材料热力学和动力学答案.docx

Gibbs-Thomson effect:The Gibbs–Thomson Effect, in common?physics?usage, refers to variations in vapor pressure or chemical potential across a curved surface or interface. The existence of a positive interfacial energy will increase the energy required to form small particles with high curvature, and these particles will exhibit an increased vapor pressure. See?Ostwald–Freundlich equation.More specifically, the Gibbs–Thomson effect refers to the observation that small crystals are in equilibrium with their liquid melt at a lower temperature than large crystals. In cases of confined geometry, such as liquids contained within porous media, this leads to a depression in the freezing point / melting point that is inversely proportional to the pore size, as given by the Gibbs–Thomson equation.Why at a relatively lower temperature solute transport tends to become more effective via grain boundary than through the lattice or through dislocation? Please have an example material to clear.（为什么在一个相对较低的温度，溶质趋向于通过晶界的运输比晶格和位错运输更有效？请举一种材料作为例子详述）答：在多晶体中的扩散除了再晶粒点阵内部进行之外，还会沿表面、晶界、位错等缺陷部位进行。由于这些部位的点阵畸变较大，原子处于较高的能量状态，易于跳动，因而沿表面、晶界、位错迁移的扩散系数恒大于原子穿越点阵内部的体扩散系数。晶界扩散的作用因温度不同而不同，在温度较低时，由于晶界激活能比点阵激活能小得多，晶界扩散对整个扩散起了重要作用。这也就是为什么在一个相对较低的温度，溶质趋向于通过晶界的运输比晶格和位错运输更有效。但随着温度的升高，晶内空位浓度逐渐增加，点阵扩散系数相应增大，比例很小的晶界扩散伴随着温度的升高其作用逐步减弱。例如：单晶体银与多晶体银自扩散系数进行比较实验中可以发现，在温度较低时，多晶体银的自扩散系数要远远大于单晶银的自扩散系数。而当温度上升到700oC时，二者相当。After nucleation of both phases, the colony can grow edgewise by the movement of the incoherent interfaces that a pearlite growth into the austenite grain with which is does not have on orientation relationship.（两相形核之后，集落能够通过不连续的界面沿边生长，一个珠光体长成两个无定向关系的奥氏体晶粒）答：当温度达到一定温度后，先在形核晶界处形成一小片渗碳体（片状是为了减小应变能），然后通过临近原子沿着不连续界面聚集长大，一个珠光体长成两个无定向关系的奥氏体。The advantage and disadvantage between DSC and DTA（DSC曲线和DTA曲线相比的优缺点）DTA与DSC两种方法的主要差别是DTA测定的是试样与参比物的温度差△T，而DSC测定的是保持试样与参比物温差为零时的热流率（功率差）dH/dt。尽管两者曲线形状及定量校正方法都很相似，但其原理和曲线方程是不同的。DSC的主要优点是热量定量方便，分辨率高好，灵敏度高。DSC的第一个缺点是使用温度低，最高只能用到800℃，一般在600℃以上，基线明显变坏已不能用最高灵敏度档。DSC仪器使用温度提不高的原因，一