14,789 research outputs found
Investigação eletroquímica da superfície de titânio tratada por oxidação térmica
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde, Programa de Pós-Graduação em Odontologia, Florianópolis, 2014O processo de oxidação térmica melhora as características na superfície das ligas de titânio pelo aumento da camada de TiO2. Nesta pesquisa, foi avaliado o comportamento da liga Ti-6Al-4V termo oxidada em diferentes temperaturas e duração de tratamento na saliva artificial em diferentes pH. Para compreender as alterações no processo de corrosão, o teste de espectroscopia de impedância eletroquímica fornece a caracterização que ocorre sobre a superfície metálica. Foram utilizadas 60 amostras de discos de liga de Ti-6Al-4V, divididas em 20 grupos(n=3), comparando a relação da saliva artificial com alteração de pH (3e 6.5), temperatura (200°C, 400°C e 700°C) e duração de tratamento (1,3 e 6 horas) em relação ao grupo controle Ti-6Al-4V, que não recebeu tratamento de superfície. Para análise eletroquímica das amostras, foi utilizado teste com OCP, EIS e polarização potenciodinâmica. Os resultados foram avaliados por análise de variância e teste de Bonferroni (pAbstract: The thermal oxidation process improves the surface characteristics of titanium alloys by increasing the TiO2 layer. In this study, we evaluated the behavior of Ti-6Al-4V term oxidized at different temperature and duration of treatment in artificial saliva at different pHs. To understand the changes in the corrosion process of the electrochemical impedance spectroscopy test provides a characterization that happens on the metal surface. It was used 60 samples of Ti-6Al-4V alloy discs divided into 20 groups (n = 3) to analyze the effect of pH (3 and 6.5) in artificial saliva, temperature (200°C, 400°C and 700°C), and duration of treatment (1, 3 and 6 hours) compared to the control group Ti-6Al-4V which received no surface treatment. Electrochemical tests, such OCP, EIS and potentiodynamic were used in a controlled environment to compare the surface reaction. The results were evaluated by analysis of variance and Bonferroni test (p <0.05). The surfaces were examined by white light interferometry microscopy, scanning electron microscopy (SEM) and FTIR. Samples treated by thermal oxidation showed improvement in corrosion resistance compare to the control group in potentiodynamic test. The test groups showed better results at treatments of 200°C and 400°C compared at the control group. The duration of treatment was not a determining factor for improved corrosion resistance and the samples were less resistant to corrosion in acidic pH
Investigation of Cutting Tools and Working Conditions Effects when Cutting Ti-6al-4V using Vegetable Oil-Based Cutting Fluids
No full textPower consumed in metal cutting is typically converted into heat near the cutting tool edge. Cutting fluids are then provided to a cutting zone in order to improve the tribological characteristics of machining processes and to dissipate the generated heat. The use of conventional cutting fluids however has lately been questioned due to the adverse impact on the environment and human health. Therefore, trends are directed to various alternatives such as vegetable oils (VOs). VOs offer a combination of good biodegradability and high lubricity, eco-friendly and compatibility with additives, low toxicity and volatility, high flash points and high viscosity indices. This paper details preliminary experimental results when turning Ti-6Al-4 V. The impact of VO-based cutting fluids, cutting tool materials and working conditions were investigated. Two sets of experimental plans were designed comprising 25 and 27 tests with analysis of variance (ANOVA) employed to evaluate the effect of process variables on Ra and tool flank wear. In general, surface roughness Ra ranged between 0.56 μm and 1.81 μm and statistical analysis showed that the main contributing factor for Ra is feed rate having a high Percentage Contribution Ratio (PCR) of 94.4%. Noticeable increase in tool tip flank wear was recorded when higher cutting speeds were used
Development of a Self-assembly Technique for Drug-Delivering Hydroxyapatite Coatings for Ti-Based Implants
No full textPhD 2010 QMTo facilitate the long term osteointegration of Ti implants of various forms,
methods aiming to facilitate hydroxyapatite deposition and enhance its adhesion to
the Ti surfaces have to be developed. This work investigates the novel route of Ti
surface functionalization with self-assembled monolayers (SAMs) in order to
facilitate hydroxyapatite deposition and strengthen its bonding with the Ti surface and
further equip the surface with localized antibiotic delivery to combat
post-implantation infections. The main findings demonstrate that the formation of
SAMs on non-model Ti substrates is challenging, since it requires the simultaneous
control of many factors to achieve a densely packed well-organized SAM on a large
surface area. By pre-treating the substrate with techniques such as electropolishing,
the initial surface contamination can be kept at minimum while the hydroxylated
surface remains smooth for the formation of well-oriented SAMs. Hence, after
electropolishing, the Ti surface could be functionalized with molecules carrying
reactive or neutral groups to facilitate hydroxyapatite deposition and/or antibiotic
immobilization. Such a surface functionalization is found to facilitate hydroxyapatite
deposition. The hydroxyapatite formed on SAM-modified Ti surfaces is made of
small crystals of 6 nm and a 12 μm thick hydroxyapatite film, which can grow in 1
month. The SAM modified surfaces are covered with hydroxyapatite spheres in less
than 7 days, while no spheres are observed on the unmodified Ti surface under
similar conditions. Enhanced hydroxyapatite deposition rates on SAM-modified
surfaces are explained by a decrease of nucleation barrier for hydroxyapatite.
Additionally, preliminary investigations demonstrate the possibility of further
functionalizing the Ti surface to allow the immobilization of antibiotic (Ciprofloxacin
here) simultaneously with hydroxyapatite growth. The release of Ciprofloxacin was
found to occur after 1 day and continue up to 20 days. The combination of these two
functionalities on the Ti surfaces could find applications in load-bearing implants
Big Browser Manning the Thin Blue Line:Computational Legal Theory Meets Law Enforcement
No full textThis paper analyses some current jurisprudential and conceptual issues in evidence and procedure from the perspective of a computational legal theory. It introduces a specific investigative device, Trojans operated by police during crime investigation, and analyses whether current formal approaches to legal reasoning can be modified in such a way that the software code underlying this device can represent the relevant legal constraints that should govern its operation. We will argue that traditional formalist theories of legal reasoning are typically restricted to reasoning within a system, and incapable therefore of making the notion of 'legal system' sufficiently explicit. We discuss possibilities to expand on these approaches and identify the necessary elements of a computational theory of legal reasoning in an age of porous borders
Revealing the influence of Mo addition on interphase precipitation in Ti-bearing low carbon steels
No full textMo is widely used as an effective microalloying element to improve mechanical performance of interphase precipitation steels, but the precise role of Mo in interphase precipitation behavior is not fully understood. In this contribution, interphase precipitation behavior in a series of Ti-Mo-bearing low carbon steels is systematically studied, and the role of Mo in interphase precipitates and its coarsening behavior is revisited. It is found that (Ti, Mo)C precipitates instead of TiC are formed in the Mo-containing alloys, and the average site fraction of Mo in (Ti, Mo)C is almost independent of the bulk Mo content. Moreover, the number density of interphase precipitates can be substantially enhanced by a minor addition of Mo, albeit it does not further rise with increasing the bulk Mo content. This is because the Mo fraction in (Ti, Mo)C rather than the bulk Mo content governs the driving force for precipitation nucleation and the interfacial energy of the (Ti, Mo)C/α and (Ti, Mo)C/γ interfaces. In addition to the reduced interfacial energy, decrease of Ti trans-interface diffusivity has been identified as another key reason for the enhanced carbide coarsening resistance in Mo-containing alloys.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Novel Aerospace Material
Lateral Inverse Proximity Effect in Ti/Au Transition Edge Sensors
No full textWe report measured Tc of superconducting Ti/Au bilayer strips with a width W varying from 5 to 50 µm. The strips were fabricated based on a Ti/Au bilayer that consists of a 41-nm-thick Ti layer to which a 280-nm-thick Au layer was added. We find that the Tc drops as W decreases and the declining trend almost perfectly follows Tc/ [mK] = - 738.4 [μ m] 2/ W2+ 91.0 , where Tc(W= ∞) of 91 mK is consistent with the intrinsic Tc of the bilayer. The result is interpreted as a consequence of the lateral inverse proximity effect originated in normal-metal microstructures, namely Au overhangs that exist at the edges of the Ti/Au bilayer. The Tc shift from the intrinsic Tc should be anticipated in addition to the longitudinal proximity effect from superconducting Nb leads when one designs Ti/Au TESs.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Optic
REGIONAL CUSTOMS DIRECTORATES MANAGEMENT
No full textThe management of a regional customs directorate is analyzed. A new approach of the managerial system, in the European integration context, is presented.The customs system is one of the first “doors” to a new economic, social and cultural community. ForPerformance management, strategic management, human resource management
X-ray absorption study of Ti-bearing silicate glasses
No full textTi K-edge XANES spectra have been collected on a series of Ti-bearing silicate glasses with metasilicate and tetrasilicate compositions. The intensity of the preedge feature in these spectra has been found to change with glass composition and varies from 29 to 58% (normalized intensity) suggesting a variation in structural environent around the absorbing atom. The pre-edge peak intensity increases for the alkali titanium tetrasilicate glasses from 35% to 58% in the order Li < Na < K < Rb, Cs whereas for the metasilicate compositions there is a maximum for the K-bearing glass. The pre-edge peak intensity remains constant for the alkaline earth titanium metasilicate glasses, Ca and Sr (34%) but increases slightly for Ba (41%). As the intensity of this feature is inversely correlated with coordination number, a comparison of the pre-edge intensity data for the investigated glasses with those of materials of known coordination number leads us to establish a regression equation and to infer that the average coordination number of Ti in these glasses ranges from 4.8 to 5.8. Large alkali cations appear to stabilize a relatively low average coordination number for Ti in silicate melts. The Ti structural environment results appear also to vary as a function of SiO2 content within the K2O-TiO2-SiO2 system. A number of physical properties of the melts from which these glasses were quenched and of other Ti-bearing silicate melts, have been determined in recent years. Clear evidence of a variable coordination number of Ti, consistent with the interpretation of the present XANES data is available from density measurements. These and other property determinations are compared with the present spectroscopic observations in an attempt to relate structure and properties in these melts which contain a major component with variable coordination number
Microstructures and surface roughness of EBM produced Ti-6Al-4V
No full textThe work presented in this dissertation is concerned with the microstructures and
surface roughness of test slabs of Ti-6Al-4V produced by one of powder based Additive
Manufacturing (AM) technique namely Electron Beam melting (EBM). The effects of process
parameters of a EBM system and geometry factors of a EBM build such as slabs’ thickness and
height etc. on the microstructure and the surface roughness of the EBM produced Ti-6Al-4V
have being investigated. The processing parameters of the EBM system involved in the present
work include beam current, scan speed, offset focus and scanning length etc. In this study three
different batches of samples were prepared. Microstructures of EBM built Ti-6Al-4V were
studied using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Transmission
Electron Microscopy (TEM), and X-ray diffraction (XRD). Confocal microscopy and image
analysis codes ImageJ’s routine SurfCharJ were used to quantify the surface roughness of the test
slabs. The microstructures of EBM built Ti-6Al-4V in general consist of columnar grains of prior
β phase. Inside the columnar grains there is a typical (α+β) microstructure of titanium alloys
containing Widmanstätten α platelets and rod-shaped β phase. Grain boundary α layer has also
been observed on the grain boundaries of prior b columnar grains. By using TEM, the β phase in
EBM built Ti-6Al-4V has been identified as a rod-like structure located on the grain boundaries
of the fine a grains and often grows up along the build direction. The size of the β rods is about
200nm and the distance between the β rods is ranged between 0.5 -2μm. Chemical compositions
for different phases have been measured by TEM/EDX and volume fraction of the β phase in the
EBM Ti-6Al-4V has been determined to be 2.7%. The phase transformation sequence in EBM
built Ti-6Al-4V has been discussed according to processing history and microstructures
observed. It has been observed that, the size, number and geometry of prior β columnar grain
depend on the sample thickness and other process parameters setting. The diameter of columnar
grain varies between 2-70μm. The increase in size, number and regularity of columnar grains has
been observed with increase in sample thickness, beam energy density and scanning length.
While with increase in height of the build it decreases. The length and smoothness of α platelets
increases with increase in diameter of prior β columnar grain. The β phase rods are unaffected by
sample thickness and process parameter settings. The sample thickness and beam energy density
has a strong effect on the surface roughness of the test slabs. The value of surface roughness
coefficient Ra for different test slabs varies between 1-20μm. It is observed that the surface
roughness increases of the test slab increases with increase in thickness of the slab and beam
energy density. The possible reasons for these variations in microstructures and surface
roughness have been discussed
The Structure and Photocatalytic Function of Hydroxyapatite with Doped Ti (IV) Ion
No full textP(論文)Hydroxyapatite (HAp) has a molecular structure in which Ca^, PO_4^ and OH^- are major components. When hydroxyapatite is formed the Ca^, PO_4^ and OH^- ions can be substituted with other specific ions. When a specific ion is purposely replaced in the forming hydroxyapatite crystal, there is a possibility that the new hydroxyapatite might demonstrate properties that could be attributed to the substituted ion. This change in hydroxyapatite properties has been demonstrated when F^- has been substituted for OH^-, F^- has significant acid resistance. The acid resistance property of F^- was observed when F^- was substituted for OH^- in hydroxyapatite. Therefore, the author performed the following experiment : The first portion of the experiment was the synthesis of HAp using the coprecipitation method substituting Ti^ for Ca^. The Ti^ was doped to the Ca^ position in the forming hydroxyapatite crystal. In the next phase of this experiment the author analyzed whether the HAp had obtained photocatalytic function that is a major character of Ti^. HAp using the coprecipitation method was synthesized with different concentrations of Ti^. Respectively the HAp was prepared with Ti^ concentrations of 0.01, 0.005, 0.0025 and 0 moles. The determination of the elementary composition of the synthesized TiHAp was investigated with ICP analysis. The structure of the TiHAp crystal was also investigated by X-ray diffraction. The TiHAp was irradiated by ultraviolet light to determine and measure the presence of photocatalytic function. The formation of radicals and their strength were also measured by ESR spin trapping. A specimen was prepared with 1% TiHAp combined with polypropylene and a second specimen was prepared with 1% TiHAp combined acrylic denture base resins. These specimens were then investigated by a facilitated deterioration exposure test. The photocatalytic function of each specimen was also investigated. The following conclusions of the experiment were obtained : 1. The X-ray diffraction of the TiHAp showed a. reversed correlative phenomenon when anatase dioxide titanium was at 25° (2θ) and the peak strength of HAp was at 26° (2θ) due to the doped Ti^. Therefore, the observed change in the HAp must be a consequence of the doped Ti^ into the HAp molecule. The mole ratio of the Ca/P in the synthetic substance showed that the Ti^ concentration was dependent on the successful doping of Ti^ for Ca^. It was observed that the more successful the dope of Ti^ for Ca^ the mole ratio showed a rectilinear decrease. Therefore, this observation confirmed that Ti^ had replaced Ca^. 2. The OH radical was identified from the post ultraviolet irradiated synthesized substance. The strength of the OH radical increased when the success of the substitution of Ti^ for Ca^ increased. 3. The observation of a clear OH radical signal by ultraviolet irradiation was confirmed from the outer layers of both the polypropylene and acrylic denture base resins that had been combined with 1 % of the synthesized TiHAp. It was observed that there was delayed depletion in the resins that had been combined with the synthesized TiHAp. The results of this experiment provided these conclusions : When a desired concentration of Ti^ has been successfully substituted for Ca^ in a synthesized hydroxyapatite crystal the newly synthesized HAp obtained photocatalytic function that is a special characteristic of titanium.departmental bulletin pape
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