Although many typical defects deriving from its geological nature and/or from the extraction techniques employed may lead to its rejection as an aggregate, these same defects are of less importance in embankment, subgrade and sub-base construction in transportation infrastructures and, indeed, in most cases they can be mitigated by granular or chemical stabilization. The investigation described here embraces this philosophy. Starting from the chemical physical characterization of seven different mucks derived from tunnelling activities on the Italian side of the Alps, the paper aims to explore the potential benefits deriving from their re use as a construction material. The test methods used all adhere to prescriptive and performance based construction specifications. Notwithstanding the unfavourable geological origin of some of the considered materials, they all exhibited mechanical properties that would encourage their almost complete re-use in infrastructure construction projects

Microstructural and Mechanical Response of NiTi Lattice 3D Structure Produced by Selective Laser Melting

Nowadays, additive manufacturing (AM) permits to realize complex metallic structural parts, and the use of NiTi alloy, known as Nitinol, allows the integration of specific functions to the AM products. One of the most promising designs for AM is concerning the use of lattice structures that show lightweight, higher than bulk material deformability, improved damping properties, high exchange surface. Moreover, lattice structures can be realized with struts, having dimensions below 1 mm—this is very attractive for the realization of Nitinol components for biomedical devices. In this light, the present work regarded the experimental characterization of lattice structures, produced by selective laser melting (SLM), by using Ni-rich NiTi alloy. Differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD), and compression testing were carried out for analyzing microstructure, martensitic transformation (MT) evolution, and superelasticity response of the SLMed lattice samples. The lattice microstructures were compared with those of the SLMed bulk material for highlighting differences. Localized martensite was detected in the nodes zones, where the rapid solidification tends to accumulate solidification stresses. An increase of martensitic transformation temperatures was also observed in lattice NiTi

Role of microstructure in the exploitation of self-healing potential in form-stable composite phase change materials based on immiscible alloys

Metallic Phase Change Materials (PCMs), based on solid-liquid transitions, represents one of the most promising technologies for efficient Thermal Energy Storage (TES), due to their superior thermal conductivity and energy storability per unit volume, but suffer of limited solutions for their handling at the molten state. The use of Miscibility Gap Alloys (MGAs) allows to manage PCM volume expansion and keep it confined when molten, preventing interaction with the environment. A relevant example is provided by the Al-Sn system, where Al covers the role of the high-temperature stable and highly thermal-conductive passive matrix and Sn the active PCM. The alloy can thus be considered a Composite PCM (C-PCM). The response fastness of these systems depends on their thermal diffusivity, subjected to abrupt variations under the presence of discontinuities and damages. In this sense, the authors investigated the possibility to employ molten Sn mobility in a potentially damaged C-PCM for self-healing purposes, aimed to restore, at least partially, the material continuity and thus its thermal diffusivity. Exudation heat treatments above the melting temperature of Sn were performed on sets of Al-40%wt. Sn metallic composites, produced either with powder metallurgy or liquid metal routes, in order to quantify and assess the mobility of the Sn under simulated operating conditions. Exudation tests assess Simple Mixed powders and liquid metal routes sample as the ones with the highest healing potential. Al dissolution and re-deposition was established by EDS analyses as one of the principal Sn mobility mechanisms. Laser Flash Analysis tests, as well as microstructural investigations, were performed on the samples before and after both healing-focused and simulated service heat treatments to evaluate the changes of thermal diffusivity. Healing-focused treatment at 250°C for 1 hour generally displayed a moderate thermal diffusivity recovery and simulated service by shorter cycles between 170°C and 270°C slightly reduce it. The beneficial role of healing focused heat treatments at 250°C for 1 hour suggests that the presence of fully molten Sn phase during service for relatively long time could be beneficial for functional healing. The requirements of suitable Al-Sn microstructures for self-healing purposes, granting at the same time the C-PCM functionalities, i.e., thermal energy storage and form-stability, were set

Water megamaser emission in hard X-ray selected AGN

Water megamaser emission at 22 GHz has proven to be a powerful tool for astrophysical studies of AGN allowing an accurate determination of the central black hole mass and of the accretion disc geometry and dynamics. However, after searches among thousands of galaxies, only ~ 200 of them have shown such spectroscopic features, most of them of uncertain classification. In addition, the physical and geometrical conditions under which maser activates are still unknown. In this work we aim at characterizing the occurrence of water maser emission in an unbiased sample of AGN, investigating the relation with the X-ray properties and the possible favorable geometry needed to detect water maser. We have searched for 22 GHz maser emission in a hard X-ray selected sample of AGN, taken from the INTEGRAL/IBIS survey above 20 keV. Of the 380 sources in the sample, only half have water maser data. We have also considered a sub-sample of 87 sources, volume limited, for which we obtained new Green Bank Telescope and Effelsberg observations (for 35 sources), detecting one new maser and increasing its radio coverage to 75%. The detection rate of water maser emission in the total sample is 15+/-3%, this fraction raises up to 19+/-5% for the complete sub-sample, especially if considering type 2 and Compton thick AGN. These results demonstrate that the hard X-ray selection may significantly enhance the maser detection efficiency over comparably large optical/infrared surveys. A possible decline of the detection fraction with increasing luminosity might suggest that an extreme luminous nuclear environment does not favour maser emission. The large fraction of CT AGN with water maser emission could be explained in terms of geometrical effects, being the maser medium the very edge-on portion of the obscuring medium.Comment: 21 pages, 3 figures. Accepted for publication in A&A June 202

Preformulation studies for the development of a microemulsion formulation from Ambrosia peruviana All., with anti-inflammatory effect

Natural products are considered an important source of the therapeutic arsenal currently available. Among these alternatives are the seeds of Ambrosia peruviana (altamisa), whose extract has shown an anti-inflammatory effect. The main objective of this work was to perform a preformulation study of Ambrosia peruviana seeds ethanolic extract, where the main factors that affect the physical, chemical, and pharmacological stability of the extract were evaluated, as well as a compatibility study by differential scanning calorimetry (DSC) analysis against different excipients. A dry extract was obtained by rotary evaporation of the seeds macerated with 96% ethanol. The anti-inflammatory activity was determined by measuring its effect on NO production in RAW 264.7 macrophages, stimulated with LPS. The results showed that the dry extract maintained its stability over time when stored at a temperature of 4 and 25ºC, demonstrating its biological activity, the content of phenolic compounds, and its physicochemical parameters remain practically invariable. However, when exposed to high temperatures (60 ºC) it was affected. The thermal analysis revelated that the behavior of most of the selected excipients and the dry extract was maintained, which indicates that it did not present incompatibilities, therefore they can be candidates for formulating a microemulsion

Electrospun Silk Fibroin Scaffolds for Tissue Regeneration: Chemical, Structural, and Toxicological Implications of the Formic Acid-Silk Fibroin Interaction

The dissolution of Bombyx mori silk !broin (SF) !lms in formic acid (FA) for the preparation of electrospinning dopes is widely exploited to produce electrospun SF scaffolds. The SilkBridge® nerve conduit is an example of medical device having in its wall structure an electrospun component produced from an FA spinning dope. Though highly volatile, residual FA remains trapped into the bulk of the SF nano!bers. The purpose of this work is to investigate the type and strength of the interaction between FA and SF in electrospun mats, to quantify its amount and to evaluate its possible toxicological impact on human health. The presence of residual FA in SF mats was detected by FTIR and Raman spectroscopy (new carbonyl peak at about 1,725 cm!1) and by solid state NMR, which revealed a new carbonyl signal at about 164.3 ppm, attributed to FA by isotopic 13C substitution. Changes occurred also in the spectral ranges of hydroxylated amino acids (Ser and Thr), demonstrating that FA interacted with SF by forming formyl esters. The total amount of FA was determined by HS-GC/MS analysis and accounted for 247 ± 20 !mol/g. The greatest part was present as formyl ester, a small part (about 3%) as free FA. Approximately 17% of the 1,500 !mol/g of hydroxy amino acids (Ser and Thr) theoretically available were involved in the formation of formyl esters. Treatment with alkali (Na2CO3) succeeded to remove the greatest part of FA, but not all. Alkali-treated electrospun SF mats underwent morphological, physical, and mechanical changes. The average diameter of the !bers increased from about 440 nm to about 480 nm, the mat shrunk, became stiffer (the modulus increased from about 5.5 MPa to about 7 MPa), and lost elasticity (the strain decreased from about 1 mm/mm to about 0.8 mm/mm). Biocompatibility studies with human adult dermal !broblasts did not show signi!cant difference in cell proliferation (313 ± 18 and 309 ± 23 cells/ mm2 for untreated and alkali-treated SF mat, respectively) and metabolic activity. An in-depth evaluation of the possible toxicological impact of residual FA was made using the SilkBridge® nerve conduit as case study, following the provisions of the ISO 10993-1 standard. The Potential Patient Daily Intake, calculated from the total amount of FA determined by HS-GC/MS, was 2.4 mg/day and the Tolerable Exposure level was set to 35.4 mg/day