Dy Powders Research Articles

Enhancing Microstructural Characteristics and Mechanical Properties of Ti-Al-Dy Alloy through Ball Milling and SPS Consolidation

In this study, pure Ti, Al, Dy powders were ball-milled with zirconia balls in argon atmosphere for 3 h at 800 rpm, producing a Ti- 6 wt.% Al- 4 wt.% Dy alloy powder. The alloy powder was consolidated by SPS technique at 1373 K for 15 min under 50 MPa pressure in vacuum. The sintered body had approximately 99% in density and 6 μm in grain size. XRD and TEM revealed the presence of the second phases such as Ti3Al, Al3Dy and Ti4Al20Dy phases, and their sizes were approximately 50 nm. Microhardness was approximately 960 Hv at room temperature, which decreased as temperature increased. However, there remained the micro-hardness significantly higher compared to the commercial Ti-6Al-4V alloy. After hardness test at 1173 K, XRD analysis did not show any difference in peaks, while the grain size and second phases size increased by ~4 μm and ~2 nm, respectively.

The influence of Dy3+ ions doping and annealing temperature on structural, morphological, and spectroscopic properties of lanthanum orthovanadate (LaVO4) material

In the current work, we present the results of nanocrystalline lanthanum orthovanadate (LaVO4) doped with dysprosium ions, which was synthesized by a high-energy ball milling (HEBM) process. Lanthanum, vanadium, and dysprosium oxides were employed as starting reagents. These materials were turned into LaVO4:Dy3+ powder with two polymorphic phases after HEBM and subsequent heating that was carried out in the air in the temperature range from 800 °C to 1200 °C. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and DRS (UV–vis) spectroscopy were used to characterize the obtained Dy-doped LaVO4 powders. The excitation and photoluminescence (PL) emission spectra, and time decay (lifetime) curves of the dysprosium (III) ions in LaVO4 material were measured and analyzed. The influence of annealing temperature and the concentration of dysprosium (III) ions (1%, 2%, and 3% at.) on spectroscopic properties was discussed. The qualitative phase analysis of Dy-doped LaVO4 powders indicated the dominant presence of a monoclinic LaVO4 structure. The presence of the tetragonal solid-solution (La, Dy)VO4 phase was also revealed. The structural transformation consists of an increase of Zr type LaVO4:Dy3+ phase, resulting in a higher structure and site symmetry of t-LaVO4:Dy3+. With increasing Dy3+ content, the relative fraction of the tetragonal (La, Dy)VO4 phase was also increased in all samples. Furthermore, XRD investigations showed that Dy3+ ions were incorporated mainly into the t-(La, Dy)VO4 structure. The increase of the amount of tetragonal phase in polymorphic LaVO4:Dy3+ material results in higher emission intensity caused by more efficient energy transfer from VO43− vanadate group to Dy3+ ions. The average sizes of the m-LaVO4 crystallites, estimated using the Rietveld method, were in a narrow range from 53 to 77 nm. Two main intense emission peaks were observed in the blue (466–495 nm) and yellow (557–594 nm) wavelength ranges and can be ascribed to transitions involving 4F9/2 to the stark split sublevels of 6H15/2 and 6H13/2, respectively. The overall intensity of the emission strongly depends on the annealing temperature. The best results were achieved for powder heated at 1200 °C. The values of the calculated average decay lifetime τavg of the LaVO4 powders doped with 1%, 2%, and 3% at. Dy heated at 800 °C, 1000 °C and 1200 °C were very similar, but one can observe that with increasing heating temperature the average decay lifetime of LaVO4:Dy powders slightly decreased regardless of the Dy concentration.

Evaluation of SrAl2 O4 :Eu, Dy phosphor for potential applications in thermoluminescent dosimetry.

PurposeTo evaluate the use of commercial‐grade strontium aluminate phosphorescent powder as a thermoluminescent (TL) dosimeter for clinical radiotherapy beams.Materials and MethodCommercially available Eu2+, Dy3+ co‐doped strontium aluminate powder (SrAl2O4:Eu, Dy) was annealed and then irradiated using 20 × 20 cm2 field size, with 6‐MV (PDD10 = 70.7) and 18‐MV (PDD10 = 79.4) photon beams and and 9‐MeV (R50 = 3.6), 15 MeV (R50 = 5.9) and 18‐MeV (R50 = 7.2) electron beams. To calibrate the relationship between the TL readings and the irradiated doses, TL glow curves were acquired for doses up to 600 cGy at all beam energies. For the percentage depth dose (PDD) measurement, the SrAl2O4:Eu, Dy powder was sandwiched by solid water phantoms, with varying thickness of solid water placed above to determine the depth. PDDs were measured at four representative depths and compared against the commissioning depth dose data for each beam energy.ResultsLinear dose response models of doses up to 200 cGy were created for all beam energies. Superlinearity was observed with doses greater than 200 cGy. The PDD measurement acquired experimentally agrees well with the commissioning data of the medical linear accelerator. Trapping parameters such as order of kinetics, activation energy and frequency factor have been obtained via TL glow curve analysis.ConclusionThe linear dose response demonstrates that SrAl2O4:Eu, Dy is a potential TLD dosimeter for both electron beams and photon beams at different beam energies. The PDD measurements further support its potential use in quality assurance and radiation dosimetry.

Structure and magnetic properties of nanocrystalline dysprosium powders

In this current study, nanocrystalline Dy powders were prepared by melt-spinning and subsequent high-energy ball-milling. The effect of ball-milling time on the structure and magnetic properties of the powders was studied. The crystal structure and microstructure of the melt-spun ribbons and ball-milled powders were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Magnetic measurement of all samples was performed with vibrating sample magnetometer (VSM). XRD results indicate that the average crystal grain size of the powders decreases from 90.09 nm of the ribbons to 10.42 nm of the 4-h ball-milled powders. Further TEM observation shows that the grains are fine and uniform. The Neel temperature (TN) decreases from 182 K of the ribbons to 172 K of the powders, while the Curie temperature (TC) increases from 100 to 130 K, demonstrating that the grain size has substantial influence on the magnetic transition process. Moreover, at 60 K, as the ball-milling time increases, the coercivity of the powders increases first, peaking at 0.48 T for 2-h milling, then drops again, while the remanence of the powders decreases monotonically. As a result, the powders milled for 2 h exhibit an optimal maximum energy product of 64.0 kJ·m−3, demonstrating the good potential of these powders as a permanent magnet at low temperatures.

Coercivity enhancement of Nd–Fe–B sintered magnets with intergranular adding (Pr, Dy, Cu)−Hx powders

Forming Nd2Fe14B/(Nd, Dy)2Fe14B core–shell structure by intergranular adding Dy-containing sources into Nd–Fe–B sintered magnets is effective to improve coercivity and to minimize remanence loss simultaneously. However, the excessive Dy located in the intergranular regions has nearly no hard magnetic contribution, causing its low utilization efficiency. In this work, diluted Dy powders (Pr37Dy30Cu33)–Hx were prepared and incorporated into Nd–Fe–B sintered magnets via a dual-alloy approach. The coercivity increases rapidly from 15.0 to 18.2kOe by 21.3% with 2.0wt% (Pr, Dy, Cu)–Hx addition (the equivalent Dy is only 0.32at%). The deduced coercivity incremental ratio is 10.0kOe per unit Dy at%. Dehydrogenation reaction of (Pr, Dy, Cu)–Hx occurs during sintering, which favors Dy diffusion towards the 2:14:1 phase grains as well as smoothing the grain boundaries (GBs). The enhanced local anisotropic field and the well decoupled 2:14:1 phase grains contribute to such rapid coercivity enhancement. This work suggests that adding diluted Dy hydrides is promising for fabricating high coercivity Nd–Fe–B sintered magnets with less heavy rare-earth consumption.

Structural, Magnetic, and Magnetocaloric Properties of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) Perovskite Manganites

Structural, magnetic, and magnetocaloric properties of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) powder samples, synthesized using the solid-state reaction at high temperature, have been experimentally investigated. X-ray diffraction analysis using the Rietveld refinement show that La0.5Bi0.1Sr0.4MnO3 sample is single phase and crystallizes in the rhombohedral system with \(R\overline{3}c\) space group whereas a mixture of orthorhombic (Pbnm) and rhombohedral (\(R\overline{3}c\)) phases is observed for M=Eu, Gd, and Dy compounds. The Curie temperature, TC, shifts to lower temperature with decreasing the average A-site ionic radius 〈rA〉, which is consistent with large cationic disorder. Arrott plots show that all our samples exhibit a second order magnetic phase transition. From the measured magnetization data of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) samples as a function of magnetic applied field, the associated magnetic entropy change |ΔSM| has been determined. In the vicinity of TC, |ΔSM| reached, in a magnetic applied field of 1 T, maximum values of 0.98 J/kg K, 1.01 J/kg K, 0.81 J/kg K, and 0.77 J/kg K for M=Bi, Eu, Gd, and Dy, respectively.

Effective Red Compensation of Sr2SiO4 : Dy3+ Phosphor by Codoping Mn2+ Ions and Its Energy Transfer

Mn2+ ions codoped Sr2SiO4 : Dy3+ phosphors were prepared by the solid‐state reaction method using NH4Cl as the flux. Their phase compositions, photoluminescence properties, and the energy transfer process were systematically investigated. All Mn/Dy codoped powders were α′‐Sr2SiO4. The codoping concentration range of Mn2+ was ≤4.0 mol% to keep the structure undamaged. The broad red emission of Mn2+ centered at 647 nm in Sr2SiO4 : Mn, Dy powders, which effectively compensated the red emission of Sr2SiO4 : Dy3+ phosphor. The CIE chromaticity coordinates dramatically changed from (0.310, 0.340) to (0.332, 0.326) due to the red enhancement via the energy transfer from Dy3+ to Mn2+. This energy transfer is realized by the exchange interaction. But the luminescence quenching of Sr2SiO4 : Dy, Mn phosphor was mainly caused by the electric multipoles interaction. The concentration optimized (Sr0.96, Mn0.02, Dy0.02)2SiO4 phosphor with high and almost pure white emission has great potential to act as a single‐matrix white phosphor for white LEDs.

Luminescence and x-ray absorption measurements of persistent SrAl2O4:Eu,Dy powders: Evidence for valence state changes

The development of new efficient afterglow phosphors is currently hampered by a limited understanding of the persistent luminescence mechanism. Radioluminescence (RL) and x-ray absorption measurements on the persistent phosphor SrAl${}_{2}$O${}_{4}$:Eu,Dy were combined to reveal possible valence state changes for the rare earth (co)dopants. Traps in the phosphor material are quickly filled when exposing thermally emptied SrAl${}_{2}$O${}_{4}$:Eu,Dy powder to x rays. On the same time scale a partial oxidation of Eu${}^{2+}$ to Eu${}^{3+}$ is observed by x-ray absorption near-edge spectroscopy (XANES), while for the trivalent dysprosium the valence state remains unchanged. The impact of these observations on the recently proposed models for persistent luminescence is discussed.

Positron lifetime studies of CaSO4: Dy thermoluminescence phosphors

AbstractPositron lifetime studies have been carried out on CaSO4:Dy phosphors with and without Teflon binder. The effect of Co‐60 gamma irradiation exposure in these samples has been investigated. Unexposed CaSO4:Dy embedded Teflon discs exhibited four lifetime components viz., 228, 755, 3865 and 77 ps with intensities of 62%, 18%, 14% and 6%, respectively. Since Teflon is used as a binder in these phosphors, the long lived components are understood to arise from this. Upon radiation exposure there is a clear change in these resolved lifetime components. To understand the variation of these lifetime components better, positron lifetime studies was carried out on pure CaSO4:Dy powder (without Teflon) as well as pure Teflon discs exposed to varying radiation doses. The variation of positron lifetime parameters of CaSO4:Dy powder showed systematics, ascribable to SO–4 ion formation due to γ‐ray exposure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation and Characterization of SrAl<sub>2</sub>O<sub>4</sub>: Eu,Dy Powders

A new method for preparing long afterglow phosphor and properties had been studied in the paper. In the new process the activated Al-Sr alloy powder hydrolyzes in pure water. The hydrolysates contain the mixture of Sr(OH)2.8H2O and Al(OH)3 in main, included a little Al(OH)3, AlOOH, SrCO3, and 3SrO.Al2O3. 6H2O. After heat treatment at 700°C for 1 hour, the mixture of SrO and α-Al2O3, γ-Al2O3 were formed. As a precursor, the hydrolysates after heat treatment had been used to prepare long after phosphor Eu, Dy co-doped SrAl2O4. The crystal structure of hydrolysates and Eu, Dy co-doped SrAl2O4 was analyzed by XRD. The luminescent properties of long afterglow material were studied. The Results showed the emission spectra of Eu and Dy co-doped SrAl2O4 lied near 520nm, resulted from the character transition of 4f5d-4f of Eu2+ ion. The method can improve afterglow properties dramatically. The initial luminescent intensity of long afterglow material reached 18cd/m2, and the duration time lasted 46 h.

Combustion synthesis of three-dimensional reticular-structured luminescence SrAl 2O 4:Eu,Dy nanocrystals

Three-dimensional reticular-structured luminescence SrAl 2O 4:Eu,Dy powders were prepared by refluxing- and sonication-combustion synthesis without using any surfactant for the first time and were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy. All the samples have a very porous, open and spongelike morphology with fractal properties. The excitation and emission spectra of the products have been measured by Edinburgh FLS920 at room temperature. The new formation-mechanism of the three-dimensional reticular-structure was proposed in this article.

A Portable TLD System for Environmental Monitoring of Hungary's Paks Nuclear Power Plant

The microprocessor-controlled, portable, rechargeable battery operated TLD system Pille 94E developed in the Atomic Energy Research Institute (AERI) is being utilised for environmental monitoring of the Paks Nuclear Power Plant (NPP). The CaSO 4 :Dy bulb dosemeters of the system are sited at 25 points within a radius of 30 km of the NPP. At these same locations, CaSO 4 :Dy powder dosemeters for laboratory reading are also sited and at eight locations the dose is also measured with a GM counter telemetric system. The reproducibility and time dependence of the doses measured with the portable system are given and compared with those measured by the other two systems. The results, in most cases, were in good agreement. Based on this experience both for the routine monitoring and for a possible accident assessment, it is considered that the portable system should be used instead of the classical TLD method.

Behaviour of CaSO 4:Dy embedded teflon discs at high annealing temperatures

The behaviour of CaSO 4:Dy embedded Teflon (PTFE) thermostimulated luminescent dosimeters (TLDs) at high annealing temperatures (500–800°C) has been studied for the first time. The study reveals the complete evaporation of Teflon at annealing temperatures above 500°C. The residual powder weighed only half that of the CaSO 4:Dy powder contained originally in the disc. X-ray diffraction study indicates that this is due to the conversion of CaSO 4 to CaF 2 and DyF 3 during the breakdown of Teflon polymer. As a result, the weight and TL sensitivity of the residual powder, say after a 700°C, 1 h annealing treatment, were only 50 and 29% respectively of that of the virgin CaSO 4:Dy phosphor powder of similar grain size.

Low Dose Measurements with CaSO<sub>4</sub>:Dy, CaSO<sub>4</sub>:Tm and CaSO<sub>4</sub>:Dy Teflon Dosemeters - A Comparative Study

A comparative study of the low dose measurement capabilities of CaSO4:Dy, CaSO4:Tm in powder form and CaSO4:Dy embedded Teflon discs was carried out. The detection threshold of CaSO4:Dy powder is lower than that of Teflon discs because there is less spurious TL from powder and most of it is removable with nitrogen flow. Preliminary studies indicate that the spurious TL from CaSO4:Dy Teflon discs is higher and not entirely removable with nitrogen flow, which results in the overestimation of radiation doses at low dose levels. Higher sensitivity and other desirable dosimetric properties of CaSO4:Tm made in Hungary, such as reduced intensity of the fast fading low temperature TL peak near 100 oC and reduced spurious TL, are confirmed. The ratio of TL sensitivities of CaSO4:Tm (Hungary), CaSO4:Dy (Hungary) and CaSO4:Dy (India) is 1.5:1.26:1.0.

ＡｇおよびＤｙ混合粉末のメカニカルアロイング挙動

Ag30Dy70 alloy was mechanically alloyed from pure crystalline Ag and Dy powders by high energy ball milling (Fritsch Pulverisette 7) with the speed settings 7 or 3 in an argon atmosphere. The alloying process was investigated by X-ray diffraction, optical microscopy and differential scanning calorimetry.In the first milling stages, the Ag and Dy powders have a well-aligned layered microstructure. This microstructure is typical for mechanical alloyed specimens during the early stages of milling and gets finer with increasing milling time. At this stage intermetallic compound AgDy has obtained. After 200 h of milling, the X-ray diffraction peaks of AgDy and Dy powders have hardly changed in intensity and the broad peak characteristic of an amorphous Ag30Dy70 powder was not produced by mechanical alloying from crystalline elemental powders.

Measurement of beta radiation using graphite-mixed thermoluminescent CaSO4:Dy

Abstract New thermoluminescent detectors (TLDs) were prepared from mixtures of CaSO4:Dy powder with graphite. The concentration of graphite varied from 0.5 to 20% by weight. The response of these mixed detectors to gamma radiation and to some beta radiation was studied, using 147Pm, 204T1, and 90(Sr/Y) as radiation sources. It was found that the relative beta response of graphite-containing detectors increases, relative to the 60Co response, with increasing graphite content. Results obtained are discussed and analysed from the points of view of beta radiation detection and dosimetry. Some remarks on the problem gamma-X-beta mixed field dosimetry are also given.

Studies on the effect of grain size on the response of a CaSO4:Dy Teflon disc dosemeter for monoenergetic electrons and beta rays

CaSO4:Dy Teflon discs are fabricated and used in the author's laboratory for routine personal monitoring and research. CaSO4:Dy powder and Teflon are mixed in the ratio 1:3 by weight. The discs are 13.5 mm in diameter and 0.8 mm thick. The response of this radiation detector is studied using cavity theory. CaSO4 is considered to be the cavity and Teflon the medium. The relationship between the absorbed dose in the cavity to that in the medium is calculated using Burlin's (1966) expression and Almond's (1970) modified expression.

Preparation and dosimetric properties of a highly sensitive CaSO4:Dy thermoluminescent dosimeter.

A description of a preparation method for CaSO4:Dy is presented. We undertook to improve the dosimetric properties of CaSO4:Dy powder by varying the dopant concentration, the temperature of dysprosium incorporation, the thermal treatment and the source of reagents. Results characterizing a phosphor prepared with CaSO4 X 2H2O from Baker doped with 0.1 mol% of dysprosium yielded a highly sensitive and very stable TL dosimeter having a fading of about 4%/yr and a TL response which fit to a straight line on the logarithmic scale within the range from 3 mu Gy to 10(2) Gy.

Estimation of TL Response of Phosphors to Beta Rays by Measuring Energy Spectrum of Absorbed Beta Particles

Abstract The beta energy absorbed in the thermoluminescent (TL) phosphor was determined directly from the difference in the pulse height spectrum between incident and transmitted beta particles to and from the phosphor, in order to examine the sensitivity of commercially available powdered phosphors, LiF (TLD-100) and CaF2:Dy (TLD-200), to beta particles. A beta ray spectrometer equipped with plastic scintillator and GM tube was used, instead of an extrapolation chamber. The TL sensitivity of LiF powder to the beta particles emitted from sources of 45Ca, 204Tl, 90Sr/90Y, and 32P was found to be 0.18-0.22 Gy.µJ-1 per 5 mg of phosphor expressed in equivalent air kerma of 60Co gamma rays. The sensivity of CaF2:Dy powder to beta rays was approximately 8 times that of LiF. It is suggested that a beta dosemeter capable of estimating the beta energy or a two-element or multi-element dosemeter is necessary for measurement of beta dose in a deep skin.

Estimation of TL Response of Phosphors to Beta Rays by Measuring Energy Spectrum of Absorbed Beta Particles

The beta energy absorbed in the thermoluminescent (TL) phosphor was determined directly from the difference in the pulse height spectrum between incident and transmitted beta particles to and from the phosphor, in order to examine the sensitivity of commercially available powdered phosphors, LiF (TLD-100) and CaF2:Dy (TLD-200), to beta particles. A beta ray spectrometer equipped with plastic scintillator and GM tube was used, instead of an extrapolation chamber. The TL sensitivity of LiF powder to the beta particles emitted from sources of 45Ca, 204Tl, 90Sr/90Y, and 32P was found to be 0.18-0.22 Gy.µJ-1 per 5 mg of phosphor expressed in equivalent air kerma of 60Co gamma rays. The sensivity of CaF2:Dy powder to beta rays was approximately 8 times that of LiF. It is suggested that a beta dosemeter capable of estimating the beta energy or a two-element or multi-element dosemeter is necessary for measurement of beta dose in a deep skin.