山田 泰弘

Interactions of metal cations such as Li+, Na+, K+, Mg+, Ca2+, Sr+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+ with ammonia-treated graphene sheets (G) and thermal stability of metal cations coordinated with oxygen- and nitrogen-containing functional groups on G were investigated by rinsing G coordinated with metal cations (G-Metal) in 2-propanol using sonication and by heating G-Metal at 773 K, respectively. Monovalent alkali metal cations, divalent alkaline-earth metal cations, divalent transition metal cations such as Mn2+, and the other metal cation such as Zn2+ were removed by rinsing because of either no interaction or weak interactions between metal cations and G including various thermally stable nitrogen- and oxygen-containing functional groups. Trivalent transition metal cations such as Cr3+ and Fe3+ were agglomerated by heat treatment at 773 K, whereas divalent transition metal cations such as Co2+, Ni2+, and Cu2+ remained without severe agglomeration. Phenanthroline-like groups on edges of graphene showed the strongest interaction with Ni2+ among all of investigated nitrogen- and oxygen-containing functional groups as results of density functional theory calculation. The thermal stability of N-Ni bonding was confirmed as above 873 K as results of heat treatment of a standard compound (Ni phthalocyanine) in a glass ampoule. (C) 2014 Elsevier Ltd. All rights reserved.

Catalytic activity of rare earth oxides (REOs) in the vapor-phase dehydration of 1,4-butanediol to produce 3-buten-1-ol varies with lattice parameters of REOs. In order to clarify the adsorption structure and the reaction mechanism, adsorption energy of 1,4-butanediol on bixbyite REO, such as Sc2O3, Y2O3, Dy2O 3, Ho2O3, and Er2O3, {2 2 2} surface was calculated with density functional theory (DFT), and paired interacting orbitals (PIO) calculation of the adsorption state between 1,4-butanediol and Er2O3 was executed. The DFT study elucidates that the catalytic activity is correlated with adsorption energy. The PIO study clarifies the interactions between the reactive atoms of 1,4-butanediol and Er2O3 surface: tridentate interactions between a position-2 hydrogen atom of diol and an oxygen anion on Er 2O3 and between each OH group of diol and erbium cations on Er2O3, and an intramolecular repulsive interaction between the position-1 carbon atom and the oxygen atom of OH group are observed. These results suggest that the position-2 hydrogen atom is firstly abstracted by a basic oxygen anion and that the position-1 hydroxyl group is subsequently abstracted by an acidic erbium cation. Another OH group on position 4 plays an important role of anchoring the diol to the Er2O3 surface. Therefore, it is proved that the dehydration of 1,4-butanediol over REOs proceeds via acid-base concerted mechanism. © 2013 Elsevier B.V. All rights reserved.

X-ray photoelectron spectroscopy (XPS) has been commonly used to determine the nitrogen-containing functional groups of graphene. However, reported assignments of C1s shifts of nitrogen-containing functional groups are unclear. Most works discuss peak shifts of only N1s spectra and C1s shifts and the full width at half maximum (FWHM) are excluded. Thus, peak shifts and FWHMs of C1s and N1s XPS spectra of graphene with nitrogen-containing functional groups such as pyridinic, phenanthroline-like, sp(2)C-NH2, sp(3)C-NH2, pyrrolic, imine, pyridazine-like, pyrazole-like, sp(2)C-CN, sp(3)C-CN, and valley quaternary nitrogen (Q-N) on edges and sp(3)C-NH2, center amine, and center Q-N in the basal plane were simulated using density functional theory calculation. Main peaks of C1s spectra were shifted positively and negatively by the electron-withdrawing and electron-donating functional groups, respectively. FWHMs of the main peaks of C1s spectra were influenced by mainly electron-withdrawing functional groups on edges and most functional groups in the basal plane. Sp(2)C-NH2 on zigzag edges is suggested as a reference functional group to adjust the N1s spectra because influence of the functional group on the shift of main peak and the FWHM of C1s spectrum was small. (C) 2013 Elsevier Ltd. All rights reserved.

Epoxide is one of the simplest functional groups on fullerenes, but mechanisms for migration of oxygen atoms and formations of CO and CO2 gases upon heat treatment are still unclear. In this work, epoxidized fullerenes were heated in helium gas up to 673 K and the pyrolyzed structures of epoxidized fullerenes were analyzed using X-ray photoelectron spectroscopy, infrared spectroscopy, direct-injection mass spectrometry, elemental analysis, and density functional theory calculation. Functional groups such as C=0 and lactone groups were formed by heat treatment of the epoxidized fifflerenes at 523 K. At 673 K, lactone groups were decomposed into CO and CO2 gases. The amount of the CO2 gas was more than that of the CO gas. This suggests that a formation of CO2 gas from lactone groups is energetically more favorable than that of CO gas. Moreover, the ratio of CO2 gas to CO gas increased, as the amount of oxygen atoms on fullerenes increased. The formation of CO and CO2 gases at 673 K indicates that the presence of carbene sites with either vacancy defects or ether groups on fullerenes.

Mechanisms for pyrolysis of epoxidized fullerene involving formation of CO, CO2, and O-2 gases were studied using density functional theory calculation. From two oxygen atoms on fullerene, a lactone group is formed through migration of an oxygen atom. The lactone group is transformed into either CO2 gas with a monovacancy defect or a combination of an ether group and a ketone group. The ketone group in the combination of the ether group and the ketone group decomposes into CO gas. All of these mechanisms proceed endothermically, but CO gas tends to form more than CO2 gas because the activation energy required for the formation of CO gas is lower than that of CO2 gas. From three oxygen atoms on fullerene, a combination of a lactone group and a ketone group is generated and decomposes into CO and CO2 gases. CO2 gas tends to form more than CO gas because the activation energy required for the formation of CO2 gas is lower than that of CO gas. O-2 gas is difficult to desorb because of the high activation energy.

The vapor-phase hydrogenolysis of glycerol was performed at a gradient temperature and ambient hydrogen pressure over a commercial Cu/Al2O3 catalyst modified with silver. Addition of Ag into Cu/Al2O3 catalysts was found to be efficient in inhibiting the decomposition of glycerol to produce ethylene glycol and gave a yield of 1,2-propanediol higher than that of the original Cu/Al2O3 without Ag. To minimize the ethylene glycol formation, the suitable loading of Ag was 1 wt.%. Since the Ag loading decreases the hydrogenation ability of the Cu/Al2O3 catalyst, 1 wt.% Ag-loaded Cu/Al2O3 catalyst was placed on the upper layer of the fixed catalyst bed and the Cu/Al2O3 catalyst was placed on the bottom layer for achieving much higher 1,2-propanediol yield. The effect of temperatures of the top, the interlayer, and the bottom of the catalyst bed on the yield was also examined: a high 1,2-propanediol yield of 98.3%, which is the highest value under ambient H-2 pressure conditions, was achieved at a gradient temperature from 170 to 105 degrees C and a glycerol concentration of 15 wt.%. (C) 2014 Elsevier B.V. All rights reserved.

Vapor-phase dehydration of 3-methyl-1,3-butanediol to 3-methyl-3-buten-1-ol was investigated over carbon-modified alumina, C/Al2O3, which was prepared by depositing carbonaceous species, i.e. coke, on Al 2O3 with contacting Al2O3 surface with 3-methyl-1,3-butanediol vapor at 250 C. Temperature-programmed desorption of adsorbed NH3 revealed that the strength of acid sites of fresh Al2O3 was weakened by the coke deposition. It was found that the selectivity to 3-methyl-3-buten-1-ol was increased by the coke deposition over Al2O3 catalysts in the dehydration of 3-methyl-1,3-butanediol at 200 C. Generation of the main by-products such as isobutylene and 4,4-dimethyl-1,3-dioxane were prohibited by the acid sites weakened by the coke deposition. The 13C NMR and IR measurement elucidated that the deposited coke had CC, CO, COO, CH2, CH 3, and OH groups, which indicates that the coke consisted of polymeric unsaturated alcohol. The coke content that is effective in inhibiting the decomposition of 3-methyl-1,3-butanediol into isobutylene was ca. 15 wt.% of C/Al2O3. © 2014 Elsevier B.V. All rights reserved.

Vapor-phase catalytic dehydration of 2,3-butanediol was investigated over metal oxides such as CeO2, La2O3, Yb 2O3, ZrO2, Al2O3, TiO2, ZnO, Fe2O3, NiO, and Cr2O 3. In the dehydration of 2,3-butanediol, 3-buten-2-ol was preferentially produced over monoclinic ZrO2 along with major by-products such as butanone and 3-hydroxy-2-butanone. Over ZrO2 calcined at 900 C, 3-buten-2-ol was produced with a maximum selectivity of 59.0% at 300 C without producing 1,3-butadiene. © 2014 Elsevier B.V.

The basal plane of graphene has been known to be less reactive than the edges, but some studies observed vacancies in the basal plane after reaction with oxygen gas. Observation of these vacancies has typically been limited to nanometer-scale resolution using microscopic techniques. This work demonstrates the introduction and observation of subnanometer vacancies in the basal plane of graphene by heat treatment in a flow of oxygen gas at low temperature such as 533 K or lower. High-resolution transmission electron microscopy was used to directly observe vacancy structures, which were compared with image simulations. These proposed structures contain C = O, pyran-like ether, and lactone-like groups.

Vapor-phase catalytic dehydration of 1,2-propanediol was investigated over several solid acid catalysts, such as alumina, silicaalumina, HY zeolite, and α-zeolite. These acids catalyzed the dehydration of 1,2-propanediol to produce propanal (Figure 1), while zeolites were particularly deactivated because of deposition of carbonaceous species. An amorphous silicaalumina was modified with metals such as Ag and Cu to stabilize the catalytic activity under hydrogen flow conditions. Ag-modified silicaalumina is a promising catalyst for the production of propanal from 1,2-propanediol. © 2014 The Chemical Society of Japan.

© 2014 Elsevier B.V. All rights reserved. Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) was investigated over several metal oxides loaded on well-crystallized monoclinic ZrO2. In the dehydration of 2,3-BDO, unsaturated alcohol, i.e. 3-buten-2-ol (3B2OL), was preferentially produced together with major by-products such as butanone and 3-hydroxy-2-butanone over ZrO2-based catalysts. The selectivity to 3B2OL over monoclinic ZrO2 was greatly enhanced by the alkaline-earth oxides such as CaO, SrO, and BaO. At a CaO loading of 3 wt% on the monoclinic ZrO2, a Ca-O-Zr hetero-linkage was formed to generate new basic sites, and the selectivity to 3B2OL exceeded 76% at 350 °C. Poisoning experiments using CO2 and NH3 strongly suggest that the formation of 3B2OL from 2,3-BDO proceeds over base-acid concerted sites.

© 2014 The Chemical Society of Japan. Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) was investigated over rare earth oxide (REO) catalysts as well as In2O3. In the dehydration of 2,3-BDO, 3-buten-2-ol (3B2OL) was produced together with 3-hydroxy-2-butanone (3H2BO), butanone (MEK), 2-methylpropanal (IBA), 2-methyl-1-propanol (IBO), etc. Sc2O3 and In2O3 showed hi gher 3B2OL select ivities than other REOs. In particular, Sc2O3 converted 2,3-BDO into 3B2OL with an excellent selectivity of 85.0% at 99.9% conversion.

X-ray photoelectron spectroscopy (XPS) is among the most powerful methods to determine the surface chemical properties of carbon materials. Because heat-treated graphite oxide includes various defects, analyses of the structure by XPS help us understand the structures of various carbon materials. Thus, XPS spectra of graphene-related materials containing various functional groups and other defects on edges and in the basal plane were simulated and full width at half maximums (FWHMs) and peak shifts were obtained by density functional theory calculation. Shifts of whole C1s spectra were influenced by the electron-withdrawing functional groups such as C=O-containing functional groups. FWHMs of the main peak of C1s spectra were influenced by mainly electron-withdrawing functional groups in addition to defects such as vacancy, pentagons, and heptagons. Analyses using only XPS provide us limited information, even though the peak tops and FHWMs of simulated XPS spectra are used for assignment. Combination use of peak shifts and FWHMs of XPS spectra, infrared spectroscopy, and density functional theory calculation provided more reliable assignments of defects including oxygen-containing functional groups of carbon materials than commonly used methods using only peak shifts of XPS spectra.

Syntheses of unsaturated alcohols in the vapor-phase catalytic dehydration of alkanediols over rare earth oxides are reviewed. CeO2 effectively catalyzes the dehydration of 1,3-butanediol to produce 3-buten-2-ol and trans-2-buten-1-ol. Heavy rare earth oxides such as Er2O3, Yb2O3, and Lu2O3 selectively catalyze the dehydration of 1,4-butanediol to produce 3-buten-1-ol. In the dehydration of 1,5-pentanediol, Yb2O3, Lu 2O3, and Sc0.5Yb1.5O3 catalysts efficiently work to produce 4-penten-1-ol. The active and selective oxides are composed of large particles with well-crystallized fluorite or bixbyite structure. Small oxide particles with poor crystallinity decrease the selectivity to unsaturated alcohols because of their dehydrogenation ability. In the reactions of different alkanediols, the reactivity of alkanediol depends on the length between the OH groups as well as on the geometry of the catalyst surface, which is affected by the distance between rare earth cations. For example, over CeO2, the reactivity order of the alkanediols is 1,3-butanediol > 1,4-butanediol > 1,5-pentanediol > 1,6-hexanediol. Quantum calculations support a probable reaction mechanism: OH groups and the H of the position-2 methylene group of 1,3-butanediol are interacted with the surface Ce4+ to form a tridentate coordination, and the abstraction of the position-2 H by Ce4+ is the initial step of 1,3-butanediol dehydration in the formation of unsaturated alcohols. © 2013 American Chemical Society.

Vapor-phase synthesis of 3,4-2H-dihydropyran (DHP) from tetrahydrofurfuryl alcohol (THFA) was investigated over acidic catalysts modified with transition metals. Catalytic activity of alumina was seriously deactivated in the reaction of THFA in nitrogen at 300 °C although the initial activity was high. Tetragonal ZrO2 showed the catalytic activity to produce DHP at 350 °C. Alumina modified with Cu exhibits stable catalytic activity with high selectivity to DHP under hydrogen flow conditions, and the optimum activity was obtained at CuO contents of 5-10 wt.%: the selectivity to DHP was as high as 85%. Prior to the reaction, CuO was reduced to metallic Cu, which probably works as a product remover together with hydrogen to prevent coke formation. The reaction pathway from THFA to DHP was discussed: it is speculated that THFA is initially rearranged into 2-hydroxytetrahydropyran, which rapidly dehydrated to DHP. © 2012 Elsevier B.V.

Solvent-free Diels-Alder reactions were carried out by heating a mixture of a volatile diene, such as 1,3-butadiene, isoprene, or 2,3-dimethyl-1,3- butadiene, and a dienophile, such as methyl vinyl ketone, methyl acrylate, or maleic anhydride, in a closed batch reactor. High yields of Diels-Alder products were obtained without using solvents and catalysts within a short reaction time in most of the reactions. In particular, several reactions of dienophiles with 1,3-butadiene, which is known as a diene with low reactivity because of its gaseous form, also proceeded with high yields of Diels-Alder products in the closed batch reactor under conditions pressured by the reactant vapor. Solvent-free reactions provided high yields compared to reactions in solvent since the reaction heat directly resulted in increasing the reaction temperature and pressure. Energy in the exothermic reaction was used effectively in the closed batch system under solvent-free conditions. © 2013 The Chemical Society of Japan.

Dimerization of 1,3-butadiene was investigated in a closed batch system under high-pressure conditions. 4-Vinylcyclohexene was mainly produced without using any solvents or catalysts at temperatures of 150215 °C. The conversion of 1,3-butadiene was significantly dependent on the temperature and pressure. 1,3-Butadiene was converted to 4-vinylcyclohexene at selectivity higher than 90mol% with by-products of 1,5-cyclooctadiene and 1,2-divinylcyclobutane. Large charges of reactant are efficient in achieving high conversions of 1,3-butadiene. Use of solvents, which dilute the reactant and absorb the reaction heat, is not favorable in the present dimerization of 1,3-butadiene under pressured conditions. © 2013 The Chemical Society of Japan.

Electrochemical behavior of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) separated by agarose gel chromatography was analyzed as electrodes of electric double-layer capacitor (EDLC). Due to the doping of ions to semiconducting SWCNTs, the cyclic voltammogram of semiconducting SWCNTs showed amphoteric behavior, which is analogous to that of dopable conducting polymers. As the potential was increased or decreased from the flat band potential, the capacitance of semiconducting SWCNTs was increased, but that of metallic SWCNTs was slightly increased. The high capacitance of semiconducting SWCNTs at the high potential is beneficial for EDLC due to the possible limitation of capacitance. © 2011 Elsevier Ltd. All rights reserved.

Er 2O 3 nanorods were successfully prepared with hydrothermal treatment without using organic additives such as surfactant, fatty acid, or alcohol. Er2 O3 nanorods were obtained under high temperature and/or long reaction times. Er 2O 3 nanorods mainly exposed {440} and {400} facets on the surface. Er 2O 3 nanorods showed excellent catalytic activity compared to commercial Er 2O 3 nanoparticles in the dehydration of 1,4-butanediol to produce 3-buten-1-ol. © 2012 The Chemical Society of Japan.

In the vapor-phase synthesis of 2,3-dimethyl-1,3-butadiene from pinacolone over modified alumina catalysts, it was found that alumina modified with transition metals such as Co stabilized the conversion of pinacolone and produced 2,3- dimethyl-1,3-butadiene selectively under hydrogen flow conditions, whereas the catalytic activity of pure alumina was seriously deteriorated irrespective of its high initial activity. © 2012 The Chemical Society of Japan.

Silica-supported silver exhibited high catalytic activity in the dehydration of glycerol: glycerol was dehydrated into hydroxyacetone with the selectivity higher than 86% at 91% conversion over Ag/SiO 2 in H 2 flow at 240°C. Silver metal provides an active site and showed stable catalytic activity for the glycerol dehydration in H 2 atmosphere, while the dehydration activity decreased in N 2 atmosphere. The hydrogenation of hydroxyacetone into 1,2-propanediol and the decomposition to ethylene glycol did not proceed over silver. © 2012 The Chemical Society of Japan.

Exfoliated graphene ligands were prepared by heating exfoliated graphene sheets in ammonia gas at 1023 K. The functional groups of the functionalized exfoliated graphene ligands were mainly pyridine on the edges of the vacancy defects. Copper cations were coordinated with the ligands. Even after being heated at 773 K, coordinated copper did not show severe agglomeration. On the other hand, copper supported on exfoliated graphene sheets prepared by the conventional method agglomerated and ca. 20 nm of copper oxide was formed. This difference clearly shows that exfoliated graphene ligands stabilized copper cations. (C) 2011 Elsevier Ltd. All rights reserved.

A series of rare earth oxides were investigated as catalysts in the ketonization of acetic acid. High selectivity to acetone over 99% was obtained by reacting acetic acid over rare earth oxides such as La2O3, CeO2, Pr6O11, and Nd2O3. Especially, Pr6O11 showed the highest yield of 80% at 350 degrees C among the 14 rare earth oxides. The bulk structure of CeO2 was stable during the ketonization, while the surface acetate species were observed over CeO2 after ketonization. In contrast, the other active rare earth oxides such as La2O3, Pr6O11, and Nd2O3 were mainly basic oxides due to the formation of bulk oxyacetate such as MO(AcO), where M is La, Pr, and Nd and AcO indicates CH3COO group, in the initial period of the reaction. In any case, the catalytic ketonization proceeds over the surface of the oxyacetates and CeO2. Catalytic cycle of the ketonization is composed of two steps: the decomposition of surface M2O(AcO)(4) to produce MO(AcO), acetone, and carbon dioxide and the regeneration of surface M2O(AcO)(4) by reacting MO(AcO) and acetic acid to produce water. (C) 2011 Elsevier B.V. All rights reserved.

Vapor-phase catalytic reactions of several terminal diols were investigated over several rare earth oxides, such as Sc2O3, Y 2O3, CeO2, Yb2O3, and Lu2O3. Sc2O3 showed selective catalytic activity in the dehydration of terminal diols with long carbon chain, such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol, to produce the corresponding unsaturated alcohols. In the dehydration of 1,6-hexanediol, 5-hexen-1-ol was produced with selectivity over 60 mol%, together with by-products such as ε-caprolactone and oxacycloheptane. In the dehydration of 1,10-decanediol, 9-decen-1-ol was produced with selectivity higher than 70 mol%. In addition to Sc 2O3, heavy rare earth oxides such as Lu2O 3 as well as monoclinic ZrO2 showed moderate selectivity in the dehydration of the terminal diols. © 2010 Elsevier B.V. All rights reserved.

Pore structures and electrochemical performances of mass-produced metal-free single-walled carbon nanotubes (mf-SWCNTs) heated in either CO 2 gas or dry air were investigated. Pore structures, defects, and electrochemical performances of mf-SWCNTs were analyzed mainly using the N 2 adsorption method, apparent density measurement, Raman spectroscopy, and cyclic voltammogram. mf-SWCNT sheets heated in CO2 gas showed a remarkable increase of the specific surface area up to 1900 m 2 g-1, but sheets heated in air showed an increase of only up to 1400 m2 g-1. Propan-2-ol, 4-methyl-1,3-dioxolan-2- one, or ionic liquid was impregnated in the inner space of mf-SWCNTs to confirm whether the inner space of mf-SWCNTs is filled with each liquid. mf-SWCNTs heated in air were completely filled, but mf-SWCNTs heated in CO2 were partially filled. From these results, it is estimated that holes of the size of 0.56 nm or larger are opened on the side wall of mf-SWCNTs. A combination of two heat treatments maximized the effective specific capacitance of heated mf-SWCNTs up to 100 F g-1, which is 1.6 times higher than that of as-grown mf-SWCNTs because of the removal of the carboneous component and the creation of defects on the sidewall of mf-SWCNTs, which allow the electrolyte into the inner space of mf-SWCNTs. © 2010 American Chemical Society.

Vapor-phase catalytic dehydration of 1,3-butanediol was investigated over rare earth oxides (REOs) calcined at different temperatures. In the dehydration of 1,3-butanediol over REOs such as Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, and Y2O3, 3-buten-2-ol and 2-buten-1-ol were preferentially produced. REOs exhibited different catalytic activities in the dehydration of 1,3-butanediol depending on their crystal structures. CeO2 showed the highest formation rate with the highest selectivity to the unsaturated alcohols among the REOs. Cubic REOs also selectively produced the unsaturated alcohols: cubic Er2O3, Yb2O3, and Lu2O3 showed high formation rate of the unsaturated alcohols. Since the formation rates of the unsaturated alcohols over Er2O3 and CeO2 were suppressed in CO2 and NH3 carrier gas flows more than in H2 flow, it is probable that the acid-base sites play a major role of the formation of the unsaturated alcohols. © 2010 Elsevier B.V. All rights reserved.

Vapor-phase catalytic dehydration of 1,2-propanediol was investigated over several catalysts, such as acidic oxides and supported heteropoly acids. These acids catalyze the dehydration of 1,2-propanediol to produce propanal. In particular, silica-supported silicotungstic acid showed the highest catalytic activity in the formation of propanal. At low conversions, however, propanal reacted with another 1,2-propanediol to produce a cyclic acetal (2-ethyl-4-methyl-1,3-dioxolane). Such acetal formation reduced the selectivity to propanal. Under optimum reaction conditions, 100% conversion was attained with propanal selectivity higher than 93 mol% at 200 °C. © 2009 Elsevier B.V. All rights reserved.

The correlation between capacitance and the structure of carbon nanotubes (CNTs) was revealed. The electrochemical behaviors of single- and double-walled CNTs were characteristic due to the electrochemical doping mechanism of semiconducting nanotubes, which are amphoteric and can be doped by both donors and acceptors. The capacitance and the sheet conductance of CNTs, as capacitor electrodes were dependent on their porous and electronic structure. High specific capacitance was obtained for uncapped single-walled CNTs having inner micropores with a diameter of <1 nm. © 2009 The Electrochemical Society. All rights reserved.

The three-dimensional microstructuring of carbon is useful for microelectromechanical devices and electrode arrays. A microstructure in the form of a microscale bridge (consisting of a girder and two adherent substructures) on an alumina substrate with a surface roughness of 1-2 μm (which allowed bonding by mechanical interlocking) was attained by using a novel low-cost process that involved thermoplastic spacer (paraffin wax) evaporation during pyrolysis of an epoxy-based film that coated the spacer and parts of the substrate. Fillers were chosen to reduce the shrinkage during pyrolysis and to increase the electrical conductivity. Multiwalled carbon nanotube as a filler was particularly effective for reducing the cracking tendency. Carbon black and silver nanoparticles as sole fillers were ineffective, producing cracked bridges. The total filler content (nanotube, optionally along with silver nanoparticles) had to exceed 3 vol.% in order to attain good control of the shape of the bridge. The method used a novolac epoxy resin in combination with an amine curing agent (without ultra-violet curing). The epoxy was chosen for low viscosity and strong bonding to the substrate. A bridge with a girder of length 90-300 μm, separated from the substrate by a height of 5-15 μm, was attained. © 2008 Elsevier Ltd. All rights reserved.

Carbon-based films (0.8-13 μm thick) with good bonding to the substrate and high processability were produced at 650 °C on an alumina substrate, using SU 2.5 bisphenol-A type novolac epoxy (plus triethyleneteramine curing agent) as the carbon precursor. This precursor gave crack-free and scratch resistant carbon films. Interconnected filamentary nickel nanoparticles were more effective for conductivity enhancement than silver nanoparticles or multiwalled carbon nanotubes at 5 vol.% or below, in spite of the high conductivity of silver and the high aspect ratio of nanotubes. The carbon film with 2.5 vol.% nickel showed resistivity 6 × 10-3 Ω cm. © 2008 Elsevier Ltd. All rights reserved.

Heat dissipation from aircraft is important. Carbon fiber polymer-matrix structural composites have high in-plane thermal conductivity, but low through-thickness conductivity. A nanostructuring method involving carbon black at the interlaminar interface was developed to improve the through-thickness conductivity. Ethylene glycol monoethyl ether (EGME) was used for dispersing the carbon black and to partially dissolution of the epoxy resin on the fiber-epoxy prepreg surface. EGME evaporated from the prepreg surface prior to composite fabrication. The optimum carbon black content in EGME for attaining high through-thickness conductivity was 0.8 wt.% for both unidirectional and crossply configurations. Applying EGME without carbon black improved the conductivity by up to 36%, but in the case with carbon black, the improvement was up to 210%. For the same interlaminar interface modification (except for EGME with 1.2 wt.% carbon black), the conductivity and its fractional increase were higher for the crossply configuration than the corresponding unidirectional configuration. The through-thickness compressive modulus and the flexural modulus were increased by up to 14% and 11%, respectively by using EGME with carbon black. The average thickness of the interlaminar interface increased with increasing carbon black content, but it was decreased by the use of EGME alone. © 2008 Elsevier Ltd. All rights reserved.

This work provides phase-change thermal interface materials (TIMs) with high thermal stability and high heat of fusion. They are based on antioxidants mainly in the form of hydrocarbons with linear segments. The thermal stability is superior to paraffin wax and four commercial phase-change materials (PCMs). The use of 98.0 wt.% thiopropionate antioxidant (SUMILIZER TP-D) with 2.0 wt.% sterically half-hindered phenolic antioxidant (GA80) as the matrix and the use of 16 vol.% boron nitride particles as the solid component give a PCM with a 100°C lifetime indicator of 5.3 years, in contrast to 0.95 year or less for the commercial PCMs. The heat of fusion is much higher than those of commercial PCMs; the values for antioxidants with nonbranched molecular structures exceed that of wax; the value for one with a branched structure is slightly below that of wax. The phase-change properties are degraded by heating at 150°C much less than those of the commercial PCMs. The stability of the heat of fusion upon phase-change cycling is also superior. The viscosity is essentially unaffected by heating at 150°C. Commercial PCMs give slightly lower values of the thermal contact conductance for the case of rough (12 μm) mating surfaces, in spite of the lower values of the bond-line thickness.

The use of a diepoxide resin in the form of 1,4-butanediol diglycidyl ether as the epoxy resin, lithium perchlorate (20 wt.%) as the ionic salt, a hardener (4,7,10-trioxatridecane-1,13-diamine, 15 wt.%) as the curing agent, and a poling DC electric field of 720 V/m gives an electret that exhibits a maximum voltage of 3.4 V during poling (30 min) and a stabilized voltage of 0.67 V after depoling (7.0 h). An epoxy system that hardens slowly (such as one with less hardener) is preferred, due to the longer time during poling for the ions to remain mobile. The rate of hardening rather than that of curing is the governing factor. The lithium salt hastens the curing, but it provides the ions and stabilizes the electret voltage, particularly during the first 30 min of depoling. After the first 30 min of depoling, crosslinking significantly enhances the stability of the electret voltage. The time constant for depoling is 0.8 h during the first 30 min of depoling and is 9 h afterward. Decrease of the lithium salt proportion from 20 to 10 wt.% still provides an effective electret, although the performance is reduced. An epoxy resin produced from Bisphenol F and epichlorohydrin is ineffective due to the high viscosity and fast hardening. © 2008 Springer Science+Business Media, LLC.

The thermal stability of polyol-ester-based thermal pastes is evaluated by weight loss, viscosity and thermal contact conductance measurements. A high degree of thermal stability has been attained by using a half-hindered phenolic primary antioxidant and a thiopropionate secondary antioxidant. By using either carbon black or boron nitride particles as the solid component, a thermally conductive paste with a high degree of thermal stability has been attained. The antioxidants cause the residual weight (excluding the solid component) after oven aging at 200 °C for 24 h to increase from 36 to 97 wt.%. They cause the viscosity not to increase upon heating and they reduce the thermal cracking tendency. They do not affect the thermal contact conductance measured across mating surfaces that sandwich the paste. The use of a fully-hindered phenolic primary antioxidant is less effective. Both carbon black and boron nitride serve as antioxidants in the presence of either primary antioxidant or secondary antioxidant at 200 °C, though, in most cases, they degrade the thermal stability in the presence of both primary and secondary antioxidants, particularly at 220 °C. Below 180 °C and in the presence of primary and secondary antioxidants, boron nitride is particularly effective in promoting the thermal stability. Boron nitride paste shows an estimated lifetime of 19 years at 100 °C, compared to 1.3 years for the carbon black paste, and 0.10 year for commercial polyol-ester-based Arctic Silver 5. Carbon black paste has a lower tendency for cracking after heating than boron nitride paste, due to the low volume fraction of the solid component. © Springer Science+Business Media, LLC 2007.

Carbon black pastes were found to be effective as coatings for improving the performance of thermal gap-filling materials, including flexible graphite, aluminum and copper. The thermal contact conductance across copper mating surfaces was increased by up to 180%. A fluidic form of carbon black paste (based on polyethylene glycol) was more effective than a thixotropic form (based on polyol esters). The carbon black pastes were much more effective as coatings than a commercial silver paste. With a carbon black paste coating, aluminum foil (7 μm thick) was a superior gap-filling material compared to similarly coated flexible graphite (130 μm thick). However, without a coating, flexible graphite was superior to aluminum. Commercial silicone-based gap-filling materials were inferior to flexible graphite or aluminum (whether coated or not). © 2005 Elsevier Ltd. All rights reserved.

Polyol-based phase-change thermal interface materials that exhibit high thermal contact conductance and thermal stability have been developed for micro-electronic cooling. By using a diol (polycaprolactone or polyester diol in the form of 2-oxepanone) of molecular weight 1,000-2,000 amu, along with 4 vol.%hexagonal boron nitride particles, this work attained thermal contact conductance (at 70°C, across copper surfaces) that is higher than that attained by using paraffin wax, polyether glycol, polyethylene glycol, or tetradecanol (in place of the diol) and that attained by commercial phase-change thermal interface materials. The thermal stability of the diol is superior to the other phase change materials mentioned above, although the heat of fusion is lower. Boron nitride is more effective than carbon black (also 4 vol.%) for enhancing the conductance, but carbon black diminishes the heat of fusion less than does boron nitride.

This paper addresses thermal interface materials for thermal conduction of excess heat for microelectronic applications. Carbon black (30 nm) thixotropic paste based on polyol ethers is comparable to carbon black fluidic paste based on polyethylene glycol (PEG) in its effectiveness as a thermal paste, and in its dependence on pressure history. Prior pressure (up to 0.69 MPa) application is helpful. The optimum carbon black content is 2.4 vol.% for the thixotropic paste. The thermal contact conductance across copper surfaces is 30 ×104 and 11 × 104 W/m2-°C for surface roughness of 0.05 μm and 15 μm, respectively. The volume electrical resistivity is 3 × 103 Ω-cm. Boron nitride (BN) (5-11 μm) and graphite (5 μm) thixotropic pastes are less effective than carbon black thixotropic paste by up to 70% and 25%, respectively, in thermal contact conductance, due to low conformability.