Zone melting

Japanese: ゾーンメルティング（英語表記）zone melting

Zone melting is a method devised by Pfann in 1952 for the purpose of purifying germanium, and is also called zone refining [Pfann: 1957, 1958]. In general, normal solidification refers to a molten substance solidifying from one end. If the distribution coefficients of the components are different, the component concentrations between the solid and liquid will gradually change, and if a part of the target object is melted and moved in one direction, segregation of the components will occur. If the melting zone is passed only once, there will be little segregation of the components, which is almost the same as normal solidification, but if the material is passed through the melting zone repeatedly, an extremely high purity product can be obtained. This is the zone melting method, and it requires a heating source to create a stable molten part and cooling the opposite side to solidify the molten material. Harris applied this idea to the Earth, and thought that zone melting occurs during the process of molten magma rising, and later Kushiro also took up this process as a differentiation process during magma rising [Harris: 1957, Kushiro: 1968]. There is a temperature gradient from the depths to the surface of the Earth, and it is possible for rocks to melt at a suitable depth. If the temperature of the magma is higher than the surroundings when the molten material rises, heat including the temperature drop of the magma due to cooling and the latent heat of solidification will flow out, and the outflow of heat will continue until the surroundings rise and become the same temperature. The outflow of heat will not return to the original magma unless there is heat generation due to a reaction or other reason. In order for this solidification process to proceed upward inside the Earth, the magma needs to heat the part directly above it to the melting temperature and then supply additional latent heat to melt the same amount of rock as the original magma. Even if magma rises adiabatically from a high-pressure depth, it does not have enough heat for this to happen. A large number of zone melting events are necessary for the segregation effect to occur, but this is not expected to occur repeatedly in nature. Considering the amount of heat and temperature involved in the solidification of magma, it is impossible for magma differentiation to occur through a mechanism similar to the zone melting method [Suzuki: 1994].

Source: Asakura Publishing Dictionary of Petrology Information

Japanese:

ゾーンメルティング法（zone melting）はファンによって1952年にゲルマニウムの精製を目的として考案された方法で，帯熔融精製（zone refining）とも呼ばれる［Pfann : 1957, 1958］．一般に熔融状態の物質が一端から凝固することを正常凝固という．この際に成分の分配係数が異なると，固体と液体の間の成分濃度は次第に変化し，対象物の一部分を熔融させてその部分を一方向に移動させると成分の偏析が起こる．熔融帯が一回通過しただけでは成分の偏析は少なく正常凝固とほとんど変わらないが，繰り返し熔融帯を通過させると極めて高純度のものが得られる．これがゾーンメルティング法で，この方法には安定な熔融部分を作る加熱熱源と，反対側を冷却して熔融体が固化させることが必要である．ハリスはこの考えを地球に応用し，熔融したマグマの上昇の過程でゾーンメルティングが起こると考え，その後，久城もこの過程をマグマの上昇中の分化作用として取り上げた［Harris : 1957, Kushiro : 1968］．地球には深部から地表にかけて温度勾配があり，適当な深さで岩石が熔融することは可能である．その熔融物質が上昇する場合にマグマの温度が周囲よりも高ければ，冷却によるマグマの温度低下と固化の際の潜熱を含めた熱量は流出して，周囲の温度が上昇し同じ温度になるまで熱の流出は継続する．流出した熱量は反応などによる発熱がないかぎり再び元のマグマに戻ることはない．この凝固過程が地球内部で上方向に進行するためには，マグマは直上部分を熔融温度まで加熱して，さらに潜熱を供給して元のマグマと同じ量の岩石を熔融する必要がある．また圧力の高い深度からマグマが断熱的に上昇したとしても，マグマにはそのような十分な熱量はない．偏析の効果が現れるためには数多くのゾーンメルティング作用が必要であるが，このようなことが天然で繰り返し起こることは期待できない．このようにマグマが固結する際の熱量や温度を考慮すれば，ゾーンメルティング法と同様の機構でマグマの分化作用が起こることは不可能である［鈴木 : 1994］．

出典　朝倉書店岩石学辞典について　情報

<<: Damage relief - Somen

>>: La Somme (English spelling)