An atomic layer deposition diffusion-reaction model for porous media with different particle geometries.

This work presents a diffusion-reaction model for atomic layer deposition (ALD), which has been adapted to describe radial direction reactant transport and adsorption kinetics in a porous particle. Specifically, we present the effect of three particle geometries: spherical, cylindrical and a slab in the diffusion-reaction model. The reactant diffusion propagates as a unidimensional front inside the slab particle, whereas with cylinder and spherical particles, the reactant diffusion approaches the particle centre from two and three dimensions, respectively. Due to additional reactant propagation dimensions, cylindrical and spherical particles require less exposure for full particle penetration. In addition to the particle geometry effect, a sensitivity analysis was used to compare the impact of the particles' physical properties on the achieved penetration depth. The analysis evaluates properties, such as the combined porosity and tortuosity factor, mean pore diameter, specific surface area, pore volume, and particle radius. Furthermore, we address the impact of the reactant molar mass, growth-per-cycle (GPC), sticking probability, reactant exposure and deposition temperature on the simulated diffusion and surface coverage profiles. The diffusion-reaction model presented in this work is relevant for the design and optimization of ALD processes in porous media with different particle geometries.

Modelling atomic layer deposition overcoating formation on a porous heterogeneous catalyst.

Atomic layer deposition (ALD) was used to deposit a protective overcoating (Al2O3) on an industrially relevant Co-based Fischer-Tropsch catalyst. A trimethylaluminium/water (TMA/H2O) ALD process was used to prepare ∼0.7-2.2 nm overcoatings on an incipient wetness impregnated Co-Pt/TiO2 catalyst. A diffusion-reaction differential equation model was used to predict precursor transport and the resulting deposited overcoating surface coverage inside a catalyst particle. The model was validated against transmission electron (TEM) and scanning electron (SEM) microscopy studies. The prepared model utilised catalyst physical properties and ALD process parameters to estimate achieved overcoating thickness for 20 and 30 deposition cycles (1.36 and 2.04 nm respectively). The TEM analysis supported these estimates, with 1.29 ± 0.16 and 2.15 ± 0.29 nm average layer thicknesses. In addition to layer thickness estimation, the model was used to predict overcoating penetration into the porous catalyst. The model estimated a penetration depth of ∼19 µm, and cross-sectional scanning electron microscopy supported the prediction with a deepest penetration of 15-18 µm. The model successfully estimated the deepest penetration, however, the microscopy study showed penetration depth fluctuation between 0-18 µm, having an average of 9.6 µm.

Ultrasound irradiation as an effective tool in synthesis of the slag-based catalysts for carboxymethylation.

Waste minimization strategy was applied in the current work for synthesis of the catalysts from industrial solid waste, namely desulfurization slag. The starting slag material comprising CaCO3, Ca(OH)2, SiO2, Al2O3, Fe2O3, and TiO2 was processed by various treating agents systematically varying the synthesis parameters. A novel efficient technique - ultrasound irradiation, was applied as an additional synthesis step for intensification of the slag dissolution and crystallization of the new phases. Physico-chemical properties of the starting materials and synthesized catalysts were evaluated by several analytical techniques. Treatment of the industrial slag possessing initially poor crystal morphology and a low surface area (6 m2/g) resulted in formation of highly-crystalline catalysts with well-developed structural properties. Surface area was increased up to 49 m2/g. High basicity of the neat slag as well as materials synthesized on its basis makes possible application of these materials in the reactions requiring basic active sites. Catalytic performance of the synthesized catalysts was elucidated in the synthesis of carbonate esters by carboxymethylation of cinnamyl alcohol with dimethyl carbonate carried out at 150 °C in a batch mode. Ultrasonication of the slag had a positive effect on the catalytic activity. Synthesized catalysts while exhibiting similar selectivity to the desired product (ca. 84%), demonstrated a trend of activity increase for materials prepared using ultrasonication pretreatment. The choice of the treating agent also played an important role in the catalytic performance. The highest selectivity to the desired cinnamyl methyl carbonate (88%) together with the highest activity (TOF35 = 3.89*10-7 (mol/g*s)) was achieved over the material synthesized using 0.6 M NaOH solution as the treating agent with the ultrasound pre-treatment at 80 W for 4 h.

Key roles of carbon solubility in single-walled carbon nanotube nucleation and growth.

Elucidating the roles played by carbon solubility in catalyst nanoparticles is required to better understand the growth mechanisms of single-walled carbon nanotubes (SWNTs). Here, we highlight that controlling the level of dissolved carbon is of key importance to enable nucleation and growth. We first performed tight binding based atomistic computer simulations to study carbon incorporation in metal nanoparticles with low solubilities. For such metals, carbon incorporation strongly depends on their structures (face centered cubic or icosahedral), leading to different amounts of carbon close to the nanoparticle surface. Following this idea, we then show experimentally that Au nanoparticles effectively catalyze SWNT growth when in a face centered cubic structure, and fail to do so when icosahedral. Both approaches emphasize that the presence of subsurface carbon in the nanoparticles is necessary to enable the cap lift-off, making the nucleation of SWNTs possible.

Water and carbon oxides on monoclinic zirconia: experimental and computational insights.

Zirconium oxide (ZrO2, zirconia) is an interesting catalytic material to be used in biomass conversion, e.g., gasification and reforming. In this work, we show that reducing and hydrating pretreatments affect the surface sites on monoclinic zirconia. The multitechnique approach comprises temperature-programmed surface reactions (TPSR) under CO and CO2 at 100-550 °C, in situ DRIFTS investigations of the surface species and density functional theory (DFT) calculations. The key findings of the work are: (1) formates are formed either directly from gas-phase CO on terminal surface hydroxyls or via the linear CO surface species that are found exclusively on the reduced zirconia without water treatment; (2) formates are able to decompose at high temperature either reversibly to CO or reductively to CO2 and H2via surface reaction between formates and multicoordinated hydroxyls; and (3) a new weak reversible binding state of CO is found exclusively on ZrO2 that is first reduced and subsequently hydrated.

Precise determination of the threshold diameter for a single-walled carbon nanotube to collapse.

Closed-edged bilayer graphene nanoribbons were formed by the spontaneous collapse of large-diameter single-walled carbon nanotubes (SWNTs) grown on gold nanoparticles by chemical vapor deposition. Such bilayer graphene nanoribbons could adopt different stacking configurations, such as AB-stacking or stacking order with any rotation angle, correlated with the chiral angles of their parent rounded SWNTs. On the basis of the electron diffraction characterizations on a good number of collapsed and uncollapsed SWNTs, the threshold diameter for SWNTs to collapse was precisely determined to be 5.1 nm, independent of the chiral angle of the SWNTs. The determination is consistent with that calculated by both classical adaptive intermolecular reactive empirical bond order force field and density functional theory after having taken the stacking effect and thermal fluctuation into account.

Growth of single-walled carbon nanotubes with large chiral angles on rhodium nanoparticles.

Single-walled carbon nanotubes (SWNTs) grown on rhodium (Rh) nanoparticles were demonstrated to have large chiral angles and a preference for metallic tubes.

Chiral-selective growth of single-walled carbon nanotubes on lattice-mismatched epitaxial cobalt nanoparticles.

Controlling chirality in growth of single-walled carbon nanotubes (SWNTs) is important for exploiting their practical applications. For long it has been conceptually conceived that the structural control of SWNTs is potentially achievable by fabricating nanoparticle catalysts with proper structures on crystalline substrates via epitaxial growth techniques. Here, we have accomplished epitaxial formation of monometallic Co nanoparticles with well-defined crystal structure, and its use as a catalyst in the selective growth of SWNTs. Dynamics of Co nanoparticles formation and SWNT growth inside an atomic-resolution environmental transmission electron microscope at a low CO pressure was recorded. We achieved highly preferential growth of semiconducting SWNTs (~90%) with an exceptionally large population of (6, 5) tubes (53%) in an ambient CO atmosphere. Particularly, we also demonstrated high enrichment in (7, 6) and (9, 4) at a low growth temperature. These findings open new perspectives both for structural control of SWNTs and for elucidating the growth mechanisms.

Increasing operating room productivity by duration categories and a newsvendor model.

PURPOSE: Previous studies approach surgery scheduling mainly from the mathematical modeling perspective which is often hard to apply in a practical environment. The aim of this study is to develop a practical scheduling system that considers the advantages of both surgery categorization and newsvendor model to surgery scheduling. DESIGN/METHODOLOGY/APPROACH: The research was carried out in a Finnish orthopaedic specialist centre that performs only joint replacement surgery. Four surgery categorization scenarios were defined and their productivity analyzed by simulation and newsvendor model. FINDINGS: Detailed analyses of surgery durations and the use of more accurate case categories and their combinations in scheduling improved OR productivity 11.3 percent when compared to the base case. Planning to have one OR team to work longer led to remarkable decrease in scheduling inefficiency. PRACTICAL IMPLICATIONS: In surgical services, productivity and cost-efficiency can be improved by utilizing historical data in case scheduling and by increasing flexibility in personnel management. ORIGINALITY/VALUE: The study increases the understanding of practical scheduling methods used to improve efficiency in surgical services.

Diameter and chiral angle distribution dependencies on the carbon precursors in surface-grown single-walled carbon nanotubes.

Carbon nanotubes grown from discrete Fe-containing nanoparticles dispersed on a silicon nitride transmission electron microscope grid were systematically studied. The (n,m) indices of produced single-walled carbon nanotubes (SWNTs) were deduced from their electron diffraction patterns. Relatively small diameter SWNTs with a narrow diameter distribution (0.7-1.6 nm) were produced using CO as the carbon source at 800 °C, while large diameter SWNTs ranging from 1.0 nm to 4.7 nm were synthesized when using CH(4) as the carbon source. The chiral angle distributions of the SWNTs produced from different carbon sources are also different, which are attributed to the preferred cap nucleation associated with the carbon feed rate on the catalyst instead of carbon nanotube growth kinetics. Furthermore, growth of carbon laminar nanoclusters inside carbon nanotubes was achieved at a higher growth temperature, suggesting that dissociated carbon diffuses across the nanoparticle during the nanotube growth process.

Speed and quality in coronary artery bypass graft (CABG) surgery: is there a connection?

In this paper we study the connection between coronary artery bypass graft (CABG) operation time and quality. Our quality metric was the improvement in health related quality of life (HRQoL) survey score in a sample of 432 patients admitted to Kuopio University Hospital. Patients were interviewed with a structured questionnaire a day before the procedure and the follow-up questionnaires were mailed 6 and 12 months after the surgery. However, the HRQoL metric used did not have high retest reliability. Subsequently, we did not find any connection between CAGB operation times and HRQoL. Likewise, we did not find the speed of the surgeon to have any connection to HRQoL improvement.

Cardiac surgery productivity and throughput improvements.

PURPOSE: The high variability in cardiac surgery length--is one of the main challenges for staff managing productivity. This study aims to evaluate the impact of six interventions on open-heart surgery operating theatre productivity. DESIGN/METHODOLOGY/APPROACH: A discrete operating theatre event simulation model with empirical operation time input data from 2603 patients is used to evaluate the effect that these process interventions have on the surgery output and overtime work. A linear regression model was used to get operation time forecasts for surgery scheduling while it also could be used to explain operation time. FINDINGS: A forecasting model based on the linear regression of variables available before the surgery explains 46 per cent operating time variance. The main factors influencing operation length were type of operation, redoing the operation and the head surgeon. Reduction of changeover time between surgeries by inducing anaesthesia outside an operating theatre and by reducing slack time at the end of day after a second surgery have the strongest effects on surgery output and productivity. A more accurate operation time forecast did not have any effect on output, although improved operation time forecast did decrease overtime work. RESEARCH LIMITATIONS/IMPLICATIONS: A reduction in the operation time itself is not studied in this article. However, the forecasting model can also be applied to discover which factors are most significant in explaining variation in the length of open-heart surgery. PRACTICAL IMPLICATIONS: The challenge in scheduling two open-heart surgeries in one day can be partly resolved by increasing the length of the day, decreasing the time between two surgeries or by improving patient scheduling procedures so that two short surgeries can be paired. ORIGINALITY/VALUE: A linear regression model is created in the paper to increase the accuracy of operation time forecasting and to identify factors that have the most influence on operation time. A simulation model is used to analyse the impact of improved surgical length forecasting and five selected process interventions on productivity in cardiac surgery.

Optimal sampling of color spectra.

We explain a method for calculating the optimal sampling interval of color spectra. The 1269 measured Munsell matt reflectance spectra set is used as the test set. The effect of light sources on the required sampling interval with different types of spectra is studied. It is shown that a 20 nm interval is enough for the smooth Munsell set alone, but 10 nm is not enough for the same set matched with a fluorescent light source. However, 5 nm is shown to be enough in most situations.