Incipient Reaction Research Articles

Insight into the chemistry of TNT during shock compression through ultrafast absorption spectroscopies.

Thin films of trinitrotoluene (TNT) were shock compressed using the ultrafast laser shock apparatus at Los Alamos National Laboratory. Visible (VIS) and mid-infrared (MIR) transient absorption spectroscopies were simultaneously performed to probe for electronic and vibrational changes during shock compression of TNT. Three shock pressures (16 GPa, 33 GPa, and 45 GPa) were selected to observe no reaction, incipient reaction, and strongly developed reactions for TNT within the experimental time scale of <250 ps. Negligible absorption changes in MIR or VIS absorptions were observed at 16 GPa. At 33 GPa, MIR absorptions in the 3000 cm-1-4000 cm-1 range were observed to increase during the shock and continue to increase during the rarefaction, in contrast to the VIS absorption measurements, which increased during the shock and almost fully recovered during rarefaction. At 45 GPa, both VIS and MIR absorptions were strong and irreversible. The intense and spectrally broad MIR absorptions were attributed to short lived intermediates with strong, spectrally broad absorptions that dominate the spectral response. The MIR and VIS absorption changes observed at 33 GPa and 45 GPa were credited to shock induced chemistry, most likely including the formation of a very broad hydrogenic stretch feature. The results from these experiments are consistent with the chemical mechanisms that include O-H or N-H formation such as CH3 oxidation or C-N homolysis.

Incipient chemical weathering at bedrock fracture interfaces in a tropical critical zone system, Puerto Rico

Abstract The processes that control chemical weathering of bedrock in the deep critical zone at a mm-scale are still poorly understood, but may produce 100 s of meters of regolith and substantial fluxes of silicate weathering products and thus may be important for modeling long-term, global CO2. Weathering controls are also difficult to ascertain, as laboratory determined dissolution rates tend to be 2–5 orders of magnitude faster than field determined dissolution rates. This study aims to establish (i) the incipient processes that control the chemical weathering of the Bisley bedrock and (ii) why weathering rates calculated for the watershed may differ from laboratory rates (iii) why rates may differ across different scales of measurement. We analyzed mineralogy, elemental chemistry, and porosity in thin sections of rock obtained from drilled boreholes using Scanning Electron Microscopy (SEM) with energy dispersive spectrometry, electron probe microanalysis, and synchrotron-based Micro X-ray Fluorescence (µXRF) and X-ray Absorption Near Edge Structure (XANES). Weathering ages were determined from U-series isotope analysis. Mineral specific dissolution rates were calculated from solid-state mineralogical gradients and weathering ages. Mineralogical and elemental transects across thin sections and SEM images indicate that trace pyrite is the first mineral to dissolve. Micro-XRF mapping at 2 µm resolution revealed sulfate in pore space adjacent to dissolving pyrite, indicating that the incipient reaction is oxidative. The oxidative dissolution of pyrite produces a low pH microenvironment that aids the dissolution of pyroxene and chlorite. The rate-limiting step of weathering advance, and therefore the creation of the critical zone in the Bisley watershed, is pyrite oxidation, despite the low abundance (∼0.5 vol%) of pyrite in the parent rock. The naturally determined dissolution rates presented here either approach, converge with, or in some cases exceed, rates from the literature that have been experimentally determined. The U-series weathering age data on the mm-scale integrates the weathering advance rate over the ∼4.2 ± 0.3 kyrs that the weathering rind took to form. The weathering advance rate calculated at a watershed scale (from stream chemistry data) represents a contemporary weathering advance rate, which compares well with that calculated for the weathering rind, suggesting that the Bisley watershed has been weathering at steady-state for the last ∼4 kyrs.

Treprostinil reduces endothelial damage in murine sinusoidal obstruction syndrome

Sinusoidal obstruction syndrome (SOS) is a major complication after hematopoietic stem cell transplantation and belongs to a group of diseases increasingly identified as transplant-related systemic endothelial disease. Administration of defibrotide affords some protection against SOS, but the effect is modest. Hence, there is unmet medical need justifying the preclinical search for alternative approaches. Prostaglandins exert protective actions on endothelial cells of various vascular beds. Here, we explored the therapeutic potential of the prostacyclin analog treprostinil to prevent SOS. Treprostinil acts via stimulation of IP, EP2, and EP4 receptors, which we detected in murine liver sinusoidal endothelial cells (LSECs). Busulfan-induced cell death was reduced when pretreated with treprostinil in vitro. In a murine in vivo model of SOS, concomitantly administered treprostinil caused lower liver weight-to-body weight ratios indicating liver protection. Histopathological changes were scored to assess damage to liver sinusoidal endothelial cells, to hepatocytes, and to the incipient fibrotic reaction. Treprostinil indeed reduced sinusoidal endothelial cell injury, but this did not translate into reduced liver cell necrosis or fibrosis. In summary, our observations provide evidence for a beneficial effect of treprostinil on damage to LSECs but unexpectedly treprostinil was revealed as a double-edged sword in SOS.Key messagesMurine liver sinusoidal endothelial cells (LSECs) express prostanoid receptors.Treprostinil reduces busulfan-induced cell death in vitro.Treprostinil lowers liver weight-to-body weight ratios in mice.Treprostinil positively affects LSECs in mice but not hepatic necrosis/fibrosis.

Evolution of flame kernel in one eddy turnover of high-speed droplet laden shear layers

A high-speed droplet-laden reacting shear layer is modeled numerically to analyze the dynamics of flame kernel for better understanding ignition and extinction processes in spray combustion. The droplet-laden shear layer, separating a hot-air stream from a monodisperse spray-laden air stream, is modeled by the Eulerian-Lagrangian approach, in which the continuous phase is governed by the compressible Navier-Stokes equations together with species transport equations and the discrete droplets are tracked by the Lagrangian method. The convective flux terms of the conservative equations are solved by an adaptive central-upwind WENO scheme. Two-way coupling interactions consider exchanges of mass, momentum, and energy between the carrier-gas fluid and the liquid-fuel spray. The shear layer convective Mach number is specified as 0.4 in the present study, and hence, large scales of motion dominate both the fluid mixing and the droplet dispersion. The preferential concentration of droplets is observed. Auto-ignition kernels occur in the high-strain regions where sufficient fuel vapors distribute near the hot stream-boundary. The incipient chemical reaction consumes the available fuel vapors through a diffusion flame combined with a thin premixed flame, as a lean deflagration propagates across the mixing layer towards the spray. The present results unveil two different types of extinction behavior depending on the local strain rate and the available fuel for the reaction kernel. The latter type of extinction originates when the separated flame kernel is entrained into the core of an adjacent vortex but droplets cannot be entrained in the eddies to produce gaseous fuels for the chemical reaction due to the preferential segregation effect. The dynamics of ignition and extinction in the shear flows depend on the droplet dispersion, the droplet evaporation rate and the diffusion of fuel vapor.

Influence of the composition of solid biomass in the flammability and susceptibility to spontaneous combustion

Biomasses are materials highly demanded nowadays for energy production. One of the main features of these materials is that they present a great variability in terms of chemical composition and physical behavior (O/C and H/C ratios, granulometric structure, ash content…). Nowadays, there is a lack of information concerning its characterization to determine its flammability and explosibility behavior. The objective of this study is to provide flammability and explosibility data as well as some parameters to assess the spontaneous combustion tendency of these products and to relate this thermal susceptibility with the composition. Initial results showed that risk assessments based on the activation energy were not effective for biomass as it is for coals, and that a greater tendency to self-ignition was observed in those biomasses having higher H/C ratios, on the contrary than in coals. This behavior can be explained because the most important stage for coals is the beginning of the self-heating reaction, which present a different resistance (activation energy) depending on its ranking, while biomasses present an initial stage easily achievable even at moderate temperatures, so the differentiation for biomasses should be found in the ability to spread this incipient reaction.

Simple synthesis of water-dispersible and photoactive titanium dioxide nanoparticles using functionalized poly(ethylene oxide)s

Versatile and direct synthesis of water-dispersible titanium dioxide (TiO2) nanoparticles in the presence of functionalized poly(ethylene oxide)s (PEO) having carboxylic acid groups is presented. The functionalized PEOs, such as PEO-folate conjugate and PEO-b-poly(maleic acid) (PEO-b-PMAc) as polymeric surfactants, were employed for in situ synthesis of TiO2 nanoparticles through hydrolytic sol-gel process of titanium tetrachloride as a precursor in eco-friendly alcoholic media at a relatively low temperature. Both of the two polymers were found to be very effective for stabilizing TiO2 nanocrystals, exhibiting not only fairly good photocatalytic activities but also water-dispersible property. The core TiO2 crystallites in the size range of 8∼11 nm could be readily controlled in ethanol at a relatively low reaction temperature (70 °C), irrespective of the incipient reaction condition, which showed mixed polymorphs. The TiO2 nanoparticles consist of a few percentages (<10%) of brookite and mostly anatase phases. This process provides a simple and useful in situ preparative route to obtain water-dispersible TiO2 nanoparticles. Open image in new window

Dynamics of thermal ignition of spray flames in mixing layers

AbstractConditions are identified under which analyses of laminar mixing layers can shed light on aspects of turbulent spray combustion. With this in mind, laminar spray-combustion models are formulated for both non-premixed and partially premixed systems. The laminar mixing layer separating a hot-air stream from a monodisperse spray carried by either an inert gas or air is investigated numerically and analytically in an effort to increase understanding of the ignition process leading to stabilization of high-speed spray combustion. The problem is formulated in an Eulerian framework, with the conservation equations written in the boundary-layer approximation and with a one-step Arrhenius model adopted for the chemistry description. The numerical integrations unveil two different types of ignition behaviour depending on the fuel availability in the reaction kernel, which in turn depends on the rates of droplet vaporization and fuel-vapour diffusion. When sufficient fuel is available near the hot boundary, as occurs when the thermochemical properties of heptane are employed for the fuel in the integrations, combustion is established through a precipitous temperature increase at a well-defined thermal-runaway location, a phenomenon that is amenable to a theoretical analysis based on activation-energy asymptotics, presented here, following earlier ideas developed in describing unsteady gaseous ignition in mixing layers. By way of contrast, when the amount of fuel vapour reaching the hot boundary is small, as is observed in the computations employing the thermochemical properties of methanol, the incipient chemical reaction gives rise to a slowly developing lean deflagration that consumes the available fuel as it propagates across the mixing layer towards the spray. The flame structure that develops downstream from the ignition point depends on the fuel considered and also on the spray carrier gas, with fuel sprays carried by air displaying either a lean deflagration bounding a region of distributed reaction or a distinct double-flame structure with a rich premixed flame on the spray side and a diffusion flame on the air side. Results are calculated for the distributions of mixture fraction and scalar dissipation rate across the mixing layer that reveal complexities that serve to identify differences between spray-flamelet and gaseous-flamelet problems.

Studies on Selective Hydroxylation of Aliphatic C-H Bonds Using Tridentate NHC-Amidate-Alkoxide Pd(II) Complexes

Catalytic functionalization of unreactive sp C-H bonds under mild conditions is a highly desirable prospect that has generated a considerable amount of interest in recent years. Numerous studies have been carried out in an effort to develop efficient methods; nonetheless, controlling selectivities in these reactions remains a challenge. The chemo-, stereo-, and/or enantioselectivity of these reactions have been particularly difficult to control, especially in those intended to produce hydroxylated products, as overoxidation to ketones and even C-C bond cleavage products are prevalent. Under relatively mild conditions, overoxidation can be reduced significantly to offer hydroxylation products somewhat selectively while some starting material usually remains. As shown in Scheme 1, Sen developed relatively mild conditions using oxygen instead of other reactive oxidants, which converted 59% of the starting acid 1 to produce an equimolar mixture of βand γ-hydroxylated products. Surprisingly, α-hydroxylation was not observed whereas remote C-H functionalization was efficient. Recently, we introduced a unique tridentate NHC-amidate Pd catalyst which showed surprising reactivity toward unreactive C-H bonds under mild conditions. We wondered if our new Pd catalysts with a unique architecture of tridentated ligands would be able to effect improved regioselectivity and furthermore promote asymmetric functionalization. This report describes initial results on regioselectivity and enantioselectivity using new catalysts 5 and 6 depicted in Figure 1. We examined hydroxylation of butyric acid using catalyst 5 and hydrogen peroxide (Scheme 2). Contrary to Sen’s conditions, we observed hydroxylation on all three possible centers with poor regioselectivity, which was also observed from n-hexane (7) in a very similar way. Using cyclic substrates, we found that cyclopentane (8) and cyclohexane (9) furnished mixed selectivities, which might imply relocation of reaction centers during the course of the reactions. Catalyst 6 gave rise to similar results on acyclic and cyclic substrates, 1 and 8, respectively (Scheme 3). We also learned that this enantiopure catalyst induced high enantioselection on the β-hydroxylation product 3 which could be due to direct C-H activation by Pd. Although we did not pursue identification of the absolute configuration, we conducted an NMR study with a chiral shift reagent to confirm the optical purity of 83% ee. It is evident that this type of catalyst can facilitate chiral induction at an unreactive C-H site. In addition, we found that ketone 10 provided high β-selectivity in the beginning of the oxidation, thus we hypothesized that the incipient reaction center would be β-center to the carbonyl,

Estudio arqueométrico y evaluación del deterioro de los materiales cerámicos de la fachada de la iglesia de Santa Maria del Carmine (Pavía, Italia)

We performed an archaeometric study of the ceramic materials from the facade of the church of Santa Maria del Carmine in Pavia (Italy). We obtained useful information about the firing temperatures, the provenance of raw materials and the type of oven used. The ceramics used in the facade are mineralogically rich in quartz, feldspar and phyllosilicates, and newly formed calcium silicate phases were detected in some samples. Microtextural observations revealed the presence of incipient reaction rims, phyllosilicate sintering and partial vitrification of the matrix. Ceramics show high porosity (32 to 45%) and pore sizes of between 0.4 and 1.3 µm. Our study of the different types of decay collected on the facade of the church (green and black patinas and efflorescences) revealed the presence of gypsum, whewellite, thenardite and moolooite.

Infrared spectra of SF6−∙(H2O)n (n=1–3): Incipient reaction and delayed onset of water network formation

We present data on the microsolvation of an extended charge distribution with SF(6)(-) as a model system. Infrared spectroscopy, aided by ab initio calculations, shows that the first two water molecules attach to the ion by a combination of single ionic H bonds, sharing one of the F atoms, and weak electrostatic interactions with other F atoms in the ion. No water-water bonds are formed at the dihydrate level, which is an unusual observation, given the strong propensity of water to form H-bonded networks. The onset of water networks occurs with the addition of the third water molecule. Moreover, the attachment of the first two water molecules considerably weakens the SF bond of the F atom involved in bonding to both ligands, indicating a possible mechanism for water-induced reactions.

Thermoanalytical study on the oxidation of sulfide minerals at high temperatures

An experimental study on the oxidation of chalcopyrite (CuFeS2), pyrite (FeS2), covellite (CuS) and chalcocite (Cu2S) particles was conducted by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The oxygen concentration in the process gas was set to 40% and 70% (by volume) and a heating rate of 40°C/min was used. Response variables included the temperature of incipient reaction, the total exothermic heat of reaction, particle mass, morphology and mineralogy of the reacted particles. Based on the experimental data and phase stability calculations, reaction mechanisms were proposed to represent the behavior of the particles during oxidation. The reaction mechanisms were verified by X-ray diffraction (XRD) analyses of the oxidized particles and by thermo chemical and mass balance calculations to reproduce the DSC and TGA data. Overall kinetic models were developed to represent the evolution of the exothermic heat of reaction as a function of time.

A straight way toward phase pure complex oxides

Great majority of the electroceramic materials to date are complex oxides. Phase purity, high crystallinity and small grains with narrow size distribution are almost always required. Quick nucleation and limited growth are essential for that purpose. The author concentrates himself on a straight way toward this goal by taking three components into account, i.e. (1) active nucleation sites in high concentration, (2) short diffusion path for growth and (3) achievement of kinetic stabilization. Soft-mechanochemical synthesis is one of the best shortcuts to the goal. The main spirit is the incipient chemical reaction at the boundary between dissimilar particles through homogenization of the starting mixture by exerting as small mechanical energy as possible. Case studies are devoted to the syntheses of various complex perovskites, recently carried out in the author's own laboratory.

Effect of experimental variables on the inertization of galvanic sludges in clay-based ceramics

The incorporation of several industrial wastes in ceramic matrixes had been attempted as an effective low expense technique for the fixation of metallic species in usable products or simply to reduce the residue volume for further disposal. However, the dominant mechanism of the inertization process and the relevant influent parameters are still unknown, mostly due to the complexity of the systems. This work reports the effect of several processing parameters such as the mixing time, the calcination temperature and duration, the relative amount of sludge, and the physical aspect of the sample (powdered or pressed pellets) on the fixing level of relevant species (SiO 2, SO 4 2−, Zn, Ni, Ca, Cu, Cr) by leaching in different media (aqueous, acetate, and citrate). Statistical tools were used to define the relevance of each experimental variable on the inertization process of the used galvanic sludge. The relative amount of sludge in the mixture, the calcination temperature and the agglomeration state of the sample were found to be the most influent parameters of the inertization process. The incipient reaction between sludge and ceramic matrix components points out for the dominance of a macro-encapsulation mechanism.

Infrared spectroscopy of V+(H2O) and V+(D2O) complexes: Solvent deformation and an incipient reaction

V + ( H 2 O ) Ar n and V+(D2O)Arn complexes are studied with mass-selected infrared photodissociation spectroscopy in the O–H (O–D) stretch region. Two vibrational bands are measured 50–80 cm−1 to the red from the symmetric and asymmetric stretches in free water. Rotational analysis for V+(H2O)Ar indicates a C2v geometry with argon opposite water and significant expansion of the H–O–H angle. The v=1 level in the asymmetric stretch undergoes distortion consistent with selective excitation into the coordinate of an insertion reaction.

Hydrogenation of sulfur dioxide to hydrogen sulfide over Fe/γ-Al2O3 catalysts

Hydrogenation of sulfur dioxide to hydrogen sulfide was investigated over a series of γ-Al2O3 supported iron catalysts with Fe/γ-Al2O3 weight ratios of 0.01–5. These catalysts were prepared by a slurry method using iron sulfate and iron nitrate as the iron precursors. Surface areas of these catalysts decreased continuously with the increase of iron loading. The hydrogenation was carried out in a flow reactor at a temperature range of 180–400°C, elemental sulfur was found to be the sole sulfur product when SO2 conversion was <70%. Catalyst activity, evaluated in terms of SO2 conversion and the incipient reaction temperature needed to achieve 100% H2S yield, depended strongly on its composition. The optimum Fe/γ-Al2O3 weight ratio was found to be 2–3 in spite of the difference in iron precursors. X-ray diffraction (XRD) measurements indicated that FeS2 was the active species for SO2 hydrogenation. The proposed mechanism suggested that the best Fe/γ-Al2O3 catalyst should have the best cooperation action between the hydrogenation function (FeS2+H2=FeS+H2S) and the acidic catalytic function (H2S+1/2(SO2)=3/4(S2)+H2O).

Ultrastructural Changes in a Standard Strain of Bartonella henselae After Passages Through BALB/cAn Mice

Human bartonelloses are a group of illnesses of poorly understood pathogenesis. Bartonella henselae is one of the most studied bacterium of its genus. The objective of this study was to observe whether passages of these bacteria, in vivo, would determine ultrastructural changes in them. For this purpose, isogenic mice were inoculated with a standard strain of B. henselae (I). These were initially retrieved from genetically immunodeficient animals (II) and then inoculated in immunocompetent ones. The bacterial colonies obtained (III) were compared, by transmission electron microscopy, with colonies I and II. Loss of fimbriae and an abundant bleb formation were the most common morphological changes found in colony III. Also, on day 6 postinfection, the main histological abnormalities were the endothelial proliferation presented in immunodeficient animals and the incipient granulomata reaction found in one of the immunocompetent inoculated mice, which died spontaneously. These features agree with the Bartonella human disease clinical and histological observations. This study demonstrates that B. henselae in vivo passages induce significant morphological changes in the bacteria and that these abnormalities could explain their seemingly greater virulence. Most of these observations have not been previously described. Thus, further studies on the Bartonella species pathogenesis should consider these data.

Charge transfer and hetero-bonding across the solid–solid interface at room temperature

Mechanisms of an incipient chemical reaction at the contact points of oxide particles are elucidated on the basis of various experimental analyses as well as molecular orbital calculation. By milling a mixture of metal oxides, homogeneity on nanometer scale increases, accompanied by partial or total amorphization. Simultaneously, charge transfer is promoted by OH groups at the state of low coordination. Both of them are predominantly caused by local plastic deformation. A primary consequence of charge transfer is an incipient chemical reaction at the contact points of dissimilar particles, by virtue of hetero-bridging bonds between dissimilar metal atoms mediated by an oxygen atom. A mixture at this stage serves as a precursor or an intermediate to accomplish complex oxides by subsequent heating at temperatures much lower than conventional reactions in solid state.

チタン酸鉛合成反応に対する原料混合ゾルへの超音波照射および摩砕の効果

Ferroelectric perovskite lead titanate is synthesized from titania sol and lead oxide sol via various precursors. Ultrasonication and milling were performed either separately or simultaneously during precursor preparation. By these treatments, agglomerates were significantly disintegrated, with concomitant mechanochemical incipient reaction toward PbTiO3. Dispersion state of the product precursor is significantly improved when mechanochemical effects are combined with ultrasonication.

Determination of the oxidation characteristics of solid copper matte particles by differential scanning calorimetry and thermogravimetric analysis

An investigation of the oxidation reactions of two industrial copper mattes was performed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) at heating rates of 20°C and 8°C/min, respectively. The temperature of incipient reaction, the total exothermic and endothermic heats of reaction and the weight change during the oxidation process were measured as functions of the oxygen concentration in the oxidizing gas, matte grade and matte particle size. The temperatures of incipient reaction measured from the DSC experiments were found to increase monotonically with all three input variables. TGA experiments showed that Cu2O and CuO·CuSO4 are formed before the complete oxidation of Cu2S to CuO.

Addition of nucleophiles to electron-deficient alkenes: structural studies on the incipient reaction and the zwitterionic intermediate

Three distinct interactions between a Me2N group and an electron-deficient alkene located in the peri positions of a naphthalene ring comprise an almost complete cyclisation, an incipient reaction, and a less favourable orientation of the nitrogen lone pair with respect to the alkene, which can be related to the electronic characteristics of the alkene substituents; the cyclised material is zwitterionic and is composed of the enolate of a β-dicarboxylic diester and a trialkylarylammonium cation.