Rapid fabrication of diffusion barrier between metal electrode and thermoelectric materials using current-controlled spark plasma sintering technique

A continuous, stable diffusion barrier between PbTe thermoelectric material and Ni conducting electrode was generated using the current-controlled spark plasma sintering technique. This new method creates a diffusion barrier layer by utilising the melt generated in the area of contact between components, also called the weld nugget in a resistance spot welding process. The current-controlled spark plasma sintering process bonds the solid workpieces in a fraction of the time required to fabricate interphase layers using powder components with the common temperature-controlled spark plasma sintering. The substantially reduced time of bonding compared to previous methods is beneficial to the thermoelectric properties of materials due to their limited exposure to high temperatures, which occasionally are much higher than the operating temperatures of devices. This work introduces a rapid and efficient bonding technique that can be applied to a wide variety of materials

The effect of foamy slag in electric arc furnaces on electric energy consumption

In electric arc furnace steelmaking units, the essential parameters that considered important are reducing price, increasing production and decreasing environmental pollution. Electric arc furnaces are the largest users of electric energy in industry. The most important techniques that can be used to reduce the electric energy consumption in electric arc furnaces are scrap preheating, stirring, use of burners and hot charge and foamy slag. Between these methods, use of foamy slag is the most useful and economic factor. Foamy slag can reduce the amount of energy, electrods, refractory consumption, tap to tap time and increases productivity. In this research, method of production and optimum conditions for foamy slag in 200 tons electric arc furnace were investigated. The use of foamy slag in this research shows that it can reduce the electric energy consumption from 670 to 580 kwh/ton and also the melting time from 130 to 115 min. and the electric power input can be increase with foamy slag. It also shows that with foamy slag the optimum amount of FeO in slag is 20-24 percent and the optimum basicity is 2-2.2

Influence of microalloying elements (Ti, Nb) and nitrogen concentrations on precipitation of pipeline steels—A thermodynamic approach

A CALculation of PHase Diagrams (CALPHAD) approach was used to study the precipitation of nitrides and carbonitrides in pipeline steels, aligned with new developments of complex chemical compositions and thermomechanical processing of High Strength Low Alloyed (HSLA) Steels. This is in response to growing demand for improved mechanical and chemical properties, manufacturing flexibility and reduced production cost. The calculated results indicated that the precipitation temperatures of nitrides in Ti‐Nb microalloyed steels increased by titanium concentration, while the niobium concentration significantly increased the precipitation temperature of niobium carbonitrides. Carbonitride precipitates formed at much lower temperatures (∼100 K) in low carbon steels (0.1 wt%), suggesting precipitates larger in size. This is in good agreement with independent experimental data from the literatures, where austenite grain growth was studied in similar steel compositions. Although the dissolution and growth of precipitates are controlled kinetically, these results proved that the thermodynamic calculation can efficiently predict compositions and sequence of precipitation in chemically complex systems, guiding more accurate designs of experiments to identify critical temperatures of grain coarsening during reheating, recrystallisation during hot rolling, and transformation during cooling. This can minimize the number of tests required to obtain optimum chemical compositions and heat treatment procedures

Recent Progress in Multiphase Thermoelectric Materials

Thermoelectric materials, which directly convert thermal energy to electricity and vice versa, are considered a viable source of renewable energy. However, the enhancement of conversion efficiency in these materials is very challenging. Recently, multiphase thermoelectric materials have presented themselves as the most promising materials to achieve higher thermoelectric efficiencies than single-phase compounds. These materials provide higher degrees of freedom to design new compounds and adopt new approaches to enhance the electronic transport properties of thermoelectric materials. Here, we have summarised the current developments in multiphase thermoelectric materials, exploiting the beneficial effects of secondary phases, and reviewed the principal mechanisms explaining the enhanced conversion efficiency in these materials. This includes energy filtering, modulation doping, phonon scattering, and magnetic effects. This work assists researchers to design new high-performance thermoelectric materials by providing common concepts

Diabetes and all-cause mortality, a 18-year follow-up study

This study compared mortality rates and decline in life expectancy of Iranian patients with type 2 diabetes (T2DM) with the general population. A retrospective study of 2451 patients with T2DM was conducted in the Isfahan Endocrine and Metabolism Research Center, Iran, between 1992 and 2010. The mean (SD) of diabetes duration and median (Q1,Q3) of follow-up period were 15.5(8.0) and 8(5, 10) years. The main outcome was all-cause mortality. 732(29.87%) of patients died during the follow-up. Overall mortality rates (95%CI) per 1000 person-years in men and women were 56.3(52.0-62.1) and 27.3(24.5-30.4), respectively. The relative risks (95%CI) of all-cause mortality in males vs. females with T2DM aged 45-49, 50-54, 55-59, 60-64, 65-69, 70-74 were [3.02(1.49-6.11) vs. 2.09(0.96-4.57)], [4.05(2.73-6.01) vs. 2.29(1.52-3.45)], [4.13(3.26-5.24) vs. 1.70(1.23-2.35)], [2.42(1.90-3.07) vs. 1.82(1.46-2.27)], [2.36(2.02-2.76) vs. 1.49(1.25-1.78)] and [1.71(1.50-1.95) vs. 1.04(0.88-1.23)] times more than the general population, respectively. Men and women living with diabetes lost an average of 13.2(6.3) and 13.9(6.0) life-years from the year of diagnosis, respectively (p = 0.101). The estimated life-years lost were greater in younger patients and a gradual decline was observed with increasing the age at diagnosis. In conclusion, Iranians with diabetes had higher risk of death and lower life expectancy compared to the general population

Preparation of n-type Bi2Te3 Films by Electrophoretic Deposition

A high quality crack-free film of Bi2Te3 material has been deposited for the first time using electrophoretic deposition (EPD) and microstructures of various films have been investigated. One of the most important thermoelectric (TE) applications is Bi2Te3 to manufacture TE generators (TEG) which can convert waste heat into electricity targeting the global warming issue. However, the high cost of the manufacturing process of TEGs keeps them expensive and out of reach for commercialization. Therefore, utilizing EPD as a simple and cost-effective method will open new opportunities for TEG’s commercialization. This method has been recently used for advanced materials such as microelectronics and has attracted a lot of attention from both scientists and industry. In this study, the effect of media of suspensions has been investigated on the quality of the deposited films as well as their microstructure. In summary, finding an appropriate suspension is a critical step for a successful EPD process and has an important effect on both the film’s quality and its future properties

Solid-state bonding of bulk PbTe to Ni electrode for thermoelectric modules

The efficiency of thermoelectric generators is defined by the thermoelectric performance of materials, as expressed by the thermoelectric figure-of-merit, and their contacts with electrodes. Lead chalcogenide thermoelectric materials, and in particular PbTe, perform well in the 500 - 900 K temperature range. Here, we have successfully bonded bulk PbTe to Ni electrode to generate a diffusion barrier, avoiding continuous reaction of the thermoelectric legs and conducting electrodes at the operating temperature. We have modified the commonly used spark plasma sintering assembly method to join Ni electrode to bulk PbTe by driving the total supplied electrical current through the Ni and PbTe solid interfaces. This permits the formation of a thin diffusion layer, roughly 4.5 µm in thickness, which is solely comprised of nickel telluride. This new technique towards the bonding of PbTe with the electrode is beneficial for thermoelectric materials, since high temperatures have proven to be damaging to the quality of bulk material. The interphase microstructure, chemical composition, and crystallographic information were evaluated by a scanning electron microscope equipped with electron back-scattered diffraction analysis. The obtained phase at the Ni/PbTe contact is found to be β2 Ni3±xTe2 with a basic tetragonal crystallographic structure of the defective Cu2Sb type

Thermoelectric performance of electrophoretically deposited p-type Bi2Te3 film

In this study, p-type Bi2Te3 films were fabricated using a fast, cost-effective, electrophoretic deposition method for thermoelectric applications. The sintering process was carried out at 693K, which resulted in compact, dense coatings. SEM investigations showed the uniform and even thicknesses across the green and sintered films. In addition, their microstructures were examined in more depth. Furthermore, the Seebeck coefficient measurements of the green and sintered films were compared and the highest in-plane Seebeck coefficients of 239μV/K have been recorded for the sintered film at 500 K

Suspension characteristics and electrophoretic deposition ofp-Type Bi2Te3Films for thermoelectric applications

Electrophoretic deposition (EPD) was utilized to prepare uniform crack-free Bi2Te3 films for thermoelectric applications effectively. A p-type Bi2Te3 film with a coherent structure and even thickness was deposited from Tetrahydrofuran (THF) suspensions and examined using a scanning electron microscope (SEM). The specific weights of the depositions, the effective percentile coverage of the films on the substrate, the zeta potential and the electrical conductivity of different suspensions and the in-plane Seebeck coefficients of the Bi2Te3 films were measured. Although the Seebeck coefficient value of the EPD film (126 μV/K) was approximately 25% lower than the highest value reported for Bi2Te3 in the open literature via the co-sputtering method (160 μV/K), one of the most complex and expensive routes, the cost-effectiveness and speed of the simple EPD process is an undeniable advantage. This could open up new opportunities in the application of films to commercialize thermoelectric generators (TEG). It is interesting to note that the value of the Seebeck coefficient for our EPD-fabricated film was higher than for some of the other types of coatings prepared via more expensive and sophisticated fabrication routes, such as the electrodeposition technique (80 μV/K), for example

Electrophoretic Deposition of p-Type Bi2Te3 for Thermoelectric Applications

Electrophoretic deposition (EPD) of p-type Bi2Te3 material has been accomplished, and a high quality crack-free thick film has been achieved for thermoelectric (TE) applications. TE generators (TEG) can convert waste heat into electricity, which can potentially solve global warming problems. However, TEG is expensive due to the high cost of materials, as well as the complex and expensive manufacturing process. EPD is a simple and cost-effective method which has been used recently for advanced applications. In EPD, when a DC electric field is applied to the charged powder particles suspended in a suspension, they are attracted and deposited on the substrate with the opposite charge. In this study, it has been shown that it is possible to prepare a TE film using the EPD method and potentially achieve high TE properties at low cost. The relationship between the deposition weight and the EPD-related process parameters, such as applied voltage and time, has been investigated and a linear dependence has been observed, which is in good agreement with the theoretical principles of EPD. A stable EPD suspension of p-type Bi2Te3 was prepared in a mixture of acetone-ethanol with triethanolamine as a stabilizer. To achieve a high quality homogenous film on a copper substrate, the optimum voltage and time of the EPD process was investigated. The morphology and microstructures of the green deposited films have been investigated using a scanning electron microscope (SEM). The green Bi2Te3 films have shown good adhesion to the substrate. In summary, this study has shown that not only EPD of p-type Bi2Te3 material is possible, but its thick film is of high quality for TE applications