Thermal behaviour of CO2 laser-irradiated CeO2 doped with Yb2O3

Results concerning the thermal behaviour of Yb₂O₃-doped CeO₂ samples irradiated with CO₂ laser beams in continuous wave are presented.

---

Zusammenfassung Es werden Ergebnisse einer Untersuchung des thermischen Verhaltens von CeO₂-Proben dargelegt, die mit CO₂-Laser bestraht wurden.

     

Report on the extremely low threshold for the CO2 laser induced multiple photon absorption and dissociation processes in chromyl chloride

We have studied the behaivior of the CrO₂Cl₂ molecule upon irradiation with an unfocused, low power (0.45 J/cm² pulsed CO₂ laser using a visible dye laser as a probe of the population changes in the vibrationless ground electronic state and various low-lying vibrational levels. Wavelength and time-resolved measurements indicate that the vibrationless ground state is depleted as a result of the CO₂ laser pumping and that the recovery of the ambient population does not take palce even after 5.0 milliseconds. Mass spectroscopic analysis of the CO₂ laser irradiated samples suggests an extremely low thereshold for dissociation in the case of CrO₂Cl₂.     

Analysis of the temperature dependence of the high-frequency EMR spectra of Mn ions in the lithium-ion battery material LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

This paper deals with the analysis of the temperature dependence of high-frequency EMR (HF-EMR) spectra due to Mn³⁺ and Mn⁴⁺ ions in the lithium manganese spinel LiMn₂O₄. A range of powder samples obtained by the sol-gel method with calcinations in several temperature ranges were prepared for this study. Based on the initial characterization carried out by a number of techniques, the physicochemical and structural properties of the samples were earlier determined. Independently, temperature magnetization and HF-EMR measurements were carried out. The EMR spectra vary strongly between samples, indicating possible structural or chemical changes. Quantitative analysis of the temperature dependence of the HF-EMR spectra due to Mn³⁺ and Mn⁴⁺ ions in LiMn₂O₄ is presented in this paper. The spectral analysis concerns the line shape, linewidth, intensity and g-factors. Fittings using the Lorentzian spectral shape and, to a certain extent, the Gaussian spectral shape have been carried out in order to parameterize the temperature dependence of the HF-EMR spectra. This parameterization of the HF-EMR experimental data enables a deeper characterization of the samples. Subsequently, a better insight into the role of the Mn³⁺ and Mn⁴⁺ ions in accounting for the characteristics most suitable for application of LiMn₂O₄ as a cathode material may be gained.     

SO2 absorption of the CO2- laser emission measured by the photoacoustic technique

Spectra of coincidence of SO₂ IR absorption with CO₂-laser emission at pressure of 50,100 and 450 Torr were recorded by the use of a photoacoustic detection method in the whole range of CO₂-laser emission. The spectra show that SO₂ absorbs many CO₂-laser lines in the range 1084–1071 cm⁻¹ with the strongest absorption at 1082.29cm⁻¹, laser line R(26). The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of line spectra, characteristic of lower pressure samples, disappear as pressure is increased.     

CH3F absorption of the CO2-laser emission measured by the photoacoustic technique

Spectra of coincidence of CH₃F IR absorption with CO₂-laser emission at pressures of 2, 10 and 60 Torr were recorded by the use of a photoacoustic detection method in the whole range of CO₂-laser emission. The spectra show that CH₃F absorbs many CO₂-laser lines in the range 1084–1071 cm⁻¹ with the strongest absorption at 1046.80cm⁻¹, laser line P(20). Absorption is predominantly due to the fundamental of v₃, which is well spread over the whole laser emission range. The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of the line spectrum, characteristic of lower pressure samples, disappears as pressure is increased.     

TEA CO2 laser-induced reaction of CH3NO2 with CF2HCl: A mechanistic study

Dissociation of nitromethane has been observed when a mixture of CF₂HCl and CH₃NO₂ is irradiated using pulsed TEA CO₂ laser at 9R (24) line (1081 cm^-1), which is strongly absorbed by CF₂HCl but not by CH₃NO₂. Under low laser fluence conditions, only nitromethane dissociates, whereas at high fluence CF₂HCl also undergoes dissociation, showing that dissociation occurs via the vibrational energy transfer processes from the TEA CO₂ laser-excited CF₂HCl to CH₃NO₂. Time-resolved infrared fluorescence from vibrationally excited CF₂HCl and CH₃NO₂ molecules as well as UV absorption of CF₂ radicals are carried out to elucidate the dynamics of excitation/dissociation and the chemical reactions of the dissociation products.     

A comparative study on the dispersion behaviors and surface acid properties of molybdena on CeO2 and ZrO2 (Tet)

Dispersion of molybdena on CeO₂, ZrO₂ (Tet), and a mixture of CeO₂ and ZrO₂ (Tet), was investigated by using laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and temperature programmed reduction (TPR). The results indicate that molybdena is dispersed on both individual oxide support and mixed oxide support at the adopted molybdena loadings (0.2 and 0.8 mmol Mo⁶⁺/100 m²) and the structure of the supported molybdena species is intimate association with its loading amount. Two molybdena species are identified by Raman results, i.e. isolated MoO²⁻₄ species at 0.2 mmol Mo⁶⁺/100 m² and polymolybdate species at 0.8 mmol Mo⁶⁺/100 m². IR spectra of ammonia adsorption prove that isolated MoO²⁻₄ species are Lewis acid sites on the Mo/Ce and/or Zr samples, and the polymolybdate species are Brönsted acid sites on the Mo/Ce and/or Zr samples. Moreover, a combination of the Raman, IR and TPR results confirms that at 0.2 mmol Mo⁶⁺/100 m² Ce + Zr, molybdena is preferentially dispersed on the surface of CeO₂ when a mixed oxide support (CeO₂ and ZrO₂) is present, which was explained in term of the difference of the surface basicity between CeO₂ and ZrO₂ (Tet). Surface structures of the oxide supports were also taken into consideration.     

Infrared multiphotonic excitation and the cell geometry problem: case of CH3Br and SF6

Gas samples of CH₃Br and SF₆ were irradiated by a focused CO₂ laser beam. Three cells with different sizes were used. With CH₃Br, fluorescence and decomposition were observed which depended upon the cell's dimensions. With SF₆ we always obtained decomposition and enrichment in ³⁴S by irradiation with the P(16) line.     

Structure alterations in microporous (Mg,Fe)2Al4Si5O18 crystals induced by energetic heavy-ion irradiation

The microporous framework structure of (Mg_1−xFe_x)₂Al₄Si₅O₁₈ (=cordierite) has been subject to a comparative study on the effect of structural alterations originating from exposure to high-energy heavy ions. Oriented samples (with x=0.061, 0.122, and 0.170) were irradiated with swift ¹²⁴Xe, ¹⁹⁷Au and ⁹⁶Ru ions with 11.1 MeV per nucleon energy and fluences of 1×10¹² and 1×10¹³ ions/cm². Irradiated and non-irradiated samples were investigated by means of X-ray diffraction, Mössbauer spectroscopy and optical absorption spectroscopy. Structural investigations reveal an essentially unchanged Al,Si ordering, which appears to be unaffected by irradiation. The most remarkable macroscopic change is the ion-beam induced colouration, which could be assigned to electronic charge transfer transitions involving the Fe cations. Mössbauer spectra indicate an increased amount of ^[4]Fe³⁺ for the irradiated sample. The most noticeable structural alteration concerns irradiation-induced dehydration of extra-framework H₂O, which is accompanied by a reduction in the molar volume by ∼0.2 vol%.     

IR Photolysis of Liquid Hexamethyldisiloxane by Pulse CO2Laser Radiation

The IR photolysis of liquid hexamethyldisiloxane [(CH₃)₃Si]₂O by pulse CO₂laser radiation was studied. The experiments were performed both with and without a graphite powder as a sensitizer. The presence of the graphite sensitizer increases the efficiency of dissociation. To provide the highest penetration of the laser emission into a medium, the irradiation of samples were carried out with tuning far from the maximum of the Si–O bond absorption band (1055 cm^–1) using the 10P16 line (_las= 947.78 cm^–1). This tuning makes it possible to separate the process of IR multiphoton dissociation of the vapor over the liquid phase and to carry out the reaction in the liquid at a low (1 J/cm²) energy fluence of laser radiation. The IR spectra of irradiated liquid samples indicate the formation of linear and cyclic polystructures.     

Effect of γ-radiation on radionuclide retention in compacted bentonite

Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ) under anoxic conditions. Because of this, the effects of γ-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs⁺ and Co²⁺ were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co²⁺ than for Cs⁺, which generally showed no significant differences between irradiated and unirradiated clay samples. For Co²⁺ however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that γ-radiation may alter the surface characteristics contributing to surface complexation of Co²⁺. With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained D_a values.     

Laser assisted selective chemical metalization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films

Thick aluminum oxide films are prepared on Al plates by anodizing. On the ceramic surface thus obtained a very thin Ag film is deposited via vacuum thermal evaporation. The Ag/Al₂O₃/Al samples prepared are irradiated by Nd:YAG laser through a suitable metal mask in order to remove the top metal film in the exposed areas. Thus, a negative silver image of the copied mask is obtained. Further, the samples are processed in Ni electroless chemical bath activated by the rest of silver. All processing steps are studied by scanning electron microscopy (SEM). EDS X-ray mapping is applied to study the final distribution of Al and Ni in the processed areas. In addition, the DC conductivity of the fabricated Ni wires obtained is measured. The proposed new method for selective chemical deposition of electroconductive Ni onto laser microstructured Ag/Al₂O₃/Al samples is simple, versatile and not restricted to the metal/ceramic system studied as well as to the electroless deposited metal.     

Immobilization of invertase in germania matrix and a study of its enzymatic activity

A novel and easy synthesis route to mesoporous nanocrystalline TiO₂ samples using soluble starch as the structural agent and mainly titanium(IV) isopropoxide as the inorganic precursor was described. The effect of key parameters, including soluble starch removal process, the solvent nature and the type of titanium precursor were discussed. Using soluble starch in cyclohexane as non polar solvent, a surface area of 94 m².g⁻¹ associated with 23 nm crystallites size was obtained. TiO₂ samples were characterized by means of N₂ adsorption-desorption, X-ray Diffraction (XRD), TG-DTA, Scanning Electron Microscopy (SEM) and ATR-FTIR spectroscopy. Dedicated to Dr. Jean-Claude Volta on the occasion for his retirement     

Mitochondrial Responses of Normal and Injured Human Skin Fibroblasts Following Low Level Laser Irradiation—An In Vitro Study

Laser irradiation has proved to be very efficient in speeding and improving the quality of healing in pathological conditions of diverse etiologies. However, the mechanisms by which the beneficial effects are attained are not clear. Mitochondria are the primary phototargets during irradiation. The study aimed to establish if laser irradiation had an effect on hypoxic and acidotic cells. The study also aimed to use existing information regarding the possible mechanism of action (established in wounded cells) and apply these principles to acidic and hypoxic irradiated cells to determine whether laser has a stimulatory or inhibitory effect. Cell cultures were modified to simulate conditions of hypoxia (hypoxic gas mixture 95% N₂ and 5% O₂) and acidosis (pH 6.7) whereas the central scratch model was used to simulate a wound. Cells were irradiated with a helium–neon (632.8 nm, 3 mW cm^?2) laser using 5 or 16 J cm^?2 on days 1 and 4. Mitochondrial responses were measured 1 or 24 h after laser irradiation by assessing changes in mitochondrial membrane potential (MMP), cyclic AMP, intracellular Ca²⁺ and adenosine triphosphate (ATP) cell viability. Hypoxia and acidosis significantly reduced MMP when compared with normal nonirradiated control cells. Wounded, hypoxic and acidotic cells irradiated with 5 J cm^?2 showed an increase in mitochondrial responses when compared with nonirradiated cells while 16 J cm^?2 showed a significant decrease. The study confirmed that laser irradiation with 5 J cm^?2 stimulated an increase in intracellular Ca²⁺ which resulted in an increase in MMP, ATP and cAMP, which ultimately results in photobiomodulation to restore homeostasis of injured cells.     

Radiation-induced darkening of ionic liquid [C4mim][NTf2] and its decoloration

The radiation effect on a hydrophobic room-temperature ionic liquid (RTIL), 1-butyl-3-methyl-imidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₄mim][NTf₂]), was studied by γ-irradiation under nitrogen atmosphere. Accompanied by color darkening and increase of light absorbance in a wide wavelength range, a distinct absorption peak at around 290 nm for irradiated [C₄mim][NTf₂] appeared when acetonitrile was used as solvent, and the intensity of the peak enhanced with increasing dose. The spectrophotometric study on the irradiated RTILs containing 1,3-dialkylimidazolium cations associated with different inorganic anions revealed that the peak is ascribed to the radiolysis products of the [C₄mim]⁺. And the wavelength of the peak was affected by alkyl chain length on imidazolium cation, while the intensity of the peak was influenced by anions. With incorporating a little amounts of oxidants, such as KMnO₄ and HNO₃ into irradiated [C₄mim][NTf₂], the intensity of the peak at 290 nm decreased obviously and the decoloration of [C₄mim][NTf₂] occurred, suggesting that the peak at 290 nm is assigned to the colored species and the species can be oxidized.     

The Selective CO2 Adsorption and Photothermal Conversion Study of an Azo-Based Cobalt-MOF Material

A new metal–organic framework (MOF), [Co₂(L)₂(azpy)]_n (compound 1, H₂L = 5-(pyridin-4-ylmethoxy)-isophthalic acid, azpy = 4,4′-azopyridine), was synthesized by a solvothermal method and further characterized by elemental analysis, IR spectra, thermogravimetric analysis, single-crystal and powder X-ray diffraction. The X-ray single-crystal diffraction analysis for compound 1 indicated that two cis L2²⁻ ligands connected to two cobalt atoms resulted in a macrocycle structure. Through a series of adsorption tests, we found that compound 1 exhibited a high capacity of CO₂, and the adsorption capacity could reach 30.04 cm³/g. More interestingly, under 273 K conditions, the adsorption of CO₂ was 41.33 cm³/g. In addition, when the Co-MOF was irradiated by a 730 nm laser, rapid temperature increases for compound 1 were observed (temperature variation in 169 s: 26.6 °C), showing an obvious photothermal conversion performance. The photothermal conversion efficiency reached 20.3%, which might be due to the fact that the parallel arrangement of azo units inhibited non-radiative transition and promoted photothermal conversion. The study provides an efficient strategy for designing MOFs for the adsorption of CO₂ and with good photothermal conversion performance.     

Laser driven synthesis of BHCl2 from BCl3 and H2

Mixtures of BCl₃ and H₂ have been irradiated by a pulsed CO₂ laser yielding BCHl₂ and HCl as the only products. Approximately 50% conversion of the reagents was obtained with a quantum efficiency of 122 10.6 μ photons per BCHl₂ molecule. The product yield is observed to scale with laser power as (P/P₀)^1.26.     

掺杂Fe2O3对吸附相反应技术制备TiO2的形貌和光催化性能的影响

利用吸附相反应技术制备得到了掺杂不同浓度的Fe₂O₃的TiO₂复合光催化剂。通过透射电子显微镜(TEM)、紫外可见光谱和X射线衍射(XRD)研究不同掺杂浓度对TiO₂形貌和结晶过程的影响,并利用3种波长光源下的甲基橙光降解实验考评了各个复合光催化剂的催化活性。结果表明,掺杂后复合光催化剂中Fe₂O₃分散性较好较均匀。在TiO₂紫外可见吸收光谱中由于Fe₂O₃的掺杂而出现了红移,而且随着掺杂浓度增加红移越来越明显,复合光催化剂的禁带宽度也越来越小。在焙烧过程中无定形Fe₂O₃或Fe³⁺进入了TiO₂的晶格结构,从而抑制了TiO₂的结晶过程。半导体禁带宽度的减少以及TiO₂结晶过程的抑制作用,都导致紫外光下复合光催化剂催化活性的降低。但Fe₂O₃的掺杂也使得复合光催化剂在可见光区出现了一定的光催化活性。     

Application de l’Analuyse par Radioactivation Neutronique et du Calcul Electronique au Dosage non Destructif de Traces de Chlore dans les Silices-alumines

A method applicable for serial determination of traces of chlorine in SiO₂−Al₂O₃ catalysts by neutron activation is described. The results are evaluated by means of a computer. The³⁸Cl activity is subtracted from the activity of the interfering components (⁵⁶Mn,²⁴Na) and this enables a direct γ-spectrometric determination. In praxis ten samples should be irradiated simultaneously and for this reason 3 standards are irradiated together with the samples to correct for the fluxus gradient. The reproducibility of the method is better than 2 per cent for 10–300 mg samples with a Cl content of 10 ppm.      

Impurity and radiation defects in LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> crystals. The nature of centers in LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> crystals,which are responsible for coloration during the long-term operation of optical elements

An attempt is made to explain the causes of coloration of LiB₃O₅ crystals after their long-term operation as laser elements. By EPR and optical spectroscopy the impurity and radiation centers are studied in as-grown LiB₃O₅ crystals and in the crystals whose color appeared after the long-term operation as laser elements. In a number of as-grown crystals a copper impurity is detected. EPR spectral parameters and the structural positions of Cu²⁺ ions are found. Defect formation features in electron irradiated as-grown LiB₃O₅ crystals and in the most colored regions of crystals of spent laser elements are analyzed. It is shown that in both growth crystals and crystals after long-term operation as laser elements the same set of radiation defects is observed: oxygen O^– in the interstitial position, an O^– hole center in the crystal structure, and the B²⁺ electron center due to the removal of an oxygen atom near the lithium vacancy. The only distinction is that the concentration of these radiation defects in crystals long used as laser elements is higher than that in growth ones by an order of magnitude. The results obtained enable the conclusion that the cause of coloration of LiB₃O₅ crystals is photo-induced diffusion of lithium atoms and their capture by cation vacancies in the dark part of the crystal, which provides the formation and accumulation of lithium vacancies in the region where the laser beam passes.