Coprecipitation synthesis and sintering property of (YbxSm1-x)2Zr2O7 ceramic powders

Abstract

Abstract

(Yb_xSm_1-x)₂Zr₂O₇ (0<x<1·0) ceramic powders were synthesised with chemical coprecipitation and calcination method. Thermal decomposition behaviour of precipitates was studied by differential scanning calorimetry-thermogravimetry. The powders were characterised by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy. The synthesised powders have a particle size of about 100?nm, and exhibit to a certain extent agglomeration. The sintering behaviour of (Yb_xSm_1-x)₂Zr₂O₇ powders was studied by pressureless sintering method at 1550-1700°C for 10?h in air. The relative densities of (Yb_xSm_1-x)₂Zr₂O₇ ceramics increase with increasing sintering temperature, and reach above 95% when sintered at 1700°C for 10?h in air. Sm₂Zr₂O₇ and (Yb_0·1Sm_0·9)₂Zr₂O₇ ceramics have a pyrochlore structure; however, (Yb_xSm_1-x)₂Zr₂O₇ (0·3<x<1·0) ceramics exhibit a defective fluorite type structure.     

湿法制备超细锰锌铁氧体前驱粉工艺条件研究

以软锰矿，闪锌矿，硫铁矿为原料，经酸浸取对浸出液进行除杂，精制，采用碳铵共沉淀法制取锰锌铁氧体微粉，对工艺条件进行了研究，该工艺具有生产成本低，产品回收率高，节省能源等优点。     

模拟偶氮染料废水处理的共沉淀型催化剂研制

实验采用催化湿式氧化法对甲基橙模拟偶氮染料废水进行处理;催化剂的制备采用共沉淀方法,以 Cu、Fe 为催化剂活性组分,Ce 、La 为催化助剂,而制备多组分复合催化剂,研究了催化剂组分构成对催化剂性能的影响.实验中以催化剂的活性和稳定性综合对催化剂性能的评定,活性以水样的脱色率表示,而稳定性以原子吸收对组分的溶出浓度来表示.通过现代测试技术 FT-IR、XRD、原子吸收等的测定,对催化剂性能进行检测.实验结果表明,双组分催化剂 Cu1Fe1的性能优于单组分的 Cu 或 Fe 催化剂,而 Cu-Fe-Ce-La=1∶1∶1∶1的性能更优一步.     

沉淀法制备条件对氧化钛相变的影响

采用沉淀方法制备了纳米TiO2,探讨了制备过程中前驱体及溶剂对二氧化钛从锐钛矿到金红石相变的影响。结果表明:采用钛酸四丁酯(Ti(OBu)4)、异丙醇钛(TTIP)及钛酸四乙酯(Ti(OEt)4)为前驱体时,TiO2相变温度顺序为Ti(OBu)4>TTIP>Ti(OEt)4;不同溶剂制备的TiO2相变的温度不同,从锐钛矿转化为金红石晶相的温度由乙二醇<甲醇<乙醇方向增加。     

Comparison of Preparation Methods of Iron‐Based Catalysts for High‐Temperature Water‐Gas Shift Reaction

The influence of preparation methods on structural and catalytic properties of the Fe₂O₃‐Cr₂O₃‐CuO catalyst during the high‐temperature water‐gas shift reaction was determined. The prepared samples were characterized by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller method (BET), and temperature‐programmed reduction (TPR). The results revealed that the type of coprecipitation, i.e., simple, inverse, and differential, had a significant effect on both structural and catalytic properties. The catalyst prepared by the simple precipitation method exhibited higher activity than the catalysts generated by inverse and differential coprecipitation and the commercial catalyst. The types of precipitation agent and iron and chromium precursors were found to have a significant impact on the structural and catalytic features.     

Crystal structure and near-infrared reflective properties of Fe3+ doped AlPO4 pigments

Novel non-toxic orange yellow inorganic pigments Al_1−xFe_xPO₄(x=0.00, 0.03, 0.05, 0.08) with high near-infrared reflectance (NIR) have been synthesized by a coprecipitation method. The structures of samples were investigated by XRD and Raman spectroscopy, and the reflective properties were tested by UV–vis–NIR spectrophotometer. Results demonstrated that with more Fe³⁺ added, the color of the powder samples changed from white to orange yellow and the near-infrared reflectance decreased from 98.03% to 72.56%, which is higher than the commercial orange yellow pigment (61.99%). The near-infrared reflectance of corresponding coatings decreased from 69.35% to 59.10%, which is higher than the commercial coating with the similar color (51.88%). From the XRD diffraction spectrogram, we can see the peaks did not change with more Fe³⁺ added. However, because of ionic radius of Fe³⁺(0.63 Å) is a little larger than Al³⁺(0.53 Å), the cell volume increases a little when more Fe³⁺ is added. Furthermore, from the Raman spectrogram, we can see that doping with Fe³⁺, there is a new Raman peak which is assigned to the asymmetric [FeO₄] stretch. In addition, replacing Fe³⁺ for Al³⁺ in AlPO₄ caused the band gap decreased from 5.98eV to 3.60 eV, which can cause the absorption of more near-infrared radiation and that is the reason of the decrease of near-infrared reflectance.     

Investigation of Promoted Cu/ZnO/Al2O3 Methanol Steam Reforming Nanocatalysts by Full Factorial Design

A Cu/ZnO/Al₂O₃ nanocatalyst was applied for hydrogen production via steam reforming of methanol in a fixed‐bed reactor. Modified forms of the catalyst were prepared by adding small amounts of Ba, Zr, and Ce oxides. The catalysts were characterized by means of N₂ adsorption‐desorption, X‐ray diffraction, and scanning electron microscope techniques. Full factorial design was used to optimize the required number of experiments and evaluate the catalytic activity in a fixed‐bed reactor. The oxide additives reduced the production of carbon monoxide and increased the selectivity of carbon dioxide as well as the yield of hydrogen production. Among the studied catalysts, the Cu/ZnO/Al₂O₃/CeO₂/ZrO₂ catalyst presented the best performance.     

Effects of alumina incorporation in coprecipitated NiO–Al2O3 catalysts

The effect of Al₂O₃ levels on the properties of NiO in coprecipitated NiO–Al₂O₃ samples were investigated, using samples with up to 60.7 wt.% Al₂O₃ that had been calcined in the range 300–700°C. Characterization techniques included BET surface area of fresh and reduced catalysts, X-ray diffraction analysis of structure and crystallite size, magnetic susceptibility measurements, oxidizing power, and reducibility in H₂. Only NiO was detected in samples with up to 4.1 wt.% Al₂O₃ for all sample calcination temperatures. Surface areas were similar for all fresh samples but decreased rapidly after calcination at high temperatures. The surface area loss was less for the higher Al₂O₃-containing samples. Nickel oxide crystallite sizes increased at higher calcination temperatures, but remained approximately the same for each Al₂O₃ level.

The NiO was nonstoichiometric (NiO_1+x), with x decreasing at higher calcination temperatures and increasing with small amounts of added Al₂O₃ through a maximum at about 3 wt.% Al₂O₃. However, this did not correlate well with microstrain in the NiO crystallites nor with reducibility, which decreased with Al₂O₃ addition. At higher levels of Al₂O₃ (13.6 wt.% and above), surface areas increased with higher Al₂O₃ loadings, but NiO crystallite sizes remained approximately the same, independent of both Al₂O₃ content and calcination temperature. X-ray diffraction patterns were very diffuse, and it was not possible to rule out the presence of pseudo-spinel combinations of NiO and Al₂O₃. Reducibility was more difficult than with low Al₂O₃ levels, and nonstoichiometry was low and independent of Al₂O₃ content.

Reducibilities of all samples calcined at 300°C correlated well with the final BET surface area of the reduced samples, indicating that more dispersed NiO crystallites are more difficult to reduce, a conclusion that supports a model for reduction proposed previously.     

The Elimination of Channeling and Foam Overturning in Continuous Mode Adsorbing Colloid Flotation with a Sodium Dodecylsulfate/Dodecanoic Acid Mixture

Abstract

The effect of hydraulic loading, surfactant concentration, and air flow rate on the removal of Cr(III), Ni(II), and Zn(II) from chromium stream electroplating wastewater by adsorbing colloid flotation using a sodium dodecylsulfate/dodecanoic acid mixture was investigated. Typically, heavy metal concentrations of 81 ppm Cr(III), 55 ppm Ni(II), and 3.3 ppm Zn(II) were reduced to 1.2 ppm Cr(III), 3.2 ppm Ni(II), and 0.05 ppm Zn(II) at a hydraulic loading of 22.9 m³/m²·h (3 L·min^?1), an air flow rate of 45.8 m³/m²·h (6 L·min^?1), 40 ppm dodecanoic acid, and 80 ppm sodium dodecylsulfate, and using a 10-cm inner diameter column. A novel mode of operation (high liquid carryover) was used whereby a large proportion of the liquid entering the column leaves the column with the foam.     

Nearly full-dense and fine-grained AZO:Y ceramics sintered from the corresponding nanoparticles

ABSTRACT: Aluminum-doped zinc oxide ceramics with yttria doping (AZO:Y) ranging from 0 to 0.2 wt.% were fabricated by pressureless sintering yttria-modified nanoparticles in air at 1,300 [DEGREE SIGN]C. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, a physical property measurement system, and a densimeter were employed to characterize the precursor nanoparticles and the sintered AZO ceramics. It was shown that a small amount of yttria doping can remarkably retard the growth of the as-received precursor nanoparticles, further improve the microstructure, refine the grain size, and enhance the density for the sintered ceramic. Increasing the yttria doping to 0.2 wt.%, the AZO:Y nanoparticles synthetized by a coprecipitation process have a nearly sphere-shaped morphology and a mean particle diameter of 15.1 nm. Using the same amount of yttria, a fully dense AZO ceramic (99.98% of theoretical density) with a grain size of 2.2 mum and a bulk resistivity of 4.6 [MULTIPLICATION SIGN] 10[MINUS SIGN]3 [OHM SIGN][MIDDLE DOT]cm can be achieved. This kind of AZO:Y ceramic has a potential to be used as a high-quality sputtering target to deposit ZnO-based transparent conductive films with better optical and electrical properties.