Carbonization of polycyclic aromatics. 1. Carbonization of anthracene in carbon tetrachloride

Carbonization of anthracene in carbon tetrachloride has been investigated in the temperature range from 200 to 500 °C using a batch autoclave. Anthracene reacted with carbon tetrachloride above 200 °C and the main products were carbonaceous substances, methane, and hydrogen chloride. The benzene-insoluble carbonaceous substances contained chlorine atoms transferred from the carbon tetrachloride molecule. The reaction was considered to be induced by radicals derived from dissociation of the carbon tetrachloride molecule. The development of an anisotropic structure was observed even in the products prepared at 240 °C for 8 h. Around 400 °C a small amount, and around 250 °C a large amount, of carbon tetrachloride promoted the development of anisotropic structure. The graphitizability of the carbonaceous product paralleled the development of anisotropy. The yields of the cokes, their elemental composition and their anisotropic structure were examined in relation to reaction conditions such as temperature, time and the ratio of carbon tetrachloride to anthracene.     

Thermal transition behavior of polybutadiene containing polyurethanes

The thermal transition behavior of a series of hydroxy terminated polybutadiene (HTPBD) containing segmented polyurethanes has been studied by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA). Four transition regions are observed; the soft segment T_g, at ?74°C, two hard segment transitions T₁, at 40°C and T₂ at 103°C and a softening region by TMA at 180°C, presumed to arise from the dissociation of allophonate bonding, The low T_g, only 7°C higher than the T_g of free HTPBD, indicates nearly complete phase segregation despite the amorphous nature of the hard segment structure. The dependence of T₁, on hard segment length and thermal cycling suggests that it represents domains consisting primarily of shorter hard segments units. Factors contributing to the rather low mechanical properties of HTPBD polyurethanes are also discussed.     

Fast scanning calorimetry clarifies the understanding of the complex melting and crystallization behavior of polyesteramide multi‐block copolymers

Fast scanning calorimetry has been applied in order to understand the phase transitions in thermoplastic elastomers (TPEs) based on well‐defined multi‐block copolymers made of ‘soft’ polytetrahydrofuran and ‘hard’ terephthalate ester diamides. The intrinsically complex chemical structure of TPEs leads to complex phase transitions. By changing their thermal history over a wide range of temperature (from ?100 °C to 200 °C) and cooling rates (from 10 to 4000 °C s^?1), we clarify the origins of the various phases present in these materials. In particular, we study the different possibilities for the hard segments to associate depending on their mobility during the quenching phase, forming either strong and stable structures or weaker and metastable ones. Besides, we demonstrate that a minimal cooling rate of 800 °C s^?1 is necessary to keep these TPEs (made of short and monodisperse hard segments) amorphous leading to a subsequent cold crystallization when heating back, at around 30 °C. Finally, we validate our interpretations by varying the copolymer composition (from 10 wt% to 20 wt% hard segments), revealing the thermal invariance of poorly organized domains. Based on these data, we also discuss the importance of chain diffusion in the crystallization process. Applying fast scanning calorimetry allows us to link fundamental understanding to industrial application. © 2018 Society of Chemical Industry     

Structure-property relationships in thermoplastic elastomers: I. Segmented polyether-polyurethanes

Segmented poly(ether-b-urethanes) have been synthesized with 2000 MW polypropylene oxide coupled with diisocyanates and diol type chain extenders. The diisocyanates used were symmetric rigid 4, 4′-diphenylmethane diisocyanate (MDI), linear aliphatic hexamethylene diisocyanate (HDI), and unsymmetric rigid toluene-2, 4-diisocyanate (TDI). The chain extenders were symmetric N, N′-bis(2-hydroxyethyl) terephthalamide (BT) and N, N′-bis(2-hydroxyethyl)-hydroquinone (BH) unsymmetric N, N′-bis(2-hydroxyethyl)isophthalamide, and linear aliphatic 1, 4-butanediol (B). Hard segment contents ranged from 20 to 40 wt percent. The thermal behavior of these materials is consistent with phase separation into separate hard and soft domains, In order of increasing temperature above the soft segment T_g, there are transitions which occur in the regions ?56 to ?36°C (T_a), 70 to 90°C (T_b), and 138 to 168°C (T_m). The former is probably associated with soft segment change from a viscoelastic to an elastomeric state. Values of T_a are ～ ?51 C and ?56°C for the MDI-BT and HDI-BT polymers, respectively, and are independent of hard segment content. Microscopy showed that the former polymers have spherulitic morphology, so these materials have good microphase separation and exhibit crosslinked elastomeric properties. The TDI-BT or BI and MDI-B polyurethane have composition-independent T_a values of ?41 and ?36°C, respectively. These materials probably have considerable “domain-bound-ary-mixing”. At low hard segment content the MDI-B polymers behave as non-crosslinked elastomers. Only the MDI-BI polymers have _Ta values, which are strongly affected by composition, increasing in magnitude with increasing of hard segment content. This is interpreted as significant “mixing-in-domains” and is supported by morphology observed by microscopy. The next higher transition, T_b, probably involves dissociation of interdomain hydrogen bonding. In the case of the MDI-BT polyurethanes, the spherulites associated with the hard domains had disappeared at 141°C and the few small spherulites in the MDI-BI polymers disappeared at 130°C. The T_b values are 70, 83 to 90, and 100°C for the MDI-B, HDI-BT, and HDI-BI polymers, respectively. The melting transitions occurred between 138 to 168°C for the various polyurethanes except for the MDI-BT systems which decompose before melting. Thermal decomposition is a two-stage process. Hard segments decompose between 200 and 300°C. The initial decomposition temperatures are lowered in the presence of strong acid. Soft segments decompose at higher temperatures. The mechanical properties of the MDI-BI polyurethanes are charateristic of crosslinked elastomer, the results of which will be presented in a subsequent paper.     

海藻酸钠的热分解研究

用热重法 ( TG)和差示扫描量热法 ( DSC)并结合 IR详细研究了海藻酸钠的热分解过程。研究表明 ,海藻酸钠的热分解共分四步 :60～ 170°C之间海藻酸钠脱去内部结合水 ;2 2 0～ 2 80°C之间海藻酸钠裂解为中间产物 ;3 0 0～ 3 70°C之间中间产物进一步裂解并部分碳化 ;5 60°C左右最终氧化生成 Na2 O。并用三步判别法对人们较感兴趣的第二步反应的机理和动力学进行了研究。     

Synthesis and evaluation of mechanical and thermal properties of segmented condensation polyurethanes

Abstract

Condensation polyurethanes with different hard segment (HS) content were prepared by condensation reaction of urea, phenol sulphonic acid and formaldehyde and tested for their mechanical, physical and thermal properties. Obtained polyurethane (PUR) films were first heated at 50°C for 120 min and then treated at 135°C for 15 min or 160°C for 10 min. The tensile strength of samples thermally treated at 50°C then at 135°C was 120% higher than for samples treated only at 50°C. The obtained polyurethanes exhibited segmented structures with phase separation between HSs and soft segments (SSs). Films containing 19 and 21%HSs heated at 50°C then 135°C exhibited acceptable mechanical properties and water resistance. The lower and higher end use temperatures of PUR films were affected mainly by the polymer composition. Moreover, the polyurethane samples containing 19 and 21%HSs have shown the highest decomposition temperature (i.e. >165°C), compared to 80°C for polymers with 32%HSs.     

Synthesis and microstructure evolution of WCoB based cermets during spark plasma sintering

WCoB based cermets were prepared by spark plasma sintering at sintering temperature among 600°C-1200 °C. The phase evolution was investigated by detecting density behavior, phase composition, microstructure and mechanical properties during sintering process. The sintering process can be divided into three stages: powder densification, solid phase reaction and liquid phase sintering. WCoB hard phase forms at 1000 °C during solid phase sintering, showing better mechanical properties than Co₂B, especially on Vicker's hardness. WCoB hard phase forms on the basis of Co₂B binary boride and its content increases in liquid phase sintering stage with high density. The Vicker's hardness and transverse rupture strength (TRS) reach the maximum value of 1262 Hv and 1212 MPa at 1200 °C and 1170 °C, respectively. The fracture toughness reaches the maximum value of 21.8 MPa m^1/2 at 1050 °C, and the inter-granular fracture is the main fracture mechanism.     

Pulsed laser deposition of hard and superhard carbon thin films from C60 targets

In the present study, carbon films were deposited by a pulsed laser deposition method. A C₆₀ fullerene target has been irradiated by a frequency doubled Nd:YAG laser with a pulse duration of 7 ns. The carbon films grown on Si(111) substrates at different substrate deposition temperatures (30, 300 and 500 °C) were characterized by Raman, X-ray Photoelectron and X-ray Auger Electron Spectroscopies, Energy Dispersive X-Ray Diffraction, Scanning Electron and Atomic Force Microscopies, and Vickers microhardness technique. The composition, structure, morphology and mechanical properties of films were found to be strongly dependent on the substrate temperature. At 30 °C and 300 °C deposition temperature, superhard and hard diamond-like films have been obtained, respectively. In the case of 500 °C deposition, a hard film, composed of crystalline C₆₀ and diamond-like carbon, has been prepared.     

Effect of the hard‐segment structure on the dielectric relaxation of crosslinked polyurethanes

Two series of crosslinked polyurethanes based on poly(tetramethylene ether) glycol soft segments and hexamethylene diisocyanate/1,4‐butane diol and glycerin or castor oil as a hard segments were synthesized, and their dielectric properties were examined. We examined the influence of the structural heterogeneity of the copolymers (as a function of the quantity and structure of the hard segments and crosslinking density, as measured by comonomer composition), frequency, and temperature as experimental variables by observing changes in the dielectric behavior. Two relaxation peaks were observed in the temperature range of −30 to 40°C for polyurethanes with various hard‐segment contents. The dangling chains of the castor oil presented a plasticizing effect that was exerted during the relaxation processes, an effect that was studied. It was found that both the amount and the structure of the hard segment strongly affected the dielectric behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Manufacture and characterization of a new Si-Ca-P biphasic ceramic

A ceramic of eutectoid composition based on a silicocarnotite (S)- tricalcium phosphate (TCP) sub-system was prepared, and the morphology of the structure investigated. The ceramic material, obtained by a solid-state reaction and slow solidification (6?°C/min) through the eutectoid temperature region (1158?±?2?°C), presented a typical eutectoid microstructure of alternate layers of both silicocarnotite and α-TCP_ss phases. The microstructure of the two phases was homogeneous and free of crystalline and structural defects. High-resolution electron microscopy revealed that the interfaces between the α-TCP_ss and silicocarnotite lamellae within the eutectoid grains were faultless and no sign of an intermediate region between both phases. Moreover in both phases, the lattice planes resolved at the interface were free of defects. The orientation relation between the lamellae of the eutectoid grains was determined as follows: {130} α-TCP_ss // {302} silicocarnotite. This eutectoid lamellae structure presents a new approach for the bioengineering application for hard tissue replacement as the material combines unique structural and bioactive properties and provides a platform for direct integrations with natural tissue.     

Thermomechanical studies of semicrystalline polyether–ester copolymers. Effect of thermal,mechanical, and solvent treatment

The thermomechanical spectra of a series of elastoplastic polyether–ester copolymers were determined at 110 Hz and between ?120°C and 200°C at five compositions. Emphasis was given to samples containing an increasing amount of poly(tetramethylene terephthalate) constituting the hard segment in these copolymers. The effects of thermal history, uniaxial drawing, and solvent absorption were examined. Specimens cut from injection-molded slabs were also included in the study. Thermal and mechanical treatment had an important effect on the dynamic mechanical properties. The relaxation spectra do not indicate distinct phase separation, but rather a structure of closely interacting hard and soft segments. The molecular origin of the various relaxations was characterized, and it is shown that as the amount of the hard component increases, features in the relaxation spectrum characteristic of poly(tetramethylene terephthalate) become prominent.     

Plasma polymerized tetramethyl germanium films deposited at elevated substrate temperatures

Thin plasma polymerized films of tetramethyl germanium are deposited at various substrate temperatures. The influence of substrate temperature on the deposition rate, composition, structure, and electrical properties of the films is discussed. With an increase in the substrate temperature from 25°C to 150°C under similar plasma deposition conditions, the conductivity of the film increased by four orders of magnitude. Films of plasma polymerized tetramethyl germanium deposited at 150°C show typical semiconducting behavior (increasing conductivity with increasing temperature) and have a sheet conductivity of 1.0 × 10^?6 S cm^?1 at 25°C. There is a direct correlation between the conductivity and the composition of the films, i.e., the higher the conductivity the higher the ratio of germanium to carbon at the surface. At deposition temperatures of 25 and 75°C the germanium to carbon ratio was essentially the same, but at a deposition temperature of 150°C, this ratio was considerably higher.     

Tuning the microstructure,magnetostatic and magnetodynamic properties of highly Al-substituted M-type Sr/Ca hexaferrites prepared by citrate-nitrate auto-combustion method

Double substitution of strontium hexaferrite by calcium and aluminum leads to a tremendous rise of hard magnetic properties, such as coercivity and natural ferromagnetic resonance frequency (NFMR). However, the properties are also inextricably linked to the material microstructure (especially, particle size), to the solid solution inhomogeneity as well as aluminum ions distribution among iron sites in crystal structure. In this work, we obtained M-type hexaferrite particles Sr_1-x/12Ca_x/12Fe_12-xAl_xO₁₉ (x = 4–6) via a facile citrate-nitrate auto-combustion method and studied the influence of the annealing temperature in a broad range on the microstructure, features of crystal structure and hard magnetic properties. At low annealing temperatures (900–1000°С) hexaferrite nanoparticles with 90% of nominal Al content and a wide chemical distribution are formed. Next, with an increase in the annealing temperature the distribution significantly narrows, chemical composition becomes close to the nominal one and particles size transfer firstly to submicron, then to micron range. The aluminum distribution over iron sites is independent distinctly on the annealing temperature. For all the compositions single domain particles with the maximum coercivity values between 22.8 and 36 kOe are obtained at 1200 °C. At 900–1000 °C the samples demonstrate coercivities up to 25 kOe, while above 1300 °C, the crystallites begin to pass into a polydomain state with a reduced coercivity. The hexaferrites with narrow chemical distribution reveal resonance absorption in sub-terahertz band. The highest NFMR frequency of 270 GHz was observed for x = 5.5 sample annealed at 1400 °C.     

Graphitization studies of anthracites by high resolution electron microscopy

Thirteen anthracites of various origin were studied by modern electron microscopy techniques, microdiffraction, bright field, dark field and lattice imaging in the raw and progressively heat-treated state. The anthracites are known to behave like hard carbons below HTT 2000°C and like soft carbons above 2500°C. We have found that flattening of the pores, which is not present in hard carbons, occurs in anthracites and that this flattening induces a preferred orientation of the carbon planes above 1700°C, which in turn allows graphitization. This evolution of the carbon structure, demonstrated for the first time, is the essential phenomenon for anthracites. It becomes hidden by the promoting effect of impurities included in anthracites, if their concentration is too high.     

Effects of reaction and cure temperatures on morphology and properties of poly(ester‐urethane)

Poly(ester‐urethane) was synthesized from poly(ethylene glycol adipate) (PEG) and 2,4‐toluene diisocyanate (TDI) to study the effects of reaction temperature and cure temperature on the crystallization behavior, morphology, and mechanical properties of the semicrystalline polyurethane (PU). PEG as soft segment was first reacted with TDI as hard segment at 90, 100, and 110°C, respectively, to obtain three kinds of PU prepolymers, coded as PEPU‐90, PEPU‐100, and PEPU‐110. Then the PU prepolymers were crosslinked by 1,1,1‐tris (hydroxylmethyl) propane (TMP) and were cured at 18, 25, 40, 60, and 80°C. Their structure and properties were characterized by attenuated total reflection Fourier transform infrared, wide‐angle X‐ray diffraction, scanning electron microscopy, dynamic mechanical analysis, and tensile testing. With an increase of the reaction temperature from 90 to 100°C, the crystallinity degree of soft segment decreased, but interaction between soft and hard segments enhanced, leading to the increase of the glass transition temperature (T_g) of soft domain and tensile strength. When the cure temperature was above 60°C, miscibility between soft and hard segments of the PEPU films was improved, resulting in relatively low crystallinity and elongation at break, but high soft segment T_g and tensile strength. On the whole, all of the PEPU‐90, PEPU‐100, and PEPU‐110 films cured above 60°C possessed higher tensile strength and elongation at break than that of the films cured at other temperatures. The results revealed that the reaction temperature and cure temperature play an important role in the improvement of the crosslinking structure and mechanical properties of the semicrystalline PU. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 708–714, 2006     

Segmented block copolymers of natural rubber and propylene glycol-toluene diisocyanate oligomers

Segmented block copolymers were synthesized from hydroxyl terminated liquid natural rubber (HTNR) and polyurethane oligomers based on 1,2-propylene glycol and toluene diisocyanate (TDI) by one-shot and two-shot processes in solution. They were completely phase segregated. Structural features were characterized by infrared and nuclear magnetic resonance spectroscopies. The two-phase morphology was deducted from thermal analysis and dynamic mechanical analysis (DMA). The soft segment glass transition temperature was about ?64°C and the hard segment glass transition was between 70°C and 100°C depending on the polyurethane content. The two-phase morphology was corroborated by a two-stage thermal decomposition of the products. The morphology consisted of a heterogeneous dispersion of beads in a continuous matrix. The large size and the nature of the beads suggest that they are independent of the block copolymer structure and are formed by the agglomeration of the polyurethane homopolymers, which remain unbonded to the rubber chains during chain extension. At lower hard segment contents the materials behaved like quasi-elastomers, and at higher hard segment contents, they were like tough plastics. At intermediate compositions they behaved as rigid elastomers. Variations in hardness and tear strength were consistent with this behavior.     

The effect of substrate temperature on the growth of CNx films with β-C3N4-like microcrystallites by an inductively coupled plasma (ICP) sputtering method

The effect of substrate temperature on the formation of β-C₃N₄-like crystallites by an inductively coupled plasma sputtering method has been investigated. Transmission electron diffraction patterns reveal that the structure of the microcrystallites formed is close to the theoretically predicted structure of β-C₃N₄. By using 100 W of radio-frequency (RF) power for the deposition, the N/C atomic ratio in the film decreases from 0.35 to 0.07 upon increasing the substrate temperature from 100°C to 500°C. However, the crystallinity of the grains improves upon increasing the substrate temperature from 100°C to 400°C and then deteriorates drastically at 500°C, probably due to a deficiency of nitrogen in the film. By using 500 W of RF power to increase the degree of gas dissociation, the formation of β-C₃N₄ crystallites is enhanced upon increasing the substrate temperature from 400°C to 800°C, with the N/C atomic ratio in the film decreasing only slightly from 1.0 to 0.85. At 800°C, the film deposited consists of large sizes of crystallites, as evidenced from the highly spotty electron diffraction pattern, and contains a high percentage (90%) of sp³ CN bonding (i.e., the bonding of C₃N₄ crystallites) as estimated from X-ray photoelectron spectroscopy. The results suggest that, at a high degree of gas dissociation, the high substrate temperature is favorable for the synthesis of β-C₃N₄ crystallites.     

Superior high-temperature oxidation resistance of magnetron sputtered Hf–B–Si–C–N film

A hard and optically transparent amorphous Hf₇B₂₃Si₁₇C₄N₄₅ film with a contamination level less than 4 at%, prepared by reactive pulsed dc magnetron sputtering, was subjected to systematic investigation of high-temperature oxidation behavior in air up to 1700 °C. We focus on thermogravimetric analysis of the film in air and on the evolution of the film structure, microstructure and elemental composition with an annealing temperature ranging from 1100 °C to 1700 °C. The film exhibits a superior oxidation resistance up to 1600 °C due to a formation of a nanocomposite protective oxide layer on the surface above 1000 °C. The layer consists of monoclinic and tetragonal (or orthorhombic) HfO₂ nanocrystallites surrounded by a SiO₂-based amorphous matrix, most probably containing boron. The HfO₂ nanocrystallites exhibit a gradient in size with a dense population of small (a couple of nm) crystallites next to the interface and larger but dispersed crystallites close to the surface.     

Annealing-induced morphological changes in segmented elastomers

Thermal analysis has been used to study annealing-induced ordering in segmented elastomers. Twelve segmented elastomers were studied each having approximately 50% by wt hard segment content. Seven general classes of materials were examined including polyether and polyester polyurethanes, polyether polyurethane-urea, and polyether-polyester. Materials were slow cooled (?10°C min^?1) from the melt to an annealing temperature (?10°, 20°, 60°, 90° or 120°C) where they were annealed (16, 12, 8, 6 or 4 days, respectively). Annealing was followed by slow cooling (?10°C min^?1) to ?120°C after which a d.s.c. experiment was run. In general, annealing resulted in an endothermic peak at a temperature 20°–50°C above that of the temperature of annealing. This phenomenon was observed in both semicrystalline and amorphous materials. The closer the annealing endotherm was to a crystalline endotherm without exceeding it in temperature, the larger its size. Annealing endotherms resulted from hard or soft segment ordering. Only one annealing endotherm was observed for a given annealing history, even though in some materials hard and soft segments could exhibit annealing-induced morphological changes. Hard segment homopolymers were studied yielding results similar to the block polymers containing shorter sequences of the same material. This suggests that annealing-induced ordering is an intradomain phenomenon not associated with the interphase between domains, or necessarily dependent on the chain architecture of segmented elastomers.     

Mechanical properties of acrylic based latex blend coatings

A complete characterization of the mechanical properties of acrylic based latex blend coatings comprising hard (T_g = 45°C) and soft (T_g = ?5°C) phases is presented. Although clear and transparent in appearance, these blends remain phase separated through the entire range of compositions based on their hard phase content. Blends with less than 50% hard phase (soft blends) show a typical rubber‐like behavior with large elongation to break and low stiffness, whereas those with more than 50% hard phase (hard blends) exhibit a progressively glassy behavior. The values of effective Young's moduli and Poisson's ratios lie within the bounds calculated from Hashin‐Shtrikman models and exhibit a sigmoidal shaped profile as a function of composition, in close agreement with the solutions of Hill‐Budiansky equations. These results, along with interpretations based on a percolation theory, indicate that a phase inversion to a continuous hard matrix from the soft one occurs around 30–40% hard phase content, a conclusion further supported by scanning electron micrographs of the fracture surfaces.