Qiang Zhang

Abstract: Based on three-dimensional (3D) acceleration sensing, an intelligent particle spy capable of detecting, transferring, and storing data, is proposed under the name of Particle Measurement Sensor (PMS). A prototype 60-mm-dia PMSwas tested to track its freefall in terms of velocity and displacement, and served as a particle spy in a fluidized bed delivering the in situ acceleration information it detects. With increasing superficial gas velocity in the fluidized bed, the acceleration felt by PMS was observed to increase. The variance of the signals, which reflect the fluctuation, increased at first, reaching a maximum at the gas velocity (Uc) which marks the transition from bubbling to turbulent fluidization. Through probability density distribution (PDD) analysis, the PDD peak can be divided into the emulsion phase peak and the bubble phase peak. The average acceleration of emulsion and bubble phase increased, while the variance of both phases reached a maximum at Uc, at the same time. However, the difference between the variances of two phases reached the maximum at Uc. Findings of this study indicate that PMS can record independent in situ information. Further, it can provide other in situ measurements when equipped with additional multi-functional sensors.

Abstract: A surfactant-free two-step shearing strategy was applied to disperse vertically aligned carbon nanotube (VACNT) arrays into individually dispersed CNTs. First, big blocks of VACNT arrays were sheared into fluffy CNTs. The fluffy CNTs were composed of CNT bundles with a diameter of 1-10 mum and a length of several millimeters. After that, the fluffy CNTs were further sheared in liquid phase to obtain individually dispersed CNTs. As comparison, sonication and grinding were also employed for further dispersion of the fluffy CNTs. The length of CNTs dispersed by shearing method was the longest and up to several hundred micrometers. The CNT dispersions from the three methods can be used to fabricate transparent conductive films (TCFs). The TCFs from CNTs dispersed by shearing method showed the highest conductivity at the same transparency. VACNT arrays with a small diameter ( approximately 10 nm) were dispersed by the shearing method as well, from which the TCF with a surface resistance of 2.5 kOmega/ and a transparency of 78.6% (at 500 nm) was obtained. The ratio of dc to optical conductivity (sigma(dc)/sigma(op)) of the as-dispersed CNT array was 0.711, which can compare beauty with that of single-walled CNTs and double-walled CNTs grown by the CVD process.

Abstract:

Abstract: Fluffy carbon nanotubes (CNTs), which are cotton-like macroscopic structures, are obtained by simple high-speed shearing of vertically aligned CNT (VACNT) arrays. The fluffy CNTs are composed of CNT bundles with a diameter of several micrometers, and have an extremely low apparent density of 3–10 g/L. A requisite for their formation is the alignment of CNTs in the initial array. The shear between the rotor and the arrays tears the arrays along the axial direction and this results in their dispersion into low density fluffy CNTs.

Abstract: Large amount of vertically aligned carbon nanotube (CNT) arrays were grown among the layers of vermiculite in a fluidized bed reactor. The vermiculite, which was 100–300 μm in diameter and merely 50–100 μm thick, served as catalyst carrier. The Fe/Mo active phase was randomly distributed among the layers of vermiculite. The catalyst shows good fluidization characteristics, and can easily be fluidized in the reactor within a large range of gas velocities. When ethylene is used as carbon source, CNT arrays with a relatively uniform length and CNT diameter can be synthesized. The CNTs in the arrays are with an inner diameter of 3–6 nm, an outer diameter of 7–12 nm, and a length of up to several tens of micrometers. The as-grown CNTs possess good alignment and exhibit a purity of ca. 84%. Unlike CNT arrays grown on a plane or spherical substrate, the CNT arrays grown in the fluidized bed remain their particle morphologies with a size of 50–300 μm and the good fluidization characteristics were preserved accordingly.

Abstract: The scaled-up mass production of carbon nanotubes (CNTs) was reviewed by a multiscale analysis from the delicate catalyst control needed at the atomic level, CNT agglomerate formation at the mesoscopic scale, to the continuous mass production process on the macroscopic scale. A four level analysis that considered CNT assembly, agglomerate structure, reactor hydrodynamics and coupled processing was used. Atomic scale catalyst design concepts were used to modulate the CNT structure. On the reactor scale, the design consideration was on getting suitable CNT and catalyst agglomerates with good fluidization behavior and transport properties. A pilot plant with high yield (15 kg/h) and purity (N99.9%) was

Abstract: We report the cushioning behavior of highly agglomerated carbon nanotubes. The nanotube agglomerates can be repeatedly compacted to achieve large volume reduction (>50%) and expanded to nearly original volume without structural failure, like a robust porous cushion. At a higher pressure range (10-125 MPa), the energy absorbed per unit volume is 1 order of magnitude higher than conventional cushion materials such as foamy polystyrene. The structure of hierarchical agglomerates can be controlled for tailoring the cushioning properties and obtaining a lower cushioning coefficient (higher energy absorption) over a wide range of pressures (1-100 MPa). The mechanism was studied in terms of morphology evolution of the nanotube aggregates and pore size distribution during compression.

Abstract: A simple floating catalyst method was used to produce carbon nanotube (CNT) carpets or arrays, tens of micrometers in length on the host inorganic fibers (aluminum silicate or quartz fibers), to form a CNT-inorganic oxide coaxial fiber or brush structure. The insulating inorganic oxide fiber had been changed into an electrical conducting material with a volume resistance of 2–6 Ω cm. The differences in density, length and straightness of the CNTs on different fibers were mainly attributed to the acidic surface properties of the aluminum silicate and quartz fibers.

Abstract: This study sought to produce carbon nanotube (CNT) pulp out of extremely long, vertically aligned CNT arrays as raw materials. After high-speed shearing and mixing nitric acid and sulfuric acid, which served as the treatment, the researchers produced the desired pulp, which was further transformed into CNT paper by a common filtration process. The paper’s tensile strength, Young’s modulus and electrical conductivity were 7.5 MPa, 785 MPa and 1.0 × 104 S/m, respectively, when the temperature of the acid treatment was at 110°C. Apart from this, the researchers also improved the mechanical property of CNT paper by polymers. The CNT paper was soaked in polyethylene oxide, polyvinyl pyrrolidone, and polyvinyl alcohol (PVA) solution, eventually making the CNT/PVA film show its mechanical properties, which increased, while its electrical conductivity decreased. To diffuse the polymer into the CNT paper thoroughly, the researchers used vacuum filtration to fabricate a CNT/PVA film by penetrating PVA into the CNT paper. After a ten-hour filtration, the tensile strength and Young’s modulus of CNT/PVA film were 96.1 MPa and 6.23 GPa, respectively, which show an increase by factors of 12 and 7, respectively, although the material’s electrical conductivity was lowered to 0.16×104 S/m.

Abstract: Vertically aligned carbon nanotube (VACNT) arrays grown on ceramic spheres are obtained from ethylene using a floating catalysis process. The exhaust gas mainly contains light gaseous hydrocarbons, which decreases the contamination at the outlet of the reactor. Linear synchronous growth of the VACNT arrays is demonstrated and the morphology evolution of VACNT array grown on spheres is shown. The VACNT arrays on the spheres crack radially into a flower-like structure when the length of CNT is above 400 μm. The VACNT arrays grown on spheres still possess good flowability even when the length of the array reaches 1100 μm after a 2-h growth at 800 °C. The arrays on the spheres show good alignment, high purity and good graphitization. Meanwhile, with a decrease in temperature, the diameter of CNTs in the array correspondingly decreases, the distribution becomes narrower, and the growth rate decreases. The apparent activation energy is 180 ± 8 kJ/mol, indicating that ethylene is a good carbon source for fast and continuous radial growth of millimeter VACNT arrays on ceramic spheres.

Abstract: Electrospinning provides a simple and versatile method for generating ultra thin fibers with diameters ranging from nanometer to micron out of various materials. However, there are still challenges in the alignment of electrospun nanofibers, which is an important step toward the exploitation of these fibers in applications. In this letter, we report a method using the gas flow to assist the alignment of electrospun nanofibers, which can form well-aligned super long polymeric nanofibers over large areas with the length of more than 20 cm. The improved collector is built by coupling a "T"-shaped electrode and a rectangle electrode, and it can make the electrospun nanofiber form a fixed site at the "T"-shaped electrode under the electric field and make it possible to use an assisting gas flow (AGF) to draw the other part of the nanofiber to fly toward the upside of the rectangle electrode and obtain well-aligned long nanofibers. These well-aligned long nanofibers can be further applied easily without disturbing the aligned structure, which is convenient for the measurement and device fabrications.

Abstract: The formation of a vertically aligned carbon nanotube (VA-CNT) array in a floating catalyst process was described as a synchronous growth that resulted from the interaction of fast growth and slow growth CNTs. The array growth was characterized by the observations that straight and curved CNTs were formed during growth, and the tortuosity change of the curved CNTs and a G band Raman shift during growth. These were used to deduce that pristine stress was present in the CNTs. A model of the stresses as caused by space limitation and different growth rates was used to explain the development of a synchronous growth of the VA-CNT array. The tortuosity of the curved CNTs and Raman shift decreased and were constant after the growth of a certain length of the array, indicating that constant stresses were maintained in the growing array after the growth of this length. This indicated that an ordered CNT structure was formed and a transition from random structure to ordered structure growth had taken place in the growth. The transition was explained by a thermodynamic argument using the Onsager virial theory. Based on the vapor−liquid−solid model and bottom up growth for a single CNT, the description of a synchronous growth made possible by existent stresses gives a view that accounts for the interaction between CNTs in an array, and it can provide guidelines for a more precise control of the array structure.

Abstract: Carbon nanotubes (CNTs) with totally hollow channels and/or totally filled copper nanowires have been fabricated by methane decomposition using copper microgrid as a catalyst at 1173 K. The formation mechanism of CNTs with totally hollow channels is carbon precipitation at carbon-metal interface via the preferable surface diffusion mode of carbon. The selectivity of these CNTs can be improved by increasing the purity of copper catalysts and adding hydrogen in the feed gas. To form long and continuous copper nanowires up to 8–10 μm the filling of copper in the CNT channel requires the liquid or quasi-liquid state capillary adsorption of nanosized copper at 1173 K under the thermal driving force. The filling volume ratio of copper to total nano-channel of the CNTs is firstly increased to about 50%. The copper inside the CNTs is of single crystalline form and face centered cubic (fcc) structure. The method is useful for further controlled synthesis of CNTs with totally hollow channels and/or totally copper filled nanowires.