Application of heat pipe technology in thermal analysis of metals

Summary Thermal analysis has been used in foundry applications to assess the quality of the melt before casting. The high-end thermal analysis techniques such as DSC or DTA are expensive and not suitable for foundry applications. The Computer-Aided Cooling Curve Analysis (CA-CCA) method based on one thermocouple has been widely used as a batch process with poor control over heat extraction and cooling rates during solidification. A heat pipe apparatus has been developed as a thermal analysis tool. The apparatus can assess the melt quality more accurately, as well as, allow for better control of heating and cooling rates. Moreover, the solidification process can be modeled more accurately, and thus the casting parameters affecting the casting quality can be closely simulated and consequently controlled. In this paper the principles of a heat-pipe assisted thermal analysis system are highlighted. The advantages of the new system are described and the possibility of its adoption in melt assessments is discussed.     

Differential scanning calorimetry and the advanced solidification processing of metals and alloys

This paper describes some examples of the use of differential scanning calorimetry (DSC) in providing information for advanced solidification processing of metals and alloys. Spray forming, squeeze casting, grain refinement and crystallization of amorphous alloys are all discussed. DSC measurements are shown to be valuable for testing kinetic theories of nucleation and growth, and validating solidification process models.     

The role of thermal analysis in detecting impurity levels during aluminum recycling

Recycling of aluminum scrap has gained interest owing to its economic and ecological benefits. Unfortunately, during the collection of scrap from a mixer of junk from various sectors it is difficult to ensure that the recycled alloy has the same chemical composition as that of already existing commercial alloys. Consequently, some of the alloying elements become trace/tramp elements in the recycled alloy. Therefore, in order to obtain high performance recycled alloys, controlling the impurity levels of the aluminum melt is of vital importance. Normally, computer aided cooling curve analysis (CA-CCA) is used to find the relationship between cooling curve parameters, melt treatments, alloy composition, and properties. In the present study, the first differential thermal analysis (DTA) approach has been used to detect and quantify impurity elements in scrap-like liquid aluminum alloys.     

Determination of the latent heat of fusion and solid fraction evolution of metals and alloys by an improved cooling curve analysis method

Journal of Thermal Analysis and Calorimetry - In this work, a new computer-aided cooling curve analysis method (CA-CCA) called metal/mold energy balance method (MEB) is presented. Its originality...     

Spectrophotometric determination of traces of several metals in ferrous and nonferrous metals and alloys after isolation by iodide extraction

Methods are presented for the determination of traces of lead, cadmium, indium, bismuth, copper, and antimony in most of the important metals and alloys used in industry. The trace metals are isolated by hexone extraction of their iodides from 5% hydrochloric acid solution and then determined spectrophotometrically. The attractive feature of the proposed procedures is that the method used for each of the trace metals is applicable to all of the matrix metals and alloys being considered.     

微量元素Sr对Al—Si合金凝固过程的影响

用差热分析法系统地研究了Sr对Al-Si共晶、亚共晶及超共晶合金的动态凝固过程的影响。结果表明,Sr既可促进α-Al成核,使其初晶析出温度比二元合金中α-Al相析出温度明显提高,又能抑制初晶Si成核,使超共晶中初晶Si相析出温度较二元合金中Si的初晶的实际析出温度明显降低,还能促使共晶合金成核,使加Sr后的共晶析出温度明显提高。     

Mathematical analysis of the heat measured by a power-compensated differential scanning calorimeter during the solidification of a multiphase alloy

The determination of the solidification characteristics of alloys using differential scanning calorimetry (DSC) is difficult because of the unknowns associated with the kinetic of phase transformations and the thermal resistance between the sample and the temperature measuring device. This paper shows how appropriate assumptions coupled with a thermodynamic software package and an accurate mathematical analysis of a power-compensated DSC, can enable a direct comparison between the experimental and the theoretical heat evolutions obtained during the solidification of a multiphase alloy. This comparison is helpful in order to assess the thermodynamic database and to validate the different assumptions made in the solidification model.

     

Effect of cooling rate and Al content on solidification characteristics of AZ magnesium alloys using cooling curve thermal analysis

The solidification behavior of AZ Magnesium alloys in various cooling conditions was investigated using a computer-aided cooling curve thermal analysis method. In each case, the cooling curve and its first and second derivative curves have been plotted using accurate thermal analysis equipment and solidification characteristics were recognized from these curves. The cooling rates used in the present study range from 0.22 to 8.13 °C s^?1. The results of thermal analysis show that the solidification parameters of AZ alloys such as nucleation temperature (T _N,α), nucleation undercooling (?T _N,α), recalescence undercooling (?T _R,α), range of solidification temperature (?T _S) and total solidification time (t _f) are influenced by variation of cooling rate. Also, the effect of Al content on these parameters was studied. Microstructural evaluation was carried out to determine the correlation between the cooling rate and secondary dendrite arm spacing.     

Spontaneous electrochemical transport reactions in ionic and ionic-electronic salt melts: The production of diffusion coatings

Extensive material concerning the interaction of metals in ionic and ionic-electronic salt melts is presented. The mechanism and character of the phenomenon of the directed spontaneous transport of metals by their ions in salt melts are established. Examples of application of this phenomenon for depositing diffusion coatings on metals and alloys (by aluminum, beryllium, boron, zinc, titanium, chromium, silicon, and so on, as well as by two-component coatings) are presented.     

伏安法在镀液分析中的应用

根据镀液中待测组份或杂质的电化学特性和添加剂对金属电沉积过程的阻化或活化效应,建立了测定某些镀液组份、一些杂质和常用添加剂的浓度的直接伏安法、间接伏安法和金属沉积层阳极溶出伏安法。这些方法测定步骤简单、快速,适合于电镀生产监控和电镀工艺研究。     

Development of the electrocrystallization theory

The problems of nucleation at electrocrystallization of metals and alloys are considered. The thermodynamics and kinetics of nucleation in stationary and nonstationary modes, the atomistic approach to the formation of nuclei and their growth (isolated and overlapped), the dependence of the nucleation rate on the adsorption of surfactants, the deposit grain size as a function of overpotential, and the grain size of eutectic alloys are discussed. Conclusions are drawn on the most important factors which should be taken into account during the analysis of processes of electrochemical nucleation and cluster growth.     

Electrochemical study on the adsorption of carbon oxides and oxidation of their adsorption products on platinum group metals and alloys

CO(2) reduction and CO adsorption on noble metals (Pt, Rh, Pd) and their alloys (Pt-Rh, Pd-Pt, Pd-Rh, Pd-Pt-Rh) prepared as thin rough deposits have been studied by chronoamperometry (CA), cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The influence of alloy surface composition on the values of surface coverage, eps (electron per site) and potential of the oxidation of CO(2) reduction and CO adsorption products is shown. The oxidation of the adsorbate on Pt-Rh alloys proceeds more easily (at lower potentials) than on pure metals. On the other hand, in the case of Pd-Pt and Pd-Rh alloys the adsorbate oxidation is more difficult and requires higher potentials than on Pt or Rh. The analysis of the EQCM signal is presented for the case of adsorption and oxidation of carbon oxide adsorption products on the electrodes studied. The comparison of adsorption parameters and the EQCM response obtained for platinum group metals and alloys leads to the conclusion that reduced CO(2) cannot be totally identified with adsorbed CO.     

Surface films and metallurgy related to lubrication and wear

The nature of the tribological surface is identified and characterized with respect to adhesion, friction, wear, and lubricating properties. Surface analysis is used to identify the role of environmental constituents on tribological behavior. The effect of solid to solid interactions for metals in contact with metals, ceramics, semiconductors, carbons, and polymers is discussed. The data presented indicate that the tribological surface is markedly different than an ideal solid surface. The environment is shown to affect strongly the behavior of two solids in contact. In certain instances, the environment can dominate surface characteristics. With metals in contact with metals, adhesion is found to be related to the cohesive binding energy. Strong adhesive bonding occurs for metals in contact with ceramics, semiconductors, carbons, and polymers. Bond strength at the interface is, with some exceptions, stronger than the bond strength of the cohesively weaker of the two materials. Many different surface properties of metals and alloys influence tribological performance. These include (1) surface energy, (2) crystallographic orientation, (3) amorphous versus the crystalline state, (4) grain boundaries, (5) texturing of the surface, (6) crystal structure, and (7) order-disorder transformations. At sufficiently high loads or sliding velocities, metals or alloy surfaces are shown to undergo recrystallization effecting tribological properties. The chemical valency, d-valence-bond characteristics, of metal surfaces affect adhesion, friction, and wear. The greater the percent d-bond character, the lower the friction and wear. The ideal tensile and shear strengths of simple transition metals correlate with friction coefficients. Results presented also show that small amounts of alloying elements in base metals can alter markedly adhesion, friction, and wear by segregating to the solid surface.     

Analysis of alloys of titanium,niobium and tantalum by ion exchange

A procedure for the analysis of alloys of titanium, niobium and tantalum is described. After dissolution the metals are separated by ion exchange in hydrochloric-hydrofluoric acid media. Finally the metals are determined spectrophotometrically,     

Thermal behavior of several Fe-Ni alloys prepared by mechanical alloying and rapid solidification

Several Fe-Ni-P-Si alloys were produced in an amorphous state by mechanical alloying and rapid solidification. Thermal behavior of the as prepared alloys was analyzed and compared with identical alloys stored during 1 and 2 years. During annealing time, several exothermic processes related to the structural relaxation were detected at low temperature and with further crystallization at high temperature. As increasing the storage time, the powdered samples were relaxed at lower temperatures. The activation energy, E, of the main crystallization process varies between 2.7 and 4.7 eV at.^-1. The E values obtained remains similar with the storage time. Small contamination from the milling tools was found. Furthermore, powdered alloys are more sensible to oxidation processes than as quenched ribbons.     

Titanium distributions in zone melted materials measured by SIMS

Using a zone melting apparatus the influence of the different solidification processes on the Ti distribution has been investigated in model alloys and a technical steel. The concentration profiles after the conventional zone melting process have been measured using secondary ion mass spectrometry and were used for the determination of the distribution coefficients of Ti in pure Fe-Ti- and Fe-C-Ti-alloys. The registration of lateral elemental maps helps to identify and to eliminate measuring artefacts and allows the investigation of dendritic solidification structures.     

Titanium distributions in zone melted materials measured by SIMS

Using a zone melting apparatus the influence of the different solidification processes on the Ti distribution has been investigated in model alloys and a technical steel. The concentration profiles after the conventional zone melting process have been measured using secondary ion mass spectrometry and were used for the determination of the distribution coefficients of Ti in pure Fe-Ti- and Fe-C-Ti-alloys. The registration of lateral elemental maps helps to identify and to eliminate measuring artefacts and allows the investigation of dendritic solidification structures.     

Applications of Low-Melting-Point Metals in Rechargeable Metal Batteries

Low-melting-point (LMP) metals represent an interesting family of electrode materials owing to their high ionic conductivity, good ductility or fluidity, low hardness and/or superior alloying capability, all of which are crucial characteristics to address battery challenges such as interfacial incompatibility, electrode pulverization, and dendrite growth. This minireview summarizes recent research progress of typical LMP metals including In, Ga, Hg, and their alloys in rechargeable metal batteries. Emphasis is placed on mainstream electrochemical storage devices of Li, Na, and K batteries as well as the representative multi-valent metal batteries. The fundamental correlations between unique physiochemical properties of LMP metals and the battery performance are highlighted. In addition, this article also provides insights into future development and potential directions of LMP metals/alloys for practical applications.     

微量Na元素的变质作用对Al—Si合金凝固过程的影响

对不同Na含量的Al-Si共晶合金各相中Na的分布进行了分析,并结合显微结构的变化,用DTA方法研究了合金的凝固过程。结果表明:Si相中的Na含量随着合金中Na的重量百分比的增加而增加,在一定的冷却速度下,加入Na可提高Al-Si共晶合金的共晶析出温度,降低Al-Si共晶合金的生长速度,变质效果越好的样品,这种变化越明显,说明,Na的变质作用不是抑制其成核而是促使其成核。     

Determination of trace elements in metals and alloys by atomic-absorption spectroscopy using an induction-heated graphite well furnace as atom source

An induction-heated graphite furnace, coupled to a Unicam SP 90 atomic-absorption spectrometer, is described for the direct determination of trace elements in metals and alloys. The furnace is capable of operation at temperatures up to 2400 degrees , and has been used to obtain calibration graphs for the determination of ppm quantities of bismuth in lead-base alloys, cast irons and stainless steels, and for the determination of cadmium at the ppm level in zinc-base alloys. Milligram samples of the alloys were atomized directly. Calibration graphs for the determination of the elements in solutions were obtained for comparison. The accuracy and precision of the determination are presented and discussed.