• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 61
  • 19
  • 14
  • 10
  • 6
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 144
  • 144
  • 32
  • 27
  • 21
  • 19
  • 16
  • 15
  • 15
  • 14
  • 13
  • 13
  • 12
  • 12
  • 10
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Structure-property relationships in polyurethane-carbon particle nanocomposites

Jirakittidul, Kittimon January 2013 (has links)
In this research work, the relationships between structure and properties in micro-composites and nano-composites of polyurethane (PU) and conductive carbon particles have been studied. PU is a class of block copolymers containing the urethane linkage (-NHCO-O-) within its structure. Most PU block copolymers consist of alternating ‘soft’ and ‘hard’ segments. The hard segment used in this study was based on 4,4’-methylenebisphenylisocyanate (MDI) and 2-methyl 1,3 propanediol (MP-Diol) which produced a stiff aromatic polyurethane. Two soft segments; poly(tetrahydofuran) (PTHF) and poly(propylene oxide) based polyol end-capped with ethylene oxide (PPO-EO) were used to study the effects of soft segment structure on PU properties. DMTA, DSC and modulated-DSC indicated that PU-PTHF had higher microphase separation due to greater immiscibility between PTHF and the MDI/MP-Diol hard segments. In order to improve the electrical and mechanical properties of PU, conductive carbon particles were incorporated. The critical factor was the dispersion of these conductive fillers in the PU matrix to obtain optimum properties. The first carbon filler studied was carbon black (CB). PU composites prepared by the adding of MP-Diol plus ultrasonication (MU) gave the best dispersion of CB aggregates resulting in higher thermal decomposition temperature and good conductivity. However, the mechanical toughness was reduced. In subsequent studies, PU composites incorporating three different treated multiwalled carbon nanotubes (MWCNT) were investigated. MWCNT were disentangled and shortened by ultrasonication and acid cutting treatments. The ultrasonicated MWCNT (MWCNT_U) had longer length than the acid-cut MWCNT (MWCNT_AC). Ultrasonication was the best technique for dispersing MWCNT since the storage modulus was increased by ~200% at low MWCNT_U loading and the toughness remained the same as unfilled PU. PU/MWCNT_AC nanocomposites at 1 – 3 wt% of MWCNT_AC exhibited similar electrical conductivities to unfilled PU at an order of 10-8 S/cm, implying that the acid cutting treatment might disturb the inherent conductivity in MWCNT. The conductive percolation thresholds of composites were determined following the percolation theory. It was found that the percolation thresholds for MWCNT-filled composites were significantly lower than that of CB-filled composites. The lowest percolation threshold was observed in MWCNT_U-filled composite at 0.31 wt%.

Alumina - silicon carbide composites from kaolinite-carbon precursors by hot-pressing

Penugonda, Madhusudhan R. January 1987 (has links)
The system kaolinite - carbon black consisting of cheap precursors has been investigated, in terms of its potential to form A1₂ O₃ - SiC composites. The carbothermal reduction process of mullite and silica was studied, in detail, in the range 1275° to 1810° C and over different periods, both under sintering as well as hot-pressing conditions. It was established that the reduction of mullite and silica starts around 1450° C, where the rate of reaction is very slow. Until about 1800° C during the reduction of mullite, SiO₂ gets preferentially reduced, thus forming a composite ceramic consisting of SiC and A1₂ O₃ phases. The kinetics of the formation of SiC + A1₂ O₃ were followed in the range 1590° - 1660° C and it was noted that under hot-pressing conditions they follow a contracting cylinder model. The rate of reaction increased with the increase in temperature and followed a parabolic path with time because of the geometry of the hot-pressed specimens at each temperature. This indicated that the gas diffusion in and out of the system along the edges of the cylindrical specimens is the rate controlling step. The activation energy of the reduction process was calculated to be 922 KJ/mole. The application of pressure prior to the carbothermal reduction process seemed to be not favourable for the formation of SiC and A1₂ O₃, however, when applied after the beginning of soaking period, this greatly improved the densities and formation of SiC and A1₂ O₃. The microstructure of the samples was analysed using SEM and TEM. It was found that the grain size of the composite ceramic was of the order of 0.2μm. SiC was present mainly in the form of fine platelets. Finally, the isothermal compaction behaviour of the system was studied under a constant pressure in the temperature range 1200° C - 1800° C, during which the formation and carbothermal reduction of mullite and silica took place. A mathematical model based on the least squares fitting was used to fit the compaction curves. Due to the complex nature of the compaction data an empirical approach was used to interpret the data and a viscoelastic model was developed. It was found that the interactive-double-Kelvin unit having two elastic and two viscous components explained the type of compaction behaviour observed in the kaolinite + C system. One of the viscous components (η₁) and one of the elastic components (M₁) were found to be temperature sensitive. It is concluded that starting from the cheap precursors (kaolinite and carbon black) a particulate composite of A1₂ O₃,-SiC can be produced by hot-pressing technique. SiC-whisker formation is not encountered in this system. The very fine grain size of the paniculate composite, resulting in a small flaw size, should provide the composite ceramic with good mechanical properties. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A constitutive equation for carbon black filled elastomers

Oswal, Ravinder Kumar. January 1980 (has links)
Thesis: M.S., Massachusetts Institute of Technology, Department of Chemical Engineering, 1980 / Includes bibliographical references. / by Ravinder Kumar Oswal. / M.S. / M.S. Massachusetts Institute of Technology, Department of Chemical Engineering

Comparison of Carbon Black and Silica on Crack Growth Resistance

Park, Hanki January 2014 (has links)
No description available.

Mathematical modelling and simulation of dispersive mixing

Alsteens, Bernard 11 May 2005 (has links)
Rubber and plastics companies are using mixing equipment (‘internal mixers') which was invented by Banbury in 1916 and which has hardly evolved since then. There is an urgent need for the modernization of such equipment and the market is demanding higher and higher performances for rubber goods. The physics of the dispersion of porous or fibrous agglomerates in a flow field has not been widely addressed in the past, despite of its importance. This is mainly due to the technical difficulties associated with the observations of the kinetics of this disagglomeration and the wide range of size that must be probed. Two mechanisms are recognized : erosion and rupture. Actually, different software solutions to simulate the 3D transient behavior of a flow in internal batch mixer are available. In all existing codes, it is assumed that mixing and flow calculations are decoupled : the analysis of the mixing (distributive or dispersive mixing) is performed after the calculation of the flow. To sum-up, hierarchical modeling including micro-macro models is considered in this work. In this thesis, we developed new distributive tools and new dispersive mathematical model. We compared the numerical prediction with several experiments. Finally, we use this model to design a new rotor shape in the framework of a European project.

Synthesis of Carbon Nanomaterials and Their Applications in the Oilfield

Lu, Wei 16 September 2013 (has links)
This dissertation explores the potential applications of nanotechnology in the oilfield including poly(vinyl alcohol) stabilized carbon black nanoparticles for oil exploration and temperature-responsive carbon black nanoparticles for enhanced oil recovery. Also, it describes the rational design of graphene nanoribbons via intercalating reactive metals into multi-walled carbon nanotubes followed by addition of vinyl monomers or haloalkanes. Efficient production and modification of these aforementioned nanomaterials will make them more attractive for applications in the oilfield and electronics materials. A method is reported for detecting the hydrocarbon in the porous media with stabilized nanoparticles that are capable of efficiently transporting hydrophobic molecules through oil-containing rocks and selectively releasing them when a hydrocarbon is encountered. Nano-sized carbon black was oxidized and then functionalized with poly(vinyl alcohol) via a coupling reaction between the polymer's hydroxyl groups and the carboxylic groups on oxidized carbon black. Breakthrough curves show that poly(vinyl alcohol)-coated oxidized carbon black was stable in synthetic sea brine at room temperature and could carry the 14C-labeled radioactive tracer 2,2ˊ,5,5ˊ-tetrachlorobiphenyl through rocks and then released the tracer upon exposure to hydrocarbon. Due to the temperature-sensitivity of hydrogen bonds, higher molecular weight poly(vinyl alcohol) was used to improve the stability of carbon black nanoparticles in synthetic sea brine at higher temperatures. After sulfation, high molecular weight poly(vinyl alcohol) could stabilized carbon black nanoparticles in American Petroleum Institute standard brine at high temperatures. Those nanoparticles could efficiently transport mass-tagged probe molecules through a variety of oil-field rock types and selectively released the probe molecules into the hydrocarbon-containing rocks. Those proof-of-concept chemical nanoreporters can potentially be used under conditions commonly observed in the reservoir, and aid in the recovery of oil that remains in place. Amphiphilic carbon nanoparticles have been prepared that are capable of reversibly transferring across the water/oil interface in a temperature-controlled manner. Nano-sized carbon black was oxidized and then functionalized with amphiphilic diblock polyethylene-b-poly(ethylene glycol) copolymers that were water-soluble at low-to-moderate temperatures but oil-soluble at higher temperatures. The correlation between the phase transfer temperature and the melting temperature of the hydrophobic block of the copolymers and the weight percent of hydrophilic block were investigated. The amphiphilic nanoparticles were used to stabilize oil droplets for demonstrating potential applications in reducing the water/oil interfacial tension, a key parameter in optimizing crude oil extraction from downhole reservoirs. Graphene nanoribbons free of oxidized surfaces can be prepared in large batches and 100% yield by splitting multi-walled carbon nanotubes with potassium vapor. If desired, exfoliation is attainable in a subsequent step using chlorosulfonic acid. The low-defect density of these GNRs is indicated by their electrical conductivity, comparable to that of graphene derived from mechanically exfoliated graphite. Additionally, cost-effective and potentially industrially scalable, in situ functionalization procedures for preparation of soluble graphene nanoribbons from commercially carbon nanotubes are presented. To make alkane-functionalized graphene nanoribbons, multi-walled carbon nanotubes were intercalated by sodium/potassium alloy under liquid-phase conditions, followed by addition of haloalkanes, while polymer-functionalized graphene nanoribbons were prepared via polymerizing vinyl monomers using potassium-intercalated graphene nanoribbons. The correlation between the splitting of MWCNTs, the intrinsic properties of the intercalants and the degree of graphitization of the starting MWCNTs has also been demonstrated. Those functionalized graphene nanoribbons could have applications in conductive composites, transparent electrodes, transparent heat circuits, and supercapcitors.

The correlation between the conductivity of the carbon nanotubes and its growth process

Chen, I-ting 28 July 2011 (has links)

Electrical conductivity of segregated network polymer nanocomposites

Kim, Yeon Seok 02 June 2009 (has links)
A set of experiments was designed and performed to gain a fundamental understanding of various aspects of the segregated network concept. The electrical and mechanical properties of composites made from commercial latex and carbon black are compared with another composite made from a polymer solution. The percolation threshold of the emulsion-based composite is nearly one order of magnitude lower than that of the solution-based composite. The segregated network composite also shows significant improvement in both electrical and mechanical properties with low carbon black loading, while the solution-based composite achieves its maximum enhancement at higher carbon black loading (~25wt%). The effect of the particle size ratio between the polymer particle and the filler was also studied. In order to create a composite with an extremely large particle size ratio (> 80,000), layer-by-layer assembly was used to coat large polyethylene particles with the carbon black. Hyper-branched polyethylenimine was covalently grafted to the surface of polyethylene to promote the film growth. The resulting composite has a percolation threshold below 0.1 wt%, which is the lowest percolation threshold ever reported for a carbon-filled composite. Theoretical predictions suggest that the actual percolation threshold may be lower than 0.002 wt%. Finally, the effect of the emulsion polymer modulus on the segregated network was studied. Monodispersed emulsions with the different glass transition temperature were used as the matrix. The composites made using the emulsion with higher modulus show lower percolation threshold and higher conductivity. Higher modulus causes tighter packing of carbon black between the polymer particles. When the drying temperature was increased to 80°C, the percolation thresholds became closer between some systems because their moduli were very close. This work suggests modulus is a variable that can be used to tailor percolation threshold and electrical conductivity, along with polymer particle size.

The role of surface interactions on the properties of c - irradiated polydimethylsiloxane-silica composites.

Brender, Harold. January 1971 (has links)
No description available.

Array-based vapor sensing using conductive carbon black-polymer composite thin film detectors : thesis /

Severin, Erik Jon. January 1999 (has links)
Thesis (Ph.D.)--California Institute of Technology, 1999. / "UMI number: 9941121"--T.p. verso. Includes bibliographical references. Also available on microfilm. On-line version available via Caltech Library System.

Page generated in 0.0504 seconds