Zr Specimens Research Articles

Effect of Powder Spreading Parameters on Laser Absorption Behavior and Processability of High‐Strength Aluminum Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) of rare‐earth‐modified high‐strength aluminum alloys presents a novel approach for manufacturing complex components with enhanced structural performance, particularly in aerospace applications. This study fabricates Al–Mg–Sc–Zr specimens using various powder spreading parameters to explore their impact on laser processability. The investigation reveals that varying the powder layer thickness from 30 to 70 μm yields the smallest irradiation diameter of 135 μm at an optimal thickness of 50 μm, attributable to effective multiple reflections, high laser absorption rates, and stability. With an optimal laser power of 400 W, a scanning speed of 600 mm s−1, and a hatching spacing of 60 μm, the sample produced at 50 μm layer thickness achieves a relative density of 99.23%, a top surface roughness of 15.42 μm, and a refined grain size of 1.67 μm. Following aging at 325 °C for 4 h, this sample exhibits a tensile strength of 518 MPa and an elongation of 15.6%. The findings establish a theoretical basis for controlling the morphology and properties of high‐strength aluminum alloys in laser additive manufacturing.

In Vitro Evaluation of Color and Surface Roughness Changes of Polyetheretherketone, Monolithic Zirconia, and Resin Nanoceramics Exposed to Staining Liquids.

This study aims to investigate color stability and surface roughness of polyetheretherketone (PEEK), zirconia, and hybrid ceramics while stored in different liquids. A total of 240 specimens were prepared from monolithic zirconia, PEEK, and hybrid ceramics. All specimens were polished using rubber sets with different grain sizes. Color parameters (L*, a*, b*) were measured three times using a dental spectrophotometer in standard D65 lightning. Each group was divided into eight different groups to be kept in eight different solutions as distilled water, cola, red wine, tea, coffee, heptane, citric acid, and 50% ethanol. Specimens were held in solutions at 37°C for 12 days. Color measurements were repeated, and color change (ΔE) was calculated using the CIE Lab formula. The color difference of PEEK specimens was found above the clinically acceptable limit; however, color differences for monolithic zirconia produced by coffee were found within the clinically acceptable limits. ZR and HC specimens' color change values were found between threshold values (1<ΔE < 3.3). The differences observed in surface roughness levels amongst the ZR specimens could be caused by the polishing instrument and procedure. The color change of the materials was within acceptable limits, whereas the surface roughness increased more than 0.2 µm. Especially cola, heptane, and red wine significantly increased the mean surface roughness.

Characterization of micro-burnup treat irradiated U-22.5 at.% Zr and U-52.8 at.% Zr foils by transmission electron microscopy and X-ray diffraction

The uranium-zirconium (U-Zr) fuel system has been studied for decades, yet there remains a data gap of micro-burnup (BU) studies where the microstructure undergoes an initial transformation from as-fabricated to the true starting microstructure present in reactor. This study focusses on two U-Zr specimens, U-(22.5 and 52.8) at.% Zr, irradiated to <0.001 at.% BU (∼4.33E+15 F/cc) at 660 °C in the Transient Reactor Test Facility (TREAT). The samples were rapidly gas quenched (4–5 °C/min) to maintain the in-pile structure for post irradiation characterization and modeling input. The bulk features of the U-22.5 at.% Zr specimen were retained, suggesting an impact (beyond crystallographic texture) of the as-fabricated system. It was also found that Zr solubility in α-U increases to ∼18 at.%Zr at 660 °C, and subsequently influences phase fractions and grain boundary density. The U-52.8 at.% Zr alloy fully transformed into an equiaxed granular microstructure immediately upon reactor insertion, implying single phase γ-U-Zr at 660 °C. This work also identifies the retention of a face-centered-cubic Zr rind on the surface of the sample, suggesting that the mechanism of Zr-rind decomposition is not a trivial phase transformation at temperature, but rather likely a diffusion-based process.

Comparison of Fluorescence of Tooth Enamel, Resin Composite, Lithium Disilicate and Monolithic Zirconia Under Thermocyclic Ageing

The aim was to compare the fluorescence intensity of tooth enamel, resin composite, lithium disilicate, and monolithic zirconia before and after thermocyclic aging. Lithium disilicate (LD) and monolithic Zirconia ceramic samples were fabricated with the CAD-CAM method. Resin composite specimens, of shades A1, A2, and A3, were prepared with photo-polymerization and putty mold. Extracted second molar teeth were obtained and sectioned to produce enamel specimens. Fluorescence assessment prior to thermocycling was performed using flurolog-Qm system before and after thermocycling. Samples were exposed to thermocycling (TC) for 30,000 cycles in distilled water at 5 °C and 55 °C for 30 s each, with 5 s between the baths. The means and standard deviations were compared using, t-test, analysis of variance, and Tukey–Kramer multiple comparisons test. The initial fluorescence intensities before thermocyclic ageing were highest in LD ceramic specimens (42579±817.1). The lowest fluorescence was observed in monolithic Zr specimen 14750±584.7. The reduction in fluorescence intensity after thermocyclic ageing was highest in LD specimens, however, the lowest difference was noted in composite A3 specimens. LD ceramic showed significantly high fluorescence among all materials before and after ageing. The fluorescence of the tested materials reduced with ageing and is expected to decrease intraorally with time.

A comparison study of change in hardness and microstructures of a Zr-added FeCrAl ODS steel irradiated with heavy ions

FeCrAl oxide dispersion strengthened (ODS) steel is regarded as one of the most promising candidate materials for nuclear fission reactors such as supercritical pressurized water reactor (SCPWR), sodium-cooled fast reactor (SFR), and lead bismuth-cooled fast reactor (LFR) and so on, since it has excellent irradiation resistance and good corrosion resistance of super-critical water and Pb–Bi coolants. In the present work, irradiation response of a Zr-added FeCrAl ODS steel (15Cr–4Al-0.1Ti-0.6Zr) together with an Al-free ODS (16Cr-0.1Ti) steel and a non-ODS steel T91 was studied. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructures including grains, dislocations, and oxides in the pristine specimens and irradiation defects in the irradiated specimens. Nano-indentation tests were used to evaluate the change in hardness after irradiation. The oxides in the 15Cr–4Al-0.1Ti-0.6Zr specimen are slightly larger than those in the 16Cr-0.1Ti specimen, but with a similar number density. After irradiated with 9.45 MeV 83Bi35+ to 26 dpa at ambient temperature, hardening was observed in all the specimens. Irradiation hardening of the 15Cr–4Al-0.1Ti-0.6Zr specimen is slightly higher than the 16Cr-0.1Ti specimen but significantly lower than the non-ODS steel T91. The irradiation defects in the ODS steel specimens are apparently smaller than those in T91 with a similar number density. By calculating sink strength of the initial microstructures such as grains, dislocations and oxides, the evolution of irradiation defects was discussed. A linear relationship between the irradiation hardening and the sink strength was established. A similar linear relationship between the calculated irradiation hardening using the TEM data (based on dispersion barrier hardening model (DBH) and Friedel-Kroupa-Hirsch (FKH) model, respectively) and sink strength was also found. The calculated irradiation hardening is relatively lower than the experimental value, indicating the possible contribution of Cr segregation to hardening which needs further study.

Preparation of Cu–Cr–Zr alloy by selective laser melting: Role of scanning parameters on densification, microstructure and mechanical properties

The evolution of the microstructure and mechanical properties of Cu–Cr–Zr manufactured by selective laser melting (SLM) with different scanning parameters was studied. Accordingly, the Cu–Cr–Zr specimens with high relative density (99.5 ± 0.3%) were obtained by optimizing the scanning parameters and they also possessed the highest strength (280 ± 6 MPa) and ductility (23.4 ± 0.4%) compared to other SLM manufactured specimens. The crystallographic texture and the grain microstructure of the specimens for the horizontal and vertical planes all exhibit the same anisotropic trend, which is independent of the volumetric laser energy density and the defects in the specimen. The formation of twins in the specimen is mainly due to the combined effects of large residual stress, low stacking fault energy and intrinsic heat treatment. The Cr–Zr–Cu nano precipitates formed in the specimen can be attributed to the effect of intrinsic heat treatment during the SLM process. These twins and nano precipitates in the microstructure both contribute to the abovementioned excellent mechanical properties of SLM manufactured specimens.

Characterizing dislocation loops in irradiated polycrystalline Zr alloys by X-ray line profile analysis of powder diffraction patterns with satellites.

This work extends the convolutional multiple whole profile (CMWP) line profile analysis (LPA) procedure to determine the total dislocation density and character of irradiation-induced dislocation loops in commercial polycrystalline Zr specimens. Zr alloys are widely used in the nuclear industry as fuel cladding materials in which irradiation-induced point defects evolve into dislocation loops. LPA has long been established as a powerful tool to determine the density and nature of lattice defects in plastically deformed materials. The CMWP LPA procedure is based on the Krivoglaz-Wilkens theory in which the dislocation structure is characterized by the total dislocation density ρ and the dislocation arrangement parameter M. In commercial Zr alloys irradiation-induced dislocation loops broaden the peak profiles, mainly in the tail regions, and occasionally generate small satellites next to the Bragg peaks. In this work, two challenges in powder diffraction patterns of irradiated Zr alloys are solved: (i) determination of the M values from the long tail regions of peaks has been made unequivocal and (ii) satellites have been fitted separately, using physically well established principles, in order to exclude them from the dislocation determination process. Referring to the theory of heterogeneous dislocation distributions, determination of the total dislocation density from the main peaks free of satellites has been justified. The dislocation loop structure has been characterized by the total dislocation density of loops and the M parameter correlated to the dipole character of dislocation loops. The extended CMWP procedure is applied to determine the total dislocation density, the dipole character of dislocation loops, and the fractions of 〈a〉- and 〈c〉-type loops in proton- or neutron-irradiated polycrystalline Zr alloys used in the nuclear energy industry.

Shear Bond Strength of Veneered Zirconia Repaired Using Various Methods and Adhesive Systems: A Comparative Study.

The aim of the present study was to investigate the shear bond strength of five different repair methods and adhesive systems for zirconia (Zr) cores layered with feldspathic porcelain. Seventy-five Zr specimens (10 × 10 × 4 mm3) were prepared, sintered, layered with 2 × 10 × 10 mm3 of feldspathic porcelain, and fired. The ceramic was fractured, and the load recorded using a shear-bond test. Specimens were thermocycled and randomly divided into 5 groups (n = 15/group) based on the repair methods. Composite repair blocks with similar dimensions to the layered ceramic (2 × 10 × 10 mm3) were built according to each repair method. Shear bond strength testing of the specimens with composite built up was carried out using a universal testing machine (Instron®5960, Massachusetts, USA). The shear bond strengths of the adhesive interface between repaired composite and the Zr were recorded for all the test groups. The fractured specimens’ surfaces were examined under a scanning electron microscope (Jeol, Musashino, Akishima, Tokyo, Japan) for evaluation of the type of failure and surface characteristics. Shear bond strength of the veneered ceramic bonded to the Zr for all the test groups was non-significant (ANOVA, p = 0.062). Shear bond strength after the repair revealed significant differences (ANOVA, p = 0.002). Group-C (13.79 ± 1.32) and Group-D (9.77 ± 4.77) showed the highest and lowest shear bond strength values, respectively. Paired Sample T-tests showed significantly lower values (p = 0.000) for the repaired (composite) Zr compared to the layered (ceramic) Zr. Multiple comparisons revealed differences (significant) between the shear bond strength of Group-D with Groups A (p = 0.010) and C (p = 0.003, Post Hoc Tukey test). The repair methods tested showed variations in their respective shear bond strengths. Complete ceramic/zirconia repair systems showed better bonding between the repaired composite and Zr core. The mean shear bond strength for the repaired fractured layered Zr showed acceptable outcomes in terms of clinical perspective, but was, however, unpredictable.

Effect of the addition of zirconium on the electrical, optical, and mechanical properties and microstructure of ITO thin films

Indium Tin Oxide (ITO) thin films are doped with zirconium (Zr) by varying the direct current (DC) power sources to investigate the effects of Zr doping on surface morphology, microstructure, and mechanical, electrical, and optical properties. The ITO:Zr specimens possess more grains with the (400) orientation when the DC power is elevated. Crystallinity and surface roughness are highly dependent on grain size. The product value of crystallinity and grain size is observed to be positively correlated to the surface roughness. Reduced modulus and hardness of specimen are lowered by increasing the DC power, and these two parameters are also positively correlated to the product of crystallinity and grain size. In this study, the choice of 35 W as the power can bring in the highest transmittance (>81%) in the wavelength region of 380–2600 nm and the lowest resistivity of all specimens. Increasing the power to be higher than 35 W will produce more excessive carriers to reduce the carrier concentration and mobility, thus elevating the resistivity. A significant rise in the infrared transmittance (800–2600 nm) compared to the undoped ITO thin film is achieved by doping the Zr into ITO with a DC power of 35 W.

Color Masking Ability of Lithium Disilicate Ceramic for Titanium Alloy Implant Abutments

The aim was to assess the acceptable thickness of monolithic Lithium Disilicate (LD) ceramic in masking of Titanium (Ti) implant abutment by comparison to Zirconium (Zr) crowns through color matching. Forty LD and 10 Zr copings (control) using Hot-pressing and CAD-CAM techniques were fabricated. A standard Ti abutment (Straumann, ITI, Basel, Switzerland) was used as foundation substrate. LD crowns were divided into different thickness [1.0 mm (n = 10), 1.2 mm (n = 10), 1.5 mm (n = 10) and 1.8 mm (n = 10)] and 10 Zr copings (control) had 0.5 mm thickness. Different crown materials and crown thicknesses resulted in 5 study groups designated as Zr-Ti-0.5, LD-Ti1.0, LD-Ti-1.2, LD-Ti-1.5 and LD-Ti-1.8. Specimens were cemented to Ti abutments and using a spectrophotometer the difference of color for specimen and controls was determined by comparing ΔL, Δa and Δb (CIELab color system) and an overall ΔE. These were statistically compared using analysis of variance and Tukey post hoc multiple comparisons. Among LD specimens with Ti abutments, lowest color difference was achieved for LD-Ti-1.8 (2.3 ± 0.31) and the highest color difference was for LD-Ti-1.0 (4.93 ± 0.45). The lowest ΔE was recorded for Zr copings (control), which was lower than (p &lt; 0 01) LD crowns of 1.0 and 1.2 mm thickness. LD crown thickness had a significant effect on ΔE (color difference) on Ti abutments. Masking of Ti abutments by 1.5 mm LD crowns was comparable to Zr specimens (control). Lithium disilicate crown of 1.5 mm thickness showed statistically comparable color stability to 0.5 mm Zr copings on Ti implant abutments.

Relationship between electrical resistivity and Al3(Zr,Sc) core–shell dispersoids of Al–Zr–Sc electrical transmission cable: Modeling and experimental results

Theoretical models for predicting the change of electrical resistivity of Al–Zr–Sc cable with Al3(Zr,Sc) core–shell dispersoids during aging were developed through integrating thin slices of core–shell cell. The theoretical electrical resistivity decreased with increasing volume fraction and size of dispersoids. As the aging time at 350°C increased from 0.2 to 400h, the experimental electrical resistivity of aged Al–Zr specimens decreased from 3.46 to 2.77μWcm, and that of Al–Zr–Sc specimen decreased from 3.65 to 2.93μΩcm. Meanwhile, the theoretical electrical resistivity of aged Al–Zr–Sc specimen ranged from 3.6 to 2.85μΩcm, showing the prediction matched well the experimental results. The difference in the electrical resistivity between Al–Zr and Al–Zr–Sc specimens may be caused by the shell of the Al3(Zr,Sc) dispersoids. The possible scope of electrical resistivity difference value ranged from 0.05 to 0.20μΩcm.

Impact of Cleaning Procedures on Adhesion of Living Cells to Three Abutment Materials.

To test the adhesion properties of live gingival fibroblasts to three different implant abutment materials after five different cleaning procedures. Highly polished discs of lithium disilicate (LS), zirconium dioxide (Zr), and titanium alloy (Ti) were fabricated. The specimens were cleaned by one of five different methods: steam (S), argon plasma (AP), ultrasound and disinfection (UD), ultrasound and sterilization in an autoclave (UA), or photofunctionalization with high-intensity ultraviolet light (PF). Cell detachment force (adhesion) was measured by single-cell force spectroscopy, which is a method to quantify cell adhesion at the single cell level. Data were statistically analyzed using parametric tests (analysis of variance [ANOVA], t tests). Cell detachment forces in the low nN regime were recorded in all experiments. Significant differences in cell adhesion on the different materials were found as a function of the cleaning method (P ≤ .0001). For LS abutments, no significant differences between the cleaning methods could be found (P > .05). For Zr specimens, the AP method showed the highest cell detachment forces, followed by UD, PF, S, and UA (S/UD, S/UA, S/PF, AP/UD, and UD/PF were not significantly different from each other). For Ti abutments, UD showed the highest cell detachment forces, followed by S, AP, and UA/PF (S/UD, S/UA, S/PF, AP/U, and UA/PF were not significantly different from each other). All cleaning methods provided comparable cell detachment forces for LS abutments. AP/PF or ultrasonic cleaning were the most suitable methods for strong cell adhesion on Zr. UD provided the best cell adhesion for Ti.

Effect of atmospheric control during MA-HIP process on mechanical properties of oxide dispersion-strengthened Cu alloy

In this study, mechanical properties of Dispersion Strengthened (DS)-Cu-Al (aluminum) and Zr (zirconium) alloys, which were fabricated by an MA-HIP method, were investigated for application to the heat sink materials of fusion reactors. The effect of air exposure before the HIP process was studied using a NIFS-Sealing Device. Cu–Al specimen with air exposure before HIP was broken during wire-electrical discharge formation. Cu–Al specimen without air exposure exhibited high fracture strength, but without yielding. Cu–Zr specimen, both with and without the exposure, yielded and exhibits elongation. An increase in yield and tensile strength by approximately 61% and 45%, respectively, were obtained for Cu–Zr specimen by avoiding air exposure. The results showed that Cu–Zr specimen is less susceptible to the atmosphere of the MA-HIP process than Cu–Al.

The hot deformation behavior and microstructure evolution of HA/Mg-3Zn-0.8Zr composites for biomedical application

The hot deformation behavior of nano-sized hydroxylapatite (HA) reinforced Mg-3Zn-0.8Zr composites were performed by means of Gleeble-1500D thermal simulation machine in a temperature range of 523–673K and a strain rate range of 0.001–1s−1, and the microstructure evolution during hot compression deformation were also investigated. The results show that the flow stress increases increasing strain rates at a constant temperature, and decreases with increasing deforming temperatures at a constant strain rate. Under the same processing conditions, the flow stresses of the 1HA/Mg-3Zn-0.8Zr specimens are higher than those of the Mg-3Zn-0.8Zr alloy specimens, and the difference is getting closer with increasing deformation temperature. The hot deformation behaviors of Mg-3Zn-0.8Zr and 1HA/Mg-3Zn-0.8Zr can be described by constitutive equation of hyperbolic sine function with the hot deformation activation energy being 124.6kJ/mol and 125.3kJ/mol, respectively. Comparing with Mg-3Zn-0.8Zr alloy, the instability region in the process map of 1HA/Mg-3Zn-0.8Zr expanded to a bigger extent at the same conditions. The optimum process conditions of 1HA/Mg-3Zn-0.8Zr composite is concluded as between the temperature window of 573–623K with a strain rate range of 0.001–0.1s−1. A higher volume fraction and smaller grain size of dynamic recrystallization (DRX) grains was observed in 1HA/Mg-3Zn-0.8Zr specimens after the hot compression deformation compared with Mg-3Zn-0.8Zr alloy, which was ascribed to the presence of the HA particles that play an important role in particle-stimulated nucleation (PSN) mechanism and can effectively hinder the migration of interfaces.

Biological efficacy of two mineral trioxide aggregate (MTA)-based materials in a canine model of pulpotomy.

The aim of this study was to compare the biocompatibility of Endocem Zr® and ProRoot MTA® by histopathologic analysis in a canine model of pulpotomy. This study utilized 39 teeth of two beagle dogs. The exposed pulp tissues were treated by pulpotomy using ProRoot MTA (n=19) or Endocem Zr (n=20). After 8 weeks, the teeth were extracted and processed with hematoxylin-eosin staining for histologic evaluation. Most of the specimens in both groups developed a calcific barrier at the pulp amputation site and formed an odontoblast layer. However, some of the Endocem Zr specimens showed less calcific barrier formation with a greater inflammatory response and less odontoblast layer formation when compared with the ProRoot MTA specimens. ProRoot MTA and Endocem Zr specimens developed a calcific barrier; however, ProRoot MTA was more biocompatible than Endocem Zr.

Study on the Friction and Wear Characteristics of Tungsten Carbide and Zirconium With Phosphor-Containing Liquid

The dispenser ejects the ceramic filler and phosphor-containing liquid for making various products. When the particle-containing liquid is ejected under high-velocity conditions, however, the ejection reliability decreases because of the wear of the contact surface between the rod and nozzle even though these components are made of hard materials. It is therefore necessary to characterize the friction and wear properties of the hard materials, tungsten carbide (WC) and zirconium (Zr), with the high-viscosity liquid-containing nitride or yttrium aluminum garnet (YAG) particles under reciprocating conditions. Particle contents of 15 wt.% and 30 wt.% are added to the liquid. A reciprocating test was implemented to this end, and WC and Zr specimens were used. The liquid used in the experiment contains nitride and YAG. The experimental results show that the particles inside the liquid are worn out, leading to particle lubrication and the decrease in the coefficient of friction. Also, it is confirmed that the more the particles are, the less the coefficient of friction is due to particle lubrication. For each experimental condition, the coefficient of friction is measured and compared. Moreover, the contact surface of the specimen is analyzed using an electron microscope, and a profilometer is used to measure the surface roughness of the specimen before and after the test. The reciprocation friction and wear characteristics of WC and Zr with phosphor-containing liquid are evaluated by analyzing the experimental results.

Pitting Corrosion Behavior of Zirconium in a Simulated Body Fluid Containing Chloride Ions

[Introduction] Zr has similar properties to those of Ti that is widely used as metallic biomaterials. On the other hand, Zr shows much lower magnetic susceptibility than Ti. In addition, Zr does not form calcium phosphate on its surface in body fluid, so that new bone formation is not accelerated unlike Ti. These unique properties of Zr are considered as advantages in magnetic resonance imaging during implantation and removal surgery after healing. Thus, Zr is expected as a new implant material whichcan substitute some medical devices consisting of Ti. For metallic biomaterials, corrosion resistance is always necessary because metal ions may cause toxicity on living body. Nevertheless Zr is known to show excellent corrosion resistance, it also shows localized corrosion sensitivity by chloride ion while Ti does not corrode in the same environment. However, there is extremely limited information about corrosion reaction of Zr in chloride-present conditions. The corrosion behavior of Zr in the chloride solution must be elucidated for the application of Zr to implant devices because chloride ion is major component of body fluid. Thus, in this study, the pitting corrosion reaction has been investigated in a simulated boy fluid. To clarify the initiation point of the pitting corrosion reaction on Zr, the combination of the microscopic observation and micro-area electrochemical measurement were performed. The effect of heat treatments on the pitting potential of Zr was also investigated. [Materials and Methods] Pure Zr (99.2%, Nilaco Corp., Japan) was employed in this study. In addition to the as-received specimen, the heat-treated specimens with the solution treatment and quenching (STQ) and the solution treatment and annealing (STA) were also prepared. The specimen surfaces were mechanically ground with #800 grit SiC abrasive paper. Some of the specimens were additionally polished to expose mirror surface with 0.04 mm SiO2 paste. Surface observations were performed using a laser microscope (OLS4000, Olympus Corp., Japan) and a scanning electron microscope with energy-dispersive X-ray spectrometer (SEM/EDS, S-3400NX, Hitachi High-Technologies Corp., Japan) prior to the electrochemical measurement. Potentiodynamic polarization was performed in physiological saline (0.9mass% NaCl aq.). Ag/AgCl and Pt were used as reference and counter electrodes, respectively. After exposure to the solution, linearly-increasing anodic potential with the scanning rate of 1 mV min-1 was applied. The pitting potential (E pit) was determined from the polarization curve. [Results and Discussion] The E pit and corrosion potential (E corr) of each specimen are shown in Fig. 1. The E pit of the as-received Zr in the saline with standard measurement area (0.35 cm2) condition ranged to be 0.9-1.4 VSCE. The E pit of the Zr was much higher than that of stainless steel used for implant devices (type 316L), however, it was widely scattered. It was almost no difference in the E pit among the as-received and the heat-treated specimens at this experimental condition. When the measurement area was limited to be less than 0.001 cm2, the E pit of the as-received Zr raised and the E pit invariably occurred at very narrow potential range between 2.0 and 2.1 VSCE. From the results of the microscopic analyses, there were a number of small inclusions containing 5 to 20% Fe exposed on the specimen surface. We found that one of these inclusions acted as an initiation site of the pitting at the potential range between 2.0 and 2.1 VSCE. These Zr/Fe inclusions were disappeared after STQ, and the E pit of this Zr specimen was higher than 2.1 VSCE. From these results, we confirmed that the corrosion resistance of Zr is hindered by Fe as an impurity element. On the other hand, when the electrochemical measurement was performed with the macroscopic area (15.2 cm2), the pitting corrosion often occurred at the lowest potential around 0.4 VSCE. This means that the most critical defect must be still hidden and it rarely expose to the Zr surface unless the testing is performed on much larger area than that of general condition. To reveal this rare defect which totally determines the corrosion resistance of Zr, further experiments and more-detailed microscopic analyses are necessary. Figure 1

The effect of repair protocols on shear bond strength to zirconia and veneering porcelain

The aim of this study was to evaluate the shear bond strength (SBS) of a new repairing material including zirconia primer to zirconia and veneering porcelain after various surface treatments. A total of 60 specimens (30 zirconia-Zr and 30 feldspathic porcelain-Feld) were prepared and divided into 6 groups (n = 10). Two surface preparations (air abrasion-AA and Erbium Yag (Er-YAG) Laser-Las) were applied to the specimens. Zr and Feld specimens treated with a grinding bur according to manufacturer advice, were used as control (C). Repair material (Cimara Zircon, VOCO, Germany) was applied to the specimens 2 mm in height. The SBS was measured in a universal testing machine at 1 mm/min crosshead speed. The SBS data (MPa) were analyzed using two-way ANOVA and Tukey HSD multiple comparison tests (α = 0.05). Significant effects of the material type (p = 0.005) and the surface treatment strategy (p = 0.000) were found. Interaction terms were also significant (p = 0.000). While the Zr-C (68,4 MPa) showed the highest SBS (p < 0.05), Zr-Las (16,4 MPa) had the lowest SBS (p < 0.05). The highest SBS value was obtained when both zirconia and veneering porcelain were treated with a grinding bur without any additional surface treatment.

Effects of 3.5 MeV proton irradiation on pure zirconium

The effects of high energy proton irradiation on pure zirconium were investigated in this study. The annealed Zr specimens (50 mm × 3 mm × 0.8 mm) were irradiated by 3.5 MeV hydrogen ions with dose ranges from 1×1013 to 1 × 1015 ions/cm2 at 335 K. The range of the proton beam penetration was measured to be 68-70 μm, depending on the surface, which is in good agreement with the SRIM simulation results. X-ray diffractometer analysis revealed that the peak intensity of the basal plane increased and the position of the peak shifted due to the proton irradiation. Field emission scanning electron microscopy results showed that with increasing irradiation dose hydrogen micro-bubbles formed, concentrated, interconnected, and eventually burst due to the excessive hydrogen pressure inside, causing surface-crack development. Measured yield and ultimate tensile strength seemed to be insignificantly affected by the proton irradiation.

Differences in the calcification of preosteoblast cultured on sputter-deposited titanium, zirconium, and gold.

In this study, osteogenic differentiation and calcification of preosteoblast (MC3T3-E1) cultured on sputter-deposited titanium (Ti), zirconium (Zr), and gold (Au) on cover glasses were evaluated to understand the differences in bone formation ability among these three metals; these metals show the same high corrosion resistance, but Ti and Zr are covered by surface passive oxide film while Au is not covered by the oxide film. Ti and Zr promoted cellular proliferation without osteogenic differentiation. Cells cultured on Ti and Zr expressed higher levels of Runx2, Col1α1, and Akp2 at an earlier stage, which indicated faster promotion of osteogenic differentiation, as compared to those cultured on Au. Moreover, after 21days of culture, the Bglap1 and Ifitm5 expression peaks in cells cultured on Ti and Zr were higher than those in cells cultured on Au, which indicated faster promotion of calcification. Cells cultured on Ti showed an advantage in osteogenic differentiation at an early stage, while cells on Zr showed better calcification promotion with a long-term culture. The amount of extracellular calcified deposits was in good agreement with the gene expression results. On the other hand, the intracellular calcium content of cells on Au specimens was higher than that of cells on Ti and Zr specimens. The results indicate that preosteoblasts on Ti and Zr showed faster osteogenic differentiation and calcification than those on Au, whereas Au improved the intracellular calcium content. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 639-651, 2016.