Giuseppe Pezzotti

Bio: Giuseppe Pezzotti is an academic researcher from Kyoto Institute of Technology. The author has contributed to research in topics: Raman spectroscopy & Residual stress. The author has an hindex of 44, co-authored 551 publications receiving 8884 citations. Previous affiliations of Giuseppe Pezzotti include Loma Linda University & Tokyo Medical and Dental University.

Mechanical Properties of Dental Zirconia Ceramics Changed with Sandblasting and Heat Treatment

Abstract: Two types of tetragonal zirconia polycrystals (TZP), a ceria-stabilized TZP/Al2O3 nanocomposite (CZA) and a conventional yttria-stabilized TZP (Y-TZP), were sandblasted with 70-microm alumina and 125-microm SiC powders, then partially annealed at 500-1200 degrees C for five minutes Monoclinic ZrO2 content was determined by X-ray diffractometry and Raman spectroscopy Biaxial flexure test was conducted on the specimens before and after the treatments Monoclinic ZrO2 content and biaxial flexure strength increased after sandblasting, but decreased after heat treatment However, in both cases, the strength of CZA was higher than that of Y-TZP Raman spectroscopy showed that a compressive stress field was introduced on the sample surface after sandblasting It was concluded that sandblasting induced tetragonal-to-monoclinic phase transformation and that the volume expansion associated with such a phase transformation gave rise to an increase in compressive stress on the surface of CZA With the occurrence of such a strengthening mechanism in the microstructure, it was concluded that CZA was more susceptible to stress-induced transformation than Y-TZP

Current status of zirconia used in total hip implants.

Abstract: “Zirconia Ceramics or `By Night, All Cats Are Grey.'”1 This was the curious title given four years ago to a French study regarding the controversy over zirconia in total hip replacement. The authors of that study commented: “In the absence of rigorous scientific clarification, information on biomaterials is frequently a source of confusion and misleading generalisations worrying to orthopaedic surgeons.” Indeed, from their inception eighteen years ago, the performance of zirconia ceramic balls (Fig. 1) has been both confusing and controversial. Given the diversity of clinical results, it may well be true that not all zirconia balls were created equal. Thus, the above quotation appears as salient today as it was in 1999. A more recent French study reinforced this opinion: Hamadouche et al. noted that they could find only two studies that demonstrated favorable clinical results with the use of zirconia balls2. The literature published by major ceramic companies has also noted that certain clinical groups found higher rates of osteolysis with the zirconia-ultra-high molecular weight polyethylene couple3,4. How was this possible after an eighteen-year history of use of zirconia implants, with more than 400,000 zirconia implants reportedly sold worldwide5,6? Fig. 1 Retrieved ceramic balls at Loma Linda University Medical Center. From left to right: alumina, black zirconia, and white zirconia. We must assume that the majority of implanted zirconia balls are performing very well today and that only a small percentage of patients have experienced some wear or other problems. However, it is imperative that we determine the mode and reason or reasons for the failures that have occurred. Thus, our collaborative goal was to determine the stability of zirconia balls following one to ten years of use in vivo and whether the reported variations in clinical results are …

Hot Isostatic Press Sintering and Properties of Silicon Nitride without Additives

Abstract: Fully densified silicon nitride without additives was fabricated by means of hot isostatic pressing. The sintering process of highly pure powder was investigated with special interest in the evolution of α–β phase transformation, densification, and microstructure development. It was observed that the transformation occurred without a liquid phase below 1730°C, which corresponds to the melting point of SiO2. Above 1730°C, the densification and β-grain elongation accelerated concurrently because of the appearance of liquid SiO2. However, full densification was attained at 1950°C together with marked grain growth. Flexural strength, microhardness, fracture toughness, and Young's modulus of sintered bodies were measured as a function of temperature. In the sintered body started from highly pure powder, excellent MOR behavior was found up to 1400°C. Impurity content of a few hundred ppm was found to be sufficient to make densification easy and to degrade high-temperature strength.

Effect of Notch‐Root Radius on the Fracture Toughness of a Fine‐Grained Alumina

Abstract: The dependence of K IC on the notch-root radius has been examined for a notch radius as small as a few micrometers in a dense, fine-grained, polycrystalline alumina ceramic. The notch radius can be systematically varied by using a semimanual procedure in a special jig which polishes out rather than cuts the specimen. K IC is independent of the notch sharpness for notch-root radii <10 μm. The results are critically compared with those obtained by other standard techniques and discussed in terms of residual compressive stresses introduced during the notching procedure

Ceramics and Ceramic Coatings in Orthopaedics

Abstract: Advanced bioceramics have played integral roles in treatment modalities for damaged or diseased human joints and osseous defects. This paper reviews the uses and properties of ceramics and ceramic coatings variously employed as articulation devices in hip, knee, shoulder, and other joints, either as self-mated surfaces, or against polyethylene (both conventional and highly cross-linked versions), or for osseous- fixation as arthrodesis devices, bone scaffolds, and substitutes in the spine or extremities. The modern uses of oxide and non-oxide materials in these applications will be discussed, followed by an assessment and comparison of their mechanical and physicochemical properties. Recent developments in new bioceramic materials and composites along with advanced processing and testing methods are presented. Advanced bioceramics and coatings are expected to have increasing use in orthopaedics because of their unique combination and range of properties including strength and toughness, hardness and wear resistance, biocompatibility, bacteriostasis, and osseointegration.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Refractory Diborides of Zirconium and Hafnium

Abstract: This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB2) and hafnium diboride (HfB2) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre-ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine-grained ZrB2 and HfB2 have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B2O3 volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi2 improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB2 and HfB2 ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re-entry, and rocket propulsion.

Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics

Abstract: Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers. (2) Special microstructural features of PDCs. (3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines. (4) Processing strategies to fabricate ceramic components from preceramic polymers. (5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available.