晶体熔化和凝固实验的改进

针对晶体熔化和凝固实验的难点及不足,采用间歇式加热的方法来探究晶体熔化和凝固实验.通过实验数据可以看出,晶体在熔化和凝固时,温度保持一段时间不变,基本上揭示了晶体熔化和凝固时的客观规律.     

萘的熔化过程实验的改进

学生亲自观察体验晶体在熔化与凝固的过程中虽然吸热或放热但并不升温或降温这一事实很有意义.然而,这个实验不易成功,主要原因是萘受热不均匀.因此,常采用搅拌或加入热的良导体等办法解决这一问题.改进之后,实验虽有所改善但还是不甚理想.下面介绍一个制作容易,操作简单,实验可靠的改进实验.     

晶体熔化和凝固实验的改进

对晶体熔化和凝固实验的实验装置和加热方式进行了改进，提出了控制实验时间的方法。     

探究物质的熔化和凝固的实验改进

物理实验是学生感受物理思想、领悟物理科学精髓的最主要、最有效的途径之一,让全体学生参与并自主完成相关物理实验是教材编撰者及物理教师的努力目标,《物理》八年级上册第二章第3节"熔化和凝固中探究熔化和凝固的特点"是初中物理教学中比较难做的实验之一,许多教师都把这个实验改成了演示实验.原因是该实验的目的是使学生通过     

基于用D I S系统对晶体凝固和熔化的研究

本文采用D I S数字化信息系统对晶体的熔化与凝固实验进行了研究. 在按照初中物理教材的实验安 排, 用海波水浴加热法测量晶体的熔化曲线的基础上, 本文做了两个改进, 一是选择用水替代海波, 先让水凝固成 冰, 然后再利用空气浴法让冰在空气中自然熔化, 从而测量冰的凝固与熔化过程温度 时间曲线( 即凝固曲线和熔 化曲线) , 全程观察冰的凝固与熔化过程其温度及状态的变化; 二是采用D I S温度传感器来替代液体温度计人工测 量温度, 实时记录了冰的凝固曲线和熔化曲线. 实验结果表明, 采取上述改进后, 既提高了该实验的准确性、 可靠性 和直观性, 也增强了实验的说服力     

传感器在固体熔化凝固实验中的运用

基于固体的熔化和凝固实验的传统做法,结合现代测量技术对其进行了改进,对晶体海波和非晶体石蜡的熔化和凝固进行了全程监控,取得了很好的实验效果并节省了实验时间,提高了实验的准确性.     

“熔化和凝固”说课稿

如何说课是很多教师关心的问题,文章从教材分析、教学目标、教学重点和难点、教学准备、学情、教法与学法、教学过程、板书设计几个方面来阐述"熔化和凝固"这节课.     

让“物质熔化和凝固”实验真正成为学生随堂实验

实验探究是科学课堂的重要组成部分,让学生通过对实验的设计、操作和分析培养学生的思维能力,提高学生的技能水平,是科学教学的重要手段.然而,面对许多随堂实验在多种不利因素下产生局限陛时,教师不得不舍本逐末,寻找其他替代的方法.就"物质熔化和凝固"的实验部分教学而言,普遍存在如下两种现象:(1)日常教学用"嘴巴实验"或"媒体实验"代替;(2)公开课,基于本演示实验现象能见度差、可以自圆其说的特点,用"演示实验"配合媒体进行.     

细节决定成败——谈晶体的熔化和凝固实验中应注意事项

“晶体的熔化和凝固”在初中物理实验教学具有重要的地位,但是做起来难以成功;其主要原因是,萘本身的导热性不强,且萘粉颗粒之间充满空气,而空气也是热的不良导体,致使真实的熔化过程是从外到内进行的．经常出现的情况就是当外层萘熔化完成,温度高于80℃时,内层萘尚处于固态,温度低于80℃．凝固过程也类似;     

巧用食盐水改进冰熔化实验

苏科版八年级物理第二章第三节"熔化和凝固"一节中安排了探究活动———"探究冰、蜡烛的熔化特点"的实验,可是"冰熔化"实验并不容易成功.首先在于实验的背景,按照教学进度,此节内容     

晶体熔解和凝固实验的小改进

将一团蓬松的细铁丝或铜丝先放到试管的底端,以增加海波的导热性能,使海波在48℃开始熔解,直到全部熔解温度仍保持48℃.     

The melting and solidification of nanowires

A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition.     

Effect of pressure on melting and solidification of metal nanoparticles

A thermodynamic model was developed to clarify the dependence of melting temperature on hydrostatic pressure in the nanoscopic scale. It is based on the classic Clausius-Clapeyron relation and the size dependence of the melting entropy. The melting of nanoparticles in matrix with coherent and incoherent boundaries was also under consideration. It was shown that external hydrostatic pressure leads to the appearance of extrema of the melting temperature that was considered as a function of the characteristic size of nanoparticles.     

The molecular dynamics of a naphthalene crystal near melting

It is suggested that atom-atom potential functions become more appropriate for molecular dynamics calculations for systems as they approach melting. A simulation for naphthalene shows the molecular rate of reorientation about the axis of greatest inertia to be approaching 100 MHz within 20 K from melting. Self-correlations for this motion are highly significant, though neighbour correlations appear to be random in this case. Such behaviour is contrasted with plastic crystal behaviour where neighbour correlations are high, and it is suggested that this characterises the difference between a true crystal and a plastic crystal. For naphthalene this result contrasts with an experimental conclusion where the motion about the axis of least inertia is though to be responsible for the onset of melting.     

Velocity-selection problem for combined motion of melting and solidification fronts

We discuss a free boundary problem for two moving solid-liquid interfaces that strongly interact via the diffusion field in the liquid layer between them. This problem arises in the context of liquid film migration (LFM) during the partial melting of solid alloys. In the LFM mechanism the system chooses a more efficient kinetic path which is controlled by diffusion in the liquid film, whereas the process with only one melting front would be controlled by the very slow diffusion in the mother solid phase. The relatively weak coherency strain energy is the effective driving force for LFM. As in the classical dendritic growth problems, also in this case an exact family of steady-state solutions with two parabolic fronts and an arbitrary velocity exists if capillary effects are neglected [D. E. Temkin, Acta Mater. 53, 2733 (2005)]. We develop a velocity-selection theory for this problem, including anisotropic surface tension effects.     

Depression of the 3He melting curve by adsorptive solidification on carbon substrates

The depression of the ³He melting curve by up to one bar lower than the bulk melting curve for temperatures varying from the mK range up to 0.5 K was observed. Adsorptive solidification isotherms at several different temperatures were studied.     

Linear dependence of thermal and caloric equations of state on solidification and melting curves

Based on the entropy representation of the configurational energy in the Mie-Gruneisen form and representation of the anisotropic liquid as a conformal, with respect to van der Waals, orientational mixture, and assuming that the configurational entropy is constant on the solidification and melting curves (including orientational), the relation E/Y_o + PV/Z_o = RT is obtained, where E is the internal energy, Y_o and Z_o are the characteristic constants of the substance. By taking into account other rules as well, an equation is obtained that permits calculating the internal energy along the melting curve by integrating the lattice sums.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 3–7, March, 1982.     

Studies of pulsed laser melting and rapid solidification using amorphous silicon

Pulsed laser melting of ion implantation-amorphized silicon layers, and the subsequent solidification of undercooled liquid silicon, have been studied experimentally and theoretically. Measurements of the time of the onset of melting of amorphous silicon layers, during an incident laser pulse, have been combined with measurements of the duration of melting, and with modified melting model calculations to demonstrate that the thermal conductivity, K_a, of amorphous silicon is very low (K_a0.02 W/cm K). K_a is also found to be the dominant parameter determining the dynamical response of amorphous silicon to pulsed laser radiation; the latent heat of fusion and melting temperature of amorphous silicon are relatively unimportant. Transmission electron microscopy indicates that bulk (volume) nucleation occurs directly from the highly undercooled liquid silicon that can be prepared by pulsed laser melting of amorphous silicon layers at low laser energy densities. A modified thermal melting model has been constructed to simulate this effect and is presented. Nucleation of crystalline silicon apparently occurs at a nucleation temperature, T_n, that is higher than the temperature, T_a, of the liquid-to-amorphous phase transition. The model calculations demonstrate that the release of latent heat by bulk nucleation occurring during the melt-in process is essential to obtaining agreement with experimentally observed depths of melting. These calculations also show that this release of latent heat accompanying bulk nucleation can result in the existence of buried molten layers of silicon in the interior of the sample after the surface has solidified. It is pointed out that the occurrence of bulk nucleation implies that the liquid-to-amorphous phase transition (produced using picosecond or ultraviolet nanosecond laser pulses) cannot be explained by purely thermodynamic considerations.     

The effect of matrix on melting and solidification behaviours of embedded Pb-Sn alloy nanoparticles

The present investigation is aimed at understanding the effect of a matrix on the phase transformation of biphasic embedded Pb–Sn alloy nanoparticles. The melting and solidification behaviours of eutectic (Pb_26.1Sn_73.9) nanoparticles embedded in icosahedral (IQC) as well as decagonal quasicrystalline (DQC) matrix have been studied. Electron microscopic observations reveal that the major portion of the alloy nanoparticle consists of body-centred tetragonal β-(Sn) with face-centred cubic (Pb) constituting the cap. (Pb) bears specific orientation relationships (OR) with the surrounding IQC matrix, whereas β-(Sn) does not have any specific OR. For alloy particles embedded in the DQC matrix, both (Pb) and β-(Sn) bear specific OR. In case of IQC matrix, differential scanning calorimetric measurements reveal sharp melting but diffuse solidification peaks for the embedded nanoparticles. On the other hand, sharp melting and solidification peaks are observed for the nanoparticles embedded in the DQC matrix. The IQC and DQC are heat-treated at different temperatures to observe the effect of the matrix on the phase transformation of the alloy nanoparticles. The formation of well- developed facets in the nano-particles and defects in the matrix have been found to play a crucial role in determining the phase transformation of the alloy nanoparticles in the heat-treated samples. The experimental observations are rationalized using available literature.