Morphological Control of Zirconia Nanoparticles through Combustion Aerosol Synthesis

Ceramic oxide nanoparticles produced by flame-based processes are typically agglomerated, which can limit their use in some applications. In this paper, a novel combustion synthesis method that utilizes the spraying of combustible droplets into a premixed flame to produce nanoscale crystalline particles of agglomerated and unagglomerated morphologies is described. Although the same flame-based experimental setup is used in both cases, variation in peak flame temperatures results in a corresponding variation between fractallike agglomerates and single isolated spherical particles. TEM/ED analysis shows that both classes of particles are the tetragonal crystal phase of zirconia. In the case of the unagglomerated spherical particles, results indicate that each precursor solution droplet, which acts as the feed, produces multiple spherical ceramic nanoparticles with a number mean diameter of 90 nm. The use of an inertial impaction stage in the precursor feed line to eliminate large feed droplets leads to a decrease in the number mean diameter to 60 nm, suggesting that crystalline spherical nanoparticles can be produced in a continuous flame-based process through control of the feed droplet size.     

Hydrothermal Synthesis of Weakly Agglomerated Nanocrystalline Scandia-Stabilized Zirconia

A pure cubic phase of weakly agglomerated, nanocrystalline, 8-mol%-Sc₂O₃-stabilized zirconia (8ScSZ) was synthesized by a two-step hydrothermal treatment in the presence of urea: a stock solution of metal nitrates and urea was heated at 80°C for 48 h and then at 180°C for 72 h. The omission of the first low-temperature treatment resulted in more monoclinic phase. The effects of urea concentration and calcining temperature on the crystallization of the as-synthesized nanocrystalline 8ScSZ are also discussed.     

Zirconia Nanoparticles Made in Spray Flames at High Production Rates

Synthesis of zirconia nanoparticles by flame spray pyrolysis (FSP) at high production rates is investigated. Product powder is collected continuously in a baghouse filter unit that is cleaned periodically by air-pressure shocks. Nitrogen adsorption (BET), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) are used to characterize the product powder. The effect of powder production rate (up to 600 g/h), dispersion gas flow rate, and precursor concentration on product particle size, crystallinity, morphology, and purity is investigated. The primary particle size of zirconia is controlled from 6 to 35 nm, while the crystal structure consists of mostly tetragonal phase (80–95 wt%), with the balance monoclinic phase at all process conditions. The tetragonal crystal size is close to the primary particle size, which indicates weak agglomeration of single crystals.     

Nanocrystalline Zirconia Surface-Doped with Alumina: Chemical Vapor Synthesis, Characterization, and Properties

Nanocrystalline zirconia with a grain size of ∼5 nm was surface-doped with 3 and 30 mol% alumina by chemical vapor synthesis using two sequential hot-wall reactors. The powders were characterized by high-resolution transmission electron microscopy, X-ray diffractometry (XRD), and nitrogen adsorption. Aqueous dispersions were studied by zeta-potential measurements and photocorrelation spectroscopy. Green and sintered ceramic bodies were investigated by high-resolution scanning electron microscopy, XRD, and nitrogen adsorption. Zirconia surface-doped with 3 mol% of alumina displays substantial changes in dispersability and sinterability compared with pure nanocrystalline zirconia.     

Nonisothermal Synthesis of Yttria-Stabilized Zirconia Nanopowder through Oxalate Processing: I, Characteristics of Y-Zr Oxalate Synthesis and Its Decomposition

To obtain powder with a composition of 3 mol% Y₂O₃–97 mol% ZrO₂, a process of Y-Zr oxalate powder production has been optimized, to produce an oxalate with minimal particle size. The methodology of the nonisothermal decomposition of Y-Zr oxalate has been explained. Characteristics of the nonisothermal decomposition of different oxalates have been studied. Nanocrystalline Y₂O₃-stabilized ZrO₂ (YSZ) powder with a narrow size distribution of primary particles and aggregates was produced. The zirconia powder that was obtained from the smallest oxalate powder via nonisothermal decomposition had a particle size of 8–10 nm. The YSZ powder was weakly aggregated, with a narrow aggregate-size distribution of 70–90 nm.     

Sintering Behavior and Electrical Properties of Nanosized Doped-ZnO Powders Produced by Metallorganic Polymeric Processing

Homogeneous and nanosized (28 nm crystallite size) doped-ZnO ceramic powders were obtained by a metallorganic polymeric method. Calcining and granulating resulted in green compacts with uniform powder packing and a narrow pore-size distribution (pore size 19 nm). Dense ceramic bodies (>99% of theoretical) were fabricated by normal liquid-phase sintering at 850° and 940°C for 1–5 h. Apparently, the low pore-coordination number allowed a uniform filling of the small pores by the liquid formed in the early stages of sintering, and, consequently, high shrinkage and rapid densification occurred in a short temperature interval (825°–850°C). At these sintering temperatures, limited grain growth occurred, and the grain size was maintained at <1 μm. Ceramics so-fabricated showed a nonlinear coefficient, α, of ≥70, and a breakdown voltage, V _b (1 mA/cm²), of ≥1500 V/mm. The high electrical performance of the doped-ZnO dense ceramics was attributed to liquid-phase recession on cooling, which enhanced the ZnO-ZnO direct contacts and the potential barrier effect.     

纳米ZrO2前驱物表面电性能的研究

利用3000HS型ζ-电位分析仪研究了ZrOCl2浓度、pH值、分散剂等因素对纳米氧化锆前驱物表面ζ-电位的影响.结果表明:低浓度ZrOCl2溶液生成的ZrO2前驱物的ζ-电位对pH值变化更加敏感;添加2%(质量分数,下同)的PEG6000和PEG20000使ZrO2前驱物的表面ζ-电位有所降低,添加2%的PEG100对前驱物ζ-电位的影响更为显著.     

电熔氧化锆生产锆铁红色料的发色效果及应用

本文简要对比特种电熔锆与普通电熔锆、化学锆之间的物理化学性质的差异,并研究它们在不同条件下,制成的锆铁红色料的发色情况。结果表明:采用特种电熔锆生产的锆铁红色料,其发色效果及耐温性能等指标都达到甚至超过化学锆的标准,在工业化生产应用中取得了较好的效果。     

Nanostructured Dense ZrO2 Thin Films from Nanoparticles Obtained by Emulsion Precipitation

Nonagglomerated spherical ZrO₂ particles of 5–8 nm size were made by emulsion precipitation. Their crystallization and film-forming characteristics were investigated and compared with nanosized ZrO₂ powders obtained by sol–gel precipitation. High-temperature X-ray diffraction indicated that the emulsion-derived particles are amorphous and crystallize at 500°C into tetragonal zirconia, which is stable up to 1000°C. Crystallite growth from 5–20 nm occurred between 500°–900°C. Films of 6–75 nm thickness were made by spreading, spin coating, and controlled deposition techniques and annealed at 500°–600°C. The occurrence of t -ZrO₂ in the emulsion-precipitated powder is explained by the low degree of agglomeration and the corresponding low coarsening on heating to 500°–800°C, whereas the agglomerated state of the sol–gel precipitate powder favors the occurrence of the monoclinic form of zirconia under similar conditions.     

Morphology and Phase Stability of Nitrogen–Partially Stabilized Zirconia (N-PSZ)

The surface layer of yttria-doped tetragonal zirconia materials that have been heat-treated with zirconium nitride was observed to consist of a nitrogen-rich cubic matrix with nitrogen-poor tetragonal precipitates. The precipitates had a thin, oblate-lens shape, similar to those observed in magnesia–partially stabilized zirconia. Because of the fast diffusion of N⁴⁻ ions, the precipitates grew rather large, up to ∼5 μm in length, and remained stabilized in the tetragonal form at room temperature. Because the nitrided layer grew in the two-phase field, the size and distribution of the precipitates each was very irregular. The nitrogen content was observed to determine the proportion of cubic and tetragonal phases in the same way as in conventional cation-stabilized partially stabilized zirconia. A ternary phase diagram for the zirconium(yttrium)–nitrogen–oxygen system was suggested to explain the concentration gradient in the cubic matrix and the phase distribution of the nitrided layer.     

Combustion and Coprecipitation Synthesis of Co–Zn Ferrite Nanoparticles: Comparison of Structure and Magnetic Properties

In this study, we used urea and ammonia to synthesize zinc cobalt ferrites via microwave‐assisted hydrothermal method from metallic nitrates. It was figured that despite the common synthesis method and equal amount of nitrates, magnetic properties of nanoparticles were different. Changes in magnetic properties are discussed based on factors such as nanoparticles’ size, surface atom spins, cationic distribution, magnetocrystalline energy. Nanoparticles synthesized with ammonia showed lower magnetization while higher magnetocrystalline energy and greater coercivity was obtained due to better cationic distribution. It was also revealed that by increasing magnetization, the susceptibility of nanoparticles increases and then declines.     

Self-Catalyzed Synthesis of Organo-Silica Nanoparticles

A procedure has been developed which utilizes aminopropyltriethoxysilane (APS) as the catalyst and a comonomer in the production of hybrid organo-silica nanoparticles. Particles ranging from ca. 100 to 500 nm can be prepared using organo-silanes of the type R'Si(OR)₃, where R'= Me, vinyl, allyl, or other hydrophobic groups and R = Me or Et, in a water/surfactant solution. Based on elemental analysis, up to 10 mol% of APS was incorporated into the siloxane particle network. It is thought that the amino groups are located mainly on the surface due to their hydrophilicity and APS' relatively slow rate of hydrolysis and condensation.     

Effect of Titanium and Zirconia Nanoparticles on Human Gingival Mesenchymal Stromal Cells

Nano- and microparticles are currently being discussed as potential risk factors for peri-implant disease. In the present study, we compared the responses of human gingival mesenchymal stromal cells (hG-MSCs) on titanium and zirconia nanoparticles (<100 nm) in the absence and presence of Porphyromonas gingivalis lipopolysaccharide (LPS). The primary hG-MSCs were treated with titanium and zirconia nanoparticles in concentrations up to 2.000 µg/mL for 24 h, 72 h, and 168 h. Additionally, the cells were treated with different nanoparticles (25–100 µg/mL) in the presence of P. gingivalis LPS for 24 h. The cell proliferation and viability assay and live–dead and focal adhesion stainings were performed, and the expression levels of interleukin (IL)-6, IL-8, and monocyte chemoattractant protein (MCP)-1 were measured. The cell proliferation and viability were inhibited by the titanium (>1000 µg/mL) but not the zirconia nanoparticles, which was accompanied by enhanced apoptosis. Both types of nanoparticles (>25 µg/mL) induced the significant expression of IL-8 in gingival MSCs, and a slightly higher effect was observed for titanium nanoparticles. Both nanoparticles substantially enhanced the P. gingivalis LPS-induced IL-8 production; a higher effect was observed for zirconia nanoparticles. The production of inflammatory mediators by hG-MSCs is affected by the nanoparticles. This effect depends on the nanoparticle material and the presence of inflammatory stimuli.     

Raman Spectroscopy of Nanocrystalline Ceria and Zirconia Thin Films

The results of Raman-scattering studies of nanocrystalline CeO₂ and ZrO₂:16% Y (YSZ) thin films are presented. The relationship between the lattice disorder and the form of the Raman spectra is discussed and correlated with the microstructure. It is shown that the Raman line shape results from phonon confinement and spatial correlation effects and yields information about the material nonstoichiometry level.     

Synthesis and Characterization of Zirconia Nanorods

ZrO₂ nanorods are prepared by annealing precursor powders produced in the novel inverse microemulsion system. The length and diameter of ZrO₂ nanorods are a few micrometers and 40–100 nm, respectively. The microstructure of the resultant nanorods are studied by XRD, TEM, selected area electron diffraction, and Raman spectroscopy. The ZrO₂ nanorods are single crystalline and have monoclinic structure. The formation of ZrO₂ nanorods is discussed.     

氧化锆活性对烧结性能的影响

分别以化学法和电熔法制备的氧化锆及二者混合共磨粉为原料,通过造粒、成型、干燥、烧成制得样品,对烧成样品物理性能和微观结构进行分析,研究原料活性对烧结性能的影响.研究结果表明:在加入同样稳定剂的条件下,电熔氧化锆活性较差,烧结后气孔率较高,化学氧化锆烧结后收缩大,开裂严重,两者都无法满足作为制备氧化锆质定径水口基质原料要求,当二者的混合比例为1:1时,试样的烧结温度合适,气孔率、烧成收缩、耐压强度等各项理化指标较好,满足用作制备氧化锆质定径水口基质要求.     

Nonisothermal Synthesis of Yttria-Stabilized Zirconia Nanopowder through Oxalate Processing: II, Morphology Manipulation

A novel, nontraditional route for controlling the morphology of yttria-stabilized zirconia nanopowders is explained. For understanding the real nature of yttrium zirconium oxalate nonisothermal decomposition and for the development of nanosize 3 mol% Y₂O₃·97mol% ZrO₂, mass spectrometry, X-ray, and TEM investigation were used. Characteristics of zirconia crystallization under nonisothermal heating conditions were studied. Morphology evolution during Y-Zr oxalate nonisothermal decomposition was investigated to optimize the heating schedule of calcination. The nonlinear heating regime has been used to produce nanosized Y₂O₃-stabilized tetragonal ZrO₂ powder with the finest primary crystallites and narrowest secondary aggregate size distribution.     

纳米氧化锆添加量对氧化锆制品性能的影响

在电熔单斜氧化锆原料中添加不同数量的CaO稳定剂,制备部分稳定氧化锆,研究CaO加入量和稳定相数量的关系.在制备的CaO部分稳定氧化锆中添加纳米氧化锆粉体,经过造粒、200 MPa压力成型、干燥、1650 ℃×2 h烧成制得试样.测试试样的物理性能、分析矿物相组成、观察显微结构,研究纳米氧化锆粉体添加量对试样性能的影响.研究结果表明:2Ca-PSZ、3Ca-PSZ、4Ca-PSZ试样中,4Ca-PSZ试样稳定化程度最高;3Ca-PSZ试样显气孔率小,体积密度较大,耐压强度高.在3Ca-PSZ试样中加入纳米氧化锆粉体,随着加入量的增加,试样的显气孔率下降、烧成收缩率增加、耐压强度提高.其中纳米氧化锆粉体添加比例为8wt%时,试样气孔率为9.4%,体积密度为5.08 g/cm3,抗压强度达到381 MPa.与3Ca-PSZ试样相比,气孔率下降40%,体积密度提高5%,耐压强度提高70%.