Thermodesorption Spectra Research Articles

Аналитические возможности термодесорбционного спектрометра с поверхностно-ионизационным детектированием молекул органических веществ в воздухе

Abstract This paper presents the results of research on the development of a mathematical model of thermal desorption spectrometry with a surface ionization method for detecting molecules of organic substances, as well as an analysis of the capabilities of a thermal desorption spectrometer operating on the basis of this method. The mathematical model of the method was developed on the basis of the regularities of thermal desorption spectrometry, as well as the regularities of surface ionization of molecules of organic substances under non-stationary conditions. The spectrometer consists of a surface ionization detector and an evaporator of substances heated in a thermally programmed mode. The adjustment and selection of the operating mode of the spectrometer were carried out on the basis of the mathematical model of the method. The analytical capabilities of the spectrometer were studied by comparing the thermodesorption spectra of a mixture of chromatographically pure cannabinoids and an extract of the biological fluids of a marijuana user (blood, urine), as well as the spectra of chromatographically pure morphine and urine extracts of a heroin user. The results of the analysis showed the perspectives of the proposed method and instrument for the detection and analysis of drugs and psychotropic drugs in extracts of biomaterials of consumers of these substances without chromatographic separation.

Analytical capabilities of a thermodesorption spectrometer with a surface-ionization detection of organic molecules in air

This paper presents the results of research on the development of a mathematical model of thermal desorption spectrometry with a surface ionization method for detecting molecules of organic substances, as well as an analysis of the capabilities of a thermal desorption spectrometer operating on the basis of this method. The mathematical model of the method was developed on the basis of the regularities of thermal desorption spectrometry, as well as the regularities of surface ionization of molecules of organic substances under non-stationary conditions. The spectrometer consists of a surface ionization detector and an evaporator of substances heated in a thermally programmed mode. The adjustment and selection of the operating mode of the spectrometer were carried out on the basis of the mathematical model of the method. The analytical capabilities of the spectrometer were studied by comparing the thermodesorption spectra of a mixture of chromatographically pure cannabinoids and an extract of the biological fluids of a marijuana user (blood, urine), as well as the spectra of chromatographically pure morphine and urine extracts of a heroin user. The results of the analysis showed the perspectives of the proposed method and instrument for the detection and analysis of drugs and psychotropic drugs in extracts of biomaterials of consumers of these substances without chromatographic separation. Keywords: biosamples of drug users, mathematical model of the method, thermal desorption spectrum, identification and quantitative analysis.

Parametric optimisation based on TDS experiments for rapid and efficient identification of hydrogen transport materials properties

A novel identification technique of hydrogen transport parameters using FESTIM (Finite Element Simulation of Tritium In Materials) has been demonstrated. FESTIM is a finite element code developed with FEniCS performing hydrogen transport simulations. The trapping parameters (detrapping energies and trap densities) are identified for various materials (Tungsten, Aluminium, EUROFER and Beryllium) by automatically reproducing thermo-desorption experiments. Several optimisation algorithms are tested and the Nelder–Mead algorithm shows the best efficiency. An optimisation test problem with five free parameters took only a few hours to solve whereas optimisation cases with two free parameters took a few minutes. Limitations of this technique are shown and discussed. • An automated technique for materials properties identification is presented. • Thermo-desorption spectra are automatically reproduced. • Tungsten, EUROfer, Aluminium and Beryllium are analysed.

Thermodesorption Spectrometer of Hard-Volatile Active Organic Compounds

The results of developing a new type of the gas-analytical device for detection of hard-volatile active organic compounds such as drugs, psychotropic preparations and their metabolites, environmental contaminants have been presented. It is based on the principle of thermodesorption in combination with surface ionization of analyte molecules. The trace amounts of an analyte (beginning with 0.1 ng) in sample extracts have been identified by comparing the thermodesorption spectra and their amounts have been defined according to the calibration curves of the reference samples available in the spectrometer electronic database.

Deuterium concentration’s in austenitic stainless steel by deuterium irradiation. Effects temperature irradiation

Using the deuterium thermodesorption spectra from the 18Cr10NiTi steel samples exposed to different doses, we have plotted the total amount of deuterium desorbed from the sample as a function of the radiation dose and the irradiation temperatures. Temperature 100 K. The maximum attainable concentration of deuterium in steel is C=1 (at.D/at.met.= 1/1). At C≥0.5, two hydride phases are formed in the steel, the decay temperatures of which are 240 K and 275 K. The hydride phases are formed in the bcc structure resulting from the martensitic structural transformation in steel [1]. Temperature 295 K. The medium-dose region is characterized by radiation induced action on the steel in the presence of hydrogen. The process results in the formation of the energy-stable crystalline nanostructure of steel, having a developed network of intercrystalline boundaries. The basis for this developed network of intercrystalline boundaries is provided by the amorphous state. The total concentration of the accumulated deuterium in the region of medium implantation doses makes 7 to 8 at.% [2]. Temperature 380; 420; 600 and 900 K. In a deuterium thermodesorption spectra the extended area of deuterium desorption in a range of temperatures 450-900 K is observed, caused by formation of local structure in a radiation induced layer. Formation of local structure can be caused by a segregation of a steel component in the course of deuterium implantation (radiation induced local structure at deuterium presence).The total concentration of the accumulated deuterium in the region of medium implantation doses makes 1 to 3 at.%.

Structural Transformations in Austenitic Stainless Steel Induced by Deuterium Implantation: Irradiation at 295K.

Deuterium thermal desorption spectra were investigated on the samples of austenitic steel 18Cr10NiTi pre-implanted at 295 K with deuterium ions in the dose range from 8 × 1014 to 2.7 × 1018 D/cm2. The kinetics of structural transformation development in the steel layer was traced from deuterium thermodesorption spectra as a function of deuterium concentration. Three characteristic regions with different low rates of deuterium amount desorption as the implantation dose increases were revealed: I—the linear region of low implantation doses (up to 1 × 1017 D/cm2); II—the nonlinear region of medium implantation doses (1 × 1017 to 8 × 1017 D/cm2); III—the linear region of high implantation doses (8 × 1017 to 2.7 × 1018 D/cm2). During the process of deuterium ion irradiation, the coefficient of deuterium retention in steel varies in discrete steps. Each of the discrete regions of deuterium retention coefficient variation corresponds to different implanted-matter states formed during deuterium ion implantation. The low-dose region is characterized by formation of deuterium-vacancy complexes and solid-solution phase state of deuterium in the steel. The total concentration of the accumulated deuterium in this region varies between 2.5 and 3 at.%. The medium-dose region is characterized by the radiation-induced action on the steel in the presence of deuterium with the resulting formation of the energy-stable nanosized crystalline structure of steel, having a developed network of intercrystalline boundaries. The basis for this developed network of intercrystalline boundaries is provided by the amorphous state, which manifests itself in the thermodesorption spectra as a widely temperature-scale extended region of deuterium desorption (structure formation with a varying activation energy). The total concentration of the accumulated deuterium in the region of medium implantation doses makes 7 to 8 at.%. The resulting structure shows stability against the action of deuterium ion implantation. This manifests itself in a nearly complete ceasing of deuterium accumulation from a newly implanted dose (radiation-resistant structure).

Structural transformations in austenitic stainless steel induced by deuterium implantation: irradiation at 100K.

Deuterium thermal desorption spectra were investigated on the samples of austenitic stainless steel 18Cr10NiTi preimplanted at 100 K with deuterium ions in the dose range from 3 × 1015 to 5 × 1018 D/cm2. The kinetics of structural transformation development in the implantation steel layer was traced from deuterium thermodesorption spectra as a function of implanted deuterium concentration. At saturation of austenitic stainless steel 18Cr10NiTi with deuterium by means of ion implantation, structural-phase changes take place, depending on the dose of implanted deuterium. The maximum attainable concentration of deuterium in steel is C = 1 (at.D/at.met. = 1/1). The increase in the implanted dose of deuterium is accompanied by the increase in the retained deuterium content, and as soon as the deuterium concentration attains C ≈ 0.5 the process of shear martensitic structural transformation in steel takes place. It includes the formation of bands, body-centered cubic (bcc) crystal structure, and the ferromagnetic phase. Upon reaching the deuterium concentration C > 0.5, the presence of these molecules causes shear martensitic structural transformations in the steel, which include the formation of characteristic bands, bcc crystal structure, and the ferromagnetic phase. At C ≥ 0.5, two hydride phases are formed in the steel, the decay temperatures of which are 240 and 275 K. The hydride phases are formed in the bcc structure resulting from the martensitic structural transformation in steel.

Microstructure and hydrogen storage properties of MgH2–TiB2–SiC composites

Abstract The influence of TiB2 and SiC ceramics on H-desorption kinetics from MgH2 based composites was investigated and correlated with the microstructure and morphology of the composites. The mechanism of desorption and the activation energy for desorption was investigated by applying non-isothermal kinetic analysis of thermodesorption spectra. It has been shown that TiB2 addition leads to significant decrease of the activation energy for desorption, while SiC addition has effect on the interface reaction between hydride and hydroxide. The mechanism of desorption change from Avrami–Erofeev n=3 for pure MgH2 to Avrami–Erofeev n=4 for composite materials. The change from 3 to 4 can be due to the modification of the nucleation process or a change in the dimensionality of the growth. Those high values of n discard a diffusion control as a rate limiting step.

Fine structure of the thermal decomposition kinetics of polymethylmethacrylate filled with detonation nanodiamonds

A comparison has been made of the specific features of the fine structure of thermodesorption spectra of polymethylmethacrylate and its composites with nanocarbon fillers: detonation nanodiamonds, fullerene C60, and multiwalled carbon nanotubes. The influence of the fillers on the shape of the thermodesorption spectra has been interpreted as a result of the chemical interaction between functional groups of macromolecules of the polymer matrix and active centers of filler nanoparticles.

Behavior of helium in steel 16Cr12W2VTaB under various implantation temperatures

Gaseous porosity formation and helium behavior have been investigated in the reduced activation ferritic–martensitic steel 16Cr12W2VTaB irradiated with 40 keV He + ions up to a fluence of 5 × 10 20 m −2 at temperatures from 290 to 900 K in two initial conditions: normalized + tempered (HT-1), and cold rolled + annealed (HT-2). After HT-1, cavitation was observed above 770 K, where bubbles with a maximum diameter 1 nm were formed. Large bubbles with a mean diameter 8 nm formed when irradiated at 900 K. On the other hand, a high density of small bubbles formed at the lower irradiation temperature of 570 K after HT-2. At 900 K, bubbles had an extremely nonuniform distribution in size, depending on their locations. The helium thermodesorption spectra had two intensive peaks owing to polymorphic transformation during heating. The peaks widened and gas release began at higher temperatures with formation of large bubbles.

Deuterium retention in rhenium-doped tungsten

Deuterium retention in rhenium doped tungsten (W–Re) was investigated by means of the thermodesorption technique. W–Re alloys of different structures and concentrations of Re were investigated. All tungsten rhenium alloys had a common structural feature – micron size voids in the bulk. The samples were irradiated by 200eV deuterium ions in the fluence range 1022–1024D/m2. The thermodesorption spectra of polycrystalline W measured with a linear ramp of 5K/s has two peaks at ∼450 and 650K. In TDS of W–Re alloys an additional high-temperature peak was found at 850K. The observed retention in W–Re alloys depends strongly on materials structure. In the range of 1–10%Re admixture the Re concentration in W–Re alloy does not influence noticeably the deuterium retention. Structure changes (filling of voids in material) was found to take place both at annealing and low-energy deuterium irradiation.

On the Equilibrium Nature of Thermodesorption Processes. TPD-NH3 Studies of Surface Acidity of Ni/MgO−Al2O3 Catalysts

This article deals with a quantitative analysis of thermodesorption spectra of ammonia: a technique commonly applied to study the surface acidity of solids. The method used for determination of adsorption energy distributions of ammonia is the same as that published recently for the case of hydrogen thermodesorption (Panczyk, T.; et al. Langmuir 2005, 21, 7311). The developed theoretical expression describing the thermodesorption process is based on the statistical rate theory (SRT) and its analysis leads to the conclusion that majority of thermodesorption processes, carried out under flow conditions, are in fact quasi-equilibrium ones. Similar conclusion has already been drawn by some authors applying the classical absolute rate theory (ART) for analysis of thermodesorption data. This conclusion has important practical consequences. Namely, it greatly simplifies the quantitative analysis of thermodesorption processes since there is no need to use any kinetic approaches to that purpose. The quantitative analysis of thermodesorption spectra can thus be based on commonly accepted relations following from equilibrium thermodynamics. It is worth noting that in quasiequilibrium conditions either the SRT or the ART lead to this same expression with only a slightly different meaning of some constants. Thus, in quasiequilibrium conditions there is no need to decide which theoretical approach should be applied. As an illustration, the ammonia thermodesorption spectra from the modified nickel catalysts are analyzed. The catalysts were prepared by the coprecipitation method and differ by the amount of MgO and NiO, whereas the amount of Al(2)O(3) is constant and equals 30%. It was stated that the presence of MgO reduces the number of acid centers corresponding to high values of ammonia adsorption energy.

Thermodesorption Studies of Energetic Properties of Ni/MgO−Al2O3 Catalysts. Determination of Adsorption Energy Distribution Functions

The thermodesorption spectra of hydrogen from coprecipitated catalysts (70-x)NiO-xMgO-30Al(2)O(3) (x = 0-50%(wt)) are reported. The catalysts were calcined at 400 degrees C and reduced with H(2) at 20-800 degrees C and for 3 h at 800 degrees C. NiO reduction degree was between 49.3 and 92.1%. The active surface areas changed from 8.4 to 32.4 m(2)/g whereas mean size of nickel crystallites was between 3.7 and 9.7 nm. The TPD spectra were next analyzed in order to determine the adsorption energy distributions functions. To obtain these functions a theoretical model of adsorption/desorption kinetics based on the statistical rate theory (SRT) was applied. This approach allows for determination of the adsorption energy at nonequilibrium conditions as well as at quasiequilibrium conditions. The resulting distribution functions reveal the presence of two main bands of adsorption energy. Some correlation is found between the determined distributions of adsorption energy and the size of nickel crystallites determined using the XRD method. The presence of MgO favors creation of high energy adsorption sites on Ni crystallites.

The influence of a small amount of active sites on the adsorption kinetics of nitrogen on ruthenium

Recently, Dahl et al. [S. Dahl, A. Logadottir, R.C. Egeberg, J.H. Larsen, I. Chorkendorff, E. Törnqvist, J.K. Nørskov, Phys. Rev. Lett. 83 (1999) 1814; S. Dahl, E. Törnqvist, I. Chorkendorff, J. Catal. 192 (2000) 381] have proposed very interesting hypothesis that the rate of dissociation and adsorption of nitrogen on Ru(0 0 0 1) facet is totally dominated by the presence of a small amount of step sites on Ru(0 0 0 1) terraces. Following this idea, a kinetic model, based on applying the Statistical Rate Theory approach, was developed in order to explain if such mechanism is able to explain the observed features of the system N 2/Ru(0 0 0 1). As a result, it was stated that the activation barrier for adsorption on the active (step) sites is equal to 36 kJ/mol; in turn, the adsorption energy of nitrogen atoms on the active sites is 43 kJ/mol. It implies that the rate of adsorption via the active sites is much faster than direct adsorption on the three-fold hollow sites; moreover, the occupation of the active sites is always close to zero at the investigated temperatures, so they are not blocked and may act as an indirect channel for adsorption. Thus, the rate of nitrogen adsorption on Ru(0 0 0 1) surface is governed by the rate of diffusion of nitrogen atoms from the active sites into the three-fold hollow sites. The analysis of thermodesorption spectra revealed an important role of repulsive interactions between the N atoms adsorbed on the hollow sites, the associated interaction parameter between nearest neighbors was estimated to be 5 kJ/mol. The presence of small amount of gold on Ru(0 0 0 1), apart of blocking the active sites, seems to remove the repulsion between nitrogen atoms.

Monte Carlo simulations of controlled rate thermal analysis spectraThe influence of surface energetic heterogeneity and lateral interactions between adsorbed molecules

Monte Carlo simulations of controlled rate thermal analysis (CRTA) spectra are presented. Calculations are performed for a few kinds of energetically heterogeneous surface, characterized by symmetrical and unsymmetrical desorption energy distributions. It is shown that the shape of the CRTA spectra corresponds with the shape of integral form of desorption energy distribution on the surface. A simple way of estimation of the upper limit of desorption energy is proposed. The influence of lateral interactions on the shape of the CRTA spectra is also discussed. It is stated that strong attractive interactions cause the desorption temperature to be constant. As a result of repulsive interactions two steps on the desorption temperature curve are observed. For the case of repulsive interactions between the nearest-neighbors and next-nearest-neighbors the CRTA spectra do not reveal the existence of multiple steps, contrary to the classical thermodesorption spectra (TPD) where, in such a case, multiple peaks are observed.

Monte Carlo simulations of controlled rate thermal analysis spectra: The influence of surface energetic heterogeneity and lateral interactions between adsorbed molecules

Monte Carlo simulations of controlled rate thermal analysis (CRTA) spectra are presented. Calculations are performed for a few kinds of energetically heterogeneous surface, characterized by symmetrical and unsymmetrical desorption energy distributions. It is shown that the shape of the CRTA spectra corresponds with the shape of integral form of desorption energy distribution on the surface. A simple way of estimation of the upper limit of desorption energy is proposed. The influence of lateral interactions on the shape of the CRTA spectra is also discussed. It is stated that strong attractive interactions cause the desorption temperature to be constant. As a result of repulsive interactions two steps on the desorption temperature curve are observed. For the case of repulsive interactions between the nearest-neighbors and next-nearest-neighbors the CRTA spectra do not reveal the existence of multiple steps, contrary to the classical thermodesorption spectra (TPD) where, in such a case, multiple peaks are observed.

Pyrolysis kinetics of silicon hydrides on a Si(100) surface

Specific features of the decomposition of silicon hydrides on a Si(100) surface have been considered. Simulation of thermodesorption hydrogen spectra revealed three possible ways of hydrogen desorption from the surface and the occurrence of only one bimolecular decomposition reaction of SiH2 molecules. All the kinetic parameters were unambiguously determined from the comparison of the simulated and experimental spectra. The influence of the initial surface coverage on the thermodesorption spectra is also studied.

The binding energy of molecules in thin fullerene films

Thin fullerene films formed using the methods of pulsed supersonic molecular beam (SMB) deposition and thermal deposition (TD) in vacuum were studied by thermodesorption (TDS) mass spectroscopy. The TDS spectra of SMB films show a significantly higher temperature of desorption (827.8 K) of fullerene molecules as compared to the value (583 K) observed in the spectra of TD films. It is suggested that the higher binding energies of fullerene molecules in the former films are explained by the formation of polymer structures due to heating in the course of TDS measurements.

A quantitative study of solid surface heterogeneity based on the statistical rate theory for analyzing spectra of controlled-rate thermal analysisThe work was carried out at both ICSC-PAS Krakow (Poland) and LEM-INPL Nancy (France).

Controlled-rate thermal analysis (CRTA) spectra are obtained by adjusting the heating rate in such a way that the rate of desorption can be constant. A quantitative analysis of the obtained spectra is presented, based on more refined theoretical treatment that offers new possibilities of getting more information from the experimental CRTA thermodesorption spectra. The method we propose makes it possible to obtain a desorption energy distribution function without any additional experimental information. For the purpose of illustration, an analysis is made of water desorption from a synthetic apatite mineral under CRTA conditions. Also, numerical simulations of the CRTA spectra are presented showing some basic features of the equations used for the analysis of experimental data. All calculations are based on the statistical rate theory.

Thermodesorption study of barium and strontium cerates

The method of thermodesorption spectroscopy has been used for study of kinetic of hydrogen, oxygen and water molecule release from doped and undoped barium and strontium cerates. It was found that oxygen and water molecules are released from doped barium cerate samples whereas only water molecule desorption took place from doped strontium cerate samples. Shapes of thermodesorption spectra for pure barium cerate indicate that phase transformations take place in low and high temperature regions. It was shown that oxygen molecule desorption from doped barium cerates can be described by a second-order kinetic equation and an activation energies of reaction were determined.