The Microstructure and Dielectric Properties of SiBCN Ceramics Fabricated Via LPCVD/CVI

Low‐pressure chemical vapor deposition and infiltration was used for the first time to fabricate SiBCN ceramics with proper dielectric properties to lower the preparation temperature. SiBCN ceramics indicated by thermodynamic phase diagram with different phase compositions from CH₃SiCl₃–NH₃–BCl₃‐H₂ could be obtained through adjustable parameters. The as‐prepared SiBCN ceramics fabricated above 900°C showed proper dielectric properties with dielectric loss of about 0.1, which was due to the generation of amorphous carbon and SiC nanocrystals.     

A new dual luminescent pillared cerium(IV)sulfate–diphosphonate

A new pillared cerium(IV) sulfate–diphosphonate with formula Ce₂(2H₂O)[(O₃PCH₂)–NC₁₀H₁₈N–(CH₂PO₃)(SO₄)₂] · 6H₂O has been hydrothermally synthesized and its structure has been solved ab initio from laboratory X-ray powder diffraction data.The luminescent and thermal properties of this compound have been preliminarily studied and the encouraging results place it in the field of functional hybrid materials.     

Three new polyoxometalate-based hybrids prepared from choline chloride/urea deep eutectic mixture at room temperature

Three new polyoxometalate-based hybrids {[(CH₃)₃N(CH₂)₂OH]₂(H₃O)}[Na₂(H₂O)₆][IMo₆O₂₄]·H₂O 1 , {Na₂[(CH₃)₃N(CH₂)₂OH]₄}[Al(OH)₆Mo₆O₁₈]₂·8NH₂CONH₂·4H₂O 2 and {Na₆(H₂O)₁₈[(CH₃)₃N(CH₂)₂OH]₂(CON₂H₅)₂}[NaMo₇O₂₄]₂·4NH₂CONH₂·H₂O 3 were successfully synthesized in the choline chloride/urea deep eutectic mixture at room temperature. Reactant quantities of water presents in the nonaqueous eutectic mixture solvent may influence the structure of the products. The three compounds are fully characterized by elemental analyses, IR, UV–vis, TG analyses, power X-ray diffraction and single-crystal X-ray diffraction. The photocatalytic properties of 1 and 2 are investigated.     

The Photodissociation of Pyridine at 193 nm

Using photofragmentation translational spectroscopy, the primary processes involved in the photodissociation of pyridine are investigated at 193 nm. Upon absorption of a single photon, HCN + C₄H₄, CH₃ + C,H₂N, C₃H₃ + C₂H₂N, and H + C₅H₄N are the observed primary pathways, with relative yields of 59%, 21%, 11%, and 9%, respectively. This paper reports the experimental details and results of this study. Comparison of the results of this study with a previous study in our laboratory investigating the photolysis of benzene serves as a direct measure of the strong influence substitution of a heteroatom in an aromatic ring can have on a molecule's photochemistry.     

Mechanisms of hydrodesulfurization and hydrodenitrogenation

To study the problems inherent in deep hydrodesulfurization (HDS), the separate and simultaneous HDS of 4,6-dimethyldibenzothiophene and hydrodenitrogenation (HDN) of pyridine were investigated over a Ni-MoS₂/γ-Al₂O₃ and a Pd/γ-Al₂O₃ catalyst. The HDS of 4,6-dimethyldibenzothiophene and its three intermediates, 4,6-dimethyl-tetrahydro-dibenzothiophene, 4,6-dimethyl-hexahydro-dibenzothiophene and 4,6-dimethyl-dodecahydro-dibenzothiophene, demonstrated that, over the Pd catalyst, the (de)hydrogenation reactions were relatively fast compared to the C–S bond breaking reactions, whereas the reverse was true over the metal sulfide catalyst. The methyl groups of 4,6-dimethyldibenzothiophene strongly hinder the direct desulfurization HDS pathway over both catalysts. On the Pd catalyst the hydrogenation pathway is strongly promoted by the methyl groups, so that the total HDS rate does not decrease. Pyridine and piperidine were strong poisons for the hydrogenation pathway and H₂S was a strong poison for the direct desulfurization pathway.HDN of nitrogen-containing aromatic molecules occurs by hydrogenation of the aromatic heterocycle followed by C–N bond breaking. The C–N bond breaks by substitution of the alkylamine by H₂S to form an alkanethiol, followed by the loss of H₂S by elimination or hydrogenolysis. The NH₂-SH substitution does not occur by a classic organic substitution reaction but through a multi-step reaction pathway via an alkylimine. DFT calculations showed that the hydrogenolysis of ethanethiol to ethane and the elimination of ethane are relatively easy reactions.     

Correlation between crystal structure and modified microwave dielectric characteristics of Cu2+ substituted Li3Mg2NbO6 ceramics

Structural characteristics exert significant influences on microwave dielectric properties, and ion substitution is widely adopted to modify material performances by adjusting the crystal structure. In this work, low loss Li₃Mg_2-xCu_xNbO₆ (x?=?0–0.04) ceramics were prepared by Cu²⁺ substitution. The impacts of Cu²⁺ substitution for Mg²⁺ sites on the microwave dielectric characteristics and crystal structure were discussed in detail. Rietveld refinement results implied that a single Li₃Mg₂NbO₆ phase was formed. Additionally, a dense and homogeneous microstructure with grain sizes of 7–9?μm could be achieved, and moderate Cu²⁺ substitution could significantly promote the grain growth. The correlation between microwave dielectric characteristics and crystal structure was discussed by calculating some structural parameters. The ε_r was determined by the polarizability. The Q?×?f was influenced by the packing fraction. The τ_f value was dependent on the NbO₆ octahedron distortion, and the τ_f value could be adjusted to near zero for x?=?0.02. Typically, the Li₃Mg_2-xCu_xNbO₆ (x?=?0.02) composition exhibited remarkable microwave dielectric performances: ε_r?=?15.75, Q?×?f?=?92,134?GHz (9.86?GHz) and τ_f?=??2?ppm/°C, making it a promising candidate for temperature-stable millimeter-wave applications.     

Dielectric study of β-relaxation in some cellulosic substances

6-(2-Cyanoethylamino)-6-deoxycellulose (Cell-CEA) as a novel cellulose derivative was prepared from 6-bromo-6-deoxycellulose. The influence of the reaction conditions on the degree of substitution was studied in detail. The dielectric characteristics of a Cell-CEA sample having degree of substitution of 0.86, together with those of microcrystalline and regenerated celluloses, have been investigated in the temperature range from −60 to 120°C, and frequency range 30 Hz to 100kHz. One relaxation process, designated as β, was recognised, which was attributed to side-group motions, probably −CH₂X (X = OH or NHCH₂CH₂CN). The higher activation energy of this process and the shift to higher temperature in Cell-CEA, compared with microcrystalline and regenerated celluloses, reflects the enhanced steric constraints involved in the motion of the bulkier, −CH₂NHCH₂CH₂CN, side groups. The results obtained are discussed in terms of the dielectric parameters ϵ″_max′ β and Δϵ.     

Comparative investigations of coal pyrolysis under inert gas and H2 at low and high heating rates and pressures up to 10 MPa

Five German hard coals of 6–36 wt% volatile matter yield (maf) were pyrolysed at pressures up to 10 MPa, using two different apparatuses, which mainly differ in the heating rates. One consists of a thermobalance where a coal sample of ≈ 1.5 g is heated at a rate of 3 K min ^?1 under a gas flow of 3 I min^?1. The other apparatus is constructed for rapid heating (10²?10³ K s^?1) of a small sample of ≈10 mg of finely-ground coal distributed as a layer between the folded halfs of a stainless-steel screen, heated by an electric current. The product gas composition was determined by quantitatively analysing for H₂, CH₄, C₂H₄, C₂H₆, CO, CO₂ and H₂O. The amounts of tar and char were measured by weighing. The heating rate, pressure and gas atmosphere were varied. Under an inert gas atmosphere, high heating rates result in slightly higher yields of liquid products, e.g. tar. The yields of light hydrocarbon gases remain the same. With increasing pressure, the thermal cracking of tar is intensified resulting in high yields of char and light hydrocarbon gases. Under H₂, pyrolysis is influenced strongly at elevated pressure. Additional amounts of highly aromatic products are released by hydrogenation of the coal itself, particularly between 500 and 700°C. This reaction is less effective at higher heating rates because of the shorter residence time and diffusion problems of H₂. The yield of light gaseous compounds CH₄ and C₂H₆ increases markedly under either heating condition owing to gasification of the reactive char.     

Structure/permeability and permselectivity relationship of polyetherimides from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride. I

Gas permeability coefficients of a series of aromatic polyetherimides, which were prepared from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and various aromatic diamines, to H₂, CO₂, O₂, N₂ and CH₄ have been measured under 7 atm pressure and over the temperature range 30–150°C. A significant change in permeability and permselectivity, which resulted from a systematic variation in chemical structure of the polyetherimides, was found. Generally, increases in permeability of the polyetherimides are accompanied by decreases in permselectivity. The order of decrease of the permeability coefficients is as follows: HQDPA–IPDA > HQDPA–DDS > HQDPA–MDA > HQDPA–ODA > HQDPA–DABP > HQDPA–BZD. However, HQDPA–DMoBZD and HQDPA–DMoMDA, with bulky methoxy side-groups on the aromatic rings of the diamine residue, display both high permeability coefficients and high permselectivity. The favourable gas separation property, excellent thermal and chemical stability, and high mechanical strength make HQDPA–DMoBZD and HQDPA–DMoMDA promising candidates for membrane-based gas separation applications.     

Carbon nitride films deposited from organic solutions by electrodeposition

An electrodeposition process was applied to synthesize and deposit CN_x thin films from organic solution. The depositions from acetonitrile (CH₃CN) and dicyandiamide–acetone (C₂H₄N₄–C₃H₆O) solution were reported. The processes were performed near to room temperature. The films deposited from acetonitrile liquid contained 25% nitrogen, the nitrogen content in the films obtained from dicyandiamide solution reached to 48%. X-ray photoelectron spectrometry (XPS) and Fourier transform infrared (FTIR) were used to characterize the structure of the films. It indicated that high nitrogen content films contained CN bonds besides the CN, and CN bonds which composed both films.     

Darstellung,Struktur und Reaktivität quartärer Ammoniumcellulosate

Tetraalkylammonium cellulosates were prepared by means of an exchange reaction between cellulose and tetraalkylammonium methoxides in anhydrous methanol and dimethylsulfoxide up to a degree of substitution of about 0,7 without chain degradation. The course of this reaction and the structure of the cellulosates in comparison to lithium and sodium cellulosate has been studied. The reaction rate and the equilibrium substitution decreased with increasing size of the cation in the methoxide. The distribution of the alcoholate groups in equilibrium at C-2, C-3 and C-6 of the glucopyranosyl unit in the cellulosates, which was investigated by methylation, hydrolysis of the methylcelluloses, and analysis of the methylglucoses by gas chromatography, was independent of the nature of the cation. Under the given reaction conditions the hydroxyl group at C-2 was more acidic than those at C-3 and C-6, while for the latter practically no difference was found. The tetraalkylammonium cellulosates are highly reactive intermediates for the preparation of cellulose derivatives. The reactivity of the cellulosates increased with increasing size of the cation, Li^⊕ < Na^⊕ < N(CH₃)₄^⊕ <[(CH₃)₃N? CH₂? C₆H₅]^⊕.     

Influence of the methyl group on the dielectric constant of boron carbon nitride films containing it

LSI interconnect insulators made using low dielectric constant (low-k) materials are required for high performance devices with a small RC delay. We investigated a boron carbon nitride film containing the methyl group (Me–BCN) using tris-di-methyl-amino-boron (TMAB: B[N(CH₃)₂]₃) gas as a low-k material. In addition, we studied the influence of the methyl group on the dielectric constant (k-value) and the properties of the Me–BCN films. It was found that the k-value of the Me–BCN films decreases with increasing number of C–H bonds due to the methyl group (CH₃). The number of O–H bonds due to water incorporation is suppressed by increasing the number of C–H bonds. Consequently, we suggested that a lower k-value can be realized by the suppression of water invasion by a hydrophobic surface due to methyl bonds. Thus, the control of the methyl group is important to achieve a low-k material using Me–BCN films.     

Micromechanical properties of BN and B–C–N coatings obtained by r.f. plasma-assisted CVD

We have obtained highly transparent and hard BN films in a capacitively coupled r.f. plasma-assisted CVD reactor from three different gas mixtures: B₂H₆–H₂–NH₃, B₂H₆–N₂ and B₂H₆–N₂–Ar. It was found that the films were smooth, dense, and had a textured hexagonal structure with the basal planes perpendicular to the film surface. The microhardness, friction coefficient and adhesion of these coatings were measured by nanoindentation and microscratching. BC_xN_y films were also prepared in the same plasma-assisted CVD reactor from B₂H₆–N₂–CH₄ gas mixtures. The carbon content in the films was varied by using different CH₄ flow rates. These films had a less ordered structure. The mechanical properties of these films had been compared to those of hexagonal BN films. Microhardness measurements showed that there is a correlation between film composition and hardness of the BCN films.     

Darstellung,Konfigurationen und NMR-Daten der Säuren CH3(SR)  CHCOOH (R  C6H5, CH2C6H5, CH2COOH)

Preparation, Configurations and N.M.R. Dates of the Acids CH₃(SR)CHCOOH (R  C₆H₅, CH₂C₆H₅, CH₂COOH) The cis and trans isomers of the acids CH₃(SR)CHCOOH (R  C₆H₅, CH₂C₆H₅, CH₂COOH) were prepared by addition of HSR to CH₃CCCOOH in alkaline water solution and by alkaline hydrolysis of CH₃C(SR)₂CH₂COOC₂H₅ (R  C₆H₅, CH₂C₆H₅, CH₂COOC₂H₅). The oxidation products CH₃C(SO₂R)  CHCOOH (R  C₆H₅, CH₂COOH) were also prepared. The n.m.r. dates of the acids were obtained and some relations between them were discussed.     

The effects of chemical structure on gas transport properties of poly(aryl ether ketone) random copolymers

The physical properties and gas permeation behavior of a series of homo/random copolymers of 4,4′-difluorobenzophenone (DFBP)–2,2-bis(4-hydroxy-phenyl)propane (BPA)/2,2-bis(4-hydroxy-3,5-dimethyl-phenyl)propane (TMBPA) have been investigated by systematically varying the diol ratios. The tetramethyl substitution group on the phenyl rings simultaneously increases polymer free volume and chain stiffness. These were confirmed by experimental and simulated methods. With the increase in TMBPA content, the gas permeation coefficients, diffusion and solubility coefficients of H₂, O₂, N₂, CO₂ and CH₄ were found to increase. The gas transport coefficients of the copolymers predicted from the additional rule were compared with the experimental results and the results obtained were within the expectations. In addition, the logarithm of gas permeation coefficients and the reciprocal of fractional free volume (1/FFV) also exhibited a good correlation. However, with the incorporation of TMBPA moiety, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂ and CO₂/CH₄ remains reasonably high. As a result, the gas separation performance of TMBPA modified poly(aryl ether ketone) approaches the upper bound of the corresponding gas pairs. After comparing this work with gas separation performance of other methyl substituted polymers, one may conclude there is a general phenomenon that methyl substitution increases the gas permeability of the modified polymer with a small loss in gas selectivity for small gas pairs.     

Mechanism study of the Mn-substituted magnesium borate: Decreased sintering temperature and improved dielectric property

The influence of manganese substitution on the sintering and dielectric properties of Mg₃B₂O₆ (MBO) was studied, and the detailed mechanism of variation was discussed using density functional theory calculations. The characterization method involved a network analyser, differential–thermal analyses, thermomechanical analyses, X-ray diffraction, and scanning electron microscopy. Manganese substitution formed a two-phase system (MBO and Mg₂B₂O₅), improved the dielectric property, densified the microstructure, lowered the activation energy, decreased the crystallite size, modified the band structure property, and strengthened the covalency of MgO₆ octahedron. The 7% mole substitution of manganese to magnesium improved the dielectric properties of MBO to 7.06 for ε_r and 61 100 GHz at 15 GHz for Q × f, −54.8 ppm/°C for τ_f. The intrinsic densification temperature decreased from 1350 to 1175°C with 97.7% relative density.     

Effects of Zn2+/Mg2+ ratio on dielectric properties of BaTiO3-based ceramics with excellent temperature stability: Experiments and the first-principle calculations

To satisfy the development of MLCC devices, the dielectric properties and temperature stability of ceramic materials urgently needs to be improved. In our work, the 0.9BaTiO₃-0.1Bi(Zn_xMg_0.5-xY_0.5)O_2.75 ceramics with x=0.0–0.5 are successfully prepared based on a traditional solid-state method. Meanwhile, the ceramic sample (core-shell structure) with x = 0.1 exhibits excellent dielectric properties and temperature stability (ε_r: 1207, tanδ: 0.009 and ε_r/ε₂₅ ≤±15% within ?80 to 200 °C), which satisfies the Electronic Industries Association (EIA) X9R (-55–150 °C, Δε_r/ε₂₅ ≤±15%) specification. In addition, the physical mechanism behind dielectric properties and temperature stability is systematic investigated based on experimental characterization and the first-principle calculations. The interface polarization is regarded as the primary cause affecting the dielectric properties, and has a close relationship with shell structure of ceramic samples. The lattice deformation of shell structure is caused by the introduction of heterovalent ions and non-equivalent substitution. Dielectric constant may be advance as content of Zn²⁺ ions increases due to the electronic enrichment around the zinc site in distorted lattice matrix. However, the weaken force between atom and electron results in the poor temperature stability.     

A convenient method for the synthesis of [Pd{[(η5-C5H3)–CHN–(CH2)2–NMe2]Fe(η5-C5H5)}Cl] and the study of its reactivity with diphosphines

A one-pot method for the preparation of [Pd{[(η⁵-C₅H₃)–CHN–(CH₂)₂–NMe₂]Fe(η⁵-C₅H₅)}Cl] is described. Its X-ray crystal structure and its reactions with the diphosphines Ph₂P–(CH₂)_n–PPh₂ {with n=1 (ddpm) or 2 (dppe)} are also reported.     

Impact of H+ ion beam irradiation on Matrimid®. II. Evolution in gas transport properties

Ion beam irradiation is an easily controlled method to modify the chemical structure and microstructure of polymers including the fractional free volume, free volume distribution and chain mobility, thus altering the gas transport properties of the irradiated polymers. The previous paper focused on the impact of H⁺ ion beam irradiation on chemical structural evolution of the polyimide Matrimid®. This paper focuses on the impact of H⁺ ion beam irradiation on microstructure and gas permeation properties of Matrimid®. Irradiation at low ion fluence resulted in slight decreases in permeabilities for five gases (i.e., He, CO₂, O₂, N₂, and CH₄) with increases in permselectivities for some gas pairs (e.g., He/CH₄ and He/N₂). In contrast, irradiation at relatively high ion fluences resulted in simultaneous increases in permeabilities and permselectivities for most gas pairs (e.g., He/CH₄, He/N₂, O₂/N₂, and CO₂/CH₄). While Matrimid® has bulk gas permeation properties that are below the range of commercially interesting polymers, samples irradiated at high ion fluences exhibited significant improvement in gas separation performances. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1670–1680, 2007     

Structural and electric properties of polycrystalline Bi1−xErxFeO3 ceramics

Polycrystalline Bi_1?xEr_xFeO₃ ceramics were synthesized by the solid state reaction method followed by rapid liquid phase sintering. The effects of Er substitution on the structure, morphology and electrical properties of the BiFeO₃ multiferroic ceramics were investigated. X-ray diffraction and Raman studies reveal that the structure of BiFeO₃ is changed from rhombohedral to orthorhombic in the Er concentration range of 0.10–0.15, and the impurity phases decrease both due to Er substitution. The X-ray photoelectron spectroscopy shows that Fe²⁺ could be suppressed by Er substitution. The SEM investigations suggest that the Er substitution could significantly reduce the grain sizes and increase the density of the samples. The leakage current is found to be decreased with increasing Er concentration. The dielectric and ferroelectric measurements show that dielectric constant, dielectric loss and ferroelectric properties are strongly dependent on the Er concentration. Er substitution can significantly improve the dielectric constant and remnant polarization, and decrease the dielectric loss by reducing the leakage current.