Zirconium (Zr) is an important industrial metal that is widely used in nuclear engineering, chemical engineering, and space and aeronautic engineering because of its unique properties. The ...high-pressure behaviors of Zr have been widely investigated in the past several decades. However, the controversies still remain in terms of the phase transition (PT) pressures and the isostructural PT in β-Zr: why the PT pressure in Zr is so scattered, and whether the β to β’ PT exists. In the present study, to address these two issues, the Zr sample with ultra-high purity (>99.99%) was quasi-hydrostatically compressed up to ~70 GPa. We discovered that both the purity and the stress state of the sample (the grade of hydrostaticity/nonhydrosaticity) affect the PT pressure of Zr, while the stress state is the dominant factor, the nonhydrostaticity significantly promotes the PT of Zr. We also propose two reasons why the β-β’ isostructural PT was absent in the subsequent and present experiments, which call for further investigation of Zr under quasi-compression up to 200 GPa or even higher pressures.
The zirconium silicotungstate (ZrSiW) was studied as an effective sorbent material to be used in the .sup.113Sn/.sup.113mIn generator. The results elucidated that the distribution coefficient of ....sup.113Sn (3700 mL/g) is greater than .sup.113mIn (275 mL/g) from 0.1 M HCl acid solution to the ZrSiW material. The maximum sorption capacity of Sn (IV) was found to be 33 mg per gram ZrSiW (~ 0.3 mmol/g). The elution yield of .sup.113mIn was found to be > 78 ± 6.4% with an acceptable purity of radionuclidic and radiochemical (greater than or equal to 99.99 and 96.8%, respectively). The rigorous separation of .sup.113mIn from the .sup.125Sb was carried out due to its long half-life (2.758 years) and beta emission that causes tissue damage. Zr, W and Si levels are below the permitted limit in the .sup.113mIn eluate.
Crystals of the KTi1–xZrxOPO4 concentration series with a zirconium content y (in atomic fractions) in the melt ranging from 0 to 0.13 have been grown by the flux method. The Zr impurity distribution ...coefficient in potassium titanyl phosphate crystals at y ≤ 0.07 has been determined by two methods to be 1.64 ± 0.11. Saturation is found to occur at y > 0.07; the zirconium concentration in the samples is about x = 0.12 atomic fractions.
In this study, mechanical properties of bioactive glass (BAG) synthetic bone graft substitute was improved by containing ZrO2 (ZrO2‐BAG), while maintaining advantageous biological properties of BAG ...such as osteoinductive and osteoconductive properties. The ZrO2‐BAG was produced by adding ZrO2 in the following proportions to replace Na2O in 45S5 BAG: 1% (Zr1‐BAG), 3% (Zr3‐BAG), 6% (Zr6‐BAG), and 12% (Zr12‐BAG). Properties including XRD, XPS, SEM, DSC, fracture toughness, and Vickers microhardness were evaluated. To assess the biological properties, Ca/P apatite formation, ion release, degradation rate, cell proliferation, ALP activity (ALP), and alizarin red S staining assay (ARS) were evaluated. Also, expression of osteogenic differentiation markers, Osteopontin (OPN), confirmed by immunofluorescence staining. Finally, an in vivo test was carried out to by implanting ZrO2‐BAG into the subcutaneous tissue of rats. The results of each test were statistically analyzed with one‐way ANOVA followed by Tukey's post hoc statistical test. Amorphous ZrO2‐BAG was successfully produced with increased mechanical properties as the ZrO2 content was increased. Additionally, ZrO2‐BAG exhibited a slower ion release and degradation rate compare to BAG without ZrO2. Bioactivity of ZrO2‐BAG was confirmed with apatite layer formed on the surface, significantly higher proliferation rate and significantly enhanced ALP and the degree of ARS of the cells compare to respective controls. The tissue reactions observed in the in vivo study showed neo‐formed vessels after implantation of ZrO2‐BAG.
•Oxidation of Cr-coated Zr alloys is studied under steam up to 1500 °C.•Oxidation kinetics vary depending on the actual protectiveness of the Cr coating.•Different underlying diffusion mechanisms are ...highlighted.•Cr volatilization appears to be negligible.•Effect of Zr-Cr eutectic beyond 1300 °C is studied.
The oxidation of chromium-coated zirconium-based alloys is studied under steam at temperatures ranging from 800 °C up to 1500 °C and for oxidation times ranging from a few minutes up to a few hours. For oxidation temperatures up to 1300 °C, the overall oxidation kinetics is nearly parabolic at the beginning of oxidation, when the Cr outer layer is protective. Finally, it significantly accelerates and hydrogen is absorbed during a short period. These steps correspond to different oxidation and diffusion mechanisms, involving: growth of outer chromia scale; Zr-Cr interdiffusion, inducing Zr(Cr,Fe)2 intermetallic layer thickening then disappearance due to transformation into metallic chromium and zirconia; transport of oxygen through residual chromium (in particular along grain boundaries) and into the zirconium substrate, and finally growth of a sub-coating zirconia. The additional effect of the Zr-Cr eutectic reaction occurring when the oxidation temperature is increased beyond 1300 °C is also studied and briefly discussed.
The transition mechanism is of significance to the corrosion behavior of zirconium alloys. Two important phenomena may be the causes of transition, which are the undulated wavy interface and the ...existence of tetragonal zirconia at the metal/oxide interface. There is little detailed study on the correlation between these two features. Micro-scale Raman imaging of intensity and Raman shifts was conducted in this study to further evaluate the connection. It was studied based on the oxide films formed on Zr-0.5Sn-0.15Nb-0.5Fe-0.2 V and N36 claddings corroded in 500 °C/10.3 MPa steam. The stress in interfacial tetragonal zirconia has relationship with the amplitude to wavelength ratio of the undulated part and it is always found to be larger at the convex parts of interface. These parts are prone to crack formation. At one convex position that the oxide cracked, t-ZrO2 is found to be preserved beneath and above the crack. Stress is also preserved, but partially released. When interfacial t-ZrO2 exists, the stress in the surrounding monoclinic phase is observed to be small. This provides us a more detailed figure of the stress distribution in oxide film. Tetragonal phase is mainly distributed near the metal/oxide interface. More intense tetragonal signals are frequently found at the convex positions of interface. This might result from large tetragonal grains or aggregation of small t-ZrO2 grains. These grains are stabilized at convex parts because of the large compressive stress and might be unstable once the grain size exceeds a critical value or once cracks are formed at such positions. An illustration of the connection between t-ZrO2 and undulated interface is then proposed. Possible reasons that facilitate the formation of lateral cracks and possible reasons for the existence of t-ZrO2 at the convex positions are discussed.
•T-ZrO2 phase is mainly distributed in the oxide near metal/oxide interface.•Convex position of interface is the favorite place for the existence of intense tetragonal signals.•Larger lattice distortion always exists in the interfacial t-ZrO2 at the convex part.•Interfacial t-ZrO2 is preserved and its stress is partly released after formation of lateral crack.•Destabilization of large tetragonal grains and formation of cracks have cause-and-effect relationship.
Transition of zirconium alloys during uniform corrosion is not expected but inevitable, since it accelerates the degradation of corrosion property. Up to now, proposed transition mechanisms have not ...clearly illustrated the critical behavior of interfacial t-ZrO2 and other oxide features under the critical transition condition. Therefore, study on the under-transition sample was carried out. Microscopically, the monoclinic stress increases after transition, strongly supporting the occurrence of transformation from t-ZrO2 to m-ZrO2. A sudden stress decrease in t-ZrO2 occurs in pre-transition region of the under-transition sample. This decrease might be attributed to formation of permeable paths which induce consumption of interfacial oxygen vacancies. This critical behavior possibly destabilizes the grown t-ZrO2 grains. And the post-transition regions will propagate after t-ZrO2 transformation. The transition region in the oxide consists of lateral cracks propagated transgranularly and large numbers of interconnected pores, both of which may originate from t-ZrO2 transformation. Current works suggest that three critical behaviors of t-ZrO2 induce oxide fracture and corrosion transition. The growth nature and evolution mechanism of t-ZrO2 are further illustrated. Even though t-ZrO2 layer similarly evolve as the ZrO suboxide layer, the unstable nature of t-ZrO2 indicates that it is severely affected by grain size, stress value and chemical composition.
•Single-rod oxidation tests in steam with commercially produced Cr coated Optimized ZIRLO cladding segments were carried out up to very high temperatures of over 1500 °C.•All coatings resulted in ...significantly reduced oxidation rates until failure of the protective coating.•The effects of different coating methods (cold spray and PVD) with different coating thicknesses were investigated.•Pre-damage of the coating by scratches only led to locally increased oxidation.•Quenching with water at 1100 and 1200 °C did not cause the Cr coating to flake off.
Chromium-coated zirconium alloys are one of the promising candidates for accident-tolerant fuel cladding (ATF) tubes for light water reactors (LWRs). In this study, the high temperature oxidation and degradation of two types of Cr coatings (cold spray and physical vapor deposition) with and without pre-damage by scratches were investigated on prototype rod segment samples filled with ZrO2 pellets and tightly sealed with welded end caps. Isothermal tests at 1100 and 1200 °C were terminated by quenching with water; transient tests were performed up to 1500–1600 °C until complete coating failure. The positive effect of both types of Cr coatings was observed in all tests. Pre-damaged specimens showed only locally increased oxidation of the scratched zone, but no negative effects on the adjacent Cr coating. The behavior of the two types of coatings is compared and the degradation mechanisms are discussed based on hydrogen release data, extensive metallographic post-test examinations, and the current state of global research.
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