Differences In Crystallite Size Research Articles

Development of graphitic and non-graphitic carbons using different grade biopitch sources

The growing demand for bio-renewable alternatives to fossil fuels in the production of sustainable carbon materials, aimed at reducing environmental impact, is crucial for advancing a greener future. This research explores an innovative approach for producing biopitches from bio-oils, which are subsequently utilized as a sustainable precursor for developing advanced graphitic carbons (GC) and non-graphitic carbons (NGC) through carbonization and graphitization processes. The study emphasizes the impact of the chemical composition of bio-oils and biopitches, including heteroatom structures, aromatic/aliphatic ratio, and oxygen content with oxygen-bearing functional groups, on the production of GC and NGC. The research also examines their structural parameters at various heating temperatures using characterization techniques such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. XRD analysis revealed that GC samples have lower interplanar spacing (d002) and larger crystallite size than NGC, while Raman shows more short-range order and defects in NGC. Furthermore, HRTEM images and fringe analysis demonstrated differences in lamellae structures, tortuosity, and fringe length. These observations, unveiling differences in crystallite size and degree of graphitization between GC and NGC, underscore the influence of temperature on structural order and defect annealing, which is crucial for optimizing material properties.

Insights in the Structural Hierarchy of Statically Crystallized Palm Oil

Palm oil (PO) is still widely used for the production of all types of food products. Due to its triacylglycerol (TG) composition, PO is semisolid at ambient temperature, offering possibilities for many applications. In order to tailor the fat crystal network for certain applications, it remains imperative to understand the structural build-up of the fat crystal network at the full-length scale and to understand the effect of processing conditions. In this study, PO was crystallized under four temperature protocols (fast (FC) or slow (SC) cooling to 20 °C or 25 °C) and was followed for one hour of isothermal time. A broad toolbox was used to fundamentally unravel the structural build-up of the fat crystal network at different length scales. Wide-angle and small-angle X-ray scattering (WAXS and SAXS) showed transitions from α-2L to β’-2L over time. Despite the presence of the same polymorphic form (β’), chain length structure (2L), and domain size, ultra-small-angle X-ray scattering (USAXS) showed clear differences in the mesoscale. For all samples, the lamellar organization was confirmed. Both cooling speed and isothermal temperature were found to affect the size of the crystal nanoplatelets (CNPs), where the highest cooling speed and lowest isothermal temperature (FC and 20 °C) created the smallest CNPs. The microstructure was visualized with polarized light microscopy (PLM) and cryo-scanning electron microscopy (cryo-SEM), showing clear differences in crystallite size, clustering, and network morphology. Raman spectroscopy was applied to confirm differences in triglyceride distribution in the fat crystal network. This study shows that both cooling rate and isothermal temperature affect the fat crystal network formed, especially at the meso- and microscale.

Control of API release with matrix polymorphism in tristearin microspheres

Glycerides are widely employed as solid matrices in a range of pharmaceutical intermediates and dosage forms. Diffusion-based mechanisms are responsible for drug release, with both chemical and crystal polymorph differences in the solid lipid matrix cited as controlling factors in drug release rates. This work uses model formulations composed of crystalline caffeine embedded in tristearin to study the impacts to drug release from the two primary polymorphic states of tristearin and dependencies on the conversion routes between them. Using contact angles and NMR diffusometry, this work finds that drug release from the meta-stable α-polymorph is rate limited by a diffusive mechanism relating to its porosity and tortuosity, but initial burst release occurs due to ease of initial wetting. Poor wettability resulting from surface blooming can be rate limiting for the β-polymorph, resulting in slower initial drug release relative to the α-polymorph. The route to achieve the β-polymorph strongly impacts the bulk release profile due to differences in crystallite size and packing efficiency. API loading enhances the effective porosity, leading to enhanced drug release at high loadings. These findings offer generalizable principles to guide formulators on the types of impacts to drug release rates that one may expect due to triglyceride polymorphism.

Determination of the crystalline size of hexagonal La1-xSrxMnO3 (x = 0.3) nanoparticles from X-ray diffraction - a comparative study.

The electronic, magnetic, optical and elastic properties of nanomaterials are governed partially by the crystallite size and crystal defects. Here, the crystalline size of hexagonal La1-xSrxMnO3 (x = 0.3) nanoparticles was determined using various methods. Single-phase La0.7Sr0.3MnO3 nanopowders were produced after 10 h of milling in a commercial high-energy SPEX 8000D shaker mill, and then they were heated at 700 °C and 800 °C to study the effect of calcined temperature on the crystallization of nanoparticles. The modified Scherrer, Williamson-Hall, size-strain, and Halder-Wagner methods were used to determine the crystallite sizes and the elastic properties, such as intrinsic strain, stress, and energy density, from the X-ray diffraction peak broadening analysis. The obtained results were then compared with one another. The difference in crystallite sizes calculated from the different methods was due to the different techniques.

Effect of Carbon Nanotube Content and Mechanical Milling Conditions on the Manufacture of AA7075/MWCNT Composites

Aluminium matrix composites (AlMCs) of AA7075 aluminium alloy reinforced with 0.5 and 1 wt.% multiwall carbon nanotubes (MWCNTs) were fabricated with powder metallurgy techniques using three different mechanical milling strategies, varying the milling energy and the stage in which the reinforcements were added to the pre-alloyed matrix powders. In this paper, we focus on the influence of these parameters on the dispersion of MWCNTs. Characterization of the obtained composite powders by X-ray diffraction and scanning electron microscopy showed that the evolution of the particle size and morphology of the composite powders is influenced by milling conditions and MWCNT content; however, under the conditions tested in this study, there were no significant differences in crystallite size and lattice strain. The best distribution of the reinforcements was obtained after milling 7075 powders and MWCNTs in a high-energy cycle (HEBM), varying the rotation speed between 1200 and 1300 rpm. Raman spectroscopy was used to assess the damage induced by the milling process in the nanotubes, and no reaction products were detected under any of the tested conditions. Nanoindentation tests were performed to measure the elastic modulus and hardness of the composite powders, revealing that the best mechanical behaviour was achieved by the 7075-0.5 wt.% MWCNT composites obtained by the HEBM route.

Mineralogy, Geochemistry and Genesis of Agate—A Review

Agate—a spectacular form of SiO2 and a famous gemstone—is commonly characterized as banded chalcedony. In detail, chalcedony layers in agates can be intergrown or intercalated with macrocrystalline quartz, quartzine, opal-A, opal-CT, cristobalite and/or moganite. In addition, agates often contain considerable amounts of mineral inclusions and water as both interstitial molecular H2O and silanol groups. Most agate occurrences worldwide are related to SiO2-rich (rhyolites, rhyodacites) and SiO2-poor (andesites, basalts) volcanic rocks, but can also be formed as hydrothermal vein varieties or as silica accumulation during diagenesis in sedimentary rocks. It is assumed that the supply of silica for agate formation is often associated with late- or post-volcanic alteration of the volcanic host rocks. Evidence can be found in association with typical secondary minerals such as clay minerals, zeolites or iron oxides/hydroxides, frequent pseudomorphs (e.g., after carbonates or sulfates) as well as the chemical composition of the agates. For instance, elements of the volcanic rock matrix (Al, Ca, Fe, Na, K) are enriched, but extraordinary high contents of Ge (>90 ppm), B (>40 ppm) and U (>20 ppm) have also been detected. Calculations based on fluid inclusion and oxygen isotope studies point to a range between 20 and 230 °C for agate formation temperatures. The accumulation and condensation of silicic acid result in the formation of silica sols and proposed amorphous silica as precursors for the development of the typical agate micro-structure. The process of crystallisation often starts with spherulitic growth of chalcedony continuing into chalcedony fibers. High concentrations of lattice defects (oxygen and silicon vacancies, silanol groups) detected by cathodoluminescence (CL) and electron paramagnetic resonance (EPR) spectroscopy indicate a rapid crystallisation via an amorphous silica precursor under non-equilibrium conditions. It is assumed that the formation of the typical agate microstructure is governed by processes of self-organization. The resulting differences in crystallite size, porosity, kind of silica phase and incorporated color pigments finally cause the characteristic agate banding and colors.

Efficient PL Emission from p-type Porous Silicon: A Comparative Study for Selection of Effective Anodization Parameters

The physical mechanism of highly efficient photoluminescence (PL) emission from p-type silicon is described by a comparative study of the effectiveness of the etching parameters in an electrochemical anodization technique. Two series of porous silicon samples were prepared in a combination of anodization current and time, to maintain the total amount of anodic charge transfer constant. Photoluminescence studies show that irrespective of the amount of charge transfer, the samples prepared with comparatively higher current density show an efficient PL as well as stronger blueshift in the emission energy vis-a-vis the samples prepared for longer durations. An overall decrease in crystallite size, as estimated by Raman spectral analysis, was observed for both series of samples with the progress of charge transfer. Comparative analysis shows a marginal difference in crystallite size for both series of samples in the initial state of charge transfer, whereas major differences arise at higher values. This is explained with the formation of silicon suboxide on the porous surface at higher current density, leading to initiation of side wall reaction, and higher reduction rate in crystallite size as well as strong luminescence due to the carrier quantum confinement effect.

Combustion synthesis of Co-Cu-Mn oxides deploying different fuels

Ternary spinel-like oxides such as CuFeMnO4, CoCuMnOxand CuCr2O4 are attractive materials due to their absorbent properties when used as pigments for selective surfaces thus improving solar heaters efficiency. These materials are obtained through sol-gel and sol-gel-combustion methods. This work proposes the synthesis of mixed oxides of Co, Cu and Mn by means of original one-step stoichiometric combustion methods starting from Mn(NO3)2,Co(NO3)26H2O, Cu(NO3)23H2O and Aspartic acid (Asp) or Lysine( Lys) as fuels. The resulting ashes after the combustion were calcined at 500 °C. The obtained ashes and the calcined powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and by Brunauer-Emmett-Teller method (BET), and TG-DTA analysis. In calcined powders obtained with Lys (CoCuMnOx-Lys), the phase corresponding to CoCuMnOx and others segregated phases were identified. However, in calcined powders obtained with Asp (CoCuMnOx-Asp) only the phase corresponding to CoCuMnOxwas identified. The sample CoCuMnOx-Lys presented an average crystallite size of 44 nm and a specific surface area of 23 m2/g while in CoCuMnOx-Asp, 54 nm and 13 m2/g values were obtained throughout FT-IR vibrational modes associated with spinel metallic oxides for both calcined powders (Asp and Lys) were observed. Additionally, by means of TEM, polyhedral particles with an average size of 20 to 100 nm were observed. In particular, it was determined in CoCuMnOx-Lys an average size of 44nm. According to the different fuels used (Asp and Lys), an evident variation in the obtained phases was observed. However, it was not obtained any difference in crystallite size and specific area surface values. It is of considerable importance the study of further syntheses processes to verify this trend.

An estimation of the correctness of XRD results obtained from the analysis of materials with bimodal crystallite size distribution

36 powder artificial mixtures and 2 usual samples with a bimodal crystallite size distribution have been prepared and examined by an X-ray diffraction method. We estimated the capability of the Rietveld refinement at a “double-phase model” mode and the correctness of the results. The homogeneity and the crystallite sizes of pure phases used in the preparation of the mixtures were checked by TEM. In most cases, Rietveld refinement at a “double-phase model” mode provided reliable information about both the crystallite size and percentage of constituents. Reliability of XRD results was higher for the powder mixtures with a larger difference in crystallite sizes. It was found that the shape of the crystallites can have a significant impact on the analysis results, and for columnar crystals, the employed method did not always provide correct results. When size distribution of the material deviates from a bimodal one, the correctness of the result decreases. Such an investigation was performed for the first time.

The formation and microstructural properties of uniform α-GaOOH particles and their calcination products

Uniform α-GaOOH submicron particles of different shapes (spindles, rhombic rods, rhombic prisms, hierarchical particles) were synthesized by simple low-temperature (at 60°C) or hydrothermal (at 160°C) precipitation from the mixture of aqueous solutions of gallium(III) chloride and organic alkali tetramethylammonium hydroxide (TMAH) at various pH values (5, 7 or 9). The growth mechanism of these particles was discussed. Crystallographic directions and crystal planes in α-GaOOH particles were identified. Differences in crystallite size, thermal and infrared properties of α-GaOOH particles were observed and discussed. Uniform α-Ga2O3 and β-Ga2O3 particles of the same or similar shapes, containing holes due to dehydroxylation, were obtained by calcination of the corresponding α-GaOOH particles at 500 or 900°C, respectively. Differences in crystallite size and infrared properties of obtained gallium oxide samples, as well as differences in photoluminescence properties of β-Ga2O3 samples were observed and discussed.

Induced magnetic anisotropy features in FeCrSiBNbCu nanocrystalline alloy: Role of stress distribution proven by direct X-ray measurements

Fe73.5−xCrxSi13.5B9Nb3Cu1 (x=1, 2, and 3) amorphous ribbons were prepared by single roller rapid quenching technique. Both conventional and stress annealing at 520°C for 2h at the value of the specific load of 150MPa resulted in the formation of a nanocrystalline structure with average grain size about 13nm. No significant differences in crystallite size were observed for all samples under consideration. The crystallite orientations were practically isotropic indicating no texture in the samples of all types. For all conventionally annealed ribbons a longitudinal effective magnetic anisotropy with an easy magnetization axis parallel to the ribbon axis was observed. For all stress annealed ribbons a transverse induced magnetic anisotropy with the anisotropy constant value of about 1800±50J/m3 was evident. Induced magnetic anisotropy features in FeCrSiBNbCu nanocrystalline alloy, namely an importance of the stress distribution was proven by direct X-ray measurements. A very good correlation between the induced magnetic anisotropy constant values and anisotropic stress distribution was observed.

LLDPE/TiO2 nanocomposites produced from different crystallite sizes of TiO2 via in situ polymerization

Nano-TiO2 particles with a range of crystallite sizes were synthesized by a conventional sol-gel method, and then used as nanoparticle substrates in the synthesis of LLDPE/TiO2 nanocomposites via in situ polymerization of ethylene/1-hexene with zirconocene/MMAO catalyst. It was found that the size of the nano-TiO2 crystallite nanoparticles can influence the catalytic activity in the polymerization system. The larger nano-TiO2 crystallites provided better catalytic activity in the polymerization system due to more space for monomer attack. In addition, by thermo-gravimetric analysis, it can be seen that the larger nano-TiO2 crystallites also exhibited lower interaction with available MMAO. Consequently, the MMAO reacted more efficiently with the zirconocene catalyst during the activation process, and enhanced polymerization catalysis. All the polymer nanocomposites products did not have well defined melting temperature indicating non-crystalline polymers. This is due to the high amount of hexene incorporation (based on 13C NMR). The difference in crystallite sizes of the nano-TiO2 also affected how 1-hexene became incorporated into the polymer nanocomposites. The smaller crystallite size of nano-TiO2 allowed greater 1-hexene incorporation due to depression of the reactivity of the ethylene. The contribution of this work helps develop a better understanding of the role of nano-TiO2 in the catalytic activity of the polymerization system and in the microstructure of the polymer composite product. However, this study only considers work on the laboratory scale, so for commercial application of these results, it is necessary to scale up the polymerization process. It is only at this stage, that other physical properties, such as the mechanical properties of these materials can be sensibly determined.

QUANTIFICAÇÃO POR DRX DOS COMPONENTES CARBONOSOS PRESENTES NO PÓ DE BALÃO DO ALTO FORNO

X-ray diffraction (XRD) is a standard technique of characterizing structure of materials. The aim of this work is to identify and quantify carbonaceous components (coal, char and coke fines) in the off-gas blast furnace (BF) through the use of the XRD technique and ultimate analysis. The dust collected in the off-gas BF, which contains char, coke fines, metallic oxides, etc., was fractioned and chemically analyzed. In addition, the fractions were grounded, demineralized and analyzed by ultimate analysis and XRD. This technique reveals differences in crystallite size of the carbonaceous materials. The coke structure shows to be more ordered (bigger L c ) than the char structure. Based on these differences, it is possible to quantify the fines proportions of char and coke in the blast furnace flue dust. The estimated char proportion in the carbonaceous material of the flue dust is 7%.

Investigation of the Formation of CuInS2Nanoparticles by the Oleylamine Route: Comparison of Microwave-Assisted and Conventional Syntheses

The formation of copper indium disulfide nanoparticles via the oleylamine route using copper iodide, indium chloride, and elemental sulfur has been investigated by applying conventional thermal heating as well as microwave irradiation. Oleylamine thereby acts as a capping ligand as well as a solvent. In an initial set of experiments, the onset of the reaction was determined to be around 115 °C by an in situ X-ray study using Synchrotron radiation. Using comparatively low synthesis temperatures of 120 °C, it is already possible to obtain nanoparticles of 2-4 nm with both heating methods but with irregular shape and size distribution. By applying higher temperatures of 220 °C, more crystalline and larger nanoparticles were obtained with slight differences in crystallite size and size distribution depending on the synthesis route. The size of the nanoparticles is in the range of 3-10 nm depending on the heating time. Using microwave irradiation, it is possible to obtain nanoparticles in only 90 s of total synthesis time. Control experiments to probe a nonthermal microwave effect were carried out ensuring an identical experimental setup, including the heating profile, the stirring rate, and the volume and concentration of the solutions. These experiments clearly demonstrate that for the preparation of CuInS(2) nanoparticles described herein no differences between conventional and microwave heating could be observed when performed at the same temperature. The nanoparticles obtained by microwave and thermal methods have the same crystal phase, primary crystallite size, shape, and size distribution. In addition, they show no significant differences concerning their optical properties.

Subchondral bone architecture and quality in osteoarthritis

Osteoarthritis (OA) is traditionally seen as a disease of articular cartilage. However, changes in the bone that have long formed part of the radiological diagnosis – subchondral sclerosis, cysts and osteophytosis – are increasingly recognised as being an integral part of the disease. It is curious that cysts, regions of bone loss, are found in sites that are loaded, whereas osteophytes grow at the joint margins in sites that might be expected to be relatively lightly loaded. This is contrary to normal expectations of mechanical regulation of bone formation and resorption. Evidence from animal models of idiopathic OA suggests that bone changes may precede cartilage deterioration, which would indicate that they are part of the primary disease process. Patients with OA changes evident on hip radiographs were found to have a higher than average bone mineral density not only in the hip, but also in the distal radius, vertebrae and calcaneus. These gross changes in the bone are reflected in the composition, structure and organisation of the trabecular bone and in the subchondral bone plate. There is massive proliferation of cancellous bone, by up to 60% by volume, throughout the femoral head and neck. Corresponding to this, histomorphometry has shown an increase in trabecular thickness, with a concomitant reduction in trabecular number, and an increase in osteoid width and eroded surfaces. A reduction in mineralisation is found in subchondral trabecular bone, perhaps reflecting a more rapidly formed woven bone-like tissue seen using scanning electron microscopy. This is reflected in a lower material density. Scanning electron microscopy also showed instances of abnormal bone formation in the trabecular spaces and a much greater number of Howship's lacunae indicating enhanced osteoclastic activity. A thickening of the subchondral bone plate has been reported in humans and cynomolgus macaques with OA, which also suggests an imbalance between bone formation and resorption. Changes are not limited to the affected joint. The iliac crest in women with hand OA has been found to have more bone, but with a mineralization profile shifting to higher densities, suggesting reduced bone turnover. The proliferation of subchondral bone results in an increase in apparent, or tissue, modulus. Although the apparent modulus increases, the reduction in mineral content results in a reduction in the modulus of the bone matrix itself. Indentation studies showed a reduced hardness, and by implication modulus, in the subchondral bone matrix. Using thermal analysis and X-ray diffraction, we found no differences in crystallite size, unit cell dimensions or decomposition properties indicating, however, that the nature of the mineral itself, a carbonated apatite, was not altered. Studies have implicated the receptor activator of NF-κB/receptor activator of NF-κB ligand/osteoprotegerin regulatory pathway by showing increased levels of mRNA for receptor activator of NF-κB and a decrease in the ratio of receptor activator of NF-κB ligand to osteoprotegerin. This ratio then failed to correlate with bone remodelling indices, unlike in the normal controls, suggesting a disruption of the regulation of bone remodelling. In addition, it has been suggested that the co-regulation of the mechanical properties of bone and cartilage does not function as normal. We have also shown that the femoral head contains twice the amount of fat per unit volume of cancellous bone tissue (including bone marrow) as osteoporotic bone and has elevated levels of (n-6) fatty acids, especially arachidonic acid. Considerable changes in bone composition, architecture, quality and regulation are hallmarks of OA. It is still not clear whether these changes follow, precede or accompany the widely studied changes in articular cartilage. Subchondral bone does not appear to play a biomechanical role in the initiation of the disease. The widespread changes in bone, the frequent presence of multiple joint involvement and the link with obesity has lead to the suggestion of a systemic musculoskeletal disorder, in contrast to the traditional cartilage-first hypothesis.

Properties of calcium phosphate coatings before and after exposure to simulated biological fluid

The surface qualities of calcium phosphate (CaP) implants are important factors determining the nature and degree of cellular behaviour, especially cellular attachment, proliferation and differentiation. Thus, in this study, the chemical composition and crystallographic properties of radiofrequency sputter-deposited CaP coatings prior to and after in vitro immersion in a physiological solution were characterized. Significant differences in crystallite size were observed with different heat treatments, with coatings heat treated at 850 dgC (CA8) having larger crystallites compared to coatings heat treated at 700 °C (CA7). However, no statistical difference in the Ca P ratio, carbon concentration and surface energy were observed with different heat treatments. After immersion in a physiological solution, the crystallite size was significantly increased. The crystallite size for the CA8 and CA7 coatings remained statistically different after 1-week immersion in solution. An increase in carbon concentration was also observed for both samples after 1-week immersion in solution. However, no significant differences in the Ca P ratio and surface energy were indicated between the two coatings after 1-week immersion in solution. In addition, no statistical difference in surface energy was observed for both samples initially and after 1 week.

Crystallization and Phase Transformation Process in Zirconia: An in situ High‐Temperature X‐ray Diffraction Study

Amorphous zirconia precursors were made by the precipitation of a zirconium tetrachloride solution with either slow (8 h) or rapid additions of ammonium hydroxide at a pH of 10.5. Following calcination at 500°C for 4 h, the rapidly precipitated precursor exhibited predominantly monoclinic ZrO2 phase, while the slowly precipitated precursor produced the tetragonal ZrO2 phase. The crystallization and phase transformations were followed by in situ high‐temperature X‐ray diffraction (HTXRD) for both specimens in helium and in air. Each amorphous precursor first crystallizes as the tetragonal phase at about 450°C. A tetragonal‐to‐monoclinic phase transformation of the rapidly precipitated material was observed on cooling at about 275°C. Surface impregnation of sulfate ions following precipitation inhibited the tetragonal‐to‐monoclinic transformation for the rapidly precipitated ZrO2 sample. The crystallite size for the t‐ZrO2 of all samples, irrespective of whether they transform to monoclinic, was approximately 11 nm, indicating that the t→m transformation in these materials is not controlled by differences in crystallite size. It is therefore suggested that anionic vacancies control the tetragonal‐to‐monoclinic phase transformation on cooling, and that oxygen adsorption triggers this phase transformation.

Characterization of Ferroelectric PZT Thin Films - Line Broadening Study (Using Grazing Incidence Geometry)

AbstractFerroelectric polycrystalline thin films are being pursued as materials for use in the next generation of radiation hardened nonvolatile semiconductor memories, optical switches and optical computers. Of particular interest are PZT films with a composition near the morphotropic phase boundary. In order to fully understand the the difference in electrical properties as a function of processing parameters it is necessary to fully characterize phase composition and crystallographic properties of these films. Since some films are produced by either spinning or dipping successive layers to obtain the desired thickness it was necessary to compare the properties of each layer.X-ray diffraction techniques employing parallel beam optics with grazing incidence angle geometry were used to characterize the films. Experimental procedures using sealed tube xray diffraction systems to determine differences in crystallite size and microstrain as a function of depth into the films are a rather unique application of this technique. Discerning the contribution to line broadening due to phase changes, grazing incident angle geometry, crystallite size and microstrain are key to the success of this technique.This paper discusses the experimental techniques employed and will demonstrate how we were able to successfully determine microstrain as a function of depth into the film. We use transmission electron microscopy (TEM) to aid in the characterization of the films. A brief description of the processing procedures used to produce the films is also provided.

Some new results on transport and density of state distribution in glow discharge microcrystalline silicon

The electronic properties of the material are discussed on the basis of the grain boundary trapping model proposed for polycrystalline Si. In spite of the difference in crystallite sizes it is shown that the model is applicable, leading to 10 11 cm −2 filled states between crystallites. Gap state densities between 2 × 10 18 and 4 × 10 18cm −3eV −1 are deduced from field effect measurements.

Microstructural Variations in Commercial Carbon Blacks

Abstract Conventional and diffracted beam electron microscopy can be used to resolve the ultimate crystallite units in standard and heat treated carbon blacks. They are very sensitive in the detection of small differences in crystallite size and orientation. Combined with x-ray diffraction methods and conventional vulcanizate testing, high resolution electron microscopy appears to be a useful and practical means to study carbon black surface activity. All commercial blacks appear to conform in part to the Heckman and Harling concentric crystallite model. Surface activity appears to be related to the extent of this alignment; the less the tangential orientation of the graphite layer planes to the surface, the greater the surface activity. Heating carbon blacks in an inert atmosphere for varying times and temperatures (850 to 1400° C) causes a gradual depression of surface activity with increasing treatment severity, defined by increases in the size and concentric orientation of surface crystallites. At no time was the effect of carbon black on vulcanizate properties changed significantly by heat treatment without disrupting the initial orientation of surface crystallites. Carbon blacks differ in the rate of change of crystallite orientation in response to heat treatment. The initial degree of crystallinity, porosity, and surface volatile content all appear to affect the rate of crystallite orientation and growth. Increases in average crystallite height, Lc, are a good measure of effects of heat treatment in excellent agreement with changes in surface crystallite size and orientation observed with the electron microscope. Commercial ISAF carbon blacks of varied structure have relatively minor differences in surface crystallite orientation, indicating small differences in surface activity. The higher modulus and treadwear associated with the use of high structure blacks appear to be predominantly a result of the chain structure itself. Further evidence was obtained showing that black structure and surface activity are independent properties each of which can have a significant influence on vulcanizate properties such as modulus, treadwear, and hysteresis.