Thermal Treatment Of Powders Research Articles

Structural and Luminescence Behavior of Nanocrystalline Orthophosphate KMeY(PO4)2: Eu3+ (Me = Ca, Sr) Synthesized by Hydrothermal Method.

KMeY(PO4)2:5% Eu3+ phosphates have been synthesized by a novel hydrothermal method. Spectroscopic, structural, and morphological properties of the obtained samples were investigated by X-ray, TEM, Raman, infrared, absorption, and luminescence studies. The microscopic analysis of the obtained samples showed that the mean diameter of synthesized crystals was about 15 nm. The KCaY(PO4)2 and KSrY(PO4)2 compounds were isostructural and they crystallized in a rhabdophane-type hexagonal structure with the unit-cell parameters a = b ≈ 6.90 Å, c ≈ 6.34 Å, and a = b ≈ 7.00 Å, c ≈ 6.42 Å for the Ca and Sr compound, respectively. Spectroscopic investigations showed intense 5D0 → 7F4 transitions connected with D2 site symmetry of Eu3+ ions. Furthermore, for the sample annealed at 500 °C, europium ions were located in two optical sites, on the surface of grains and in the bulk. Thermal treatment of powders at high temperature provided better grain crystallinity and only one position of dopant in the crystalline structure. The most intense emission was possessed by the KSrY(PO4)2:5% Eu3+ sample calcinated at 500 °C.

Microstructure and properties of in-situ Al–Si/Al2O3 composites prepared by displacement reaction

ABSTRACT In this work, we have studied the displacement reaction of Al and SiO2 powder blends by mechanical alloying (MA) for 20 h and low-temperature sintering. The microstructural evolution of powder and compacted specimens were studied by X-ray diffraction and scanning electron microscopy. The extent of the milling on the displacement reaction was studied by differential thermal analysis (DTA). The results show that the reaction between Al–SiO2 couple does not initiate after milling up to 20 h but occurs after thermal treatment of powders. DTA results indicate a lowering in the reaction temperature of Al–SiO2 couple after milling. Following the DTA results, we densified the Al–SiO2 powder compacts at 700°C to produce an in-situ Al–Si/Al2O3 composite. The physical, mechanical, and tribological performance of the composite at different milling times are also reported here.

Photoluminescence properties of glassy yttrium aluminum borate powders: Dopant-free phosphors for solid-state lighting

Glassy yttrium aluminum borate powders (g-YAB) obtained by the polymeric precursor method show intense photoluminescence (PL) in the visible range under near-ultraviolet (NUV) excitations. The PL properties strongly depend on the thermal treatment of powders as well as the excitation wavelengths. The broad PL of g-YAB powders cover whole visible spectral range between 380nm and 780nm under NUV excitations. The PL internal quantum yield (i-QY) was determined using the integrating sphere method and is found to reach up to 91±5% under 365nm light emitting diode (LED) excitation. Moreover, the associated color coordinates in transmission mode revealed preferably warm-white light with correlated color temperature (CCT) tunable between 2800K and 5300K, ideal for general household and workplace lighting. The use of NUV-LED excitation accompanied with broadband visible emission profile helps in achieving high color-rendering ability with color-rendering index (CRI) higher than 90. Furthermore, these g-YAB phosphors exhibit excellent PL thermal stability (>200°C) and stability with time under device operating conditions. The overall favorable PL properties and low cost synthesis suggest huge potential of g-YAB phosphors as new lanthanide (Ln)-free white light phosphors with very high CRI under NUV-violet LED excitations.

Persistent luminescence in powdered and ceramic polycrystalline Gd3Al2Ga3O12:Ce

This paper studies powders of Gd3Ga3Al2O12:Ce, a promising scintillator composition, as a possible object for express pre-characterization of scintillation kinetics and level of persistent luminescence. Garnet phase powders with uniform microstructure, consisting of 1-2 μm grains, were obtained by co-precipitation approach. It was shown, that both scintillation decay time and presence of persistent luminescence are influenced by both powder thermal treatment temperature and strong Ga deficit.

Synthesis And Characterization Of SnO2 Nanoparticles: Effect Of Hydrolysis Rate On The Optical Properties

Nanocrystalline SnO 2 oxides particles have been successfully synthesized via polyol process using diethylene glycol (DEG) as a solvent, followed by powder thermal treatment. The general ap plicability of the process is shown and the advantages in terms of properties and processability are described. The powders thus prepared were investigated using X - ray diffractometry. (XRD), scanning electron microscopy (SEM), transmission electron microsc opy (TEM), and photoluminescence spectra (PL). The X - ray diffraction patterns of the samples were indexed to the rutile phase for SnO 2 .The TEM images show uniform isotropic morphologies with average sizes close to10 nm. This decrease in particle size is ac companied with a decrease in the band - gap value from 3.55 eV for SnO 2 down to 3.27 eV as shown by UV - visible spectra. It is demonstrated that the crystallite size less than 10 nm can be controlled by changing the quantity of added water (rate hydrolysis h= n H 2 O/n Metal).

Nonlinear ceramics for tunable microwave devices part I: materials properties and processing

Nonlinear dielectrics are promising materials for tunable microwave components. However, dielectric loss, tunability, and temperature dependence of such dielectrics are crucial parameters and have to be optimized for an application as microwave device. In part I of this split publication, the impact of doping and processing on the material performance of Ba0.6Sr0.4TiO3 (BST) ceramics and thick films are presented. A phenomenological model developed by Vendik (Vendik and Zubko 2000) was used to characterize the influence of doping on the material performance of BST as tunable microwave dielectrics. It is shown that acceptor (iron, Fe)—donor (fluoride, F) codoping can positively influence the tunability of BST fundamentally. This impact is interpreted by charged defects influenced by doping and/or related defect formations. In addition to doping, it is shown that thermal treatment of powders and thick films as well as the deposition method show a strong impact on dielectric performance of the final thick-films. In the following part II, metallization, component design, and RF-characterization of tunable microwave devices will be discussed.

Formation of structure and properties during the thermal treatment of powder steels with different carbon-containing components

The effect that thermal treatment has on the formation of the structure of hot-stamped powder carbon steels with different carbon-containing components (CCCs) is determined. Processes of thermal treatment such as quenching, tempering, and annealing are investigated. The inheritance of the initial structure was observed at all steps of thermal treatment.

Effect of powder thermal treatment on the microstructure and electrical properties of doped ceria ceramics

Ce 0.8Sm 0.2O 2 − δ electrolytes were prepared by sol–gel methods with different thermal treatment conditions. It was found that the particle size of the powders thermally treated in N 2 could be controlled less than 10 nm, due to the fact that carbons that enwrapped the precursors could inhibit their crystallization. At the same time, the nano-sized precursors could form larger nuclei at the initial stage of sintering, resulting in the formation of electrolyte with higher density and larger grain size. At the same consent of oxygen vacancies, the enhancement of electrical properties for the electrolyte was correlated to its microstructure obtained by the N 2 thermal treatment.

Modified Pechini synthesis of Na3Ce(PO4)2 and thermochemistry of its phase transition

Effect of the synthesis conditions of Pechini technique on crystallinity and purity of Na3Ce(PO4)2 compound was investigated. Nano-sized cerium-sodium phosphate obtained when EDTA was used as an additional chelating agent for Ln3+. The total enthalpy change of Na3Ce(PO4)2 phase transition was determined as 14.2±0.7 kJ mol−1 for sample synthesized by conventional solid-solid reaction. The phase transition process was confirmed to occur at 1060°C or in temperature range 920–1060°C depending on thermal treatment of powders.

TSEFLAR™ – the centrifugal flash reactor for rapid thermal treatment of powdered materials

The concept of the centrifugal thermal activation (CTA) of powdered materials on a rotating solid heat carrier is developed. A compact centrifugal flash reactor has been manufactured and tested. The tested set-up provided: the heating of gibbsite powder to the temperature of 400–900 K with the rate more than 103 K/s; the duration of the powder thermal treatment less than 1.5 s; the regulation of the treatment duration by changing the speed of the plate rotation and the shape of the rotating heat carrier; the product output up to 40 dm3/h; the removal of the extracted steam containing gases and rapid quenching of the thermally activated solid products. The device tested has been used for the thermal activation of commercial aluminium hydroxide Al(OH)3 (gibbsite). The obtained thermally activated product possesses a high reactivity and can be used for the preparation of various alumina-based compounds.

Nanocrystalline Powders Based on ZrO2 for Biomedical Applications and Power Engineering

An 80 mass% ZrO2 ― 20 mass% Al2O3 powder was produced using a complex method which integrates sol-gel technology and hydrothermal synthesis. The specific surface areas of the powder varied from 39 to 5.3 m2/g depending on the thermal treatment conditions. Metastable F-ZrO2 formed after powder annealing at 400°C. The phase transformation F-ZrO2 → T-ZrO2 (traces of M-ZrO2) occurred under powder thermal treatment from 700 to 1000°C. Only Θ-Al2O3 was detected under experimental conditions. The powder was characterized by sintering activity. Operating the processes under powder thermal treatment in the ZrO2 ― Y2O3 ― CeO2 ― Al2O3 system will allow one to produce a variety of ceramic microstructures from fine-grained to “self-reinforced.” These powders can be used in manufacturing surgical cutting tools as well as in ceramic passive bioimplants and solid electrolytes for fuel elements.

Desorption of gases from the surface of silicon nitride powders

The influence of fabrication and treatment techniques and of carbon coating onto silicon nitride powders on the process of gaseous component desorption has been studied. The N2, H2O, CO2, and CO molecules, as well as OH and NH radicals, were revealed to be absorbed on the particle surface. Different hydrocarbons are the products of reaction in the gas phase and on the surface. Carbon coating on the powder particle surface alloys one to protect the surface from absorbed gases and from chemosorbed compounds, in particular hydroxylic groups. The results obtained permit one to determine the conditions of intended modification of surface and thermal treatment of powders in order to activate their sintering.