Potassium Sulfate: A New Candidate to Explore Non-Photochemical Laser-Induced Nucleation Mechanisms

In this paper, we report a study on the nucleation behavior of potassium sulfate (K2SO4) from aqueous solutions under the influence of unfocused nanosecond laser pulses. The objective is to contribute to the general understanding of the Non-Photochemical Laser-Induced Nucleation (NPLIN) mechanism. First, the influence of several parameters such as supersaturation as well as laser parameters (pulse energy, number of pulses, and laser polarization) on induction time, probability of nucleation and mean number of crystals in comparison with spontaneous nucleation was investigated. Then, we examined the influence of gas composition (i.e., degassing and gas bubbling (CO2 and N2)) of the supersaturated solutions on the NPLIN kinetics, showing no correlation between gas content (or nature) on the crystallization behavior. Our study questions the role of impurities within the solution regarding the mechanism of laser-induced nucleation.

New approaches in the process of crystallization of sucrose in the production of sweets with fondant bodies

Конфеты на основе помадных корпусов пользуются большим спросом у населения. Расширение ассортимента конфет и совершенствование технологии является актуальной проблемой. Актуальными остаются вопросы по расширению ассортимента популярных конфет с сохранением качества не только на производстве, но и при хранении изучение процессов, протекающих при хранении конфет с помадными корпусами, остаются в фокусе научных интересов исследователей. Поставленные задачи наиболее актуальны в производстве конфет на основе помадных корпусов - энергетически неустойчивых систем, имеющих высокую концентрацию сахарозы (более 80 %), простой химический состав, что является причиной быстрой потери потребительских свойств в процессе хранения. Решение указанных проблем возможно за счет введения в рецептуру продуктов переработки амаранта Amaranthus cruentus. Частицы порошка шрота амаранта, являясь влагоудерживающими компонентами, играют также роль компонентов кристаллизации сахарозы в высокопересыщенных растворах. Sweets based on fondant bodies are in great demand among the population. Expanding the assortment of sweets and improving technology is an urgent problem. Questions on expanding the assortment of popular sweets while maintaining quality not only in production, but during storage remain topical. The study of the processes occurring during the storage of sweets with fondant bodies remains in the focus of the scientific interests of researchers. The tasks set are most relevant in the production of sweets based on fondant bodies - energetically unstable systems with a high concentration of sucrose (more than 80 %), a simple chemical composition, which is the reason for the rapid loss of consumer properties during storage. The solution of these problems is possible due to the introduction of Amaranthus cruentus amaranth processed products into the formulation. Particles of amaranth meal powder, being water-retaining components, also play the role of components of crystallization of sucrose in highly supersaturated solutions.

Lithological controls on the expansion of unbound aggregates in Dublin, eastern Ireland: two contrasting cases

Pyrite-bearing unbound fills, widely used in eastern Ireland have heaved, causing serious structural damage to thousands of buildings. This study compares calcareous mudstones that degenerated rapidly, causing severe structural damage, with argillaceous limestones that did not. Framboidal pyrite in the mudstones is widely dispersed – every aggregate particle contains abundant framboidal pyrite. Oxidation of this produced sulfuric acid that reacted with calcite producing supersaturated solutions of CaSO4 and CO2 gas. It is suggested that the latter exerted pressures approaching 5 MPa within rock particles, creating micro-fractures into which gypsum crystallised. Antitaxial growth of gypsum continued expansion, a process analogous to the formation of mineral veins in rocks. Heave of the fill took place since all the loadbearing particles expanded. The limestones have a lower pyrite content, which occurs mainly in the shaly seams and is concentrated in the fines; limestones suffered similar oxidation, but the coarser aggregate remains unaltered, and gypsum is mainly pore-filling; little expansive force was generated. It is concluded that the actual amount of pyrite present is a less important factor controlling expansion of unbound fills than its crystal size, and its distribution throughout the aggregate.

Framboids

Framboids may be the most astonishing and abundant natural features you have never heard of. These microscopic spherules of golden pyrite consist of thousands of even smaller microcrystals, often arranged in stunning geometric arrays. There are probably 1030 on Earth, and they are forming at a rate of 1020 every second. This means that there are a billion times more framboids than sand grains on Earth, and a million times more framboids than stars in the observable universe. They are all around us: they can be found in rocks of all ages and in present-day sediments, soils, and natural waters. The sulfur in the pyrite is mainly produced by bacteria, and many framboids contain organic matter. They are formed through burst nucleation of supersaturated solutions of iron and sulfide, followed by limited crystal growth in diffusion-dominated stagnant sediments. The framboids self-assemble as surface free energy is minimized and the microcrystals are attracted to each other by surface forces. Self-organization occurs through entropy maximization, and the microcrystals rotate into their final positions through Brownian motion. The final shape of the framboids is often actually polygonal or partially facetted rather than spherical, as icosahedral microcrystal packing develops. Their average diameter is around 6 microns and the average microcrystal size is about 0.1 microns. There is no significant change in these dimensions with time: the framboid is an exceptionally stable structure, and the oldest may be 2.9 billion years old. This means that they provide samples of the chemistry of ancient environments.

Controlled Growth of Strontium Sulfate Particles in Aqueous Solution: Inhibition Effects of a Bubble Column Evaporator

In the oil industry, strontium sulfate (SrSO4) scale deposits have long plagued oilfield and gas production operations. This remains an unsolved problem. We here show how the bubble column evaporator (BCE) can be used to control aqueous precipitation from salt solutions. Mixtures of strontium nitrate and sodium sulfate in the BCE system were used to precipitate strontium sulfate at different degrees of supersaturation. The effectiveness of the BCE system was compared to standard mechanical stirring. The precipitation of strontium sulfate in both processes was monitored through turbidimeter, particle counting, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). The results show that the BCE system has a significant inhibition effect and so can be used to control precipitation growth rate, even from supersaturated solutions. This remarkable effect also provides new insights into mechanisms of crystallisation, of bubble interactions and mineral flotation.

Variation in Properties of Pre-Nucleation Calcium Carbonate Clusters Induced by Aggregation: A Molecular Dynamics Study

Numerous studies have speculated calcium carbonate (CaCO3) nucleation induced by pre-nucleation clusters (PNCs) aggregation. However, it is challenging for experiments to directly obtain the relationship between PNCs aggregation and nucleation. Herein, we employ molecular dynamics simulations to explore the variation during PNCs aggregation, which can describe the beginning stage of CaCO3 nucleation induced by PNCs aggregation in supersaturated solutions. The results reveal that the formation of CaCO3 nucleus consists of PNCs spontaneous growth, PNCs solubility equilibrium, and aggregation of PNCs inducing nucleation. The PNCs aggregation, accompanied by the variation in the configuration and stability of CaCO3 aggregate, breaks the solubility equilibrium of PNCs and creates conditions for the formation of the more stable nucleus. Besides, the CaCO3 nucleus with the higher coordination number and the lower hydration number form when decreasing the CaCO3 concentration or increasing the temperature. This work not only sheds light on the formation of the CaCO3 nucleus but also contributes to the explanation for CaCO3 polymorphism.

Homogeneous nucleation of NaCl in supersaturated solutions

The Seeding method is an approximate approach to investigate nucleation that combines molecular dynamics simulations with classical nucleation theory. This technique has been successfully implemented in a broad range of...