Some properties of sintered ceria ceramics

Conclusions Sintering of finely dispersed ceria occurs intensely in the 1300–1500°C range.In an atmosphere of inert gas and in vacuum the sintered CeO₂ is reduced with changes in crystal structure, which is accompanied by a reduction in the refractory and thermomechanical properties of the material.Unreduced CeO₂ is a highly refractory material which in oxidizing conditions can be used at temperature above 1900°C.     

Effect of variation of NiO on properties of NiO/GDC (gadolinium doped ceria) nano-composites

In the present work, systematic study of series of NiO_x GDC_(1?x) where x = 0.1–0.6; has been reported for the first time. For the synthesis of homogeneous NiO–GDC nanocomposite powders, the nano-powders of NiO and Ce_0.9Gd_0.1O_1.95 (GDC10) synthesized by solution combustion synthesis were mixed in mol % proportion. NiO–GDC nanocomposite can be reduced in situ to form Ni–GDC cermet anode. Hence the Ni–GDC cermet anode combines the catalytic activity and high electronic conduction property of Ni and ionic conductivity of GDC. Nano-crystalline constituents in the NiO–GDC nano composite are believed to give better anodic performance than microcrystalline constituents. Hence the efficient study of the atomistic structure and the accurate characterization of the structural parameters, such as crystallite size and internal strains, are of considerable interest. Therefore the NiO_x–GDC10_1?x nanocomposite powders were characterized by XRD and FTIR spectroscopy. Further these powders were pelletized, sintered and characterized by FE-SEM and d.c. conductivity.     

Far infrared properties of sintered NiO

Far infrared reflection spectra of NiO polycrystals sintered at 1100 °C for various times (30–240 min) were measured at room temperature using a FTIR Spectrometer—Brucker 113V. The measured spectra depended on the sintering time due to differences in the microstructural morphology of the material and were compared with the NiO single crystal reflectivity diagram. Numerical analyses of the experimental spectra were performed using Kramers-Kronig analysis, a four-parameter model of coupled oscillators and the effective medium modeling theory. In the three-component effective medium model based on Bruggeman's theory we assumed the presence of pores, intergranular material and crystalline grains. The intergranular material and crystalline grains were defined as single and coupled ionic oscillators.     

硫酸渣对水泥性能的影响

研究了河北辛集、广西柳州的硫酸渣对水泥性能的影响。结果表明，硫酸渣对水泥性能的影响与一般火山灰质材料基本一致，不同的是硫酸渣具有改善水泥的体积安定性、提高耐硫酸盐侵蚀和后期强度增进率小的特点。     

Effect of borate addition on the sintered properties of pulverised fuel ash

The effect of borate addition on the properties of sintered pulverised fuel ash (PFA) has been investigated. PFA from a major coal-fired power station in the UK has been formed into monolithic ceramic samples using dry powder compaction and sintering. Borax pentahydrate (Na₂B₄O₇·5H₂O), anhydrous borax (Na₂B₄O₇) and boric acid (H₃BO₃) were individually added to the PFA and the effects of firing between 1000 and 1200 °C have been investigated. Physical properties (density, water absorption and linear shrinkage), mechanical properties (bending strength and Vickers hardness), phase composition (X-ray diffraction) and sintered microstructure (scanning electron microscopy) are reported. Milling PFA containing 8% (by weight) of borax pentahydrate, to an average particle size of 7.25 μm and sintering at 1130 °C for 1 h, produces ceramics with properties comparable to those of commercial unglazed ceramic wall and floor tiles. The results indicate that PFA could be used to produce commercial ceramics using an economic manufacturing process, although current formulations display excessive shrinkage.     

镁砂细粉含量对铝镁质浇注料性能的影响

研究了镁砂细粉含量对MgO -SiO2 -H2 O系结合的矾土基铝镁浇注料的流动性、常温物理性能及抗渣性的影响。结果表明 :随镁砂细粉含量的增加 ,浇注料烘后强度增加 ,但过多的镁砂细粉又使强度下降 ;随镁砂细粉含量的增加 ,浇注料的抗渣性逐渐恶化 ,特别是抗渣渗透性下降严重。     

镁砂粉加入量对RH浸渍管浇注料性能的影响

以烧结刚玉为主要原料 ,同时加入镁砂粉、铝酸钙水泥、α Al2 O3微粉等 ,研究了镁砂粉加入量对RH浸渍管用刚玉质浇注料的抗热震性、抗渣性和热膨胀性的影响。结果表明 ,在刚玉质浇注料中加入适量的镁砂粉 ,高温下可以形成镁铝尖晶石 ,这是提高浇注料的热震稳定性和抗渣侵蚀性的主要原因。镁砂粉的加入量为 6 %时 ,RH管浇注料的上述性能良好     

Al粉加入量对树脂结合MgO-CaO材料性能的影响

以烧结镁钙砂、电熔镁砂和铝粉为原料,热塑性无水树脂为结合剂,混练后在180 MPa压力下成型,经200℃12 h烘烤后,制备了树脂结合MgO-CaO材料试样,并研究了Al粉加入量(质量分数分别为0、2%、4%、6%)对试样的常温物理性能、高温抗折强度和抗热震性的影响及其与物相组成和显微结构的关系。结果表明:加入Al粉后,试样的高温抗折强度(1400℃)显著提高,从未加Al粉时的5.6 MPa提高到17.7~31.6 MPa;抗热震性保持较好的水平,1100℃风冷3次后的抗折强度保持率为66%~88%。这类材料具有良好高温力学性能的原因为:试样中Al粉在埋焦炭加热过程中与C和N2反应,原位生成的AlN和Al4C3填充、穿插在方镁石或方钙石结构中,起到增强、增韧的作用,提高了材料的高温力学性能。     

Effect of Si addition on the mechanical and thermal properties of sintered reaction bonded silicon nitride

Advanced silicon nitride (Si₃N₄) ceramics were fabricated using a mixture of Si₃N₄ and silicon (Si) powders via conventional processing and sintering method. These Si₃N₄ ceramics with sintering additives of ZrO₂ + Gd₂O₃ + MgO were sintered at 1800 °C and 0.1 MPa in N₂ atmosphere for 2 h. The effects of added Si content on density, phases, microstructure, flexural strength, and thermal conductivity of the sintered Si₃N₄ samples were investigated in this study. The results showed that with the increase of Si content added, the density of the samples decreased from 3.39 g/cm³ to 2.92 g/cm³ except for the sample without initial Si₃N₄ powder addition, while the thermal diffusivity of the samples decreased slightly. This study suggested that addition of Si powder, which varied from 0 to 100%, in the starting materials might provide a promising route to fabricate cost-effective Si₃N₄ ceramics with a good combination of mechanical and thermal properties.     

Effects of carbonyl nickel powder addition on the mechanical properties,microstructure, and yttrium segregation of sintered 3YSZ composites

In this study, the effects of the addition of carbonyl nickel powder on the density, microstructure, and mechanical properties of sintered yttria-stabilized zirconia (3YSZ) were investigated. Sintering at 1300 °C resulted in the optimum comprehensive mechanical properties. The addition of 5 vol% carbonyl Ni increased the fracture toughness and flexural strength from 9.51 MPa m^1/2 to 14.5 MPa m^1/2 and from 747 MPa to 873 MPa, respectively. The addition of carbonyl nickel showed greater improvement than did the addition of spherical Ni powder. The dendritic morphology improved the interface bonding between the ceramic and the metal, enabling a bridging mechanism of the ductile phase. However, further Ni addition decreased the mechanical properties. X-ray diffraction results showed that the amounts of the monoclinic phase (M) and cubic phase (C) of 3YSZ increased, whereas the amount of the tetragonal phase (T) decreased. The Y segregation near the Ni particles, which was confirmed by an energy dispersive spectrometer (EDS), caused the phase changes. The segregation of Y occurred during the cooling stage, rather than the holding stage, of sintering. During the cooling stage, the heat mismatch between Ni and ZrO₂ resulted in strong elastic strain energy, which promoted Y segregation.     

Effect of precursor characteristics on zirconia and ceria particle morphology in spray pyrolysis

Ultrasonic spray pyrolysis of acetate-based precursors with precisely measured precursor drop size was employed to produce ZrO₂ and CeO₂ particles. A bimodal size distribution of the product particles indicates a significant influence of the gas-to-particle conversion mechanism in addition to the conventionally accepted one-particle-per-drop mechanism. Due to the differences in solubility of the precursors, ZrO₂ particles are spherical in shape and smooth on their surfaces while the CeO₂ particles are bowl-like in shape with uneven surfaces. Spherical and monodispersed particles with a peak diameter <100 nm can be obtained by reducing the precursor concentrations to 0.01 wt.% in both the different precursor system.     

Physical and chemical properties of powder produced from spray drying of inulin component extracted from Jerusalem artichoke tuber powder

In this study, inulin was extracted from Jerusalem artichoke tuber (JAT) powder and then concentrated before spray drying. The aims of this study were to (1) determine the drying condition that provided high powder yield together with superior qualities of JAT inulin powder and (2) investigate the chemical and physical properties of inulin powder. The inulin extracts at different concentrations of 10, 20, and 30 °Brix were spray-dried and then compared. The spray drying experiments were conducted at the inlet/outlet air temperatures of 150/90, 170/90, and 190/90?°C for the chosen concentration of inulin extract. It appeared that spray drying of the 30 °Brix extract at the inlet/outlet drying air temperatures of 190/90?°C resulted in the highest value of powder recovery, bulk density, water solubility and the lowest moisture content and hygroscopicity in comparison with its counterparts. SEM micrographs showed that the powder produced by this condition was more stable and less sticky than others. The sugars, total fructo-oligosaccharides (1-kestose, nystose, and 1^F-β-fructofuranosyl nystose) and inulin-type fructans contents of powder were 12.88, 11.12, and 64.36?g/100?g of powder, respectively. The moisture sorption data and models developed in this work could be used for determining the suitable condition of surrounding air for inulin powder storage.     

Effect of liquid addition on the bulk and flow properties of fine and coarse glass beads

The effect of water on the packing and flow properties of fine and coarse particles was experimentally investigated. Four different particle sizes of glass beads, from 5 to 275 μm, were studied with increasing water weight‐percentages. Using a FT4 Powder Rheometer, changes in bulk properties were collected as a function of water content and particle size. The results show that water content plays a significant role on the packing and flow of the particles. Small amounts of water created porous aggregates due to liquid bridging. Greater amounts of water resulted in the filling of the void‐spaces. This was indicated by an increase in basic flow energy, density, and pressure drop, with a decrease in porosity. A greater understanding of bulk properties of wetted material is useful to develop standard systems that can be used to examine the behavior of more complex situations, and implement changes to improve materials handling and processing. © 2015 American Institute of Chemical Engineers AIChE J, 62: 648–658, 2016     

Effects of annealing on the structural and magnetic properties of flame spray pyrolyzed MnFe2O4 nanoparticles

In this study, manganese ferrite (MnFe₂O₄) nanoparticles were produced through flame spray pyrolysis (FSP). To investigate the effects of heat treatment, the nanoparticles were annealed between 400 and 650°C for 4 h in air in a comparative manner. The structural, chemical, morphological, and magnetic properties of the nanoparticles were evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), dynamic light scattering (DLS), and vibrating sample magnetometry (VSM), respectively. The XRD results showed that the nanoparticles synthesized by the FSP method exhibited the MnFe₂O₄ spinel ferrite structure. The annealing process led to the decomposition of MnFe₂O₄ into various phases. According to the morphological analysis, the as-synthesized particles were hemispherical–cubic in shape and had an average particle size of less than 100 nm. In addition, the chemical bond structures of the nanoparticles were confirmed in detail by XPS elemental analysis. The highest saturation magnetization was recorded as 33.50 emu/g for the as-produced nanoparticles. The saturation magnetization of the nanoparticles decreased with increasing annealing temperature, while coercivity increased.     

Synergistic effect of La+Mo addition and optimum pH on the photocatalytic dye decomposition efficiency of spray pyrolyzed ZnO thin films

This work explores the photocatalytic degradation efficiency of lanthanum (La) and molybdenum (Mo) incorporated ZnO films deposited by nebulizer spray pyrolysis onto glass slides. The influence of La and (La + Mo) doping on certain physical properties was investigated. Photocatalytic behavior of the films was studied against methyl orange (MO) and methylene blue (MB) dyes. The impacts of dye adsorption, point of zero charge, and dye solution pH on the catalytic activity of ZnO:La:Mo films were probed and compared with those of their counterparts ZnO and ZnO:La thin films. The obtained results demonstrated that ZnO:La:Mo photocatalyst exhibited greater efficiency, reaching 98% and 85% degradation after 60 min for the cationic and anionic dyes, respectively for optimum pH. The degradation reactions follow the first-order kinetics and the rate of degradation increases by adding La and (La + Mo) to ZnO. The ZnO:La:Mo thin film exhibits excellent recyclability and stability even after five runs. A possible photocatalytic mechanism has also been proposed.     

Effect of divalent cation addition on structure,conductivity and grain boundary properties in La doped ceria oxygen ion conductors

The aim of this work is to investigate the effect of divalent cations on the structure and electrical properties of Ce_0.85La_0.1D_0.05O_2-δ (D = Ca, Sr and Ba) oxygen ion conductors. The X-Ray structural analysis confirms the presence of CeDO₃ minor phase in addition to cubic fluorite phase of ceria in Sr²⁺ and Ba²⁺ added compositions. The lattice parameter of the compositions significantly depends on the ionic radius of dopants and the presence of D²⁺ ions in ceria lattice. The Ca²⁺ added composition shows the highest free oxygen vacancy concentration due to its lowest association energy and complete dissolution of Ca²⁺ ions into ceria lattice. The dopant-vacancy association energy and grain interior conductivity changes with the ionic radii of the divalent dopants. The grain boundary capacitance depends on dielectric constant, grain size and grain boundary thickness. The grain boundary conductivity shows 46% over total conductivity for Sr²⁺ added composition. The presence of CeDO₃ phase and space charge layer promotes the grain boundary resistances and affects the ion dynamics. Schematic models are proposed to understand the ion migration in grain boundaries. The scavenging effect is found to be highest in Sr²⁺ ions added composition. The defect structures, the presence of CeDO3 phase and electrical properties are correlated with each other.     

Effect of spray drying conditions and feed composition on the physical properties of black mulberry juice powder

In this study, the effects of some processing parameters on moisture content, water activity, drying yield, bulk density, solubility, glass transition temperature (T_g), and microstructure of spray dried black mulberry (Morus nigra) juice powders were investigated. A pilot-scale spray dryer was employed for the spray drying process and maltodextrin with different dextrose equivalent (6, 9, and 20DE) and gum Arabic were used as carrier agent. Independent variables were inlet air temperature (110, 130, and 150 °C), compressed air flow rate (400, 600, and 800 L/h), concentration of drying aids (8, 12, and 16%) and percent replacement of maltodextrin (6 and 9DE) by gum Arabic and maltodextrin 20DE (25, 50, and 75%). Between the different drying aids, maltodextrin 6DE shows the best effect on the properties of black mulberry juice powders. The process drying yield ranges from 45 to 82%. The highest drying yield (82%) and solubility (87%) refer to the blend of maltodextrin 6DE and gum Arabic. The lowest moisture content powders (1.5%) produced at the compressed air flow rate of 800 L/h. Inlet air temperature negatively influenced the bulk density due to the increase of powder's porosity. The lower the bulk density, the higher the solubility of powder is. With regard to morphology, powders produced with maltodextrin and gum Arabic presented the smallest size.     

加入Si粉对低碳铝镁碳材料性能的影响

以82%(质量分数,下同)的电熔白刚玉(3~0.088mm)、10%的镁铝尖晶石(≤0.088mm)、5%的氧化铝微粉(d50=2.4μm)、3%的电熔镁砂(≤0.088mm)以及占总粉体质量5%的酚醛树脂结合剂为基础配方,分别用2%、4%、6%的Si粉(≤0.088mm)取代等量的白刚玉,分别于1400℃3h和1600℃3h埋炭烧成后制备了不同Si粉含量的低碳铝镁碳材料,对材料的显气孔率、体积密度、强度、抗热震性、抗氧化性及抗渣性进行了检测,并借助XRD、SEM和EDAX研究了材料的物相组成和显微结构。结果表明:随着Si粉加入量的增加,经1400℃3h和1600℃3h埋炭烧成后,材料的体积密度逐渐降低,显气孔率增大,耐压强度明显提高(但Si粉加入量超过4%后材料的耐压强度有所降低),高温抗折强度(1400℃)逐渐提高,抗热震性得到改善,抗氧化性能增强,抗渣性能明显提高。材料性能的这种变化主要同材料中酚醛树脂的残碳与Si粉原位生成β-SiC,以及材料气孔中有Mg-Si-Al-O-N物相生成相关。     

Effect of pitch powder addition on the microstructure and properties of carbon blocks for blast furnace

The phase composition and microstructural evolution of pitch-containing matrix sample with additive of silicon had been compared with pitch-free or resin-containing matrix sample to illustrate the strengthening effect of pitch. Two different pitch powders (CARBORES^@P and High temperature pitch) were then incorporated into carbon blocks, respectively and the effect of pitch powder addition on microstructure and properties of carbon blocks fired at 1000?°C and 1400?°C in a coke bed was evaluated systematically. The results showed that compared with amorphous carbonized resin, carbonized pitch was a kind of highly graphitized carbon and could react with silicon and form SiC whiskers at 1400?°C. In carbon blocks, pitch powder accelerated the formation of AlN at 1000?°C and growth of β-SiC whiskers at 1400?°C, respectively, which enhanced the cold compressive strength, thermal conductivity and hot metal erosion resistance of carbon blocks. Moreover, carbon blocks containing CARBORES^@P pitch with higher carbon yield exhibited better properties because of formation of more ceramic whiskers. The strengthening mechanism of pitch powder for carbon blocks was attributed to the pore-blocking effect of pitch carbonization and more in-situ formed whiskers derived from the reaction between carbonized pitch with silicon at 1400?°C.     

The effect of NiO addition on the grain boundary behavior and electrochemical performance of Gd-doped ceria solid electrolyte under different sintering conditions

It has been reported that some transition metal oxides are effective aids both for the densification and the grain boundary behavior of ceria-based electrolytes. In the present work, NiO which is the most popular component of the anode of solid oxide fuel cells was added directly into the electrolyte ceramic, Ce_0.8Gd_0.2O_1.9, to investigate the effects of the presence of NiO on the properties of GDC electrolyte. All of the samples possess a single phase with cubic fluorite structure. The grain size is increased by the addition of NiO when the sintering temperature is 1400 °C. This modification in chemical composition also results in a decrease in activation energy and thus a tendency to enhance grain boundary mobility. The maximum power density of the composite electrolyte single cell is higher than that of a GDC single cell. Therefore, NiO can be used as an effective aid for ceria-based electrolytes.