Papers by Author: Giuseppe Pezzotti

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Authors: Giuseppe Pezzotti
Abstract: Photo- and electro-stimulated probes have been employed for quantitatively evaluating highly graded residual stress fields generated at the surface of alumina hip joints. Optical calibrations revealed large differences in probe size, which strongly affected the detected magnitude of residual stress. A comparison between the responses of Raman and fluorescence probes in polycrystalline alumina showed that the depth of those probes spread to an extent in the order of the tens of microns even with using a confocal probe configuration. On the other hand, the electro-stimulated luminescence emitted by oxygen vacancy sites (F+ center) in the alumina lattice represented a suitable choice for confining to a shallow volume the stress probe. The electron probe enabled confining the measurement depth to the order of the tens of nanometers. Maps of surface residual stress were collected on both main-wear and non-wear zones of an alumina femoral head. A comparison among stress maps taken at exactly the same location, but employing different probes, clarified the averaging probe effects on surface stress magnitude.
Authors: Giuseppe Pezzotti, Atsuo Matsutani, Maria Chiara Munisso, Wen Liang Zhu
Abstract: With the proliferation of several types and classes of high performance ceramic materials, the screening, evaluation and integration of new materials into structures and devices require a new and more effective approach. Evaluation on the nano-scale of the mechanical characteristics of new ceramic materials requires multiple complementary metrology tools. We report here about an advanced metrology tool, cathodoluminescence (CL) spectroscopy, which has a potential to rapidly screen and evaluate residual stress characteristics in advanced ceramic materials and structures. Nano-scale stress measurements are made in situ into an integrated metrology vacuum chamber in a field-emission gun scanning electron microscope (FEG-SEM). Complementing this tool, we also describe a new image analysis based on CL emission for fast screening and ranking of domain structures in ferroelastic ceramics. The end result of this paper is to show how crystallographic and mechanical characteristics of ceramics can be quantitatively characterized in a hybrid device combining electro-stimulated imaging and spectroscopic outputs.
Authors: Ian C. Clarke, Giuseppe Pezzotti, S. Sakakura, Besim Ben-Nissan
Authors: L. Sharma, Giuseppe Pezzotti
Authors: Giuseppe Pezzotti, Nobuhiko Sugano
Abstract: The most advanced options nowadays available in joint arthroplasty rely on the application to diseased joints of human-made bearing surfaces consisting of microstructurally engineered polyethylene and ceramics as substitutes for the damaged joint cartilage and, partly, for bone. However, it is progressively becoming clear that, whatever superior the biomaterial designed for this purpose, owing to the quite severe structural requirements for human joints, including high contact stresses and aggressive environment at the load-bearing surface, it will have a necessarily limited service lifetime. Giving a quite critical but fundamentally true statement, one could say that, so far, no single product has yet been capable to meet all such severe requirements. Moreover, it is not clear if such a perfect biomaterial will ever exist. This is the main reason for pursuing repair (rather than replacement) of damaged cartilage. In this paper, we inquire about the present status and expected progress in healing osteoarthritis (OA) of chronically damaged joints, and surmise that such innovative procedures could sometime, in the near future, replace the current joint arthroplasty procedures, thus avoiding the unavoidably intrusive surgery associated with nowadays total joint replacements. After reviewing the state of art in the new field of joint cartilage healing, we shall stress the potential importance of vibrational spectroscopy both in diagnostics and in accelerating discoveries through the future developments of therapeutic approaches to cartilage diseases.
Authors: Giuseppe Pezzotti, Ian C. Clarke, C. Jobe, T. Donaldson, Kengo Yamamoto, Toshiyuki Tateiwa, T. Kumakura, R. Tsukamoto, Junji Ikeda
Abstract: A survey of confocal Raman/fluorescence microprobe spectroscopic techniques is presented with emphasis placed on surface analysis of artificial hip joints. Suitable instrumental configurations are first explained in some details in order to describe the versatility of the spectroscopic microprobes to biomedical materials analyses. Then, these notions, which represent the foundation for structural and mechanical analyses of joint surfaces, are applied to selected cases of paramount importance in hip arthroplasty.
Authors: Kiyotaka Yamada, Masahiro Nawa, Giuseppe Pezzotti
Abstract: Zirconia ceramics have been widely used for new generation of bearing materials in biomedical applications. In this context, a zirconia-matrix, stabilized with cerium oxide and dispersed with fine alumina particles (Ce-TZP/Al2O3 nanocomposite) was recently developed and this material experienced significant improvements in both fracture toughness and strength above the standard mechanical performance of monolithic zirconia. In this paper, we used confocal Raman spectroscopy to provide quantitative assessments with high spatial resolution of phase structure and residual stress fields developed in the Ce-TZP/Al2O3 nanocomposite. According to confocal Raman spectroscopy, we have directly visualized patterns of phase transformation and residual stress fields stored on the very surface of the material around an indentation print. These spectroscopic assessments may open a perspective in understanding the micromechanical behavior of the Ce-TZP/Al2O3 nanocomposite when subjected to local surface impingement and shocks.
Authors: Kiyotaka Yamada, Junji Ikeda, Giuseppe Pezzotti
Abstract: The electro-stimulated luminescence spectrum of a rare-earth ion added to zirconia (ZrO2) lattice was investigated with the aim of using it as a sensor for nano-scale stress (fluorescence piezo-spectroscopy) and phase transformation assessments in a field emission scanning electron microscope (FE-SEM). In this paper, the selected rare-earth fluorescent ion Eu, added to ZrO2 as a raw oxide powder (Eu2O3) before sintering (in the amount of 1.0 wt. %). Spectroscopic results indicated that the spectral shift of some fluorescent band of the selected rare-earth ion was sensitive to residual stress and that the electron-stimulated spectra of Eu2O3-doped ZrO2 in its tetragonal and monoclinic polymorphs were different to each other. Based on these findings, the luminescent substance can be useful as a “stress and phase transformation sensor”, in order to clarify the elementary mechanisms behind synthetic ZrO2.
Authors: Goffredo de Portu, L. Micele, D. Prandstraller, G. Palombarini, Giuseppe Pezzotti
Abstract: Multilayered composite specimens consisting of Al2O3 / Al2O3+ 3Y-TZP (A/AZ) layers with different compositions and thicknesses were prepared starting from ceramic sheets obtained by tape casting. Residual stresses arisen from mismatch in thermal expansion coefficient during sintering were evaluated using luminescence piezo-spectroscopy. The stress in the superficial A layer was found to be compressive, and its value depended on the ratio between thickness of A and AZ layer. The influence of the superficial compressive stress on the abrasive wear resistance was investigated using microscale ball cratering test; results were correlated with the superficial compressive stress and compared with a specimen of pure unstressed Al2O3 prepared both by lamination and by cold isostatic pressing. Experiments show an improvement of performances in the samples containing compressive residual stress in the surface.
Authors: Giuseppe Pezzotti, Andrea Leto, Kiyotaka Yamada, Alessandro Alan Porporati
Abstract: Electro-stimulated piezo-spectroscopy (PS) can be quantitatively used for obtaining information about applied and residual stress fields piled up in ceramic materials and devices. PS experiments can be conducted in a field-emission-gun scanning electron microscope (FEG-SEM) equipped with a high spectral resolution cathodoluminescence (CL) spectrometer. Micromechanical information can be thus added to the microscopic crystallographic and chemical information already available in conventional SEM devices. Independent of the physical mechanisms behind CL emission, the spectral position of selected bands in ceramics is shown to possess high stress sensitivity. In addition, given the high scanning flexibility and spatial resolution of the electron beam, residual stress assessments can be performed on relatively large areas with significantly improved spatial resolution as compared with the more popular photo-stimulated PS approach (i.e., using a laser beam as the excitation source). In this paper, we first quantitatively characterize the stress dependence of the spectroscopic bands observed in ruby. Then, based on this knowledge, an application is shown of bi-dimensional residual stress mapping around an indentation print.
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