Yttrium Silicate Research Articles

Yttrium Silicate Coatings on Chemical Vapor Deposition‐SiC‐Precoated C/C–SiC: Thermodynamic Assessment and High‐Temperature Investigation

Yttrium silicates are promising materials for improved oxidation and erosion protection for carbon fiber‐reinforced composites. A two‐layer coating system of low‐pressure plasma‐sprayed yttrium silicate on chemical vapor deposition‐SiC‐precoated C/C–SiC was tested under atmospheric re‐entry conditions simulated within a plasma wind tunnel test facility. The thermal expansion behavior of Y2SiO5 and Y2Si2O7 was investigated. The chemical compatibility with and without increasing oxygen partial pressure at the interface of the two‐layer system was calculated by the CALPHAD method. The calculations were compared with experimental results. Furthermore, a thermodynamic explanation is presented to understand and predict the observed coating failure mechanism, identified as blister formation.

Physical and electrical analysis of RuxYy alloys for gate electrode applications

This letter describes RuxYy as a potential candidate for dual metal complementary metal–oxide–semiconductor applications. The characterization of RuY alloys indicate that the effective work function can be controlled from 3.9to5.0eV as the yttrium composition in the RuxYy is decreased in film for both PMOS and NMOS application. From x-ray photoelectron spectroscopy analysis, it was found that the Ru3d peaks do not change as the Y composition is changed, indicating the Ru–Y bonding is very weak or undetectable in RuxYy film. However, it was also found that Y reacts with the underlying SiO2 to form yttrium silicate. In addition, in situ x-ray diffraction results did not detect the presence of Ru–Y compound in the RuxYy films. Capacitance–voltage (C–V) characterization indicated that the oxide thickness decreased as the Y composition increased. We extracted the effective barrier height of RuxYy at the metal–oxide interface via Fowler–Nordheim current analysis. The barrier height decreases as the Y composition increased. This agrees with the change of RuxYy work function which was extracted from the C–V analysis.

White light emission from rare earth activated yttrium silicate nanocrystalline powders and thin films

We present a potential rare earth activated white-emitting nanocrystalline phosphor powders produced by combustion synthesis and report their luminescent properties and thin films deposited by pulsed laser ablation. Effects of varying the atomic concentration of rare earth dopants in Y2SiO5:Cex,Tby (0.0065 < x < 0.0085, 0.010 < y < 0.040), along with morphological, microstructural and photoluminescence (PL) properties were investigated in order to produce white-light emission close to D65 with optimized luminescent efficiency. Characteristic electronic transitions measured from photoluminescence spectra at λem = 544 nm (5D4 → 7F5) in Tb3+ and λem = 418 nm (5d → 2F7/2) in Ce3+ show that an inductive energy transfer occurs when Tb3+ ions absorbs the energy from Ce3+ upon excitation with long-UV photons (λexc = 358–380 nm). The optimal concentration for the best luminescence intensity has been obtained in Y2SiO5:Ce0.0075,Tb0.025, and the closest to daylight white emission was found with a composition of Y2SiO5:Ce0.0075,Tb0.040. These activated phosphors with two rare earth ions in the yttrium silicate host (Y2SiO5) represent an efficient way to produce white-light emission close to D65 with chromaticity coordinates of x = 0.225 and y = 0.320.

Preparation and characterization of 50SiO 2–50Y 2O 3 sol–gel coatings on glass and SiC(C/SiC) composites

Yttrium silicate (Y 2SiO 5) coatings can complement internal SiC coatings for protecting carbon-fiber-reinforced SiC composites (C/SiC). 50SiO 2–50Y 2O 3 coatings were prepared by dipping samples into sol–gel solutions. The coatings were deposited on soda-lime glass substrates to evaluate their homogeneity and critical thickness. Crack-free coatings were obtained at withdrawal rates below 16 cm/min with a critical thickness of 80 nm. Thicker coatings (2 μm) were prepared on SiC-coated C/SiC composites using a multilayer deposition process. The gelled sol was also studied by transmission electron microscopy (TEM), thermal analysis (TGA–DTA) and X-ray diffraction (XRD).

Europium-doped yttrium silicate nanoparticles embedded in a porousSiO2 matrix

Europium-doped yttrium silicate nanoparticles were grown inside a porous siliconoxide matrix by chemical impregnation of porous silicon layers, followed by heattreatments. The average size of the nanoparticles is 50 nm and they are dispersedalmost uniformly within the whole porous layer. Local composition measurementsdemonstrate that Y and Eu are found only in nanoparticles, indicating a good phaseseparation efficiency. There is indirect evidence that yttrium silicate nanoparticlesare nucleated around Eu ions. The crystalline phase of the particles is pureα-Y2Si2O7, with notrace of Y2O3 or Y2SiO5 orother Y2Si2O7 polymorphs. Structural purity is an advantage for this method, as in the case of powder orsol–gel methods single-phase yttrium silicate formation is hardly possible, even at highfiring temperatures.

Microstructure and electrical characterizations of yttrium oxide and yttrium silicate thin films deposited by pulsed liquid-injection plasma-enhanced metal-organic chemical vapor deposition

Results on yttrium oxide and yttrium silicate films elaborated by an innovative metal-organic chemical vapor deposition process combining plasma assistance and a liquid precursor supply setup are presented. Plasma assistance enables deposition at a much lower substrate temperature and the pulsed-liquid precursor source allows an accurate control of the injected reactive species. According to x-ray photoelectron spectroscopy (XPS) analyses, we show that ultrathin yttrium oxide deposition can be performed at temperature less than 380°C. Yttrium oxide films contain carbon contamination that can be reduced by increasing the deposition temperature. The plasma plays a key role in the deposition mechanisms and thus in the chemical structure of the films and of the interface. It is shown that the injection frequency, i.e., the reactive species incoming frequency, plays a significant role in the silicate and interface formation. A detailed study is presented using angle-resolved XPS. A high injection frequency limits the formation of SiO2 interfacial layer and also of the silicate and favors the growth of yttrium oxide. In addition, silicate formation also depends on the deposition temperature. Electrical results show that as-deposited film at 350°C has a low leakage current (J&amp;lt;10−7A∕cm2) and a high breakdown field (∼8MV∕cm).

WGA-coated yttrium oxide beads enable an imaging-based adenosine 2a receptor binding scintillation proximity assay suitable for high throughput screening.

Adenosine receptors belong to the superfamily of G protein-coupled receptors and are involved in a variety of physiologic functions. Traditionally, binding assays to detect adenosine 2a (A2a) antagonists and agonists have used filtration methods that are cumbersome to run and not amenable to HTS. We developed scintillation proximity assays (SPA trade mark ) utilizing HEK293 RBHA2AM cell membranes, either wheat germ agglutinin (WGA)-coated yttrium silicate (YSi) or red-shifted yttrium oxide (YO) beads and the A2a-selective radioligand [(3)H]SCH 58261. Both beads gave windows (total binding/nonspecific binding) of >5 and K(d) values of 2-3 nM for the radioligand, in agreement with results obtained by filtration. In contrast, WGA-polyvinyltoluene as well as other bead types had windows of <3 and significant radioligand binding to the uncoated beads. A 384-well WGA-YO bead SPA was optimized utilizing a LEADseeker imaging system and an automated trituration process for dispensing the dense yttrium-based beads. Signals were stable after 4 h, and Z' values were 0.7-0.8. The LEADseeker imaging assay tolerated 2% dimethyl sulfoxide and generated IC(50) values of 3-5 nM for the A2a antagonist CGS 15943, comparable to that obtained by the filtration method. A number of adenosine and xanthine analogues were identified as hits in the Library of Pharmacologically Active Compounds (LOPAC). This imaging-based A2a SPA enables HTS and is a major improvement over the filtration method.

Mullite phase formation in oxide mixtures in the presence of Y2O3, La2O3 and CeO2

The effect of oxides (Y2O3, La2O3, and CeO2), on phase formation of mullite, reaction sequence and microstructure evolution, in the mixtures of Al2O3 and SiO2, has been investigated. All three dopants showed a positive effect on the mullitization behavior, lowering the mullite formation temperature by about 100 °C. The improved mullitization behavior was attributed to the formation of the low-viscosity liquid phase due to the addition of dopants. The reaction sequence was different in the three doping cases. Two types of yttrium silicate were found in the samples doped with Y2O3, with one being favored at low temperature and another at high temperature. No reaction was observed between CeO2 and Al2O3 or SiO2, while La2O3 was not detected by the X-ray diffraction (XRD) measurement for all doping levels. The samples with La2O3 had the best densification behavior among the three doping cases, while the effect of CeO2 on densification was slightly better than that of Y2O3. The difference in the effects of the three oxides on the mullitization and densification behavior of the doped samples implied the difference in the characteristics of the low-viscosity glass phases formed at high temperatures.

Ion beam induced luminescence of doped yttrium compounds

Rare earth doped yttrium oxide (yttria) and silicate, Y 2O 3:Eu and Y 2SiO 5:Tb, are the most promising phosphors for advanced devices such as flat panel field-emission-displays. However, their light yield for electron excitation has proven to be lower than that predicted by early models. New experimental data are needed to improve the theoretical understanding of the cathodoluminescence (CL) that will, in turn, lead to materials that are significantly brighter. Beside the existing CL and photo luminescence (PL) measurements, one can provide new information by studying ion-induced luminescence (IL). Ions penetrate substantially deeper than electrons and their light yield should therefore not depend on surface effects. Moreover, the energy density released by ions can be much higher than that of electrons and photons, which results in possible saturation effects, further testing the adequacy of models. We exposed the above yttrium compounds to three ion beams, H (3 MeV), C (20 MeV), Cu (50 MeV), which have substantially different electronic stopping powers. H was selected to provide an excitation close to CL, but without surface effects. The C and Cu allowed an evaluation of saturation effects because of their higher stopping powers. The IL experiments involved measuring the transient light intensity signal radiating from thin phosphor layers following their exposure to ∼200 ns ion beam pulses. We present the transient yield curves for the two materials and discuss a general model for this behavior.

Novel fluffy carbon balls obtained from coal which consist of short curly carbon fibres

also investigated in the oxidation test. For this the samples were placed on a corundum support and were taken in and out of the furnace directly into air for about 10 s. During the oxidation test, the sample endured 10 thermal cycles between 1773 K and room temperature, and no visible cracks or spallation were found, from which it could be inferred that the coating has excellent thermal shock resistance. This is because of the formation of the SiC gradient bonding layer and the good match of thermal expansion coefficient between the yttrium silicate coating and the SiC internal layer, and also between the glass outer layer and the gradient yttrium silicate layer. In conclusion, the SiC/gradient yttrium silicate/glass multi-layer coating produced by pack cementation, plasma spray and subsequent sintering shows excellent thermal shock resistance is a good oxidation protective coating for C/C composites. It could protect the C/C composites from oxidation perfectly in air flowing by natural convection at 1773 K for 164 h.

Mullite phase formation in oxide mixtures in the presence of Y 2O 3, La 2O 3 and CeO 2

The effect of oxides (Y 2O 3, La 2O 3, and CeO 2), on phase formation of mullite, reaction sequence and microstructure evolution, in the mixtures of Al 2O 3 and SiO 2, has been investigated. All three dopants showed a positive effect on the mullitization behavior, lowering the mullite formation temperature by about 100 °C. The improved mullitization behavior was attributed to the formation of the low-viscosity liquid phase due to the addition of dopants. The reaction sequence was different in the three doping cases. Two types of yttrium silicate were found in the samples doped with Y 2O 3, with one being favored at low temperature and another at high temperature. No reaction was observed between CeO 2 and Al 2O 3 or SiO 2, while La 2O 3 was not detected by the X-ray diffraction (XRD) measurement for all doping levels. The samples with La 2O 3 had the best densification behavior among the three doping cases, while the effect of CeO 2 on densification was slightly better than that of Y 2O 3. The difference in the effects of the three oxides on the mullitization and densification behavior of the doped samples implied the difference in the characteristics of the low-viscosity glass phases formed at high temperatures.

Yttrium Silicate Powders Produced by the Sol—Gel Method, Structural and Thermal Characterization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Yttrium Silicate Powders Produced by the Sol–Gel Method, Structural and Thermal Characterization

Yttrium silicate (Y2SiO5) powders of high purity have been synthesized using the sol–gel method. Alkoxide precursors were used with commercial tetraethyl orthosilicate as the silica source and yttrium propoxide synthesized from YCl3. Powders calcined from the xerogel showed submicrometer crystal sizes. These powders were sintered at temperatures &lt;1300°C and are suitable for coating applications such as a thermal barrier system for SiC/SiC composites.

Preparation and characterization of a double-layered porous film to assay for surface radioactive contamination

Double-layered polysulfone (PSF) membranes, containing cerium activated yttrium silicate (CAYS) as a fluor, were prepared from double casting of two polymeric solutions, and their morphology and radioactive capacity were compared with those of single-layered membranes. The backing, the bottom layer of double-layered membranes, was made of a binary casting solution of polysulfone and methylene chloride (MC), its cast film being solidified by vacuum evaporation. The second casting solution with dimethylformamide (DMF) as solvent was cast over the solidified backing film and coagulated by being immersed into a nonsolvent bath of water or methanol. The prepared membranes revealed two distinct, but tightly attached, double layers, their attachment being identified by the morphology of the interface between the two layers. Membranes prepared with CAYS in the casting solution have more developed macropores than those prepared without CAYS. In the radionuclide detection test of the CAYS-impregnated membranes, the membranes solidified by water precipitation showed better detection efficiency than those solidified by methanol precipitation. Its superior efficiency is not due to better holding of the radioisotopes, but due to greater density of CAYS in the membrane surface region. In the comparison with single-layered membranes, the double-layered membranes showed a greater ability in holding the radionuclides, spotted on the surface, as well as an improvement in physical strength because of the dense backing layer.

Green-emitting yttrium silicate phosphor particles prepared by large scale ultrasonic spray pyrolysis

Tb doped Y2SiO5 phosphor particles with spherical morphology, fine size, high crystallinity and good photoluminescence intensity were prepared by spray pyrolysis. The colloidal solution obtained by adding the fumed silica particles was introduced to control the characteristics of Y2SiO5: Tb phosphor particles. The particles prepared from the colloidal solution had a spherical and filled morphology even after post-treatment. The particles post-treated below 1,200 ‡C had X1 type crystal structure but the crystal structure changed from X1 to X2 after post-treatment above 1,300 ‡C. When crystal structure was changed from X1 to X2, the PL intensity greatly increased. The maximum PL intensity of particles, which were prepared from the solution with 120% excess of stoichiometric fumed silica, was about 4 times higher than that of the particles prepared from the stoichiometric solution. The particles prepared from the stoichiometric solution of yttrium nitrate and fumed silica had mixed phases of X1 and X2 type and had impurity as Y2O3. On the other hand, the particles prepared from the solution with 120% excess of stoichiometric fumed silica had high crystallinity of X2 type.

Improving the efficiency of a blue-emitting phosphor by an energy transfer from Gd 3+ to Ce 3+

The low-voltage efficiency of the blue-emitting phosphor, cerium activated yttrium silicate (Y 1− m Ce m ) 2SiO 5, has been improved by co-activating with gadolinium, (Y 1− m− n Ce m Gd n ) 2SiO 5. Gd 3+ improves the efficiency by transferring energy to Ce 3+, and makes this phosphor a more promising candidate for low-voltage field emission flat panel displays. Low-voltage cathodoluminescence and photoluminescence measurements were made to determine the optimum concentrations of Gd 3+ that yielded the most luminous efficient phosphor. For photoluminescence, Ce 3+ most efficiently luminesces at the excitation wavelength λ ex=358 nm. Co-activating with Gd 3+ did not improve the photoluminescent efficiency because Gd 3+ does not absorb at Ce 3+ excitation energy, and thus cannot transfer energy. For low-voltage cathodoluminescence, co-activating with Gd 3+ did improve the efficiency since Gd 3+ was sufficiently excited, with the optimum composition found to be (Y 0.8425Ce 0.0075Gd 0.15) 2SiO 5.

Scintillation proximity assay of inositol phosphates in cell extracts: High-throughput measurement of G-protein-coupled receptor activation

The phosphatidylinositol turnover assay is used widely to measure activation, and inhibition, of G q-linked G-protein-coupled receptors. Cells expressing the receptor of interest are labeled by feeding with tritiated myo-inositol. The label is incorporated into cellular phosphatidylinositol 4,5-bisphosphate, which, upon agonist binding to the receptor, is hydrolyzed by phospholipase C to inositol 1,4,5-trisphosphate (IP 3) and diacylglycerol. In the presence of Li +, dephosphorylation of IP 3 to inositol is blocked, and the mass of soluble inositol phosphates is a quantitative readout of receptor activation. Current protocols for this assay all involve an anion-exchange chromatography step to separate radiolabeled inositol phosphates from radiolabeled inositol, making the assay cumbersome and difficult to automate. We now describe a scintillation proximity assay to measure soluble inositol phosphate mass in cell extracts, thus obviating the need for the standard chromatography step. The method uses positively charged yttrium silicate beads that bind inositol phosphates, but not inositol. We have used this assay to measure activation of recombinant and endogenous muscarinic acetylcholine receptors and activation of recombinant neuropeptide FF2 receptor coupled to IP 3 production by coexpression of a chimeric G protein. Further, we demonstrate the use and functional validity of this assay in a semiautomated, 384-well format, by characterizing the muscarinic receptor antagonists pirenzepine and atropine.

Investigation of the physical properties of a blue-emitting phosphor produced using a rapid exothermic reaction

The blue-emitting phosphor cerium activated yttrium silicate, (Y 1−mCe m) 2SiO 5, was prepared via a novel synthesis technique called combustion synthesis. Combustion synthesis involves a highly exothermic redox reaction between metal nitrates and an organic fuel to produce a solid powder. The combustion synthesis parameter, the fuel-to-oxidizer ratio, has a direct effect on the physical properties of the as-synthesized powders due to the reaction temperature being dependent on the variation of this ratio. Thus, varying the fuel-to-oxidizer ratio produced powders with varying crystallite sizes, carbon contamination and surface areas, which in turn affected the luminescent efficiencies of the as-synthesized powders. The reaction temperature was found to reach a maximum with a 60% fuel rich mixture, with the powders exhibiting the largest crystallite sizes, smallest surface area and carbon contamination, and highest luminescent efficiency in the as-synthesized state. As-synthesized powders exhibit a high degree of porosity due to the large amount of gas to solid formed. To more accurately predict the specific surface areas of porous powders, the standard geometrical model used for gas absorption measurements was modified for porous particles and found to more accurately predict the specific surface area of highly porous powders.

Thermal Expansion of Yttrium Silicate and Yttrium Disilicate Coatings

Thermal Expansion of Yttrium Silicate and Yttrium Disilicate Coatings

Characterization of silicate/Si(001) interfaces

Many of the proposed high permittivity gate dielectrics for silicon-based microelectronics rely on a stack configuration, with an SiO2 buffer layer to provide an interface. We describe a means for creating gate dielectrics with a direct yttrium silicate–silicon interface through the solid-state reaction of yttria and silicon oxynitride, avoiding the preparation of an oxide-free silicon surface. Characterization by medium-energy ion scattering indicates complete consumption of the underlying oxide through silicate formation during high-temperature annealing. Furthermore, the silicate dielectric exhibits small flat-band voltage shifts, indicating low quantities of charge, without passivation steps. Creation of a silicate–silicon interfaces by a simple route may enable the study of an alternate class of dielectrics.