Approaching non-destructive surface chemical analysis of CMSX-4 superalloy with double-pulsed laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) was performed on the CMSX-4 Ni-based superalloy using a femtosecond pulsed laser. An orthogonal double-pulse technique was used to minimize surface damage associated with LIBS. With this technique, the depth of ablation craters was reduced from 200 nm for single-pulse LIBS down to less than 60 nm using orthogonal double-pulse LIBS. The technique also allowed the average velocity of the ablated material to be determined, which ranged from 4720 ± 560 m/s at a pump laser fluence of 3.1 J/cm² to 8150 ±1800 m/s at 10.1 J/cm².     

Thermogravimetric analysis of superalloys used for blade and vane applications in industrial gas turbine

The thermogravimetric analysis is the most suitable technique to study the effect of reactive gas on nickel-base superalloys used in high temperature zone for industrial gas turbines. This work presents the results of behaviour of superalloys IN 738, IN 792 and MA 6000 under environmental conditions simulating those of service in a power plant. The kinetics and the mechanism of environmental degradation on the integrity of turbine blades and vanes are discussed with reference to component performance and lifetime.     

Role of heat and gas transport processes in thermal analysis

In the course of solid phase reactions heat and gas transport processes play a dominant role. Therefore, it would be necessary to standardize the experimental conditions which succeeded only in part with the elaboration of the simultaneous techniques. Likewise the two transport processes are responsible for the fact that on the basis of non-isothermal curves one cannot calculate kinetic parameters of the reactions. The quasi static-methods seem to be suitable for the elimination of the pernicious effect of these transport processes.     

Quantitative analysis of target components by comprehensive two-dimensional gas chromatography

Quantitative analysis using comprehensive two-dimensional (2D) gas chromatography (GC) is still rarely reported. This is largely due to a lack of suitable software. The objective of the present study is to generate quantitative results from a large GC x GC data set, consisting of 32 chromatograms. In this data set, six target components need to be quantified. We compare the results of conventional integration with those obtained using so-called "multiway analysis methods". With regard to accuracy and precision, integration performs slightly better than Parallel Factor (PARAFAC) analysis. In terms of speed and possibilities for automation, multiway methods in general are far superior to traditional integration.     

Thermodynamic analysis of a process for producing high-octane gasoline components from catalytic cracking gas

The results from a thermodynamic analysis of high-octane gasoline component production from catalytic cracking gases using zeolite catalyst OMNIKAT-210P modified with Ni, Co, Cr are presented. The equilibrium constants of the reactions assumed to occur in this process are calculated, along with the equilibrium yield of the reactions.     

Solution for underflow problem in linkage and segregation analysis

Finding genes for complex traits is one of the major challenges of modern human genetics. Current developments of molecular techniques facilitated use of large pedigrees and marker sets of thousands of single-nucleotide polymorphisms (SNPs). However, one of the problems occurring in statistical analysis of such large data sets is that the likelihood is very low and underflow may easily occur. In this work we describe a method permitting to avoid underflow during computation of a likelihood function, using different algorithms. Our method makes practically possible analysis of thousands of individuals and thousands of SNPs. The method is easy to implement without major change of the code of existing programs. It also helps to reduce the amount of computer memory used in analysis without noticeable alteration of the program running time. The algorithm was implemented in the software packages for segregation and linkage analysis, which are available from http://mga.bionet.nsc.ru/.     

Formation and decomposition of gas hydrates of natural gas components

Based on our theoretical and experimental work carried out during the last decade, our understanding of the thermodynamics and the kinetics of formation and decomposition of gas hydrates is presented. Hydrate formation is modelled as a crystallization process where two distinct processes (nucleation and growth) are involved. Prior to the nucleation the concentration of the gas in the liquid water exceeds that corresponding to the vapor-liquid equilibrium. This supersaturation is attributed to the extensive structural orientation in the liquid water and is necessary for the phase change to occur. The growth of the hydrate nuclei or the decomposition of a hydrate particle are modelled as two-step procedures. Only one adjustable parameter for each hydrate forming gas is required for the intrinsic rate of formation or decomposition. In addition the inhibiting effects of electrolytes or methanol on hydrate formation are discussed and experimental data on methane gas hydrate formation in the presence of aqueous solutions of 3% NaCl and 3% NaCl + 3% KCI, are presented along with the predicted values. Finally, the relevence of the ideas to the technological implications of gas hydrates as well as areas where future research is needed are discussed.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Development and testing of granular catalysts for combustors of regenerative gas turbine plants

Two types of granular catalysts for effective methane combustion in combustors of gas turbine plants (GTPs) were developed: (1) catalysts based on noble metals with a low Pd content (1–2 wt %), characterized by a low methane ignition temperature, and (2) catalysts based on manganese oxides and hexaaluminates, which have an increased thermal stability. The methane oxidation kinetics was investigated, and combustion in the catalyst chamber of the GTP was simulated. For optimizing the combustion technology, the following two-step process using a combined catalytic package is suggested. The inlet zone of the combustor is filled with a highly active Pd catalyst, which initiates methane oxidation and ensures that the temperature at the exit of this zone is the initial temperature of methane combustion. This takes place in the next zone, which is filled with an oxide catalyst tolerant to high temperatures. The pilot testing of the catalysts was carried out in a model catalytic combustor. The results are in satisfactory agreement with calculated data. Long-term tests indicate the high stability of the catalysts. The Pd catalyst was demonstrated to retain its high activity and to provide an ignition temperature of 240°C. The initial activity of the hexaaluminate-based catalysts remains unchanged after tests at 930°C. The use of a combined charge of the palladium (7–15%) and manganese (85–93%) catalysts in the model GTP combustor allows a high natural gas combustion efficiency to be achieved at a low level of hazardous emissions (NO _x , 0–1 ppm; CO, 1–3 ppm; hydrocarbons, 3–10 ppm).     

Chemometrics-assisted gas chromatographic-mass spectrometric analysis of volatile components of olive leaf oil

Iranian olive leaf essential oil components were extracted by microwave-assisted hydrodistillation and analyzed using gas chromatography-mass spectrometry. Ninety-seven components were identified by direct similarity searches for olive leaf essential oil. Chemometrics was used to find more components with the help of multivariate curve resolution methods. Eigenvalues-based methods and Malinowski functions were used for chemical rank determination of GC–MS data. Multivariate curve resolution-alternative least squares as an iterative method was used for resolving the overlapped and embedded peaks. With the use of this method the number of 97 components was extended to 127 components. Major constituents in the olive leaf essential oil are 2-decenal-(E) (20.43 %), benzeneacetaldehyde (4.00 %), 2-undecenal (3.71 %) and valencen (3.31 %).     

Synthesis of magnesium silicate by heat treatment of sols and mechanical activation of solid components

A layered magnesium silicate, an analog to natural talc, was synthesized by mechanical treatment of a mixture of magnesium hydroxide and hydrated silicic acid powders, as well as by heat treatment of aqueous dispersions containing magnesium hydroxide particles and silica sols prepared from different precursors.     

Mechanisms effecting analysis of volatile flavour components by solid-phase microextraction and gas chromatography.

Quantitative properties of solid-phase microextraction (SPME) have been studied in order to investigate a simple and reliable method for analysing volatile flavour components in strawberries. Monitoring the chemical composition profile of berries will be of interest for the producers in order to optimise growth and storage conditions. By the use of SPME and capillary gas chromatography selected standard components were quantified with accuracy within +/-7% and a linear response were found in all concentration ranges studied, covering three orders of magnitude. Equilibrium constants that describe how various components are distributed between the three phases present, sample, headspace and fibre coating were determined. In the system studied, the majority of analytes remained in the sample. This means that repeated analysis can be performed from a single sample without significantly changing the results. The mass transfers of the flavour components, from the sample and into the fibre, were fitted to a transport model assuming that the rate-controlling step is diffusion within the fibre. The experimental results agreed well with the model for most of the components studied. The response for three of the components (geraniol, linalool and trans-2-hexenyl butanoate) did not agree with the model. These components were present in the gas phase in only minute amounts explaining the deviation from the model. Such components will require a long absorption time (longer than 30 min). For quantitative analysis, it is important to use a very precise pre-determined absorption period and well defined sampling conditions. Internal standards can be omitted.     

Wavelength-modulated fabry-perot interferometry for quantitation of trace gas components

The change in refractive index of a gas sample caused by molecular absorption is monitored by Fabry-Perot interferometry in a continuous flow system. To reduce the background noise level from other absorption processes, wavelength modulation is incorporated into the excitation laser. An enhancement in the signal-to-noise ratio of up to 146 s is found for the present method relative to intensity-modulated schemes or Stark-modulated schemes.     

Energy and exergy analysis and optimization of a gas turbine cycle coupled by a bottoming organic Rankine cycle

Journal of Thermal Analysis and Calorimetry - In this study, the numerical analysis of energy and exergy has been performed for a gas turbine cycle coupled with an ORC cycle. Validation of current...     

Improved method for the determination of sulfur components in natural gas

Determination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection. The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame-based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m³. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL.     

基于香气成分气相色谱-质谱指纹图谱的判别分析和相似度评价用于绿茶等级差异研究

该文以研究指纹图谱在绿茶等级判别方面应用的可行性为目的。以信阳毛尖茶为研究对象，以茶汤香气成分为研究目标，采用顶空固相微萃取与气相色谱-质谱联用技术，筛选其香气特征成分，建立不同等级信阳毛尖茶香气成分GC-MS指纹图谱。发现运用判别分析法可以对2个系列7个等级41个信阳毛尖茶样进行很好的等级区分；通过不同等级色谱指纹图谱的相似度计算发现，相似度与茶样等级之间具有较好的相关性，尤其是对于品质较好的茶样，这种相关性更好。表明运用判别分析法和相似度计算方法能够反映绿茶等级之间的差异性，且基于相似度评价的方法具有客观量化的特征。     

Characterization of oxide scales on coatings for gas turbine blades by infrared reflection-absorption spectroscopy

The oxidation of chromia (Cr₂O₃) and alumina (Al₂O₃) forming alloys for the protection of gas turbine blades has been studied by Infrared Reflection Absorption Spectroscopy (IRAS). The Berreman-Effect (i. e. minimum of reflectivity of p-polarized light at oblique incidence) allows an unambiguous distinction between Al₂O₃ and Cr₂O₃ for thin scales (<0.1 m) as well as for thick scales (6 m). The position of interference fringes in the non-absorbing region of the spectrum results in simultaneous thickness determinations.     

Two-dimensional gas chromatography analysis of components in fuel and fuel additives using a simplified heart-cutting GC system

Multidimensional gas chromatography (MGC) using heart cutting is an old idea that can benefit from the performance of modern instruments and capillary columns to provide fast, reliable separation of target analytes from complex sample matrices. A simplified heart-cutting switch is described that uses these improvements to provide very narrow precise heart cuts between columns of different selectivity. This system is used to analyze ppm levels of 4,6-dimethydibenzothiophene in diesel fuel using a standard flame ionization detector instead of a complex sulfur-selective detector. MGC systems also offer the possibility of faster analysis speed by using two short columns of different selectivity instead of very long columns to resolve compounds from complex matrices. The analysis of alcohols in denatured fuel ethanol using the MGC system is performed over six times faster than the standard American Society for Testing and Materials methodology.     

Separation and kinetic analysis of the thermo-oxidative reactions of polyacrylonitrile upon heat treatment

A polyacrylonitrile (PAN) homopolymer and a copolymer with methyl acrylate were analyzed by differential scanning calorimetry (DSC) in order to establish a method for the kinetic analysis of the stabilization reaction steps during heat treatment. The application of a program rarely used for the study of the chemical transformation of PAN and its copolymers resulted in five separate steps, which can be assigned with large probability to various cyclization and oxidation reactions. A more exact identification of the reactions needs further measurements and considerations. Overlapping peaks appearing in the DSC traces were deconvoluted and then quantitatively analyzed to obtain kinetic parameters. The kinetics of the processes were described by the Kissinger model. The model could be fitted well to four of the five processes that may indicate that these belong to individual reactions of the first order. The parameters obtained agree well with the few values of similar investigations published in the literature up to now. The results have large practical relevance, since the kinetic parameters obtained can be used in the preparation of intermediates and for the optimization of the stabilization process.