Topic
Cubic zirconia
About: Cubic zirconia is a research topic. Over the lifetime, 13841 publications have been published within this topic receiving 218313 citations.
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TL;DR: In this article, the content of free ZrO2 in partially stabilized zirconia ceramics by X-ray diffraction techniques was determined by linear calibration curves.
Abstract: Linear calibration curves were developed for determining the content of free ZrO2 in partially stabilized zirconia ceramics by X-ray diffraction techniques. Two methods were studied. The matrix method, in which free ZrO2 was considered to be distributed in a matrix (the cubic phase), gave approximately equal mass absorption coefficients for the monoclinic and cubic phases. The polymorph technique, in which the cubic phase was considered to be a polymorph of ZrO2 and in which integrated intensities were used, gave the better results.
1,302 citations
TL;DR: In this article, it is shown that many of these attractive features of zirconia, especially fracture toughness and strength, are compromised after prolonged exposure to water vapor at intermediate temperatures (∼30°-300°C).
Abstract: Zirconia ceramics have found broad applications in a variety of energy and biomedical applications because of their unusual combination of strength, fracture toughness, ionic conductivity, and low thermal conductivity. These attractive characteristics are largely associated with the stabilization of the tetragonal and cubic phases through alloying with aliovalent ions. The large concentration of vacancies introduced to charge compensate of the aliovalent alloying is responsible for both the exceptionally high ionic conductivity and the unusually low, and temperature independent, thermal conductivity. The high fracture toughness exhibited by many of zirconia ceramics is attributed to the constraint of the tetragonal-to-monoclinic phase transformation and its release during crack propagation. In other zirconia ceramics containing the tetragonal phase, the high fracture toughness is associated with ferroelastic domain switching. However, many of these attractive features of zirconia, especially fracture toughness and strength, are compromised after prolonged exposure to water vapor at intermediate temperatures (∼30°–300°C) in a process referred to as low-temperature degradation (LTD), and initially identified over two decades ago. This is particularly so for zirconia in biomedical applications, such as hip implants and dental restorations. Less well substantiated is the possibility that the same process can also occur in zirconia used in other applications, for instance, zirconia thermal barrier coatings after long exposure at high temperature. Based on experience with the failure of zirconia femoral heads, as well as studies of LTD, it is shown that many of the problems of LTD can be mitigated by the appropriate choice of alloying and/or process control.
1,132 citations
TL;DR: In this article, the influence of controlled porosity on the compression strength of sintered pure alumina and of partly magnesia-stabilized zirconia was investigated.
Abstract: The influence of controlled porosity on the compression strength of sintered pure alumina and of partly magnesia-stabilized zirconia was investigated. Bodies with porosities ranging from approximately 3 to 60% by volume were prepared utilizing hydrogen peroxide to induce pore formation. Cubes of approximately 1.2-cm, unit length were used in testing for compression strength at room temperature. The spatial arrangement of pores in sintered alumina was found to exert an influence, inasmuch as bodies with pores lined parallel to the pressure direction revealed a higher strength than bodies of the same porosity but with pores lined mainly perpendicular to this direction. It was found that an increase of porosity by 10 volume % decreased the strength of both sintered alumina and sintered zirconia by half of their initial respective values.
926 citations
TL;DR: Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics.
Abstract: Summary Objective: The present study is the second part of an investigation of strength, fracture toughness and microstructure of nine all-ceramic materials. In the present study, DC Zirkon, an experimental yttria partially stabilized zirconia, In-Ceram Zirconia slip and In-Ceram Zirconia dry-pressed were compared. Methods: Strength was appraised on ten bar-shaped specimens for each material (20 £ 4 £ 1.2 mm) with the three-point bending method. The fracture toughness (Indentation Strength) was measured on twenty specimens (20 £ 4 £ 2 mm) for each ceramic. The volume fraction of each phase, the dimensions and shapes of the grains and the crack pattern were investigated with SEM. Phase transformation was investigated with X-ray diffraction. Data were compared with an ANOVA and Sheffe ´ post hoc test ðp ¼ 0:05Þ: Results: Means of strength (MPa) and fracture toughness (MPa m 1/2 ) values and their standard deviation were: In-Ceram Zirconia dry-pressed 476 (50) 1 , 4.9 (0.36) 1 ; InCeram Zirconia slip 630 (58) 2 , 4.8 (0.50) 1 ; the experimental yttria partially stabilized zirconia 680 (130) 2 , 5.5 (0.34) 2 ; DC-Zirkon 840 (140) 3 , 7.4 (0.62) 3 . Values with the same superscript number showed no significant statistical difference. Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics. Significance: the zirconia-based dental ceramics are stronger and tougher materials than the conventional glass-ceramics. Better properties can have positive influence on the clinical performance of all-ceramic restorations. Q 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
828 citations
TL;DR: In this paper, a comparison of their catalyst compositions with literature in this area suggests that the increase in activity due to the addition of silica or zirconia may be a result of higher surface acidity.
Abstract: Sol-gel prepared mixtures of silica or zirconia with titania are shown to have significantly higher activities than pure titania for the complete photocatalytic oxidation of ethylene. These higher activities are only apparent when the respective catalysts are stabilized by sintering. The differences become even more pronounced when the catalysts are used in a tubular reactor. Optimum mixture concentrations are found to be 12 wt % zirconia and 16 wt % silica in titania. Both catalyst types exhibit activity maxima with respect to sintering temperature. It is hypothesized that the maxima arise from opposing effects of densification and phase transformation versus beneficial sintering. A comparison of our catalyst compositions with literature in this area suggests that the increase in activity due to the addition of silica or zirconia may be a result of higher surface acidity. However, isoelectric point measurements employing the unsintered and sintered catalysts show no conclusive increase in surface acidity...
647 citations