Quinoline Insoluble Particles Research Articles

Observations of crystal strains in filler and QI particles through TEM examination – Effect of processing and grain size

Nuclear graphite serves as a moderator and structural support in British Advanced Gas-cooled Reactors (AGRs) and is a candidate for the next generation of nuclear reactors. Graphite is comprised of three main phases: binder, filler and porosity; which are dependent on the manufacturing process and raw materials. During the graphitisation process, graphite components are subjected to high temperatures which may lead to significant strains and also creation of cracks known as Mrozowski cracks. Transmission electron microscopy observations confirmed the existence of strain fields generated by Mrozowski cracks, manufacturing and neutron irradiation in multiple graphite grades. This research confirms the existence of crystal strains in filler particles and quinoline insoluble (QI) particles. The observations gathered in this research indicate that crystal strains provide different degrees of rigidity to the filler and binder phase. A comparison between crystal strains of QI particles and filler particles may explain the irradiation response of these phases.

Ion-beam-assisted characterization of quinoline-insoluble particles in nuclear graphite

The irradiation behavior of graphite is essential for its applications in nuclear industry. However, the differences between graphite's behaviors are not well understood because of the very limited knowledge of microstructural differences between graphites. One typical structure, quinoline insoluble (QI) particle, was investigated using IG-110 and NBG-18 graphite. After irradiation, the QI particles on the polished surface were proved to become hillocks and can be easily identified by using a scanning electron microscope (SEM). Thus a method combining ion irradiation and SEM characterization was proposed to study the distribution and concentration of QI particles in graphite. During irradiation, the QI particles were found to evolve into densified spheres which have weak bonding with the surrounding graphite structures, indicating that the densification of QI particles does not contribute obviously to graphite dimensional shrinkage. A much higher concentration of QI particles in NBG-18 than IG-110 was characterized and is suggested to be responsible for the smaller maximum dimensional shrinkage of NBG-18 than IG-110 during irradiation.

Highly fluorescent carbon dots from quinoline insoluble residues in coal tar

Coal is the most abundant and affordable carbonaceous material. However, to use as a combustible energy resource material coal to coke conversion is necessary and during the conversion, coal tar is produced. In this coal tar, Quinoline Insoluble (QI) residues are found as a solid carbon particle. Till date, the utility of the QI particles is very limited. Different spectroscopic characterizations show that QI particles are easy to oxidize and we have successfully synthesized highly fluorescent carbon dots (CDs) from the QI particles using different oxidizing agents. The fluorescent properties of CDs are strongly depended on the degree of oxidation as well as their size. The emission wavelengths, quantum yield can be tuned by changing the oxidizing agents. Further, the excited state lifetime is also determined and the average lifetime of the CD is in nano-seconds region. Therefore, it can be utilized for different optoelectronic and biological imaging applications. Thus, the simple strategy can provide an easy route to bulk scale commercial synthesis of CD materials as its precursor materials are cheap and easily available.

The effect of carbon black on reforming of pyrolysis fuel oil for a binder pitch

Pyrolysis fuel oil (PFO) has been reformed to increase the quinoline-insoluble (QI) content by adding carbon black for use as a binder pitch because petroleum-based pitch generally has a low QI content. The prepared pitch was analyzed for its aromaticity (fa), QI content, molecular weight distribution, coking value (CV), softening point (SP), and carbonization yield. The QI content of the reformed pitches increased from 0.4% to 14.1%, whereas the average molecular weight of only quinoline-soluble content decreased by increasing the carbon black content. These results indicate that carbon black adsorbs low-molecular-weight compounds and serves as nuclei for the growth of QI particles. For these reasons, the SP and carbonization yield showed a decreasing tendency, but increased when QI sharply increased.

Neutron irradiation induced microstructural changes in NBG-18 and IG-110 nuclear graphites

This paper reports the neutron-irradiation-induced effects on the microstructure of NBG-18 and IG-110 nuclear graphites. The high-temperature neutron irradiation at two different irradiation conditions was carried out at the Advanced Test Reactor National User Facility at the Idaho National Laboratory. NBG-18 samples were irradiated to 1.54dpa and 6.78dpa at 430°C and 678°C respectively. IG-110 samples were irradiated to 1.91dpa and 6.70dpa at 451°C and 674°C respectively. Bright-field transmission electron microscopy imaging was used to study the changes in different microstructural components such as filler particles, microcracks, binder and quinoline-insoluble (QI) particles. Significant changes have been observed in samples irradiated to about 6.7dpa. The closing of pre-existing microcracks was observed in both the filler and the binder phases. The binder phase exhibited substantial densification with near complete elimination of the microcracks. The QI particles embedded in the binder phase exhibited a complete microstructural transformation from rosettes to highly crystalline solid spheres. The lattice images indicate the formation of edge dislocations as well as extended line defects bridging the adjacent basal planes. The positive climb of these dislocations has been identified as the main contributor to the irradiation-induced swelling of the graphite lattice.

Microstructural Characterization of Next Generation Nuclear Graphites

This article reports the microstructural characteristics of various petroleum and pitch based nuclear graphites (IG-110, NBG-18, and PCEA) that are of interest to the next generation nuclear plant program. Bright-field transmission electron microscopy imaging was used to identify and understand the different features constituting the microstructure of nuclear graphite such as the filler particles, microcracks, binder phase, rosette-shaped quinoline insoluble (QI) particles, chaotic structures, and turbostratic graphite phase. The dimensions of microcracks were found to vary from a few nanometers to tens of microns. Furthermore, the microcracks were found to be filled with amorphous carbon of unknown origin. The pitch coke based graphite (NBG-18) was found to contain higher concentration of binder phase constituting QI particles as well as chaotic structures. The turbostratic graphite, present in all of the grades, was identified through their elliptical diffraction patterns. The difference in the microstructure has been analyzed in view of their processing conditions.

Nanostructures of carbon in nuclear graphite

A variety of nanostructures of carbon in nuclear graphite were revealed by transmission electron microscopy (TEM) and high resolution TEM. Theses nanostructures include nanosized graphite particles, quinoline insoluble particles, a chaotic structure and a non-graphitizable structure of carbon. The basic structure of these nanostructures was observed to be nanosized packets of graphitic sheets or nanosized graphene.

The microstructure of nuclear graphite binders

The microstructures of the binder in two grades of nuclear graphite, Gilsocarbon graphite and Pile Grade A graphite, were characterized by light microscopy, transmission electron microscopy and high resolution transmission electron microscopy. A variety of structures of carbon were observed, including a well-graphitized structure, nanosized graphite particles, quinoline insoluble (QI) particles, chaotic structures and non-graphitizing carbon. QI particles were observed on the surface of mesophase spheres as well as inside mesophase spheres. The aggregation of QI particles on the surface of mesophase spheres, or very near the surface in mesophase spheres, appears to have a significant influence on the development of the mesophase structure, resulting in refinement of the mesophase spheres before their coalescence. The chaotic structure, which is turbostratic and isotropic, is suggested to have developed from the isotropic pitch remaining between mesophase spheres. The non-graphitizing carbon consisted of flat and curved single layer graphene fragments with a size typically less than 1 nm. The formation of the various structures in the two graphites is attributed to the introduction of different pitches at stages of the graphite manufacture.

Influence of wet and preheated coal charging on the nature of quinoline insolubles of coal tars and their derived pitches

Differences between primary quinoline insoluble (QI) material of coal tars and their derived pitches caused by preheating carbonization have been studied using microscopic techniques, Coulter Laser particle size analysis and solid-state 13C NMR. The selected tars were produced from the same coal using wet and preheated charging at the INCAR experimental coking test plant, which operates on a semi-industrial scale. Specific operational conditions were successfully applied not only to reduce the ash content and the QI and toluene insoluble (TI) contents in the tars produced by the preheating process, but also to modify the nature of the QI particles. In addition, structural changes in the insoluble materials formed during the pitch production from the tar have been monitored.

Measurement of an intrinsic softening temperature for coal-tar pitch by proton magnetic resonance thermal analysis

The measurement of a softening temperature of the amorphous continuous phase in a composite by means of proton magnetic resonance thermal analysis (PMRTA) is described. A coaltar pitch with various quinoline insoluble (QI) particle levels was used to demonstrate that PMRTA can be used to obtain an intrinsic softening point of the amorphous continuous phase. Standard methods for measuring a softening point for pitch determine a value influenced by the presence of the QI particles.

Influence of QI on mesophase structure

The influence of quinoline insoluble (QI) particles on the transformation of isotropic pitch to mesophase has been studied using light microscopy, scanning electron microscopy, and transmission electron microscopy. The authors conclude that QI does not significantly affect either the nucleation of mesophase spheres or the rate at which mesophase forms. However, QI does profoundly affect the structure of the pitch at all stages of conversion and the structure of carbons derived from mesophase. QI particles appear to “pin” the mesophase structures in their vicinity, making the mesophase behave as a much more viscous material than would otherwise be the case; this is consistent with the many changes of layer plane orientation observed within QI-rich mesophase. The complex structure caused by the QI persists through to the stage of solidification so that some properties of the carbon product may be much modified by controlling the occurrence of QI in the parent pitch. All as-received pitch samples, including nominally “QI-free pitches” contain significant numbers of QI particles.

290. Characteristics of quinoline insoluble particles and their influence on coal tar pitches

290. Characteristics of quinoline insoluble particles and their influence on coal tar pitches

Shapes of Meso-Carbon Microbeads

Quinoline-soluble coal-tar pitch, coal-tar pitch containing 3.4% free-carbon (quinolineinsoluble particles) and petroleum asphalt containing 5.4% sulphur were heat-treated for 120 min., 90 min. and 60 min. at 430°C respectively. Formation of mesophase spherules was observed by using a polarized-light microscope.The mesophase spherules were separated by solvent extraction from heat-treated pitches. The separated mesophase spherules were named meso-carbon microbeads and classified into type C, type M and type P according to above mentioned raw pitches. The shapes of meso-carbon microbeads were studied with a scanning electron microscope.The shapes of type C and type P can be divided into two classes, that is, the shapes of meso-carbon microbeads having larger size than about 5μm are approximately true spheres and those having smaller size than about 3μm are lemon-like spheroid. It is not obvious that the meso-carbon microbeads showing lemon-like shapes have the same lamellae structure as those larger than about 5μm, because the sensitive-tint technique can not be used for the meso-carbon microbeads smaller than about 3μm according to the resolving power of optical microscope.The shapes of type M are irregular, although their sizes are almost the same, and the free-carbon smaller than about 1μm are retained over the surface of mesophase.