Turbostratic Layer Research Articles

Graphite Made from Coal by High-Temperature Treatment: An Insight into the Nanometric Carbon Structural Evolution

Graphite made from coal will not only widen the graphite mineral resource, but also significantly improve the value of coal utilization. In this study, anthracite coal was heated in the temperature range of 500 to 2900 °C to study the size increase of nanometric graphite crystallites from anthracite to real graphite. The carbon content rapidly increases to 99.2% when heated from room temperature to 1600 °C, and then gradually increases to 100% when the treated temperature increases to 2900 °C. The FTIR results show that methyl, methylene, and aromatic hydrocarbon, preexisting in the raw anthracite, were preserved in the JZS-500 sample, but that when the treated temperature ≥ 1000 °C, these C-H bonds almost disappear. The basic structural units (nano graphitic carbon) grow into distorted columns, and the basic structural units and micro-columns re-oriented and coalesced to form local molecular oriented domains with the temperature increase from anthracite to JZS-1500. When the temperature ≥ 1600 °C, amorphous carbon, onion-like carbon, turbostratic layers, and graphitic carbon co-occur within the graphitized coals. At the sub-micron scale, carbonization is a homogenous process, whereas graphitization is a heterogenous process. The average graphite crystalline size (La, lateral extension; Lc, stacking height) rapidly increases as the treatment temperature increases from 1600 to 2300 °C. Three coal structural transformation stages were classified according to the nanometric carbon structural evolution with temperature. This study will contribute to the efficient and value-added utilization of coal to make graphite materials.

Analysis of the turbostratic structures in PAN-based carbon fibers with wide-angle x-ray diffraction

Carbon fiber (CF) is a versatile material renowned for its excellent mechanical, thermal, and electrical properties. Polyacrylonitrile (PAN)-based CFs dominate the market in part due to their high tensile strength, rendering them suitable for structural applications in a wide variety of applications ranging from sporting goods to aerospace. Over five decades of commercial development of PAN-based CF has resulted in a range of varieties with different tensile moduli and tensile strengths. The microstructures, nanostructures, and crystal structures of PAN-based CF all play pivotal roles in the macroscale properties of this material. In particular, the crystal structure and crystallite orientation in CF is closely related to the mechanical properties. The crystal structure of PAN-based CF generally consists of turbostratic carbon, a disordered form of graphite, the characteristics of which can be effectively characterized in a bulk format through wide-angle x-ray diffraction (WAXD). In this work, we employed a three-part approach to the analysis of WAXD patterns collected from four intermediate modulus PAN-based CFs. The approach incorporates a Scherrer analysis, a Debye analysis, and an orientational analysis to provide precise estimates of crystallite sizes, crystallite distributions, and crystallite orientations with the fiber axis. The results presented here suggest that intermediate modulus PAN-based CF mostly consists of small turbostratic crystallites (<4 nm), with larger crystallites having increased orientation with the fiber axis. The results here imply the presence of curvature and/or wrinkling of the turbostratic layers within the CF structure.

Low-Temperature Direct Growth of Nanocrystalline Multilayer Graphene on Silver with Long-Term Surface Passivation.

A wide variety of transition metals, including copper and gold, have been successfully used as substrates for graphene growth. On the other hand, it has been challenging to grow graphene on silver, so realistic applications by combining graphene and silver for improved electrode stability and enhanced surface plasmon resonance in organic light-emitting diodes and biosensing have not been realized to date. Here, we demonstrate the surface passivation of silver through the single-step rapid growth of nanocrystalline multilayer graphene on silver via low-temperature plasma-enhanced chemical vapor deposition (PECVD). The effect of the growth time on the graphene quality and the underlying silver characteristics is investigated by Raman spectroscopy, X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and cross-sectional annular dark-field scanning transmission electron microscopy (ADF-STEM). These results reveal nanocrystalline graphene structures with turbostratic layer stacking. Based on the XPS and ADF-STEM results, a PECVD growth mechanism of graphene on silver is proposed. The multilayer graphene also provides excellent long-term protection of the underlying silver surface from oxidation after 5 months of air exposure. This development thus paves the way toward realizing technological applications based on graphene-protected silver surfaces and electrodes as well as hybrid graphene-silver plasmonics.

Influence of Ni on the structural evolution of polymer-derived SiOC ceramics

Polymer derived ceramics (PDCs) technique is an advanced method for preparing high performance ceramics, in which pyrolysis process is an important step. In order to study the effect of the Ni transition metal on the pyrolysis process of polysiloxane, different contents of Ni acetate tetrahydrate (Ni(ac)2·4H2O)-impregnated polysiloxane (PSO) precursors were pyrolyzed in argon atmosphere between 1000 °C and 1300 °C. The organic-inorganic conversion behavior of precursors, the elemental and structural characterization of the Ni-free and Ni-containing SiOC ceramics were investigated. The results revealed that the presence of Ni not only enabled the growth of carbon nanotubes (CNTs) but also promoted the crystallization of carbon and SiC phase during the pyrolysis process. Additionally, high Ni content and pyrolysis temperature raised the diameters of CNTs and crystallinity of turbostratic layer carbon and SiC.

Turbostratic Boron-Carbon-Nitrogen and Boron Nitride by Flash Joule Heating.

Turbostratic layers in 2D materials have an interlayer misalignment. The lack of alignment expands the intrinsic interlayer distances and weakens the optical and electronic interactions between adjacent layers. This introduces properties distinct from those structures with well-aligned lattices and strong coupling interactions. However, direct and rapid synthesis of turbostratic materials remains a challenge owing to their thermodynamically metastable properties. Here, a flash Joule heating (FJH) method to achieve bulk synthesis of boron-carbon-nitrogen ternary compounds with turbostratic structures by a kinetically controlled ultrafast cooling process that takes place within milliseconds (103 to104 K s-1 ) is reported. Theoretical calculations support the existence of turbostratic structures and provide estimates of the energy barriers with respect to conversion into the corresponding well-aligned counterparts. When using non-carbon conductive additives, a direct synthesis of boron nitride is possible. The turbostratic nature facilitates mechanical exfoliation and more stable dispersions. Accordingly, the addition of flash products to a poly(vinyl alcohol) nanocomposite film coating a copper surface greatly improves the copper's resistance to corrosion in 0.5 m sulfuric acid or 3.5 wt% saline solution. FJH allows the use of bulk materials as reactants and provides a rapid approach to large quantities of the hitherto hard-to-access turbostratic materials.

Novel class of precursor-derived Zr–La–B–C(O) based ceramics containing nano-crystalline ultra-high temperature phases stable beyond 1600 °C

In this work, a novel ultra-high temperature resistant precursor-derived ceramic containing Zr, La, B, and C was synthesized through precursor modification of phenol formaldehyde resin. The thermal stability and resistance to crystallization of the ceramic at a temperature of 1600 °C was investigated and was found to be profoundly influenced by the boron content in the starting precursors. The ceramics remained amorphous at 1600 °C for 2 h in argon and upon sustained heat-treatment for up to 16 h resulted in nano-crystalline ultra-high temperature phases such as ZrB 2 , ZrC, LaB 6 and La 2 Zr 2 O 7 . Thermodynamic equilibrium phase calculations show that even longer durations of heat treatment may be required to achieve thermodynamic equilibrium. High-resolution transmission electron microscopy revealed encapsulation of nanocrystals (<5 nm) in an amorphous matrix surrounded by turbostratic layers of carbon inhibiting its growth. Spectrochemical techniques confirmed the presence of boron substituted carbon in the amorphous matrix of the ceramic. The unique nature of the amorphous matrix lends the ceramic resistance to crystallization and chemical degradation that can surpass the likes of classical silicon-based precursor-derived ceramics.

Synthesis of turbostratic nanoscale graphene via chamber detonation of oxygen/acetylene mixtures

AbstractA study of the detonation synthesis method to make graphene and the properties of the resulting graphene is presented. The gaseous precursors are mixtures of oxygen and acetylene with oxygen/carbon molar ratios of O/C = 0.25 to 0.75. Chamber pressure and temperature data indicate pressures ≤ 300 psi and temperatures of 2550 ± 100K after initiation of the reaction mixture. The graphene material collected from the chamber after the detonation was characterized by Raman, XRD (X‐ray diffraction), BET, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and so on. The material properties divide into two groups: low O/C (≤ 0.45) and high O/C (≥ 0.5). Low O/C graphene appears as a low density, aerosol gel with ∼8 weakly associated, disordered turbostratic layers with a lateral extent of 20 to 30 nm. High O/C graphene appears as a denser powder with ∼30 weakly associated turbostratic layers, with a lateral extent of 100 to 200 nm. We conclude, as we have previously, that the high detonation temperature during the reaction is the primary reason that graphene is formed rather than soot. Differentiation into two types of graphene products is hypothesized to be a result of aggregation kinetics to form a static gel that pre‐empts layering (stacking) when O/C is low.

HRTEM observation of morphological and structural evolution of aromatic fringes during the transition from coal to graphite

The maximum reflectance of vitrinite or graphite microcrystals in Yongan Coalfield, Fujian Province, China, ranges from 5.33% to 10.21%, comprising meta-anthracite, semi-graphite, and graphite. The morphological characteristics of aromatic fringes during different evolution stages were quantitatively analyzed using high-resolution transmission electron microscopy and image processing techniques. The results show that a nonlinear evolution of aromatic fringe morphology in the process of coal graphitization is manifested in four aspects, involving the rapid connection and growth, enhancement of ordering alignment, increase of stacking and development of straightening. In meta-anthracite samples, 3 × 3 aromatic rings representing short aromatic fringes are dominated, a majority of aromatic fringes were curved, disjoint or separate, and show a turbostratic layers, with poorly aligned. The spacing between adjacent aromatic fringes exceeded the range of graphitized carbon, and structural defects, such as nanopores were generally visible. In semi-graphite samples, in addition to 3 × 3 aromatic rings, the proportion of >8 × 8 aromatic rings represented longer aromatic fringes increasing significantly, along with ordering alignment and straightening. Stacking with two more layers increased and the spacing between adjacent aromatic fringes decreased to the range of graphitized carbon, and the structural defects decreased considerably. In graphite sample, the proportion of >8 × 8 aromatic rings increase significantly, the length, stacking, and ordering alignment of aromatic fringes increased abruptly, the spacing between adjacent aromatic fringes remained within the range of natural graphite, and a rapid graphite-like structure with flat aromatic fringes formed. A stage evolution of aromatic fringe morphology, whereas remaining almost constant of mainly organic elements, which imply the evolution of aromatic fringes in meta-anthracite originated from ring condensation dominated by late coalification, graphitization starts at semi-graphite stage and enhanced during graphite stage. The making up, originating from linkup and pileup, considered as a special mechanism for the graphitization of aromatic fringes.

Highly effective gating of graphene on GaN

By using four-layered graphene/gallium nitride (GaN) Schottky diodes with an undoped GaN spacer, we demonstrate highly effective gating of graphene at low bias rendering this type of structure very promising for potential applications. An observed Raman G band position shift larger than 8.5 cm−1 corresponds to an increase in carrier concentration of about 1.2·1013 cm−2. The presence of a distinct G band splitting together with a narrow symmetric 2D band indicates turbostratic layer stacking and suggests the presence of a high potential gradient near the Schottky junction even at zero bias. An analysis based on electroreflectance measurements and a modified Richardson equation confirmed that graphene on n-GaN separated by an undoped GaN spacer behaves like a capacitor at reverse bias. At least 60% of G subband position shifts occur at forward bias, which is related to a rapid reduction of electric field near the Schottky junction. Our studies demonstrate the usefulness of few layer turbostratic graphene deposited on GaN for tracing electron–phonon coupling in graphene. Multilayer graphene also provides uniform and stable electric contacts. Moreover, the observed bias sensitive G band splitting can be used as an indicator of charge transfer in sensor applications in the low bias regime.

Optical and morphological properties of soot particles generated by the miniCAST 5201 BC generator

The miniCAST 5201 black carbon (BC) generator is a novel soot generator able to produce soot particles with a wide range of properties in a stable and reproducible manner. In this study, particles generated with diffusion and premixed flames were comprehensively analyzed, with a special focus on particle morphology, nanostructure, and optical properties. It was found that aggregate BC particles with a mean electrical mobility diameter of about 160 nm generated with an overall near-stoichiometric diffusion flame consist of primary particles with turbostratic layers and onion-like structures. Moreover, they possessed an absorption Ångström exponent (AAE) close to 1, low single scattering albedo (SSA), and a mass absorption cross-section MAC870nm,total (calculated from photoacoustic absorption coefficient and total particle mass) of 4.3 m2/g. With premixed flames under fuel-lean conditions, particles with mean mobility diameters of 50 nm, 75 nm, and 100 nm could be generated with high elemental carbon to total carbon mass fractions (>85%). These particles had a high structural order, exhibited an AAE of 1.1–1.2, low SSA and MAC870nm,total of 3.0–3.3 m2/g. The similarities of the properties of the miniCAST generated soot particles to real-world engine-emitted soot particles indicate that the miniCAST 5201 BC generator is a very promising source of reference aerosols for the calibration of BC diagnostic instruments and engine-exhaust particle counters.

Investigation of the carbon structure of naturally graphitized coals from Central Hunan, China, by density-gradient centrifugation, X-ray diffraction, and high-resolution transmission electron microscopy

A suite of six naturally graphitized coals were separated by density-gradient centrifugation (DGC). The density profiles of anthracite and meta-anthracite samples show an average density increase from 1.50 g/mL to 1.93 g/mL with increased rank. Components of partially graphitized coals were separated into two distinct density peaks: a low-density peak at ~1.82 g/mL, and a high-density peak at ~2.0 g/mL; sample SL-3 also showed a shoulder at around 2.14 g/mL. The separated density fractions of the partially graphitized samples were examined by X-ray diffraction (XRD) and optical microscopy. This revealed that the lower density portions contain vitrinite and inertinite, whereas microcrystalline graphite along with needle and flake graphite are the primary components of the higher density portions, demonstrating that DGC can be used to separate components in metamorphosed coals. Carbon phases including local molecular oriented domains (LMODs) and turbostratic layers are observed in the partially graphitized coals under high-resolution transmission electron microscopy (HRTEM). The average density of the most graphitized coal is 2.18 g/mL, which together with the XRD pattern suggests a carbon structure close to that of graphite. In anthracite, basic structural units (BSUs) are distributed throughout the disordered carbon structure matrix; whereas graphitic lamellae are the primary constituent in the most graphitized coals, indicating the transformation of the carbon structure from amorphous-like anthracite to ordered graphite during natural graphitization. The co-occurrence of different carbon phases and structural units in the same sample demonstrates the heterogeneous nature of graphitized coals. The presence of novel carbon structures (such as BSUs, LMODs, turbostratic structure, and onion-like carbon, etc.) in the naturally graphitized coal series suggests potential use in the future development of new coal-based carbon materials.

Growth of glassy carbon thin films and its pH sensor applications

Glassy carbon (GC) thin film was successfully deposited via thermal pyrolysis of ethanol vapor by means of chemical vapor deposition at 1000 °C without any catalysis. The Raman spectra of the grown GC film showed typical peaks of D1, G, and 2D1 including derivative peaks of D2 band and a combinational peak of D1 + G that indicates the film is glassy carbon. XPS analysis of the C 1s core showed the deposited films have carbon atoms consisting of an almost sp2 binding structure. A picture of the cross-sectional transmission electron microscope showed the stacking layers of a disordered carbon have a turbostratic layer with a few nanometers graphitic domain, about 13 nm estimated by Raman spectra. Two types of pH sensor were fabricated. One is a GC based field-effect transistor with a top gate of a solution (GC-FET), and the other is a GC extended gate electrode connected to commercial Si FET (GC-EGFET). The average pH sensitivity of GC-FET and GC-EGFET is 21.5 mV/pH and 26.5 mV/pH, respectively, which are comparable for graphene-based solution gating pH sensors that have appeared in the recent literature.

Structural response of phyllomanganates to wet aging and aqueous Mn(II)

Naturally occurring Mn(IV/III) oxides are often formed through microbial Mn(II) oxidation, resulting in reactive phyllomanganates with varying Mn(IV), Mn(III), and vacancy contents. Residual aqueous Mn(II) may adsorb in the interlayer of phyllomanganates above vacancies in their octahedral sheets. The potential for interlayer Mn(II)-layer Mn(IV) comproportionation reactions and subsequent formation of structural Mn(III) suggests that aqueous Mn(II) may cause phyllomanganate structural changes that alters mineral reactivity or trace metal scavenging. Here we examine the effects of aging phyllomanganates with varying initial vacancy and Mn(III) content in the presence and absence of dissolved Mn(II) at pH 4 and 7. Three phyllomanganates were studied: two exhibiting turbostratic layer stacking (δ-MnO2 with high vacancy content and hexagonal birnessite with both vacancies and Mn(III) substitutions) and one with rotationally ordered layer stacking (triclinic birnessite containing predominantly Mn(III) substitutions). Structural analyses suggest that during aging at pH 4, Mn(II) adsorbs above vacancies and promotes the formation of phyllomanganates with rotationally ordered sheets and mixed symmetries arranged into supercells, while structural Mn(III) undergoes disproportionation. These structural changes at pH 4 correlate with reduced Mn(II) uptake onto triclinic and hexagonal birnessite after 25days relative to 48h of reaction, indicating that phyllomanganate reactivity decreases upon aging with Mn(II), or that recrystallization processes involving Mn(II) uptake occur over 25days. At pH 7, Mn(II) adsorbs and causes limited structural effects, primarily increasing sheet stacking in δ-MnO2. These results show that aging-induced structural changes in phyllomanganates are affected by aqueous Mn(II), pH, and initial solid-phase Mn(III) content. Such restructuring likely alters manganese oxide reactions with other constituents in environmental and geologic systems, particularly trace metals and redox-active compounds.

Pressure-induced transformations in carbon nano-onions

Carbon nano-onions (CNOs) with an average diameter of 43 nm have been studied under pressure. The interlayer d-spacings of the CNOs are expanded by about 3% compared to those of the larger CNOs with average diameter of 150 nm studied earlier. High pressure study on the G-band of the small CNOs indicates that a bonding change was initiated at 23.4 GPa, which is higher than that of the larger CNOs. The small CNOs were destroyed into amorphous fragments at above 48 GPa with a large applied deviatoric stress, showing a lower high pressure stability compared with the larger CNOs. These features are qualitatively similar to the size effects observed in the compression behavior of some nanocrystalline materials, showing that a reduced cluster size gives similar physical effects in the two classes of materials. The present results for CNOs can be rationalized by the interlayer expansion and the highly turbostratic layer structure of the studied material. The fact that CNOs with different diameters behave differently upon compression is important when selecting materials for applications.

Presolar Graphitic Carbon Spherules: Rocks from Stars

Graphitic carbon spherules found in primitive meteorites have large carbon isotope anomalies, indicating that they are carbonaceous stardust (also known as presolar grains) expelled from dying stars prior to the formation of the Sun. Presolar spherules show varying degrees of graphitization, ranging from poorly graphitic, turbostratic layers in low-density spherules to well-crystallized graphitic outer shells in high-density ones, and some spherules also contain a polycrystalline phase in their core. Within the spherules, grains of other refractory phases (including carbides and metals) are common, and these assemblages can be studied as one would study a rock. The isotopic and microstructural information available from these presolar graphitic assemblages gives insights into nucleosynthesis and grain condensation in late-stage carbon-rich stars.

Influence of heat treatment conditions on the structure of hollow carbon fibers prepared from solid PVA fibers using iodine pretreatment

The influence of heating conditions on the structure of hollow carbon fibers (H-CFs) during their fabrication from solid poly(vinyl alcohol) (PVA) fibers is reported. The hollow structure of PVA-derived carbon was formed by selective iodination and subsequent stabilization of precursor PVA fiber close to the fiber surface followed by carbonization. The broadening of X-ray diffraction peaks due to disorder and the small size effects of the (002) plane were strongly reduced by increasing the heat treatment temperature (HTT) from 800 to 3000 °C, but the asymmetric shape of (10) and (110) reflections suggests turbostratic layer stacking. The increase of HTT to 3000 °C increased the degree of graphitization evident from the decrease of interplanar spacing from 0.360 to 0.338 nm and the intensity ratio of D to G bands in Raman spectra from 0.93 to 0.58. The crystallite size, orientation and electrical conductivity of the resultant H-CFs were also improved with higher HTT. Besides, the size of the hollow core was also influenced by the HTT and both wall thickness and carbon yield decreased with higher HTT. The core of the H-CFs could be easily filled with polymer by bulk polymerization of monomer.

Kinetic effect of boron on the thermal stability of Si–(B–)C–N polymer-derived ceramics

The isothermal mass loss of two polymer-derived ceramics with compositions SiC 1.4N 0.9 and SiC 1.5N 1.0B 0.05 were measured as a function of time using thermal gravimetric analysis at various temperatures ranging between 1580 and 1720 °C. The process of mass loss, attributed to the reaction Si 3N 4 + 3C → 3SiC + 2N 2 ↑, takes substantially more time for the boron-containing ceramic compared with the boron-free one. The continuous formation of SiC crystallites as the product of the reaction between Si 3N 4 and C was revealed through X-ray diffraction (XRD) measurements during the course of the reaction. The kinetics of this reaction was studied using a generalized model for the analysis of chemical reaction kinetics. Consequently, the effective activation energies for the Si 3N 4 degradation were estimated to be 11.6 ± 0.5 eV and 17.1 ± 0.7 eV for the Si–C–N and Si–B–C–N ceramics, respectively. Moreover, the results obtained indicate that the dominant mechanisms of the Si 3N 4 degradation are strongly influenced by the presence of boron. For the Si–C–N ceramic, the chemical reaction at interfaces of the reactants and the crystallization of SiC as the reaction product are proposed to be the main probable stages controlling the progress of the investigated reaction. However, the local diffusion of C out of BNC x turbostratic layers surrounding the Si 3N 4 nanocrystals and the gas (N 2) release from the reaction zone are suggested to be the most plausible processes limiting the progress of Si 3N 4 degradation for the Si–B–C–N ceramic.

Structural Changes during Oxidation Process of Anisotopic Mesophase Carbon fibers(I) - TEM and XRD Study

Structural changes during oxidation of anisotopic mesophase carbon fiber(AMCFs) have been observed with TEM and XRD. It was shown that the AMCFs are three dimensionally stacked structure of turbostratic layers, and are non-homogeneous structure which consist of the highly ordered areas and the random areas. The <TEX>$d_{ 002}$</TEX>, Lc, and La of AMCFs which were measured by XRD were 3.44, 146, and <TEX>$135\AA$</TEX>, respectively. It was observed that the oxidation initiated at the random areas, because the <TEX>$d_{002}$</TEX> / decreased to the value of 3.41 <TEX>$\AA$</TEX> during initial oxidation stage. It was also observed that the La of the oxidized AMCFs increased up to 182 <TEX>$\AA$</TEX> during the whole oxidation process, and the <TEX>$d_{002}$</TEX> of that increases up to 9.44 <TEX>$\AA$</TEX> when the burn-off is over the degree of 20%. Therefore, it was suggested that the micro-crystalline grew up by heat treatment effects during the fibers were oxidized, In addition, it was shown that there was difference in the measured value of La by XRD and TEM, in case of 39% oxidized fibers for example, the measured La was <TEX>$ 165\AA$</TEX> by XRD and in the range of 180∼220 <TEX>$\AA$</TEX> by TEM.

Structural changes of fullerene by heat-treatment up to graphitization temperature

Structural changes of the C60 and C70 mixture during heat-treatment up to 2400 °C were studied by observing the carbonized disk of the fullerene with Raman spectroscopy, X-ray diffraction, FE-SEM, TEM, and AFM/STM. The fullerene lost its five-membered ring and its fcc crystal structure by heat-treatment at 800 °C, as revealed by the Raman spectra and X-ray diffraction, forming hexagonal planes which were randomly arranged by 1300 °C. Further heat-treatment allowed some stacking of layers which grow to dominate, reducing the randomly oriented planes. The graphitized temperature up to 2400 °C provided a very sharp peak at 26 °, suggesting formation of stable turbostratic layers. The TEM characterized turbostratic stacking of 3 to 4 layers. A series of observation under AFM/STM and TEM indicate the crystal of the fullerene, amorphous grain of the hexagonal planes, and the hollow sphere are all in the same range of size around 10–20 nm. Such microdomains induced micro-roughness as observed by FE-SEM on the surface of the carbon disk. Superstructure of hexagonal plane was observed on the surface. A kind of solid state carbonization of the fullerene is suggested to maintain the dimensions of its crystal into the spherical microdomain, even if its marked structural changes take place within the unit.

Preparation of carbon fibers from polyoxadiazole.

The structure of carbon fibers from polyoxadiazole (POD) was investigated in relation with preparation conditions of starting POD fibers. Two types of POD were synthesized from a hydrazine and terephthalic acid system and a hydrazine, terephthalic acid and isophthalic acid system, and were spun to fibers by wet spinning. The wet spun POD fibers were then pyrolyzed at 1300 and 2800°C. With increase in draw ratio of starting POD fibers, the carbon layer stacks of resulting carbon fibers increased their sizes and orientation. Carbon fibers showed a turbostratic layer structure at the stage of heat-treatment at 1300°C. By heat-treatment at 2800°C, the structure of the carbon fibers from drawn POD fibers changed to that with three-dimentional order. A coaxial-lamellar texture was represented in the cross-section of carbon fibers heat-treated at 2800°C. No marked difference attributable to the difference in chemical composition between the starting polymers was observed for the structure of carbon fibers.