CO Evaporation Research Articles

Comparative Study on Triclosan Interactions in Solution and in the Solid State with Natural and Chemically Modified Cyclodextrins

The aim of this study was to investigate the interactions of triclosan (TRI), a poorly water-soluble antimicrobial drug, with natural crystalline cyclodextrins (α-, β- and γ-Cd) and the corresponding hydroxypropylated amorphous derivatives (HPα-, HPβ-, and HPγ-Cd) and evaluate their effectiveness as complexing and solubilizing agents towards the drug. Equimolar solid systems were prepared using different techniques (physical mixing (PM), kneading (KN) and coevaporation (COE)) in order to evaluate the influence of the preparation method on the performance of the end products. Drug–carrier interactions were investigated both in aqueous solution, using phase-solubility analysis, fluorescence and circular dichroism (CD) techniques, and in the solid state, using differential scanning calorimetry (DSC) supported by thermograumetric analysis (TGA), X-ray powder diffractometry (XRPD) and scanning electron microscopy (SEM) analysis. Among the native cyclodextrins, β-Cd seemed to have the most suitable cavity to fit the drug molecule, whereas the α-Cd cavity was too small and the γ-Cd cavity too large to establish stable interactions with the guest. However, due to the BS-type phase solubility diagram, its solubilizing efficiency was very limited. The presence of the hydroxypropylic substituents improved, in all cases, Cd solubilizing and complexing efficacies towards the drug. This was particularly evident in the case of HPγ-Cd, whose stability constant was about 200-fold higher than that of the native γ-Cd. HPβ-Cd was the most effective carrier for TRI, showing a solubilizing power about 20 times higher than the corresponding native Cd and about 2-fold that of the other hydroxypropyl derivatives. Moreover, a clear influence of the preparation method on the properties of the final products was observed. The COE method with hydroxypropylated cyclodextrins seemed the most suitable technique in achieving the complete drug amorphization and/or inclusion complexation.

Effect of P, B4C, and (Ti, Cr)C Additives on the Kinetics of High-Temperature Oxidation of Chromium Carbide Alloys at 1000°C

We have used the thermogravimetric method to study the effect of B4C, (Ti, Cr)C, and phosphorus additives on the kinetics of oxidation of chromium carbide alloys of the type 85% Cr3C2 ― 15% Ni (KKhN15) and 85% Cr3C2 ― 15% (Ni ― P) (KKhNF15), in air under isothermal heating conditions at 1000°C from 0 to 5 h. We have established that the alloys are characterized by insignificant increase in mass in the initial oxidation period (≈3 h), after which the degree of oxidation increases somewhat. The nature of the oxidation kinetics for KKhNF15 alloys, containing 0.016-0.64% B4C, varies from some mass increase in the initial period (≈20 min) to later mass loss in connection with formation of CO, CO2 and rapid evaporation of boron anhydride B2O3. The maximum resistance to oxidation is exhibited by alloys of the type KKhN15 and KKhNF15, the mass increase of which is 0.128-0.256 mg/cm2 after 5 h of heating at 1000°C.

Er doping of Si and Si 0.88Ge 0.12 using Er 2O 3 and ErF 3 evaporation during molecular beam epitaxy A transmission electron microscopy study

The incorporation behavior of Er into Si and Si 0.88Ge 0.12 using ErF 3 and Er 2O 3 as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. Dissociation of Er 2O 3 took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4×10 19 cm −3 using Er 2O 3 and a high F background pressure. Using ErF 3 compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF 3 molecules, but also from CF x ( x=1–4) and F background species, which are present due to a reaction between the ErF 3 source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1×10 19 cm −3 and without observable defects using ErF 3 as source material. For the case of Er-doping of Si 0.88Ge 0.12 using ErF 3, we observed contrast along lines in the growth direction at an Er concentration of 1×10 19 cm −3, which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro- and photoluminescence.

Adsorbed CO chain condensation and evaporation on Pt{110}-(1×2) at 30–70 K studied by RAIRS

At very low CO coverages on Pt{110}-(1×2) at 30 K, two C–O stretch infrared bands are observed. Warming to >40 K results in the loss of the high-frequency band and growth of the low-frequency band. Further warming to ⩾60 K reverses this process. This reversal is attributed to a thermodynamic transition between 1D islands, or chains, of CO molecules and a 1D gas. The process at ⩾40 K is attributed to the onset of surface diffusion, when chain condensation occurs from the adsorbate randomly formed at 30 K.

Carbon production in comet West 1975n

Rocket-ultraviolet spectra of comet West 1975n are reported which were obtained with scanning spectrophotometers in the wavelength range from 1200 to 1300 A. The principal emission features observed include lines of C, O, and C(+), as well as bands of OH, CO, CO(+). The estimated fluxes of the C, O, H, CO, and OH features are found to be consistent with a photodissociation source in which the CO evaporation rate is about one-third that of water. The presence of a large number of carbon atoms in the metastable 1D state is indicated and taken to suggest that dissociative recombination is important near the cometary nucleus, that CO must originate in the nucleus, and that CO is the primary carbon constituent of the comet.