J.W. Ning

Surfactants assisted processing of carbon nanotube-reinforced SiO2 matrix composites

The dispersion homogeneity of carbon nanotubes (CNTs) is one of the most critical problems in carbon nanotube matrix composites. The dispersive role to CNTs of three kinds of surfactant including cetyltrimethyl ammonium bromide (C16TMAB cationic), polyacrylic acid (PAA anionic) and C16EO (CH3(CH2)14CH2(OC2H5)10OH nonionic) was investigated. The dispersion mechanism may include steric repulsive effect and static electric effect. CNT/SiO2 (5 vol.%) composites with and without C16TMAB were fabricated by sol–gel process. The average bending strength and fracture toughness of sample prepared with C16TMAB, compared with monolithic SiO2 glass, were enhanced 88 and 146% respectively. The properties of sample fabricated without C16TMAB were enhanced only 48 and 118%.

A novel synthesis of phase-pure ultrafine YAG:Tb phosphor with different Tb concentration

Ultrafine luminescent yttrium aluminum garnet (YAG):Tb powders doped with different Tb concentration are prepared by a nitrate–citrate sol–gel combustion process. Single-phase cubic YAG:Tb crystalline is obtained at 800 °C by directly crystallizing from amorphous materials as determined by X-ray diffraction (XRD) techniques. The resultant YAG:Tb powders heat-treated at 1000 °C are uniform and in good dispersity with particle size of about 100 nm. The photoluminescence (PL) spectrum of Tb3+ substituted for Y3+ in YAG with different contents has been measured on samples calcined at 1000 °C.

Synthesis of ultrafine YAG:Tb phosphor by nitrate–citrate sol–gel combustion process

Ultrafine terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders are prepared by a nitrate-citrate sol-gel combustion process using 1:1 ratio of citrate/nitrate. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) techniques. Single-phase cubic YAG:Tb crystalline powder is obtained by calcinating the amorphous materials at 900 deg. C and no intermediate phase is observed. Transmission electronic microscope (TEM) morphology shows that the resultant YAG:Tb powders have uniform size and good homogeneity. The particle size of the product is investigated as a function of the calcination temperature. The photoluminescence (PL) spectrum of Tb{sup 3+} substituted for Y{sup 3+} in YAG with 5.0% content has been measured on samples calcined at different temperatures.

Low-temperature synthesis of single-phase nanocrystalline YAG:Eu phosphor

Crystalline yttrium aluminum garnet (Y3Al5O12, YAG) exists in the cubic form with a garnet structure [1, 2]. Host crystal with yttrium aluminum garnet (YAG) structure has the advantage of relatively stable lattice and large thermal conductivity, so YAG substituted with Eu, Ce, or Tb is known as a rather efficient phosphor material [3]. YAG phosphors doped with activators are mainly synthesized by solid-state reaction techniques [4, 5]. To achieve desired phase purity and required particle size, the process of solid-state reaction usually needs lengthy high temperature treatment (>1600 ◦C) and extensive ball milling, which generally introduces additional impurities and defects. Furthermore, high temperature processing does not yield sufficient fine particles required to achieve enhanced screen resolution in phosphor applications. A few wet-chemical methods [6–10] are also used to prepare YAG powders. However, due to the coexisting of two detrimental phases, YAP (YAlO3) and/or YAM (YAl4O9) as intermediate phases, hightemperature calcining is necessary to achieve desired phase purity. In this letter, we describe a novel preparation method for nanocrystalline YAG:Eu phosphor by nitrate-citrate sol-gel combustion process. The sample prepared in the present work is designed to have an overall composition (Y1−0.05Eu0.05)3Al5O12. Al(NO3)3 · 9H2O (analytical grade), Y(NO3)3 · 6H2O (99.99% pure), Eu2O3 (99.99% pure), and C6H8O7 · H2O (hydrated citric acid, analytical grade) were used as starting materials. Highpurity Eu2O3 was dissolved in HNO3 and then dissolved in deionized water with a stoichiometric amount of yttrium nitrate, aluminum nitrate and an appropriate dosage of citric acid. After the mixed solution was heated at 60 ◦C and continuously stirred using a magnetic agitator for several hours, the solution turned to yellowish sol. Then, heated at 80 ◦C and stirred constantly, the sol transformed into transparent sticky gel. The gel was rapidly heated to 180 ◦C and an auto combustion process took place companying with the evolution of brown fume. Finally, a yellowish product, fluffy precursor, was yielded. The precursor was then heattreated at varying temperatures from 600 ◦C to 1000 ◦C for two hours in a muffle furnace in air. The crystalline development of the product was identified by X-ray diffraction analysis (XRD, Model

Fabrication and Properties of Carbon Nanotube/SiO2 Composites

Novel Carbon nanotube (CNT)-reinforced SiO 2 composites were fabricated with mixture powders synthesized by rapid Sol-gel method and sintered by hot-press ure. The incorporation of CNT enhances the mechanical property greatly and improves the ther mal properties. The microstructure of sample has been observed and discussed with relat on to the nature of matrix and the properties mentioned above.

Effect of Surfactants on the Properties of Carbon Nanotube-Reinforced SiO2 Matrix Composites

The dispersion homogeneity of carbon nanotubes (CNTs) is one of the most critical problems in carbon nanotube matrix composites. The dispersive role and mechanism to CNTs of three kinds of surfactant including Cetyltrimethyl ammonium bromide (C16TMAB cationic), Polyacrylic acid (PAA anionic) and C16EO (CH3(CH2)14CH2(OC2H5)10OH nonionic) were investigated. The bending strength and fracture toughness of sample prepared with C16TMAB, compared with monolithic SiO2 glass, were enhanced 133% and 146% respectively. The properties of sample fabricated without C16TMAB were enhanced only 48% and 118%.

Effect of Coating Microstructure on Ni/Al2O3 Composites

The feasibility of preparing a thin layer of alumina on the sur face of nickel grains was react-sintered from raw materials of aluminum isopropoxide[Al(C 3H7O)3] and a basic nickel carbonate[NiCO3·2Ni(OH)2·4H2O]. A redox reaction to form Ni/Al 2O3 mixture powders was performed. Then the mixture was sintered under 30MPa at 1400 C in Ar atmosphere for 30mins. Ni/Al 2O3 composites a achieving density of 97.7% and show a coating microstruct ure. The effect of coating thickness on the mechanical properties and the coating microst ru ture formation process were investigated in this paper. The bending strength and the fra cture toughness of Ni/Al 2O3 composites are 882 MPa and 6.32 MPa×m , respectively. The phase and microstructure of Ni/Al 2O3 composites were investigated by X-ray diffraction (XRD), sca nning electron microscopy (SEM), and transmission electron microscopy (TEM). Introduction The metal/ceramic composites were widely studied in the 60 th of 20 century. The researchers expected to show each advantage property of the metal and ceramics in their composites so that a material with better mechanical property was obtained in that ti me. The studied systems included those of the oxide-metal, carbide-metal, nitride-metal and silica te-metal. Metal-alumina composites provide an exceptional mechanical property for high temperature struct ural applications[1,2]. Thus, the interface and microstructure are two of the key factors in determining the performance of the composite. The formation conditions of metal-ceramic request three int rconnected topics as following: 1) there is better wetting of ceramics by metals (both liquid and solid). The ceramic particles exist in the metal net, 2) there is not severely r eaction between the metal and ceramics, and 3) it is expected that the thermal expansion coefficients betwee n th metal and ceramics are close. However, the composite toughness decreases after the metal networ k gradually oxidizing because the oxide can easily diffuse into the microstructure through the m etal network and bring an oxidization reaction. A converse method is used to this research. Al 2O3 coats the surface of the Ni grains owing to the different surface energy of the raw material powders in the sintering process. This design is to improve the oxide resistance of Ni/Al 2O3 composite. Experimental Procedure Al(C3H7O)3 (Zhejiang Orientation Chemical Factory, China) and NiCO 3·2Ni(OH)2·4H2O (Shanghai No.1 Reagent Factory, China) was used as the oxidizer and reducer. They were dissolved in water with different PH values, respectively. Three compositions of Ni: Al 2O3 (volume ratio) were 95:5, 90:10, and 85:15. Then the mixtures were sintered under 40MPa at 1400 C in Ar atmosphere for 30mins. The fabrication process is shown in Fig. 1. The strength at room temperature was measured by the three-point bending test with a specimen size of 3T×4W×36L mm. The test was conducted by using the Inst ron’ materials testing machine that the deformation rate of 0.5 mm/min and span of 30mm. The fracture to ughness of the materials was evaluated using the indentation measurement. The calculation equation is as f ollowing: 2 / 3 0726 . 0 C F K IC = (1) Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 249, pp 55-60 doi:10.4028/www.scientific.net/KEM.249.55