Progress Towards Metal Additive Manufacturing Standardization to Support Qualification and Certification

As the metal additive manufacturing (AM) industry moves towards industrial production, the need for qualification standards covering all aspects of the technology becomes ever more prevalent. While some standards and specifications for documenting the various aspects of AM processes and materials exist and continue to evolve, many such standards still need to be matured or are under consideration/development within standards development organizations. An important subset of this evolving the standardization domain has to do with critical property measurements for AM materials. While such measurement procedures are well documented, with various legacy standards for conventional metallic material forms such as cast or wrought structural alloys, many fewer standards are currently available to enable systematic evaluation of those properties in AM-processed metallic materials. This is due in part to the current lack of AM-specific standards and specifications for AM materials and processes, which are a logical precursor to the material characterization standards for any material system. This paper summarizes some of the important standardization activities, as well as limitations associated with using currently available standards for metal AM with a focus on measuring mission-critical properties. Technical considerations in support of future standards development, as well as a pathway for qualification/certification of AM parts enabled by the appropriate standardization landscape, are discussed.     

Unpromoted and Mn‐Promoted Cobalt Catalyst Supported on Carbon Nanotubes for Fischer‐Tropsch Synthesis

Langmuir‐Hinselwood (LH) and power rate equations were applied to describe the kinetics of the Fischer‐Tropsch reaction on cobalt catalysts and manganese‐doped cobalt catalysts supported on carbon nanotubes (CNTs). LH‐based kinetics characterize the activity behavior of the unpromoted Co/CNT system satisfactorily, but fail with respect to the manganese‐promoted Co/CNT catalyst. An alternative LH equation is able to fit the experimental data, but the fitting parameters are out of the range of usual values and underrate the activity at ambient pressure regardless of manganese promotion. Application of power law rate expressions results in satisfying characterization of the kinetics in the whole CO pressure range in the promoted case and within a defined range of CO pressure in the unpromoted case.     

Condensed tannins: A factor limiting the use of cassava forage

Cassava (Manihot esculenta, Crantz), an important tropical root crop, is considered to have a good potential for use as a forage because leaf blades generally contain <20% crude protein (CP). However, neutral-detergent fibre (NDF) obtained from cassava leaf blades contains condensed tannins (CTs) and high levels of CP. The amount of CP in the NDF that is insoluble when treated with pepsin or protease is highly correlated with the amount of CTs in the NDF. CTs in the NDF are rich in prodelphinidin. CTs may be an important factor limiting the nutritive value of cassava forage.     

Modeling of Multi‐Tubular Reactors for Fischer‐Tropsch Synthesis

The results of the simulation of multi‐tubular Fischer‐Tropsch reactors based on a two‐dimensional pseudo‐homogeneous model are presented. The model takes into account the intrinsic kinetics of two commercial iron and cobalt catalysts, intraparticle mass transfer limitations, and the radial heat transfer within the fixed bed and to the cooling medium (boiling water). The effective rate with Co is slightly higher than with Fe. Hence, a temperature level can be used for Co that is 20 °C lower compared to Fe. The conversion and product selectivies are then almost the same and the reactor can be operated safely without a temperature runaway. The results of the simulations are consistent with literature data and show that there is still room for improvement of fixed bed FT reactors, e.g., by an enhanced heat transfer.     

Influence of Particle Size and Single‐Tube Diameter on Thermal Behavior of Fischer‐Tropsch Reactors. Part I. Particle Size Variation for Constant Tube Size and Vice Versa

Simulation of a single tube of a wall‐cooled multitubular Fischer‐Tropsch (FT) reactor with a cobalt catalyst indicates that the reactor performance is improved by enlarging the catalyst particle diameter. This aspect is studied for variation of the particle size for a fixed tube diameter and vice versa. For a syngas conversion per pass of about 30 % as target and a typical industrially used single‐tube diameter of 40 mm, a particle size of > 3 mm is appropriate with regard to a high production rate of higher hydrocarbons. For a particle diameter of < 3 mm, a temperature runaway can only be avoided by rather low cooling temperatures, and the target conversion cannot be reached. In addition, the pressure drop then gets rather high. The reasons for this behavior are: (i) the heat transfer to the cooled tube wall for a given tube size is considerably enhanced by increasing the particle size; (ii) the influence of pore diffusion on the effective rate gets stronger with rising particle size which decreases the danger of temperature runaway.     

Multi‐laboratory validation of a standard method for quantifying proanthocyanidins in cranberry powders

BACKGROUND: The objective of this study was to validate an improved 4‐dimethylaminocinnamaldehyde (DMAC) colorimetric method using a commercially available standard (procyanidin A2), for the standard method for quantification of proanthocyanidins (PACs) in cranberry powders, in order to establish dosage guidelines for the uropathogenic bacterial anti‐adhesion effect of cranberry. RESULTS: Commercially available cranberry samples were obtained (five from U.S. sources and six from European sources) for PAC quantification in five different analytical laboratories. Each laboratory extracted and analyzed the samples using the improved DMAC method. Within‐laboratory variation (mean ± SD) was 4.1 ± 1.7% RSD (range, 2.3–6.1% RSD) and the between laboratory variability was 16.9 ± 8.5% RSD (range, 8–32% RSD). For comparative purposes, the cranberry samples were alternatively quantified using weights of extracted PACs (gravimetric). The correlation coefficient between the two methods was 0.989. CONCLUSION: This improved DMAC method provides a simple, robust and relatively specific spectrophotometric assay for total PACs in cranberry samples using commercially available procyanidin A2 dimer as a standard. DMAC is most useful within a given type of food such as cranberries, but may not be appropriate for comparing concentrations across different food types, particularly in those cases where large differences exist among the relative amounts of each oligomer and polymer. Copyright © 2010 Society of Chemical Industry     

In situ Monitoring of Coke Deposits during Coking and Regeneration of Solid Catalysts by Electrical Impedance‐based Sensors

The activity of solid catalysts is often substantially reduced by the formation of coke. The in situ monitoring of the coke load of catalyst particles could therefore be a controlling instrument of high value. Such sensors could be useful to measure the axial coke profile in a fixed bed reactor, both during coke formation and regeneration by coke burn‐off. As a contribution to the development of such sensors, single particles of an alumina oxide catalyst were used as a model system. The particles were electrically contacted and characterized by electrical impedance spectroscopy. The coke formation/burn‐off and the impedance were simultaneously measured in a magnetic suspension balance. A clear relationship between the coke loading and the respective electrical impedance signal could be observed, both during coke formation and during the regeneration by coke burn‐off. Kinetic studies were conducted to verify the influence of mass transfer limitations on the impedance signal.     

Forecasting long-term global fertilizer demand

Fertilizer demand forecasts are key to the success of long term plans for global food security and the profitability of the fertilizer industry. The study forecasts fertilizer demand in relation to soil nutrient status in nine regions. Asia is expected to account for about 40% of the global forecast of 187.7 million Mt in 2015 and 223.1 million Mt in 2030. Sub-Saharan Africa, where soil nutrient depletion is prevalent, will remain the region with the lowest consumption, about 1.1% of global consumption. Soil nutrient drawdown in regions with inadequate fertilizer use indicates soil nutrient depletion, which will in the long run exacerbate food shortages and undermine biofuels production plans. Food and fertilizer policy, farmer education, research and technology development, and other actions will be required to counter soil nutrient depletion.     

3T3-L1 adipocytes express two isoforms of phospholipase D in distinct subcellular compartments

Phospholipase D has been implicated as an important enzyme in a range of cellular responses, including regulated secretion and the formation of secretory vesicles, cell proliferation and control of cell morphology. As insulin treatment of adipocytes has been shown to stimulate a phosphatidylcholine-specific phospholipase D and also modulates membrane trafficking, we wished to determine which isoform(s) of phospholipase D were present within adipocytes, to identify their subcellular distribution, and examine how this distribution may change in response to insulin. Using RT-PCR, 3T3-L1 adipocytes were found to express two isoforms of phospholipase D, specifically PLD1b and PLD2a. Using isoform-specific antibodies, PLD1 and PLD2 were found to be present predominantly in intracellular membranes, unlike the situation reported in other cells. Detailed analysis of the intracellular localisation of PLD1 and PLD2 revealed that these isoforms are differentially localised within adipocytes, implying functionally distinct roles for PLD activity in distinct subcellular compartments.