• Korean Journal of Materials Research
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• v.33 no.2
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• pp.63-70
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• 2023

In this study, crystallization was effectively suppressed in Al-based metallic glasses (Al-MGs) during pulverization by cryo-milling by applying an extremely low processing temperature and using a surfactant. Before Al-MGs can be used as an additive in Ag paste for solar cells, the particle sizes of the Al-MGs must be reduced by milling. However, during the ball milling process crystallization of the Al-MG is a problem. Once the Al-MG is crystallized, they no longer exhibit glass-like behavior, such as thermoplastic deformation, which is critical to decrease the electrical resistance of the Ag electrode. The main reason for crystallization during the ball milling process is the heat generated by collisions between the particles and the balls, or between the particles. Once the heat reaches the crystallization temperature of the Al-MGs, they start crystallization. Another reason for the crystallization is agglomeration of the particles. If the initially fed particles become severely agglomerated, they coalesce instead of being pulverized during the milling. The coalesced particles experience more collisions and finally crystallize. In this study, the heat generated during milling was suppressed by using cryo-milling with liquid-nitrogen, which was regularly fed into the milling jar. Also, the MG powders were dispersed using a surfactant before milling, so that the problem of agglomeration was resolved. Cryo-milling with the surfactant led to D50 = 10 um after 6 h milling, and we finally achieved a specific contact resistance of 0.22 mΩcm² and electrical resistivity of 2.81 μΩcm using the milled MG particles.

• Applied Microscopy
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• v.47 no.4
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• pp.223-225
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• 2017

Cryo-electron microscopy (cryo-EM) is arguably the most powerful tool used in structural biology. It is an important analytical technique that is used for gaining insight into the functional and molecular mechanisms of biomolecules involved in several physiological processes. Cryo-EM can be separated into the following three groups according to the analytical purposes and the features of the biological samples: cryo-electron tomography (cryo-ET), cryo-single-particle reconstruction, and cryo-electron crystallography. Cryo-tomography is a unique EM technique that is used to study intact biomolecular complexes within their original environments; it can provide mechanistic insights that are challenging for other EM-methods. However, the resolution of reconstructed three-dimensional (3D) models generated by cryo-ET is relatively low, while single-particle reconstruction can reproduce biomolecular structures having near-atomic resolution without the need for crystallization unless the samples are large (>200 kDa) and highly symmetrical. Cryo-electron crystallography is subdivided into the following two categories according to the types of samples: one category that deals with two-dimensional (2D) crystalline arrays and the other category that uses 3D crystals. These two categories of electron-crystallographic techniques use different diffraction data obtained from still diffraction and continuous-rotation diffraction. In this paper, we review crystal-based cryo-EM techniques and focus on the recently developed 3D electron-crystallographic technique called microcrystal-electron diffraction.

• Resources Recycling
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• v.29 no.4
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• pp.58-66
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• 2020

Carbonation (step I) and cryo-crystallization (crystallization at low temperature) (step II) were performed to synthesize Na compounds from sodium concentrated solution. In the step 1, the solubility and pH of carbon dioxide (95 wt.%) affecting carbonation could be changed by the variation of reaction temperature. The step II was performed at 2 ℃ after carbonation. The injection of carbon dioxide was carried out twice for the stable production and the saturated solubility of carbonate ions in solution. Firstly, we tried to inject CO₂ for controlling the solubility of CO₂ by changing the reaction temperature from 35 ℃ to 10 ℃, and the second injection was aimed at 10 ℃ for inducing nucleation of Na compound through carbonation after NaCl solution addition. In the cryo-crystallization step, the crystal growth of Na compounds could be induced by slowing the carbonation rate through reaction temperature change from 10 ℃ to 2 ℃. In this study, the effect on NaOH concentration was examined and the purity of Na compound was increased when 2M NaOH was used. In addition, the synthesized Na compounds were mostly rod-shaped and consisted of sodium carbonate or sodium carbonate with monohydrate.