Microstructural characterization of diamond films deposited on c-BN crystals

The morphology and structure of diamond films, deposited on cubic boron nitride (c-BN) crystals by microwave-plasma-enhanced chemical vapor deposition, is studied by high-resolution scanning electron microscopy and micro-Raman spectroscopy. The c-BN crystals, with sizes of 200 to 350 μm and grown by a high-temperature/high-pressure technique, were embedded in a copper holder, and used as substrates in deposition runs of 15 min to 5 h. The nucleation centers for diamond appear as well-shaped cuboctahedral crystallites, having diameters of approximately 100 nm. With increasing deposition time the diamond crystallites grew larger, forming islands on the c-BN faces. In some cases, epitaxial growth was observed on the (111) c-BN faces where coalesced particles gave rise to very smooth regions. A number of diamond crystals with peculiar shapes are observed, such as a pseudo five-fold symmetry due to multiple twinning. Moreover, both randomly distributed carbon tubes, about 100 nm in diameter and 1 μm in length, and spherically shaped features are observed in samples prepared under the typical conditions of diamond deposition, this effect being ascribed to the influence of plasma-sputtered copper contamination. Quite unusual diamond crystals with a deep, pyramidal-shaped hole in the middle grew on the copper substrate between the c-BN crystals.     

Diamond nanoparticles to carbon onions transformation: X-ray diffraction studies

Carbon onions prepared by high temperature annealing of ultradispersed diamond nanoparticles of about 5 nm in average diameter have been studied by X-ray diffraction using synchrotron radiation. The X-ray diffraction patterns show transformation of the diamond nanoparticles with sp³ bonds into spherical carbon onions containing remaining diamond-like core and then into polyhedral onions with facets on their outer part and pure sp² graphitic bonds. The prepared onions form concentric-shell particles which comprise of about ten shells with an intershell distance of 0.35-0.36 nm. The large intershell distance suggests a considerable reduction in intershell interaction when compared to perfect graphite. The X-ray data are related to the previously performed studies by electron energy-loss spectroscopy and electron spin resonance.     

A stable suspension of single ultrananocrystalline diamond particles

As the result of successful disintegration of tight aggregates in detonation nanodiamond by stirred-media milling with microbeads, stable colloid of nanodiamond particles with a mean core size of 4 nm is obtained for the first time, but the colloid is colored deep black. X-ray diffraction, Raman scattering, HRTEM, UV–vis absorption spectra and viscosity data were used to characterize the colloid. It was suggested that the reason for the unexpected black color of the suspension is a result of graphitic partial surface (π-electrons formation of 4 nm diamond particles) induced by strong collision with beads during milling process. π-electrons are a reason of double electric layer formation and high viscosity of the suspension. Theoretical estimations fitted experimental data.     

In-situ transmission electron microscopy observation of particle size effect of nanoscale platinum catalysts on the formation of fullerenelike carbon shells

Drastically different catalytic behaviors of nanometer-sized platinum particles which have diverse sizes are observed using in-situ transmission electron microscopy. For small platinum catalyst particles (with diameters less than 5 nm), carbon shells form on the surfaces of the platinum catalyst particles. The formation of the carbon shells starts from the nucleation of amorphous carbon on the preferred (1 1 1) planes of platinum nanoparticles. For these small platinum catalyst particles encapsulated in graphitic shells, they are passivated by the carbon shells and their coalescence is hindered by the surrounding shells. After the platinum catalyst particles ultimately coalesce, they interact to form a compact platinum particle after breaking the encapsulating shells. For larger platinum nanoparticles (with diameters larger than 5 nm), no encapsulation of platinum nanoparticles is observed and there occurs only the coalescence of platinum nanoparticles.     

Catalytic graphitization by iron of isotropic carbon from polyfurfuryl alcohol, 725–1090 K. A high resolution electron microscope study

Iron as ferrocene was added to furfuryl alcohol. The doped monomer was polymerized to polyfurfuryl alcohol which was carbonized to heat treatment temperatures of 725–1090 K. Thin sections of these carbons were examined by high resolution electron microscopy to reveal the stacking arrangements of the constituent layers and the state of dispersion of the iron added as ferrocene. In the polyfurfuryl alcohol it was not possible to detect any aggregates of iron. However, small aggregates, ~5 nm, appear at 725 K and are distinct at 943 K. Significant catatylic graphitization by iron particles occurs at the relatively low temperature of 875 K (600°C) to produce a turbostratic graphite. Small aggregates of iron, ~20 nm diameter, are responsible for this form of graphitization, the particles having mobility or remaining stationary within the carbon matrix. An activation energy of 400 kJ mol^?1 is derived for this form of graphitization.     

Deaggregation of ultradispersed diamond from explosive detonation by a graphitization–oxidation method and by hydroiodic acid treatment

The deaggregation of ultradispersed diamond (UDD) from explosive detonation has been carried out by a graphitization–oxidation method and by a hydroiodic acid (HI) treatment. The first method is used to break the crystalline bridge between the diamond primary particles, and the second one is employed to break down C–O–C ethereal linkages formed between the diamond crystallites. The samples after the above-mentioned chemical treatments were suspended in water by ultrasonic waves and the resulted suspensions were examined by a dynamic laser scattering method to obtain particle size distributions of samples in water. Experimental results show that after graphitization–oxidation treatment, nearly 35% of the particles, and after further HI treatment 43% of the diamond aggregates were reduced to less than 50 nm, and the particle size of nearly 98% of the aggregates is less than 200 nm in diameter. Thus, these two methods are useful for the deaggregation of UDD from detonation. But it is evident that the results obtained are far from the monodispersion state of UDD. In order to reach an even higher level of deaggregation, further study to improve treating methods is needed.     

A Study of Optical Properties of Soot Aggregates Composed of Poly-Disperse Monomers Using the Superposition T-Matrix Method

The diameters of soot monomers may not be constant in the single fractal aggregated soot particle. The optical properties of light absorbing soot particles aggregated with poly-disperse monomers were studied using the superposition T-matrix method. Soot aggregates were generated with different log-normal probability distribution functions (PDF) of soot monomer diameter, according to the same soot volumes and monomer numbers. The single scattering properties of soot particles were calculated at a wavelength of 550 nm, assuming a soot refractive index of 1.95 + 0.79i and a mass density of 1.8 g/cm³. The random-orientation averaging results indicated that the optical properties of soot aggregates were fairly varied for the different distributions of the monomer diameters. In these simulations, the extinction and absorption of soot aggregates were slightly (<10%) affected by the monomer poly-dispersity. The simulated mass absorption cross-sections (MAC) of fresh dry soot particles aggregated with poly-disperse monomers reached up to 6.62 ± 0.07 m²/g, which was closer to the measurement (7.5 ± 1.2 m²/g) than the assumption of volume-equivalent mono-disperse monomer (6.36 ± 0.06 m²/g). Moreover, the optical properties of soot coated with an organic shell were calculated, and the optical results showed that the absorption cross-sections of the internally mixed soot particles were also slightly (<8%) influenced by the monomer poly-dispersity. We found that the effect of the monomer poly-dispersity on the light scattering and the single scattering albedo may be considerably large (up to ?50% in extreme cases) for fresh dry soot aggregates. This effect on light scattering should be taken into account for those aggregates composed of monomers with widely distributed diameters.

Copyright 2015 American Association for Aerosol Research     

Controlled aggregation of colloidal particles for toner applications

Micrometer‐sized particles were formed by controlled aggregation of carboxylated polystyrene colloidal spheres having a mean diameter of about 200 nm with a commercial cationic coagulant. To identify the parameters governing the size and structure of the aggregates, the aggregate size distribution was studied over a period of time with dynamic light scattering. The effect of the particle concentration, pH, and ionic strength on the aggregation behavior was investigated. The coagulant concentration used for present studies was 5 parts per hundred on the basis of the polystyrene particles and the particle concentrations used were 10–15%. The particle size distribution for the latex suspensions was also investigated with a 10% aluminum sulfate [Al₂(SO4)₃·14H₂O] solution as a model coagulant. With the commercial coagulant, aggregation was found to be slower at lower pH than at neutral pH. At pH 6, the particles started to aggregate within minutes and form aggregates of about 1000 nm. We expected that lowering the pH would reduce interparticle repulsive forces and enhance the collision efficiency. However, at a lower pH of 2, the aggregation process slowed down. Increasing the ionic strength at neutral pH led to a broader aggregate size distribution, and the population of larger aggregates increased. The suspensions with the model coagulant showed similar behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Formation of carbon nanotubes through ethylene decomposition over supported Pt catalysts and silica-coated Pt catalysts

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.     

Fabrication of New Cemented Carbide Containing Diamond Coated with Nanometer-Sized SiC Particles

A simple process for depositing a coating of silicon carbide (SiC) crystallites ∼10 nm in size onto diamond particles has been developed. SiO powders react with diamond in a vacuum at 1350°C to form a uniform β-SiC polycrystalline layer ∼60 nm thick. The SiC coating improves the oxidation resistance of the diamond. A cemented carbide material containing 20-vol%-SiC-coated diamond particles was sintered to a relative density of 99.5% by pulsed-electric-current sintering. A Vickers hardness and indentation fracture toughness of 15 GPa and 16.3 MPa·m^1/2, respectively, were obtained. This toughness is two times higher than that of cemented carbide containing no particles. The higher toughness is attributed to deflection and blockage of crack propagation by the diamond particles.     

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.     

Fabrication of polymer/ZnS nanoparticle composites by matrix-mediated synthesis

Zinc sulfide nanoparticles are obtained as primary particles in a polymer matrix by a matrix-mediated synthesis. Two types of matrix polymer are synthesized via the copolymerization of hydrophobic, cation-exchange, and cross-linking monomers. The ZnS nanoparticles are affected by the composition of the matrix polymer, and especially by its hydrophobicity. In a low-hydrophobicity copolymer matrix, aggregates of ZnS nanoparticles are observed in the matrix using transmission electron microscopy (TEM) and X-ray diffraction (XRD). In a high-hydrophobicity cation-exchange copolymer matrix, primary particles of ZnS with 2–5 nm diameters are observed in the matrix by TEM. However, the ZnS pattern is not distinguishable in XRD measurements because the particle sizes are too small to diffract X-rays.     

Electrospinning Zirconia Fiber From a Suspension

A zirconia suspension containing 5–10 nm size zirconia particles was modified by adding different amounts of polymer solution to enable electrospinning of zirconia fibers from a range of compositions. The electrospun fibers were heat treated at 600° and 1200°C, and analysis of size distribution reveals that zirconia fibers down to about 200 nm in diameter can be prepared in this way, in contrast to other spinning processes, which are able to produce zirconia fibers having diameters ≥3000 nm.     

Particle Emission Characteristics of a Gas Turbine with a Double Annular Combustor

The total climate, air quality, and health impact of aircraft black carbon (BC) emissions depend on quantity (mass and number concentration) as well as morphology (fractal dimension and surface area) of emitted BC aggregates. This study examines multiple BC emission metrics from a gas turbine with a double annular combustor, CFM56-5B4-2P. As a part of the SAMPLE III.2 campaign, concurrent measurements of particle mobility, particle mass, particle number concentration, and mass concentration, as well as collection of transmission electron microscopy (TEM) samples, allowed for characterization of the BC emissions. Mass- and number-based emission indices were strongly influenced by thrust setting during pilot combustion and ranged from <1 to 208 mg/kg-fuel and 3 ×× 10¹² to 3 ×× 10¹⁶ particles/kg-fuel, respectively. Mobility measurements indicated that mean diameters ranged from 7 to 44 nm with a strong dependence on thrust during pilot-only combustion. Using aggregation and sintering theory with empirical effective density relationships, a power-law relationship between primary particle diameter and mobility diameter is presented. Mean primary particle diameter ranged from 6 to 19 nm; however, laser-induced incandescence (LII) and mass-mobility-calculated primary particle diameters demonstrated opposite trends with thrust setting. Similarly, mass-mobility-calculated aggregate mass specific surface area and LII-measured surface area were not in agreement, indicating both methods need further development and validation before use as quantitative indicators of primary particle diameter and mass-specific surface area.

Copyright 2015 American Association for Aerosol Research     

Thin-film particles of graphite oxide. 2: Preliminary studies for internal micro fabrication of single particle and carbonaceous electronic circuits

Some preliminary studies to realize a carbonaceous electronic circuit were carried out using the liquid-dispersible thin-film particles of graphite oxide and their conductive reduction product. (1) The affinity of insulator substrates (diamond, silicon carbide, silicon, sapphire and three kinds of glass) for the particles was improved by heating and immersion in water. (2) The electric conductivity was measured for a wide wiring pattern formed by a large number of the reduced thin-film particles mounted on the substrate, and the value was 1600 S/m after heating at 500 °C. (3) To make the prototype of a narrow wiring or a micro device, the internal micro fabrication (position-selective removal) of a single particle was attempted using focused ion beam. Many kinds of patterns which contain narrow wiring having a width of 200 nm etc. were formed in the reduced thin-film particle having about 10 nm thickness. (4) The simple model calculation of anisotropic conductivity was executed for thin graphite which has a small number of layers and finite size. In the case of the fine graphitic carbonaceous devices and circuits, much attention must be paid to their sizes in all directions.     

Controlled synthesis of PDDA stabilized Au–Pd bimetallic nanostructures and their activity in hydrogenation of acetylene

Pd hydrosol was synthesized by reducing PdCl₂ solution with dissolved H₂ in the presence of PDDA [poly(diallyldimethylammonium chloride)] as ionic stabilizer. O₂ treatment resulted in the reappearance of ligand to metal charge transfer bands of PdCl ₄ ²⁻ . Repeated oxidation and hydrogen treatments caused aggregation/agglomeration of the Pd particles yielding big spherical aggregates of 30–50 nm but still keeping the size of the 5–6 nm primary particles. Aggregation was attributed to the reduction of PdCl ₄ ²⁻ anion having high local densities around Pd particles surrounded by PDDA polycation. Au–Pd bimetallic hydrosols were synthesized by reduction with 2-propanol and by pulse radiolysis technique in the presence of PDDA. Both reduction modes synthesize Au core–Pd shell structures. The mode of reduction was observed to affect the particle size and the thickness of the Au core and Pd shell. At the Au rich samples the differences in the optical spectra were attributed to different dispersions of the Au–Pd particles. Au–Pd bimetallic hydrosols were adsorbed on Aerosil 200 and the supported samples were tested in gas phase hydrogenation of acetylene.     

A TEM-based method as an alternative to the BET method for measuring off-line the specific surface area of nanoaerosols

At the present time, no stabilised method exists allowing an estimation of the specific surface area for airborne nanostructured particles (nanoaerosols). Recent toxicological studies have, however, revealed biological effects linked to the surface area of these particles. Only the BET method, which can determine the specific mass surface area of a powder, constitutes a reference both in toxicology and in the materials domain. However, this technique is not applicable to nanostructured aerosols given the mass quantities of particles required (between approximately some mg to hundreds of mg taking into account the limit of quantification of existing BET instruments).To characterise the specific surface area of airborne nanostructured particles, a method based on analysing transmission electron microscopy (TEM) images is proposed. This has recourse in particular to previous work carried out in the area of nanoparticles originating from combustion (soot), and takes into account structural parameters of nanostructured particles including the number distribution of primary particles, their overlap coefficient and the fractal dimension of agglomerates and aggregates.The approach proposed in this work was applied to five commercially-available nanostructured powders of differing natures (SiO₂, ZrO₂, Al₂O₃, Fe₂O₃ and Fe₃O₄). This first involved their prior analysis by the BET method and then being placed in suspension in aerosol form using a vortex-type shaker system. The procedure to calculate the specific surface area using image analysis was then applied to the sampled aerosols and compared to the BET measurements. The experimental results obtained on the five nanostructured powders cover a range of specific surface areas from 20 to 200 m²/g, the primary particles having mean diameters varying from 7 to 47 nm. Close agreement was observed between the two approaches which, taking into account measurement uncertainties, are statistically equivalent at significance level α = 0.05.     

Nanometer rough,sub-micrometer-thick and continuous diamond chemical vapor deposition film promoted by a synergetic ultrasonic effect

In this paper we report on a surface treatment to seed substrates for the promotion of diamond nucleation. This surface treatment consists of an ultrasonic abrasion process using poly-disperse slurry composed of a mixture of small diamond particles (<0.25 μm) and larger particles (>3 μm) which may consist of diamond, alumina, titanium, etc. Whereas ultrasonic abrasion with a mono-disperse diamond slurry results in a diamond nucleation density of ∼2–3×10⁸ particles/cm², treatment with poly-disperse slurries results in diamond nucleation density of values up to ∼5×10¹⁰ particles/cm². This effect was found to display a similar effectiveness on a variety of substrates such as silicon, sapphire, quartz, etc. The enhancement in diamond nucleation is interpreted by a ‘hammering’ effect whereby the larger particles insert very small diamond debris onto the treated surface, thus increasing the density of nuclei onto which diamond growth takes place during the chemical vapor deposition process. By increasing the nucleation density to values of ∼5×10¹⁰ particles/cm², continuous diamond films of thickness of less than ∼100 nm were grown after only 5 min of deposition. The roughness of continuous diamond films grown on substrates treated at optimum conditions obtains values of 15–20 nm. The effect of ultrasonic treatment on silicon substrates and the deposited films was investigated by atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.     

The pore structure of chrominophosphate catalysts

A series of chrominophosphates (CrPs) with various P/Cr ratios were prepared by the precipitation method. The pore structures of these catalysts were characterized by nitrogen adsorption and mercury-penetration porosimetry. The results indicated that the micro-pores with diameters less than 20 nm were due to the dehydration process and had a slit-shaped geometry. There were two types of large pores (meso- and macro-) with diameters greater than 20 nm. These pores had a cylindrical pore-shape. The meso-pores can be attributed to the packing of particles and the macro-pores are essentially due to the packing of the aggregates of the particles.     

聚合物乳液法表面修饰改性Fe_3O_4磁性纳米粒子特性研究

探讨了一种聚合物乳液在机械搅拌下,改性修饰Fe3O4纳米粒子表面,制备Fe3O4-聚合物复合粒子的方法。含羧基基团的柔软的聚合物乳胶粒子在机械搅拌作用下,与Fe3O4纳米粒子碰撞,变形,并通过物理粘附及羧基活性基团的化学吸附作用来包覆Fe3O4纳米粒子。在透射电子显微镜下可看到Fe3O4粒径约为5~20 nm,被聚合物包覆,虽存在团聚,但团聚体尺寸也仅100 nm左右,且团聚体中的Fe3O4纳米粒子也为聚合物隔开,纳米粒子得到了良好的分散。通过红外、热失重、接触角等的测试分析,进一步证实乳液聚合物对Fe3O4纳米粒子实现了表面修饰。实验结果表明,改性用聚合物的Tg以及复合温度是影响聚合物对Fe3O4纳米粒子包覆的重要因素之一。