Synthesis and structural characterisation of new ettringite and thaumasite type phases: Ca6[Ga(OH)6•12H2O]2(SO4)3•2H2O and Ca6[M(OH)6•12H2O]2(SO4)2(CO3)2, M = Mn, Sn

Investigations into the formation of new ettringite-type phases with a range of trivalent and tetravalent cations were carried out to further study the potential this structure type has to incorporate cations covering a range of ionic radii (0.53–0.69 Å). We report the synthesis and structural characterisation of a new ettringite-type phase, Ca6[Ga(OH)6•12H2O]2(SO4)3•2H2O, which was indexed in space group P31c with the unit cell parameters a = 11.202(2) Å, c = 21.797(3) Å and two new thaumasite-type phases Ca6[M(OH)6•12H2O]2(SO4)2(CO3)2, M = Mn, Sn which were indexed in space group P63 with the unit cell parameters a = 11.071(5) Å, c = 21.156(8) Å and a = 11.066(1) Å, c = 22.420(1) Å respectively. These new phases show the versatility of the ettringite family of structures to tolerate a large range of cation sizes on the octahedral M site and highlights the preference of tetravalent cations to crystallise with the thaumasite structure over the ettringite structure

A simple, low-cost, and robust system to measure the volume of hydrogen evolved by chemical reactions with aqueous solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates

Synthesis of activated ferrosilicon-based microcomposites by ball milling and their hydrogen generation properties

Ferrosilicon was activated toward hydrogen generation by processing using ball milling. An activation energy of 62 kJ/mol was determined for the reaction of ball-milled ferrosilicon powder with sodium hydroxide solution, which is ca. 30 kJ/mol lower than that previously reported for unmilled ferrosilicon. A series of composite powders were prepared by ball milling ferrosilicon with various additives. Three different classes of additives were employed: salts, polymers and sugars. The effects of these additives on hydrogen generation from the reaction of ferrosilicon with 2 wt.% aqueous sodium hydroxide were investigated. It was found that composites formed of ferrosilicon and sodium chloride, potassium chloride, sodium polyacrylate, sodium polystyrene sulfonate-co-maleic acid or fructose showed reduced induction times for hydrogen generation compared to that observed for ferrosilicon alone, and all but fructose also led to an increase in the maximum hydrogen generation rate. In light of its low cost and toxicity and beneficial effects, sodium chloride is considered to be the most effective of these additives for activating ferrosilicon toward hydrogen generation

An old solution to a new problem? Hydrogen generation by the reaction of ferrosilicon with aqueous sodium hydroxide solutions

The chemical hydrogen storage properties of ferrosilicon were investigated. A hydrogen yield of ~4.75 wt.% (with respect to the mass of ferrosilicon) was estimated by the reaction of varying quantities of ferrosilicon with 5 mL of 40 wt.% sodium hydroxide solution. The reaction of ferrosilicon with aqueous sodium hydroxide solution to form hydrogen was found to have an activation energy of 90.5 kJ mol −1 by means of an Arrhenius plot. It was observed that the induction period of the hydrogen generation reaction varies exponentially with temperature. Although this combination of high activation energy and a lengthy induction period at low temperatures reduces the attractiveness of ferrosilicon for portable hydrogen storage applications unless methods can be developed to accelerate the onset and rate of hydrogen generation, its low cost and widespread availability make it attractive for further studies focused on higher temperature stationary applications

Elucidating the process of hydrogen generation from the reaction of sodium hydroxide solution and ferrosilicon

For the first time, the process of hydrogen evolution from ferrosilicon 75 using sodium hydroxide solution has been investigated as a function of temperature using a combination of X-ray photoelectron spectroscopy, X-ray diffraction and physical measurements. Ferrosilicon 75, a mixture of silicon (~50wt.%) and iron disilicide (~50wt.%), has been shown to produce hydrogen by the action of sodium hydroxide solution on the silicon only, with the iron disilicide acting in the role of spectator/protector species for the silicon. Neither iron disilicide alone nor ferrosilicon 45, which does not contain a pure metallic silicon phase, was found to generate hydrogen under similar reaction conditions, further indicating that the presence of a pure metallic silicon phase is essential for hydrogen generation. As the iron disilicide acts as a diluent for the active silicon, it is hypothesized that this would result in a slower release of hydrogen than that which would be obtained from the reaction of silicon alone, which may be useful for applications which require a long-term, sustained release of hydrogen. A hydrogen yield of 462.5mL/g and a maximum hydrogen generation rate of 83mL/min g were obtained within 10min of reaction with 40wt.% NaOH at 348K

An assessment of the viability of hydrogen generation from the reaction of silicon powder and sodium hydroxide solution for portable applications

The gravimetric hydrogen storage efficiency of silicon has been widely reported as 14wt.%, suggesting that this material should be an excellent hydrogen generation source for portable applications. However, in the case of the reaction of silicon powder with 20wt.% sodium hydroxide solution at 50°C, the observed production of hydrogen fails to realize these high expectations unless a large excess of basic solution is used during the reaction, rendering the use of silicon in such systems uncompetitive compared with chemical hydride based technologies. By investigating the molar ratio of water:silicon from a large excess of water towards the stoichiometric 2:1 ratio dictated by the reaction equation, this study shows that for the reaction of silicon in 20wt.% sodium hydroxide solution, the quantity of hydrogen produced decreases as the 2:1 ratio expected from the equation for the reaction is approached. Furthermore, in order to reach 80% of the theoretical efficacy, a molar ratio of 20:1, or 12mL of 20wt.% sodium hydroxide solution per gram of silicon, would be required. These results suggest that the actual gravimetric hydrogen storage capacity is less than 1%, casting doubts as to whether the use of silicon for hydrogen generation in real systems would be possible

Introducing DASC-PM: A Data Science Process Model

Data-driven disciplines like data mining and knowledge management already provide process-based frameworks for data analysis projects, such as the well-known cross-industry standard process for data mining (CRISP-DM) or knowledge discovery in databases (KDD). Although the domain of data science addresses a much broader problem space, i.e., also considers economic, social, and ecological impacts of data-driven projects, a corresponding domain-specific process model is still missing. Consequently, based on a total of four identified meta requirements and 17 corresponding requirements that were collected from experts of theory and practice, this contribution proposes the empirically grounded data science process model (DASC-PM)—a framework that maps a data science project as a four-step process model and contextualizes it among scientific procedures, various areas of application, IT infrastructures, and impacts. To illustrate the phase-oriented specification capabilities of the DASCPM, we exemplarily present competence and role profiles for the analysis phase of a data science project

Activation of silicon towards hydrogen generation by pelletisation

One of the barriers to the use of the silicon-water reaction to generate hydrogen for hydrogen fuel cells in portable devices is the lengthy induction period of the reaction caused by the presence of the native oxide layer on the surface of the silicon. Herein is presented a simple pelleting process which can be used to effectively eliminate the induction period in the reaction of pressed silicon powders with 2 wt% sodium hydroxide solution by means of disrupting the native oxide layer. The activation energy of the reaction was found to be 73 kJ/mol by means of an Arrhenius plot. It was also found that the rate of reaction of hydrogen generation could be enhanced by mixing sodium chloride and sodium polyacrylate with the silicon powder before pressing