Further studies on the use of Raman spectroscopy and X-ray diffraction for the characterisation of TiC-containing carbon–carbon composites

Raman spectroscopy and X-ray diffraction are used to study the crystalline structure of carbon–carbon and TiC-containing composites. The advantages and drawbacks of these techniques for the characterisation of carbon–carbon composites are analysed in the light of the distribution and arrangement of their components and the microstructural orientation of the supporting matrix. Analyses performed on longitudinal and transverse sections of the composites confirm that the measurements are affected by the orientation of the crystals. The overall crystalline parameters calculated by X-ray diffraction were unequivocally resolved for each single component by means of Raman spectroscopy. A significantly higher degree of order was observed in the TiC-containing matrix as a result of the catalytic graphitisation of the carbon achieved by the addition of titanium. In addition, Raman spectroscopy corroborated that the incorporation of TiC into the carbon matrix does not disrupt the orientation of the graphene planes of the matrix parallel to the fibre axis, a necessary characteristic for achieving an optimum heat transfer through the material.     

Molecular and crystal structure of poly(tetramethylene adipate) α form based on synchrotron X-ray fiber diffraction

The molecular and crystal structure of the α form of poly(tetramethylene adipate) (PTMA) was analyzed using synchrotron X-ray fiber diffraction data. The crystals belong to the monoclinic system of space group P2₁/n. The unit cell constants are a=0.6776(6), b=0.7904(6), c (fiber axis)=1.442(1) nm and β=135.6(1)°. The final crystal structure was obtained by the linked-atom least-squares refinement, which gave an R-factor of 0.130 for 103 observed spots and 64 unobserved reflections. The molecular structure deviates slightly from the fully extended conformation in the ester part. The torsional angle CH₂-CH₂-O-C(O) was found to be 155°. The CO groups of the corner and center chains in a unit cell are closely located along the c-axis and are related by the crystallographic 2₁-axes along the b-axis at z=1/4 and z=3/4. The total dipole moment arising from the CO groups is oriented in one direction at z=1/4, and in the opposite direction at z=3/4. Owing to the close arrangement of the CO groups between neighboring chains along the fiber axis, the c-projected cell dimensions and the setting angle of the polymer chain are different from those of the orthorhombic form of polyethylene and the β form of PTMA.     

In situ X-ray diffraction study of the growth of nitrogen-doped carbon nanofibers by the decomposition of ethylene–ammonia mixtures on a Ni–Cu catalyst

The growth of nitrogen-doped carbon nanofibers (N-CNFs) by the decomposition of ethylene–ammonia mixtures on a Ni–Cu catalyst was studied using in situ X-ray diffraction analysis. The catalyst consists of the Ni-enriched (Ni_0.85Cu_0.15) and Cu-enriched (Cu_0.95Ni_0.05) alloys. It was found that the growth of N-CNFs, similar to the growth of carbon nanofibers, proceeds on the Ni-enriched alloy, whereas the Cu-enriched alloy remains inactive. During the N-CNF growth, carbon dissolves in the Ni_0.85Cu_0.15 alloy with the formation of a oversaturated solid solution, but without formation of bulk nickel carbide. It was supposed that nitrogen also dissolves in this alloy, but the driving force is the primary dissolution of carbon.     

Improving the interfacial and flexural properties of carbon fiber–epoxy composites via the grafting of a hyperbranched aromatic polyamide onto a carbon fiber surface on the basis of solution polymerization

Hyperbranched aromatic polyamide (HBP) was grafted successfully onto carbon fibers (CFs) on the basis of solution polymerization to enhance the interfacial adhesion strength of CF-reinforced epoxy resin composites. The microstructure and interfacial properties of the CFs before and after decoration were researched. The results indicate that HBP was deposited uniformly onto the CFs with γ-aminopropyl triethoxysilane as the bridging agent. The active groups, roughness, and surface energy of the modified fiber [hyperbranched aromatic polyamide grafted carbon fiber (CF–HBP)] increased visibly in comparison with those of the untreated CFs. The CF–HBP composites revealed simultaneous remarkable enhancements (65.3, 34.3, and 84.8%) in their interfacial shear strength, flexural strength, and modulus, respectively; this was attributed to the improvement in the fiber–epoxy interface through enhanced chemical interactions, mechanical interlocking, and wettability. These agreed with the scanning electron microscopy observations from the fracture surface morphologies of the composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47232.     

Solid state 27Al NMR and X-ray diffraction study of alumina–carbon composites

The structural and chemical transformations occurring in alumina–carbon composites upon heat treatment were investigated by using a combination of X-ray diffraction (XRD) and solid-state ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Two different carbon precursors were employed: a commercial activated carbon and a char obtained by carbonization of the endocarp of babassu coconut at 700 °C. The alumina–carbon composites were prepared by aqueous impregnation of the carbon supports with aluminum nitrate and, after filtering and drying, the as-synthesized powders were heat-treated under argon flow at temperatures up to 1000 °C. The Al compounds present in the as-synthesized samples were identified by XRD and solid-state ²⁷Al NMR as nanocrystalline aluminum oxyhydroxides or hydroxides, depending on the synthesis conditions. All Al-containing phases were XRD-amorphous in the char-derived nanocomposites, with the presence of a distribution of AlO₆ (octahedral Al site), AlO₅ (pentacoordinated Al) and AlO₄ (tetrahedral Al site) units revealed by solid-state ²⁷Al NMR spectroscopy. The heat treatments caused the formation of transition aluminas dispersed over the carbon supports, with the occurrence of different amounts of AlO₆, AlO₅ and AlO₄ units depending on the heat treatment temperature and on the type of carbon precursor used for the preparation of the composites.     

Fischer-Tropsch synthesis in the presence∣ of cobalt-containing composite materials based on carbon

The Fischer-Tropsch synthesis in the presence of composite materials prepared by the IR pyrolysis of polyacrylonitrile (PAN) with cobalt salts immobilized on it was studied. The catalysts were small granules containing PAN carbonization products and to 80% cobalt metal particles of size 10–17 nm. The synthesis was performed in flow reactors with a fixed bed and a catalyst bed suspended in a liquid at 2–3 MPa and 200–310°C. It was established that the activity of the catalyst depends on the nature of the cobalt salt used, the temperature of IR pyrolysis, and the synthesis conditions. The catalyst prepared with the use of cobalt carbonate exhibited the greatest activity. The yield of liquid hydrocarbons on it reached ～70 g/m³ at ～60% selectivity. It was found that the test composite materials were characterized by an extremely high productivity of 2–5 kg (kg Co)^?1 h^?1.     

X-ray powder diffraction data on salts of α-sulfonated long chain acids

This paper reports x-ray powder diffraction study for twentyfour salts of α-sulfonated normal long chain fatty acids. Acid and neutral sodium, potassium lithium, cesium, calcium, magnesium, and triethanolammonium salts of α-sulfolauric, myristic, palmitic, stearic, and behenic acids were examined. The method can be used to identify and distinguish the individual salts and has possible application to the analysis of mixtures.     

Effect of carbon and oxygen on the high-temperature properties of silicon carbide–hafnium carbide nanocomposite fiber

The polymer-derived ceramics (PDCs) technique enables relatively low-temperature fabrication of Si-based ceramics, with silicon carbide fiber as a representative product. Polycarbosilane (PCS) has Si-C backbone structures and can be converted to silicon carbide. In the PDCs method, residual or excess carbon is generated from the precursor (C/Si ratio = 2 for polycarbosilane). Because of the non-stoichiometry of SiC, the physicochemical properties of polymer-derived SiC are inferior to those of conventional monolithic SiC. Herein, a silicon carbide-hafnium carbide nanocomposite fiber was optimized by crosslinking oxygen into the PCS fiber by regulating the oxidation curing time. During pyrolysis, carbothermal reduction, and sintering, carbon was removed by reaction with hydrogen and cross-linked oxygen. Non-destructive techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and high-temperature thermomechanical analysis) were used to investigate the effects of excess carbon. The microstructure of the near-stoichiometric SiC-HfC nanocomposite fiber was more densified, with superior high-temperature properties.     

Effect of boron trioxide on coke’s inner carbon solution loss reaction

Boron Trioxide (B₂O₃) was adsorbed on coke through boric acid (H₃BO₃) solution, of which the concentration was 0.1%, 0.5%, 1.0%, 2.0% respectively. The existence form and distribution of boron (B) adsorbed on coke were characterized by X-Ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Inductive coupled plasma (ICP), effect of B₂O₃ adsorbed on coke was investigated by carbon solution loss reaction (CSLR) under the condition of the same weight loss. Results show that: H₃BO₃ changes into B₂O₃ after adsorption treatment, and is adsorbed on coke success-fully; B₂O₃ exhibits negative effect on coke CSLR; with the solution concentration increases, the negative effect is strengthened, and coke’s inner reactivity becomes severer, which is not beneficial for coke strength.     

Effect of fiber architecture and density on the ablation behavior of carbon/carbon composites modified by Zr–Ti–C

Three carbon/carbon (C/C) composites modified by Zr–Ti–C, with different fiber architecture in preforms and the same density, were prepared using chemical vapor infiltration and reactive melt infiltration methods. Two other samples with the same architecture in preforms and different density were also fabricated by the same methods. Their ablation behaviors were examined by oxy-acetylene flame. The results showed that the samples with chopped web needled perform had better ablation resistance than that of the samples with needle-integrated and fine-weave pierced perform. In the models of ablation behaviors, the sealing time of pores and gaps on the ablated surfaces has been defined to indirectly estimate the ablation property. The analysis of models also indicated that high density of the composites and appropriate small diameter of bundles of carbon fibers led to the short sealing time and good ablation resistance of the C/C–carbide composites.     

Team formation on the basis of Belbin’s roles to enhance students’ performance in project based learning

This paper presents a method that instructors have designed and implemented to form balanced teams based on Belbin's roles, with the aim of boosting positive interdependence and individual accountability within the teams and improving their performance in a project-based learning environment. Students’ performance has been measured through the scores obtained during the project, individual exam and Individual Accountability Factor (IAF) and compared with cohorts of previous years, in which team composition was self-selected by students. Belbin teams (18/19–19/20) have performed significantly better than self-selected teams (16/17–17/18). Additionally, students’ feedback experience and opinion has been collected. Students belonging to Belbin teams acknowledge that they attend classes more regularly, they need less time for study outside the classes and they show a higher interest for the subject at the end of the course. They also agree that working on Belbin teams has helped them to mainly improve interpersonal relationships and social skills, followed by positive interdependence and individual accountability. This team forming method gives students the opportunity to identify their own strengths and weaknesses and understand the roles (behaviours) of their teammates as well as their strengths and weaknesses. Besides, it encourages learners to focus explicitly on group work skills.     

Effects of carbon additives on the properties of ZrB2–based composites: A review

This review presents the recent achievements on carbon additives incorporated in ZrB₂ ceramics, improved properties, and their advancements. Monolithic ZrB₂ ceramics have broad potential applications, but their critical drawbacks such as poor damage tolerance, and weak oxidation and ablation resistance confines their applicability. It is an important issue to resolve these shortages in physiochemical properties by engineering the composite ingredients and process design of the ceramic counterparts for an extensive production and applications, which are especially essential in high–tech industries and products. Carbon additives have exceptional characteristics including low density, low cost, and excellent thermo–mechanical stability. These materials have been incorporated in ZrB₂ ceramics to enhance their efficiency and form practical composite ceramics. Although addition of the secondary carbonaceous phases is generally supposed to improve the mechanical properties of ZrB₂ composites, it may also result in a decrease in other aspects of performance, comparing with monolithic ZrB₂ ceramics. In this work, we reviewed the methods and strategies for the preparation of carbon modulated ZrB₂ ceramic composites. Moreover, the advantages, disadvantages, and the productivity of the introduced composite ceramics have been explored and featured.     

Influence of diamond particles content on the critical load for crack initiation and fracture toughness of SiOC glass–diamond composites

The crack initiation load and fracture toughness were characterized as a function of diamond particle content, up to 25 vol%, in silicon oxycarbide glass matrix by means of Vickers indentation and single edge notch beam (SENB) technique, respectively. The larger fracture toughness value of 3.21 ± 0.3 MPa m^1/2 was reached for 20 vol% diamond content composites and the value was 4 times higher than that of the unreinforced glass. The addition of diamond particles greatly influenced the crack initiation load, which increased from 2.9 to 49.0 N. The enhancement in the fracture toughness and crack initiation load can be explained by both the intrinsic mechanical properties of diamond (especially the elastic properties; E ～ 1100 GPa) and the diamond/SiOC glass interfacial bonding. A clear correlation was found between the fracture energy, the reinforced interparticle spacing and the residual stress arising upon cooling due to thermal expansion mismatch between the matrix and the diamond particles.     

Investigating the effect of SPS‎ parameters on densification ‎and fracture toughness of ZrB2-SiC nanocomposite‎

In this study, the effect of sintering parameters on densification and fracture toughness of spark plasma sintering ZrB₂-SiC nanocomposites was evaluated. For this purpose, ZrB₂-??30?vol% SiC nanocomposites in the conditions of ?1600?°C-4?min, 1700?°C-4?min, 1800?°C-4?min, 1800?°C-8?min, 1800?°C-12?min? were sintered.? Scanning Electron Microscopy (SEM) was used in order to investigate the ?microstructural variations. The bulk density was measured accoring to ASTM C 373–88. Single edge notch beam (SENB) method was used to ?determine the fracture toughness of samples. Microstructural observations showed that ?an increase in sintering temperature led to slight ?increase in SiC grains size but no sensitive variation in ZrB₂. However, increasing the sintering time resulted to increase both ZrB₂ and SiC grain size. Also, it was found, temperature and time ascent always increases the relative density. In addition, it was concluded that optimal temperature and time to reach the highest fracture toughness are 1800?°C and 8?min, respectively. Investigation of SEM images of the Vickers indent and their path propagation showed that the deviation and branching of crack are the most important toughening ?mechanisms in ZrB₂-SiC nanocomposites.?     

A quantitative analysis of the effect of interface delamination on the fracture behavior and toughness of multilayered propylene–ethylene copolymer/low density polyethylene films by the essential work of fracture (EWF)

The multilayered propylene–ethylene copolymer (CPP)/low density polyethylene (LDPE) composite sheets were prepared by the microlayered coextrusion system. The essential work of fracture (EWF) method was firstly used to quantitatively evaluate the fracture behavior of layered materials. The experimental results indicated that the two-dimensional layered interfaces in the multilayered materials could play an important role in the fracture behavior. The specific essential work of fracture, w_e, increased with the layers due to interfacial delamination. Additionally, the different testing speeds had a dual effect on the increscent trend of the specific essential work of fracture, w_e, with increasing layers.     

Young׳s modulus,Vickers hardness and indentation fracture toughness of alumino silicate glasses

A wide range of alumino silicate glasses with different network modifier ions (Li, Mg, Na, Ca, Zn, La, Ba, Sr, and Pb) was prepared. The glasses were studied with respect to their mechanical properties: Poisson׳s ratio, Young׳s modulus, Vickers hardness and indentation fracture toughness. These properties were mostly affected by the field strength of network modifier ions. All determined properties increase with increasing field strength of the network modifier ions. The mixed modifier alumino silicate glasses with zinc and magnesium show a positive deviation from linearity with two maxima. Lanthanum containing glasses show larger values of mechanical properties for higher lanthanum concentrations. For magnesium alumino silicate glasses the mechanical properties get smaller with increasing SiO₂ concentration; an effect of the magnesium concentration is not observed. Furthermore, if up to 9 mol% MgO is replaced by MgF₂ the mechanical properties are not significantly affected. Compared to models predicting Young׳s moduli of all studied glass compositions, significant deviations are found.     

Quantitative determination of the adhesive fracture toughness of CVD diamond to WC–Co cemented carbide

Well-separated diamond particles were nucleated and grown by hot filament chemical vapor deposition (HFCVD) onto WC–Co cemented carbide pretreated by Murakami’s reagent and H₂O₂+H₂SO₄ solution. The adhesive strength of diamond particles to WC–Co cemented carbide was quantitatively determined in terms of interface toughness by directly applying an external load to the CVD diamond particles. From the measurement of the maximum load required to scratch off the particles, we determined that the adhesive toughness was 14 J/m². This value is more than twice as high as that of CVD diamond on smooth silicon substrate and comparable to the cleavage fracture energy of diamond. The newly developed procedure will allow to check the effectiveness of substrate surface pretreatments for further improving the adhesion level of diamond films on WC–Co.     

Shock-wave data as evidence of the presence of carbon in the earth’s core and lower mantle

The standard density and average atomic weights of hypothetical materials contained in the inner layers of the Earth are calculated from results of shock-wave studies using a previously proposed method for determining the velocity of sound in materials at high pressures and density, and from seismic data. These data turned out to be sufficient to refine the elemental composition of the Earth’s interior. It is shown that the iron-nickel core of the Earth should contain ≈10% (by weight) carbon, partly in the diamond phase. According to the calculations, the lower mantle can contain up to 20% carbon, which probably comes from the core. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 108–114, July–August, 2000. The results of the work can be supported by measurements of velocities of sound in magnetically oriented, diamond-containing mixtures, measurements of velocities of sound behind SW fronts in diamond-containing iron nickel alloys, iron carbides, and other materials, and comparison of the results with seismic data.     

Effect of incorporation of hafnium diboride nanofibers on thermomechanical properties of carbon fiber–phenolic composites

Carbon fiber/phenolic (C/Ph) composites were modified with different weight ratios of hafnium diboride (HfB₂) nanofibers to apperceive thermomechanical properties of C/Ph–Hf nanocomposites. Mechanical properties, thermal stability, and ablation resistance of C/Ph–Hf nanocomposites were found to be optimum when the weight percentage of HfB₂ was equal to one. Maximum flexural strength and modulus were obtained with 118 MPa and 1.9 GPa for C/Ph–1%Hf nanocomposite, respectively. Increasing the proportion of HfB₂, by delaying the temperature of thermal degradation of nanocomposites, enhanced the thermal stability and residual of C/Ph–Hf relative to C/Ph in both nitrogen and air environments. In the oxyacetylene flame test at 2500°C for 160 s, the optimum mass ablation rate of C/Ph–1%Hf nanocomposites was found to be 0.0150 g/s compared to 0.068 g/s for blank C/Ph, along with reducing the back surface temperature by 51%. The ablation mechanism of C/Ph–Hf nanocomposites after the oxyacetylene torch test was concluded from the derivations obtained from X-ray diffraction, energy dispersion spectroscopy, and microstructure analyses. These clarified that the formation of high-temperature species, such as HfO₂, HfC, and B₄C owing to oxidation of HfB₂ and subsequent reaction products with char, resulted in an increased ablation resistance of the nanocomposites.