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1.
Polymers (Basel) ; 14(24)2022 Dec 08.
Artigo em Inglês | MEDLINE | ID: mdl-36559742

RESUMO

The reported study was devoted to the investigation of viscoelastic behavior for solid and porous ultra-high molecular weight polyethylene (UHMWPE) under compression. The obtained experimental stress curves were interpreted using a two-term Prony series to represent the superposition of two coexisting activation processes corresponding to long molecular (~160 s) and short structural (~20 s) time scales, respectively, leading to good statistical correlation with the observations. In the case of porous polymer, the internal strain redistribution during relaxation was quantified using digital image correlation (DIC) analysis. The strongly inhomogeneous deformation of the porous polymer was found not to affect the relaxation times. To illustrate the possibility of generalizing the results to three dimensions, X-ray tomography was used to examine the porous structure relaxation at the macro- and micro-scale levels. DIC analysis revealed positive correlation between the applied force and relative density. The apparent stiffness variation for UHMWPE foams with mixed open and closed cells was described using a newly proposed three-term expression. Furthermore, in situ tensile loading and X-ray scattering study was applied for isotropic solid UHMWPE specimens to investigate the evolution of internal structure and orientation during drawing and stress relaxation in another loading mode.

2.
Nat Commun ; 13(1): 5816, 2022 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-36192380

RESUMO

Cracking from a fine equiaxed zone (FQZ), often just tens of microns across, plagues the welding of 7000 series aluminum alloys. Using a multiscale correlative methodology, from the millimeter scale to the nanoscale, we shed light on the strengthening mechanisms and the resulting intergranular failure at the FQZ. We show that intergranular AlCuMg phases give rise to cracking by micro-void nucleation and subsequent link-up due to the plastic incompatibility between the hard phases and soft (low precipitate density) grain interiors in the FQZ. To mitigate this, we propose a hybrid welding strategy exploiting laser beam oscillation and a pulsed magnetic field. This achieves a wavy and interrupted FQZ along with a higher precipitate density, thereby considerably increasing tensile strength over conventionally hybrid welded butt joints, and even friction stir welds.

3.
Opt Express ; 30(11): 19185-19198, 2022 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-36221703

RESUMO

Aberrations introduced during fabrication degrade the performance of X-ray optics and their ability to achieve diffraction limited focusing. Corrective optics can counteract these errors by introducing wavefront perturbations prior to the optic which cancel out the distortions. Here we demonstrate two-dimensional wavefront correction of an aberrated Kirkpatrick-Baez mirror pair using adaptable refractive structures. The resulting two-dimensional wavefront is measured using hard X-ray ptychography to recover the complex probe wavefield with high spatial resolution and model the optical performance under coherent conditions. The optical performance including the beam caustic, focal profile and wavefront error is examined before and after correction with both mirrors found to be diffraction limited after correcting. The results will be applicable to a wide variety of high numerical aperture X-ray optics aiming to achieve diffraction limited focussing using low emittance sources.

4.
ACS Appl Mater Interfaces ; 14(27): 31396-31410, 2022 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-35759353

RESUMO

To explore an effective route of customizing the superelasticity (SE) of NiTi shape memory alloys via modifying the grain structure, binary Ni55Ti45 (wt) alloys were fabricated in as-cast, hot swaged, and hot-rolled conditions, presenting contrasting grain sizes and grain boundary types. In situ synchrotron X-ray Laue microdiffraction and in situ synchrotron X-ray powder diffraction techniques were employed to unravel the underlying grain structure mechanisms that cause the diversity of SE performance among the three materials. The evolution of lattice rotation, strain field, and phase transformation has been revealed at the micro- and mesoscale, and the effect of grain structure on SE performance has been quantified. It was found that (i) the Ni4Ti3 and NiTi2 precipitates are similar among the three materials in terms of morphology, size, and orientation distribution; (ii) phase transformation happens preferentially near high-angle grain boundary (HAGB) yet randomly in low-angle grain boundary (LAGB) structures; (iii) the smaller the grain size, the higher the phase transformation nucleation kinetics, and the lower the propagation kinetics; (iv) stress concentration happens near HAGBs, while no obvious stress concentration can be observed in the LAGB grain structure during loading; (v) the statistical distribution of strain in the three materials becomes asymmetric during loading; (vi) three grain lattice rotation modes are identified and termed for the first time, namely, multi-extension rotation, rigid rotation, and nondispersive rotation; and (vii) the texture evolution of B2 austenite and B19' martensite is not strongly dependent on the grain structure.

5.
Polymers (Basel) ; 14(9)2022 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-35566962

RESUMO

This work evaluated the fracture toughness of the low-temperature carbonized elastomer-based composites filled with shungite and short carbon fibers. The effects of the carbonization temperature and filler content on the critical stress intensity factor (K1c) were examined. The K1c parameter was obtained using three-point bending tests for specimens with different l/b ratio (notch depth to sample thickness) ranging from 0.2 to 0.4. Reliable detection of the initiation and propagation of cracks was achieved using an acoustic sensor was attached to the samples during the bending test. The critical stress intensity factor was found to decrease linearly with increasing carbonization temperature. As the temperature increased from 280 to 380 °C, the K1c parameter was drastically reduced from about 5 to 1 MPa·m1/2 and was associated with intense outgassing during the carbonization step that resulted in sample porosity. The carbon fiber addition led to some incremental toughening; however, it reduced the statistical dispersion of the K1c values.

6.
Phys Chem Chem Phys ; 24(15): 8901-8912, 2022 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-35363241

RESUMO

Siliceous diatom frustules represent an up-and-coming platform for a range of bio-assisted nanofabrication processes able to overcome the complexity and high cost of current engineering technology solutions in terms of negligibly small power consumption and environmentally friendly processing combined with unique highly porous structures and properties. Herein, the modification of diatomite - a soft, loose, and fine-grained siliceous sedimentary rock composed of the remains of fossilized diatoms - with gold nanoparticles using layer-by-layer technology in combination with a freezing-induced loading approach is demonstrated. The obtained composite structures are characterized by dynamic light scattering, extinction spectroscopy, scanning (SEM) and transmission electron microscopy (TEM), and photoacoustic imaging techniques, and tested as a platform for surface-enhanced Raman scattering (SERS) using Rhodamine 6G. SEM, TEM, and energy dispersive X-ray spectroscopy (EDX) confirmed a dense coating of gold nanoparticles with an average size of 19 nm on the surface of the diatomite and within the pores. The photoacoustic signal excited at a wavelength of 532 nm increases with increasing loading cycles of up to three polyelectrolyte-gold nanoparticle bilayers. The hybrid materials based on diatomite modified with gold nanoparticles can be used as SERS substrates, but also as biosensors, catalysts, and platforms for advanced bioimaging.


Assuntos
Diatomáceas , Nanopartículas Metálicas , Terra de Diatomáceas , Diatomáceas/química , Congelamento , Ouro/química , Nanopartículas Metálicas/química , Análise Espectral Raman/métodos
7.
Nanomaterials (Basel) ; 12(6)2022 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-35335811

RESUMO

Electrospinning is a well-established method for the fabrication of polymer biomaterials, including those with core-shell nanofibers. The variability of structures presents a great range of opportunities in tissue engineering and drug delivery by incorporating biologically active molecules such as drugs, proteins, and growth factors and subsequent control of their release into the target microenvironment to achieve therapeutic effect. The object of study is non-woven core-shell PVA-PEG-SiO2@PVA-GO fiber mats assembled by the technology of coaxial electrospinning. The task of the core-shell fiber development was set to regulate the degradation process under external factors. The dual structure was modified with silica nanoparticles and graphene oxide to ensure the fiber integrity and stability. The influence of the nano additives and crosslinking conditions for the composite was investigated as a function of fiber diameter, hydrolysis, and mechanical properties. Tensile mechanical tests and water degradation tests were used to reveal the fracture and dissolution behavior of the fiber mats and bundles. The obtained fibers were visualized by confocal fluorescence microscopy to confirm the continuous core-shell structure and encapsulation feasibility for biologically active components, selectively in the fiber core and shell. The results provide a firm basis to draw the conclusion that electrospun core-shell fiber mats have tremendous potential for biomedical applications as drug carriers, photocatalysts, and wound dressings.

8.
Bioact Mater ; 9: 358-372, 2022 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-34820576

RESUMO

To reflect human development, it is critical to create a substrate that can support long-term cell survival, differentiation, and maturation. Hydrogels are promising materials for 3D cultures. However, a bulk structure consisting of dense polymer networks often leads to suboptimal microenvironments that impedes nutrient exchange and cell-to-cell interaction. Herein, granular hydrogel-based scaffolds were used to support 3D human induced pluripotent stem cell (hiPSC)-derived neural networks. A custom designed 3D printed toolset was developed to extrude hyaluronic acid hydrogel through a porous nylon fabric to generate hydrogel granules. Cells and hydrogel granules were combined using a weaker secondary gelation step, forming self-supporting cell laden scaffolds. At three and seven days, granular scaffolds supported higher cell viability compared to bulk hydrogels, whereas granular scaffolds supported more neurite bearing cells and longer neurite extensions (65.52 ± 11.59 µm) after seven days compared to bulk hydrogels (22.90 ± 4.70 µm). Long-term (three-month) cultures of clinically relevant hiPSC-derived neural cells in granular hydrogels supported well established neuronal and astrocytic colonies and a high level of neurite extension both inside and beyond the scaffold. This approach is significant as it provides a simple, rapid and efficient way to achieve a tissue-relevant granular structure within hydrogel cultures.

9.
J Adv Res ; 29: 167-177, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33842014

RESUMO

In the past years, a significant amount of effort has been directed at the observation and characterisation of caries using experimental techniques. Nevertheless, relatively little progress has been made in numerical modelling of the underlying demineralisation process. The present study is the first attempt to provide a simplified calculation framework for the numerical simulation of the demineralisation process at the length scale of enamel rods and its validation by comparing the data with statistical analysis of experimental results. FEM model was employed to simulate a time-dependent reaction-diffusion equation process in which H ions diffuse and cause demineralisation of the enamel. The local orientation of the hydroxyapatite crystals was taken into account. Experimental analysis of the demineralising front was performed using advanced high-resolution synchrotron X-ray micro-Computed Tomography. Further experimental investigations were conducted by means of SEM and STEM imaging techniques. Besides establishing and validating the new modelling framework, insights into the role of the etchant solution pH level were obtained. Additionally, some light was shed on the origin of different types of etching patterns by simulating the demineralisation process at different etching angles of attack. The implications of this study pave the way for simulations of enamel demineralisation within different complex scenarios and across the range of length scales. Indeed, the framework proposed can incorporate the presence of chemical species other than H ions and their diffusion and reaction leading to dissolution and re-precipitation of hydroxyapatite. It is the authors' hope and aspiration that ultimately this work will help identify new ways of controlling and preventing caries.

10.
Polymers (Basel) ; 13(9)2021 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-33925323

RESUMO

The structure of self-reinforced composites (SRCs) based on ultra-high molecular weight polyethylene (UHMWPE) was studied by means of Wide-Angle X-ray Scattering (WAXS), X-ray tomography, Raman spectroscopy, Scanning Electron Microscopy (SEM) and in situ tensile testing in combination with advanced processing tools to determine the correlation between the processing conditions, on one hand, and the molecular structure and mechanical properties, on the other. SRCs were fabricated by hot compaction of UHMWPE fibers at different pressure and temperature combinations without addition of polymer matrix or softener. It was found by WAXS that higher compaction temperatures led to more extensive melting of fibers with the corresponding reduction of the Herman's factor reflecting the degree of molecular orientation, while the increase of hot compaction pressure suppressed the melting of fibers within SRCs at a given temperature. X-ray tomography proved the absence of porosity while polarized light Raman spectroscopy measurements for both longitudinal and perpendicular fiber orientations showed qualitatively the anisotropy of SRC samples. SEM revealed that the matrix was formed by interlayers of molten polymer entrapped between fibers in SRCs. Moreover, in situ tensile tests demonstrated the increase of Young's modulus and tensile strength with increasing temperature.

11.
Molecules ; 26(3)2021 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-33499359

RESUMO

Carbonized elastomer-based composites (CECs) possess a number of attractive features in terms of thermomechanical and electromechanical performance, durability in aggressive media and facile net-shape formability, but their relatively low ductility and strength limit their suitability for structural engineering applications. Prospective applications such as structural elements of micro-electro-mechanical systems MEMS can be envisaged since smaller principal dimensions reduce the susceptibility of components to residual stress accumulation during carbonization and to brittle fracture in general. We report the results of in situ in-SEM study of microdeformation and fracture behavior of CECs based on nitrile butadiene rubber (NBR) elastomeric matrices filled with carbon and silicon carbide. Nanostructured carbon composite materials were manufactured via compounding of elastomeric substance with carbon and SiC fillers using mixing rolling mill, vulcanization, and low-temperature carbonization. Double-edge notched tensile (DENT) specimens of vulcanized and carbonized elastomeric composites were subjected to in situ tensile testing in the chamber of the scanning electron microscope (SEM) Tescan Vega 3 using a Deben microtest 1 kN tensile stage. The series of acquired SEM images were analyzed by means of digital image correlation (DIC) using Ncorr open-source software to map the spatial distribution of strain. These maps were correlated with finite element modeling (FEM) simulations to refine the values of elastic moduli. Moreover, the elastic moduli were derived from unloading curve nanoindentation hardness measurements carried out using a NanoScan-4D tester and interpreted using the Oliver-Pharr method. Carbonization causes a significant increase of elastic moduli from 0.86 ± 0.07 GPa to 14.12 ± 1.20 GPa for the composite with graphite and carbon black fillers. Nanoindentation measurements yield somewhat lower values, namely, 0.25 ± 0.02 GPa and 9.83 ± 1.10 GPa before and after carbonization, respectively. The analysis of fractography images suggests that crack initiation, growth and propagation may occur both at the notch stress concentrator or relatively far from the notch. Possible causes of such response are discussed, namely, (1) residual stresses introduced by processing; (2) shape and size of fillers; and (3) the emanation and accumulation of gases in composites during carbonization.


Assuntos
Elastômeros/química , Nanocompostos/química , Carbono/química , Compostos Inorgânicos de Carbono/química , Simulação por Computador , Módulo de Elasticidade , Análise de Elementos Finitos , Dureza , Teste de Materiais , Microscopia Eletrônica de Varredura , Nanocompostos/ultraestrutura , Compostos de Silício/química , Estresse Mecânico , Resistência à Tração
12.
ACS Appl Mater Interfaces ; 13(5): 6795-6804, 2021 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-33507755

RESUMO

The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX-a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.

13.
Acta Biomater ; 120: 240-248, 2021 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-32438107

RESUMO

Acid-induced enamel demineralisation affects many individuals either by exposure to acidic diets, acidic gas pollution (dental erosion) or to dental plaque acids (dental caries). This study aimed to develop in situ X-ray and light imaging methods to determine progression of enamel demineralisation and the dynamic relationship between acid pH and mineral density. Hourly digital microradiograph time-lapse sequences showed the depth of enamel demineralisation in 500 µm thick sections progressed with time from the surface towards the dentine following a power-law function, which was 21% faster than the lateral demineralisation progression after exposure for 85 h to lactic acid (10%, pH 2.2). The minimum greyscale remaining (mineral content) within the induced enamel lesion followed an exponential decay, while the accumulated total greyscale loss with time was linear, which showed a constant anisotropic mineral release within the enamel architecture. This 85 h demineralisation method studied by polarised light microscopy time-lapse sequences showed that once the demineralisation front reached the enamel Hunter-Schreger bands, there was preferential demineralisation along those bands. Mineral density loss was linear with increasing pH acidity between pH 5.2 and pH 4.0 (with 0.4 pH increments) when incubated over a 3-week period exposed to 0.5% lactic acid. At pH 4.0, there was complete mineral loss in the centre of the demineralised area after the 3-week period and the linear function intercepted the x-axis at ~ pH 5.5, near the critical pH for hydroxyapatite (HAp). These observations showed how intrinsic enamel structure and pH affected the progression of demineralisation. STATEMENT OF SIGNIFICANCE: Hydroxyapatite crystallites (HAp) in human enamel dissolve when exposed to an acidic environment but little is known about how the intrinsic structures in enamel and pH influence the demineralisation kinetics. We have developed a time-lapse in situ microradiography method to quantify microscopic anisotropic mineral loss dynamics in response to an acid-only caries model. Correlation with polarised light microscopy time-lapse sequences showed that larger structures in enamel also influence demineralisation progression as demineralisation occurred preferentially along the Hunter-Schreger bands (decussating prismatic enamel). The pH-controlled enamel mineral release in a linear manner quantifying the relationship between HAp orientation and acid solubility. These findings should direct the development of improved anti-demineralisation/ remineralisation treatments to retain/ restore the natural intrinsic enamel structure.


Assuntos
Cárie Dentária , Desmineralização do Dente , Esmalte Dentário/diagnóstico por imagem , Humanos , Concentração de Íons de Hidrogênio , Desmineralização do Dente/induzido quimicamente , Desmineralização do Dente/diagnóstico por imagem , Raios X
14.
RSC Adv ; 11(51): 31884-31922, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-35495528

RESUMO

The present article overviews the current state-of-the-art and future prospects for the use of diatomaceous earth (DE) in the continuously expanding sector of energy science and technology. An eco-friendly direct source of silica and the production of silicon, diatomaceous earth possesses a desirable nano- to micro-structure that offers inherent advantages for optimum performance in existing and new applications in electrochemistry, catalysis, optoelectronics, and biomedical engineering. Silica, silicon and silicon-based materials have proven useful for energy harvesting and storage applications. However, they often encounter setbacks to their commercialization due to the limited capability for the production of materials possessing fascinating microstructures to deliver optimum performance. Despite many current research trends focusing on the means to create the required nano- to micro-structures, the high cost and complex, potentially environmentally harmful chemical synthesis techniques remain a considerable challenge. The present review examines the advances made using diatomaceous earth as a source of silica, silicon-based materials and templates for energy related applications. The main synthesis routes aimed at preserving the highly desirable naturally formed neat nanostructure of diatomaceous earth are assessed in this review that culminates with the discussion of recently developed pathways to achieving the best properties. The trend analysis establishes a clear roadmap for diatomaceous earth as a source material of choice for current and future energy applications.

15.
Polymers (Basel) ; 12(11)2020 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-33171935

RESUMO

Porous ultra-high molecular weight polyethylene (UHMWPE) is a high-performance bioinert polymer used in cranio-facial reconstructive surgery in procedures where relatively low mechanical stresses arise. As an alternative to much stiffer and more costly polyether-ether-ketone (PEEK) polymer, UHMWPE is finding further wide applications in hierarchically structured hybrids for advanced implants mimicking cartilage, cortical and trabecular bone tissues within a single component. The mechanical behaviour of open-cell UHMWPE sponges obtained through sacrificial desalination of hot compression-moulded UHMWPE-NaCl powder mixtures shows a complex dependence on the fabrication parameters and microstructural features. In particular, similarly to other porous media, it displays significant inhomogeneity of strain that readily localises within deformation bands that govern the overall response. In this article, we report advances in the development of accurate experimental techniques for operando studies of the structure-performance relationship applied to the porous UHMWPE medium with pore sizes of about 250 µm that are most well-suited for live cell proliferation and fast vascularization of implants. Samples of UHMWPE sponges were subjected to in situ compression using a micromechanical testing device within Scanning Electron Microscope (SEM) chamber, allowing the acquisition of high-resolution image sequences for Digital Image Correlation (DIC) analysis. Special masking and image processing algorithms were developed and applied to reveal the evolution of pore size and aspect ratio. Key structural evolution and deformation localisation phenomena were identified at both macro- and micro-structural levels in the elastic and plastic regimes. The motion of pore walls was quantitatively described, and the presence and influence of strain localisation zones were revealed and analysed using DIC technique.

16.
J Synchrotron Radiat ; 27(Pt 6): 1688-1695, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-33147195

RESUMO

Ptychography is a scanning coherent diffraction imaging technique which provides high resolution imaging and complete spatial information of the complex electric field probe and sample transmission function. Its ability to accurately determine the illumination probe has led to its use at modern synchrotrons and free-electron lasers as a wavefront-sensing technique for optics alignment, monitoring and correction. Recent developments in the ptychography reconstruction process now incorporate a modal decomposition of the illuminating probe and relax the restriction of using sources with high spatial coherence. In this article a practical implementation of hard X-ray ptychography from a partially coherent X-ray source with a large number of modes is demonstrated experimentally. A strongly diffracting Siemens star test sample is imaged using the focused beam produced by either a Fresnel zone plate or beryllium compound refractive lens. The recovered probe from each optic is back propagated in order to plot the beam caustic and determine the precise focal size and position. The power distribution of the reconstructed probe modes also allows the quantification of the beams coherence and is compared with the values predicted by a Gaussian-Schell model and the optics exit intensity.

17.
Polymers (Basel) ; 12(5)2020 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-32443677

RESUMO

Nylon-12 is an important structural polymer in wide use in the form of fibres and bulk structures. Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) method for rapid prototyping and final product manufacturing of thermoplastic polymer objects. The resultant microstructure of FFF-produced samples is strongly affected by the cooling rates and thermal gradients experienced across the part. The crystallisation behaviour during cooling and solidification influences the micro- and nano-structure, and deserves detailed investigation. A commercial Nylon-12 filament and FFF-produced Nylon-12 parts were studied by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) to examine the effect of cooling rates under non-isothermal crystallisation conditions on the microstructure and properties. Slower cooling rates caused more perfect crystallite formation, as well as alteration to the thermal properties.

18.
Nanomaterials (Basel) ; 10(5)2020 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-32354141

RESUMO

Silver-based low-emissivity (low-E) coatings are applied on architectural glazing to cost-effectively reduce heat losses, as they generally consist of dielectric/Ag/dielectric multilayer stacks, where the thin Ag layer reflects long wavelength infrared (IR), while the dielectric layers both protect the Ag and act as an anti-reflective barrier. The architecture of the multilayer stack influences its mechanical properties and it is strongly dependent on the residual stress distribution in the stack. Residual stress evaluation by combining focused ion beam (FIB) milling and digital image correlation (DIC), using the micro-ring core configuration (FIB-DIC), offers micron-scale lateral resolution and provides information about the residual stress variation with depth, i.e., it allows depth profiling for both equibiaxial and non-equibiaxial stress distributions and hence can be effectively used to characterize low-E coatings. In this work, we propose an innovative approach to improve the depth resolution and surface sensitivity for residual stress depth profiling in the case of ultra-thin as-deposited and post-deposition annealed Si3N4/Ag/ZnO low-E coatings, by considering different fractions of area for DIC strain analysis and accordingly developing a unique influence function to maintain the sensitivity of the technique at is maximum during the calculation. Residual stress measurements performed using this novel FIB-DIC approach revealed that the individual Si3N4/ZnO layers in the multilayer stack are under different amounts of compressive stresses. The magnitude and orientation of these stresses changes significantly after heat treatment and provides a clear explanation for the observed differences in terms of scratch critical load. The results show that the proposed FIB-DIC combined-areas approach is a unique method for accurately probing non-equibiaxial residual stresses with nano-scale resolution in thin films, including multilayers.

19.
Nanomaterials (Basel) ; 10(4)2020 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-32218203

RESUMO

Successful direct route production of silicon nanostructures from diatomaceous earth (DE) on a single crystalline silicon wafer via the magnesiothermic reduction reaction is reported. The formed porous coating of 6 µm overall thickness contains silicon as the majority phase along with minor traces of Mg, as evident from SEM-EDS and the Focused Ion Beam (FIB) analysis. Raman peaks of silicon at 519 cm-1 and 925 cm-1 were found in both the film and wafer substrate, and significant intensity variation was observed, consistent with the SEM observation of the directly formed silicon nanoflake layer. Microstructural analysis of the flakes reveals the presence of pores and cavities partially retained from the precursor diatomite powder. A considerable reduction in surface reflectivity was observed for the silicon nanoflakes, from 45% for silicon wafer to below 15%. The results open possibilities for producing nanostructured silicon with a vast range of functionalities.

20.
Dent Mater ; 35(11): 1576-1593, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31522759

RESUMO

OBJECTIVES: Yttria Partially Stabilised Zirconia (YPSZ) is a high strength ceramic which has become widely used in porcelain veneered dental copings due to its exceptional toughness. Within these components the residual stress and crystallographic phase of YPSZ close to the interface are highly influential in the primary failure mode; near interface porcelain chipping. In order to improve present understanding of this behaviour, characterisation of these parameters is needed at an improved spatial resolution. METHODS: In this study transmission micro-focus X-ray Diffraction, Raman spectroscopy, and focused ion beam milling residual stress analysis techniques have, for the first time, been used to quantify and cross-validate the microscale spatial variation of phase and residual stress of YPSZ in a prosthesis cross-section. RESULTS: The results of all techniques were found to be comparable and complementary. Monoclinic YPSZ was observed within the first 10µm of the YPSZ-porcelain interface with a maximum volume fraction of 60%. Tensile stresses were observed within the first 150 µm of the interface with a maximum value of ≈300 MPa at 50 µm from the interface. The remainder of the coping was in mild compression at ≈-30MPa, with shear stresses of a similar magnitude also being induced by the YPSZ phase transformation. SIGNIFICANCE: The analysis indicates that the interaction between phase transformation, residual stress and porcelain creep at YPSZ-porcelain interface results in a localised porcelain fracture toughness reduction. This explains the increased propensity of failure at this location, and can be used as a basis for improving prosthesis design.


Assuntos
Porcelana Dentária , Prótese Dentária , Análise do Estresse Dentário , Facetas Dentárias , Teste de Materiais , Estresse Mecânico , Propriedades de Superfície , Ítrio , Zircônio
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