Influence of thermal treatment on the glass transition temperature of thermosetting epoxy laminate

The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex^® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (T_g) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained T_g data were used for Arrhenius plots for different critical temperatures (T_g-crit. = 105–120 °C). From their slopes (?E_a/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.     

Thermodynamics of aqueous potassium carbonate,piperazine, and carbon dioxide

CO₂ solubility was measured in a wetted-wall column in 0.6–3.6 molal (m) piperazine (PZ) and 2.5–6.2 m potassium ion (K⁺) at 40–110 °C. Piperazine speciation was determined using ¹H NMR for 0.6–3.6 m piperazine (PZ) and 3.6–6.2 m potassium ion (K⁺) at 25–70 °C. The capacity of CO₂ in solution increases as total solute concentration increases and compares favorably with estimates for 7 m (30 wt.%) monoethanolamine (MEA). The presence of potassium in solution increases the concentration of CO₃²⁻/HCO₃⁻ in solution, buffering the solution. The buffer reduces protonation of the free amine, but increases the amount of carbamate species. These competing effects yield a maximum fraction of reactive species at a potassium to piperazine ratio of 2:1.A rigorous thermodynamic model was developed, based on the electrolyte nonrandom two-liquid (ENRTL) theory, to describe the equilibrium behavior of the solvent. Modeling work established that the carbamate stability of piperazine and piperazine carbamate resembles primary amines and gives approximately equal values for the heats of reaction, ΔH_rxn (18.3 and 16.5 kJ/mol). The pK_a of piperazine carbamate is twice that of piperazine, but the ΔH_rxn values are equivalent (∼−45 kJ/mol). Overall, the heat of CO₂ absorption is lowered by the formation of significant quantities of HCO₃⁻ in the mixed solvent and strongly depends on the relative concentrations of K⁺ and PZ, ranging from −40 to −75 kJ/mol.     

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s²) to He (1s¹2p¹). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m³, and an energy balance of about −4×10⁵ kJ/mol H₂ compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H₂.     

Gas permeation properties of poly(lactic acid)

The need for the development of polymeric materials based on renewable resources has led to the development of poly(lactic acid) (PLA) which is being produced from a feedstock of corn rather than petroleum. The present study examines the permeation of nitrogen, oxygen, carbon dioxide, and methane in amorphous films of PLA cast from solution. The properties of PLA are compared to other commodity plastics and it is shown that PLA permeation closely resembles that of polystyrene. At 30°C, N₂ permeation in PLA is 1.3 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and the activation energy is 11.2 kJ/mol. For oxygen the corresponding values are 3.3 (10⁻¹⁰ cm³(STP) cm/cm² s cm Hg) and 11.1 kJ/mol. The values for carbon dioxide permeation are 1.2 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and 6.1 kJ/mol. For methane values of 1.0 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and an activation energy of 13.0 kJ/mol are found. Studies with pure gases show that polymer chain branching and small changes in l:d stereochemical content have no effect on permeation properties. Crystallinity is found to dominate permeation properties in a biaxially oriented film. The separation factor for a CO₂/CH₄ mixed gas system is measured between 0 and 50°C and does not deviate significantly from the calculated ideal separation factor; at 0°C the separation factor is 16, a value that suggests continued studies of PLA as a separation medium are warranted.     

Structure characteristics contributing to flame retardancy in diazo modified novolac resins

The physical characteristics of two modified novolac resins (carbonyl phenyl azo novolac resin; CPAN and 4-(4-hydroxyphenyl azo) benzyl ester novolac resin; HPDEN) bearing nitrogen and aromatic functional groups by diazo-coupling or esterification in the branch structure of phenol novolac resin were examined. Presence of the modifiers raised the phenolic decomposition temperature (5% weight loss) from 300 °C (pure Phenolic) to 330 °C and 380 °C, while the char residue increased from 45% to 56% and 68%, respectively. The kinetics for thermal degradation energies (E_a) also rose from 151 kJ/mol K to 254 kJ/mol K (CPAN) and 273 kJ/mol K (HPDEN). The retarded decomposition kinetics is attributed both to the increase of crosslink densities and high aromatic content in the derivative resins. On the other hand, the diazo-coupling or phenyl diazenyl ester produces non-combustible gases (N₂, CO₂ and CO) during formation of aromatic char which dilute the ambient oxygen gas. Both the production of gases and the retarded kinetics due to cross-linking are definitive for the improved flame resistance.     

Cationic concentration effects on electron beam cured of carbon-epoxy composites

Electron beam (e-beam) curing is a technology that offers advantages over the thermal curing process, that usually requires high temperature and are time-consuming. E-beam curing is faster and occurs at low temperatures that help reduce residual mechanical stresses in a thermoset composite. The aim of the present study is to analyze the effects of cationic initiator (diaryliodonium hexafluoroantimonate) ranged from 1 to 3 wt% in DGEBA (diglycidyl ether of bisphenol A) epoxy resin when cured by a 1.5 MeV electron beam. The specimens were cured to a total dose of 200.4 kGy for 40 min. Analyses by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) show that the e-beam irradiated samples with 2 wt% cationic initiator were 96% cured obtained a glass transition temperature (tan δ) of 167 °C. The same epoxy resin, thermally cured for 16 h with an anhydride hardener, reached a T_g (tan δ) of 136 °C. So, the irradiated sample had its T_g increased approximately 20% and the curing process was much less time consuming.     

Kinetics of hematite chlorination with Cl2 and Cl2 + O2: Part I. Chlorination with Cl2

Preliminary tests of the chlorination of two iron oxides (wüstite and hematite) in various chlorinating gas mixtures were performed by thermogravimetric analysis (TGA) under non-isothermal conditions. Wüstite started to react with chlorine from about 200 °C generating ferric chloride and hematite as the final reaction products. The presence of a reducing and oxidizing agent in the chlorinating gas mixtures influenced the chlorination reactions of both iron oxides, during non-isothermal treatment, only at temperatures higher than 500 °C.The chlorination kinetics of hematite with Cl₂ have been studied in details between 600 and 1025 °C under isothermal chlorination. The values of the apparent activation energy (E_a) were about 180 and 75 kJ/mol in the temperature ranges of 600–875 and 875–1025 °C, respectively. The apparent reaction order with respect to Cl₂ was found to be 0.67 at 750 °C. Mathematical model fitting of the kinetics data was carried out to determine the most probable reaction mechanisms.     

Microwave spectrum and conformation of n-propyltrifluorosilane

The conformational properties of gaseous n-propyltrifluorosilane (CH₃CH₂CH₂SiF₃) have been investigated by microwave spectroscopy and high-level quantum chemical calculations. The microwave spectrum was investigated in the 20–62 GHz spectral range at a temperature of −78 °C. The spectra of the ground vibrational state and three vibrationally excited states of one conformer having an antiperiplanar conformation of the C–C–C–Si chain of atoms were assigned. No evidence for the existence of the synclinal (gauche) conformer was seen in the microwave spectrum. It is concluded that the synclinal form is at least 3.5 kJ/mol less stable than the antiperiplanar conformer in the gas phase. Density functional theory calculations have been performed for the system mainly to predict the effects of centrifugal distortion. The G3 quantum chemical method has been used to test the ability of this method to predict the energy difference between the synclinal and antiperiplanar conformers.     

Electrochemical deposition of (Mn, Co)-codoped ZnO nanorod arrays without any template

(Mn, Co)-codoped ZnO nanorod arrays were successfully prepared on Cu substrates by electrochemical self-assembly in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid at a temperature of 90 °C, and these nanorods were found to be oriented in the c-axis direction with wurtzite structure. Energy dispersive X-ray spectroscopy and x-ray diffraction show that the dopants Mn and Co are incorporated into the wurtzite-structure of ZnO. The concentrations of the dopants, and the orientations and densities of nanorods can easily be well controlled by the current densities of deposition or salt concentrations. Magnetization measurement indicates that the prepared (Mn, Co)-codoped ZnO nanorods with a coercivity of about 91 Oe and a saturation magnetization (M_s) of about 0.23 emu/g. The anisotropic magnetism for the (Mn, Co)-codoped ZnO nanorod arrays prepared in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid with current density of 0.5 mA/cm² was also investigated, and the crossover where the magnetic easy axis switches from parallel to perpendicular occurs at a calculated time of about 112 min. The anisotropic magnetism, depending on the rod geometry and density, can be explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanorods.     

Sintering kinetics study of mechanically alloyed nanocrystalline Mo–30 wt.% W

The paper details the results of sintering kinetics studies conducted on nanocrystalline Mo–30 wt.% W alloy powders prepared through mechanical alloying route. Both, constant rate of heating method as well as Stepwise Isothermal Dilatometry (SID) technique were used for studying the sintering kinetics. Measured step isothermal shrinkage data were analyzed by Mekipritti-Meng method. The shrinkage data was found to fit well with the rate equation proposed in this method and its validity was established for mechanically alloyed systems. Kinetic parameters were evaluated and sintering was found to occur through two major mechanisms operative successively, which are grain boundary diffusion and lattice diffusion with corresponding energies of activation as 230 kJ/mol and 480 kJ/mol, respectively. The results have been well supported by micro structural evaluation of specimens at different stages of sintering.     

On the kinetics of thermal electron attachment to perfluoroethers

In this Letter we report the results of the measurements of the rate coefficients for thermal attachment to several perfluoroethers namely perfluorodiglyme (C₆F₁₄O₃), perfluorotriglyme (C₈F₁₈O₄), perfluoropolyether (CF₃–(OCF(CF₃)CF₂)_n–(OCF₂)_m–OCF₃) and perfluorocrownether ((C₂F₄O)₅). Rate coefficients were obtained under thermal conditions in the temperature range 298–378 K. The increase of the rates with temperature follows the Arrhenius law and the activation energies have been obtained from the slope of the ln(k) vs. 1/T. The respective values of the rate coefficients (at 298 K) and activation energies are as follows: 7.7 ± 1.2 × 10^?11 cm³ s^?1 (0.18 ± 0.005 eV), 6.7 ± 2.1 × 10^?11 cm³ s^?1 (0.25 ± 0.004 eV), 2.1 ± 0.2 × 10^?10 cm³ s^?1 (0.16 ± 0.010 eV), 3.1 × 10^?11 cm³ s^?1 (0.27 ± 0.003 eV) for C₆F₁₄O₃, C₈F₁₈O₄, CF₃–(OCF(CF₃)CF₂)_n–(OCF₂)_m–OCF₃ and (C₂F₄O)₅.     

Solubilities of l-glutamic acid, 3-nitrobenzoic acid,p-toluic acid,calcium-l-lactate,calcium gluconate,magnesium-dl-aspartate,and magnesium-l-lactate in water

Solubilities of l -glutamic acid, 3-nitrobenzoic acid, p -toluic acid, calcium-l -lactate, calcium gluconate, magnesium- dl -aspartate, and magnesium- l -lactate in water were determined in the temperature range 278 K to 343 K. The apparent molar enthalpies of solution at T =  298.15 K as derived from these solubilities areΔ_solH_m (l -glutamic acid,m_sat =  0.0565 mol · kg ^− 1)  =  30.2 kJ · mol ^− 1,Δ_solH_m (3-nitrobenzoic acid, m =  0.0188 mol · kg ^− 1)  =  28.1 kJ · mol ^− 1, Δ_solH_m( p - toluic acid, m =  0.00267 mol · kg ^− 1)  =  23.9 kJ · mol ^− 1,Δ_solH_m (calcium- l -lactate tetrahydrate,m =  0.2902 mol · kg ^− 1)  =  25.8 kJ · mol ^− 1,Δ_solH_m (calcium gluconate, m =  0.0806 mol · kg ^− 1)  =  22.1 kJ · mol ^− 1, Δ_solH_m(magnesium-dl -aspartate tetrahydrate, m =  0.1469 mol · kg ^− 1)  =  11.5 kJ · mol ^− 1, andΔ_solH_m (magnesium- l -lactate trihydrate,m =  0.3462 mol · kg ^− 1)  =  3.81 kJ · mol ^− 1.     

Influence of temperature on the charging/discharging process of IrO2 coating deposited on p-Si substrate

The influence of temperature on the charging/discharging process of the IrO₂ coating deposited on p-Si has been investigated using cyclic voltammetry. The measured apparent activation energy (E_a) depends strongly on the used scan rate in the cyclic voltammetry measurements. In fact at low scan rates (5 mV/s), E_a for the charging/discharging process has a value of about 2.4 kJ/mol; this is related to a slow process due to diffusion of protons within the IrO₂ coating. At high scan rates (500 mV/s), E_a reaches a value close to zero. This has been attributed to the double layer capacitance, which is an instantaneous electrostatic process.     

Molecular design of prismane-based potential energetic materials with high detonation performance and low impact sensitivity

To develop new energetic materials, the eleven nitroester substitution derivatives of prismane were investigated at the B3LYP/6-311G** level of density functional theory (DFT). The gas phase heats of formation were calculated by isodesmic reactions and the solid-state heats of formation were obtained by the Politzer approach using the heats of sublimation for the designed compounds. The detonation velocities and pressures of all molecules were calculated by Kamlet–Jacobs equations based on molecular density and heat of detonation. The results show that the nitroester group in prismane is helpful for enhancing molecular detonation properties and power index. Among all molecules, 1,2,3,4-tetrnitroesterprismane has excellent detonation properties (detonation pressure = 40.05 GPa, detonation velocity = 9.28 km/s) and large power index value. The molecular stabilities were evaluated by calculating bond dissociation energies and characteristic heights (H₅₀). The results indicate that the bond dissociation energies of all molecules are above 80 kJ/mol, and all molecules have a larger H₅₀ value than hexanitrohexaazaisowurtzitane (CL-20, 12 cm). The obtained structure–property relationships may provide basic information for the molecular design of novel high-energy materials.     

A general route for the stereoselective synthesis of (E)-(1-propenyl)phenyl esters by catalytic CC bond isomerization

A general and efficient procedure for the stereoselective synthesis of (E)-(1-propenyl)phenyl esters from readily accessible allylphenols has been developed. The process involves a two-step sequence consisting of the initial acylation of the allylphenols with an acid chloride, followed by catalytic CC bond isomerization in the resulting allylphenyl esters. The latter step was performed in methanol at 80 °C using catalytic amounts (0.5 mol %) of the commercially available bis(allyl)-ruthenium(IV) dimer [{RuCl(μ-Cl)(η³:η³-C₁₀H₁₆)}₂] (C₁₀H₁₆=2,7-dimethylocta-2,6-diene-1,8-diyl). Reactions proceeded in high yields (68–93%) and short times (4–9 h) with complete E-selectivity.     

Synthesis of 2-substituted benzofuran derivatives by the palladium-catalyzed intermolecular coupling of 2-fluoroallylic acetates with phenols

We investigated the intermolecular coupling reaction of 2-fluoroallylic acetates with simple phenols by the [Pd(C₃H₅)Cl]₂, DPPF, and KHMDS at 100 °C for 16 h, and succeeded in obtaining 2-substituted benzofuran derivatives in good to high yield through the C–F bond activation and intermolecular cyclization.     

Theoretical study on the isomerization and tautomerism in barbituric acid

Isomerization and tautomerism of 16 isomers of barbituric acid (BA) were studied at the MP2 and B3LYP levels of theory. Activation energies (E _a), imaginary frequencies (υ), and Gibbs free energies (ΔG ^#) of the amine-imine and keto-enol tautomerisms and O–H internal rotations were calculated. The activation energies of amine-imine tautomerisms were in the range of 110–200 kJ/mol and for keto-enol tautomerisms were larger than 200 kJ/mol. The calculated activation energies of internal O–H rotations were smaller than 60 kJ/mol. Effect of micro-hydration on the transition state structures and activation energies of the tautomerisms were also investigated. Water molecule catalyzed the tautomerisms and decreased the activation energies of both the amine-imine and keto-enol tautomerisms about 100–120 kJ/mol.     

Synthesis of cyclic α-hydrazino acids

Synthesis of five-, six-, seven-, eight-, and nine-membered cyclic α-hydrazino acids from a common starting material ‘diethylmalonate’ with 26, 16, 34, 13.5, and 13.33% overall yields is described. Sequential allylation or homoallylation and electrophilic amination followed by cyclization gave the desired rings. The methyl esters of eight- and nine-membered rings were synthesized by RCM and the corresponding free acids were generated after hydrolysis in the presence of 1 M BBr₃ solution in DCM.     

Fused ring systems derived from reactions of half-open titanocenes with diynes: Syntheses,characterization, cage rearrangements,and structural studies

The reactions of several α,ω-diynes with half-open titanocene complexes [M(C₅H₅)(2,4-C₇H₁₁)(PR₃)] (C₇H₁₁ = dimethylpentadienyl) lead to 5 + 2 + 2 ring constructions, yielding nine-membered rings fused to four-membered and larger rings. These reactions tolerate significant functionalization, even allowing for the presence of heteroatoms such as oxygen and nitrogen. The nine-membered rings provide both allyl and diene coordination to the Ti(C₅H₅) fragments, resulting in 16 electron configurations. On standing, these species undergo cage rearrangements, via CC bond activation reactions. Structural data have been obtained for a number of the fused ring species, as well as one of the rearrangement products.     

Comparison of the spin exchange interactions in PbCu2(PO4)2 and SrCu2(PO4)2 on the basis of spin dimer analysis

The spin exchange interactions of PbCu₂(PO₄)₂ were examined by performing the spin dimer analysis based on the extended Hückel tight-binding method, and were compared with those of SrCu₂(PO₄)₂. The two strongest Cu–O⋯O–Cu super–superexchange interactions, J₁ (with Cu⋯Cu = 5.868 Å) and J₂ (with Cu⋯Cu = 5.184 Å), are strong and lead to a linear-four-spin-cluster model for both PbCu₂(PO₄)₂ and SrCu₂(PO₄)₂. Adjacent linear-four-spin-clusters interact substantially in SrCu₂(PO₄)₂, but weakly in PbCu₂(PO₄)₂. The difference in the magnetization behaviors of the two compounds was examined by calculating the magnetic excitation energies of the linear-four-spin-cluster model.