Range Of Wall Thicknesses Research Articles

Finite Element Analysis of Axial Compression Performance of Stainless Steel -Steel Tube Sandwich Concrete Columns

A finite element analysis software, ABAQUS, was used to numerically analyze nine specimens with varying inner steel tube thickness and slenderness ratio to study the axial compression performance of stainless steel - steel tube sandwich concrete columns. The influence of each parameter on the axial compression behavior was explored. The simulation results aligned closely with the experimental results, with the ultimate bearing capacity prediction error within 5%. Bulging deformation consistently occurred on the upper outer steel tube. Increasing the inner steel tube thickness improved the ultimate bearing capacity up to 20%, with the 4-6 mm wall thickness range providing the most effective capacity increase. The ultimate bearing capacity deteriorated up to 5% as the slenderness ratio increased, but the axial compression stiffness markedly decreased due to overall instability. A relationship between the stability coefficient and slenderness ratio was proposed, and the calculation results showed excellent agreement.

Investigation of The Effect of Reduced Shank Thickness of Friction Welded Yoke Shaft on Strength

Usage of friction welding method on the joints provides many advantages such as cost reduction, weight reduction and higher quality. The yoke shaft produced by rotary friction welding (RFW) involves a yoked part and a hollow round bar which are welded to each other. And so, no additional drilling method used in the way of removing material from the centre of the yoke shaft, is required to reduce the weight. The weight is inherently reduced thanks to hollow round bar used in RFW method. It is possible to use a friction welded yoke shaft in a wide range of wall thickness by removing material from the shank diameter for different applications. At this point, the key factor is strength of the friction welded yoke shaft with reduced wall thickness on the shank diameter. The aim of this study is investigation the effect of the reduced wall thickness of a yoke shaft produced by RFW on the strength. For this purpose, yoke shafts were manufactured by using RFW and consecutive processes such as turning and millings to reduce the wall thickness. The specimens in different wall thickness were tested to determine the strength. Additionally finite element analyses (FEAs) were implemented for each variation of the specimens and compared with the test results. As a result, it was determined that yoke shafts with reduced wall thicknesses, which were produced by RFW and then consecutively machining operations to obtain a specific wall thickness, can be used in drive shaft manufacturing securely.

An analysis of the influence of atrial wall thickness on the protective effects of proactive esophageal cooling during high-power short-duration radiofrequency ablation

Abstract Background The use of proactive esophageal cooling using a dedicated cooling device during radiofrequency (RF) left atrial ablation has increased, with endoscopic studies showing reductions in esophageal lesions using medium power ablation settings. With no atrioesophageal fistula yet identified using esophageal cooling, and clinical practice increasingly shifting to high-power short-duration (HPSD) ablation, additional data on the protective potential of this technique in HPSD ablation may help guide RF ablation strategies. In particular, a better understanding of the effects of anatomical variations in myocardial thickness on cooling efficacy is warranted. Purpose We sought to evaluate the influence of atrial wall thickness on the protective effects of proactive esophageal cooling during HPSD ablation. Methods Using a computer model of the left atrium and esophagus, we analyzed the esophageal damage that occurs under two HPSD ablation conditions (50 W for 10 s and 90 W for 4 s) with and without proactive esophageal cooling while varying atrial wall thickness. Injury to the esophagus was quantified using the Arrhenius equation as well as by determining the percentage of tissue reaching a 50°C lethal isotherm. Atrial thickness was varied between 0.6 mm to 2.0 mm. Esophageal cooling was set to the recommended 4°C coolant temperature. Results Using 50 W power settings in control (non-cooled) conditions, esophageal lesion transmurality ranged from 75% to 82% as calculated by the Arrhenius equation, with decreased transmurality seen as atrial wall thickness increased. With the addition of proactive cooling, lesion transmurality decreased to less than 43% in the thinnest atrial wall sections, and to less than 25% in the thickest atrial wall sections. Using 90 W power settings, control conditions showed esophageal lesion transmurality ranging from 52% to 63%, with the greatest damage seen in the middle-range atrial thicknesses (1 and 1.5 mm). Active esophageal cooling reduced this esophageal injury to less than 12% transmurality through the esophagus in all anatomic scenarios. Conclusions Modeling suggests that the use of proactive esophageal cooling significantly reduces esophageal lesion transmurality under HPSD ablation conditions across a range of typical atrial wall thicknesses, including in very thin myocardium, where the risk of esophageal injury is greatest. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): Attune

Lateral load response of large-diameter monopiles in sand

Due to the increasing demand for renewable clean energy, there has been rapid growth in the development of offshore wind energy resources in recent years. The majority of offshore wind turbines are founded on single, large-diameter, open-ended pipe piles known as monopiles. The design of these piles is often done using the p–y method, which models the soil simply as non-linear springs placed along the pile length and assumes the pile to behave as a one-dimensional beam. To develop a design method that accounts for three-dimensional pile–soil interaction and that is applicable to general conditions, a series of finite-element (FE) analyses covering a wide range of pile dimensions, wall thicknesses, slenderness ratios, load eccentricities, sand types and sand relative densities were performed using an advanced sand constitutive model. In this paper, a set of equations is proposed that can be used to estimate the critical pile length, Lcrit (the pile length beyond which the pile lateral capacity no longer increases), the lateral capacity, H, and the lateral load–rotation curve for monopiles. The proposed method produces estimates of the lateral capacity of monopiles that are in very close agreement with those from the FE analyses.

Precision Ultrasonic Measurement of Fluid Level through a “Thick” Steel Wall

Issues of the fluid level measurement through a steel wall are considered. When level measuring by signal propagation time, correlation-phase reception of complex signals provides the best accuracy. However, when such signals pass through an elastic wall, distortions of their phase structure occur. These distortions are associated with vibrations of the thickness resonances of longitudinal and transverse waves and with propagation of other nonresonance vibrations in the wall, which are interferences for the useful signal passing through the wall and the fluid layer. Herewith, to ensure the small distortions of the received signal, it is necessary to choose the characteristics of the probing signal “correctly”. Therefor it is necessary to determine regularities of wave propagation of different frequencies through the wall and in the wall. The aim of this study is to determine the mechanisms of the received signal forming, to develop the methods for the optimal probing signal forming, and to determine a possibility of correlation-phase reception using and an achievable measurement accuracy.A scheme for received signal forming is proposed. It considers a signal passing through the wall and the fluid layer; the signals of the thickness resonance vibrations of the longitudinal waves propagating through the wall and the fluid layer; the signals of the thickness resonance vibrations of the transverse waves propagating in the wall, and the signals of the nonresonance vibrations propagating in the wall. The methods for the level estimation of the referred above vibrations (and their signals) based on Lamb’ wave theory are suggested. These methods permit to predict the characteristics and spectra of the received signals. A technique for estimation of the phase structure distortions and correlation coefficient of received signal in accordance with spectral component relationship is proposed. A technique for the forming of the optimal probing signal that provides small distortions of the received signal and high correlation coefficient is propound.The theoretical estimates of the received signal spectra in different frequency ranges are given. Experimental proof of these spectra found. The theoretical estimates of the probing signal parameters providing small phase structure distortions of the received signals are given. Experimental proof of the effectiveness of such signal using found. The theoretical estimates of the ratio of the useful signal to interference in different frequency ranges are given. It is shown experimentally for a plate of 14.5 mm thick that this ratio is large in high- and mid-frequency range (597–791, 395–593 kHz), in that case a qualitative operation of a meter is ensured. This ratio is fewer in low-frequency range (197–395 kHz), but the meter’s operability is hold true. The ratio is small at lower frequencies and operability ensuring is problematic. Experimental measurements show that in the case of optimal signal using the time measurement error for all frequency ranges do not exceed 1 μs, the correlation coefficient is ~0.84–0.92 at high-frequency range, ~0.78–0.90 at mid-frequency range, and ~0.45–0.65 at low-frequency one.Application of correlation-phase reception the complex signals for time (level) measurement through a “thick” steel wall is possible at optimal probing signal parameters; it provides more effective operation and greater measurement accuracy compared to other known methods and devices. One can expect that such high indicators of accuracy and operational efficiency will hold true for a wide range of wall thicknesses, level of fluid and its characteristics.

A novelly universal theory: Toward accurately evaluating radial vibration characteristics for radially sandwiched spherical piezoelectric transducer

With the development of ultrasonic technology, some ultrasonic processing technologies require a wide processing range. In this paper, a radially sandwiched spherical piezoelectric transducer is proposed and analyzed, which is composed of a spherical piezoelectric ceramic sandwiched by two concentric spherical metal shells. The electromechanical equivalent circuits of the spherically isotropic spherical shell and the spherical piezoelectric ceramic with arbitrary wall thickness are derived from their motion equations. According to the mechanical boundary conditions, the electromechanical equivalent circuits and frequency equation of various piezoelectric composite vibration systems can be obtained, including the radially sandwiched spherical piezoelectric transducer. The correctness of the proposed theory is verified via comparison with the finite element method and the previous theoretical model. In addition, the 2nd-order effective mechanical coupling coefficient for the radially sandwiched spherical piezoelectric transducer is higher than that of 1st-order within a specific range of wall thickness, which can be designed as the high-frequency transducer. The radially sandwiched spherical piezoelectric transducer is expected to be used in underwater sound, structural health monitoring, and high-frequency ultrasound.

Damage effect of steel circular tube subjected to fire and blast

Q345B steel circular tubes are widely applied in structural engineering applications, such as offshore platforms, bridges, and other structures, and they face potential risks of being subjected to the external loads of fires, explosions, or both during their service lives. In this study, the damage of Q345B steel circular tubes due to the combined action of fire and blast loading were analyzed. A specialized experimental platform was built, and experiments were performed on Q345B steel tubes with a range of wall thicknesses (a), fire loading durations (t), and stand-off distances (R) which means the distance between the bottom of the explosive and the upper surface of tube. The experimental local deflection, compressed degree, and local deformation volume are presented and studied in a quantitative manner. As the fire duration increased, the specimens underwent more noticeable deformation and damage. The local deflection amounts of the specimens treated with fire increased by 20%–50% compared to that of the specimen not exposed to fire at R = 17 cm. When R = 12 cm, the local deflection increased by 20%–120%. In addition, based on the stress–strain curves, the effects of the blue brittleness of the Q345B steel materials on the anti-blast performances of the specimens were examined. Finally, scanning electron microscopy was employed to explore the rupturing mechanism under a microscope.

Uncertainty quantification of wall thickness of onshore gas transmission pipelines

The present study quantifies probabilistic characteristics of the wall thickness of welded pipe joints in onshore gas transmission pipelines based on about 5900 field-measured wall thicknesses collected from a pipeline system in Canada. The collected data cover a wide range of pipe nominal wall thicknesses, from 3.18 to 16.67 mm. By considering the measurement error involved in the collected wall thickness data, statistical analyses indicate that the actual-over-nominal wall thickness ratio (AONR) follows a normal distribution with a mean of 1.01 and a coefficient of variation (COV) ranging from 1.6% to 2.2% depending on the nominal pipe wall thickness. The implications of the developed AONR statistics for the reliability analysis of corroded pipe joints are investigated. This study provides key input to the reliability-based design and assessment of pipelines with respect to various threats, such as metal-loss corrosion and stress corrosion cracking.

Elastic response of hollow truss lattice micro-architectures

Elastic meta-materials, which we will treat herein as synonymous with elastic micro-architected materials, derive their unique combination of properties from the fine scale geometry of their solid and void regions. Recent advances in additive manufacturing have made the fabrication of such micro-architected materials feasible, and have driven interest in their properties. We consider the class of elastic meta-materials whose micro-architectures are composed of a network of straight struts connected at nodes arranged within a repeating unit cell; the octet truss is one well-known example of such truss lattices. Heretofore, the majority of work characterizing such truss lattices has considered solid struts and has been based on rod theory, a simplification of continuum elasticity which is accurate in the limit of low relative densities. In this paper, we use full continuum theory, solved with finite element analysis on adaptively refined meshes, to characterize the elastic performance of seven truss lattices with cubic geometric symmetry, and whose struts and nodes are hollow; we consider a wide range of strut wall thicknesses and truss relative densities. Varying the wall thickness provides an additional dimension of control, so that stiffness and anisotropy can, to an extent, be decoupled from the relative density of a given truss lattice. We show that a truss’ stiffness can be increased at fixed relative density, with bend-dominated truss lattices showing significantly greater improvement than stretch-dominated designs. Increases in stiffness by a factor of greater than five are observed, and increases by a factor of 100 or more are obtainable. Bend-dominated structures with hollow struts can be found that are stiffer than stretch-dominated ones at nearly all relative densities, contradicting a common rule of thumb. For some trusses, including the octet truss, choosing the wall thickness appropriately allows one to obtain isotropic response over a large range of volume fractions. We use topology optimization to find maximally stiff multiscale structures comprised of micro-architected materials and find that all the trusses we consider perform similarly, with anisotropic trusses resulting in slightly stiffer structures for a given load.

Simultaneous Extraction of Multiple Parameters From a Transmit–Receive Eddy Current Probe Above a Layered Planar Conductive Structure

Abstract A validated analytical model of a transmit–receive coil pair situated above two parallel plates, separated by an air gap, was used as the basis for an inversion algorithm (IA) to extract probe liftoff, second layer plate resistivity, and plate-to-plate gap from multi-frequency eddy current data. The IA was tested over a large range of first layer wall thickness (3.80–4.64 mm), second layer plate resistivity (1.7–174 µΩ cm), second layer wall thickness (1.20–4.85 mm), probe liftoff (2.8–7.9 mm), and plate-to-plate gap (0–13.3 mm). At nominal liftoff (2.8 mm), the IA achieved a gap measurement accuracy of ±0.7 mm and was able to return good estimates of the second layer resistivity within ±1 μΩ cm for low resistivity samples, but with decreasing accuracy for higher resistivities. When the gap was fixed, the IA was able to measure changes in probe liftoff (relative to nominal) to an accuracy of ±0.2 mm. The reported accuracy and a demonstration for the ability to accurately estimate parameters outside of the calibration range provide confidence in the potential utility of the algorithm.

Controllability Over Wall Thickness of Tubular Structures and Encapsulation During Co-Axial Extrusion of a Thermal-Crosslinking Hydrogel

AbstractTubular structures of the hydrogel are used in a variety of applications such as delivering nutrient supplies for 3D cell culturing. The wall thickness of the tube determines the delivery rate. In this study, we used the coaxial extrusion process to fabricate tubular structures with varying wall thicknesses using a thermal-crosslinking hydrogel, gellan gum (GG). The objectives of this study are to investigate the thermal extrusion process of GG to form tubular structures, the range of achievable wall thickness, and a possibility to form tubular structures with closed ends to encapsulate fluid or drug inside the tube. The wall thickness is controlled by changing the relative flow velocity of the inner needle (phosphate-buffered saline, PBS) to the outer needle, while keeping the velocity of outer needles (GG) constant. Two pairs of coaxial needles were used which are 18-12 gauge (G) and 20-12G. The controllable wall thickness ranges from 0.618 mm (100% relative velocity) to 0.499 mm (250%) for 18-12G and from 0.77 mm (80%) to 0.69 (200%) for 20-12G. Encapsulation is possible in a smaller range of flow velocities in both needle combinations. A finite element model was developed to estimate the temperature distribution and the wall thickness. The model is found to be accurate. The dynamic viscosity of GG determines the pressure equilibrium and the range of achievable wall thickness. Changing the inner needle size or the flow velocity both affect the heat exchange and thus the temperature-dependent dynamic viscosity.

Wall thickness dependencies of carbon nanotube reinforced nanocomposites

Indentation analyses are conducted to investigate the CNT’s wall thickness dependencies of the mechanical properties of nanocomposites. This study incorporates Berkovich nanoindentation analyses for chemically non-bonded CNT/matrix interface, including the size effects of nanocomposites. For non-bonded interface, the properties of nanocomposite are generally controlled by mechanical interlocking, thermal residual stress, Poisson’s contraction and van der Waal’s (vdW) interaction between CNT and matrix. Considering all these parameters, a series of finite element models for nano-indentation tests have been constructed, aiming to investigate the mechanical properties of CNT reinforced nanocomposites. The model is validated and numerical results are compared with that of existing experimental indentation test. Analysis has been run for ten different wall thicknesses of CNTs in a range of wall thickness starting from 0.034 nm to 0.334 nm. Elasto-plastic behavior of steel and CNT including strain gradient is considered in the program. The study on wall thickness dependencies of CNTs in nanocomposite shows that mechanical properties of nanocomposites largely depends on the wall thickness of CNTs. A minimum wall thickness for a particular tube diameter to achieve a pick value of hardness and modulus of elasticity of nanocomposites is determined. The minimum wall thickness of CNTs is suggested to be 0.2 for an outer diameter of 1nm in order to achieve the maximum value of composite properties. In addition, a wall thickness smaller than 0.05 nm may even reduce the hardness and modulus of elasticity of CNT reinforced composites compare to that of pure matrix.

A Novel Fabrication Method for Compliant Silicone Phantoms of Arterial Geometry for Use in Particle Image Velocimetry of Haemodynamics

Cardiovascular diseases (CVDs) are one of the leading causes of death globally. In-vitro measurement of blood flow in compliant arterial phantoms can provide better insight into haemodynamic states and therapeutic procedures. However, current fabrication techniques are not capable of producing thin-walled compliant phantoms of complex shapes. This study presents a new approach for the fabrication of compliant phantoms suitable for optical measurement. Two 1.5× scaled models of the ascending aorta, including the brachiocephalic artery (BCA), were fabricated from silicone elastomer Sylgard-184. The initial phantom used the existing state of the art lost core manufacturing technique with simple end supports, an acrylonitrile butadiene styrene (ABS) additive manufactured male mould and Ebalta-milled female mould. The second phantom was produced with the same method but used more rigid end supports and ABS male and female moulds. The wall thickness consistency and quality of resulting stereoscopic particle image velocimetry (SPIV) were used to verify the fidelity of the phantom for optical measurement and investigation of physiological flow fields. However, the initial phantom had a rough surface that obscured SPIV analysis and had a variable wall thickness (range = 0.815 mm). The second phantom provided clear particle images and had a less variable wall thickness (range = 0.317 mm). The manufacturing method developed is suitable for fast and cost-effective fabrication of different compliant arterial phantom geometries.

Crushing behaviors of hierarchical sandwich-walled columns

Hierarchical structures have better mechanical properties as a widely observed organization form in nature. In this paper, a series of sandwich-walled columns (SWCs) with different sandwich cells are proposed based on hierarchical route for obtaining more weight-effective protective structures. The finite element model is firstly validated via experiment testing. Then, the crushing behaviors of SWCs, regular multi-cell columns (MCs) and single-cell column (SC) under axial load are analyzed. The results show that the hierarchical sandwich design has more remarkable potential to improve mechanical behavior than regular multi-cell design, and the effect of hierarchical level N is significant for the mechanical properties. Next, the theoretical models of mean crushing force (Fm), specific energy absorption (SEA) are derived to deeply analyze the collapsing mechanism of the SWCs, and the low errors of the theoretical predictions indicate their high accuracy. Furthermore, the technique for ordering preferences by similarity to ideal solution (TOPSIS) evaluates the crashworthiness performances of all thin-walled structures, the square sandwich cell with N = 6 (S-6) is selected because of its ideal cross-section, and the wall thickness range for optimal crashworthiness in feasible design space is identified. This study offers a novel idea of designing lightweight structure with high energy absorption capacity for the crashworthy requirement.

Design and analysis of the influence of cladding tubes on novel THz waveguide

A novel terahertz (THz) waveguide was theoretically designed based on polymethylmethacrylate (PMMA) negative curvature fiber. The confinement loss decreased 3.5 times when there were optimum gaps between adjacent cladding tubes of the fibers with six tubes. Confinement loss as low as 0.08 dB/cm and transmission bandwidth of 700 GHz were obtained when the tube wall thickness and gap range of the fiber were 40 μm and 357–416.5 μm, respectively, and the power ratio of the proposed fiber was as high as 99%. When the fiber had six surrounding tubes, the optimum gap was 6 times larger than the optimum gaps in fibers composed of eight or ten surrounding tubes. The PMMA negative curvature fibers with a broad range of gap made it well-suited for THz transmission with low confinement loss and wide bandwidth.

An experimental study of localized bulging in inflated cylindrical tubes guided by newly emerged analytical results

An experimental study is conducted on localized bulging of inflated latex rubber tubes of a range of wall thicknesses and tube lengths, guided by newly emerged analytical results. In the case when the tube has one free closed end that may or may not be subjected to a dead weight, the initiation pressure for localized bulging is determined by a bifurcation condition, and the propagation pressure is determined by Maxwell’s equal-area rule. It is shown that after bulge initiation the pressure will decrease monotonically towards, but will never reach, the propagation pressure, and it is when the pressure is sufficiently close to this propagation pressure that rapid propagation of the bulge in the axial direction takes place. It is found that the experimentally observed initiation pressure is around 15% below the theoretical prediction, which is consistent with the fact that bulging initiation is a sub-critical phenomenon and is therefore sensitive to imperfections. The experimentally observed propagation pressure is always very close to the theoretical prediction, which confirms the insensitivity of this pressure to imperfections and demonstrates the predictive power of the material model fitted from our own experiments on equibiaxial stretching. In the other case when the tube is first stretched and then fixed at both ends, bulge initiation takes place in the same manner as in the previous case, but the propagation pressure is no longer determined by Maxwell’s equal-area rule. After bulge initiation the pressure will first decrease to a minimum and then rises slowly, and it is on the latter ascending path that the bulge starts to propagate rapidly in the axial direction. A semi-analytical method is proposed for the determination of the minimum pressure. Numerical simulations with the use of the software Abaqus are also conducted to verify the theoretical predictions.

Nonlinear resonances of an idealized saccular aneurysm

This paper investigates the occurrence of dynamic instabilities in idealized intracranial saccular aneurysms subjected to pulsatile blood flow and surrounded by cerebral spinal fluid. The problem has been approached extending the original 2D model of Shah and Humphrey (1999) to a 3D framework. The justification for using a 3D formulation arises from the works of Suzuki and Ohara (1978), MacDonald et al. (2000) and Costalat et al. (2011) who showed experimental evidences of intracranial aneurysms with a ratio between wall thickness and inner radius larger that 0.1. Two different material models have been used to describe the mechanical behaviour of the aneurysmal wall: Neo-Hookean and Mooney–Rivlin. To the authors' knowledge, for the first time in literature, the dynamic response of the aneurysm has been analysed using complete nonlinear resonance diagrams that have been obtained from a numerical procedure specifically designed for that purpose. Our numerical results show that, for a wide range of wall thicknesses and both constitutive models considered, the saccular aneurysms are dynamically stable within the range of frequencies associated to the normal heart rates, which confirms previous results of Shah and Humphrey (1999). On the other hand, our results also show that the geometric and material nonlinearities of the problem could bring closer than expected the resonance frequencies of the aneurysm to the frequencies of the pulsatile blood flow.

Numerical and Experimental Investigation of the Hydrostatic Performance of Fibre Reinforced Tubes

The increasing demands in subsea industry such as oil and gas, led to a rapidly growing need for the use of advanced, high performance, lightweight materials such as composite materials. E-glass fibre laminated pre-preg, filament wound and braided tubes were tested to destruction under hydrostatic external pressure in order to study their buckling and crushing behaviour. Different fibre architectures and wind angles were tested at a range of wall thicknesses highlighting the advantage that hoop reinforcement offers. The experimental results were compared with theoretical predictions obtained from classic laminate theory and finite element analysis (ABAQUS) based on the principal that the predominant failure mode was buckling. SEM analysis was further performed to investigate the resulting failure mechanisms, indicating that the failure mechanisms can be more complex with a variety of observed modes taking place such as fibre fracture, delamination and fibre-matrix interface failure.

CFD simulation of the thermal performance of an opaque water wall system for Australian climate

The thermal performance of an opaque water wall system is numerically investigated using the shear-stress transport (SST) k–ω turbulence model and the Discrete Ordinates radiation model for typical winter and summer climate conditions in Sydney, Australia. With a periodic sol-air temperature specified on the outside Perspex panel, the energy performance of the water wall system is examined over a range of water wall thicknesses. The computational fluid dynamics (CFD) model is compared with an experimentally validated transient heat balance model (THBM), and a fair agreement between the CFD model and the THBM results is achieved. The present numerical results indicate that the performance of the opaque water wall system is improved by increasing the thickness of the water column under the winter climate condition in Sydney. It is also found that less supplementary energy is required in winter than that in summer in order to maintain a comfortable interior temperature. Further, a comparison between the present water wall system and a conventional concrete wall system shows that the water wall system performs significantly better than the concrete wall system of the same thickness in the winter climate of Sydney, whereas both the water wall and concrete wall systems have a similar performance in terms of energy savings in the summer climate of Sydney.

A new method for the generation of realistic atomistic models of siliceous MCM-41

A new method is outlined for constructing realistic models of the mesoporous amorphous silica adsorbent, MCM-41. The procedure uses the melt-quench molecular dynamics technique. Previous methods are either computationally expensive or overly simplified, missing key details necessary for agreement with experimental data. Our approach enables a whole family of models spanning a range of pore widths and wall thicknesses to be efficiently developed and yet sophisticated enough to allow functionalisation of the surface – necessary for modelling systems such as self-assembled monolayers on mesoporous supports (SAMMS), used in nuclear effluent clean-up.The models were validated in two ways. The first method involved the construction of adsorption isotherms from grand canonical Monte Carlo simulations, which were in line with experimental data. The second method involved computing isosteric heats at zero coverage and Henry law coefficients for small adsorbate molecules. The values obtained for carbon dioxide gave good agreement with experimental values.We use the new method to explore the effect of increasing the preparation quench rate, pore diameter and wall thickness on low pressure adsorption. Our results show that tailoring a material to have a narrow pore diameter can enhance the physisorption of gas species to MCM-41 at low pressure.