This paper aims to analyze the structure of the Ti-25Ta-xZr system alloys (x = 0, 10, 20, 30, and 40% wt.) after melting and hot-rolling by Rietveld's technique. The results confirm that zirconium acts as a β phase stabilizer (in which the Ti-25Ta-40Zr alloy is fully β in the as-cast condition), increases the lattice parameters of the phases, decreases the c/a ratio of the α phase, consequently, decreases the elastic modulus values (86 to 72GPa) and decreases the atomic packing factor (APF) of the alloys (60% reduction compared to alloys with and without zirconium in the as-cast condition and 50% reduction in the hot-rolled condition). Concerning hot-rolling, this mechanical process induces the α phase formation and increases the atomic packing factor of the alloys (APF). By the William-Hall technique, it was possible to calculate the average crystalline size and the micro-strain of the structures.

Abstract Titanium is one of the most utilized metals for orthopedic implants. This element has excellent mechanical and biological properties. As a strategy to develop a new system of alloys that do not cause health problems to the patient, such as the Ti-6Al-4V alloy, a new group of alloys has been designed to meet these expectations. Molybdenum, when associated with titanium, reduces the transition temperature from α to the β phase. Zirconium increases the corrosion resistance, decreases the melting point, and improves the alloy's biocompatibility. The alloys with the beta phase's predominance are the most desirable for biomedical applications due to their higher mechanical compatibility with the bone tissue. This paper presents the preparation of as-cast Ti-10Mo-xZr (x= 30, 40, and 50 wt%) alloys and their characterization by measurements of density, energy dispersive spectrometry (EDS), x-ray diffraction, optical and scanning electron microscope (SEM). The density values were higher than that of pure titanium due to the zirconium and molybdenum. The EDS measurements reveal a suitable stoichiometry of the elements and no impurities contamination. In the x-ray diffraction and microscopy measurements, it was observed only peaks of the beta phase. This new system of Ti-alloys is promising for biomedical applications.

The present study produced binary titanium-niobium alloys Ti-xNb with high niobium percentage (x = 50, 80 e 90 wt.%) aiming to apply it as a base material in osseous implant devices. The produced TiNb alloys presented a cubic crystalline phase, lower corrosion rate than titanium, lower elastic modulus values, and superior cellular viability than titanium and niobium. The Ti50Nb alloy among all analyzed metallic substrates showed the best values of elastic modulus, corrosion properties, wettability, and cellular viability. Thus, this work suggests a Ti/Nb ratio close to 1 (Ti50Nb) displays optimum characteristics to apply in orthopedic devices.

RESUMO Ligas de titânio são amplamente utilizadas na área biomédica devido à sua excelente resistência à corrosão em fluídos corpóreos, elevada razão resistência mecânica/densidade, baixo módulo de elasticidade e comprovada biocompatibilidade. As ligas mais promissoras para serem utilizadas na área biomédica possuem elementos em solução sólida que diminuem a temperatura de transformação de fase do titânio. Tais elementos são denominados beta-estabilizadores e obtêm-se como resultado a diminuição do módulo de elasticidade e uma excelente resistência à corrosão. Os elementos tântalo e zircônio, quando acrescentados ao titânio, melhoram a resistência à corrosão e diminuem o módulo de elasticidade, pois o tântalo é considerado um elemento β-estabilizador e o zircônio atua como elemento estabilizador desta fase, na presença de outro elemento β-estabilizador. Neste trabalho, a liga Ti-25Ta-5Zr foi preparada por fusão à arco, visando aplicações biomédicas. As caracterizações química, estrutural, microestrutural e mecânica foram realizadas por intermédio de medidas da composição química, análise de gases, espectrometria por dispersão de energia (EDS), difração de raios X, microscopias óptica e eletrônica de varredura, microdureza Vickers e módulo de elasticidade. Os resultados obtidos mostraram uma boa estequiometria e homogeneidade da liga. As análises estrutural e microestrutural corroboraram entre si e indicaram que a liga possui a coexistência de duas fases, α” (com estrutura cristalina ortorrômbica) e β (com estrutura cristalina cúbica de corpo centrado). A microdureza elevou-se com a adição de tais elementos e o módulo de elasticidade possui valores abaixo das ligas utilizadas comercialmente, satisfatório para aplicação como implante ortopédico.

ABSTRACT Titanium alloys are widely used in the biomedical field due to its excellent corrosion resistance in bodily fluids, high mechanical strength/density ratio, low elastic modulus and good biocompatibility. The most promising alloys to be used in the biomedical field have solid solution elements that decrease the phase transformation temperature of titanium. Such elements are called beta-stabilizers and are obtained as a result of their introduction in the alloy, the decrease of the elastic modulus and an excellent corrosion resistance. Tantalum and zirconium elements, when added to the titanium, improve the corrosion resistance and diminish the elastic modulus, because tantalum is considered a β-stabilizer element and the zirconium acts as a stabilizing element of this phase, in presence of another β-stabilizer element. In this paper, Ti-25Ta-5Zr alloy was prepared by arc-melting, aiming biomedical applications. The chemical, structural, microstructural and mechanical characterizations were performed by means of chemical composition measurements, gas analysis, energy dispersive spectrometry (EDS), X-ray diffraction, optical and scanning electron microscopies, Vickers microhardness and elastic modulus. The obtained results showed a good stoichiometry and homogeneity of the samples. Structural and microstructural analyses corroborated each other and indicated that the alloy has the coexistence of two phases, α" (with orthorhombic crystalline structure) and β (with body-centered cubic structure). The microhardness increased with the addition of such elements and the elastic modulus has values below the commercially used alloys, satisfactory for application as orthopedic implant.

In this study, MAO treatment was used to enrich, with bioactive Ca, Mg and P atoms, as-casted and heat-treated Ti-15Zr-xMo (x = 0, 5, 10 and 15 wt%) alloys, for potential use as advanced metallic biomaterials. The chemical composition of the surface was evaluated by EDS and XPS measurements. The morphology and microstructure was analyzed by OM and SEM images. Crystalline structure and phase composition were characterized by XRD measurements. The results indicated that the oxide layers were porous, with microstructural features of the bulk (grain size and secondary phases) slightly affecting the surface characteristics (pore size, chemical and phase composition). The crystalline structure of the oxide layers were composed by a mixture of anatase and rutile phases (TiO2), with a minority of tetragonal zirconia (ZrO2) and traces of CaCO3 and P2O3 compounds. Chemical analysis indicated that the oxide layers were composed mainly by Ti and Zr oxides, with successful incorporation of the bioactive elements. The obtained results evidenced that the surface characteristics of MAO-treated Ti surfaces can be properly adjusted by the addition of alloying elements and implementation of specific heat treatments on the substrate. This finding can be quite useful for the development of novel biomedical implants.

Abstract High levels of shrinkage stress caused by volumetric variations during the activation process are one of the main problems in the practical application of composite resins. Objective The aim of this study is to reduce the shrinkage stress and minimize the effects caused by composite resin volumetric variation due to the photopolymerization. In this way, this work proposes a systematic study to determine the optimal dimming function to be applied to light curing processes. Material and Methods The study was performed by applying mathematical techniques to the optimization of nonlinear objective functions. The effectiveness of the dimming function was evaluated by monitoring the polymerization shrinkage stress during the curing process of five brands/models of composites. This monitoring was performed on a universal testing machine using two steel bases coupled in the arms of the machine where the resin was inserted and polymerized. The quality of the composites cured by the proposed method was analyzed and compared with the conventional photoactivation method by experiments to determine their degree of conversion (DC). Absorbance measurements were performed using Fourier-transform infrared spectroscopy (FT-IR). A T-test was performed on DC results to compare the photoactivation techniques. We also used scanning electron microscopy (SEM) to analyze in-vitro the adhesion interface of the resin in human teeth. Results Our results showed that the use of the optimal dimming function, named as exponential, resulted in the significant reduction of the shrinkage stress (~36.88% ±6.56 when compared with the conventional method) without affecting the DC (t=0.86, p-value=0.44). The SEM analyses show that the proposed process can minimize or even eliminate adhesion failures between the tooth and the resin in dental restorations. Conclusion The results from this study can promote the improvement of the composite resin light curing process by the minimization of polymerization shrinkage effects, given an operational standardization of the photoactivation process.

In this paper, the effect of substitutional Mo amounts in internal friction and interstitial diffusion mechanisms was analyzed in Ti-15Zr-based alloys. Mechanical spectroscopy was obtained from room temperature up to 730 K with frequencies between 1 Hz and 40 Hz. Internal friction spectra were composed by anelastic relaxation peaks in β-type alloys (metastable and stable), due to stress-induced ordering of oxygen and nitrogen interstitially in octahedral sites of the bcc crystalline structure. Peak decomposition analysis exhibited interactions between matrix-interstitial (Ti-O and Ti-N), substitutional-interstitial (Zr-O, Mo-O and Mo-N), and clusters (Ti-O-O and Zr-O-O). The diffusion results showed that the introduction of Mo facilitates the diffusion of interstitial elements in the metallic matrix.

Ligas de titânio representam uma importante classe de biomateriais. Além da questão da biocompatibilidade, é muito importante considerar as propriedades mecânicas de um biomaterial, que são diretamente relacionadas com a microestrutura e quantidade de elementos intersticiais presentes. No presente trabalho, a liga Ti-10%pNi foi produzida a partir da fusão dos metais titânio e níquel comercialmente puros, num forno de arco sob uma atmosfera de argônio. Em seguida, foi realizado um tratamento térmico e a amostra foi laminada. Para comprovar a composição da liga, foi realizada análise química quantitativa. A estrutura e microestrutura da liga produzida foram analisadas por difração de raios-x, microscopia óptica e microscopia eletrônica de varredura. Os resultados mostram que a liga apresenta predominantemente a fase alfa do titânio (estrutura hexagonal compacta), com precipitados lamelares proeutetóide numa matriz eutetóide composta de fase alfa e do intermetálico Ti2Ni.

Titanium alloys are an important class of biomaterials. Apart from the issue of biocompatibility, is very important to consider the mechanical properties of a biomaterial, which are directly related to the microstructure and interstitial elements quantity present. In the present paper, Ti-10wt%Ni was produced from the melting of commercially pure titanium and nickel in arc furnace under argon atmosphere. Then a heat treatment was carried out and the sample was hot-rolled. To prove the alloy composition, quantitative chemical analysis was performed. The structure and microstructure of the produced alloy were analyzed by x-ray diffraction, optical and scanning electron microscopy. The results show that the alloy presents predominantly titanium alpha phase (hexagonal compact structure), with proeutectoid lamellar precipitates in eutectoid matrix of alpha phase and intermetallic Ti2Ni.

Dynamical Elastic Moduli of the Ti-13Nb-13Zr biomaterial alloy were obtained using the mechanical spectroscopy technique. The sample with heat treatment at 1170K for 30 minutes and water quenched with subsequent aging treatment at 670 K for 3 hours (TNZ + WQ + 670 K/3 h), was characterized through decay of free oscillations of the sample in the flexural vibration mode. The spectra of anelastic relaxation (internal friction and frequency) in the temperature range from 300 K to 625 K not revealed the presence of relaxation process. As shown in the literature, the hcp structure usually does not exhibit any relaxation due to the symmetry of the sites in the crystalline lattice, but if there is some relaxation, this only occurs in special cases such as low concentration of zirconium or saturation of the stoichiometric ratio of oxygen for zirconium. Dynamical elastic modulus obtained for TNZ + WQ + 670 K/3 h alloy was 87 GPa at room temperature, which is higher than the value for Ti-13Nb-13Zr alloy (64 GPa) of the literature. This increment may be related to the change of the proportion of α and β phases. Besides that, the presence of precipitates in the alloy after aging treatment hardens the material and reduces its ductility.

Titanium alloys are widely used in the manufacture of biomedical implants because they possess an excellent combination of physical properties and outstanding biocompatibility. Today, the most widely used alloy is Ti-6Al-4V, but some studies have reported adverse effects with the long-term presence of Al and V in the body, without mentioning that the elasticity modulus value of this alloy is far superior to the bone. Thus, there is a need to develop new Ti-based alloys without Al and V that have a lower modulus, greater biocompatibility, and similar mechanical strength. In this paper, we investigated the effect of Nb as a substitutional solute on the mechanical properties of Ti-Nb alloys, prepared in an arc-melting furnace and characterized by density, X-ray diffraction, optical microscopy, hardness and elasticity modulus measurements. The X-ray and microscopy measurements show a predominance of the α phase. The microhardness values showed a tendency to increase with the concentration of niobium in the alloy. Regarding the elasticity modulus, it was observed a nonlinear behavior with respect to the concentration of niobium. This behavior is associated with the presence of the α phase.

With the increase in life expectancy, biomaterials have become an increasingly important focus of research because they are used to replace parts and functions of the human body, thus contributing to improved quality of life. In the development of new biomaterials, the Ti-15Mo alloy is particularly significant. In this study, the Ti-15Mo alloy was produced using an arc-melting furnace and then characterized by density, X-ray diffraction, optical microscopy, hardness and dynamic elasticity modulus measurements, and cytotoxicity tests. The microstructure was obtained with β predominance. Microhardness, elasticity modulus, and cytotoxicity testing results showed that this material has great potential for use as biomaterial, mainly in orthopedic applications.

Mechanical spectroscopy measurements have been extensively used in the last decades to obtain information about many aspects of the behavior of solutes in metallic materials. Metals of body-centered cubic lattice that contain heavy interstitial elements (oxygen, nitrogen and carbon) in solid solution, present anelastic relaxation peaks when submitted to cyclic tensions, due to process know stress-induced ordering. Internal friction and frequency as a function of temperature were performed between 300 K and 650 K in a polycrystalline sample of Nb, for three distinct conditions, using a torsion pendulum inverted Kê-type operating in a frequency oscillation between 1Hz and 10 Hz range, with a heating rate of 1 K/min and pressure lower than 2 x 10-5 mbar. The experimental spectra obtained for each condition of the sample, were decomposed by the successive subtraction method in elementary Debye peaks. The following metal-interstitial interactions were identified: Nb-O and Nb-N for all conditions of the sample. From the anelastic relaxation parameters obtained (relaxation strength, peak temperature, activation energy and relaxation time) and lattice parameter (obtained from x ray diffraction), the determination of the oxygen and nitrogen interstitial diffusion coefficient in Nb was possible, for each condition of the sample.

Impurity interstitial atoms present in metals with BCC structure can diffuse in the metallic matrix by jumps to energetically equivalent crystallographic sites. Anelastic spectroscopy (internal friction) is based on the measurement of mechanical loss or internal friction as a function of temperature. Due to its selective and nondestructive nature, anelastic spectroscopy is well suited for the study of diffusion of interstitial elements in metals. Internal friction measurements were made using the torsion pendulum technique with oscillation frequency of a few Hz, temperature interval from 300 to 700 K, heating rate of about 1 K/min, and vacuum better than 10-5 mbar. The polycrystalline Nb and Ta samples used were supplied by Aldrich Inc. The results obtained showed thermally activated relaxation structures due to stress-induced ordering of oxygen atoms around the Nb (or Ta) atoms of the metallic matrix. The results were interpreted by three methods and led to activation enthalpy values for the diffusion of oxygen in Nb and Ta of 1.15 eV and 1.10 eV, respectively.

Há mais de cinqüenta anos, existe a preocupação em se definir os objetivos para o laboratório didático, revisando currículos e buscando ações mais localizadas e orientadas de acordo com o avanço crescente de conhecimentos das concepções alternativas de vários tópicos da Física por parte dos alunos, levando-se em conta as dificuldades específicas enfrentadas por eles no processo ensino-aprendizagem. Podem-se identificar duas linhas filosóficas que norteiam o processo ensino-aprendizagem com relação aos objetivos do laboratório didático. Uma linha defende que para sedimentar os conceitos expostos em aulas teóricas é necessária a prática em laboratório. A outra linha defende que o alvo da prática em laboratório deveria ser a obtenção e análise de dados, levando-se em conta a teoria aprendida. Atualmente, se percebe um crescimento por parte de profissionais que entendem haver uma necessidade de planejar, definir e hierarquizar objetivos detalhados, além de propiciar atividades que favoreçam de acordo com cada classe dentro da linha filosófica a que se identifica o profissional, não se esquecendo que ainda existem profissionais que não aceitam essa postura. Dentro desta perspectiva, foi aplicado um questionário a trinta alunos do curso de Licenciatura em Física da UNESP-Bauru, que já cursaram as cinco disciplinas práticas básicas do curso. Os alunos pontuaram de acordo com a sua visão dos objetivos reais frente aos objetivos ideais do laboratório didático. Os resultados mostraram que o laboratório didático vem cumprindo seu papel na opinião dos alunos do curso de Licenciatura em Física.

In the last fifty years, there have been the worry in defining the objectives for the didactic laboratory, revising curricula and looking for more specific and guided actions in agreement with the growing progress of knowledge in the alternative conceptions of several topics of the Physics on the part of the students, taking into account their difficulties in the teaching-learning process. We can identify two philosophical lines that guide the teaching learning process with relationship to the objectives of the didactic laboratory. One line defends that it is necessary to practice in laboratory the concepts exposed in theoretical classes in order to settle them. The other line defends that the objective of the practice in laboratory should be the acquisition and analysis of data, accounting for the learned theory. Nowadays, it is notable the growing number of professionals that understand the needs of planning, defining and organizing each of the aims. Besides, it is necessary to keep activities that propitiate different and unlike insights, considering that these are professionals that do not share this philosophical concept. In this perspective, a questionnaire was applied to thirty students attending the Physics Course at UNESP-Bauru, which have studied the five basic practices disciplines of the course. The students punctuated according to its vision of the real objectives facing the ideal objectives of the didactic laboratory. The results showed that the didactic laboratory has been paying its role in a suitable way.