Preparation and characterization of uniform coated particles (Cobalt compounds on cadmium compounds)

Uniformly dispersed particles of CdCO₃ were prepared by homogeneous precipitation from aqueous solutions of cadmium sulphate and urea at the elevated temperatures. These particles were then employed as cores for coating with 2CoCO₃·Co(OH)₂·H₂O from cobalt nitrate and urea solutions at 85°C. In the absence of cores, when heated under similar conditions, the coating solutions produced nearly uniform particles of 2CoCO₃·Co(OH)₂·H₂O. On calcination at 700°C, the core [CdCO₃], coated [CdCO₃/2CoCO₃·3Co(OH)₂], and coating precursor [2CoCO₃·Co(OH)₂·H₂O] particles transformed into CdO, CdO/Co₃O₄, and Co₃O₄, respectively. No sintering occurred during calcination and the particles preserved their morphological features to a significant extent.     

The coating of nickel compounds with copper compounds

Uniform fine particles of nickel basic carbonate were synthesized by heating, aqueous solution containing 0.08 mol dm⁻³ nickel sulfate and 0.8 mol dm⁻³ urea, at 85°C for various periods of time. These particles were then coated with copper compound by heating them in aqueous dispersion, containing urea and copper nitrate, at 85°C. The coating material was found to be amorphous and was composed of Cu₂(OH)₂CO₃. The coating mixture, when heated under similar conditions in the absence of the dispersed cores, produced greenish dispersion of the precipitated particles [coating precursor solids]. The later were also amorphous in nature and had the same chemical composition [Cu₂(OH)₂CO₃] as that of the coating material of the coated particles. Air-dried core, coated, and coating precursor materials were calcined at 700°C for 1 h at the heating rate of 5°C min⁻¹ in the air atmosphere, which converted them into NiO, NiO_[core]/CuO_[coating], and CuO, respectively. Scanning electron microscopic examination showed no sintering occurred in all these solids during the calcinations process and the particles retained their identities to a significant extent.     

The coating of cadmium compounds with nickel compounds

Micrometer-sized particles of cadmium carbonate (cores) were prepared by homogeneous precipitation from aqueous solution containing urea in the presence of cadmium sulfate. These particles were then homogeneously coated with a layer of nickel hydroxy carbonate by heating their dispersion in aqueous solution, containing nickel sulfate and urea, at 85 °C for 70 min with constant agitation. The same solution mixture produced spheroids of nickel hydroxy carbonate (coating precursors), when heated under similar conditions in the absence of the cadmium carbonate particles. The existence of the coated layer on the cores and its composition was confirmed by various physical methods. The as-prepared carbonated solids (cores, coating precursors, and coated particles) were converted into their oxide forms by calcination at 700 °C. The cores became porous, whereas the coating precursors and coating layer disintegrated into smaller particles during the calcination process.     

Synthesis and characterization of uniformly coated particles (cobalt compounds on copper compounds)

Spherical particles (～3 μm) of copper(II) oxalate were produced in the form of precipitated solids by gently mixing aqueous solutions of oxalic acid and copper nitrate with predetermined concentrations at room temperature. These particles were isolated from the mother liquor and then coated with cobalt basic carbonate. The coating trials involved heating of the aqueous dispersions, containing known amounts of the dispersed copper oxalate particles (cores), urea, and cobalt nitrate, at 70–85 °C for various periods of time with constant stirring. The heating process decomposed urea, increased pH, liberated carbonate ions, which resulted in the precipitation of the dissolved cobalt ions in the form of shells of cobalt basic carbonate around each core particle. The coating process was sensitive to the applied experimental parameters, since uniformly coated particles were obtained under a narrow range of coating mixture composition. In the absence of the cores, the same reactants solutions produced coating precursor particles (cobalt basic carbonate), when subjected to similar heating conditions. Physical and chemical analyses indicated that the coating material of the coated particles and the coating precursor particles had the same chemical compositions. The as-prepared core, coating precursor, and coated particles were converted into oxide forms by heating their dry powders at elevated temperatures under controlled heating conditions. The heat treatment produced obvious changes in the surface morphology of these particles due to loss of material. Moreover, the heat-treated particles preserved shape integrity to a maximum extent, showing their thermal stability. Selected batches of the as-prepared and heat-treated products were characterized by various physical methods.     

Preparation of titanium nitride coated powders by rotary powder bed chemical vapour deposition

Titanium nitride coated powders were prepared by rotary powder bed chemical vapour deposition (CVD) in which a powder in a rotary specimen cell was heated by infrared radiation in a reactant gas stream. Titanium powder covered with TiN or Ti₂N thin film was obtained by diffusion coating treatment of titanium particles (grain size 10 to 50 µm) at 900 to 1000°C and 0.5 to 1.0 atm for 60 min in a nitrogen stream. TiN was coated on to the surface of scaly graphite particles (grain size 30 to 100 µm or 100 to 1000 µm) as well as titanium particles by CVD in the reactant system TiCl₄-N₂-H₂ at 900° C and 1 atm for 40 min. The uniformity of the coating (composition and film thickness) and the dispersability of the coated particles were considerably promoted by rotating the powder bed at about 90 r.p.m. compared with nonrotary powder bed CVD.     

Preparation of SiC–SiO<Subscript>2</Subscript>–CuO composites

SiC–SiO₂–CuO composite particles were prepared by double coating processes. SEM, DSC-TG, XRD techniques were carried out to characterize the coated composite particles and sintered compacts. It was found that a core-shell structure was constructed in the composite particles with the core of SiC and the shell of SiO₂–CuO. Cu–silicides were detected in hot-pressed compacts. SiO₂ might decompose at 1,300 °C. The decomposition product of Si would result in the transformation from Cu_6.69Si into Cu₃Si.     

Preparation and properties of composite particles made by nano zinc oxide coated with titanium dioxide

In this paper, composite particles of nano zinc oxide coated with titanium dioxide were prepared and characterized by TEM, XRD, XPS and FT-IR, and the properties of the composite particles for photo catalysis and light absorption were studied. Tetrabutyl titanate (TBT) was hydrolyzed in an alcoholic suspension of nano zinc oxide with diethanolamine (DEA) as an additive, resulting in a film with a thickness of 20–30 nm being coated on the surface of nano zinc oxide, and the composite particles contained ZnTiO₃ after drying and calcination. Photocatalysis capabilities of the composite particles for the degradation of phenol in an aqueous solution were greatly improved as compared with nano zinc oxide particles before coating, with pure nano ZnO and nano TiO₂ with similar average sizes, or with the mixture of nano ZnO and TiO₂ with the similar composition as the composite particles. The light absorption scope of the composite particles was enlarged when compared to nano titanium dioxide with same average size.     

Cd(S<Subscript>(1 − <Emphasis Type="Italic">x</Emphasis>)</Subscript> + CO<Subscript>3(<Emphasis Type="Italic">x</Emphasis>)</Subscript>) thin films by chemical synthesis

A microcrystalline mixture of cadmium carbonate (CdCO₃) and cadmium sulfide (CdS) were grown in the thin film format onto glass substrates by means of chemical bath. The temperature of the bath (T_d) was selected in the interval 23–80^∘C. At low temperatures, CdCO₃ is the compound predominant in the layers. At high temperatures CdS is the compound deposited on the substrate. At intermediate T_d-values a mixture of both materials are present, i.e., the gradual transition from an insulator (CdCO₃) to a semiconductor (CdS) growth occurs when T_d increases. Physical properties of films were studied by means of X-ray diffraction and optical absorption. The forbidden energy band gap of direct electronic transitions (E_g) was calculated by applying the α² ∝ (hν − E_g) relation to the optical absorption spectra.     

Syntheses and characterization of CdCO3 and CdO nanoparticles by using a sonochemical method

Nanoparticles of CdCO₃ were synthesized by the reaction of Cd(CH₃COO)₂ and tetramethylammonium hydroxide (TMAH) by a sonochemical method. The CdO nanoparticles were obtained by heating of CdCO₃ nanoparticles at 400 °C. The CdCO₃ and CdO nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction (XRD), TGA, DTA and FT-IR spectroscopy.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Polymer-metal chelate precursor reduced its firing temperature and time for preparing yttrium barium cuprate powder

Bulk YBa₂Cu₃O _x was prepared by a polymer chelate precursor method using poly[(N,Ndicarboxymethyl)allylamine] as a chelating polymer of which molecular weights were 3 × 10⁴ (PDAA-L) and 3 × 10⁵ (PDAA-H), respectively. X-ray diffraction (XRD) analysis of the precursor from PDAA-H shows that YBa₂Cu₃O _x (Y123) phase appeared after being calcined at 750 °C for 5 h and the mixture was completely converted to tetragonal Y123 phase after being calcined at 800 °C for 5 h. The phase evolution of the precursor from PDAA-H during isothermal experiment at 800 °C showed that pure tetragonal Y123 was produced even after the polymer chelate precursor was heated for 2 h in air, although a very small amount of BaCO₃ was recognized. This BaCO₃ phase was hardly recognized after 4 h calcination. The precursor prepared from PDAA-L was fully converted to pure tetragonal Y123 after 3 h calcining at 800 °C. On the other hand, the sample prepared from metal nitrate solution without PDAA was not fully transferred to Y123 phase after heating at 800 °C for 10 h. Large amounts of Y₂O₃, BaCO₃ and CuO were observed. These results indicated that the greater homogeneity in the polymer chelate precursor leads to reduced firing times and temperature compared with the metal nitrate precursor.     

Synthesis and characterization of biocompatible hydroxyapatite coated ferrite

Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical composition (CaO)_0.75(La₂0₃)_0.20(Fe₂O₃)₆ was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO₃)₂ and (NH₄)₂HPO₄ maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites could be useful for hyperthermia.     

Nanocoated particles: A special type of ceramic powder

Ceramic particles with sizes below 10 nm consisting of two different oxides in the core and the coating have been prepared by using a two-step microwave plasma process. Precursors for the synthesis are the chlorides. The structures occurring in such particles are demonstrated in the system alumina (Al₂O₃)-zirconia (ZrO₂). When the alumina kernels covered with zirconia are small, or alternatively when the alumina coating on the zirconia kernels are thin, no special structural features are observed. In this case, the alumina is glassy and the zirconia is crystallized. In contrast, particles consisting of a crystallized zirconia core and a crystallized γ-alumina coating exhibit structural defects similar to dislocations that adjust to the different structures. These could be sessile dislocations in the {211} plane of the γ-alumina. Additionally, maghemite (γ-Fe₂O₃) particles coated with cubic zirconia were studied. The coating of this material is free of dislocations.     

Optimum processing conditions for the purification of the YBa2Cu3O7−x powder by the sedimentation method

The superconducting YBa₂Cu₃O_7−xpowder was purified by the sedimentation method. In this method the calcined YBa₂Cu₃O _7−x powder is wet milled and then sedimentation classified. The minor phases are present in the small particles. The calcining and wet milling times were found to be critical for efficient purification. For our system, in which YBa₂Cu₃O_7−x was prepared by calcining a stoichiometric mixture of Y₂O₃ BaCO₃, and CuO at 930°C, a minimum calcination time of 20 h and an optimum wet milling time of 5 h were identified.     

Synthesis of yttrium iron garnet precursor particles by homogeneous precipitation

Yttrium iron garnet (YIG) precursor particles were obtained by homogeneous precipitation in a nitrate salt solution by a reaction involving the thermal decomposition of urea. Chemical analysis indicated that solid phases were initially precipitated with sequential iron ion content. The precipitate formed was an amorphous mixed iron oxide phase. The complex composition and the thermal decomposition of the precipitate were studied by thermogravimetry-differential thermal analysis, differential scanning calorimetry, X-ray diffraction, and Fourier transform-infrared spectroscopy. Precipitate morphology was observed by SEM and TEM. Fine-grained single-phase yttrium iron garnet (YIG:Y₃Fe₅O₁₂) powders were obtained by calcination of the precipitate at 1200 °C. YFeO₃ intermediate compound was formed at 600 °C prior to the final crystallization of YIG.     

Structural and photoluminescence properties of Tb-doped CaMoO4 nanoparticles with sequential surface coatings

The crystal structure, surface chemistry and optical properties of Tb-doped CaMoO₄ (CaMoO₄:Tb) nanoparticles and the sequentially coated CaMoO₄:Tb@CaMoO₄ and CaMoO₄:Tb@CaMoO₄@SiO₂ nanostructures have been characterized by X-ray diffraction (XRD), Thermo-gravimetric analysis (TGA), UV–vis absorption (UV–Vis), Fourier- transform infrared spectroscopy (FT-IR), Raman spectroscopy and Photoluminescence spectroscopy. The XRD results indicate that the obtained CaMoO₄:Tb is sheelite tetragonal structure and well crystallized at 150 °C. The particle size increases from 21 to 48 nm by sequential coating of CaMoO₄ and silica formation around the surface of core nanoparticles. These nanocrystals were well-dispersed in aqueous and non-aqueous solvents to form clear colloidal solutions. The colloidal solutions of three samples show well characteristic optical absorption band in UV/Visible region. The surface coating on core particles will significantly influence the structural and photoluminescence properties. The as-prepared core nanoparticles showed high photoluminescence as compared to surface coated core–shell nanoparticles because Tb³⁺ ion located at the particle surface. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices as well as optical bioprobes.     

Design of Bi-functional composite core–shell SiO2@ZnAl2O4:Eu3+ array as a fluorescent sensors for selective and sensitive latent fingerprints visualization protocol

Core–shell SiO₂@ZnAl₂O₄:Eu³⁺ (5?mol%) nanophosphor (NP) with coatings up to the level IV has been prepared by a facile solvothermal route, followed by heat treatment. Scanning electron microscopy studies of fabricated core–shell particles displays good spherical shape and non-agglomeration with a narrow size distribution. The thickness of the shell increased with increase in coating cycles. Photoluminescence (PL) studies exhibited strong red emission peaks at 612?nm corresponding to the ⁵D_o?→?⁷F₂ transition of the Eu³⁺ ions. PL intensity increased with calcination temperature and coating cycles. The color coordinates of the coated NP were turned towards intense pure red emission with color purity ～95%. Powder dusting method was used to visualize latent fingerprints (LFPs) by staining uncoated and coated NP on various porous and non-porous surfaces under UV light. It was clear that core–shell NP display high sensitivity, reproducibility, selectivity, reliability, and can obtain the complete three levels of fingerprint ridge details. Judd–Ofelt (J-O) intensity parameters and radiative properties, namely transition probabilities, radiative lifetimes, branching ratios, and quantum efficiency were evaluated. The aforementioned results established that the SiO₂@ZnAl₂O₄:Eu³⁺ (5?mol%) NP can be used as an ideal candidate for multifunctional applications such as WLEDs, LFPs, anticounterfeiting etc.     

NO decomposition by ultrafine noble metals dispersed on the rare earth phosphate hollow particles

Novel fine polymer particles containing ultrafine Pd, Pt or Rh metal dispersed on the core-shell [core, poly(styrene-co-acrylamide) or poly(styrene-co-acrylic acid); shell, LnPO₄(Ln = Ce, Nd, Pr, Sm, La)] type microsphere were prepared by the emulsifier-free emulsion polymerization of styrene with acrylamide or acrylic acid followed by the addition of PdCl₂, HPtCl₆, or RhCl₃ and finally by the addition of a mixture of Ln(NO₃)₃ and NaH₂PO₄. Pyrolysis of the resulting polymer particles at 700–900°C provides polymer-free hollow particles (diameter 450–550 nm) composed of noble metals and LnPO₄. The excellent catalytic reduction of NO gas into N₂ and O₂ was observed at 500–700°C using the rersulting particles as catalyst.     

Preparation of α-alumina nanoparticles via vapor-phase hydrolysis of AlCl3

A novel alumina precursor, represented as AlO_xCl_y(OH)_z, was prepared in a batch reactor through a vapor-phase hydrolysis of AlCl₃ at 200 °C for 1 min. The precursor particles were spherical and distributed in the size range of 30 to 200 nm, giving a number-average diameter of 70 nm. The precursor particles were calcined at 1200 °C for 6 h to obtain α-alumina nearly 100% in α-transformation degree. The weight loss upon calcination was 40%, comparable to 35% of Al(OH)₃. The surface-area equivalent diameter of the obtained α-alumina particles was calculated to be 35 nm.     

Electrochemical characterizations of surface modified LiMn2O4 cathode materials for high temperature lithium battery applications

LiMn₂O₄ spinel cathode materials were coated with 2.0 wt.% of La₂O₃ by polymeric process followed by calcinations at 400 °C and 800 °C for 6 h in air. The surface coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy. La₂O₃-coated LiMn₂O₄ coating did not affect the crystal structure and space group Fd3m of the cathode materials compared to the uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated and compact coating layer on the surface of the core materials. La₂O₃ was completely coated over the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the La₂O₃-coated LiMn₂O₄ cathode materials were carried out at 0.1 mA/g in the range of 3.0 and 4.5 V at 30 °C and 60 °C. Based on the results, La₂O_3-coated spinel LiMn₂O₄ cathode at 800 °C has improved the structural stability, high reversible capacity and excellent electrochemical performances of the rechargeable lithium batteries.