Evaluation of Metal Dusting Behavior in Reformer Tube Made of HP–Nb Alloy on the Outer Surfaces

The metal dusting behavior of Iron–Chromium–Nickel heat resistant HP–Nb steel specimen was investigated at the outer surfaces while the methane gas was passed inside the hole of the specimen. After an exposure of 130 h in a flowing methane (CH₄) gas at 680 °C, different dispersed corrosion products were formed on the outer surface of the specimen near the hole. Conventional metallography and scanning electron microscopy were used to identify the microstructure of the reaction products. Energy dispersive X-ray spectroscopy was used for microchemical analysis. The phases produced on the surface were identified by X-ray diffraction. Some of reaction products found as surface deposits on the outer surfaces of specimen near the hole contained Fe and Cr carbides, Fe, Cr and Ni oxides, scale of Ni, Fe particles and free C. Results revealed that carbon nano-filaments materials could be formed during disintegration of heat resistant HP–Nb steel under metal dusting environment.     

A Proposed Thermodynamic Model for Gas Hydrate Equilibrium in Electrolyte Solutions

In this work, the thermodynamic stability of gas hydrates is investigated in the presence of electrolyte solutions. The proposed model is based on the Van der Waals–Platteeuw model for gas hydrate equilibrium, and the Pitzer and Mayorga model is employed to calculate the water activity in the electrolyte solutions. Available values for the Pitzer model parameters are usually adjusted using experimental data at 25°C, which is usually higher than the gas hydrate formation temperature. In order to eliminate this problem, those adjustable parameters are re-optimized using experimental data from the literature at the lowest temperature. In the case of mixed electrolyte solutions and without using any adjustable parameters, a mixing rule is proposed to estimate the water activity. The new mixing rule is based on the ionic strength of the mixture and estimates the mixture water activity by using properties of the single electrolytes that constitute the mixture. The results show the proposed model can calculate hydrate equilibrium conditions with good accuracy, especially at low concentrations, which is the case for most industrial applications.     

Computing the Szeged and PI Indices of VC5C7[p,q] and HC5C7[p,q] Nanotubes

In this paper we give a GAP program for computing the Szeged and the PI indices of any graph. Also we compute the Szeged and PI indices of VC₅C₇ [ p,q] and HC₅C₇ [ p,q] nanotubes by this program.     

Correlation coefficients between different methods of expressing bacterial quantification using real time PCR

The applications of conventional culture-dependent assays to quantify bacteria populations are limited by their dependence on the inconsistent success of the different culture-steps involved. In addition, some bacteria can be pathogenic or a source of endotoxins and pose a health risk to the researchers. Bacterial quantification based on the real-time PCR method can overcome the above-mentioned problems. However, the quantification of bacteria using this approach is commonly expressed as absolute quantities even though the composition of samples (like those of digesta) can vary widely; thus, the final results may be affected if the samples are not properly homogenized, especially when multiple samples are to be pooled together before DNA extraction. The objective of this study was to determine the correlation coefficients between four different methods of expressing the output data of real-time PCR-based bacterial quantification. The four methods were: (i) the common absolute method expressed as the cell number of specific bacteria per gram of digesta; (ii) the Livak and Schmittgen, ΔΔCt method; (iii) the Pfaffl equation; and (iv) a simple relative method based on the ratio of cell number of specific bacteria to the total bacterial cells. Because of the effect on total bacteria population in the results obtained using ΔCt-based methods (ΔΔCt and Pfaffl), these methods lack the acceptable consistency to be used as valid and reliable methods in real-time PCR-based bacterial quantification studies. On the other hand, because of the variable compositions of digesta samples, a simple ratio of cell number of specific bacteria to the corresponding total bacterial cells of the same sample can be a more accurate method to quantify the population.     

Tribological behaviour of semisolid–semisolid compocast Al–Si matrix composites reinforced with TiB2 coated B4C particulates

The purpose of this paper is to provide a deeper understanding of the wear behavior of the sol–gel coated B₄C particulate reinforced A356 matrix composites. A typical microstructure of the composite consists of relatively large primary phase globules which are surrounded by B₄C particles. In fact the globules themselves are B₄C particles free and consequently the sample is not homogeneous on a scale smaller than the globule size. The wear sliding test disclosed that the wear rate of the coated B₄C reinforced composites is less than that of the unreinforced alloy and decreases with increasing volume fraction of B₄C particulates. As the hardness of the composites is higher, this reduces the cutting efficiency of the abrasives and consequently the abrasion wear loss. Once the particles fracture or loosen from the matrix alloy, they can be removed easily from the matrix, contributing to the material loss. Two kinds of debris present irregular-shaped flake, which has withstood a large of plastic deformation and then pull off from the surface. During the sliding wear, Iron is transferred to the surface of the composites from the steel counterface forming the iron-rich layer on the contact surfaces which increases with increasing the B₄C content and is substantially harder than the bulk material largely because it contains a fine mixture of Fe phase, Al and B₄C.     

On the stability of a microbeam conveying fluid considering modified couple stress theory

In this paper, the size-dependent vibrational behavior of a microbeam conveying fluid was investigated using the Modified Couple Stress Theory. For cantilever and clamped-clamped microbeams, the small amplitude vibration equation of the micro-beams was solved using a Galerkin based reduced order model and the effects of material length-scale parameter on its natural frequencies were evaluated. It was found that for the both cantilever and clamped-clamped conditions, the critical fluid velocities predicted by the modified couple stress theory are higher than those predicted by the classical beam theory. In addition, the differences between the eigen-frequencies and the critical fluid velocities predicted by the modified couple stress theory and classical beam theory depends on the ratio of the material length-scale parameter to the beam height. In addition an unexpected result in the difference between the first eigen-frequency of the cantilever micro-beam obtained by the classical and the modified couple stress theory has been achieved.     

Synthesis and properties of new thermally stable poly(amide-imide)s containing flexible ether moieties

Six new poly(amide-imide)s (PAIs) 8a-f were synthesized from the direct polycondensation reaction of 1,1-bis[4-(trimellitimido)phenoxy]methane 6 with various aromatic diamine 7a–f. The polymerization reactions produced a series of thermally stable and organosoluble PAIs with high yield and good inherent viscosity. The resulted polymers were fully characterized by means of FTIR and ¹H-NMR spectroscopy, elemental analyses, inherent viscosity, and solubility tests. Also thermal properties of the PAIs 8a–f were investigated using thermal gravimetric analysis (TGA) and derivative of thermaogravimetric (DTG) analysis. dicarboxylic acid 6 was synthesized from the reaction of 1,1-bis[4-aminophenoxy]methane 4 with trimellitic anhydride 5 in a solution of glacial acetic acid/pyridine (Py) at refluxing temperature.     

The Calculation of Oil-water Relative Permeability From Capillary Pressure Data in an Oil-wet Porous Media: Case Study in a Dolomite Reservoir

Estimating relative permeability curves from capillary pressure data is a well-known technique and the reliability of these techniques for approximation of liquid-gas relative permeability curves had thoroughly investigated. However, there is not enough information to conclude which method is the standard one for calculating oil-water relative permeability curves. The authors utilized various capillary pressure techniques such as the Corey, Brooks-Corey, Li-Purcell, and Li-Burdine methods to calculate oil-water relative permeabilities using the measured oil-water capillary pressure data in drainage process in an oil-wet Dolomite reservoir. Despite wide popularity of Purcell and Burdine methods for calculating relative permeability, the authors used new Li-Purcell and Li-Burdine methods. The calculated results were compared to the experimental data of oil-water relative permeabilities measured in a Dolomite reservoir. The Corey and Brooks-Corey models show an acceptable and nearly exact match with the measured oil relative permeability values. However, the Li-Purcell and Li-Burdine models underestimate the values for wetting phase in most cases. It is also worth mentioning that, except Li-Purcell method, the results of all other methods for calculating nonwetting phase relative permeability are almost the same and they are in good agreement with the measured data. Results of this work reveal that calculation of oil-water relative permeability using the capillary pressure data is also a reliable technique in oil-wet systems.