Sintering of Ceria-Doped Tetragonal Zirconia Crystallized in Organic Solvents, Water, and Air

Amorphous CeO₂–ZrO₂ gels were prepared by coprecipitation in ammonia solutions. The onset of crystallization of the gels, from calcining in air, was 420°C, while 200° to 250°C in the presence of water and organic solvents such as methanol and ethanol. The sintering behaviors of CeO₂–ZrO₂ powders were sensitive to the crystallizing conditions, since hard agglomerates formed when the precipitated gels were crystallized by normal calcination in air, whereas soft agglomerates formed when they were crystallized in water or organic solvents. CeO₂–ZrO₂ powders crystallized in methanol and water at 250°C were sintered to full theoretical density at 1150° and 1400°C, respectively, whereas that crystallized by calcination in air at 450°C was sintered to only 95.2% of theoretical density, even at 1500°C.     

Activation of Ground Blast-Furnace Slag by Alkali-Metal and Alkaline-Earth Hydroxides

The effects of pH, time, valence, and radius of the activator cation on the reaction products and microstructure of ground granulated iron blast-furnace slag were studied by thermogravimetry and derivative thermogravimetry, X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray microanalysis. Blast-furnace slag was activated by alkali-metal hydroxides of Li, Na, and K (12.34 pH 14.71) and alkaline-earth hydroxides of Ca, Sr, and Ba(12.47 pH 13.53) using a water/slag ratio of 0.4 and curing for 1 day to 26 months. Reactivity of the slag was more strongly dependent on pH than on time. The reaction products were mainly varieties of C─S─H, (C,M)₄AH₁₃, and minor amounts of Ca(OH)₂ and C₂ASH₈ (strätlingite). The nature of C─S─H was dependent on pH. A 1.2-nm peak appeared in X-ray diffractograms only when the activation pH was ⌣14.7. Water was present in the C─S─H in a way similar to water in tobermorite and synthetic C─S─H. Leached Ca from unreacted blast-furnace slag was present around the glass particles as an amorphous layer which crystallized into Ca(OH)₂ with time; Mg behaved similarly. The effect of the charge or ionic radius of the activator cation was insignificant.     

Hydrothermal synthesis of nickel ferrite powders,their properties and sintering

NiFe₂O₄ powders were synthesized by co-precipitation with ammonia solution using aqueous solution of NiCl₂ and FeCl₃ followed by hydrothermal treatment of the precipitate. It was found that crystallization in water led to nanometric in size and isometric in shape crystallites, whereas crystallization in sodium hydroxide solution results in particles of well defined walls. Generally, particles crystallized in water were smaller and their particle size distribution was narrower than those crystallized in NaOH solution. Behaviour of the powders under dry compaction and sintering strongly depended on the powder morphology. The powder crystallized in NaOH solution gave compacts of higher density and sintered density of this powder was also higher than that of the powder processed in water.     

Characterization of Nickel Ions in Nickel‐Doped Yttria‐Stabilized Zirconia

The distribution of Ni²⁺ ions in NiO‐doped 10YSZ powder is examined with Superconducting Quantum Interference Device magnetometry, a technique that is able to distinguish between randomly distributed Ni²⁺ ions in solid solution and ordered Ni²⁺ ions within NiO with high precision. Very high purity powders containing 0.01, 0.1, 0.5, and 1.0 mol% NiO in 10YSZ (all levels below the solid solubility limit of NiO in 10YSZ) were made from acetate precursors and a modified EDTA (ethylenediaminetetraacetic acid)‐citrate synthesis method. The powders were calcined in air at either 873 or 1273 K. The 873 K calcination leads to single phase YSZ particles about 10 nm in diameter, and almost all of the NiO dopant exists in complete solid solution. The 1273 K calcination leads to a larger YSZ particle size (55–95 nm), and also to the formation and/or growth of NiO particles, the amount of which depends on the length of time of calcination. Upon sintering the powders in air (1773 K, 1 h), the NiO dissolves back into 10YSZ. The results demonstrate that particle growth during calcination leads to the exsolution of Ni²⁺ ions to form NiO. This has important implications for the synthesis of NiO‐doped 10YSZ from chemical precursors.     

沉淀法制备纳米CuO及微结构控制

以Cu(NO3)2为铜源，分别用水，乙醇作为分散剂，NaOH,NaOH-Na2CO3作沉淀剂，采用液相沉淀法制备了CuO纳米晶粒，并用XRD，TEM等测试手段对产物的结构，晶粒大小和形貌等进行了表征，结果表明，产物的微结构与焙烧温度，分散剂和沉淀剂的种类有关。以水为分散剂，产物的形态是分散性良好的纺锤型，而以乙醇为分散剂，产物的形态是分散性较好的球型，同NaOH作沉淀上比，共沉淀法制备了产物粒径较小，但团聚较严重，此外，初步研究了不同微结构纳米CuO对氯酸铵（AP）的催化活性。     

Preparation of Spherical Yttria-Stabilized Zirconia Powders by Reactive-Spray Atomization

A new inorganic sol–gel process of zirconia (yttri-stabilized) spherical powders production has been developed. The process is based on spraying zirconia sol into an ammoniawater solution, followed by drying of the gel precipitate and calcination. The gel particles preserve the spherical shape of sprayed droplets, because of a thin solid film that forms on the drop surface via its contact with gaseous ammonia before the impact with the ammonia solution. Being dried and calcined, the gel spheres transform to free–flowing powders composed of the solid, not hollow smooth spheres of zirconia–yttria solid solutions. The particle composition, morphology, and microstructure have been investigated in detail versus the process conditions.     

柠檬酸盐法制备Na0.5Bi0.5TiO3陶瓷粉体的工艺研究

本实验采用柠檬酸盐法制备（NaBi）0.5TiO3无铅压电陶瓷粉体,系统研究了柠檬酸浓度、溶液pH值、煅烧温度等工艺条件对制备的影响。经研究分析,当柠檬酸浓度C=9%,溶液pH=7.5时,能形成透明、均匀、稳定的溶胶,且形成时间最短;650℃下煅烧2h能够合成单一的钙钛矿结构的钛酸铋钠晶相,比传统固相反应法煅烧温度降低了200℃。     

Carbon-supported Ru catalyst with lithium promoter for ammonia synthesis

The electronegativity of Li is much higher than that of Na or K, but the ammonia synthesis activities of Li-promoted Ru/AC catalysts were comparable to the values of Ru catalyst promoted with K, which were much higher than those over Ru catalyst with Na promoter. The presence of Li increased the catalytic activity by changing the chemisorption properties such as hydrogen adsorption and nitrogen adsorption for carbon-supported Ru catalysts, rather than affecting the sizes of Ru particles or the electron density of Ru metal.     

Emulsion Precipitation of Yttria-Stabilized Zirconia for Plasma Spray Coatings

Chemically uniform, high-purity, yttria-stabilized zirconia (YSZ) powders were prepared by emulsion hydrolysis of the metal alkoxides, acetates, and mixtures of alkoxides and acetates. Both the morphology and particle size of the powders can be controlled by varying the hydrolysis conditions. Spherical or granular powders with particle sizes ranging from submicrometer to a few hundred micrometers were obtained. X-ray diffraction and EDX results showed that yttria was evenly distributed throughout the zirconia particles. The crystalline phase of the powders after calcination at 800°C was 100% nontransformable tetragonal. The powders were successfully sprayed by a plasma coating technique on stainless steel coupons, and the coatings were evaluated.     

Low-Temperature Hydrothermal Synthesis of Yttrium-Doped Zirconia Powders

The feasibility of low-temperature synthesis of yttrium-doped zirconia (Y-ZrO₂) crystalline powders in aqueous solutions at lessthan equal to100°C has been evaluated, and the hydrothermal crystallization mechanism for Y-ZrO₂ powders also has been investigated. Coprecipitated (Y,Zr) hydroxide gel, mechanical mixtures of Y(OH)₃ and Zr(OH)₄ gel, and Y(OH)₃ gel have been reacted in boiling alkaline solutions. Coprecipitated (Y,Zr) hydroxide gel crystallized to cubic or tetragonal Y-ZrO₂ at pH 13.9. The yttrium content in the powder synthesized from coprecipitated (Y,Zr) hydroxide is consistent with the initial precursor solution composition, as expected from the similarity in solubility of Zr(OH)^-₅ and Y(OH)^-₄. A diffusionless mechanism for the transformation of the (Y,Zr) hydroxide gel to Y-ZrO₂ is proposed, and the phase stability in aqueous solution is discussed in terms of an in situ crystallization model. It is also demonstrated through thermodynamic arguments with experimental verification that the stable form of the Y-ZrO₂ at 25°C is the anhydrous phase, not the metal hydroxide as previously thought.     

Zirconia Gels in Concentrated NaOH

The sol-gel process was used to produce zirconia powders that were pressed into compacts. The powders were synthesized from zirconium n-propoxide, diluted in propanol, and hydrolyzed with molar ratios of water either l-to-l or lo-to-l. Zirconia compacts produced in this manner were soaked in 1N NaOH to simulate a membrane cleaning process, and their weight loss was recorded. Zirconia samples with a higher weight fraction of tetragonal phase exhibited less weight loss than samples with more monoclinic phase. The weight fraction of the tetragonal phase was controlled by synthesis conditions and tiring temperature.     

Control of the Microstructure of Alumina–Zirconia Alloys Starting from Inorganic Salts

Coprecipitated powders of alumina—zirconia, prepared from inorganic salts, crystallized differently than either of the constituents by themselves. Whereas alumina or zirconia, prepared in a similar way, began to crystallize at 370°C, the crystallization of the alloy was delayed until 800°C. When hot-pressed under 40 MPa at 1400°C, the coprecipitated powders developed crystallographic texture in the α-alumina phase. Preferred crystal growth under a uniaxial stress is offered as a possible explanation for the crystallographic texture.     

Electrokinetic Properties of Colloidal Zirconia Powders in Aqueous Suspension

Pure zirconia, yttria, and three yttria-doped zirconia powders of submicrometer size have been dispersed in various aqueous solutions. The zeta potential (zeta) of the zirconia powders is determined primarily via streaming-current (SC) detection and is confirmed using electrophoretic spectroscopy techniques. The results reveal that the isoelectric point (IEP) of these zirconia powders is in the pH range of 5.6-7.2 and zeta is controlled primarily by the yttrium content of the zirconia powders and the type of electrolyte. In addition, the yttria content strongly affects the potential and SC in zirconia suspensions only at high solids contents (>1 vol%). The electrokinetic data reveal that the surface of the yttria-doped tetragonal zirconia powder (TZP) can be modified via the adsorption of ionic molecules or polymeric species in the suspension. The adsorption of an anionic polymer can stabilize zirconia particles in a solution that is almost neutral or weakly basic (in the IEP range of pure ZrO₂). The interaction of the zirconia and yttria particles with the electrolytes in an aqueous suspension will be discussed to reveal the roles of hydrated oxide formation and zirconia surface interaction with polymeric dispersants.     

Promoting effects of alkaline cations on the Pd/Y catalyzed methylcyclopentane conversion

The conversion of methylcyclopentane over Pd/MY zeolites has been studied with catalysts containing Li, Na or K as charge compensating ions M. It is found that in the sequence M = Li, Na, K the activity for ring opening increases, while that for ring enlargement decreases and the benzene/cyclohexane ratio in the ring enlargement product increases. It is proposed that in the sequence M = Li, Na, K the acid strength of zeolite protons is lowered while electron transfer from donor sites to palladium clusters increases from Li to K.     

溶胶–凝胶法制备(Na0.50+xK0.50-2xLix)Nb0.9Ta0.1O3无铅压电陶瓷及其性能

采用溶胶–凝胶法制备Li+取代(K0.5Na0.5)+及Ta5+取代Nb5+的(K0.5Na0.5)NbO3陶瓷粉体,采用无压烧结工艺制备(Na0.50+xK0.50–2xLix)Nb0.9Ta0.1O3(x=0,0.02,0.04)陶瓷样品。研究了前驱体煅烧温度对陶瓷粉体物相组成的影响。分析了不同Li+掺杂量对样品物相组成、微观结构、体积密度及电学性能的影响。结果表明:前驱体的最佳煅烧温度为600℃,通过透射电子显微镜分析陶瓷粉体的粒径为49 nm;不同Li+掺杂量制备的(Na0.50+xK0.50–2xLix)Nb0.9Ta0.1O3陶瓷样品均为正交相钙钛矿结构;随着Li+掺杂量的增加,(Na0.50+xK0.50–2xLix)Nb0.9Ta0.1O3陶瓷的体积密度先增大后减小,介电常数逐渐升高,压电常数先降低再升高,剩余极化强度逐渐升高。Li+掺杂量x为0.04时样品的压电常数(d33=94 pC/N)、相对介电常数(εr=684.33)及剩余极化强度(Pr=98.27μC/cm2)较好。     

Preparation and stabilization of high specific area zirconia carriers

Zirconia samples have been prepared by precipitation from an aqueous solution of zirconyl nitrate followed by calcination in flowing air at temperatures up to 970 K. The textural properties (S_BET and pore size distribution) of these zirconia powders were very sensitive to the activation procedure. Calcination in carefully controlled conditions at 770 K yielded crystallized zirconia with surface area (S_BET ≈ 130 m² g⁻¹) and porosity suitable for use as a catalyst carrier.

Zirconia samples doped with yttrium, nickel or aluminium were obtained by impregnation of the amorphous hydrous oxide. For solids calcined at 770–970 K, the surface area and thermal stability were improved, but the porosity was lower.     

Sol—Gel Synthesis of Strontium-Doped Lanthanum Manganite

Strontium-doped lanthanum manganite powders were prepared using a peroxide acetate salt based solution. The stable sol was peptized by reacting ammonium hydroxide with the precursor solution. The amorphous dried gel powders exhibit a high energy level, due to their high cations coordination and small particles, to develop the perovskite phase. This crystalline phase development from powders containing monocarboxylate ligands was characterized by thermal analysis (TG, DTG, DTA), X-ray diffraction, and IR spectroscopy. The transformation from amorphous powders into a crystallized homogeneous oxycarbonate phase in a first stage corresponds to an exothermal DTA peak at 270°C. X-ray diffraction patterns and IR spectra showed similar behavior of the powders after complete organic removal, during the conversion into perovskite phase starting at approximately 630°C and achieved about 700°C and achieved about 700°C, as well as during the sintering process.     

过量Na~+对(K_(0.5)Na_(0.5))NbO_3-LiNbO_3无铅压电陶瓷相组成及结构的影响

通过固相反应法预合成0.94(K0.5Na0.5)NbO3-0.06LiNbO3(KNLN6)无铅压电陶瓷粉体。采用X线衍射仪(XRD)、扫描电子显微镜/能谱仪(SEM/EDS)和高分辨透射电子显微镜(HRTEM)对KNLN6试样进行性能表征。结果表明:按化学计量配比合成的KNLN6粉体中含有K3Li2Nb5O15(KLN)第二相;Na2CO3摩尔分数过量5%时,可有效地消除第二相KLN,从而获得单一钙钛矿结构的KNLN6粉体,同时,粉体的预烧温度降低了50℃;在1070℃下烧结2 h制备的Na2CO3过量5%的无铅压电陶瓷中,KNLN6晶体具有A位无序的单一正交钙钛矿结构,晶粒呈立方体状,平均尺寸约为10μm。     

Formation of Acicular Monoclinic Zirconia Particles under Hydrothermal Conditions

Acicular monoclinic ZrO₂, particles were prepared by hydrothermal treatmentat 250°C using sulfuric acid solutions containing zirconium ions. The formation process and morphology of the ZrO₂, particles were investigated. Two types of acicular monoclinic Zr0₂, particle morphologies were obtained, both elongated in the 〈001〉 direction, and the range of acicular ZrO₂, particle sizes changedfrom 0.3 to 1.3 μ m with hydrothermal conditions. Addition of MgSO₄, to the starting solution promoted the crystallization of the monoclinic ZrO₂, particles.     

Low-Temperature Purification of Silicon by Dissolution and Solution Growth in Sodium Solvent

Efficient low-cost processes for solar-grade Si production are needed to overcome the deficiency in the supply of Si. We have demonstrated a new method for the purification of Si crystal. Low-purity Si powder was dissolved in a Na melt (solvent), and Si grains were crystallized by Na evaporation from the Na-Si solution at 1173 K. Glow discharge mass spectrometry analysis revealed that the concentrations of impurity elements, except Na and B, were decreased in the crystallized Si grain. In particular, the concentration of Fe which was mainly included in the Si powder decreased from 3200 ppm by mass to 1.5 ppm by mass in a refined Si grain. Iron disilicide was crystallized from the solution before the crystallization of Si. It was suggested that impurities were reduced not only by crystallization from the Na-Si melt but also by the dissolution of Si into the melt. Na contaminating the refined Si grain was eliminated down to 0.055 mass ppm by heating at 1723 K under vacuum.