Eutectic crystallization in the UO2–Al2O3–HfO2 ceramic phase diagram

In the frame of the Generation IV Sodium Fast Reactor (SFR) safety studies, a core catcher with a sacrificial material could be placed at the bottom of the nuclear reactor. Its role is to dilute the (U, Pu)O₂ molten fuel in case of a hypothetical core meltdown accident. A Al₂O₃–HfO₂ ceramic is a candidate for the sacrificial material. To understand how the molten fuel would mix with this sacrificial material, the UO₂–Al₂O₃–HfO₂ system was investigated at CEA Cadarache PLINIUS corium platform. The eutectic position of the UO₂–Al₂O₃–HfO₂ was determined: the eutectic temperature is 1728±22 °C (2001±22 K) and the eutectic composition is 30 wt% UO₂–35 wt% Al₂O₃–35 wt% HfO₂. Then, the pseudo-binary UO₂–(50 wt% Al₂O₃–50 wt% HfO₂) phase diagram has been proposed.     

Single-phase silicocarnotite synthesis in the subsystem Ca3(PO4)2–Ca2SiO4

In the last years, the addition of silicon to hydroxyapatite and tricalcium-phosphate materials is being widely studied, due to the well-known influence of silicon on bone formation. Silicocarnotite (Ca₅(PO₄)₂SiO₄) presents a structure type carnotite, very close to hydroxyapatite, with a wide range of Ca²⁺, SiO₄⁴⁻ and PO₄³⁻ solid solutions. These characteristics make silicocarnotite attractive as potential biomaterial.     

Ternary phase relations in CeO2–DyO1.5–ZrO2 system

The present work explores the sub-solidus phase relations in the CeO₂–DyO_1.5–ZrO₂ ternary system. About 80 compositions in Zr_1−xDy_xO_2−x/2, Ce_1−xDy_xO_2−x/2, (Ce_0.8Zr_0.2)_1−xDy_xO_2−x/2, Zr_1−x(Ce_0.2Dy_0.8)_xO_2−0.4x, Ce_x(Dy_0.5Zr_0.5)_1−xO_1.75+x/4 systems, were synthesized and explored to investigate the phase fields in this ternary system. Detailed XRD analysis showed the existence of a variety of phase fields viz. Fluorite-type cubic, C-type cubic, biphasic fields containing both F-type and C-type phases as well as co-existence of two different fluorite type phases. A few compositions also showed the presence of monoclinic as well the tetragonal phases. The trends observed in cell parameter are found to be governed by the competing factors of average ionic radius and the repulsion between excess anions in the lattice due to the aliovalent substitution. This ternary system showed the existence of a very wide cubic phase field. This ternary phase relation has relevance to the inert matrix fuel concept.     

Micro-crystallization of the infrared transmitting chalcogenide glass in GeSe2–As2Se3–PbSe system

Micro-crystallization of the chalcogenide glass 40GeSe₂–50As₂Se₃–10PbSe has been studied in order to obtain infrared transmitting glass ceramics. Differential scanning calorimetry, IR transmission spectroscopy, X-ray diffraction, scanning electronic microscopy and thermal dilatancy have been used for characterizing the crystallization process. Performing thermal treatment on the glass sample at 250 °C (40 °C higher than T_g) for 10 h, we obtained a glass ceramic containing well-dispersed micro-crystals (<50 nm) and the obviously decreased thermal expansion coefficient.     

The role of CeO2–ZrO2 as support in the ZnO–ZnCr2O4 catalysts for autothermal reforming of methanol

Autothermal reforming of methanol for hydrogen production was investigated over ZnO–ZnCr₂O₄ supported on a series of metal oxides (Al₂O₃, CeO₂, ZrO₂ and CeO₂–ZrO₂). CeO₂–ZrO₂ mixed oxides with Ce /Zr molar ratio of 4/1 was found to be the optimal support which showed significant effect on the catalytic activity and selectivity. The ZnO–ZnCr₂O₄/CeO₂–ZrO₂ and ZnO–ZnCr₂O₄ catalysts were characterized by XRD, TEM, H₂-TPR and XPS. The results show that CeO₂–ZrO₂ mixed oxides have significant effect on the catalytic performance and the supported catalyst shows more uniform temperature distribution in the catalyst bed which was mainly due to its reasonable redox properties.     

Dehydrogenation of propane in the presence of N2O over In2O3―Al2O3 mixed oxide catalysts

Dehydrogenation of propane coupled with N₂O over a series of binary In₂O₃―Al₂O₃ mixed oxides was investigated. In contrast to the poor performance for sole N₂O decomposition, a remarkable synergy was identified between N₂O decomposition and propane dehydrogenation. Among the catalysts tested, the In₂O₃―Al₂O₃ sample containing a 20 mol% In₂O₃ showed the highest activity for propane dehydrogenation in the presence of N₂O. Moreover, stability far superior to those of the conventional iron-based materials was observed, attributable to the moderate surface acidity of the In―Al―O composite. The essential role of N₂O is suggested to generate active oxygen species facilitating propane dehydrogenation.     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

Multiferroic ceramics in BaO–Y₂O₃–Fe₂O₃–Nb₂O₅ system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba₂YFeNb₄O₁₅, and minor phases of monoclinic YNbO₄ and hexagonal Ba₃Fe₂Nb₆O₂₁. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe³⁺ and Nb⁵⁺ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics.     

Phase stability and hot corrosion behavior of ZrO2–Ta2O5 compound in Na2SO4–V2O5 mixtures at elevated temperatures

For thermal barrier coating (TBC) applications, yttria stabilized zirconia (YSZ) is susceptible to hot corrosion. This paper examines the hot corrosion performance of ZrO₂/Ta₂O₅ compounds. Different compositions of ZrO₂–Ta₂O₅ samples in the presence of molten mixture of Na₂SO₄+V₂O₅ at 1100 °C were tested. The compositions were selected to form tetragonal and orthorhombic phases of zirconium-tantalum oxides. Results show that orthorhombic zirconium-tantalum oxide is more stable, both thermally and chemically in Na₂SO₄+V₂O₅ media at 1100 °C, and shows a better hot corrosion resistance than the tetragonal phase.     

Investigation of the effect of ZrO2 and ZrO2/Al2O3 additions on the hot-pressing and properties of equimolecular mixtures of α- and β-Si3N4

In this work, hot-pressing of equimolecular mixtures of α- and β-Si₃N₄ was performed with addition of different amounts of sintering additives selected in the ZrO₂–Al₂O₃ system. Phase composition and microstructure of the hot-pressed samples was investigated. Densification behavior, mechanical and thermal properties were studied and explained based on the microstructure and phase composition. The optimum mixture from the ZrO₂–Al₂O₃ system for hot-pressing of silicon nitride to give high density materials was determined. Near fully dense silicon nitride materials were obtained only with the additions of zirconia and alumina. The liquid phase formed in the zirconia and alumina mixtures is important for effective hot-pressing. Based on these results, we conclude that pure zirconia is not an effective sintering additive. Selected mechanical and thermal properties of these materials are also presented. Hot-pressed Si₃N₄ ceramics, using mixtures from of ZrO₂/Al₂O₃ as additives, gave fracture toughness, K_IC, in the range of 3.7–6.2 MPa m^1/2 and Vicker hardness values in the range of 6–12 GPa. These properties compare well with currently available high performance silicon nitride ceramics. We also report on interesting thermal expansion behavior of these materials including negative thermal expansion coefficients for a few compositions.     

Effect of MgO addition on the crystallization and in vitro bioactivity of glass ceramics in the CaO–MgO–SiO2–P2O5 system

CaO–MgO–SiO₂–P₂O₅ glass ceramics were successfully prepared by sintering the sol–gel-derived powders. The effects of MgO addition on the samples crystallization and structure were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, samples degradation and in vitro bioactivity assays were also evaluated. With more MgO addition, the glass ceramics crystallization kinetics under non-isothermal conditions changed from bulk crystallization to surface crystallization, and new crystal phases of Ca₂MgSi₂O₇ and SiO₂ were induced. In addition, it is observed that with increasing MgO concentration, the glass ceramics degradability gradually decreased and the formation of apatite was delayed.     

H2O2/Fe2(MoO4)3体系中H2O2吸附分解及NO氧化行为的DFT研究

为阐明H₂O₂/Fe₂(MoO₄)₃体系脱硝过程中H₂O₂吸附分解及NO氧化行为，基于DFT方法首次计算了H₂O₂和NO分子单独及二者同时在Fe₂(MoO₄)₃表面的吸附构型，并通过考察吸附能、Mulliken电荷及氧化路径等特性揭示H₂O₂催化分解和NO氧化的微观机制。结果表明：H₂O₂在Fe₂(MoO₄)₃表面易分解为活性自由基，而NO则以分子形式吸附；H₂O₂和NO共吸附时，H₂O₂优先吸附于催化剂表面并随后分解，NO则分别被H₂O₂分解产...     

Effect of the B2O3 addition on the sintering behavior and microwave dielectric properties of Ba3(VO4)2–Zn1.87SiO3.87 composite ceramics

The effect of the B₂O₃ addition on the low-temperature sintering, microstructure and microwave dielectric properties of the Ba₃(VO₄)₂–Zn_1.87SiO_3.87 composite ceramics was investigated. The results indicate that the addition of B₂O₃ can effectively promote the densification and further improve the microwave dielectric properties of the composite. The low-temperature sintering mechanism was ascribed to the formation of the liquid phase owing to the reaction between the additive B₂O₃ and the residual SiO₂ in the composite. B₂O₃–SiO₂ liquid phases can not only lower the sintering temperature, but also speed up the grain growth of the composite ceramics. The rapid grain growth occurs as the B₂O₃ content is more than 6 wt%. The 3 wt% B₂O₃ doped 0.5Ba₃(VO₄)₂–0.5Zn_1.87SiO_3.87 ceramics can be well sintered at 925 °C and exhibit excellent microwave dielectric properties of Q×f∼40,800 GHz, ε_r∼10 and τ_f∼0.5 ppm/°C.     

ICP-AES法测定矾土中Fe2O3、TiO2和SiO2

采用四硼酸锂熔融试样,电感耦合等离子体原子发射光谱法(ICP-AES法)测定矾土中Fe2 O3、TiO2和SiO2。通过对熔样方法选择、铝基体以及背景的研究,确定了分析条件。结果表明,该法具有良好的精密度和准确性,回收率在94%～108%。     

On the local structure of Cd3+ centers in (BaGeO3)1 ? x ? y (Al2O3) x (0.45CaF2 · 0.55MgF2) y glasses

A correlation between the ¹⁵⁵Gd M?ssbauer spectra of the GdAlO₃ and Gd₃Al₅O₁₂ compounds and Gd³⁺-doped glasses in the (BaGeO₃)_{1 − x − y} (Al₂O₃) _x (0.45CaF₂ · 0.55MgF₂) _y system is revealed. The conclusion is drawn that, in the structure of the glasses under investigation, trivalent gadolinium atoms form structural units characteristic of mixed gadolinium and aluminum oxides. Original Russian Text ? S.A. Nemov, A.V. Marchenko, P.P. Seregin, 2008, published in Fizika i Khimiya Stekla.     

纳米TiO2/SiO2复合食品抗菌材料

以水玻璃和Ti(SO4)2为原料,制备出了多孔的纳米TiO2/SiO2复合粒子,在后处理过程中,利用无机包覆剂溶解度随温度的变化,在复合粒子表面包覆了一层无机结晶膜,经热处理除去包覆剂后,得到了以单分散纳米复合粒子组成的复合微粉.对复合微粉进行比表面和孔容测试,并运用XRD和TEM进行了表征,发现TiO2以12.6nm的纳米晶粒的形式被多孔的SiO2包覆,所形成的复合粒子则约为20nm.为了了解复合微粒的灭菌效果,运用纳米TiO2和复合粉末对4种保健食品进行对照灭菌实验,两个月以后,测得含复合微粒的样品中的菌落总数为50～120个/g,是相应保健食品企业标准许可菌落数的0.25%～0.7%,为相应空白样和纳米TiO2粉样品菌落数的0.52%～0.97%和33.3%～83.3%.     

O1/A1/O2/A2工艺处理焦化废水试验研究

通过对短程硝化反硝化工艺的研究,开发了好氧/厌氧/好氧/缺氧(O1/A1/O2/A2)生物脱氮新工艺并用于焦化废水的处理。考察了NH4+-N、COD、TN对反应器运行效果影响。结果表明,当进水COD平均为3 012.9 mg/L,NH4+-N、TN、挥发酚、总氰平均质量浓度分别为590.5、608.4、361.8、34.5 mg/L;出水COD平均为81.7 mg/L,出水NH4+-N、TN、挥发酚、总氰的平均质量浓度分别为0.1、9.9、0.1、0.1 mg/L,出水指标达到国家污水综合排放一级标准,A/O工艺处理这种焦化废水TN偏高,而用O1/A1/O2/A2工艺可以解决这一问题,实现了TN脱除。考察了温度、DO、pH对短程硝化影响。结果表明,在DO质量浓度为1.0～1.5 mg/L、温度在30～35℃、pH 7.5～8.0,系统能够进行稳定短程硝化反硝化。     

MoS2/TiO2光催化降解甲基红

利用硫化钠与钼酸钠为原料,通过盐酸酸化,在TiO2上沉积MoS2纳米片。利用甲基红为降解对象,研究合成的片状纳米MoS2/TiO2复合物的光催化性能。结果显示该复合物具有优良的光催化降解甲基红的性能;催化剂用量、甲基红初始浓度与初始pH等条件对甲基红降解存在明显影响。该催化剂在重复使用3次时,甲基红2 h的脱色率接近65%,表明催化剂具有较好的重复使用性能。     

Porous SiO2–TiO2–ZrO2 Obtained from Polymeric Systems Prepared by the Sol–Gel Process

An experimental strategy was developed to obtain Si–Ti–Zr transparent sols via the sol-gel process. The chelating agents isoeugenol (2-methoxy-4-propenylphenol, isoH), salicylaldehyde (2-hydroxybenzaldehyde, salH), and itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately to stabilize monomeric Ti and Zr precursors, in order to control their chemical reactivity, avoiding precipitation. In all cases a prehydrolyzed tetraethyl orthosilicate (TEOS) sol was the Si source. The sols were polymerized at room temperature (293 K) to obtain gels and these were dried and calcined at 873 K in air. The radial distribution functions (RDF) of the gels were obtained at room temperature. The solids were studied by scanning electron microscopy (SEM). The porosity and surface area of solids were determined by N₂ adsorption. The surface area results obtained range between 83–198 m²/g. The average pore diameters are 1.44–1.61 nm.     

Determination of the eutectic solubility lines of the ternary system NaHCO3–Na2CO3–H2O

A crystallizer was built and a procedure developed to accurately measure the eutectic solubility lines where ice and salt coexist in equilibrium with the solution, for potential application of Eutectic Freeze Crystallization. The eutectic solubility lines of the ternary system NaHCO₃–Na₂CO₃–H₂O were determined experimentally and calculated with the extended UNIQUAC model. The extended UNIQUAC model describes the experimental data quite well. Anhydrous NaHCO₃ and Na₂CO₃·10H₂O were the only two types of crystals present in equilibrium with ice crystals in the ternary system. At the quadruple point NaHCO₃ and Na₂CO₃·10H₂O are in equilibrium with a solution of about 4.34 wt% of Na₂CO₃ and 4.77 wt% of NaHCO₃ at −3.32 °C. The anhydrous NaHCO₃ crystals were needle shaped with lengths between 5 and 10 μm, that were agglomerated into particles of about 100–300 μm, while the Na₂CO₃·10H₂O crystals were hexagonally shaped with sizes between 100 and 500 μm.