Melting Point Of Sn Research Articles

Ultrahigh average zT realized in polycrystalline SnSe0.95 materials through Sn stabilizing and carrier modulation

The average zT determines the conversion efficiency, and the power factor plays an important role in average zT value. However, the inadequate electrical conductivity of SnSe materials seriously limits its application. Herein, the TaCl5-doped in polycrystalline SnSe0.95 materials synthesized using the melting method and combined with spark plasma sintering technology achieves a zT value of 1.64 at 773 K and a record zTave of 0.62 from 323 K to 773 K. The electrical conductivity increases due to the released electron carrier induced by effective TaCl5 doping. According to the DFT calculation, the energy band of TaCl5-doped samples is narrowed, which can enhance the electron transport. Besides, the Seebeck coefficient is maintained at an elevated level as a result of the incorporation of the heavy element Ta. Due to the significantly enhanced electrical conductivity and maintained high Seebeck coefficient, the power factor reaches to 622 μW·m−1·K−2 at 773 K for the SnSe0.95 + 1.75% (in mass) TaCl5 sample, which is almost 21 times higher than that of the pristine sample. Simultaneously, a high average power factor value of 334 μW·m−1·K−2 for the SnSe0.95 + 1.75% (in mass) TaCl5 sample from 323 to 773 K was obtained. It is surprisingly found that the Ta element plays another important role to improve the stability of SnSe0.95 by forming Ta2Sn3 and removing the low melting point Sn, which usually existed in n-type SnSe samples, resulting in the decreased lattice thermal conductivity. A low lattice thermal conductivity value of 0.24 W·m−1·K−1 was also obtained for the SnSe0.95 + 2.0% (in mass) TaCl5 sample at 773 K due to the multiscale defects. Consequently, the SnSe0.95 + 2.0% (in mass) TaCl5 sample obtains a peak zT value of 1.64 at 773 K and a record zTave of 0.62 from 323 to 773 K, and the theoretically calculated conversion efficiency reaches 11.2%, it can be utilized for power generation and/or cooling at a broad temperature range. This strategy of introducing high-valence halides with heavy element can optimize the thermoelectric performance for other material systems.

The role of coalescence and ballistic growth on in-situ electrical conduction of cluster-assembled nanostructured Sn films

The electrical conduction of nanostructured Sn films assembled via Supersonic Cluster Beam Deposition is studied in-situ during film growth. The kinetic energy of Sn nanoparticles, in combination with low melting point of Sn, promotes coalescence phenomena, enabling the investigation of their impact on film morphology and on percolation threshold. A percolation threshold occurring at thicknesses much larger than the dimensions of Sn nanoparticles suggests that coalescence leads to the growth of disconnected, island-like structures. The deposition rate is found to influence coalescence dynamics during the early stages of film growth, allowing for the tuning of film microstructure from a more compact, island-like morphology to a more porous structure. The percolation threshold shifts accordingly from 24 nm to 3 nm film thickness. Upon completion of the percolation phase, film resistivity settles at values 2–3 orders of magnitude larger than that of bulk Sn, attributed to the nanogranular nature of cluster-assembled films. During the “3D conduction” phase, resistivity exhibits an increasing trend with thickness following a power law with an exponent value of 0.76–0.78. This behavior is attributed to the decrease in the density of interconnections between particles in the topmost layer during film growth, consistent with expectations in ballistic growth processes.

(Poster Award - Honorable Mention) Ta2O5 Catalyst Support for Polymer Electrolyte Fuel Cells

Pt/C is widely used as polymer electrolyte fuel cells (PEFC) electrocatalysts. The cathodic environment of PEFC is prone to high acidity and high potential, which can degrade cell performance due to carbon corrosion 1. Therefore, electrocatalysts with oxide support such as SnO2 supported on carbon-based materials have been developed, achieving high durability. Further improvement of their catalytic performance is desirable, using a Pt-based alloy catalyst and a mesoporous carbon (MC) 2,3. However, studies using SnO2 as a support have suggested that the low melting point of Sn caused alloying of Pt and Sn and/or melting of metallic Sn, causing degradation of catalytic activity 3. From these reasons, here, we focus on tantalum (Ta) with much higher melting point to fabricate Ta2O5/MC electrocatalysts support, which can support Pt alloy catalysts to achieve both high durability and high activity. Ta2O5 was prepared by a sol-gel method using Ta-ethoxide, and Pt-Co alloy nano-particles were deposited via the acetylacetonate method 4. The amount of Ta2O5 on the MC was set to be 30 and 60 wt.%, and the durability was evaluated by varying the amount of Ta2O5. The molar ratio of Pt to Co was set at 3:1. The microstructure of the electrocatalyst was observed by field-emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM), and the alloy was evaluated by XRD measurements. Half-cell tests were made to evaluate electrochemical performance and durability (load cycle and start-stop cycle). From the XRD measurements, the Pt peaks were shifted and the Ta2O5 peaks were confirmed, indicating that Pt-Co alloys were formed without forming the alloy of Pt and Ta. FESEM observation revealed that Ta2O5 particles were impregnated with a diameter of about 5 nm, and Pt-Co alloy particles were impregnated with a diameter of 2 to 3 nm. Some of catalyst particles were found to be impregnated on Ta2O5, but no significant selectivity to Ta2O5 was observed. Both Pt effective surface area (ECSA) and oxygen reduction reaction (ORR) activity of the prepared catalysts were higher than of Pt/C, confirming the positive effect of Pt-Co alloy and MC on activity enhancement. Figure 1 shows that the load potential cycle durability was improved using MC, and the start-stop cycle durability was improved by using Ta2O5. In particular, the electrocatalysts with a lower loading of Ta2O5 exhibited higher durability under load potential cycling and subsequent higher ECSA compared to the Pt-Co/C electrocatalyst. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Ohma, K. Shinohara, A. Iiyama, T. Yoshida, and A. Daimaru, ECS Trans, 41(1), 775 (2011).Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K.Sasaki, J. Electrochem. Soc., 165 (14), F1164 (2018).Inoue, M. Yasutake, Z. Noda, S. M. Lyth, M. Nishihara, A. Hayashi, J. Matsuda, and K. Sasaki, ECS Trans., 109 (9), 413 (2022).Hayashi, H. Notsu, K. Kimijima, J. Miyamoto, and I. Yagi, Electrochem. Acta., 53, 6117 (2008). Figure 1

An in situ elemental migration on a nanosize Cu–Sn interface in a microscope

Elemental migration between different elements is intrinsic process for diffusion. Most of the study focused on the presentative shape or size on of Kirkendall pores, yet on the intermediate migration process. A dynamic elemental transition trajectory recording provides realtime diffusion process on a Cu–Sn nanoscale interface is thus necessary to disclose intermediated reaction on diffusion process. In this work, elemental dynamic diffusion processes were recorded and analysed on a microsize Cu–Sn couple lamella by in situ transmission electron microscopy up to Sn melting point. Factors of atomic quantity, contact condition and temperatures were studied on its diffusion behaviours. The work shed new light on conventional metallographically interfaces diffusion and provide intrinsic clues for solder design.

The CPS's pre-heating effect on the capability to withstand extreme plasma loads

This work presents experimental studies of plasma surface interactions (PSIs) during QSPA plasma impacts on the Sn Capillary Porous Structures (CPSs) in conditions, simulating disruption and ELM-like loads. The 3D tungsten target filled by Sn was exposed to the plasma streams with an energy density of up to 3 MJ/m2 which resulted in tungsten melting and evaporation. The initial temperature of a sample between plasma pulses had two options: remained at a room value for one sample, and reached 300 C which is close to Sn melting point for another one. The number of plasma irradiations reached 100 pulses. It is shown that the particle ejection was observed during PSI for pre-heated as well as cold CPS targets. The difference in values of the number of particles ejected from the targets, their velocities, and the start-time during exposition is discussed. Particles leave the target surface during all expositional pulses for both CPS targets. The threshold character of the ejection is more pronounced for the cold target. After the 100 pulses reduced Sn pool is observed. Moreover, areas without Sn occur on the exposed targets. Nevertheless, the severe damage of the W base of the CPS targets is not revealed during high-cycle powerful plasma loads.

Versatile phosphor-in-glass based on Sn–F–P–O matrix with ultra-high color rendering for white LEDs/LDs

White light with excellent color rendering property has been highly required for comfortable and healthy illumination. A facile strategy to achieve high color rendering index (Ra >90) in practical applications is using near ultraviolet chips as excitation sources combined with RGB phosphors. However, achieving high color rendering with both blue chips and near-ultraviolet (NUV) chips for commercial phosphors dispersed in phosphor-in-glass (PiGs) materials is still a big challenge. In this work, the PiG based on the ultra-low melting point Sn–F–P–O glass with commercial green (Lu3Al5O12:Ce3+) and red (SrxCa1-xAlSiN3:Eu2+) phosphors has been successfully fabricated by one-step sintering method. The phase identification and distribution of monochromatic red phosphor in glass (R-PiG) and green phosphor in glass (G-PiG) were investigated in detail. The Sn2+ ions in Sn–F–P–O matrix show the intense blue emission bands centered at 420 nm under the excitation of NUV chips (365 nm). Notably, the polychromatic red/green phosphor in glasses (R/G-PiGs) are versatile and exhibited excellent color rendering (Ra = 93, Ra = 95, Ra = 92, respectively) properties excited by both blue chips, NUV chips and laser diodes (WLD). The working temperature of R/G-PiGs is stable at ∼33 °C and ∼55 °C when employed in WLEDs/WLDs (1 W), which greatly prevented the phenomenon of “thermal quenching” for the phosphors caused by high temperature. Thus, the versatile R/G-PiG with ultra-high color rendering and excellent thermal properties indicates its promising application in high-power white LEDs/LDs.

A distinctive Pb-Sn semi-solid additive manufacturing using wire feeding and extrusion

Based on the semi-solid forming technology, the semi-solid additive manufacturing platform was built in this study, and the forming process was carried out with Pb-Sn wire as raw material. The results showed that when z-axis moving distance of monolayer stacking is 4.2 mm, extruder head temperature reaches 240 °C and heating plate temperature reaches 160 °C, the microstructure is composed of spherical grains of Pb solid solution with average diameter of 13.4 μm and low melting point Sn phase distributed at the grain boundary, the corresponding overlap surface curvature is 0.429 mm−1; The macro morphology also showed the best characteristics with forming effective degree of 0.869 and forming layer height ratio of 1.004. The mechanical properties of semi-solid additive manufacturing sample with optimized processing parameters were tested, the vertical and horizontal tensile strength of the sample are 44.2 and 47.8 MPa respectively, and the elongation in the vertical direction of sample (29.1 %) is significantly higher than that (20.1 %) in the horizontal direction because of double necking phenomena, this deformation mechanical can be explained by the existence of several bonding areas in gauge segment and soft of bonding areas due to enrich of Sn. Finally, Pb-Sn parts with different shapes were formed. This study provides a basis for the further development of semi-solid additive manufacturing for aluminum.

Spreading behavior of Sn droplets impacting Cu and stainless steel substrates

With the development of droplet 3D printing, thermal spraying, spray molding, and other technologies, the collision diffusion process of metal droplets and metal substrates has become a key aspect in controlling these processes. This study used Sn droplets as the research object. Using a pneumatic pulse jet device, molten Sn droplets were impinged on the surface of copper and stainless steel substrates. The impact process was recorded by high-speed photography. The diffusion diameter and solid-liquid contact angle were measured from these images, revealing the difference in the diffusion of Sn droplets on different surfaces. This explains the difference in the droplet diffusion ability from the perspective of driving energy. The entire impact process and final morphology were considerably similar when the substrate temperature was lower than the melting point of Sn. When the substrate temperature was higher than the melting point of Sn, the entire diffusion behavior of the tin droplet from contacting the substrate to the steady state was investigated in stages. From the driving energy analysis, it was observed that the Sn droplet is mainly driven by its internal kinetic energy in the initial stage of diffusion. When the diffusion diameter approached the maximum value, the kinetic energy of Sn droplets gradually dissipated; the surface energy and viscous force work gradually increased, and the diffusion changed from a linear diffusion state to a slow diffusion state. Simultaneously, the surface energy and viscous force of the droplet played a key role. The adhesion of Sn droplets to the surface of the stainless steel substrate was very small, and the interface did not react, which caused the Sn droplets to shrink significantly on the stainless steel surface during the retraction stage.

Systematic investigation of the effect of Ni concentration in Cu-xNi/Sn couples for high temperature soldering

High temperature solders have experienced a marked increase in demand due to the boom of high power interconnects in electric vehicles and the miniaturisation of electronic devices. Transient liquid phase (TLP) bonding is a promising technology for these applications. Alloys from the Cu-Sn system widely used in conventional soldering processes have potential for high temperature applications if the relatively low melting point Sn phase can be consumed in a TLP process. This process results in a joint composed of Cu6Sn5 or Cu3Sn intermetallic compounds (IMCs) which have higher melting points than Sn. Alloying Ni to the Cu substrate promotes the growth rate of the (Cu,Ni)6Sn5 IMCs, significantly reduces the TLP processing time and costs, while suppressing the formation of (Cu,Ni)3Sn. However, the properties of the (Cu,Ni)6Sn5 formed also change significantly depending on the Ni concentration in the system. In this work, the composition, morphology, grain sizes and crystal structure of the (Cu,Ni)6Sn5 formed via the reaction of Sn and Cu-xNi substrates of different Ni concentrations are studied in detail via electron microscopy and synchrotron powder X-ray diffraction to provide a basis for further understanding of the physical, electrical and mechanical properties. The findings are further verified by density functional theory calculations. Additionally, the complex interplay of grain boundary diffusion rates and the IMC nucleation rate which accelerate with increasing Ni concentration, along with the Cu-xNi dissolution rate and the crystal growth rate which decrease with increasing Ni concentration are identified to be the main factors affecting the IMC growth rates.

A Novel Tin-Bonded Silicon Anode for Lithium-Ion Batteries.

Poor cyclic stability and low rate performance due to dramatic volume change and low intrinsic electronic conductivity are the two key issues needing to be urgently solved in silicon (Si)-based anodes for lithium-ion batteries. Herein, a novel tin (Sn)-bonded Si anode is proposed for the first time. Sn, which has a high electronic conductivity, is used to bond the Si-anode material and copper (Cu) current collector together using a hot-pressed method with a temperature slightly above the melting point of Sn. The cycling performance of the electrode is studied using a galvanostatic method. Nanoindentation and peeling tests are conducted to measure the mechanical strength of the electrodes. Direct current polarization and galvanostatic intermittent titration techniques are applied to assess the conductivity of the composites. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy are conducted to evaluate the effect of the coating layer on the cycling ability of the composites. The Sn-bonded Si anodes show superior cycling stability and high rate performance with an improved initial Coulombic efficiency. Analyses reveal that the low-melting-point Sn helps to markedly improve the electronic conductivity of the electrodes and serves as a metallic binder as well to enhance the adhesive strength of the electrode. It is hopeful that this novel Sn-bonded Si anode provides a new insight for the development of advanced Si-based anodes for LIBs.

Development of a Thin Film Gas Microsensor of Low Power Consumption for Monitoring of Environmental Pollutants

In this work the development and microfabrication of a gas sensor is described. The microsensor consists of a thin film of SnO2 deposited on a micro-machined silicon substrate [1] . This film is heated by a microheater integrated in the microsensor to obtain a temperature between 100 and 400 °C (microhot plates). With the aim to analyze the proposed design, simulations of the mechanical (structural rigidity, maximum and minimum sizes of the structures) and thermal behaviors (distribution of temperatures and electrical powers involved) were performed [2].The manufacturing process carried out in a clean-room area involved a series of steps that include: the design and mastering of masks, photolithography operations, sputtering metal deposition, chemical attacks with dry (RIE) and wet etching (with KOH), dicing of the silicon wafer in individual sensors of 3mm x 3mm and finally, the encapsulation of the sensors by means of wire bonding (see Fig.1)It is important to note that the silicon substrate is micromachined in order to reduce its thermal inertia and the power necessary to heat the sensor film. Such a film is deposited on a silicon nitride insulating membrane that is only 250 nm thick, which significantly reduces the consumption in terms of electrical power, with respect to the known commercial sensors.The SnO2 thin films were fabricated using the technique Rheotaxial Growth and Thermal Oxidation technique (RGTO) on a microhot plate[3]. RGTO is a technique composed of two steps: depositionof a Sn thin film on the substrate maintained at the temperature slightly above the Sn melting point and oxidation at a temperature up to 400 oC. In the first step of the RGTO technique tin was deposited by sputtering DC on the central part of the membrane by means of a shadow mask. During the deposition, substrates were heated at 310 oC . Thickness of the deposited tin was 100 nm. The second step, involving the thermal oxidation of Sn thin layer, was performed in two sub-steps: 2 h at 250 oC and 60 h at 450 oC in wet air. The final result is a granular film with quasi-spherical grain shape. The microstructure was characterized by X-ray diffraction analysis and scanning electron microscopy (SEM).The characterization of the sensors with gases at different concentrations was done. In the case of ammonia in air, a linear response between 50ppm (maximum permissible limit value) and 6ppm were obtained, the latter being its detection limit (Fig 2). Also H2S were tested (Fig. 3) . The measurements were made by applying a voltage of 5 V to the heater, obtaining dissipated power between 40 and 50 mW. The operating temperature of the sensor film under these conditions was approximately 180°C. On the other hand, the sensor film is connected to a potential of 1 V. The sensor response is then measured as the variation of the electrical resistance as a function of the response time.Additionally, electronic control and signal processing was developed, suitable for incorporating sensors into portable instruments. [4]The results of this development also allow us to have a platform for the microfabrication of gas sensors at the request of other public institutions or the private sector. References 1] Mirzaei, A., Leonardi, S.G., Neri, G. Detection of hazardous volatile organic compounds (VOCs) by metal oxide nanostructures-based gas sensors: A review. Ceramics International 42, 15119–15141(2016).[2] G.Korotcenkov, B.K. Cho, Metal oxide composites in conductometric gas sensors: Achievements and challenges . Sensors and Actuators B, Vol. 244, 182–210 (2017).[3] G. Sberveglieri, G. Faglia, S. Groppelli, P. Nelli , A. Camanz. A new technique for growing large surface area SnO2 thin film (RGTO technique) . Semicond Sci. Technol. 5:1231–1233 (1990)[4] J.Vorobioff , D. F. Rodriguez, N.G. Boggio , C.A. Rinaldi . Development of an Electronic Nose for Determining the Freshness of Fish by the Desorption Constants of Sensors. Sensors Letters, Vol. 11, N° 12, 2013, pp. 2215-2217. Figure 1

The influence of Ag on the microstructure, thermal properties and mechanical behavior of Sn–25Sb-xAg high temperature lead-free solder

Abstract Adding Ag to Sn–25Sb solder to prepare Sn–25Sb-xAg (x = 0, 2.5, 3.0 and 3.5, x is the mass percentage) solder alloys. Using optical microscope, JSM-5610LV field emission scanning electron microscope, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Vickers hardness tester and tensile testing machine to test the microstructure of the solder alloy, thermal performance and mechanical performance. The microstructure test results of the solder alloys show that Ag3 (Sn, Sb) intermetallic compounds (IMCs) are formed in the Sn–25Sb-xAg (x = 2.5, 3.0 and 3.5) alloys after Ag is added, and they are dispersed in β-Sn phase. Ag3 (Sn, Sb) IMCs are pinned at the grain boundary of β-Sn and SbSn phases. Moreover, it is also found that the addition of Ag makes the β-Sn and SbSn phases in the Sn–25Sb-xAg (x = 2.5, 3.0 and 3.5) solder alloy refined. DSC analysis results show that the melting point of Sn–25Sb-xAg (x = 0, 2.5, 3.0 and 3.5) solder alloy decreases slightly after adding Ag. Among them, the pasty range of Sn–25Sb-2.5Ag solder alloy is the smallest at 12.84 °C, followed by Sn–25Sb-3.5Ag at 14.81 °C. In the mechanical performance test of the solder alloy, it is found that the ultimate tensile strength (UTS) and elongation of the Sn–25Sb-xAg solder alloy increase with the increase of Ag addition. Sn–25Sb-3.5Ag solder alloy has the highest UTS and elongation, which are 69.25 MPa and 8.02% respectively. The increase is mainly through fine-grain strengthening and dispersion strengthening mechanisms.

Effect of Ga on the Oxide Film Structure and Oxidation Resistance of Sn-Bi-Zn Alloys as Heat Transfer Fluids.

The effect of gallium on the oxide film structure and overall oxidation resistance of low melting point Sn–Bi–Zn alloys was investigated under air atmosphere using thermogravimetric analyses. The liquid alloys studied had a Ga content of 1–7 wt.%. The results showed that the growth rates of the surface scale formed on the Sn–Bi–Zn–Ga alloys conformed to the parabolic law. The oxidation resistance of Sn–Bi–Zn alloys was improved by Ga addition and the activation energies increased from 12.05 kJ∙mol−1 to 22.20 kJ∙mol−1. The structure and elemental distribution of the oxide film surface and cross-section were found to become more complicated and denser with Ga addition. Further, the results of X-ray photoelectron spectroscopy and X-ray diffraction show that Ga elements accumulate on the surface of the liquid metal to form oxides, which significantly slowed the oxidation of the surface of the liquid alloy.

Microstructure and elemental analysis of powder iron-based composite materials

This article studies the kinetics of structure formation of a composite powder material containing solid lubricants such as graphite, talc and zinc stearate. For the experiments were prepared charge containing powders, wt.%: Cu – 4-18; Sn – 1-2.0; C – 1.5-2.5; talc – 2.0-3.5; zinc stearate – 0.5, Fe – the rest. Mixing of powders was carried out in a Y-shaped mixer, pressing of charges was carried out on a hydraulic press at pressures of 400-1000 MPa, and sintering of compacts – in a conveyor furnace in a protective gas (endothermic gas) in the temperature range 850-1150°C. There is no pearlite in the microstructure of iron-bronze sintered at 850°C. This is due to the adsorption capacity of talc on the surface of iron particles, which prevents the diffusion of carbon into the iron crystal lattice. An increase in the sintering temperature to 1000°C leads to the formation of pearlite in the structure of iron-bronze, while pearlite prevails over ferrite. This indicates the partial burnout of talc from the surface of the iron particles and the open paths of carbon diffusion. At a sintering temperature of 1150°C, a pearlite structure and a network of light inclusions are formed in the microstructure of iron-bronze samples. The study of the chemical composition of light inclusions with a micro-X-ray spectral analyzer showed that these inclusions contain solid solutions of variable compositions either Fe-Cu-Sn, Cu-Fe-Sn or Cu-Sn-Fe. To confirm these assumptions, X-ray phase analysis was performed. The diffraction patterns of these samples are reflections of Fe and Cu. The absence of diffraction effects characteristic of Sn is due to its solubility in the Cu lattice. This is due to the low melting point of Sn (232°С) and its ionic radius, which allows the isomorphic substitution of Cu and Fe ions with Sn ions (their difference is no more than 15%)

Permeation behavior of low-melting-point Sn–Bi alloy in the fiber channel of pine wood

Wood and metal are the two most common materials, both with distinct advantages and disadvantages. Through the metallization process, the inherent defects of the two materials can be avoided, so that the composite material exhibits excellent structural properties and anisotropy. In this study, the pine wood was pretreated with dilute ammonia (5%), and then the low melting point Sn–Bi alloy was filled into the pine fiber without lignin at 180 °C and 3000 Pa. The density of metallic wood is about 3 times that of pine, while the impact toughness can be up to 2 times that of pine. By building the capillary buddle model, the filling mechanism of molten metal in pine wood was analyzed, and it was clear that high vacuum, high temperature, large porosity and large tracheid diameter are the conditions for rapid penetration. The conductive anisotropy was found on metalized wood, making metalized wood available in different places with requirements for electromagnetic shielding and antistatic.

Development of a Thin Film Gas Microsensor of Low Power Consumption for Monitoring of Environmental Pollutants

In this work the development and microfabrication of a gas sensor is described. The microsensor consists of a thin film of SnO2 deposited on a micro-machined silicon substrate [1] . This film is heated by a microheater integrated in the microsensor to obtain a temperature between 100 and 400 °C (microhot plates). With the aim to analyze the proposed design, simulations of the mechanical (structural rigidity, maximum and minimum sizes of the structures) and thermal behaviors (distribution of temperatures and electrical powers involved) were performed [2].The manufacturing process carried out in a clean-room area involved a series of steps that include: the design and mastering of masks, photolithography operations, sputtering metal deposition, chemical attacks with dry (RIE) and wet etching (with KOH), dicing of the silicon wafer in individual sensors of 3mm x 3mm and finally, the encapsulation of the sensors by means of wire bonding (see Fig.1)It is important to note that the silicon substrate is micromachined in order to reduce its thermal inertia and the power necessary to heat the sensor film. Such a film is deposited on a silicon nitride insulating membrane that is only 250 nm thick, which significantly reduces the consumption in terms of electrical power, with respect to the known commercial sensors.The SnO2 thin films were fabricated using the technique Rheotaxial Growth and Thermal Oxidation technique (RGTO) on a microhot plate[3]. RGTO is a technique composed of two steps: depositionof a Sn thin film on the substrate maintained at the temperature slightly above the Sn melting point and oxidation at a temperature up to 400 oC. In the first step of the RGTO technique tin was deposited by sputtering DC on the central part of the membrane by means of a shadow mask. During the deposition, substrates were heated at 310 oC . Thickness of the deposited tin was 100 nm. The second step, involving the thermal oxidation of Sn thin layer, was performed in two sub-steps: 2 h at 250 oC and 60 h at 450 oC in wet air. The final result is a granular film with quasi-spherical grain shape. The microstructure was characterized by X-ray diffraction analysis and scanning electron microscopy (SEM).The characterization of the sensors with gases at different concentrations was done. In the case of ammonia in air, a linear response between 50ppm (maximum permissible limit value) and 6ppm were obtained, the latter being its detection limit (Fig 2). Also H2S were tested (Fig. 3) . The measurements were made by applying a voltage of 5 V to the heater, obtaining dissipated power between 40 and 50 mW. The operating temperature of the sensor film under these conditions was approximately 180°C. On the other hand, the sensor film is connected to a potential of 1 V. The sensor response is then measured as the variation of the electrical resistance as a function of the response time.Additionally, electronic control and signal processing was developed, suitable for incorporating sensors into portable instruments. [4]The results of this development also allow us to have a platform for the microfabrication of gas sensors at the request of other public institutions or the private sector.

Tuning particle and phase formation of Sn/carbon nanofibers composite towards stable lithium-ion storage

Sn is an attractive anodic material for lithium-ion batteries. High-temperature reduction is large-scale technique since most elemental Sn exists in the form of oxides. However, it is still a challenge to fabricate high performance Sn-based anodes with well-dispersed Sn nanoparticles in conductive matrix due to low melting point of Sn and tendency of particle agglomeration. Herein, we systematically investigate the influences of reduction conditions on particle and phase formation of Sn/carbon nanofibers (CNF) from electrospun SnO2/polyacrylonitrile. It is shown that the SnO2 can be reduced to Sn with slight aggregation at low temperature of 500 °C in a reducing atmosphere, but the composites possess poor electronic conductivity. As raising temperature, the grain size of Sn increases accordingly leading to sluggish Li+ internal diffusion dynamics. While in an inert atmosphere, the SnO2 cannot be reduced completely at low temperature until 650 °C. By optimal control, the Sn/CNF–N2-700 calcined at 700 °C in N2 atmosphere presents the best electrochemical Li-ion storage performance among these samples, which delivers a reversible capacity of 932.2 mAh g−1 at 100 mA g−1 and stable cycling life with 760.3 mAh g−1 retention after 200 cycles. This study may provide optimization guidance for industrial manufacture of Sn-based materials.

Temperature dependency of the growth rate of (Cu,Ni)6Sn5 on Cu-xNi substrates

Cu6Sn5 is the most common intermetallic compound (IMC) in lead-free solder joints, and is also a promising anode material for advanced lithium-ion batteries. It has been reported that the growth rates of (Cu,Ni)6Sn5 in Sn-based solder alloy/Cu-xNi substrate couples are greatly accelerated compared to the intermetallic layers that form on a pure Cu substrate. Due to the faster growth rates, solidification can progress through a transient-liquid-phase reaction in commercially relevant timeframes. The complete reaction of the liquid Sn in the couple will result in a joint that is stable at high temperatures. Furthermore, the presence of Ni in the intermetallic suppresses the formation of a Cu3Sn layer and stabilises the (Cu,Ni)6Sn5 preventing a polymorphic transformation on cooling along with the associated induced strains. This study investigates the growth rates of (Cu,Ni)6Sn5 in Sn/Cu-xNi couples, where 0 <= x <= 14 wt%, and reports on the effect of temperature on the growth rates at temperatures above the melting point of Sn (231.9°C) between 232°C and 300°C. The results show the highest growth rates occur in the Sn/Cu-6Ni couples, and there is an increase of the (Cu,Ni)6Sn5 growth rate with increasing temperature due to faster diffusion and reaction rates.

Nickel–tin transient liquid phase sintering with high bonding strength for high-temperature power applications

We performed 30Ni–70Sn (wt%) transient liquid phase sintering (TLPS) bonding with micro-sized Ni and Sn powders for high-temperature power applications. A Ni–Sn paste was fabricated and TLPS bonding was performed. We investigated the interfacial reactions, transformations into Ni3Sn4 intermetallic compound (IMC) phases, and joint strength in this study. The Ni–Sn TLPS bonding was an easy and simple process under a relatively low bonding temperature and short bonding time. After TLPS bonding, low melting point Sn element was completely consumed, and the bonded joint was composed of Ni3Sn4 IMCs and the remaining Ni particles. The Ni3Sn4 IMC joint formed with remaining Ni particles was very stable. All the Ni–Sn TLPS samples had high shear strengths of over 70 MPa, and the shear strength was approximately 32% higher than that of the conventional Sn–3.0Ag–0.5Cu solder joint. The Ni–Sn TLPS bonded joints in the present study were not brittle and exhibited superior adhesion strength. This suggests high applicability of the Ni–Sn TLPS bonding for high-temperature power electronic applications in future EV/HEV systems.

Delicately designed Sn-based electrode material via spray pyrolysis for high performance lithium-ion battery

A new and feasible strategy for preparing Sn@ZnO@N-C composites as high-performance anode materials with respect to lithium ion battery (LIB) was developed through dry spray and followed by high-temperature pyrolysis. Porous MOF ZIF-8 was employed as template to provide spherical interconnected C-N framework as accommodation for active nanosize Sn and ZnO particles (designated as Sn@ZnO@N-C-y, y = 1, 2 and 3). Considering the low melting point of Sn (232 °C), pyrolysis is a sound technique to yield Sn@ZnO@N-C-y products with variable structural features through tailoring the quantity of stock SnCl2 salt in the preparation solutions. Electrochemical performance of the Sn@ZnO@N-C-y composites was examined in a form of anode in coin-type LIB devices. Results indicate that all the produced Sn@ZnO@N-C-y composites exhibit superior electrochemical performance. The quantity of the added raw SnCl2 imposes a profound impact on the formation of physical structures and consequent specific capacity and cycle life of the Sn@ZnO@N-C-y composite based anodes. Of the anode options, it is noted that Sn@ZnO@N-C-2 with a yolk-shell structure delivers the highest cycle stability, which retains a stable capacity of 1114.8 mA h g−1 after 500 cycles at a current density of 100 mA g−1. The void space in Sn@ZnO@N-C-2 is beneficial to buffer against volume variations. Meanwhile, the C-N framework enhances electronic conductivity to a great degree and N contributes dramatically to the excellent capacity retention and superior rate capability. Such a newly designed synthesis pathway provides new guidance to the design and manufacturing of nanostructured anode materials with high performance for next-generation LIB.