Papers by Keyword: Melt Quenching

Abstract: It is shown experimentally and numerically that quenching (Melt Quenching - MQ) of REM-containing (up to 40 wt.%) Fe-B-Nd melt by inert gas flow (Gas Atomisation Method - GAP) in NH3-containing atmosphere makes it possible to obtain spherical particles with a given fractional and chemical composition and characterised by increased corrosion resistance. The applicability of the obtained particles in the traditional powder technology for the formation of anisotropic and isotropic sintered magnets is established. It is shown that MQ GAP can regulate the functional properties of sintered magnets by mixing different chemical and fractional compositions. It is shown that heat treatment of MQ GAP powders improves their magnetic hysteresis properties and magnetoplasts made from them. The applicability of the obtained MQ GAP REM-containing particles for cladding technologies and additive processes is proved. Hybrid laser & micro-casting surfacing technology for additive processes of processing Fe-Nd-B ternary and MQ GAP alloys into micromagnets - 'Hybrid laser & micro-casting technology for surfacing in additive processes' is proposed. The possibility of realising the described technology for other MQ GAP REM containing alloys with multicomponent low melting eutectic in the intergranular space capable of amorphising at cooling rates of 10³÷10⁵ K/s has been shown.

Abstract: Magnetic force microscopy (MFM) and magnetometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to study the magnetic and structural properties of the (Nd,Pr)-Fe–B and (Nd,Ho)-(Fe,Co)-B alloys. The alloys are synthesized using an arc or induction furnaces. The nanocrystalline state of the (Nd,Ho)-(Fe,Co)-B alloys is reached by two techniques, namely, melt spinning (MS) and severe plastic deformation (SPD). Hydrogenation and multistage treatment of (Nd,Ho)-(Fe,Co)-B alloys, which includes severe plastic deformation of melt-quenched ribbons and subsequent heat treatment, is also used. The surface morphology and domain structure of samples are studied. These pictures are used to interpret the observed magnetic hysteresis loops of the samples. It was found that multistage treatment allows one to obtain samples with higher values of coercivity due to the formation of a special microstructure with oval grain (the aspect ratio equal to ∼ 3).

Abstract: Nd³⁺ doped lithium borotellurite glasses were successfully been prepared by conventional melt-quenching method with the chemical composition (70.0)B₂O₃-(5.0)TeO₂-(25.0-x) Li₂CO₃-xNd₂O₃ (where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 2.0 mol%) by varying the Neodymium content. The physical properties such as density, molar volume and oxygen packing density were measured. The structural properties have been studied through X-ray diffraction (XRD) analysis and Fourier Transform Infrared (FTIR) spectroscopy. The XRD pattern has been used to confirm the amorphous nature of the glass samples. There are no sharp peaks were observed in XRD patterns of the glass samples which confirmed the amorphous nature of the glass. FTIR spectra were used to analyse the functional groups present in the glass samples. The FTIR spectra reveal the presence of B-O-B, B-O, BO_3, BO_4,Te-O and characteristic of the hydrogen bond in the prepared glass samples.

Abstract: Five distinguish glass samples were prepared by melt quenching technique of the composition (81-x)H₃BO₃-19BaCO₃-xDy₂O₃ with x = 0, 0.2, 0.4, 0.6 and 0.8 mol%. The effect of Dy³⁺ to the barium borate glass can be investigated in terms of their physical properties such as density, molar volume and oxygen packing density. The structural properties were analyzed by X-Ray Diffraction (XRD) technique and Fourier Transform Infrared Spectroscopy (FTIR). The result revealed that the increment of mol% of Dy³⁺ in the compound generally will increases the density and molar volume of the glass samples. The amorphous nature of the glass system was verified from the XRD spectra pattern. Meanwhile, the FTIR spectra shown the presence of Ba²⁺, BO₃, BO₄, B-O-B linkage, H-O-H and isolated borate in the glass network.

Abstract: The Dy³⁺-doped glasses of the M₂O₃:CaO:SiO₂:B₂O₃ (M₂O₃ = Y₂O₃ and La₂O₃) materials have been successfully fabricated with the 0.5 % mol of the Dy₂O₃ concentration, and thoroughly investigated based on the physical, optical, photo- and radioluminescence properties. The developed glass materials were prepared from the compositions of 25M₂O₃:10CaO:10SiO₂:(55-x)B₂O₃:0.5Dy₂O₃ by the conventional melt-quenching technique at 1,400°C. The clear sample of the doped La₂O₃ glass demonstrated higher density and the molar volume than those of the doped Y₂O₃ glass. From the spectrophotometry, the absorption peaks of the Dy³⁺ ions were clearly observed in both glasses. The photoluminescence (PL) spectra of the developed glasses indicated two-colors with two strongest peaks at 577 nm (⁴F_9/2®⁶H_13/2) and 482 nm (⁴F_9/2®⁶H_15/2). In addition, the emission spectra from the radioluminescence (RL) were identical to those from the PL measurements. From the results of the PL and RL measurements, the Y₂O₃ glass had higher emission in the intensity than the La₂O₃ glass. The X-ray absorption near edge spectroscopy (XANES) with the synchrotron radiation was carried out in fluorescent-yield mode to determine the average oxidation number of the Dy ions dispersed in the glass matrices. The DyL₃-edge XANES spectra of both developed glasses were nearly identical with the sharp white line at 7795.5 eV and the edge energy of 7793 eV. Compared to the XANES spectrum of the pure Dy₂O₃ standard, both glasses showed the difference smaller than 0.5 eV, and therefore confirmed the oxidation number of the Dy ions of 3+.

Abstract: Borate is one of the most popular oxide glass being used in glass research world wide. Due to good reputation, therefore lead sodium borate glasses with compositions (90 - x) B₂O₃ + 10ZnO + xPbO (where = 15, 20, 25, 30 and 35 mol %) have been prepared by using melt-quenching method. In this work, their physical and structural properties with respect to PbO content has been investigated. The densities of these glass samples were increased from 3946.2 kg/m³ to 5107.2 kg/m³ with an increase in PbO concentration. The molar volume are found to vary from 23.78 × 10^-6 m³mol^-1 to 24.39 × 10^-6 m³mol^-1 with respect to PbO content as well. The density and molar volume show inversed result respectively. The FTIR spectral analysis indicates that with the addition of PbO contents in the glass network, structural units of BO₃ are transformed in BO₄. There are no sharp peaks were observed in XRD patterns of the glass samples which confirmed the amorphous nature of the glass. Meanwhile, the micro hardness of these glass samples were also increased from 189 Pa to 355 Pa with increases on PbO content. The results will be discussed and presented in details.

Abstract: Achieving tuneable photoluminescence via controlled co-doping of rare earth ions in lithium niobate based glasses are challenging. A series of Er³⁺/ Nd³⁺ co-doped tellurite glasses of composition (70-x-y) TeO₂ – 15 Li₂CO₃ – 15 Nb₂O₅ – (x) Er₂O₃ – (y) Nd₂O₃ with x = 0; 1.0 mol % and 0 ≤ y ≤ 1.0 mol % are prepared using melt quenching technique. The influence of co-dopants on the emission properties is analyzed and discussed using partial energy level diagram of rare earth ions. The dopants concentration dependent physical properties such as refractive index, molar volume, density, polarizability and molar refractions are determined. The down-converted luminescence spectra for ²G_9/2 à⁴I_9/2 transition reveal a strong green emission band centred at 497 nm is attributed to the energy transfer from erbium to neodymium ion. The emission spectra exhibit five prominent peaks centred at 497, 539, 553, 616 and 634 nm corresponding to the transitions from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 excited states to the ground state of Er³⁺ ion and the transitions from ²G_9/2, ²G_7/2, ²H_11/2 and ⁴F_9/2 excited states to ground state of Nd³⁺ ion. The highest intensity is achieved for x = y = 1.0 mol%. The excellent luminescence response suggests that our glasses may be nominated for solid state lasers and other photonic applications.

Abstract: Spectral features modification of rare earth (RE) doped tellurite glasses via controlled manipulation of metallic nanoparticles (NPs) is the current challenge in achieving enhanced lasing action. Triggering the localized surface plasmon resonance (SPR) of NPs in the glass generates tremendous applied interests especially in solid state lasers and nanophotonics. Despite several promising features of RE doped zinc-boro-tellurite glass, the low absorption and emission cross-section of RE ions prohibit them from fabricating efficient lasers. This drawback needed to overcome and significant enhancement of spectral features is required. Co-doping by rare earths and/or embedding metallic NPs (acts as sensitizer) are demonstrated to be the alternative route to surmount such shortcomings. Series of glass samples with composition 74TeO₂–15B₂O₃–10ZnO– 1Sm₂O₃ – (x)Ag, where 0 ≤ x ≤ 0.1 mol% (in excess) are prepared using melt quenching method and the impacts of silver (Ag) NPs concentrations in altering their photoluminescence properties are inspected. The XRD spectra confirmed the amorphous nature of prepared glasses and the presence of Ag NPs are evidenced in EDX spectra. TEM micrographs revealed the distribution of Ag NPs with average size 7.2 nm. Absorption spectra revealed eight bands which most intense between ⁶F_11/2 and ⁶F1_/2. Photoluminescence spectra exhibited three prominent peaks corresponding to the transition from the excited state ⁴G_5/2 to ⁶H_5/2, ⁶H_7/2, and ⁶H_9/2 states, respectively. Our observation may be useful for the development of tellurite glass based nanophotonic devices.

Abstract: Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently for improving the casting quality of the conventional HPDC process. In the MQ-HPDC process, an alloy melt with a specified dose and superheat is quenched by directly pouring the alloy melt into a preheated metallic container. The thermal mass and preheating temperature of the container is selected so that the alloy melt is quenched just below the alloy liquidus and heterogeneous nucleation takes place during the melt quenching. The quenched alloy melt is then fed immediately into the shot sleeve for component casting. In this paper we present the MQ-HPDC process and the resultant microstructures and mechanical properties of a MQ-HPDC A356 alloy.

Abstract: Bismuth-titanate ceramics containing SiO₂ and Nd₂O₃ as additives are synthesized by melt quenching method in the system Bi₂O₃-TiO₂-Nd₂O₃-SiO₂ at temperature 1450 oC. By X-ray diffraction analysis are determined the crystal phases participating in the materials: Bi₄Ti₃O₁₂, Bi₁₂TiO₂₀ and δ-Bi₂O₃ . The addition of SiO₂ allows to control the glass formation ability of the supercooled melts. The addition of Nd₂O₃ stimulates the thermal stability of the materials due to formation of solid solutions Bi_4-xNd_xTi₃O₁₂. Measurements of the electrical conductivity, capacitance and dielectric losses of selected samples are performed by DC resistible bridge and digital capacity meter (with frequency of 1 kHz) using two-terminal method and a suitable sample holder with graphite electrodes. It is established that for the investigated samples the activation energy of conductivity is in the range 1 – 1,3 eV, dielectric permittivity from 1000 to 3000 at (at 400 oC) and dielectric losses tgδ are between 0,0002 and 0,1.