Percent Zirconium Research Articles

Development of an Affordable GD-OES Support Matrix for Analysis of Non-Conducting Zirconium Powders

<span><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3"> </span> <p><span style="font-family: Times New Roman;" face="Times New Roman"><span style="font-size: medium;" size="3">Glow Discharge Optical Emission Spectroscopy (GD-OES) is an analytical technique mainly used in the analysis of solid metallic samples.</span><span style="font-size: medium;" size="3"> </span><span style="font-size: medium;" size="3">The technique requires a conductive sample as the analyte serves as the cathode when generating the glow discharge plasma. GD-OES is useful for both bulk quantification and depth profiling of thin layers of conducting materials. </span></span><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3">The objective of this study was to develop a new sample support matrix for the preparation of conductive pressed pellets suitable for the analysis of non-conducting materials with GD-OES. In previous work non-conducting powders, such as uranium oxide, have been mixed with fine metal powders such as copper, silver or tantalum. Another solution has been to use a quick setting, conductive thermoplastic, such as diallyl phthalate impregnated with copper, as support. Both of these methods are, however, expensive and fairly time consuming. </span><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3">Graphite, a cheap, readily available conductive powder, proved not to form a strong enough pellet to withstand the conditions required during the GD analysis. This limitation was overcome by the addition of a binding agent, bakelite, to produce a relatively cheap, conductive matrix for the analysis of non-conducting powders. </span><span style="font-family: Times New Roman;" face="Times New Roman"><span style="font-size: medium;" size="3">Spectroscopically pure zirconium oxide was used as a reference material and mixed with various quantities of graphite and bakelite powder. Two distinct regions of linearity were obtained. Samples with less than six percent zirconium yielded a gradient of 0.0011 with an R</span><span style="font-size: small;" size="2">2</span><span style="font-size: medium;" size="3"> value of 0.9949. Samples with higher zirconium content yielded a gradient of 0.0042 with an R</span><span style="font-size: small;" size="2">2</span><span style="font-size: medium;" size="3"> value of 0.9991. These results indicate the suitability of this sample matrix for analysis of zirconium materials by GD-OES.</span></span></p>

The mechanical properties and fracture mechanisms of wrought low carbon arc cast (LCAC), molybdenum–0.5pct titanium–0.1pct zirconium (TZM), and oxide dispersion strengthened (ODS) molybdenum flat products

Molybdenum alloys such as low carbon arc cast (LCAC) unalloyed molybdenum, oxide dispersion strengthened (ODS) molybdenum, and molybdenum–0.5pct titanium–0.1pct zirconium (TZM) molybdenum are of interest for structural applications at high temperatures, but these alloys are poorly characterized with respect to fracture toughness and the ductile to brittle transition temperature (DBTT) in the presence of a notch. Both tensile and fracture toughness testing of these flat rolled molybdenum alloys at temperatures above the DBTT are shown to produce a ductile laminate fracture mechanism, where cracks initiate along grain boundaries in the region of triaxial stresses to leave ligaments of sheet-like grains that are stretched to failure with a high degree of plasticity. The DBTT determined from toughness testing is 50–200 °C higher than determined from tensile testing, which shows the constraining effect of the notch. Use of the J-integral test method provided a more consistent and accurate measure of fracture toughness values at temperatures above the DBTT where large amounts of plasticity are observed. A transition was observed from toughness values between 5.8 and 29.6 MPa√m at temperatures below the DBTT to toughness values between 45 and 175 MPa√m for LCAC, 40–215 MPa√m for TZM, and 53–205 MPa√m for ODS. The variation in fracture toughness values at temperatures > DBTT is shown to correlate with size and number density of the ductile laminate features, where high fracture toughness values result from a fine laminate spacing. Since a finer grain size results in a smaller laminate size, the lower DBTT observed for fine grained ODS molybdenum can be understood in terms of the ductile laminate failure mode.

The fracture toughness and toughening mechanisms of wrought low carbon arc cast, oxide dispersion strengthened, and molybdenum-0.5 pct titanium-0.1 pct zirconium molybdenum plate stock

The high-temperature strength and creep resistance of low carbon arc cast (LCAC) unalloyed molybdenum, oxide dispersion strengthened (ODS) molybdenum, and molybdenum-0.5 pct titanium-0.1 pct zirconium (TZM) molybdenum have attracted interest in these alloys for various high-temperature structural applications. Fracture toughness testing of wrought plate stock over a temperature range of −150 °C to 1000 °C using bend, flexure, and compact tension (CT) specimens has shown that consistent fracture toughness results and transition temperatures are obtained using subsized 0.5T bend and 0.18T disc-CT specimens. Although the fracture toughness values are not strictly valid in accordance with all ASTM requirements, these values are considered to be a reasonable measure of fracture toughness. Ductile-to-brittle transition temperature (DBTT) values were determined in the transverse and longitudinal orientations for LCAC (200 °C and 150 °C, respectively), ODS ( DBTT, the fracture toughness values for LCAC ranged from 45 to 175 MPa√m, TZM ranged from 74 to 215 MPa√m, and the values for ODS ranged from 56 to 149 MPa√m. No temperature dependence was resolved within the data scatter for fracture toughness values between the DBTT and 1000 °C. Thin sheet toughening is shown to be the dominant toughening mechanism, where crack initiation/propagation along grain boundaries leaves ligaments of sheetlike grains that are pulled to failure by plastic necking. Specimen-to-specimen variation in the fraction of the microstructure that splits into thin sheets is proposed to be responsible for the large scatter in toughness values at test temperatures > DBTT. A finer grain size is shown to result in a higher fraction of thin sheet ligament features at the fracture surface. As a result finer grain size materials such as ODS molybdenum have a lower DBTT.

Measuring the fracture toughness of molybdenum-0.5 pct titanium-0.1 pct zirconium and oxide dispersion-strengthened molybdenum alloys using standard and subsized bend specimens

Oxide dispersion-strengthened (ODS) and molybdenum-0.5 pct titanium-0.1 pct zirconium (TZM) molybdenum have excellent creep resistance and strength at high temperatures in inert atmospheres. Fracture toughness and tensile testing was performed at temperatures between − 150 °C and 450 °C to characterize 6.35-mm-thick plate material of ODS and TZM molybdenum. A transition from low fracture-toughness values (5.8 to 29.6 MPa√m) to values >30 MPa√m is observed for TZM molybdenum in the longitudinal orientation at 100 °C and in the transverse orientation at 150 °C. These results are consistent with data reported in literature for molybdenum. A transition to low fracture-toughness values ( −150 °C, while a transition to low fracture-toughness values (12.6 to 25.4 MPa√m) was observed for the transverse orientation at room temperature. The fine spacing of La-oxide precipitates which are present in ODS molybdenum results in a transition temperature that is significantly lower than any molybdenum alloy reported to date, with upper-bound fracture-toughness values that bound the literature data. A comparison of fracture-toughness values obtained using 1T, 0.5T, and 0.25T three-point bend specimens shows that a 0.5T bend specimen could be used as a subsized geometry.

Constitutive relationships for AlZnMg, AlZnMgCr, and AlZnMgZr alloys

The effects of zinc, magnesium, chromium, and zirconium on the steady-state flow stress during hot working of both as-cast and homogenized AlZnMg(Cr/Zr) alloys were determined by means of torsion testing. The equivalent strain rates varied between 0.01/s and 10/s and the temperatures ranged from 450°C to 560°C. The zinc and magnesium concentration varied from 4.5 to 7.5 wt pct and from 0.8 to 1.8 wt pct, respectively. In addition, alloys containing typically 0.15 wt pct zirconium or 0.20 wt pct chromium were investigated. Magnesium, zirconium, and chromium were found to increase the flow stress, whereas zinc had practically no effect. The flow stress in the homogenized material was in most cases higher than in the as-cast material. Fitting of the coefficients in the hyperbolic sine constitutive equation of the experimental results showed that some of the coefficients could be related to concentrations of magnesium and zinc in solid solution, whereas others might be regarded as constants. The following relationship was determined between the coefficients α andn and the magnesium and zinc concentration: α=a·[Mg] b andn=c·[Mg] d +e·[Zn]+f. The coefficientsa, b, c, d, e, andf were determined by fitting of these relationships to the experimental data. The steady-state flow stress calculated by means of the constitutive equations was in good agreement with the experimental steady-state flow stress.

Low-cycle fatigue of niobium and Niobium-1 Pct Zirconium Alloys

Commercially pure niobium (CPNb) and a niobium-1 pct zirconium (Nb-lZr) alloy were tested under low-cycle fatigue conditions at plastic strain amplitudes in the range of 0.02 pct ≤Δepl/2≤ 0.7 pct. At low temperatures, the cyclic deformation response of body-centered cubic (bcc) metals is strongly dependent on strain rate. Thus, it was necessary to test at slow (2 x 10su-4 s-1) and fast (2 x 10-2 s-1) strain rates in order to fully characterize the cyclic deformation at ambient temperature. Only cyclic hardening was observed for both metals under all testing conditions. As expected, higher cyclic stresses were recorded at the fast strain rate compared to the slow strain rate. The Nb-lZr alloy was always stronger than CPNb, although both metals had the same cyclic life at equal plastic strain amplitudes. Further, the strain rate had no effect on the cyclic life. At the fast strain rate, intergranular cracking occurred, and a microplastic plateau was observed in the cyclic stress-strain (CSS) curve for CPNb. At the slow strain rate, no definitely intergranular cracks were detected, and a microplastic plateau was not observed for CPNb. The results of these experiments are interpreted in terms of the influence of strain rate and solute content on the relative mobilities of edge and screw dislocations.

Corrosion Behavior of Zirconium Alloy Nuclear Fuel Cladding

ABSTRACTZircaloy−2 and −4 are used as nuclear fuel cladding. Both alloys are more than ninety-eight percent zirconium and are corrosion resistant to various media. Electrochemical measurements using polarization techniques have been made on these alloys in aqueous media with a pH of 8.5 and varying ionic concentration (1X and 10X) at temperatures of 22°C and 95°C. Results showed that under the test conditions of the study these alloys passivated and had negligible corrosion rates, but there were some variations in passivation due to surface preparation and some crevice corrosion was observed. Data are presented and discussed in terms of passivity, breakdown potential and susceptibility to localized corrosion.

Effect of compositional modifications on the piezoelectric properties of spray dried lead zirconate titanate ceramics

Lead zirconate titanate powders of different compositions varying from 50 to 55 atomic percent zirconium in the solid solution have been prepared by spray-drying technique. The compositions were varied by changing the zirconium-to-titanium ratio in the solid solution and also with the addition of strontium. The amorphous character of the as-prepared powders and the formation of single phase lead zirconate titanate during calcination were also confirmed by x-ray diffraction technique. These powders were then converted to piezoelectric ceramics by compaction and sintering followed by electroding and poling. Effect of the variation of zirconium to titanium ratio and strontium additions on the piezoelectric properties of the finished ceramics have been explained on the basis of improved sintering, uniform grain size, formation of morphotropic phase boundary and subsequent shift to rhombohedral structure.

Structure and properties of rapidly solidified 7075 P/M aluminum alloy modified with nickel and zirconium

Aluminum alloy 7075 was modified by additions of 1.1 wt pct nickel and 0.8 wt pct zirconium, rapidly solidified by ultrasonic gas atomization, canned, cold compacted, hot extruded, and evaluated in terms of structure and properties. Significant improvements in tensile strength (627 MPa YS and 680 MPa UTS) and crack growth rates were realized, along with a decrease in fracture toughness (23.7 MPa√m) while maintaining ductility (10 pct elong.) as compared to nominal I/M 7075 behavior. The stress for 107 cycles fatigue life was greater than 275 MPa, which represents a 73 pct increase over that of I/M 7075. A variety of experiments was performed to evaluate effects on strength, ductility, and on structure. The variables were: powder size distribution, extrusion ratio, extrusion profile, different size fractions from the same lot of powder, and different locations of test bars in the several extrusions. Tensile properties, toughness, and fatigue properties were not importantly influenced by the location of test bars in the cross section or length of rectangular extruded bars. A comparison of mechanical properties from extruded bars prepared from −53 μm powdersvs 53 to 250 μm powders showed a small loss of ductility and fatigue stress for 107 cycles for the fine powder product. Higher extrusion ratios were beneficial for mechanical properties.

Measurement of Melting Point and Radiance Temperature (at Melting Point and at 653 nm) of Hafnium-3 (wt. %) Zirconium by a Pulse Heating Method.

A subsecond duration pulse heating method is used to measure the melting point and radiance temperature (at 653 nm) at the melting point of hafnium containing 3.12 weight percent zirconium. The results yield a value of 2471 K for the melting point on the International Practical Temperature Scale of 1968. The radiance temperature (at 653 nm) of this material at its melting point is 2236 K, and the corresponding normal spectral emittance is 0.39. Estimated inaccuracies are: 10 K in the melting point and in the radiance temperature, and 5 percent in the normal spectral emittance.

Aging induced shape instability in an elastically bent uranium + 7.5 wt pct niobium + 2.5 wt pct zirconium alloy

The uranium +7.5 wt pct niobium +2.5 wt pct zirconium alloy when quenched from 1073 K was found to exist at room temperature as a metastable phase which was a slight tetragonal distortion of the elevated temperature body-centered-cubic (bcc) phase. Flat, asquenched specimens have been elastically deformed in four-point bending to maximum outer fiber stresses below the stress required for plastic deformation to occur but into a range of stress where pseudoelastic behavior has been observed. Aging of these elastically bent specimens in an oil bath at 423 K, while constrained by the bending jig, resulted in a permanent deflection and shape change. Further isothermal aging, after removal from the bending apparatus, caused increasing deflection and continued shape instability in spite of the absence of the applied load. X-ray examination of samples cut from a bent and aged specimen revealed important preferred orientation and lattice parameter differences between the tension and compression regions and the high and low stress parts of the specimen. These observations are described and compared to previous findings on quenched samples of this alloy that had been either deformed separately or aged separately. A rationalization of the shape instability is presented. Elastic twin nucleation and growth, preferred orientations, solute segregation and the interplay of all these seem to be involved.

Simultaneous Measurements of Specific Heat, Electrical Resistivity, and Hemispherical Total Emittance by a Pulse Heating Technique: Hafnium-3 (Wt. %) Zirconium, 1500 to 2400 K.

Simultaneous measurements of specific heat, electrical resistivity and hemispherical total emittance of hafnium containing 3.12 weight percent zirconium in the temperature range 1500 to 2400 K by a subsecond duration, pulse heating technique are described. The measurements indicate decreases in specific heat (by about 13%) and in electrical resistivity (by about 8%) as the result of the α → β transformation. Estimated inaccuracies of the measured properties are: 3 percent for specific heat, 1 percent for electrical resistivity and 5 percent for hemispherical total emittance.

The effect of zirconium on the strength of thorium

The flow stress of thorium-zirconium alloys containing up to 12 at. pct zirconium was studied over a range of temperatures and strain rates. It was found that the flow stress could be analyzed as the sum of a thermally activated and an athermal component. The thermally activated component was nearly the same in the base metal and the zirconium alloys. The major effect of zirconium was a considerable increase in the athermal component. The magnitude of this increase was directly proportional to the zirconium content. Zirconium also retarded the recovery and recrystallization processes.

Investigation of an Alloy Surface with the Field Emission Microscope

The field emission microscope has been used to investigate the surface of an alloy of a few percent zirconium in molybdenum. The field emission patterns indicate that a high-temperature flash (2000°K) reduces the surface concentration of zirconium to zero. Subsequent heat treatment at 1000°K brings Zr to the emitting surface where it adsorbs preferentially in small clusters on the lattice steps of the {100} planes. These clusters are easily observed because of their high electron emission. Their emission characteristics reveal them to be smooth layers of low work function (2.94±0.01 ev) rather than protruding crystallites. When the bulk concentration of zirconium in the alloy is increased from 1% to 5% the emission patterns change markedly but there is little effect on the adsorption characteristics of the surface. Surface migration, desorption, and bulk diffusion of zirconium were found to proceed rapidly at temperatures above 1200°K, 1500°K, and 2000°K, respectively. Measurements of activation energies for surface migration and desorption gave 2.7±0.3 ev and 4.15±0.15 ev, respectively.

Aqueous Corrosion of Uranium Fuel-Element Cores Containing 0 to 20 Weight Percent Zirconium

Abstract A description is given of the design and operation of a windowed autoclave system employed in the study of corrosion by pressurized hot water. The device has been used to obtain time-lapse motion pictures of the swelling and rupture of deliberately defected zirconium-clad uranium specimens. A method is described by which corrosion rates were calculated from pressure and temperature measurements. A typical set of pictures taken during a test is presented, and corrosion rates are reported for uranium-0, 5, 10, 15, and 20 weight percent zirconium alloys subjected to 600 F water. 8.4.5

Neutron Diffraction Study of Titanium-Zirconium System

Titanium and zirconium alloy system consists of a continuous series of random substitutional solid solutions of solvent and solute atoms. Titanium scatters thermal neutrons in the opposite phase from those scattered by zirconium, the scattering amplitudes being: bTi=−0.38×10−12 cm and bZr=0.62×10−12 cm. An alloy containing 62 atomic percent titanium and 38 atomic percent zirconium is developed that gives no coherent scattering reflections in its neutron diffraction pattern, and is extremely useful in constructing devices in which scattering of thermal neutrons is not desired. Based on negative and positive scattering amplitudes of different isotopes of the same element for thermal neutrons, development of isotopic alloys is suggested.