Negative Pressure-Temperature Slopes for Reactions Formign MgSiO3 カロリメトリーによるペロブスキートによる反応の負圧-温度傾きについて
まとめ
新しい熱計技術により,MgSiOのイルメニット-ペロブスキット変換のエンタルピーが正確に測定されました. この研究は,地球のマントルを理解するための重要な熱力学データを提供します.
科学分野:
- 地質化学 地質化学
- ミネラル物理学 ミネラル物理学
- 熱力学は熱力学である.
背景:
- マグネシウムシリケート (MgSiO3) の相変化を理解することは,地球のマントルのモデリングに不可欠です.
- 高圧,高温の熱力学データは,正確な地球物理モデルに不可欠です.
研究 の 目的:
- 微小なサンプルを分析するための敏感な微分滴溶液の計熱技術を開発する.
- MgSiO3.3におけるイルメニット-ペロフスキット変換のエンタルピーを測定する.
- マントルの構成に関連するMgSiO3とMg2SiO4の相変遷の熱力学を評価する.
主な方法:
- 新しい微分滴溶液カロリメトリー法を使用した.
- 25GPaと1873Kで合成されたペロブスキットの5.18ミリグラムのサンプルを分析した.
- 計算された反応エンタルピーと圧力-温度傾き.
主要な成果:
- MgSiO3におけるイルメニット-ペロフスキット変換のエンタルピーは110.1 ± 4.1 kJ/molであると決定されました.
- 評価された2つの反応 (イルメニットからペロフスキート,スピネルからペロフスキート+MgO) は,負の圧力-温度傾斜を示している.
- -0.005 ± 0.002 GPa/Kは,MgSiO3 (イルメナイト) からMgSiO3 (ペロブスキート) になる.
- -0.004 ± 0.002 GPa/Kは,Mg2SiO4 (スピネル) からMgSiO3 (ペロブスキート) +MgO (ペリクラゼ) になる.
結論:
- 開発されたカロメトリック技術は,小さなサンプル分析に有効です.
- 負のP-T傾きは,これらの移行がマントルの動力学に影響を与える可能性があることを示唆しています.
- Spinel to perovskite + MgO反応のP-T傾きは,マントル全体のコンベクションを防ぐのに十分な負ではないかもしれません.
関連する概念動画
Constant Pressure Calorimetry
Calorimetry is a technique used to measure the amount of heat involved in a chemical or physical process or to measure the heat transferred to or from a substance. The heat is exchanged with a calibrated and insulated device called the calorimeter. Calorimetry experiments are based on the assumption that there is no heat exchange between the insulated calorimeter and the external environment. The well-insulated calorimeters prevent the transfer of heat between the calorimeter and its external...
Thermal Sigmatropic Reactions: Overview
Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
Free Energy and Equilibrium
The free energy change for a process may be viewed as a measure of its driving force. A negative value for ΔG represents a driving force for the process in the forward direction, while a positive value represents a driving force for the process in the reverse direction. When ΔGrxn is zero, the forward and reverse driving forces are equal, and the process occurs in both directions at the same rate (the system is at equilibrium).
Recall that Q is the numerical value of the mass action expression...
Recall that Q is the numerical value of the mass action expression...
Free Energy and Equilibrium
The free energy change for a process may be viewed as a measure of its driving force. A negative value for ΔG represents a driving force for the process in the forward direction, while a positive value represents a driving force for the process in the reverse direction. When ΔG is zero, the forward and reverse driving forces are equal, and the process occurs in both directions at the same rate (the system is at equilibrium).
The reaction quotient, Q, is a convenient measure of the status of an...
The reaction quotient, Q, is a convenient measure of the status of an...
Calculating Standard Free Energy Changes
The free energy change for a reaction that occurs under the standard conditions of 1 bar pressure and at 298 K is called the standard free energy change. Since free energy is a state function, its value depends only on the conditions of the initial and final states of the system. A convenient and common approach to the calculation of free energy changes for physical and chemical reactions is by use of widely available compilations of standard state thermodynamic data. One method involves the...
Gibbs Free Energy and Thermodynamic Favorability
The spontaneity of a process depends upon the temperature of the system. Phase transitions, for example, will proceed spontaneously in one direction or the other depending upon the temperature of the substance in question. Likewise, some chemical reactions can also exhibit temperature-dependent spontaneities. To illustrate this concept, the equation relating free energy change to the enthalpy and entropy changes for the process is considered:


