Thermal Synthesis Method Research Articles

The Study of a New Ceramic PZT Material Pb<sub>1-0.04</sub>Sm<sub>0.02</sub>Nd<sub>0.02</sub>[(Zr<sub>0.55</sub>,Ti<sub>0.45</sub>)<sub>1-2x</sub>,x(Y<sub>2/3</sub>,Mo</sub>1/3</sub>), x(Y<sub>2/3</sub>,Ni<sub>1/3</sub>)]O<sub>3</sub> with SEM and X-Ray Diffraction

The PZT is modified by the introduction of doping agents in A-sites and/or B-sites of perovskite structure [1]. The principal role of dopants is generally improving the properties of these materials for their adaptation to specific applications, which is the purpose of this study. Our choice fell on the mixed oxide: acceptor and donor. Five compositions with varying dopants percentage were prepared by the conventional method of thermal synthesis of mixed-oxides. Pb1-0.04Sm0.02Nd0.02[(Zr0.55,Ti0.45)1-2x,x(Y2/3,Mo1/3),x(Y2/3,Ni1/3)]O3 such that (x = 0.01, 0.03, 0.05, 0.07 and 0.1), are studied. All the samples were being sintered at a temperature ranging from 1100°C to 1180°C after being compacted in circular discs. The detailed structure was carried out for sintered specimens. The results of X-ray diffraction showed that all the ceramics specimens have a perovskite phase. The phase structure of Pb1-0.04Sm0.02Nd0.02[(Zr0.55,Ti0.45)1-2x, x(Y2/3,Mo1/3),x(Y2/3,Ni1/3)]O3 ceramics was transformed from the tetragonal to the rhombohedral, with an increase in the ratio of Zr/Ti in system. The scanning Electron Microscopy (SEM) showed an increase of the mean grain size when the sintering temperature was increased. The lattice parameter measurements showed that tetragonal and rhombohedral unit cells of the phases depend on the sintering temperature.

Facile thermal explosion synthesis and optical properties of Al-doped flatted 3C-SiC microcrystals with 4H-SiC quantum interlayers

A facile thermal explosion synthesis (TES) method is developed to in situ synthesize batches of high-quality Al-doped flatted 3C-SiC microcrystals. Structural and optical analysis reveals that one dimensional (1D) disordered regions, which structurally resemble wide band-gap 4H-SiC nano-interlays, are acquired and sandwiched in the 3C-SiC microcrystal matrix via Al doping. High-resolution transmission electron microscopy (HRTEM) studies demonstrate that both atomic arrangements with growth predominantly in the 〈111〉 direction and planar structural defects coexist in the Al-doped flatted 3C-SiC microcrystals. A stacking sequence model is adopted to explain the formation mechanism of 4H-SiC nano-interlayers induced via Al doping. The photoluminescence (PL) spectra analysis shows that a new intensive, sharp ultraviolet (UV) emission (3.5eV) was observed for the flatted 3C-SiC microcrystal, except for a blue emission (3.1eV) derived from the surface defects. It is speculated that the quantum confined effect induced by quantum barrier structures is responsible for the new sharp UV emission. This comprises the first report of using a TES method for the synthesis of flatted Al-doped SiC microcrystals. The present method suggests a unique technique for synthesizing quantum barrier structures in SiC microcrystal matrix, which could be extended to other doping elements, and gives a new insight to understand the PL behavior of SiC materials.

NaYF4:Pr3+nanocrystals displaying photon cascade emission

The quantum-cutting process is observed in nanocrystalline fluoride (NaYF(4)) doped with Pr(3+). The thermal decomposition synthesis method was used to synthesize the NaYF(4) nanocrystals with an average size of 42 nm. The morphological high resolution transmission electron microscopy (HRTEM), structural X-ray diffraction (XRD) and spectroscopy, with the use of synchrotron radiation, have been employed to characterize the material. The different excitation energies created different luminescence response of the NaYF(4):Pr(3+) nanocrystals. The quantum-cutting phenomenon has been observed under the direct excitation of the 4f5d bands of praseodymium. After excitation of the NaYF(4) matrix this process is quenched and part of the energy is released through the self-trapped excitons emission. The origin of the different types of emission transitions has been analyzed in detail.

Contribution to the study of the coexistence of phases tetragonal-rhombohedral in ceramic type PZT and general form: Pb [ZrxTi0,95-x(Mo1/3In2/3)0.05]O3

Pb[ZrxTi0,95-x(Mo1/3In2/3)0.05]O3 piezoelectric ceramics with varying Zr/Ti ratio were prepared by the conventional method of thermal synthesis of mixed-oxides.the samples structures was determined by X-ray diffractometry to demonstrate the co-existence of the tetragonal and rhombohedral phases. In the present system the MPB, in which the tetragonal and rhombohedral phases coexist, is in a composition range of 0.47≤x≤0.50. The lattice constants of the a and c axes for the samples caculeted from the XRD patterns. Microstructure of the sintered ceramics was observed by scanning electron microscopy (SEM) using free surfaces of the specimens.

Structural evaluation of Al–4Mn–5Al2O3 (wt-%) nanocomposite produced by mechanical–thermal synthesis and powder technology methods

Production of Al–5Al2O3–4Mn (wt-%) nanocomposite via ball milling and subsequent heat treating of the milled samples was investigated. Duration of milling time was considered as a variable by which microstructure of the matrix is influenced. The structural evaluation of samples was performed by means of X-ray diffraction, differential thermal analysis, scanning electron microscopy and hardness measurement. The steady state time was found to be 3–7 h, prolonged milling time that had no effect on melting point, hardness, morphology and integral breadth of X-ray reflections of milled powders. A maximum hardness of 275 HV was obtained due to the nanocrystalline structure of Al matrix and a uniform dispersion of nano- and submicron second phase particles.

SYNTHESIS OF ANISOTROPIC LEAD TITANATE POWDERS FOR TEMPLATED GRAIN GROWTH OF TEXTURED PIEZOELECTRIC CERAMICS

Needle-shaped PbTiO3 (PT) template particles were successfully synthesized using two different types of approaches, molten salt synthesis (MSS) and thermal synthesis method. In eutectic NaCl–KCl molten salt system, homogeneous and nonagglomerated needle-shaped PT particles were produced from PbO and needle-like TiO2 compound heated at 800–850°C for 2 h. The effect of heating temperature on the morphology of formed powders was studied in order to identify the optimum processing parameters. The template formation mechanism is discussed. Using thermal synthesis method, comparable needle-shaped PT crystalline particles were also obtained in one step. Plate-shaped PT powders were derived via flux synthesis. The effect of additives such as MnCl2 and LiF on the morphology of derived PT was studied. Adding a certain amount of MnCl2 led to the formation of well-defined plate-shaped PT particles. The structure and morphology of synthesized powders were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM).

Mechanical synthesis of nanostructured titanium–nickel alloys

The methods of mechanically assisted synthesis and mechanical alloying are used to obtain nanostructured TiNi shape-memory alloys. A stoichiometric mixture of Ti and Ni powders was subjected to intense mechanical treatment in a planetary ball mill. It was shown that after 30 h milling, the synthesis of the product with a mean particle size of 20–30 nm proceeded at 550 °C. XRD data show mainly the presence of TiNi, Ti 2Ni and TiNi 3 phases. Prolongation of the milling process up to 40 h leads to direct synthesis of a product with a similar phase composition. SEM and TEM analyses are used to study morphological changes of reagent and product particles in the course of mechanical treatment and after the synthesis of products. The mechanochemical synthesis routes are compared with the traditional method of thermal synthesis. The advantages of the mechanochemical methods of synthesis of nanostructured products and obtaining Ti–Ni powders with a high sinterability are also discussed. It was shown that after cold pressing and sintering at 800 °C, compacts containing even distributed pores with a mean size of 1 μm were obtained. TiNi bodies with similar structural peculiarities are suitable for the purposes of implantology.

A novel thermal electrochemical synthesis method for production of stable colloids of “naked” metal (Ag) nanocrystals

This paper describes a novel thermal electrochemical synthesis (TECS) method for producing aqueous solutions (or sols) that contain metal silver nanocrystals as small as a few nanometers. The TECS method requires mild conditions (25 to 100 °C), low voltage (1 to 50 V DC) on silver electrodes, and water or simple aqueous solutions as the reaction medium. Furthermore, a tubular dialysis membrane that surrounds the electrodes provides favorable conditions for producing nanosized (less than 10 nm) silver nanocrystals. Unlike nanocrystals reported in the literature, our nanocrystals have several unique features: (1) small nanometer-scale size, (2) “nakedness” (i.e., surfaces of metal nanocrystals are free of organic ligands or capping molecules and need no dispersant in synthesis solutions), and (3) colloidal stability in water solutions. It was discovered that silver nanoparticles with initially large size distribution can be homogenized into near-monodispersed colloidal sol by a low-power (less than 15 mW) He–Ne laser exposure treatment. The combination of the TECS technique and the laser treatment could lead to a new technology that produces metal nanoparticles that are naked, colloidally stable, and uniformly sized. In the presence of a stabilizing agent (also a supporting electrolyte) such as polyvinyl alcohol, high yields of silver nanoparticles (less than 100 nm) in the form of thick milky sols are produced.

Development of multifunctional additives based on vegetable oils for high quality diesel and biodiesel

The increasing qualitative requirements of the modern diesel fuels can be satisfied by applying environmental friendly blending components and additive-packages having high performance level. The aim of our experimental work was to produce multifunctional additives based on rapeseed oil methyl ester by applying radical initiation. This process is more environmental friendly and energy economic respect to the widely used thermal synthesis method for the production of polyisobutylene (PIB)-succinimide type additives. Beside, our aim was to use raw materials originated from partly renewable source to meet the biodegradability requirements. These synthesized additives showed same or even better detergent–dispersant properties compared to the traditional PIB-succinimides and also provided corrosion inhibiting and lubricity improving effects when applied in diesel fuel, 5% biodiesel containing diesel fuel and 100% biodiesel.

A novel synthetic route to prepare cubic BN nanorods

Cubic boron nitride nanorods were prepared at 450°C by a low pressure benzene thermal synthesis method using BCl 3 and Li 3N as the reactants. The nanorods with various lengths and diameters were observed by transmission electron microscopy. The analysis of X-ray diffraction pattern and electron diffraction pattern revealed that the nanorods are cBN with a lattice constant of 3.62 Å. The Fourier transformation infrared spectra showed that the dominant phase is cBN, and the B:N ratio of 1.15:1 can be obtained from the X-ray photoelectron spectrum.

Synthesis of SnS 2 nanocrystals via a solvothermal process

Nanoparticles of tin disulfide have been successfully prepared by the solvent–thermal synthesis method using different precursors. The X-ray powder diffraction patterns showed that the products were hexagonal SnS 2 phase and transmission electron microscope images displayed that the samples were laminar particles with the average size of about 150 nm. The Raman spectra showed a sharp peak at 311 cm −1, which is characteristic of SnS 2. The IR spectra determined the absence of tin oxides. In addition, the possible routes of the reactions were discussed.

Investigations of co-existence region in lead zirconate-titanate solid solutions: X-ray diffraction studies

Compositions with varying Zr/Ti ratio in: xPbZrO 3– yPbTiO 3– zPb(Fe 1/5, Ni 1/5, Sb 3/5)O 3 such that ( x+ y+ z)=100% and at constant z=10% were prepared by the conventional method of thermal synthesis of mixed-oxides. The characterization of these PZT ceramics was carried out with XRD and SEM. X-ray diffraction is presented to demonstrate the co-existence of the tetragonal and rhombohedral phases. In the present work it is shown that the tetragonal structure persists up to x=43, while the rhombohedral structure appears at x=46. These results suggest that the morphotropic phase boundary lies in the range 43< x<46 and therefore the width of the morphotropic transition is determined (Δ x=3%). The lattice parameter measurements showed that tetragonal and rhombohedral unit cells of the phases depend on the sintering temperature. The effects of sintering temperature on microstructure are studied by means of a scanning electron microscope (SEM).

Effect of Solvents on the Absorption Properties of GaP Nanocrystals

GaP nanocrystals were synthesized by both the organic solvent reflux and high temperature high pressure benzene thermal synthesis methods. The effect of organic solvent on the optical absorption properties of GaP nanocrystals were studied. The results show that crystal grains of the sample synthesized by the latter method have better quality and uniformity. The solvents which consist of polar molecules and form strong chemical bonds with Ga atoms cause obvious redshift of the absorption spectra of GaP nanocrystals. The absorption spectra redshift much more if the solvent molecules have π electrons which involved in the formation of complex bond between Ga atoms and solvent molecules.

Catalysis and plasma chemistry at solid surfaces

Heterogeneous and homogeneous non-equilibrium plasma chemistry offers a range of potential advantages compared to conventional thermal activation and synthesis methods. Some examples of how such low temperature electrical discharges can be effectively utilised for selective chemical reaction pathways are given. These include the fluorination of C-H bonds, the synthesis of polyozonides, selective ring opening polymerisation, and the conversion of alkali metal halides to nitrates using air.