Mechanism to Diminish the Supercooling of the Tin Freezing Point by using Graphite Powder

Abstract

The formation of crystallization centers from extremely pure molten tin is normally associated with deep supercooling. This deep supercooling is inconvenient for the operation of tin freezing-point cells, especially for sealed tin fixed-point cells without a holder to facilitate removal from the furnace. Researchers of the National Institute of Metrology (NIM) intended and succeeded in reducing this deep supercooling by adding fine and pure graphite powders to tin fixed-point cells without influencing the fixed-point temperature, but the mechanism is yet to be properly clarified. The principle of heterogeneous nucleation indicates that a decrease of the contact angle of the crystalline nucleus on the substrate surface results in a significant reduction of supercooling required for initiation of nucleation. The heterogeneous theory is utilized by the authors of this paper to give a reasonable description of the mechanism of supercooling reduction by addition of graphite powder. It is demonstrated that the freezing plateau can be realized by the natural cooling of the tin cell within the furnace without using the 'outside nucleation' technique. The maximum temperature of the freezing curves of the tin cell with graphite powder agrees well with the reference tin cell without the graphite powder, and the cells with graphite powder show good consistency.

Penerapan Iso 9001 Sebagai Dasar Pelayanan Publik Di Unit Pelayanan Pemerintah Daerah Dan Kota

“…Head dan kawan-kawan (2008). : "The freezing curves of the aluminium fixed-point decreased and increased in line with expectations derived from interpolation of previous experiments as increased amounts of impurities were introduced", walaupun untuk kasus tertentu pengotoran diperlukan untuk mempermudah tehnik realisasi seperti yang dilakukan oleh Jin Tao Zhang dan Y.N Wang (2008):" This deep supercooling is inconvenient for the operation of tin freezing-point cells, especially for sealed tin fixed-point cells". Bahwa impuritas mempengaruhi supercooling telah diketahui oleh McLaren dan Murdock (1960) yang kemudian dipertegas oleh Ovsienko, D.Yu (2001).…”

Realization of tin freezing point using a loop heat pipe-based hydraulic temperature control technique

“…However, because of the physical limitations of conventional heater wound furnaces, 20 K to 30 K fast heating after nucleation without temperature overshoots is very difficult to achieve. In order to resolve this problem, reducing the supercooling of tin with nucleation agents [6] or having a new type of temperature control method which allows fast heating of the sample by the amount of the deep supercooling of tin without overheating is needed. In this regard, as there is controversy on reducing the supercooling of tin [3], the latter is more suitable, and this necessitates a new type of temperature control technique which should be very fast, stable and predictable.…”

Controlling supercooling of encapsulated phase change nanoparticles for enhanced heat transfer

“…However there is no effective way to reduce super-cooling of metallic nanoparticles, which cannot be doped readily with non-molten impurities due to small size and lack of material with matching structure. Although previous studies have shown interface may play an important role in super-cooling of nanoparticles embedded in solid matrix [11], it is a challenge to control the interface property of shells to reduce supercooling of discrete phase change nanoparticles, which will be suspended in liquid for heat transfer. This Letter reports a method to reduce supercooling of molten indium nanoparticles by encapsulating in high-melting point semi-crystalline silica, which facilitates heterogeneous nucleation and prevents molten cores from leakage and agglomeration.…”