Porous Garnet Coatings Tailoring the Emissivity of Thermostructural Materials

The power radiated by a surface influences the energy transfer processes following a T⁴ slope. It is therefore clear that, at high temperature, the study and control of spectral emissivity of materials play a key role in many important technologies: re-entry-vehicle thermal protection shields, high temperature radiators, selective emitters in thermophotovoltaic generators, etc. We have developed a class of thick porous garnet coatings that may raise or lower the spectral emissivity of thermostructural materials in the VIS, NIR, and IR regions. The porosity of the coatings nearly cancels any emission contribution from the underlying materials due to the scattering in the inhomogeneous system: pore/high refraction garnet. The yttrium aluminum garnet polycrystals vary their emissivity as a function of the doping rare earth elements they contain. We achieved an emission control capability in the range 700–3000 nm. Porous coatings have been prepared from ceramic slips containing a reactive colloidal phase and rare earth garnet powders prepared by drying and calcining mixed oxide aqueous gels. Garnet coatings containing Er, Yb, and Tm were prepared with thickness ranging between 50 and 400 microns. The coatings have been investigated by morphological and microstructural studies. A dedicated experimental set up has been developed to measure the spectral emissivity up to 1700 K under different heating conditions.     

稀土对肝脏作用的机制

综述了稀土对肝脏作用的机制，稀土不仅能引起肝脏形态学的改变，当稀土进入肝细胞后可与多种蛋白质等分子发生相互作用，并影响多种酶的活性，还能通过信使分子干扰肝脏正常的生理功能。     

金属氧化动力学规律和耐热钢中稀土作用的研究

根据气固相反应动力学理论推导出金属氧化不同阶段和不同几何２样品的动力学方程，实验研究了耐热钢３Ｃｒ２４Ｎｉ７Ｎ高温氧化中稀土的作用实验结果表明，稀土未改变耐热钢的氧化动力学机理，理论推导的氧化动力学方程可以很好地描述实际金属氧化的动力学规律。     

Emission properties and applications of nanostructured luminescent oxide nanoparticles

Rare earth doped oxide materials are well known for their numerous applications in light emitting devices. An interesting issue is to study the emission properties of nanoparticles, with the aim to understand the influence of small size and surface effects on the emission processes. These particles could furthermore be used in new applications such as the elaboration of transparent emitting devices or new biological labels. The work presented here concerns highly luminescent rare earth doped yttrium vanadates (YVO₄:Eu) and lanthanum phosphate LaPO₄:Ce,Tb·xH₂O nanoparticles. Simple aqueous colloidal syntheses are used for the elaboration of concentrated colloids based on the progressive decomposition of polymeric precursors at moderate temperature (60–90 °C). Both types of particles exhibit strong emission (quantum yields of 25% and 45% for vanadates and phosphates, respectively), but significantly lower than that for the equivalent bulk materials. The alteration of the emission processes is discussed in terms of surface quenching effects. Improvements are obtained through the elaboration of core/shell nanostructures. Surface derivatization has been achieved through the controlled growth of an organically modified silica shell using a functionalized silane precursor. Two examples are given concerning the applications of those particles. The first one is the elaboration of transparent and highly luminescent thin films, obtained by the dispersion of the functionalized particles in a sol–gel silica matrix. The other one is the use of guanidine functionalized particles as biological labels for the single particle detection of sodium channels in cardiac cells.     

Selective determination of yttrium in geological materials by ion-interaction chromatography

Selective separation and determination of yttrium in rare earth ores have been achieved by high performance ion-interaction chromatography. Ores are decomposed by sulfuric acid and the rare earths are precipitated in a group as oxalates. Yttrium is then separated from the other rare earths on a C-18 bonded phase silica column modified with 1-octanesulfonate by linear concentration gradient elution for 20 min with 0.15 to 0.40M glycolic acid(pH 3.5). Yttrium elutes at about 10 min between samarium and neodymium, being separated selectively from all the rare earths as well as scandium, thorium and uranium. Post-column reaction detection and quantitation with Arsenazo III [2,7-bis(2-arsonophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid] are carried out at 650 nm. Quantitative results are quoted for yttrium in sophisticated, synthetic rare earth mixtures, monazite and xenotime.     

Emetteurs Selectifs: Cinetique D'augmentation De L'emissrvtte Et De Diminution: Simultanee De L'absorpttvite En Fonction De La Duree: D'elaboration De La Couche De Conversion

Selective emitters : kinetics of both emissivity increase and absorptivity decrease versus the elaboration time of the conversion film.For applications in the field of metrology, selective surfaces with high emissivity (∼.70) in the atmospheric window (8–13 μm) are synthetized by chemical and electrochemical surface treatment techniques. It is there possible to obtain emitters uded to decrease temperatures or to measure temperatures during thermal transfers.During the elaboration of selective emitters, we obtain on the surface of the materials a conversion film with an important dissolution of the substrate and a significant reduction of the materials thickness. We have here quantified both the emissivity increase and the absorptivity decrease versus the elaboration time of the conversion film. We have used the data obtained in the laboratory in recent years.     

Particle adhesion studies relevant to chemical mechanical polishing

This study describes particle adhesion experiments carried out to elucidate interactions between particles in slurries used for polishing of wafers and disks. For this purpose the packed column technique was employed, which simulated chemical mechanical polishing of copper with silica and alumina, as well as of silicic oxide with ceria. The model systems consisted of uniform copper and glass beads as collectors, representing the wafers, and colloidal dispersions of silica, alumia, and silica coated with nanosize ceria, all of well-defined properties that are used as abrasives. It was shown that a strong correlation exists between deposition and detachment results of the adhesion studies and the polish rates measured using actual substrates with the same or similar slurries.     

Reversed-phase thin-layer chromatography of the rare earth elements

Summary Partition chromatographic behaviour of the rare earth elements on C₁₈ bonded silica reversed-phase material has been investigated by thin-layer chromatography in methanol — lactate media. The rare earth lactato complexes are distributed and fractionated on bonded silica layers without ion-interaction reagents. The concentration and pH of lactate solution, methanol concentration and temperature have effects on the migration and resolution of the rare earth elements. The partition system is particularly suited to separate adjacent rare earths of middle atomic weight groups, allowing the separation of gadolinium, terbium, dysprosium, holmium, erbium and thulium to be achieved by development to 18 cm distance.     

Sedimentation and drying dissipative patterns of colloidal silica (560 nm in diameter) suspensions in a glass dish and a watch glass

The sedimentation and drying dissipative structural patterns formed during the course of drying colloidal silica spheres (CS550, 560 nm in diameter) in an aqueous suspension have been studied in a glass dish and a watch glass. Broad ring patterns were formed within 20 min in the suspension state by the convectional flow of the colloidal spheres and water. The sedimentary spheres always moved by the convectional flow of water, and the broad ring patterns became sharp with time. The sharpness of the broad rings was sensitive to the change in the room temperature and/or humidity. Colorful macroscopic structures were composed of the broad ring and wave-like patterns, and further colorful and beautiful microscopic fine patterns formed during the solidification processes based on the convectional and sedimentation structures. The drying patterns of the colloidal suspensions containing sodium chloride were different from the structures of CS550 or sodium chloride individuals, which support the synchronous cooperative interactions between the colloidal spheres and the salts.     

The microstructure of titanium-modified silica glass waveguides prepared by the sol-gel method

Waveguides were prepared by the sol-gel method at ambient temperature from titanium alkoxides and an organically modified silane using the chemically controlled condensation procedure. The structure was studied using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A biphasic structure containing (a) modified silica that may form micellar clusters and (b) titania clusters containing chelating acetate with dimensions in the nanometer range is proposed. The composite glass was doped by the pH indicator methyl red and the existence of two separate dye populations was demonstrated. This finding is attributed to dye molecules in separate phases. The optical and spectral properties of the glass are explained by its proposed structure.     

Untersuchungen zur bestimmung seltener erden durch atomabsorption mit elektrothermischer atomisierung

The determination of rare earths by atomic absorption spectrometry with electrothermal atomizationThe electrothermal atomization of traces of rare earths has been investigated with different atomizers (carbon rod, graphite furnace, tantalum ribbon). The best analytical results are obtained with a modified tantalum thermal atomizer, because the formation of rare earth carbides is then impossible. Mixed argon—hydrogen atmospheres improve the concentration of atoms in the plasma, because hydrogen reduces the rare earth oxide radicals. The optimal analytical conditions are described. The detection limits are: 25 pg Yb, 22 pg Eu, 62 pg Tm, 2000 pg Sm, 300 pg Ho, 300 pg Dy, 1300 pg Er.     

Stabilization of oil-in-water emulsions by colloidal particles modified with short amphiphiles

Emulsions stabilized through the adsorption of colloidal particles at the liquid-liquid interface have long been used and investigated in a number of different applications. The interfacial adsorption of particles can be induced by adjusting the particle wetting behavior in the liquid media. Here, we report a new approach to prepare stable oil-in-water emulsions by tailoring the wetting behavior of colloidal particles in water using short amphiphilic molecules. We illustrate the method using hydrophilic metal oxide particles initially dispersed in the aqueous phase. The wettability of such particles in water is reduced by an in situ surface hydrophobization that induces particle adsorption at oil-water interfaces. We evaluate the conditions required for particle adsorption at the liquid-liquid interface and discuss the effect of the emulsion initial composition on the final microstructure of oil-water mixtures containing high concentrations of alumina particles modified with short carboxylic acids. This new approach for emulsion preparation can be easily applied to a variety of other metal oxide particles.     

Effect of alumina nanofiller on the viscosity and electrical conductivity of glass-based seals for solid oxide fuel cells

Use of alumina nanofiller to strengthen the structure of the sealing glass used for solid oxide fuel cells (SOFCs) has been investigated by measurement of fracture strength, viscosity, and electrical conductivity at elevated temperatures. The electrical conductivity and viscosity of two glass-based seals for SOFCs were compared. Measurement of electrical conductivity and viscosity of the glass-based seals over the temperature range 400–600 °C showed that addition of 10 % nano-sized alumina powder to the sealing glass increased both the high-temperature electrical conductivity and viscosity of the sintered glass matrix. The higher conductivity and viscosity of glass composites containing alumina nanofiller were attributed to formation of bonds with bridging oxygen by partial dissolution of the alumina nanofiller in the sealing glass. Infrared spectroscopy and X-ray diffraction analysis were conducted to confirm this conclusion. Strengthening of the sealing glass structure to improve long-term durability may be possible by using glass composites containing alumina nanofiller.     

Anreicherung schwerer Yttererden aus Magnesiumnitrat-haltigen Lösungen durch basische Fällung mit MgO und fraktionierte Kristallisation der Nitrate in großem Maßstab

Summary Partial basic precipitation by magnesium oxide concentrates the heavy yttrium earths in the precipitate, while yttrium and the lighter earths remain in solution. On fractionating the above solutions by crystallisation of the nitrates, yttrium and the heavy yttrium earths concentrate in the solutions; this method seems better for the treatment of large quantities than the former one. From solutions containing 68.9 kg mixed yttrium earth oxides the heavy ones were concentrated to a great extent in 35.8 kg oxide.

     

Glass of the past: The degradation and deterioration of medieval glass artifacts

Medieval artifacts made of glass are at a serious disadvantage concerning the chemical stability compared with ancient or common modern glasses. The total amount of silica and other network formers such as alumina is very low and potassium instead of sodium was introduced into the silicate structure by using local raw material. By means of scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) a weathering mechanism governed by an ion exchange process could be determined for medieval glass paintings exposed to the ambient air for centuries. Additionally, the leached glass surface of medieval hollow glass artifacts found in a well and exposed to moist earth show a brown discoloring due to the oxidation of Mn(II) to Mn(IV) oxide. That process can be converted by a treatment of the glass objects in an aqueous hydrazine solution.     

Quantitative evaluation of thin-layer chromatograms

A commercially available scanning photometer, designed to scan paper electrophoresis strips, has been used to evaluate thinlayer chromatograms. The chromatogram may be lifted off the glass plate with cellophane tape which is then cut into strips and scanned, or the thin-layer chromatogram may be photographed and the photograph scanned. Newly developed cellulose-backed thin layers of silica or alumina may also be cut into strips and scanned. The instrument has also been modified to scan glass plates. A correction is applied for non-uniformity of the thin layer. Zones containing colourless components can be located by means of an auxiliary chromatogram, and the components present determined by carbon analysis.     

Adsorption of organic liquids on alkaline earth-metal modified silica

Summary Adsorption properties of alkaline earth-metal modified silica beads were investigated by the gas-solid chromatography (GSC) method. Silica beads, obtained from colloidal material, were characterized by their surface areas, crystallinity and amount of sorbed alkaline earth cations. Retentions of several aliphatic, alicyclic, chlorinated, and aromatic compounds were measured in the temperature range from 373 to 453 K.The gas/solid partition coefficients, K₅, and the related thermodynamic functions at zero surface coverage were determined. The results show that the specific surface areas of modified silica samples remain practically constant, whereas the modification leads to a decrease of silica surface heterogeneity.     

连铸结晶器喂稀土处理的碳锰钢夹杂物研究

为研究钢中添加稀土带来的夹杂物问题,采用金相夹杂物评级、电解夹杂分析以及电子探针和扫描电镜观察分析,对经稀土处理的微合金化碳锰钢夹杂物进行了研究.结果表明,采用铝脱氧和RH真空充分脱气的微合金化碳锰钢,经连铸结晶器喂稀土处理后,钢中的A,B,C,D类夹杂物分别不大于1.0级、1.5级、0.5级、1.5级,氧化物夹杂总量约为0.0030%.试验钢中主要形成球状稀土硫化物,同时还形成有链状"稀土硫化物包围氧化铝"的复合夹杂物,而稀土氧化物难以生成.     

飞秒激光改性玻璃微结构的化学腐蚀特性研究

采用飞秒激光改性-化学腐蚀的方法, 分别研究了3种典型玻璃的化学腐蚀性能. 通过测试材料的微观结构, 分析了不同材料的腐蚀速率与脉冲能量及腐蚀时间的关系, 从材料组成、显微结构及化学键特征讨论了玻璃改性-腐蚀机理. 结果表明, 飞秒激光改性后的碲酸盐和PbO硅酸盐玻璃不具有选择性腐蚀特性, 而石英玻璃的选择性腐蚀比高于40; 飞秒激光改性玻璃的选择性腐蚀特性与材料结构有关, 分子体积大、网络结构不紧密的材料不具有选择腐蚀特性.     

Materials doping through sol–gel chemistry: a little something can make a big difference

Several examples of sol–gel preparation of doped materials are taken to illustrate the various situations where the doping elements are responsible for the main function of the material or govern its structure. Other examples are used to illustrate that sometimes unexpected effects can be observed like structural modification and the appearance of new properties. Rare earth doped scintillators demonstrate higher homogeneity for materials prepared via sol–gel chemistry when compared with classical solid state reaction. The XRD study of rare earth doped orthoborates shows that doping can affect the vaterite to calcite phase transition observed in these compounds. A Raman spectroscopic study has been performed on doped silica xerogels and it has been shown that doping ions can modify greatly the densification process in these amorphous materials. Finally, it has been evidenced that sol–gel chemistry allows the preparation of bioactive ceramics with enhanced properties. In particular Zn-doped HAP with anti inflammatory properties has been prepared and Sr-doped bioactive glasses have demonstrated superior in-vitro bioactivity as evidenced by PIXE-RBS study.