Precipitation of Minerals from Water-Rich Fumarolic Gas Using a Flow-through Benchtop Installation

Volcanic fumaroles are openings in the earth's surface, where volcanic gases discharge to the atmosphere. Metallic and non-metallic elements contained in gases form specific mineral precipitates upon cooling. Although the presence of metals in fumarolic gases has long been known, their concentrations are generally low and difficult to measure directly. A laboratory model of a fumarole may resolve the situation if the complex gas composition could be accurately reproduced. Here we describe a new experimental approach that allows accurately simulating fumarolic gases in terms of their main components (H2O, CO2, S, HCl), as well as adding volatile metal compounds. Gas is generated inside a special flow-through reactor, at the outlet of which the elements contained in the gas form temperature-dependent mineral sequence inside the attached silica-glass tube. Using this installation, we obtained laboratory sublimates from reducing (H2S-rich) gases similar to natural ones in terms of mineral composition and mineral habits. Twenty-one phases have been identified in sublimates, among which are simple and complex chlorides, simple sulfides and six sulfosalts. Comparison of the sublimate deposition from H2O-rich gas at 1 bar with similar works performed in evacuated ampoules at low pressure showed that fumarolic gases behave like an ideal gas, in which molecules do not interact with each other, and reactive compounds in the gas serve in fact as an inert carrier of volatile metals species. Changing the composition of the gas at the outlet of the installation, its flow rate and temperature, we can observe the corresponding changes in mineral precipitates and in such a way study the factors affecting mineral formation on natural fumarolic fields.

An experiment design for schools to demonstrate the Maxwell distribution

The article describes a new version of a demonstration experiment for the Maxwell distribution. In the first part students analyse the applicability of the Gaussian distribution to the projection of the particle velocities in the suggested experiment. Further, students observe two-dimensional distribution of particles by the modulus of velocity in a mechanical demonstration model and compare the results with theoretical provisions. Demonstration of the two-dimensional version of the Maxwell distribution for particle interaction allows students to independently derive formulas for the three-dimensional Maxwell distribution for particles in an ideal gas. The use of the suggested demonstration ensures active engagement in fundamentally important physical content.

Does a container of ideal gas increase in temperature when accelerated and stopped?

An insulated container consisting of two ideal gas atoms are used. It is shown using rectilinear motion and elastic collisions with the walls of the container how the root mean square speed of the atoms change during acceleration of the container and after the container comes to a sudden stop.

Development of the Concept of Entropy: A Simpler Alternative to Carnot Cycle

The relationship between entropy and reversible heat and temperature is developed using a simple cycle, in which an ideal gas is subjected to isothermal expansion and compression and heated and cooled between states. The procedure is easily understood by students if they have knowledge of calculations involving internal energy, reversible work, and heat capacity for an ideal gas. This approach avoids the more time-consuming Carnot cycle. The treatment described here illustrates how the total entropy change resulting from an irreversible process is always positive.

Poly(ethylene glycol) Diacrylate Iongel Membranes Reinforced with Nanoclays for CO2 Separation

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to improve the mechanical properties of iongel membranes, which consists in the incorporation of montmorillonite (MMT) nanoclay, from 0.2 to 7.5 wt%, into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) network containing 60 wt% of the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][TFSI]). The iongels were prepared by a simple one-pot method using ultraviolet (UV) initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) and characterized by several techniques to assess their physico-chemical properties. The thermal stability of the iongels was influenced by the addition of higher MMT contents (>5 wt%). It was possible to improve both puncture strength and elongation at break with MMT contents up to 1 wt%. Furthermore, the highest ideal gas selectivities were achieved for iongels containing 0.5 wt% MMT, while the highest CO2 permeability was observed at 7.5 wt% MMT content, due to an increase in diffusivity. Remarkably, this strategy allowed for the preparation and gas permeation of self-standing iongel containing 80 wt% IL, which had not been possible up until now.

ANALYSIS OF LOW-TEMPERATURE EXPANSION PROCESSES OF NON-IDEAL GASES

An energy analysis of the processes of obtaining and using artificial cold in chemical technology is presented. The most well-known methods of obtaining and applying the cooling effect are considered: adiabatic expansion of vapor and gaseous bodies in expanders, throttling. Special attention is paid to the effect of object deviation from the ideal gas model.

Heat Transfer of Turbulent Gaseous Flow in Microtubes with Constant Wall Temperature

Experiments were conducted with nitrogen gas flow in two microtubes with constant wall temperature, made of stainless-steel and copper with diameters of 524 and 537 micrometers, to measure the total temperature at the inlet and outlet and quantitively determine the heat transfer rates. The temperature differences between the inlet and the wall were maintained at 3, 5 and 10 K by circulating water around the inlet and the wall. The stagnation pressures were controlled such that the flow with atmospheric back pressure reached Reynolds numbers as high as 26000. To measure the total temperature, a polystyrene tube with thermally insulated exterior wall containing six plastic baffles, was attached to the outlet. Heat transfer rates were obtained from the gas enthalpy difference by using the pressures and the total temperatures measured at the inlet and outlet. Heat transfer rates were also compared with those obtained from the ideal gas enthalpy using the measured total temperatures and from the Nusselt number for incompressible flow. It was found that the measured total temperature at the microtube outlet was higher than the wall temperature. Also, the heat transfer rates calculated from the total temperature difference were higher than the values obtained from the incompressible flow theory.

Statistical Mechanics of Unconfined Systems: Challenges and Lessons

Motivated by applications of statistical mechanics in which the system of interest is spatially unconfined, we present an exact solution to the maximum entropy problem for assigning a stationary probability distribution on the phase space of an unconfined ideal gas in an anti-de Sitter background. Notwithstanding the gas’ freedom to move in an infinite volume, we establish necessary conditions for the stationary probability distribution solving a general maximum entropy problem to be normalizable and obtain the resulting probability for a particular choice of constraints. As a part of our analysis, we develop a novel method for identifying dynamical constraints based on local measurements. With no appeal to a priori information about globally defined conserved quantities, it is therefore applicable to a much wider range of problems.