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Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100 °C to 175 °C for up to 18,000 hours. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

In this work, different types of polymer and MnO 2 cathode capacitors are tested for scintillation breakdown using a constant current stress (CCS) technique modified to allow detection of amplitudes and duration of current spikes. Monitoring of leakage currents with time under bias is used to assess the effect of scintillations. The appearance and composition of damaged sites are examined after deprocessing and cross-sectioning. Thermal processes during scintillations are analyzed, a mechanism of breakdown based on growth of conductive filaments in the dielectric is suggested, and self-healing processes in polymer and MnO 2 cathode capacitors is discussed.

Popcorning is a well-known effect in plastic encapsulated microcircuits (PEM) and it occurs in chip tantalum capacitors. The sensitivity of components to the presence of moisture during soldering is characterized by the moisture sensitivity level (MSL); however, contrary to PEMs, there is no standard procedure for establishing MSL for tantalum capacitors. The effect of absorbed moisture on soldering related degradation and failures in tantalum capacitors have not been studied properly yet, and there is no sufficient information regarding the difference in the sensitivity to soldering between polymer and MnO2 capacitors. In this work, 16 types of polymer and 9 types of MnO2 tantalum capacitors with different moisture content have been tested before and after reflow soldering. The level of moisture release during soldering has been estimated and thermo-mechanical analysis used to assess deformation of capacitors during soldering simulations. Results show that moisture uptake in similar parts is approximately two times greater in polymer than in MnO2 capacitors. Cracking of the case and degradation of parameters can occur in both types of parts, but MnO2 capacitors are much more likely to fail catastrophically with a short circuit and possible ignition during the first power-on cycle. This type of failure in MnO2 capacitors is lot-related, can occur even at derated voltages and relatively low levels of moisture sorption that corresponds to room conditions. Baking before soldering is an effective measure to prevent failures even in lots susceptible to popcorning damage.

The basic bilayer of all types of tantalum capacitors, tantalum anode, and anodic oxide film of tantalum as a dielectric is not a thermodynamically stable system. This is demonstrated by the tantalum-oxygen equilibrium diagram that does not contain two-phase equilibrium areas for pure tantalum and tantalum pentoxide]. Relaxation of the Ta-Ta2O5 system into the thermodynamically stable state occurs through oxygen migration from Ta2O5 to Ta, resulting in oxygen vacancies in the tantalum oxide dielectric. Conductivity of the dielectric and, thereby, DCL of tantalum capacitor increase exponentially with the concentration x of oxygen vacancies in the depleted with oxygen Ta2O5–x. Another reason for the thermodynamic instability of tantalum capacitors is the amorphous structure of the anodic oxide film of tantalum formed on crystalline tantalum. Amorphous dielectrics trend to ordering and crystallization spontaneously to reduce their internal energy. Growth of crystalline inclusions in amorphous matrix of the anodic oxide film induces mechanical stress in the film, which results in a disruption of the dielectric and, thereby, in the failure of the capacitor.

The automization complex device SOLARTRON-1280C was used for measurement electrical parameters of the industrial tantalum electrolytic capacitors. It was shown that the method for detection of the defective products is applied to constant current mode and impedance measurements. The impedance measurements was used for determination of the electric capacity tantalum capacitors and how it depends on the aperiodic current frequency. In addition impedance method is able to indicates on the secondary processes that occurs in the capacitor when it works in electric circuit. The general parameters of the tantalum capacitors in direct current were determined by polarization methods.

Printed Circuit Boards (PCB), secondary source of critical metals, are usually recycled to recover precious metals. Alternative routes, aiming to pre-concentrate critical metals, were tested at lab scale. An up-scaling process is proposed involving a thermomechanical separation of PCB and surface mounted devices (SMD). PCB without SMD are treated by solvolysis for desilication and debromination. Further calcination provides a presumably leachable metallic mix. Tantalum capacitors, a specific type of SMD, are treated by pyrolysis, to isolate metallic cores, which are further leached to obtain 92% pure tantalum oxide. LCA data show that tantalum recycling process is profitable for the environment.

Because of the low concentrations of Tantalum on printed wiring boards, today it is not economically viable to recycle Tantalum in pyro- and hydrometallurgical processes. However, in case the Tantalum can be up concentrated, the recycling of the Tantalum can become economically viable in the multi-stage process used to refine Tantalum from ores. Therefore, the presented research investigates the techno-economic potential of selectively removing Tantalum capacitors from PWBs prior to treating the complete PWBs in integrated precious metal smelting and refining installations. In the presented research the economic potential is analysed using return on investment analysis for automated selective dismantling and the viability of manual selective dismantling. These analyses are based on the measured metal concentration of Tantalum capacitors, the composition of a typical PWB and the results of lab experiments for the removal and detection of components using deep learning computer vision.

Contrary to conventional tantalum capacitors with MnO2 cathodes, chip polymer tantalum capacitors (CPTCs) might degrade in both high humidity and dry environments. A better understanding of the kinetics of moisture content variations in CPTCs is necessary to determine bake-out conditions for the parts before soldering to avoid pop-corning failures and to select adequate preconditioning before reliability and qualification testing. In this paper, ac characteristics in different types of CPTCs have been studied with time during moisture sorption and desorption at temperatures from room to 125 °C. Capacitance increased with moisture content from minimal to maximal values reproducibly. This allowed using tantalum slugs as humidity sensors and measurements of capacitance variations with time to describe processes of moisture diffusion. A model that relates characteristic times of capacitance variations with the size of the case and moisture characteristics of polymer materials has been developed. Temperature dependencies of the characteristic times follow Arrhenius law with activation energy in the range from 0.4 to 0.5 eV. The equivalent series resistance (ESR) remained relatively stable during environmental testing, but dissipation factors (DFs), reached maximum and increased more than 10 times at characteristic times of moisture accumulation or release. The phenomena have been explained by changes in the charge absorption processes caused by variations of the barrier at the conductive polymer/Ta2O5 interface with moisture content.

High-density, point-of-load (PoL) power conversion and power delivery are required to continue scaling electronic systems with increased functionality, more bandwidth, and smaller sizes. To meet the demands of these highly complex and miniaturized electronic systems, new 3-D integration schemes of advanced passive and active components are needed to enable the next-generation power distribution networks (PDNs). In addition, shorter interconnect lengths are required to provide low losses and better transient response in switch-based power conversion systems. Tantalum capacitors have the potential to provide some of the highest volumetric densities of any current capacitor technology, but are generally bulky components with low frequency stability, limiting their use in future 3-D power systems. In this paper, a process for the embedding and integration of ultrathin, high-density tantalum capacitors with improved frequency stability is demonstrated. The 5-V capacitors show a density of $1~\mu \text{F}$ /mm2 at 1 MHz with only a 100- $\mu \text{m}$ thickness, and are shown to be capable of direct integration on silicon for short interconnect length of $ . The electrical performance of the capacitors is tested after integration and shows that they retain high capacitance density and low equivalent series resistance (ESR), while also providing low leakage currents. The combination of low loss, high volumetric density, and 3-D integration capability make the capacitors an ideal candidate for next-generation power modules.

The dissolution of MnO2 from tantalum capacitor scrap using organic acids in various process conditions was studied. The initial materials were of two types: LTC (leaded tantalum capacitors) and SMDTC (surface-mounted device tantalum capacitors). The research materials were prepared by pyrolysis, grinding and sieving and the preparation processes were characterized. Dissolution of MnO2 was carried out with the use of sulfuric acid solutions with the addition of acetic, ascorbic, citric and oxalic organic acids. Results show that the addition of organic acids significantly improves dissolution yields (72-94 vs 90-99 % for H2SO4 and acid mixtures, respectively). In practice, a concentration of organic acid above 1 M results in the complete removal of MnO2.

Despite increasing pressure to reduce the consumption of critical resources, a number of highly relevant elements are still not being recycled from electronics, or only in the few applications, where they are used in bigger units. In high volume products and particular mobile products such as smartphones the content of these materials is low per unit, but still a large quantity when multiplied with millions of units shipped per year. The sustainably SMART projects explores the option to separate components containing tantalum, neodymium and tungsten from disassembled smartphones as these metals are lost in conventional electronics waste recycling processes. In this paper the target components are tantalum capacitors, loudspeakers, and vibration motors. Example quantities per device are explored and mirrored against current and potential recycling processes.

LTCC multilayer substrate (LTCC, Low Temperature Co-fired Ceramic) is one of the most widely used substrate in the high performance MCM (MCM, multi-chip module). Many kinds of passive elements and active devices can be integrated on the surface of the substrate. As one kind of the passive element, solid tantalum electrolytic capacitor has many advantages such as the bigger capacity per unit volume and the lower resistivity impedance, which are benefit for the emission performance of the MCM modules. In this paper, two kinds of process are used for the assembly of large-scale solid tantalum electrolytic capacitor surface mounted on the LTCC multilayer substrate. Verified experiments are carried out on the basis of soldering and experimental process analysis. A new soldering method is creatively proposed to solve the reliable problem of the soldering of solid tantalum electrolytic capacitors on the LTCC substrate. After environment tests, the resistance between tantalum capacitor lead and soldering pad is less than 100 milliohm, the shear strength of tantalum capacitor joint is larger than 50N. And this method is successfully applied in the existing products.

This paper focuses on the development of new 150°C capable surface mount polymer tantalum capacitors and the enabling technologies. The conductivity stability of the conducting polymers at high temperatures as well as the equivalent series resistance (ESR) stability of the polymer tantalum capacitors at these temperatures were investigated in this study. Analysis of the oxygen permeation paths causing polymer oxidation and materials solutions for preventing oxygen permeation and polymer oxidation are described. The development of new cathode and protective coating material technology is presented. Their effectiveness in providing high temperature ESR stability is demonstrated by high temperature life test at 150°C of polymer capacitors.

High-density passive components are needed for continued miniaturization of complex high-performance electronic systems. Tantalum (Ta) capacitors provide some of the highest volumetric densities achieved due to their combination of high-surface area and relatively high dielectric constant, but suffer from low frequency stability and large form-factors due to the electrode design. In this paper, a printed thin-film tantalum capacitor design is presented. Tantalum capacitor arrays of 1 μF/mm2 up to and beyond 1 MHz. The improved frequency stability comes from the ultra-thin structure of the capacitors, which reduces the path length of the charging and discharging current. The capacitors showed low equivalent series resistance and consistent electrical performance before and after thermal moisture testing at 65°C and 95% relative humidity for 500 h and 1000 h. Due to the ultra-low form-factor, the thin-film Ta capacitor technology can be extended to highly-miniaturized power converters with efficient substrate- or wafer-scale integration.

Recycling rare metal tantalum from waste tantalum capacitors (WTCs) is significant to alleviate the shortage of tantalum resource. However, environmental problems will be caused if the organic materials from WTCs are improperly disposed. This study presented a promising vacuum pyrolysis technology to recycle the organic materials from WTCs. The organics removal rate could reach 94.32 wt% according to TG results. The optimal parameters were determined as 425 °C, 50 Pa and 30 min on the basis of response surface methodology (RSM). The oil yield and residual rate was 18.09 wt% and 74.94 wt%, respectively. All pyrolysis products can be recycled through a reasonable route. Besides, to deeply understand the pyrolysis process, the pyrolysis mechanism was also proposed based on the product and free radical theory. This paper provides an efficient process for recycling the organic material from WTCs, which can facilitate the following tantalum recovery.

The treatment of end-of-Life products is one of the key steps for progression towards a circular economy. In this context, mobile phone recycling has attracted considerable attention in recent years due to the high metal concentrations in printed circuit assemblies (PCAs). Contrary to precious metals, the recycling technologies for tantalum and rare earths are less well established despite their high importance for future sustainable technologies. In this study, mobile phone samples were manually dismantled into their main constituents and the qualitative distribution of elements in the PCA was determined. Tantalum capacitors can be visually distinguished from other components, whereas neodymium was detected in easily separable non-magnetic components sized between 0.5 and 1.5 mm. From tantalum capacitors, a tantalum rich-powder with a grade of 50% was obtained via a leaching process followed by an oxidizing heat treatment, while neodymium-rich fractions (4 to 14%) were obtained by sieving, magnetic and density separations., SCOPUS: cp.p, info:eu-repo/semantics/published

Waste printed circuit boards (WPCBs) are valuable urban ore for recycling. Many efforts have been done to recover resources from basal boards of WPCB. In addition to basal boards, WPCBs contain many electronic components. However, the recycling technology for electronic components has been poorly developed. This study proposed an integrated and environment-friendly technology for recycling waste tantalum capacitors (WTCs) of WPCBs. Firstly, the WTCs were treated by argon pyrolysis to decompose mold resin. The pyrolysis temperature of 550 °C and holding time for 30 min were considered as the optimal parameters. Then, the pyrolysis residues were performed by crush and magnetic separation to recover nickel-iron terminals. Finally, chloride metallurgy (CM) was used to recover rare metal tantalum (Ta). The Ta recovery rate could reach 92.87 ± 0.36%. The optimal parameters were determined as temperature of 493 °C, adding FeCl 2 ·4H 2 O of 53 wt% and holding time for 150 min based on the response surface methodology (RSM). This study exploits an efficient approach for recycling WTCs and provides a reference for future industrial application.

Tantalum capacitors (TCs) are widely used in electronic appliances. The rapid replacement of electronic products results in generating large amounts of waste TCs (WTCs). WTCs, rich in valuable tantalum, are considered as high quality tantalum resources for recycling. However, environmental pollution will be caused if the organics of WTCs were not properly disposed. Therefore, effectively recycling the organics of WTCs is significant for recovering the valuable parts. This study proposed an argon (Ar) pyrolysis process to recycle the organics from WTCs. The organic decomposition kinetic was first analyzed by thermogravimetry. The results showed that the organics were decomposed in two major steps and the average activation energy was calculated to 234kJ/mol. Then, the suitable pyrolysis parameters were determined as 550°C, 30min and 100ml/min. The organics were effectively decomposed and converted to oils (mainly contained phenol homologs and benzene homologs) and gases (some hydrocarbon). These pyrolysis products could be reutilized as energy sources. Moreover, based on the products and bond energy theory, the pyrolysis mechanisms of the organics were also discussed. Finally, a reasonable technological process for products utilization was presented. This study contributes to the efficient recycling the organics before valuable material recovery from WTCs.

High temperature and high electric field applications in tantalum and niobium capacitors are limited by the mechanism of ion migration and field crystallization in a tantalum or niobium pentoxide insulating layer. The study of leakage current (DCL) variation in time as a result of increasing temperature and electric field might provide information about the physical mechanism of degradation. The experiments were performed on tantalum and niobium oxide capacitors at temperatures of about 125°C and applied voltages ranging up to rated voltages of 35 V and 16 V for tantalum and niobium oxide capacitors, respectively. Homogeneous distribution of oxygen vacancies acting as positive ions within the pentoxide layer was assumed before the experiments. DCL vs. time characteristics at a fixed temperature have several phases. At the beginning of ageing the DCL increases exponentially with time. In this period ions in the insulating layer are being moved in the electric field by drift only. Due to that the concentration of ions near the cathode increases producing a positively charged region near the cathode. The electric field near the cathode increases and the potential barrier between the cathode and insulating layer decreases which results in increasing DCL. However, redistribution of positive ions in the insulator layer leads to creation of a ion concentration gradient which results in a gradual increase of the ion diffusion current in the direction opposite to the ion drift current component. The equilibrium between the two for a given temperature and electric field results in saturation of the leakage current value. DCL vs. time characteristics are described by the exponential stretched law. We found that during the initial part of ageing an exponent n = 1 applies. That corresponds to the ion drift motion only. After long-time application of the electric field at a high temperature the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5. Here, the equilibrium between the ion drift and diffusion is achieved. The process of leakage current degradation is therefore partially reversible. When the external electric field is lowered, or the samples are shortened, the leakage current for a given voltage decreases with time and the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5, thus the ion redistribution by diffusion becomes dominant.

Summary Circular economy approaches aim to close material cycles along the value chain. As such, the circular economy can be a long-term strategy to mitigate the risks of critical raw material (CRM) supply. Tantalum, with a current end-of-life recycling rate of less than 1%, has been intermittently discussed as critical. Even though the specificity of tantalum applications and high-mass fractions of tantalum in relevant components provide good boundary conditions, recycling barriers hinder the successful implementation of recycling technologies. With this case study, we identify potentials and barriers for implementing the recovery of CRM, using the example of tantalum. To this end, information about visually identifiable tantalum capacitors (VICs) and printed circuit boards (PCBs) in various equipment types was obtained by disassembly campaigns for mobile phones, smartphones, tablets, notebooks, desktop personal computers, flat screen monitors, servers, etc., and the chemical analyses of resulting fractions. Results show great differences in the application of tantalum in various equipment types. Because of this, the tantalum potential of put-on-market (POM) or of waste electric and electronic equipment (WEEE) devices differs between products and regions. Worldwide, the highest POM tantalum flows originate from desktop computers, but in Germany they originate from notebooks. A focus on particular products leads to higher yields in recycling and supports circular economy approaches. Recycling of tantalum from WEEE is generally possible. But an accurate separation of tantalum from PCBs is not feasible solely by separation of VICs. This process also leads to the loss of silver. Further, this study reveals potential miniaturization trends, decreasing the use of VICs, with an anticipated substitution of tantalum with niobium. These barriers impede long-term recycling strategies for tantalum aimed at establishing a circular economy.

Recycling e-waste has been a significant topic for environmental protection and also for resource recovery. Waste tantalum capacitors (WTCs), widely existing in discarded small appliances, are rich in high quality tantalum (Ta) resources. However, recovering Ta from WTCs is difficult due to the tightly covered mold resin. This study proposes an efficient and environmentally friendly process using supercritical water (SCW) to decompose the organics and recover Ta from WTCs. Two methods of SCW were studied: SCW depolymerization (SCWD) and SCW oxidation (SCWO). The results indicated that the mold resin (packing) of WTCs were effectively decomposed by SCW treatments. The organic decomposition efficiency in SCWD was lower than that in SCWO. The optimal parameters for SCWD and SCWO were, respectively, considered to be 425 °C, 25 MPa, and 120 min and 400 °C, 25 MPa, and 90 min, adding a 10% volume ratio of H2O2. After SCWO treatment, Ta electrodes were directly recovered, and the purity of Ta could reach 93.18%....

Waste tantalum capacitors (WTCs), dismantled from waste printed circuit boards, are considered a high quality tantalum (Ta) resource. Ta is a rare and strategic material. Nearly half of the Ta consumption is used for manufacturing tantalum capacitors. Furthermore, large amounts of energy and chemicals are consumed during the Ta purification process. Therefore, recovering Ta from WTCs can sustainably utilize the Ta resource and reduce pollution. However, the recycling technology has been poorly developed. This study proposed vacuum pyrolysis (VP) and mechanical–physical separation (MPS) to recover Ta and other materials from WTCs. First, the WTCs were treated by VP to decompose the organics. The suitable VP parameters were considered as 400 °C, 50 Pa, and 60 min. Then, the residues were performed by MPS. Consequently, nickel–iron terminals were recovered by magnetic separation. Ta and silica were separated by corona electrostatic separation. The recovery rate and purity of Ta could reach 97.02 ± 0.85% and ...

The demand for tantalum (Ta) is rapidly increasing due to the manufacture of Ta capacitors (TCs) for electronic devices. With the increasing awareness of environmental protection and conservation of rare metal Ta, recycling of Ta from waste TCs (WTCs) is becoming a hot topic in current society. In this study, an efficient and environmentally friendly process for recycling Ta from WTCs by chloride metallurgy (CM) is proposed. In the CM process, the nontoxic FeCl2 is chosen as the chlorination agent. Thermodynamic analysis demonstrates that Ta can selectively react with FeCl2, and the generated TaCl5 can be easily separated and then condensed in the condensation zone. The recovery of Ta can reach 93.56% under the optimal chlorination parameters as follows: heating temperature of 500 °C, FeCl2 addition amount of 50%, holding time for 2 h, and particle size of Ta-rich powder less than 0.24 mm. Moreover, the kinetic mechanism is discussed, and the rate-controlling step in the chlorination reaction of Ta is det...

When the valve metal is used as anode material, the dielectric properties of sol–gel-derived thin film are greatly enhanced. That is because anodized self-healing occurs at the interface of the anode and the thin film. An oxide insulating layer with a good dielectric property is generated. Anodization heals the defects and the breakdown spots of thin film. Other than anodized self-healing, electrode contact is also an important factor, affecting the dielectric characteristics of the thin film capacitor, which cannot be ignored, especially when both factors exist in one film device. In this study, the sol–gel-derived strontium titanate thin film is used as dielectric material in the film capacitor, and platinum and aluminum as electrode materials. We find that the Schottky barrier at the interface of platinum and strontium titanate greatly reduces the leakage current. However the interface barrier restricts the anodizing of aluminum electrode and the further enhancement of the dielectric strength of the thin film capacitor.

The highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films were prepared on porous tantalum pentoxide surface as cathode for polymer tantalum capacitors (PTC). The electrical performances of PTC with PEDOT:PSS films as cathode were optimized by dimethyl sulfoxide (DMSO) bath treatment. With the DMSO-bath treatment of PTC, the equivalent series resistance (ESR) of PTC decreased from 25 mΩ to 9 mΩ. The ultralow ESR led to better capacitance-frequency performance. The device reliability investigation revealed the enhanced environmental stability of PTC. The enhanced performances were attributed to the conductivity improvement of PEDOT:PSS cathode films and the removal of excess PSS from PEDOT:PSS films.

In this study, the dielectric properties of metal-oxide-metal capacitors based on Tantalum Titanium Oxide (TiTaO) thin films deposited by reactive magnetron sputtering on aluminum bottom electrode are investigated. The structure of the films was characterized by Atomic Force Microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The dielectric properties of TiTaO thin films were studied by complex impedance spectroscopy over a wide frequency range (10 -2 - to 10 5 Hz) and temperatures in -50 °C to 325 °C range. The contributions of different phases, phases’ boundaries and conductivity effect were highlighted by Cole – Cole diagram (ɛ” versus ɛ’). Two relaxation processes have been identified in the electric modulus plot. A first relaxation process appears at low temperature with activation energy of 0.37 eV and it is related to the motion of Ti 4 + (Skanavi’s model). A second relaxation process at high temperature is related to Maxwell-Wagner-Sillars relaxation with activation energy of 0.41 eV.

The study to obtain tantalum concentration from electronic components (ECs) on Printed circuit board assembly (PCBA) of laptop was conducted. Electronic components on laptop PCBA were detached from boards by using self-developed experimental apparatus. The detached electronic components were sieved and 93.2 wt.% of tantalum capacitors were concentrated from the size interval from 2.80 mm to 6.35 mm. The tantalum capacitors were pulverized by hammer mill and electrodes (anode and cathode) were removed from the grinding products by using magnetic separators under the magnetic force of 300 Gauss. Finally, tantalum concentrate was concentrated from the magnetic separator products by using Knelson concentrator, and the maximum efficiency of 76.9% was achieved under the operating condition of bowl rotating speed of 200 rpm, and fluidizing water flowrate of 7 L/min. The grade and recovery of Ta concentrate under the condition were 81.1% and 78.8%, respectively.

Waste tantalum capacitors, containing about 30–40 wt% rare metal tantalum (Ta), are one of the main Ta secondary resources. Not just to achieve the Ta resource recovery but to realize the value-added utilization, we recycled waste tantalum capacitors to prepare Ta2O5 photocatalyst by a chlorination-sintering process. To enhance the photocatalytic performance, Ta2O5 was further decorated by polyaniline (PANI) through a chemisorption approach. The as-prepared Ta2O5 and Ta2O5/PANI photocatalysts exhibited irregular nanoparticles with the particle size of 50–80 nm. After the PANI decoration, the photocatalytic performance of Ta2O5 was significantly enhanced. The optimal simulated sunlight H2 evolution rate and RhB degradation rate constant of Ta2O5/PANI (3 wt%) could reach 200.8 μmolg−1h−1 and 0.1342 min−1, which were about 3.3 and 5.6 times higher than those of Ta2O5. The superior photocatalytic performance of Ta2O5/PANI was ascribed to the intense interfacial interaction, increased visible light absorption and efficient charge carrier separation. In short, this study demonstrates a sustainable approach to convert e-waste to high-value-added and high-efficient photocatalyst, which is significant for waste utilization and environmental protection.

Tantalum (Ta) is the one of the most critical elements according to the European Commission. Research on tantalum recovery from secondary sources such as waste electrical and electronic equipment (WEEE), bottom ash and by products of the industrial activities, however, is limited. In this study, the recovery potential of tantalum from spent tantalum capacitors was tested using bioleaching. Three different kinds of microorganisms were tested for tantalum recovery, which were Pseudomonas putida (DSM No. 6125), Bacillus subtilis (DSM No. 1088532), and Penicillium simplicissimum (DSM No. 1078). It turned out that P. simplicissimum has the ability to leach tantalum from wasted tantalum capacitors with a maximium leaching rate of 1.25 g Ta per kg sample. An unknown species achieved the highest leaching rate (9.88 g Ta / kg sample) but isolation and identification failed. The potential of tantalum recovery by bioleaching is demonstrated, however, further research needs to be carried out.

As new temperature critical applications continue to emerge, the need for components capable of enduring temperatures up to and exceeding 200°C is increasing. Advanced down-hole electronics, underhood automotive and aerospace systems rely on components delivering optimal performance while subject to extreme environmental conditions. This paper will discuss the design advances in tantalum technology that have given rise to innovative devices that provide the enabling technology for a new generation of applications. Traditionally, hermetically sealed “wet” axial tantalum capacitors (utilizing a non-solid electrolyte that promotes self-healing and long lifetime), have been used for both high bulk capacitance (to 5,600uF) and high voltage applications (to 125VDC). In recent years, this technology has been developed to meet the 200°C operational requirements of harsher environment industrial applications. For lower operating voltages (6v – 25v), SMD packages are preferred, and for several years, 200°C rated high temperature solid tantalum chip devices have been the preferred technology over “wet” tantalum for capacitances to 220uF, being smaller size, lower cost and having the combination of lower ESR and higher frequency response. More recently, hermetic SMD packaging has been developed for SMD solid tantalum capacitors. The hermetic seal enables the internal element to be operated in an inert gas environment, while offering superior resistance to moisture ingress. These two factors enable operation to 230°C, with higher capacitance (up to 330uF) and voltage (up to 63vDC) ranges. Both molded and hermetic high temperature SMD solid tantalum capacitors have been developed to be compatible with high temperature pcb or hybrid circuit assembly processes, with a range of termination finishes compatible with HMP solder, epoxy or wire bonding. Their design also harsh mechanical environment shock & vibration. This paper will discuss the evolution in materials, design and testing for each of these technologies, along with the considerations taken into account to give maximum compatibility with emerging requirements in high temperature and harsh environment applications, with emphasis on down-hole oil exploration, aerospace and military systems and underhood automotive electronics.

This paper covers technological results achieved with silicon capacitors for Aerospace applications, including stability, reliability and frequency data at high temperatures, as well as thermal stress, vibration & shock tests and radiations stress, according to ESA TRP reference (n° T723-325QT).

Experimental research was carried out under the stimulation of 10 μF tantalum capacitor discharge, to obtain the ignition characteristics of micro-energy semiconductor bridges (SCB) with different ignition compositions. Meanwhile, the critical ignition voltages of different pyrotechnics were tested by the Neyer-D optimal sensitivity test method. The results reveal that SCBs with multiple ignition compositions are entirely different in ignition voltage and current signal. These five kinds of pyrotechnics in ascending order of firing sensitivity are: refined lead styphnate, neutral lead styphnate, basic lead styphnate, zirconium/potassium chlorate, and lastly lead azide, while lead ferrocyanide/potassium perchlorate and boron/potassium nitrate are relatively insensitive to SCB.

Metallic niobium powder was produced for applications in electric capacitors via calciothermic reduction of niobium hydroxide in molten CaCl 2 . Sub-micrometer spherical metallic particles with coral-like morphologies reflected the particle size of the starting oxide powder. A fine powder was obtained from the mixtures of niobium hydroxide and CaO or Ca(OH) 2 , respectively. Sintered pellets of the metallic powder showed a higher capacitance (CV) than those of the simply reduced powder without pre-treatment, because the shrinkage during sintering was smaller. The CV was as large as that of commercially sintered pellets for tantalum capacitors. Therefore, this niobium powder would act as a higher-voltage capacitor by applying chemical anodic treatment at higher voltages, and lower oxygen content in the reduced power could realize a lower leak current.

The size of pores and throats is at the nanometer scale in tight oil and shale gas zones, and the resistivity of these reservoirs is very high, so the reservoirs show more dielectric properties than conductivity properties. The conductive and dielectric characteristics of a parallel plate capacitor full of fresh water, NaCl solutions, and solid dielectrics, for example, sands are investigated in this paper, and the capacitance data of the non-gas capacitor are measured at different salinities and frequencies by a spectrum analyzer. The experimental results illustrate that the capacitance of this kind of capacitor is directly proportional to the salinity of the solutions and inversely proportional to the measuring frequency, the same as a vacuum parallel plate capacitor. The remarkable phenomenon, however, is that the capacitance is inversely proportional to the square of the distance between two plates. The specific characteristic of this capacitor is different from the conventional parallel plate capacitor. In order to explain this phenomenon, the paper proposed a new concept, named “single micro ion capacitor”, and established a novel model to describe the characteristics of this particular capacitor. Based on this new model, the theoretical capacitance value of the single micro ion capacitor is calculated, and its polarization and relaxation mechanisms are analyzed.

Tantalum powders have been prepared by sodium reduction in melts containing potassium heptafluorotantalate (K2TaF7) heat-treated in air. Their specific surface area is three to four times that of powders obtained by reducing unheat-treated K2TaF7 under the same conditions. The increase in specific surface area is due to the reduction of tantalum oxyfluoride complexes (K3TaOF6 and K2TaOF5) and Marignac’s salt (K2Ta2O3F6) forming during heat treatment of K2TaF7. Potassium heptafluorotantalate heat-treated at temperatures from 600 to 670°C is shown to be suitable as a starting material for producing high-capacitance tantalum capacitor powder.

Heat treatment is known to improve the electrical and mechanical properties of amorphous tantalum oxide (ATO) in tantalum capacitor anodes. In-situ, multi-beam optical stress sensor (MOSS) measurements were performed on the ATO / tantalum system during heat-treatment in air and vacuum. Thermal desorption mass spectroscopy was also used to monitor species desorbing from the oxide during heating in vacuum. In addition, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the heat-treated samples. The results suggest that the ATO/Ta system undergoes changes as a function of annealing temperature and atmosphere. At temperatures below ∼400◦C, the main effects are oxide dehydration and densification, indicated by a net compressive stress. After heat-treatment at temperatures above 400◦C in air, the net stress becomes increasingly compressive with increasing temperature. Oxide growth due to oxygen uptake is the likely cause for the compressive stress. In vacuum, the net stress remains tensile even after heat-treating at high temperatures above 400◦C. Dehydration and the formation of a high density of oxygen vacancies at the metal-oxide interface during heat-treatment are the likely causes for the net tensile stress-thickness. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0091507jss] All rights reserved.

For decades the maximum recommended operating temperature of solid electrolytic capacitors was 125°C. Responding to needs in the automotive and downhole drilling industries passive component manufacturers developed surface mount tantalum capacitors rated at 150°C in 2002–2003. Since that time the industry has introduced high temperature capable tantalum capacitors generally in 25°C increments roughly every four years. Today multiple manufacturers have products rated at 230°C poised for market release. The tantalum anode, tantalum pentoxide dielectric and manganese dioxide primary cathode material stand up well to these temperatures, although some optimization of the design and manufacturing process for these materials have been required. The primary challenges encountered when developing solid electrolytic capacitors with high temperature capabilities are associated with the carbon, silver and epoxy encapsulant materials used in conventional surface mount tantalum capacitors. Capacitor manufacturers have taken different paths to overcome these challenges. We have developed a metallized plating process to avoid issues associated with silver paints utilized in conventional Ta capacitors. We have worked with suppliers, or developed in house capabilities, to manufacture the other materials required to withstand the rigors of high temperature applications. This paper will discuss these challenges and provide reliability test data on a recently developed tantalum surface mount series capable of continuous operation at 230°C.

Stability of Polymer Tantalum capacitors with pre-polymerized PEDOT (slurry PEDOT) cathodes were investigated under different environmental conditions. Capacitance dependence on temperature, frequency, and dc bias voltage were investigated in humid and dry capacitors with different dielectric thicknesses. Electrical measurements and scanning electron microscopy (SEM) were used to characterize the capacitors. Humid capacitors were observed to have higher capacitance than dry capacitors for all dielectric thicknesses. The capacitance for all dielectric thicknesses was observed to increase with temperature in both humid and dry capacitors. Humid capacitors showed a strong temperature dependence at lower temperatures while dry capacitors showed a strong temperature dependence at higher temperatures. These temperature effects were more pronounced in thinner dielectric capacitors, and the results were explained by the integrity of the dielectric-polymer interface. The capacitance for all dielectric thicknesses was also observed to decrease with an increase in frequency, both in humid and dry capacitors. The frequency effect was more pronounced in humid capacitors with thinner dielectrics. These results were explained by a distributed capacitance model, secondary transitions of the polar segments of the polymer cathode, and lower reactance and lower self-resonance frequency of the thinner dielectric capacitors. The technological principles of improving environmental stability of Polymer Tantalum capacitors are also discussed.

Tantalum is a critical metal that is widely used in electronic products. The demand for tantalum is increasing, but the supply is limited. As tantalum waste products have increased in Taiwan in recent years, the treatment of spent tantalum capacitors has become necessary and important. The recycling of tantalum from tantalum capacitors will not only decrease pollution from waste, but will also conserve tantalum resources. The tantalum content in epoxy-coated solid electrolyte tantalum capacitors (EcSETCs) is over 40 wt.%. Here, we designed a recycling process that includes pre-treatment, leaching, and solvent extraction to recover tantalum. In the pre-treatment process, epoxy resin and wires were removed. During hydrometallurgical process, pressure leaching by hydrofluoric acid was used to leach tantalum and manganese from solid electrolyte tantalum capacitors (SETCs). During our testing of this proposed process, the acid concentration, reaction time, temperature, and solid&ndash, liquid ratio were examined for leaching. After the leaching process, Alamine 336 was used to extract tantalum from the leaching solution. The pH value, extractant concentration, extraction time, and aqueous&ndash, organic ratio were investigated. Then, tantalum was stripped using HNO3, and the HNO3 concentration, stripping time, and organic&ndash, aqueous ratio were analyzed in detail. Under optimal conditions, the recovery efficiency of tantalum reached over 98%, and a final product of tantalum pentoxide with 99.9% purity was obtained after chemical precipitation and calcination.

We have studied the effect of the preparation and agglomeration conditions of tantalum powders produced by sodium reduction on the frequency dependences of the specific capacity and dielectric loss tangent for anodes fabricated from the powders.

Wet electrolytic tantalum (Ta) capacitors have historically been utilized in a variety of applications which endure harsh ambient conditions. Thermal, electrical and mechanical stresses, though, pose significant challenges to reliable performance of these capacitors in such environments. Thermal stress can increase the internal pressure of the capacitors, as well as mechanically compromise some of the components of which the capacitors are comprised. Electrical stress, in the form of current flow due to applied voltage, can elicit hydrogen gas evolution, which further exacerbates the internal pressure issue, potentially embrittles Ta components, and degrades AC performance of the capacitors. Mechanical stress, resulting from shock and vibration for example, can jeopardize the internal mechanical integrity of the capacitors. This paper elaborates on these obstacles, and offers design approaches to reliably overcome them. Also presented are results of high temperature performance, predominantly up to 230°C, but also a mention of limited 245°C results, of wet Ta capacitors manufactured with proper attention paid to these concerns.

Ionic liquids can be applied to recover tantalum capacitors from scrap printed circuit boards. Dissolution experiments with epoxy covered through-hole tantalum capacitors in Lewis acidic mixtures of dialkylimidazolium halides and aluminum trichloride show that all parts, except the tantalum anode, are dissolved in the ionic liquid. This comprises MnO2 from the capacitor's electrolyte as well as tin and silver from the metallic contacts. The latter ones can be directly recovered from the solution by electrodeposition. The tantalum anode is mechanically separated and suitable for further metallurgical processing.

Previous study has demonstrated that field crystallization of anodic tantalum oxide (ATO) films is associated with large in-plane compressive stresses that evolve in several characteristic stages. The mechanism(s) associated with this stress evolution are not well defined, and the impact of these stresses on the field crystallization process requires further understanding. This work reports investigations of the stress evolution that are designed to evaluate contributions from hydration of the amorphous Ta oxide (ATO), electrostriction and crystal growth. Stresses were monitored in situ with a multi-beam optical technique, to elucidate these different contributions. Measurements were conducted during exposure to the acid electrolyte with and without an applied field, and also during different growth stages. The stress evolution mechanisms include contributions from reactions with the electrolyte (hydration), electrostriction and growth of amorphous and crystalline oxides. In addition, a strong linear correlation between stress evolution and crystal growth was established during longer exposure to electric field.

The niobium capacitor shows somewhat more unstable characteristics than the commercial tantalum capacitors, but it will be nonetheless considered as an excellent substitute of tantalum capacitors in the future. In this study, niobium powder is fabricated by metallothermic reduction process using K2NbF7 as a raw material, KCl and KF as diluents, and Na as a reducing agent. The niobium particle size greatly decreases from 0.7 to 0.2µm as the amount of diluent increases. However, when a higher surface area of niobium powder is desired, more amounts of diluents are used in the said method. The niobium powder morphology and particle sizes are very sensitive to the amount of sodium excess, thus the particle size of niobium powder increases with increases in the amount of sodium excess. When more diluent and sodium are used, the niobium powder is contaminated further by impurities such as Fe, Cr, Ni and others. [doi:10.2320/matertrans.M2012261]