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Transition metal silicides have attracted great interest for their potential use in optoelectronic devices, photovoltaic cells, and thermoelectric conversion elements because of their high melting point, high oxidation resistance, and satisfactory thermoelectric properties. This study focuses on the effect of the deposition time and the heating temperature on the morphology and structure of the chromium silicides synthesized by the pack cementation method. A series of experiments were carried out at various temperatures (1000–1150 °C) with different deposition times (15–120 min). The morphology and the chemical composition of the samples were determined using SEM with an EDS analyzer. The structure determination and phase identification were performed by XRD analysis. The examination of the as-formed materials was completed by performing thermal stability tests. The most suitable conditions for producing CrSi2 sample with satisfactory properties and simultaneously minimizing the cost and production time are listed. It was found that the sample synthesized at 1000 °C for 15 min during the chromizing step, in combination with the siliconizing step at 1000 °C for 60 min, presents the best thermal stability and these selected temperatures offer appropriate, economical, and repeatable results.

Higher manganese silicides (HMS) are promising alternative materials for middle to high temperature thermoelectric applications as a low-cost, non-toxic and highly stable p-type leg. Many of the preparation methods that have been reported previously require long-time and energy consuming processes, as well as expensive equipment, and often do not result in a material of sufficient quality. In this study, the simple, cost-effective and eco-friendly technique of pack cementation is applied. HMS powders synthesized at different experimental conditions are studied and compared considering their structure, composition, short-term thermal stability in air and thermoelectric properties. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetry and thermoelectric measurements (in terms of Seebeck coefficient, electrical and thermal conductivity) were employed for the characterization of the material and evaluation of its performance. All samples were identified as HMS and only some negligible traces of MnSi were detected. They moderately oxidize when heated non-isothermally under air atmosphere up to 1473 K, while the presence of HMS remains dominant even at such high temperatures. Their thermoelectric properties were remarkable for an undoped material, with a maximum figure of merit (ZT) of 0.47 at 777 K. Pack cementation appeared to have a great potential as the synthesis route of high-efficiency HMS.

Copper is commonly used in many applications such as electric wires, industrial machinery, boat propellers and heat exchangers. Although Cu is resistant to corrosion in ambient conditions, it is highly susceptible when exposed to harsh environments such as high-temperature air or marine atmospheres. The application of magnesium or aluminum coatings on Cu can efficiently smooth this disadvantage without affecting its primer properties. In the herein investigation, the deposition of these coatings was accomplished by pack cementation, a simple electrochemical technique which can be easily incorporated in the industrial scale. The final coatings were tested under high temperature environments by non-isothermal (dynamic) and isothermal thermogravimetric measurements, and in artificial sea water (3.5 wt.%-NaCl) by electrochemical corrosion. The structure of both coatings was compact with elevated thickness. The oxidation and corrosion measurements revealed that the coated samples had much better performance compared to the uncoated copper coupons. Furthermore, Al coatings were found to have the best performance when exposed in high temperature environment.

Higher manganese silicides (HMS) are attractive alternative materials for high-temperature thermoelectric applications. One of the main factors that determine the sustainability of thermoelectric materials is their sufficient oxidation resistance in the desired temperatures and the ability to form oxides that impede the oxidation propagation. In the current work, the oxidation process and high-temperature oxidation resistance of HMS powder, which is innovatively synthesized by the economic and ecological method of pack cementation, are presented in a detailed study for the first time. The oxides developed during the oxidation in air are examined up to 1473 K, along with the thermal stability of HMS powder at cyclic procedures between 298 and 823 K. Additionally, the oxidation kinetics are investigated by focusing on temperatures in the range of interest for thermoelectric applications (723–793 K). The thermal analysis tests were conducted by using thermogravimetry. X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were employed for the material characterization. HMS powder demonstrated remarkable oxidation resistance up to at least 823 K with a limited mass increase of ~0.7% maximum, and a tendency to approach a stable state during the cyclic procedure. The oxidation reaction at 723–793 K was found to be more properly described by the Mampel chemical reaction model. The oxidation and thermal decomposition products detected at different temperature region include MnSi, Si, SiOx (x

Copper is widely applied however its disadvantages such as low hardness and poor oxidation resistance. TiN coatings are often used industrially for overriding such disadvantages of ferrous ...

Magnesium disilicide is a narrow gap semiconductor which can be used in several applications such as thermoelectric materials, optoelectronic devices and batteries. It has attracted special attraction because of its low cost and non-toxicity. In the herein examination the formation of this compound is investigated by a simple, one-stage process which is pack cementation. Particularly, the effect of deposition time, activator and donor material concentration was examined. Mg2Si was formed in every case without the presence of other compounds as referred to be present when formed with other coating procedures which have higher cost and are very sophisticated. The examined parameters were found to have effect only on the coating thickness up to a certain value. Moreover, the experimental results confirmed the theoretical thermodynamic calculations performed for this case.

Higher Manganese Silicides (HMS), commonly referred to as MnSi1.7, have currently attracted great attention due to their potential use in high temperature thermoelectric applications. These compounds demonstrate attractive thermoelectric properties –with a maximum value of figure of merit ZT at least 0.7 for the undoped material –good thermal and chemical stability at high temperatures, low cost of the raw materials and environmental friendliness. A wide variety of techniques has been applied for the fabrication of MnSi1.7, however, many of these are facing problems. The current study focuses on the synthesis of MnSi1.7 powder via an innovative way, using the pack cementation process which is economical, simple and ecological. The effect of main experimental parameters –e.g. synthesis temperature, composition of the initial pack powder mixture –on the formation and properties of the silicide powder were studied. The structure and phase identification of the samples were performed by X-Ray diffraction analysis (XRD), while the morphology and the chemical composition were determined by Scanning Electron Microscopy (SEM) equipped with an EDS analyzer. Additionally, in order to test the oxidation resistance selected powders were exposed to high-temperature air environment using a thermogravimetric setup (TGA). The optimized MnSi1.7 powder was successfully formed free of oxides and secondary phases, and exhibited remarkable oxidation resistance.

In the present work, the oxidation resistance and mechanism of the intermetallic compound of magnesium silicide (Mg2Si) were examined, which was formed by pack cementation technique for the first time. This method is reported to be economic, simple and environmental friendlier comparing with other coating processes. The oxidation resistance was investigated, under high-temperature air exposure by in situ thermogravimetric measurements. Moreover, the mechanism and oxidation kinetics were also examined by four different isothermal oxidations at 550, 600, 650 and 700 °C. It was found that the specimens begin to oxidize slightly over 465 °C, and over 650 °C the oxidation rate increases significantly. After isothermal oxidation tests at four different temperatures, SEM and XRD analyses of the samples revealed that the main products were MgO and Si, which were located in an additional layer formed on the surface of the specimens. Moreover, mixed oxides were also identified at the highest temperature oxidation tests.

The growth of Mg and Al coatings on copper by pack cementation is examined in this work by investigating the mechanism of the process, the effect of temperature and heating time on the coating structure. The experiments were undertaken at temperatures ranging from 550 to 600°C, while the duration of the process varied from 30 min to 3 h. It was found that the magnesium coatings consist of two phases corresponding to MgCu2 and CuMg2. These phases appeared as distinguished layers or mixed with each other, depending on the deposition temperature and duration. On the other hand, the aluminium coatings consist of a single Al4Cu9 phase whose thickness increases with deposition time and temperature. Finally, the oxidation resistance was also evaluated by thermogravimetric measurements, which revealed that the coated samples have superior resistance to bare copper, while Al coated coupons had the best performance when exposed in high temperature environment.

This work presents a study of structural and thermoelectric properties of Mg2Si coatings deposited on heavily doped p- and n-type Si substrates, at 650 °C. The as-grown layers were smooth and uniform in thickness without any texture, voids, or large density of cracks. The sign of Seebeck coefficient in deposited layers follows the one of the corresponding substrate, indicating effective doping of the grown layers with the dopant already present in Si substrate (B for p-type and As for n-type). Doping levels of ∼9 × 1018 cm−3 for p-type and ∼5 × 1018 cm−3 for n-type, were obtained. IR reflectivity analysis revealed a strong mode at 272 cm−1 and a shoulder at 316 cm−1. Thermoelectric properties were successfully modeled by a multiple-band model, with optical phonon scattering. Temperature dependence of electrical conductivity for the deposition layers. The lines represent the theoretical fitting.

Transition-metal silicides are reported to be good candidates for thermoelectric applications because of their thermal and structural stability, high electrical conductivity, and generation of thermoelectric power at elevated temperatures. Chromium disilicide (CrSi2) is a narrow-gap semiconductor and a potential p-type thermoelectric material up to 973 K with a band gap of 0.30 eV. In this work, CrSi2 was formed from Si wafers by use of a two-step, pack-cementation, chemical diffusion method. Several deposition conditions were used to investigate the effect of temperature and donor concentration on the structure of the final products. Scanning electron microscopy and x-ray diffraction analysis were performed for phase identification, and thermal stability was evaluated by means of thermogravimetric measurements. The results showed that after the first step, chromizing, the structure of the products was a mixture of several Cr–Si phases, depending on the donor (Cr) concentration during the deposition process. After the second step, siliconizing, the pure CrSi2 phase was formed as a result of Si enrichment of the initial Cr–Si phases. It was also revealed that this compound has thermoelectric properties similar to those reported elsewhere. Moreover, it was found to have exceptional chemical stability even at temperatures up to 1273 K.

In this work the feasibility of depositing magnesium coatings, on copper substrates is investigated. The deposition was accomplished by pack cementation process and the experiments were undertaken at 500°C, 550°C and 600°C for different deposition times. The purpose of these experiments was also to investigate the effect of deposition temperature on the morphology and the structure of the as-formed coatings. The characterization was performed with a SEM microscopy and XRD analysis. It was revealed that the as formed coatings mainly contain two phases corresponding to CuMg2and MgCu2. Furthermore, the coating thickness and morphology was significantly affected by temperature and time.

Magnesium silicide (Mg2Si) is a promising narrow gap semiconductor which can be used as a thermoelectric material. Chemical vapor deposition by pack cementation, which is a simple and low cost technique, was used for the first time in this work for the formation of Mg2Si compound. A series of experiments were carried out at temperatures 500–650 °C with different deposition times ranging between 15 and 180 min. As a result single phase thick layers have been prepared, depending on growth temperature and deposition time. Mg2Si was formed as a result of the Mg diffusion into the Si matrix while the film thickness increased with the deposition time, and temperature. Electrical and optical properties of the grown layers have been investigated. The examination of the as formed material was completed by performing thermal stability tests, for the determination of the safe service temperature range of the coupons. From all the experimental outcomes, it is concluded the optimum conditions for the formation of Mg2Si films is at 650 °C for a 180 min deposition period.

Magnesium silicide (Mg2Si) is a prospective narrow gap semiconductor for thermoelectric energy conversion at high temperatures. In this work, chemical vapour deposition by pack cementation process was used, for the first time, for the formation of Mg2Si compound. A series of experiments were carried out at temperatures 450°C to 650°C with deposition times at 15 to 180min. As a result thick films have been prepared, depending on growth temperature and deposition time. Mg2Si was formed as a result of the Mg diffusion into the Si matrix. The film thickness increased with the deposition time, and temperature. The identification of these films, with different methods, revealed that they contained only pure Mg2Si phase without any MgO phase.