Flame synthesis of carbon nanotubes and metallic nanomaterials

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2003.Includes bibliographical references.Carbon nanotubes are a remarkable material with many appealing properties. Despite the appeal of this material, there are few synthesis techniques capable of producing nanotubes in large quantities at low-cost. The broad objective of this study was to examine the potential of a premixed flame for the synthesis of carbon nanotubes with the view that flame synthesis may prove a means of continuous production at low-cost. The specific approach focused on the formation of metallic nanoparticles in flames; identification of nanotube formation zones, time scales, and transition conditions; characterization of material properties; and the development of a formation mechanism and associated flame-model. Carbon nanotube formation requires a source of carbon, a source of heat and the presence of metal particles. A fuel-rich flame is a high-temperature, carbon-rich environment and addition of metal is likely to give conditions suitable for nanotube growth. This study considered a premixed acetylene/oxygen/15 mol% argon flame doped with iron pentacarbonyl (Fe(CO)₅) vapor (typically 6100 ppm), operated at 50 Torr pressure and 30 cm/s cold gas feed velocity. The flame was investigated with regard to the growth of metal particles and subsequent formation and growth of carbon nanotubes. Thermophoretic samples were extracted from the flame at various heights above burner (HAB) and analyzed using transmission electron microscopy (TEM). HAB is representative of residence time in the flame. Size distribution and number density data were extracted from TEM images using a quantitative image analysis technique. The mean particle size for a precursor concentration of 6100 ppm was observed to increase from around 2 to 4 nm between 20 and 75 mm HAB.(cont.) The particle number density results showed a decreasing number density with increasing HAB, giving a complementary picture of the particle dynamics in the flame. Single-walled carbon nanotubes (SWNT) were also observed to form in the premixed flame. Thermophoretic sampling and TEM analysis gave insight into nanotube formation dynamics. Nanotube structures were observed to form as early as 30 mm HAB (20 ms) with growth proceeding rapidly within the next 10 to 20 mm HAB. The growth-rate for the nanotubes in this interval is estimated to be between 10 and 100 ptm per second. The upper region of the flame (50 to 70 mm HAB; 35 to 53 ms) is dominated by tangled web structures formed via the coalescence of individual nanotubes formed earlier in the flame. The nanotube structures are exclusively single-walled with no multi-walled nanotubes observed in any of the flame samples. The effect of carbon availability on nanotube formation was tested by collecting samples over a range of fuel equivalence ratios at fixed HAB. The morphology of the collected material revealed a nanotube formation 'window' of 1.5 < < 1.9, with lower dominated by discrete particles and higher favoring soot-like structures. These results were also verified using Raman spectroscopy. A clear trend of improved nanotube quality (number and length of nanotubes) is observed at lower . More filaments were observed with increasing concentration, however the length (and quality) of the nanotubes appeared higher at lower concentrations ...by Murray John Height.Ph.D

Rapid Bayesian optimisation for synthesis of short polymer fiber materials

The discovery of processes for the synthesis of new materials involves many decisions about process design, operation, and material properties. Experimentation is crucial but as complexity increases, exploration of variables can become impractical using traditional combinatorial approaches. We describe an iterative method which uses machine learning to optimise process development, incorporating multiple qualitative and quantitative objectives. We demonstrate the method with a novel fluid processing platform for synthesis of short polymer fibers, and show how the synthesis process can be efficiently directed to achieve material and process objectives

Comparative evaluation of antimicrobials for textile applications. Environ Int 2013; 53: 62–73

Many antimicrobial technologies are available for textiles. They may be used in many different textile applications to prevent the growth of microorganisms. Due to the biological activity of the antimicrobial compounds, the assessment of the safety of these substances is an ongoing subject of research and regulatory scrutiny. This review aims to give an overview on the main compounds used today for antimicrobial textile functionalization. Based on an evaluation of scientific publications, market data as well as regulatory documents, the potential effects of antimicrobials on the environment and on human health were considered and also life cycle perspectives were taken into account. The characteristics of each compound were summarized according to technical, environmental and human health criteria. Triclosan, silane quaternary ammonium compounds, zinc pyrithione and silver-based compounds are the main antimicrobials used in textiles. The synthetic organic compounds dominate the antimicrobials market on a weight basis. On the technical side the application rates of the antimicrobials used to functionalize a textile product are an important parameter with treatments requiring lower dosage rates offering clear benefits in terms of less active substance required to achieve the functionality. The durability of the antimicrobial treatment has a strong influence on the potential for release and subsequent environmental effects. In terms of environmental criteria, all compounds were rated similarly in effective removal in wastewater treatment processes. The extent of published information about environmental behavior for each compound varies, limiting the possibility for an in-depth comparison of all textile-relevant parameters across the antimicrobials. Nevertheless the comparative evaluation showed that each antimicrobial technology has specific risks and benefits that should be taken into account in evaluating the suitability of different antimicrobial products. The results also indicated that nanoscale silver and silver salts that achieve functionality with very low application rates offer clear potential benefits for textile use. The regular care of textiles consumes lots of resources (e.g. water, energy, chemicals) and antimicrobial treatments can play a role in reducing the frequency and/or intensity of laundering which can give potential for significant resource savings and associated impact on the environment