Zhao Yong Ding

Flame Synthesis of Carbon Nanotubes and Nanocapsules

Flame synthesis of carbon nanotubes and nanocapsules is demonstrated via a pyramid-shaped pyrolysis flame. The mixture of CO, H2, and nebulized catalyst raw material reacts in a high temperature environment formed inside the frustum of pyramid-shaped reactor heated by premixed flame of C2H2 and air outside. A sampling substrate inserted into the incomplete combusting flame of central reacting mixtures can gain the samples of carbon nanotubes and nanocapsules. The effect of sampling time and catalyst concentration is revealed via Field emission scanning electron microscope (FE-SEM) and High-resolution transmission electron microscopy (HR-TEM). 5-mins sampling time and 0.5/50 (Fe(CO)5/C2H5OH, volume ratio) of catalyst concentration is the most appropriate for carbon nanotubes synthesis. In addition, it is to say that catalyst concentration is the most important one among all the factors that can be used to determine whether the main products are carbon nanotubes or nanocapsules, and the structures of nanocapsules are also analyzed in detail.

Carbon Nanofibers from Pyrolysis Flame and Research on the Affecting Factors

Synthesis of carbon nanofibers from the V-type pyrolysis flame is a new method and it has wide application prospects. It needs simple laboratory equipments and normal atmosphere pressure. The V-type pyrolysis flame experimental system is introduced, involving V-type pyrolysis flame burner, mass flux controllers, sampling substrate etc. The carbon nanofibers were characterized by scanning electron microscope and transmission electron microscope. Carbon nanofibers with less impurities and high quality can be captured when the temperature was from 800 to 880°C, austenitic stainless steel type304 was served as sampling substrate, nickel nitrate was served as catalyst precursor and sampling time was 5 minutes. The carbon nanofibers are from 100 to 200 nm in diameter and dozens microns in length. The average diameter of catalyst particles is approximately from 20 to 50 nm. The effects of temperature, sampling substrate materials, sampling time and catalyst were analyzed. The temperature determined the diameter and shape of carbon nanofibers. The austenitic stainless steel type304 substrate containing nickel is in favor of synthesis of carbon nanofibers. The number of carbon nanofibers got more and more while the diameter got thicker firstly and then had little change with the sampling time increased within 5 minutes. In addition, experimental results also indicated that carbon nanofibers had much impurity and worse morphology if the diameter of catalyst particles was above 50nm.

Carbon Nanotubes Preparation Using Carbon Monoxide from the Pyrolysis Flame

Carbon nanotube is a new kind of carbon material. Synthesis of carbon nanotubes from V-type pyrolysis flame is a kind of novel technique. It needs simple laboratory equipments and normal atmosphere pressure. The V-type pyrolysis flame experimental system is introduced. Carbon source is the carbon monoxide which is carried to the middle pipe of V-type pyrolysis flame combustor. Heat source is from acetylene /air premixed flame. Pentacarbonyl iron, served as catalyst, is transported by spray- pyrolysis method into the burner. The carbon nanotubes were characterized by scanning electron microscope and transmission electron microscope. The diameter of carbon nanotubes is approximate 20nm and its length is dozens of microns. The impact of the temperature, reactant composition and catalyst was analyzed to reveal the rule of carbon nanotube growth. Carbon nanotubes with good form and less impurity can be captured when the temperature was from 800°C to 1000°C and carbon monoxide/hydrogen/helium mixed gas flow was supplied. The effective diameter of pentacarbonyl iron nanoparticles is approximate from 5nm to 20nm in the process of carbon nanotube formation. Mechanism of carbon nanotube base on the V-type pyrolysis flame method was proposed. The carbon “dissolved-proliferation-separate out” theory can be used to explain how the pentacarbonyl iron catalyses carbon monoxide to form carbon nanotubes.

Synthesis Mechanism of Flame Synthesized Deformity Carbon Nanotubes

Pyramid shaped pyrolysis flame is a new method to synthesis carbon nanotubes (CNTs). Oxy-acetylene flame was used as the source of heat, CO as the source of carbon, and iron pentacarbonyl (Fe(CO)5) as the source of catalyst. Field emission scanning electron microscope (FE-SEM) and High resolution transmission electron microscopy (HR-TEM) were used to illustrate the experimental results. Our results show straight, uniform and high degree graphitization CNTs were produced whereas lots of deformity tubes were present, as bamboo-shaped tubes, filled tubes, diameter changed tubes, irregular tubes, etc. In order to understand the synthesis mechanism of deformity tube, many models were presented for the different shape tubes. Synthesizing bamboo-shaped tubes maybe decide by capillary siphon and the low melting state of catalyst particles. Besides capillary siphon and the low melting state of catalyst particles, filled tubes mainly connect with the continuous supply of catalyst atom clusters. The diameter changed tubes maybe influenced by the diameter changing of catalyst particles and the action of other materials. Irregular tubes maybe affect by temperature and other factors.

Purification of Carbon Nanotubes Synthesized by Pyrolysis Flame

Pyramid shaped pyrolysis flame is a new method for carbon nanotubes (CNTs) synthesis, using this method has successfully produced high properties carbon nanotubes. But, because at the first 1min of sampling time, there are not tubes produced, so catalyst particles and carbon atom clusters assemble on the sampling substrate in the first 1min. Also, lots of amorphous carbon, deformity tubes, and graphite segment were produced in the experimental. In order to eliminate these impurities, ultrasonic treatment, aether cleaning, acid pickling, and co-processing were used. Ultrasonic treatment can separate particles from tubes, aether can clear amorphous carbon and graphite segment while acid pickling can dissolve catalyst particles. Using ultrasonic oscillation separation and aether as diluent can gain pure sample. Ultrasonic oscillation and nitric acid as diluent can purify products also, but not as good as aether as diluent. Concentrated nitric acid and long time immersion will destroy the structure of carbon nanotubes.

Influence Analysis of Sampling Time for Synthesis of Carbon Nanotubes in the V-Type Pyrolysis Flame

Synthesis of carbon nanotubes from V-type pyrolysis flame is a kind of novel method. It needs simple laboratory equipments and normal atmosphere pressure. The V-type pyrolysis flame experimental system is introduced. Carbon source is the carbon monoxide and heat source is from acetylene/air premixed flame. Pentacarbonyl iron, served as catalyst, is transported by spray- pyrolysis method into the flame. The carbon nanotubes were characterized by scanning electron microscope and transmission electron microscope. This study aims to find the formation rule of carbon nanotubes from the V-type pyrolysis flame in different sampling times. The carbon nanotubes with less impurity and high yield were captured successfully in the V-type pyrolysis flame. The diameter of carbon nanotubes was approximate between 10nm and 20nm, and its length was dozens of microns. When the sampling time was below 3 minutes, the growth of carbon nanotubes came into the preparation growth period. The length of the carbon nanotubes increased gradually and the diameter had no obvious change with the extension of sampling time. When the sampling time was continued to the 5th minute, the growth of carbon nanotubes came into the exuberant growth period. The carbon nanotubes growth was finished within 5minutes. Longer sampling time was meaningless after the carbon nanotubes formation.

Effects of Temperature for Carbon Nanotubes Synthesis

Pyramid sharp pyrolysis flame is a new method for carbon nanotubes synthesis. Oxy-acetylene flame outside the frustum of pyramid sharp reactor provides the necessary high temperature circumstance for carbon nanotubes synthesis, while inside the interior mixture of CO, H2, He, and iron pentacarbonyl (Fe(CO)5) is heated. CO is used as the source of carbon, Fe(CO)5 as the source of catalyst precursor. Special structure of the frustum of pyramid sharp reactor makes the oxy-acetylene flame folded gradually above the reactor. And it meets the condition that the interior mixture which has reacted initially under high temperature and will flow out of reactor avoids exposing to air completely and burning abundantly. Immersing a sampling substrate into the incomplete burning flame can gain carbon nanotubes. By adjusting the distance between the oxy-acetylene flame jet and the synthesis area, achieved the purpose that just changing one factor of synthesis or pyrolysis temperature while the other one constant, then respectively studied the effects of them on experimental. The perfect synthesis temperature in experimental is about 595°C, while the pyrolysis temperature is about 1000°C.

Catalyst Study for Carbon Nanotubes Synthesis by Flame

Flame offer potential for synthesis of carbon nanotubes in large quantities at significantly lower cost than that of other methods currently available. Catalyst can decide the produces category, structure, capability, etc. This study aimed to examine catalyst for carbon nanotubes synthesis. In this experimental, oxy-acetylene flame is used as the source of heat, and CO as the source of carbon. Nebulized Fe(CO)5 as catalyst gets straight, uniform, and long tubes while coated iron-aluminum compound as catalyst gets nanoparticles coated tubes, although these tubes are thin, long, and straight. Coated Fe(CO)5 as catalyst only can gets curly and short tubes, directly introduced into synthetic chamber gets particles, and Fe2O3 powder as catalyst mainly gets curly tubes. Although the tubes which iron-aluminum compound as catalyst are high capability, they must be purified before use while Fe(CO)5 as catalyst can gets smooth tubes.

Pyramid Shaped Pyrolysis Flame Catalyst Synthesis of Carbon Nanotubes

Pyramid sharped pyrolysis flame is a new method for carbon nanotubes synthesis. Oxy-acetylene flame outside the frustum of pyramid sharped reactor provides the necessary high temperature environment, while CO is used as the source of carbon, iron pentacarbonyl (Fe(CO)5) as the source of catalyst precursor in reactor. Inside, the mixture of CO, H2, and Fe(CO)5 will burn incompletely after initial reaction under high temperature. Immerging a sampling substrate into the incomplete burning flame can gain carbon nanotubes. Field emission scanning electron microscope and High resolution transmission electron microscopy were used to illustrate the results of experimental. By adjusting the distance between the oxy-acetylene flame jet and the synthesis zone, the purpose that only changing one factor of synthesis or pyrolysis temperature while the other one constant was achieved, then respectively studied the effects of them on experimental. The best synthesis temperature in experimental is about 590°C and pyrolysis temperature is about 1000°C. Effects of sampling time were also studied. 300s is economic for carbon nanotubes synthesis. Synthesis process of carbon nanotubes was discussed starting from the sampling time. The first 60s is the time for the temperature rise of sampling substrate. After the decalescence and thermal dissipation of substrate is balance, the temperature of substrate is fixed, and the main synthesis phase of carbon nanotubes begin.

Effects of Sampling Substrate for Carbon Nanotubes Synthesis

Pyramid shaped pyrolysis flame is a new method for carbon nanotubes synthesis. Oxy-acetylene flame outside the frustum of pyramid shaped reactor provides the necessary high temperature environment, while carbon monoxide is used as the source of carbon, iron pentacarbonyl (Fe(CO)5) as the source of catalyst precursor in reactor. In this experimental, substrate is the platform on which carbon nanotubes produced. The locations of 304 stainless steel and 201 stainless steel as substrates stayed in flame, 304 stainless steel pretreated or not, and different thickness of red copper and brass were studied. The results of 304 stainless steel substrate at the height of 10mm are the best, comparing with others at 7mm, 5mm, and 0mm heights. Although using 201 stainless steel as substrates has the same results, the results of it are not as good as 304 stainless steel. Pretreated 304 stainless steel as substrate can gain better properties of carbon nanotubes. Different thickness of brass and red copper can not get carbon nanotubes, only copper oxide on the surface of red copper while particles on brass.