Stabilization Of Pitch Research Articles

Influence of Oxygen Uptake on Pitch Carbon Fiber.

Carbon fiber precursor materials, such as polyacrylonitrile, pitch, and cellulose/rayon, require thermal stabilization to maintain structural integrity during conversion into carbon fiber. Thermal stabilization mitigates undesirable decomposition and liquification of the fibers during the carbonization process. Generally, the thermal stabilization of mesophase pitch consists of the attachment of oxygen-containing functional groups onto the polymeric structure. In this study, the oxidation of mesophase pitch precursor fibers at various weight percentage increases (1, 3.5, 5, 7.5 wt%) and temperatures (260, 280, 290 °C) using in situ differential scanning calorimetry and thermogravimetric analysis isinvestigated. The results areanalyzed to determine the effect of temperature and weight percentage increase on the stabilization process of the fibers, and the fibers aresubsequently carbonized and tested for tensile mechanical performance. Thefindings provide insight into the relationship between stabilization conditions, fiber microstructure, and mechanical properties of the resulting carbon fibers.

Neuromuscular embodiment of feedback control elements in Drosophila flight.

While insects such as Drosophila are flying, aerodynamic instabilities require that they make millisecond time scale adjustments to their wing motion to stay aloft and on course. These stabilization reflexes can be modeled as a proportional-integral (PI) controller; however, it is unclear how such control might be instantiated in insects at the level of muscles and neurons. Here, we show that the b1 and b2 motor units-prominent components of the fly's steering muscle system-modulate specific elements of the PI controller: the angular displacement (integral) and angular velocity (proportional), respectively. Moreover, these effects are observed only during the stabilization of pitch. Our results provide evidence for an organizational principle in which each muscle contributes to a specific functional role in flight control, a finding that highlights the power of using top-down behavioral modeling to guide bottom-up cellular manipulation studies.

Effect of the air oxidation stabilization of pitch on the microstructure and sodium storage of hard carbons

Effect of the air oxidation stabilization of pitch on the microstructure and sodium storage of hard carbons

Effect of the air oxidation stabilization of pitch on the microstructure and sodium storage of hard carbons

Hard carbon anode materials for sodium ion batteries were prepared from petroleum pitch by air oxidation stabilization followed by carbonization. The effects of the oxidation stabilization temperature on the compositions and microstructures of the oxidized samples, as well as on the morphology, microstructure and sodium storage property of the carbonized samples were investigated. Results show that air oxidation introduces a large number of oxygen-containing functional groups, induces dehydrogenation condensation and oxidative crosslinking reactions, and transforms the petroleum asphalt from thermoplastic to thermosetting. The air oxidation stabilization treatment effectively hinders the inherent tendency of asphalt to graphitize during high temperature carbonization, resulting in carbons with randomly oriented carbon layers with more defects. Electrochemical tests show that o-PDC-350-1400 (oxidation stabilization at 350 °C, carbonization at 1400 °C) has a high charging specific capacity of 276.8 mAh g−1 at 100 mA g−1 and a high initial coulombic efficiency of 73.38%. Compared with sample PDC-1400 that was directly carbonized at 1400 °C, the charging specific capacity was increased by about 1.8 times and the initial coulombic efficiency was increased by 22%. The charging specific capacity of o-PDC-350-1400 after 200 cycles reached 170.2 mAh g−1, indicating good cycling stability.

Effects of the degree of oxidation of pitch fibers on their stabilization and carbonization behaviors

The stabilization of isotropic pitch (IP)-derived pitch fibers (PFs) and mesophase pitch (MP)-derived PFsin air was performed at different heating rates and with different final stabilization temperatures. The stabilized fibers (SFs) and carbon fibers (CFs) were characterized by elemental analysis, FT-IR, TG-MS and SEM to investigate the influence of the degree of oxidation of the SFs on the microstructures and mechanical properties of the CFs. Results showed that a slow heating rate during stabilization was beneficial to the oxidative cross-linking of PFs, and the corresponding CFs had a higher carbonization yield and tensile strength at the lower heating rate. When both IPF and MPF were stabilized at 270 oC, the two resulting CFs all reached their optimal performance. In addition, the FTIR peak intensity ratio of the C=O band at about 1700 cm–1 to the C=C band at 1600 cm–1 of the SFs had a good relationship to the carbonization yield and tensile strength of the CFs, and thiscan beusedto optimize the degree of oxidation of the SFs. Moreover, insufficiently stabilized fibers released a great deal of H2 and CH4, causing some porosity in the resulting CFs with a low tensile strength, especially forthe insufficiently stabilized IPCF. While over-stabilized fibers released a large amount of CO and CO2, causing cracked textures in the corresponding CFs, especially inthe over-stabilizedMPCF. Therefore, this research into the stabilization and carbonization behaviors of pitch fibers has great significance for improving the mechanical properties of pitch-based CFs.

Remarkable promotion effect of 2,3-Dimethyl-2,3-diphenylbutane on the oxidation stabilization of coal tar pitch

Oxidation stabilization is an extremely important step for maintaining microstructure as well as boosting performance of pitch-based carbon fibers, carbon/carbon composites, etc. However, the low reactivity of pitch molecules with oxygen and the sluggish diffusion kinetics of oxygen seriously hinder the oxidation process, leading to tremendous consumption on energy and time thereby. To overcome the problem, a novel free-radical-induced oxidation strategy is proposed through the modification of raw pitch with 2,3-Dimethyl-2,3-diphenylbutane (DMDPB). The strategy allows oxidation stabilization of pitch not relying solely on oxygen diffusion and self-reactivity of pitch molecules, but also on the substantial free radicals generated from thermolabile covalent bonds of DMDPB. Particularly, the free radical concentration of the modified pitch with 10 wt.% DMDPB reaches almost 2.2 times than that of raw pitch. Consequently, the crosslinking reactions between pitch molecules are homogeneously promoted and their average molecular weight, softening point, and carbon yields are also elevated significantly. The induced reaction mechanism of DMDPB and its synergistic reaction mechanism with oxygen have also been investigated explicitly. The rapid homogeneous stabilization approach has been applied in the preparation of carbon fiber (with a diameter of ~ 18 μm) and spherical activated carbon (with a diameter of ~ 600 μm), offering an attractive perspective on low-cost preparation of pitch-based carbon materials.

Insight into the oxidative reactivity of pitch fractions for predicting and optimizing the oxidation stabilization of pitch

Oxidative stability is of particular importance to maintain the morphology and adjust physicochemical properties of pitch-based carbon products. Due to the complex composition of pitch, the oxidative reactivity of the pitch components has rarely been reported to date, so that the oxidative stabilization conditions of pitch have been mainly selected from experience. In the study, a coal tar pitch was fractionated into toluene-soluble (TS), toluene-insoluble and pyridine-soluble (PS), pyridine-insoluble and quinoline-soluble (QS), and quinoline-insoluble (QI) fractions. The molecular structural features of each fraction and their reactivity with oxygen at varying oxidation temperature were characterized and evaluated. The results reveal that light fractions (TS and PS) with more alkyl side chains exhibit a higher reactivity at the low oxidation temperature range from 200 to 250 °C, leading to the formation of more cross-linked structures. Meanwhile heavy fractions (QS and QI), with relatively rich isolated aromatic hydrogen, seem to be remarkable in O2 uptake and the formation of C–O structures until the oxidation temperature rises above 250 °C. Insight into group composition of the pitch allows predicting its oxidative stability characteristics and further allowing it to quickly fine-tune operational conditions for time-effective and energy-saving stabilization.

Suppression of vocal responses to auditory perturbation with real-time visual feedback.

Speakers can adjust pitch using auditory feedback through a short-latency corrective response known as the pitch-shift response (PSR). Suppression of the PSR denotes on-line stabilization of pitch. In this paper, the hypothesis that pitch-shift responses can be suppressed with real-time visual feedback of vocal F0 is investigated. Mandarin speakers and naive speakers without tonal language experience were instructed to produce the sustained vowel /a/ and Mandarin tone /ma1/ in an audio-only condition and a separate audio-visual condition. Both Mandarin speakers and naive speakers suppressed pitch-shift responses in the audio-visual condition, regardless of task (/a/ or /ma1/) and stimulus magnitude (25 cents or 200 cents). These findings suggest that multisensory feedback (audio-visual) can improve the stability of voice F0. The benefit of audio-visual integration is independent of language experience.

Integration and In-Field Gains Selection of Flight and Navigation Controller for Remotely Piloted Aircraft System

Abstract In the paper the implementation process of commercial flight and navigational controller in own aircraft is shown. The process of autopilot integration were performed for the fixed-wing type of unmanned aerial vehicle designed in high-wing and pull configuration of the drive. The above equipment were integrated and proper software control algorithms were chosen. The correctness of chosen hardware and software solution were verified in ground tests and experimental flights. The PID controllers for longitude and latitude controller channels were selected. The proper deflections of control surfaces and stabilization of roll, pitch and yaw angles were tested. In the next stage operation of telecommunication link and flight stabilization were verified. In the last part of investigations the preliminary control gains and configuration parameters for roll angle control loop were chosen. This enable better behavior of UAV during turns. Also it affected other modes of flight such as loiter (circle around designated point) and auto mode where the plane executed a pre-programmed mission.

Enhancing the tensile strength of isotropic pitch-based carbon fibers by improving the stabilization and carbonization properties of precursor pitch

A unique isotropic pitch composed of linear chains of polycondensed aromatic molecules was synthesized through the bromination and subsequent dehydrobromination of mixed naphtha-cracked oil (NCO) and quinoline-insoluble free coal tar (CT). Isotropic pitch-based carbon fibers obtained from the co-carbonization of an NCO/CT mixture via bromination and dehydrobromination exhibited an unprecedentedly high tensile strengths and elongations at break of 1800 and 2050 MPa, and 3.2 and 2.8% following carbonization at 800 and 1100 °C for 5 min, respectively. The aromatic components derived from the co-carbonization process were primarily condensed cyclic compounds containing four or five aromatic rings. These substructures enhanced the tensile strength of the carbon fibers up to 2050 MPa, which is a level much higher than that reported for carbon fibers derived from naphtha-cracked oil-based isotropic pitch. TOF-MS analyses indicated that the molecular weight of the NCO/CT derived pitch was higher than that of the NCO derived pitch. Both isotropic pitches exhibited Bingham behavior above their softening temperatures. However, the linear chains of the higher aromatic units of the NCO/CT derived pitch resulted in a higher degree of shear-thinning than was observed with the NCO derived pitch, resulting in a higher degree of molecular orientation during spinning.

Study on the stabilization of isotropic pitch based fibers

Evolution of chemical structure and out gases of isotropic pitch fibers were studied in terms of stabilization. As stabilization plays an important role in the mechanical properties of carbon fibers (CF), thermogravimetric analysis was performed to optimize the duration and temperature of stabilization in this study. Fourier transform-infrared spectroscopy was applied to investigate chemical structure and formation of O2 containing functional groups during the stabilization. In addition, mass spectrometry showed that O2 uptake started at around 150 ℃ along with formation of various gases such as CO, CO2, and H2O. The longer stabilization resulted in higher tensile strength of the pitch fiber with higher strain-to-failure due to intermolecular crosslinking reactions leading to a network formation of pitch molecules. The stabilized fibers were carbonized at 1500 ℃ in a furnace under nitrogen atmosphere. Maximum tensile strengths of ~900 MPa were obtained from CF stabilized for 60 min at 280 ℃. Open image in new window

Active and passive stabilization of body pitch in insect flight

Flying insects have evolved sophisticated sensory–motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.

Carbonization behaviour of modified synthetic mesophase pitches

Stabilization of naphthalene-derived synthetic mesophase pitch was achieved by controlled oxidation or reaction with phenanthrenequinone (PHQ) in order to suppress the swelling during high-temperature treatments. The modified pitches were characterized and their carbonization behaviour was studied by thermogravimetry–mass spectrometry. The results show that naphthenic groups are involved in the stabilization process. PHQ reacts via cycloaddition reactions, yielding oxygen-containing non-planar structures, a feature that accounts for the loss of anisotropic properties of the final material.

Injection and stabilization of mesophase pitch in the fabrication of carbon–carbon composites. Part I. Injection process

The fabrication of carbon–carbon composites by injection of low viscosity mesophase pitch through a fiber preform followed by stabilization and carbonization was examined. The fully transformed mesophase MOMP and AR pitches were injected through either soft or rigidized disk preforms 35 mm thick and 68 mm in diameter. Injection provided good even filling of major flow channels and fiber bundles. Flow-induced fibrous microstructures were retained by quenching and preserved by stabilization upon carbonization. A second injection cycle was effective in filling voidage created by thermal densification. A third cycle was applied, but required severe injection conditions and provided only incremental improvement. The carbon–carbon composite reached a density of 1.8 g/cm 3 after three injection cycles.

Injection and stabilization of mesophase pitch in the fabrication of carbon–carbon composites: Part II. Stabilization process

In the fabrication of carbon–carbon composites by mesophase injection through a fiber preform, it is essential to stabilize the flow-induced microstructure in the flow channels and to prevent relaxation and exudation of the mesophase. Oxidation stabilization studies were conducted on preforms injected with the naphthalene-based AR mesophase pitch. Oxidation mass gain (OMG) curves at 170, 222, and 270 °C were generated for 60°-wedges cut from full size composite disks. The rates of OMG at 170 °C of first- and second-cycle injection wedges and full-size disks were comparable to those using as-spun filaments 30 μm in diameter, and particles sieved to 200 to 340 μm. The results suggest that oxygen is accessible deep into a mesophase matrix and the transport is facilitated by connected array of shrinkage cracks. Oxidation at 170 °C has strong advantage over higher oxidation temperatures by having a higher carbon yield and lower OMG threshold and thus oxidation time required for stabilization. The 60°-wedges could be stabilized at 170 °C after a 25 h oxidation with a 7.2% OMG and attaining a carbon yield above 85%.

Injection and stabilization of mesophase pitch in the fabrication of carbon–carbon composites. Part III: Mesophase stabilization at low temperatures and elevated oxidation pressures

Micrography and infrared spectroscopy were applied to explore microstructural stabilization of mesophase pitch at oxidation temperatures as low as 130 °C. AR mesophase pitch synthesized from naphthalene was drawn to rods and thick filaments with fine fibrous microstructures that coarsen upon carbonization without adequate stabilization. At 270 °C, the stabilization front advances rapidly to a depth of about 7 μm, after which no further growth is perceptible. At low temperatures, there is a time lag before a stabilized layer can be observed near the surface, but thereafter the stabilization front advances relatively rapidly. For longer oxidation times, the low-temperature stabilization depths can exceed those attained at higher temperatures. FTIR spectra confirmed chemical reactivity and the formation of oxygen-bearing functional groups even at the low oxidation temperatures. Oxidation under a moderate pressure of 0.7 MPa can be effective in raising the oxygen uptake and increasing the stabilization depths significantly. All evidences point to the advantageous use of lower oxidative temperatures: more effective penetration of stabilization depth, lessen destructive effects of over-oxidation, and potentially shorter processing times.

Oxidative stabilization of petroleum pitch at high pressure and its effects on the microstructure and carbon yield after carbonization/graphitization

The toluene insoluble portion of petroleum pitch A240 was oxidized using pure oxygen under high pressures in the range of 100–500 psi. The effects of oxidation temperature, pressure and time on the percentage of weight gain were investigated. Carbonization of the oxidized pitch samples indicated that the pitch samples were well stabilized after high pressure oxidation. Analyses of X-ray diffraction and Raman spectra showed that the pitch samples, after high pressure oxidation, changed from an easily graphitizable carbon material to non-graphitizable. Measurements of carbon yield showed a decrease with the increase of oxidation weight gain.

Stabilization of pitch derived ultrafine particles by iodine treatment

Stabilization of pitch derived ultrafine particles by iodine treatment

Stabilization of Pitch Derived Ultrafine Particles by Iodine Treatment

Stabilization of Pitch Derived Ultrafine Particles by Iodine Treatment

95/05989 The oxidative stabilization and carbonization of a synthetic mesophase pitch, part II: The carbonization process

95/05989 The oxidative stabilization and carbonization of a synthetic mesophase pitch, part II: The carbonization process