Morphology of Oxide Particles Made by the Emulsion Combustion Method

Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X-ray diffraction. Hollow γ-Al₂O₃ particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid α-Al₂O₃ particles. Hollow spheres were obtained also for TiO₂, ZrO₂, and Y₂O₃ by ECM of TiCl₄, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe₂O₃, CeO₂, and MgO from aqueous solutions of their corresponding nitrates.     

Bismuth Oxide Nanoparticles by Flame Spray Pyrolysis

Bismuth oxide nanostructured particles were made via the flame spray pyrolysis (FSP) of bismuth nitrate that had been dissolved in a solution of ethanol/nitric acid or in acetic acid. These self-sustaining spray flames produced tetragonal β-Bi₂O₃. The use of ethanol/nitric acid solutions resulted in a mixture of hollow, shell-like, and solid nanograined particles. The particle homogeneity was improved as the content of acetic acid in the precursor solution increased. Solid bismuth oxide nanoparticles were prepared consistent with percolation theory, accounting for the specific volume of the product and the precursor. Using pure acetic acid as the solvent, the effect of FSP variables on spray flame and product powder characteristics was investigated. The specific surface area of the Bi₂O₃ particles could be controlled over a range of 20–80 m²/g by the liquid feed and oxygen gas flow rates for powder production rates of 6–46 g/h.     

Synthesis of nano-sized gadolinia doped ceria powder by aerosol flame deposition

In this work, aerosol flame deposition method was applied to deposit spherical and dense gadolinia-doped ceria (GDC) particles in the sub-micron range for the electrolyte application in solid oxide fuel cell. The particle size distribution was dependent on processing parameters such as the concentration of the precursor solution, the hydrogen gas flow rate, the oxygen gas flow rate, and flame conditions. GDC electrolyte thin layer was also fabricated from the liquid source materials by AFD method. Microstructure of synthesized powder was characterized using XRD and SEM.     

火焰法合成纳米TiO2颗粒生长过程

在新型火焰反应器生产纳米TiO2的过程中使用TEM微栅在不同火焰高度位置处进行原位取样分析,得到生长过程中纳米TiO2颗粒的粒径和形态. TiO2颗粒经历了成核、生长、聚并、烧结的过程. 调节反应物浓度为7.9×10-5~5.7×10-3 mol/L,研究了不同反应物浓度对纳米颗粒生长过程的影响,高前驱体浓度形成较高的单体浓度,使颗粒间碰撞几率增加,从而得到粒径较大的颗粒,产物粒径17~85 nm. 调节CH4和O2流量,改变温度场,研究温度对颗粒生长过程的影响,在相同反应物浓度条件下,较高的温度下形成分散性好、一次粒径为63 nm的颗粒,而在较低的温度下形成的颗粒一次粒径为35 nm,但颈部烧结严重;增加喷嘴气流速度减小了反应停留时间,颗粒粒径从63 nm减小到36 nm.     

水热法合成球状锡酸镧及其阻燃聚氯乙烯的研究

采用水热法,以锡酸钠和硝酸镧为原料,用氢氧化钠溶液调节pH分别为9、10和11,成功制备了不同粒径的类球状锡酸镧颗粒;对比研究了上述3种粒径尺寸的锡酸镧对聚氯乙烯（PVC）的阻燃和拉伸性能的影响,并采用对纯PVC 和综合性能最好的阻燃样品的残炭进行了分析。结果表明,pH=9时制备的锡酸镧阻燃PVC具有最好的阻燃和拉伸性能;当其添加量为5 g/100 g PVC时,阻燃PVC的极限氧指数为30.8 %,拉伸性能略高于纯PVC,燃烧后形成了带有封闭气孔的致密炭层。     

Preparation of YAG:Europium Red Phosphors by Spray Pyrolysis Using a Filter-Expansion Aerosol Generator

Europium-doped yttrium aluminum garnet (YAG) phosphor particles were prepared from mixed nitrate solutions by the FEAG (filter expansion aerosol generator) process. The crystallinity, morphology, and luminescence of the YAG:Eu particles were investigated. The prepared particles had an amorphous phase, which turned into phase-pure YAG particles after annealing above 1000°C. A cubic-structure YAG phase was formed by the reaction of crystalline Y₂O₃ and the aluminum component. The prepared particles had spherical morphology. The mean size of the YAG:Eu particles increased from 0.45 to 1.0 µm when the overall solution concentrations were increased from 0.02 to 1.2 mol/L. The optimum doping concentration of europium for the maximum brightness of phosphor particles was 1.3 at.%. The cathodoluminescence (CL) intensity was strongly affected by the annealing temperatures. The maximum CL value of the particles was 55 cd/m².     

Effect of Milling Treatment on the Particle Size in the Preparation of AIN Powder from Aluminum Polynuclear Complexes

Aluminum nitride powder was synthesized from aluminum polynuclear complexes. Basic aluminum chloride (BAC) provided the aluminum polynuclear complexes. The effect of the milling treatment for the precursor made from basic aluminum chloride and glucose on the particle size was investigated. BAC and glucose were dissolved in water and mixed homogeneously. AIN powder was obtained by calcining under a nitrogen gas flow after drying, milling by vibration mill, and precalcining at 800°C. Then excess carbon was removed by firing in air. It was found that the milling treatment affected the particle size of AIN powder and nitridation mechanism. Without the milling treatment, AIN powder was synthesized directly from the γ-alumina of an intermediate product. In using a milled precursor, however, α-alumina was formed during the calcining, and the particle size of the AIN powder obtained was about five times larger than that of AIN powder synthesized from a raw precursor. The formation of α-alumina phase began at the rather low temperature of 800°C. These results suggest that the mechanochemical effects added by the milling promotes the formation of α-alumina during calcining, and the α-alumina phase formed accelerates the particle growth. AIN powders obtained were very uniform. The oxygen content and the surface area of AIN powders synthesized from the raw and milled precursors were 2.9 wt% and 17.5 m²/g, and 1.1 wt% and 3.6 m²/g, respectively.     

Synthesis of hollow spherical WO3 powder by spray solution combustion and its photocatalytic properties

Hollow spherical WO₃ powder was prepared from mixed solution of ammonium metatungstate, glycine and ammonium nitrate by spray solution combustion synthesis (SSCS) method. The effects of fuel ratio, temperature, precursor solution concentration on the structure and morphology of as-prepared powder, and the SSCS mechanism have been discussed in detail. When precursor solution concentration is 0.10 mol/L, in which the fuel ratio is 2, and reaction temperature set to be 800 °C, the spherical WO₃ powder with smooth surface and a median diameter of 24.02 μm can be obtained, which consists of particles with a diameter of about 30 nm, and the specific surface area is 13.5 m²/g. Moreover, the as-synthesized WO₃ powder is applied to degrade RhB solution in visible light to evaluate its catalytic performance by PLS-SXE300/300UV. Only 10 mg powder can degrade 70.1% RhB solution within 2 h.     

Preparation of Hollow BaTiO3 and Anatase Spheres by the Layer-by-Layer Colloidal Templating Method

Hollow BaTiO₃ and anatase spheres were prepared from multilayered colloidal titanate particles. An inorganic precursor, titanium (IV) bis(ammonium lactate) dihydroxide (TALH) (chemical formula: [CH₃CH(O–)CO₂–NH₄]₂Ti(OH)₂) was used. First, a layer-by-layer (LBL) colloid-templating method was employed using TALH to generate monodispersed hollow titanate spheres. These spheres were then treated in a Ba(OH)₂ solution or distilled water under hydrothermal conditions to transform them into hollow BaTiO₃ or anatase spheres, respectively.     

Nanocrystalline α-Al2O3 Using Sucrose

Nanocrystalline α-Al₂O₃ ceramic powders have been prepared from an aqueous solution of aluminum nitrate and sucrose. Soluble Al ion-sucrose solution forms the precursor material once it is completely dehydrated. Heat treatment of the dehydrated precursors at low temperature (600°C) results in the formation of porous single-phase α-Al₂O₃. The precursor and heat-treated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET surface area analysis. The phase-pure nanocrystalline α-Al₂O₃ particles had an average specific surface area of >190 m²/g, with an average pore size between 18 and 25 nm.     

高温气相法可控制备纳米TiO2

通过火焰反应器结构设计,实现TiCl4高温气相氧化过程可控制备纳米TiO2粒子,新型火焰设计保证了TiCl4低温进入高温反应区,预热过程隔离保护喷嘴,避免了结疤堵塞;通过实验条件控制颗粒平均粒径和粒径分布,较低的TiCl4气相浓度、较高的载气流速有利于小粒径TiO2颗粒的生成。载气流速增加,中心TiCl4火焰形态由层流向湍流发展,焰长缩短,颗粒平均粒径减小。CH4燃气流量增加,高温反应区扩大,颗粒停留时间增加,颗粒尺寸增大。二次氧气的补充,提高了氧气与TiCl4的预混,有效地减小了产品TiO2颗粒的粒径。获得的TiO2产品平均粒径在20～80 nm之间。     

Low-Temperature Fabrication of Transparent Yttrium Aluminum Garnet (YAG) Ceramics without Additives

A carbonate precursor of yttrium aluminum garnet (YAG) with an approximate composition of NH₄AlY_0.6(CO₃)_1.9(OH)₂·0.9H₂O was synthesized via a coprecipitation method from a mixed solution of ammonium aluminum sulfate and yttrium nitrate, using ammonium hydrogen carbonate as the precipitant. The precursor precipitate was characterized using chemical analysis, differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. The sinterability of the YAG powders was evaluated by sintering at a constant rate of heating in air and vacuum sintering. The results showed that the precursor completely transforms to YAG at ∼1000°C via the formation of a yttrium aluminate perovskite (YAP) phase. YAG powders obtained by calcining the precursor at temperatures of ≤1200°C were highly sinterable and could be densified to transparency under vacuum at 1700°C in 1 h without additives.     

Synthesis of Lithium-Cobalt Oxide Nanoparticles by Flame Spray Pyrolysis

Crystalline LiCoO2nanoparticles were synthesized from an aqueous solution of acetate compounds of lithium and cobalt by a flame spray pyrolysis, and characterized by TEM, XRD, and BET method. We investigated the evolution of LiCoO2nanoparticles from liquid droplets sprayed along the flame and observed disintegration of aqueous precursor droplets about 10μm into smaller fragments around 50 nm in the high temperature flame, as well as decomposition/oxidation of the precursor and coalescence/coagulation. We also examined effects of process variables such as molar concentrations of the precursors and flow rates of combustible gases on the particle size and crystal structure. The average particle diameter increased with an increase in the molar concentration of the precursor. Raising the maximum flame temperature by controlling the gas flow rates also led to an increase in the average diameter of the particles. The crystalline nanoparticles synthesized were nearly spherical, and their average primary particle diameters ranged from 11 to 35 nm.     

Al/NiO复合粒子的制备与表征

以N i(NO3)2.6H2O和CO(NH2)2为主要原料,通过均匀沉淀法,90℃恒温12 h,异相成核,在片状金属铝粉表面包覆一层N i2CO3(OH)2,制备出包覆式复合粒子A l/N i2CO3(OH)2。将复合粒子在马弗炉中400℃恒温灼烧2 h,制备出了A l/N iO复合粒子。通过SEM、XRD及粒度测试等分析方法,对复合粒子的形貌、晶体结构及粒径进行了表征。     

Criteria for Flame-Spray Synthesis of Hollow, Shell-Like, or Inhomogeneous Oxides

The influence of metal precursor and solvent composition on the morphology of SiO₂, Bi₂O₃, and other oxide particles made by flame spray pyrolysis (FSP) was investigated. Silica precursors with boiling points T _bp=299–548 K dissolved in xylene were used as well as different solvents ( T _bp=308–557 K) with tetraethyl-orthosilicate (TEOS) as the silica precursor. For Bi₂O₃, nonvolatile bismuth nitrate pentahydrate was dissolved in solvents with T _bp=338–468 K. Product powders were characterized by nitrogen adsorption, X-ray diffraction, and scanning and transmission electron microscopy. From these data as well as from the literature of FSP synthesis of Bi₂O₃, CeO₂, MgO, ZnO, Fe₂O₃, Y₂O₃, Al₂O₃, and Mg–Al spinel, it is inferred that hollow/inhomogeneous particles are formed at low combustion enthalpy densities and when the solvent boiling point is comparable or smaller than the precursor melting or decomposition point.     

Preparation of Ni-coated TiC particles using potential hydrogen (pH) for dispersion into a molten metal

Titanium carbide (TiC) particles have been coated with nickel (Ni) particles to increase compatibility between the TiC particles and the metal matrix based on Ni, leading to the improvement in the dispersion of TiC particles into a molten matrix, as functions of the potential hydrogen (pH) of TiC suspension, and the heat-treatment condition. The TiC particles were dispersed into the aqueous solution with various pH values, and then nickel nitrate (Ni(NO₃)₂) as a Ni precursor was added at the TiC suspension. As the pH is increased the content of Ni phase on the surface of TiC particle is increased, due to the increment of attractive force between the TiC particle and the Ni ion by the augmentation of negative value on the surface of TiC particle. The Ni-coated TiC particles heat treated at 500 °C under H₂ atmosphere indicate the TiC and Ni phases only, whereas those heat treated at 1000 °C under Ar atmosphere show a titanium oxide (TiO₂) with the TiC and Ni phases, which is resulted from the oxidation of TiC particle by oxygen contained in Ar gas. The dispersibility of TiC particles into a molten metal would be improved through the coating of Ni particles (or phase), inducing the improvement and reliability of mechanical properties.     

Synthesis of Pd–alumina and Pd–lanthana Suspension for Catalytic Applications by One-step Liquid Flame Spray

Catalytic materials of alumina and lanthana supported nanosized palladium particles (7 wt%) in a water suspension were prepared by Liquid Flame Spray (LFS) method. The particle production rate was 90 g/h, using liquid precursors containing Al(NO₃)₃ · 9H₂O, La(NO₃)₃ · 6H₂O and Pd(NH₃)₄NO₃ in water solution. In the LFS method, a turbulent, high-temperature (T_max ∼ 2,700 °C) H₂–O₂ flame is used. The liquid precursor is atomized into micron sized droplets by high velocity H₂ flow and introduced into the flame where the droplets will evaporate. The evaporated compounds decompose and the reaction product re-condenses into particulate material. Here, the nanosized particles are formed by gas-to-particle conversion and the micron sized particles via liquid-to-solid route. In this study, the produced particulate material was collected by thermophoresis along with condensing water into a suspension (nanoparticles in water) in a one-step process. Thus, the whole suspension was produced from the end products of the flame. According to TEM-EDS analysis, the particulate material contained micron sized porous aluminum oxide or lanthanum oxide carrier particles, coated by nanosized palladium particles (∼2–10 nm). The surfactant (Rhodasurf-La 42) was injected into the suspension just after collection to reduce agglomeration. Catalytic performance of the produced Pd–lanthana containing suspension was tested in laboratory with synthetic gases, in order to use it as a possible raw material for three-way catalyst (TWC). The suspension was used as Pd raw material in TWC washcoat and dispersed onto a metallic honeycomb.     

Chemical Preparation of Lead-Containing Niobate Powders

A chemical precipitation method was developed for synthesis of typical relaxor compounds—Pb(Mg_1/3Nb_2/3)O₃ (PMN), Pb(Fe_1/2Nb_1/2)O₃ (PFN), and Pb(Sc_1/2Nb_1/2)O₃ (PSN)—from nitrate solutions. To obtain a niobium precursor compatible with the aqueous chemical routes, peroxo-niobium complex solutions were prepared by dissolving hydrated niobia precipitates in a dilute nitric acid solution with hydrogen peroxide. Powders that consisted of small particles ranging from 20 to 40 nm were successfully precipitated from the mixed nitrate solutions by hydrolysis with aqueous ammonia solutions. On calcination, these powders were highly reactive. For example, PMN precursor powder began to crystallize simultaneously to cubic pyrochlore and perovskite phases at ∼400°C and yielded ∼95% of the perovskite phase after calcination at 800°C for 1 h. PFN and PSN precursor powders calcined under similar conditions formed single perovskite phases.     

Effect of Polynuclear Complex Content on the Synthesis of Aluminum Nitride from Aluminum Polynuclear Complex

Aluminum nitride powders were synthesized from an aluminum polynuclear complex and glucose. Basic aluminum chloride (BAC) was used as the aluminum polynuclear complex. The effect of the polynuclear complex content on the nitridation reaction and particle size of the AIN powder synthesized was investigated. BAC solutions with various polynuclear complex contents were synthesized using an aqueous solution prepared from AlCl₃ and Al metal with various compositions. In this system, AlN was synthesized through γ-Al₂O₃ as an intermediate regardless of the polynuclear complex content. Polynuclear complex content affects the reactivity of nitridation and the particle size of the synthesized AIN powder. The reactivity of nitridation and specific surface area of the products increased with the polynuclear complex content. When the precursor with a polynuclear complex content of 94% was calcined at 1400°C, the AlN content reached 95%. Crystallite size by X-ray diffraction measurement and particle size calculated from the specific surface area for the products were in good agreement, indicating that AlN particles formed in the synthesis process are in the form of single crystals. AlN powder synthesized from the precursor with a polynuclear complex content above 80% had a fine particle size and narrow size distribution.     

铝酸镍和CaCO3协效体系对PVC的阻燃研究

以硝酸铝(Al(NO_3)3·9H_2O)和硝酸镍(Ni(NO_3)2·6H_2O)为原料制备出铝酸镍阻燃剂,并将铝酸镍和碳酸钙协效应用到软PVC材料的阻燃研究中。通过烟密度、氧指数、断裂伸长率和拉伸强度等测试,得出铝酸镍和碳酸钙的最佳协效比为5∶5。此时烟密度值为71.26%,氧指数值为30.2%,拉伸强度为22.80MPa,断裂伸长率为222%,并通过热分析对其降解行为进行了研究。