Contribution of Planetary Ball Milling to the Homogeneity of Pyrrhotite Reference Material for LA-ICP-MS

Recently, highly efficient CZTS solar cells using pure metal precursors have been reported, and our group created a cell with 12.6% efficiency, which is equivalent to the long-lasting world record of IBM. In this study, we report a new secondary phase formation mechanism in the back contact interface. Previously, CZTSSe decomposition with Mo has been proposed to explain the secondary phase and void formation in the Mo-back contact region. In our sulfo-selenization system, the formation of voids and secondary phases is well explained by the unique wetting properties of Mo and the liquid metal above the peritectic reaction (η-Cu6Sn5 → ε-Cu3Sn + liquid Sn) temperature. Good wetting between the liquid Sn and the Mo substrate was observed because of strong metallic bonding between the liquid metal and Mo layer. Thus, some ε-Cu3Sn and liquid Sn likely remained on the Mo layer during the sulfo-selenization process, and Cu-SSe and Cu-Sn-SSe phases formed on the Mo side. When bare soda lime glass (SLG) was used as a substrate, nonwetting adhesion was observed because of weak van der Walls interactions between the liquid metal and substrate. The Cu-Sn alloy did not remain on the SLG surface, and Cu-SSe and Cu-Sn-SSe phases were not observed after the final sulfo-selenization process. Additionally, Mo/SLG substrates coated with a thin Al2O3 layer (1-5 nm) were used to control secondary phase formation by changing the wetting properties between Mo and the liquid metal. A 1 nm Al2O3 layer was enough to control secondary phase formation at the CZTSSe/Mo and void/Mo interfaces, and a 2 nm Al2O3 layer was enough to perfectly control secondary phase formation at the Mo interface and Mo-SSe formation.

All-solid-state batteries are promising in terms of safety as well as high energy density compared to the conventional organic liquid-based lithium batteries. However, the characteristic low ionic conductivity of solid-state electrolytes is a major challenge towards commercialization of solid-state sodium ion batteries. Sulfide-based electrolytes especially in amorphous form have been reported as promising solid electrolytes owing to their relatively high ionic conductivity at room temperature. However, a fundamental understanding of the local structure of these amorphous electrolytes and its subsequent impact on the ion transport could be instrumental in establishing guidelines for designing novel solid electrolytes. In the present work, we utilize first principles and classical atomistic simulations to characterize the local structure and investigate the ion transport in amorphous sulfide electrolytes. We selected sodium thiosilicate [xNa2S – (1-x) SiS2] and sodium thiophosphate [xNa2S – (1-x) P2S5] based electrolytes as a model system wherein we characterized the local structure, ion conduction mechanism and ultimately calculated the ionic conductivity of these electrolytes. We utilized experimental X-ray and neutron scattering data for model validation. Our theoretical calculations provide fundamental insights into ion conduction mechanisms as well as correlate ionic conductivity with electrolyte structure and composition.Along with ionic conductivity, interfacial stability is extremely important factor influencing the overall performance of solid-state batteries. Interfacial instability with sulfide electrolytes is detrimental to Li-ion transport, leading to poor cycling performance. Inherent thermodynamic instability of sulfide-based solid electrolytes drives the chemical reaction across the interface leading to formation of undesired secondary phases. The secondary phases are formed dynamically during the cycling and therefore a careful investigation into the dynamics at the electrolyte-cathode interfaces is crucial. To generate fundamental understanding of the interface stability, we utilized ab initio molecular dynamics (AIMD) simulations to carefully investigate the dynamics of secondary phase formation across the Li3PS4 | LiCoO2 interfaces. High-resolution microscopy and spectroscopy studies were used to complement the the first principles simulations methods and unravel the interphases formed under different cycling conditions. These calculations provide crucial insights into formation of secondary phases across the interface, which could be leveraged to evaluate possible avenues to inhibit formation of such undesirable secondary phases.

INTRODUCTION : A one-step co-sintered solid oxide fuel cell (SOFC) stack consists of several cells sintered at high temperature at once (>1250oC). Typically, each SOFC cell is composed of a cathode (strontium-doped lanthanum manganite, LSM), an electrolyte (8YSZ), an anode (NiO/8YSZ), a ceramic interconnector and a dedicated gas distribution system [1]. It is believed that reducing the step processing should lead to cost reduction of SOFC cells fabrication and finally promote a wider use of SOFC devices. Unfortunately, several technological issues still have not had an adequate solution, mainly: thermal expansion mismatch between stack components [2] and lack of efficiency caused by formation of a high electrical resistance secondary phase at the LSM/8YSZ interface, La2Zr2O7 (LZO) or SrZrO3 (SZO) [3]. Several methods have been evaluated for reducing secondary phase formation, for instance: protector buffer layer [4], Ce addition into LSM structure [5] and A-site deficiency LSM compositions [6], etc. However, they show a limited performance or are complicated to use at the temperatures required for fabricating a one-step co-sintered SOFC stack. This work evaluates the impact of a Ni-addition, into B-site of LSM composition, on the formation of secondary phase at the LSM/8YSZ interface. Equal Ni addition (20 at%) was used in several LSM compositions, with different strontium contents, and their chemical stability with 8YSZ at 1300oC was evaluated. Moreover, a chemical stability comparison between a commercial LSM composition (La0.8Sr0.2MnO3-δ) and a similar Ni-added one (La0.8Sr0.2Mn0.8Ni0.2O3-δ) is presented. EXPERIMENTAL: La1-xSrxMn0.8Ni0.2O3-δ with x={0.1 to 0.5} compositions, hereinafter called Ni-added LSM, were fabricated by a glycine route using nitrates as reactive and glycine as fuel. Both, reactive and glycine, were dissolved in deionized water at room temperature until obtain a clear solution. Water and organic components were removed by different heat treatment at 180oC and 450oC, respectively. Afterwards, all powders were reacted and calcinated at 850oC and 1000oC for 5h, respectively. Chemical reaction with 8YSZ was evaluated by mixing Ni-added LSM powders with 8YSZ in 50/50 wt%. All samples, whatever 8YSZ mixed or not, were sintered at 1300oC for 5h. Electrical conductivity measurements were performed by using four-probe method from room temperature to 800oC in air, while chemical stability with 8YSZ was evaluated by x-ray diffraction (XRD). RESULTS AND DISCUSSION: XRD patterns from Ni-added LSM compositions showed no secondary phase formation after sintered at 1300oC for 5h (not shown). Ni-added LSM compositions with low strontium content (x≤0.3) were indexed as rhombohedral crystal structure, while at higher strontium contents (x>0.3) an orthorhombic crystal structure tends to gradually form instead of the rhombohedral one, thus at x=0.5 only orthorhombic crystal structure was indexed. Electric conductivity of La1-xSrxMn0.8Ni0.2O3-δ with x={0.1 to 0.5} compositions have a maximum (115 S cm-1) at x=0.3, well correlated with the crystal structure evolution as a function of strontium content. (not shown) Fig.1 shows XRD patterns from Ni-added LSM compositions after mixing with 8YSZ (50/50 wt%) sintered at 1300oC for 5h. No crystal structure change was observed respect to non 8YSZ mixed condition. However, at strontium contents over x≥ 0.3 a secondary phase (SZO) was observed, while below x<0.3 no secondary phase was observed. In addition, XRD patterns from a commercial La0.8Sr0.2MnO3-δ and La0.8Sr0.2Mn0.8Ni0.2O3-δ compositions mixed with 8YSZ and sintered at 1300oC for 5h were recorded. LZO secondary phase was observed only in commercial LSM composition, while it was not observed in La0.8Sr0.2Mn0.8Ni0.2O3-δ composition, even after sintering at 1300oC for 24h (not shown) Results suggest that Ni addition into the B-site of LSM (with low strontium content), could be a suitable and simple method for reducing, and eventually suppressing, the secondary phase formation at the LSM/8YSZ interface at high temperature. [1] S. Suda, J. P. Wiff and S. Shimada, ECS Trans. 57(1), 543-548 (2013) [2] B. Ahmed, S. B. Lee, R. H. Song, J. W. Lee, T. H. Lim and S. J. Park, ECS Trans. 57, 2075-2082 (2013) [3] C. Levy, Y. Zhong, C. Morel and S. Marlin, ECS Trans. 25, 2815-2823 (2009) [4] H. S. Noh, J. W. Son, H. Lee, H. R. Kim, J. H. Lee and H. W. Lee, J. Korean Ceram. Soc. 47, 75-81 (2010) [5] J. P. Wiff, K. Jono, M. Suzuki and S. Suda, J. Power Sources 196(15) 6196-6200 (2011) [6] A. Chen, J. R. Smith, K. L. Duncan, R. T. DeHoff, K. S. Jones and E. D. Wachsman, J. Electrochem. Soc. 157, B1624-B1628 (2010) Figure 1

α-MgAgSb is a very promising thermoelectric material with excellent thermoelectric properties between room temperature and 300 °C, a range where few other thermoelectric materials show good performance. Previous reports rely on a two-step ball-milling process and/or time-consuming annealing. Aiming for a faster and scalable fabrication route, herein, we investigated other potential synthesis routes and their impact on the thermoelectric properties of α-MgAgSb. We started from a gas-atomized MgAg precursor and employed ball-milling only in the final mixing step. Direct comparison of high energy ball-milling and planetary ball-milling revealed that high energy ball milling already induced formation of MgAgSb, while planetary ball milling did not. This had a strong impact on the microstructure and secondary phase fraction, resulting in superior performance of the high energy ball milling route with an attractive average thermoelectric figure of merit of 0.9. We also show that the formation of undesired secondary phases cannot be avoided by a modification of the sintering temperature after planetary ball milling, and discuss the influence of commonly observed secondary phases on the carrier mobility and on the thermoelectric properties of α-MgAgSb.

The application of mixed ionic–electronic conducting (Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ (BSCF) as gas separation membrane is up to now hampered by secondary phase formation which impairs the excellent oxygen permeation properties of this material. In this work, we have studied the impact of grain size and A/B-cation ratio on secondary phase formation in BSCF and Y-doped (Ba0.5Sr0.5)(Co0.8Fe0.2)0.9Y0.1O3−δ (BSCF10Y) by electron microscopic techniques before and after long-term thermal exposure at an application-relevant temperature (~760 °C). A large content of secondary phases is found in samples with small grain sizes because grain boundaries provide nucleation sites for secondary phases. Higher sintering temperatures increase the grain sizes and substantially reduce the content of secondary phases. Variations of the A/B-cation ratio between (Ba0.5Sr0.5)0.95(Co0.8Fe0.2)O3−δ and (Ba0.5Sr0.5)1.05(Co0.8Fe0.2)O3−δ do not lead to a change of the composition of the cubic BSCF phase but changes the volume fraction of Co3O4 precipitates which are already formed during sintering. BSCF with an excess of A-site cations contains the smallest overall amount of secondary phases in undoped BSCF due to the minimization of Co3O4 precipitation during sintering and the reduction of nucleation sites for other secondary phases at application-relevant temperatures. Secondary phase formation in BSCF10Y can be almost completely suppressed due to the stabilization of the cubic BSCF phase by Y-doping and large grain sizes after high-temperature sintering.

The cubic perovskite-type (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ (c-BSCF) is a material with mixed electronic-ionic conductivity and extraordinary high oxygen permeability which makes c-BSCF interesting for applications such as, e.g., oxygen separation membranes and cathodes in solid oxide fuel cells. However, applications are up to now hampered by the degradation of the oxygen permeability in the relevant temperature range between 700 and 900 oC. Particularly detrimental is the formation of the hexagonal (h-)BSCF phase below 840 oC [1]. Moreover, several other secondary phases were identified that are believed to also adversely affect oxygen permeation [2]. Secondary phase formation is connected with the multivalent B-site Co-cation which increases its valence state with rising temperature. Substitution of B-site Co-cations by monovalent transition metals, e.g. Y or Zr, is considered as a promising strategy to stabilize c-BSCF [3]. Another issue is related to the degradation of BSCF in CO2-containing atmospheres where the formation of carbonate precipitates on the surface [4] is accompanied by the reduction of the oxygen surface exchange coefficient [5]. In this work we will address the stabilization of c-BSCF by Y-doping and the effect of Y-doping on the degradation of the electrochemical properties in CO2-containing atmospheres. Bulk samples were prepared by the mixed oxide route with compositions of (Ba0.5Sr0.5)(Co0.8Fe0.2)1-xYxO3- δ (x = 0 and 0.1, BSCF and BSCF10Y) which were subjected to annealing for 240 h between 640 oC and 880 oC in air. In addition, symmetrical cell samples with porous BSCF and BSCY10Y layers were fabricated by screen-printing on both sides of Ce0.9Gd0.1O2-δ (CGO) substrates. The samples were in-situ sintered at 900 °C for 10 h and electrochemically characterized by electrical impedance spectroscopy (EIS) at 700 oC in synthetic air with CO2-concentrations up to 3 %. Distribution of relaxation time (DRT) curves and area specific resistances are derived from EIS data which allow to monitor degradation processes. We use scanning electron microscopy (SEM) and analytical (scanning) transmission electron microscopy ((S)TEM) combined with energy dispersive X-ray spectroscopy (EDXS) to study the structural and chemical material properties. Different phases in bulk samples are visualized by SEM imaging using the specimen preparation procedure outlined in [6]. Fig. 1 shows SEM images of bulk BSCF and BSCF10Y after annealing at temperatures between 640 oC and 880 oC for 240 h. Inserted schemes illustrate secondary phase formation. BSCF (Figs. 1a-c) contains a large volume fraction of secondary phases comprising Co3O4, Ban+1ConO3n+3(Co8O8) (n ≥ 2) (BCO) and h-BSCF depending on the annealing temperature. Secondary phase formation in BSCF10Y is completely suppressed at 880 oC. Only small volume fractions of h-BSCF are detected at grain boundaries after annealing at 760 and 640 oC. Fig. 2 presents DRT curves of BSCF/CGO/BSCF and BSCF10Y/CGO/BSCF10Y cells at T=700 °C before and after 1 % CO2 addition for 50 h. A signal at 100 Hz increases strongly in BSCF/CGO/BSCF (Fig. 2a) which is absent before CO2 addition. The same signal is present in BSCF10Y/CGO/BSDF10Y (Fig. 2c) but with a significantly lower amplitude. SEM images show a high density of small precipitates on the surface of BSCF (Fig. 2b) which are present in a much smaller concentration on BSCF10Y (Fig. 2d). The small precipitates are absent if annealing is performed without CO2. We note that the 100 Hz signal disappears after switching off CO2 indicating that the origin of the process at 100 Hz could be related to CO2-adsorption. Our study shows that Y-doping with a sufficiently high Y-concentration strongly reduces or even suppresses secondary phase formation in BSCF. Y-doping is also promising to reduce degradation of the electrochemical properties in CO2-containing atmospheres. STEM-EDXS analysis are currently carried out to analyze secondary phases after annealing in CO2-containing air.

Effect of heating rate and precursor composition on secondary phase formation during Cu2ZnSnS4 thin film growth and its properties

The present study focuses on tailoring the relative content of Fe3+ and Fe2+ ions incorporation into hydroxyapatite (HA) lattice, employing a hydrothermal approach in a closed vessel to minimize Fe2+ oxidation and secondary phase formation. Citrate molecules are used to regulate nanoparticle formation/stability, creating a mild reducing environment, while the impact of a stronger reducing agent, hydroxylamine, is explored. Fe3+ insertion was found to be less favoured than Fe2+, possibly due to charge imbalance. Iron doping significantly alters stoichiometry and crystallinity of HA, with Fe3+ enhancing OH− depletion. Morphological analysis reveals differences among samples, as induced by the different Fe ions incorporation: particularly Fe2+ ion incorporation is found to maintain rod-like structures, which changes upon Fe3+ presence. Overall, this study provides insights into controlled doping of HA with iron ions, vital for developing stable, redox-responsive nanomaterials applicable in cancer therapy and other applications where surface activity plays a relevant role.

We have investigated Cr solubility and secondary phase formation in metallorganic chemical vapor deposition (MOCVD) grown (Cr, Zn)O films on Si(100). Simultaneous deposition of Cr(TMHD) and Zn(TMHD) precursors in an oxidizing environment with a flow ratio of 1:10 resulted in secondary phase formation rather than uniform Cr doping. Based on several surface and microstructural techniques, we have identified nanocrystalline and disordered as the secondary Cr-containing phases. Analysis suggests that crystallites are dispersed throughout the film, and that disordered layer may form at the interface. These results are consistent with the tendency of Cr to exhibit octahedral, rather than tetrahedral coordination with O.

Parametric study on four station ball mill for synthesis of ultrafine powders

This study emphasizes and the testing of alumina particles via a fabricated planetary ball mill. The fabrication of planetary ball mill work began with the design of the machine. Parts were fabricated separately then assembled. The jar and grinding media were made up of stainless steel as it as a higher strength property than Alumina powder. Testing and calibration are carried out through the response surface methodology utilizing the experimental results. Test is also executed to confirm the validity and the accuracy of the developed planetary ball mill. Based on the result obtain, the alumina powders have a particle size reduction of about 50% of the original particle size. Furthermore, the shape of the alumina particle changes from angular to irregular particle shape. It is apparent that the fabricated planetary ball mill able to grind the alumina powders and produce ultrafine particles by given period and parameter set. The fabricated ball mill able to function better than conventional ball mill. The planetary ball mill will be useful for the laboratory use purpose and production of ultrafine powder production. This ultrafine powder production can be used in application of powder metallurgy and advanced material research purposes.

Influence of processing on secondary phase formation and microstructural evolution at U-10Mo alloy and Zr interlayer interfaces

The influence of crucial reaction parameters on Knoevenagel condensation in planetary ball mills was investigated. Rotation frequency (νrot), milling ball diameter (dMB), milling ball filling degree (ΦMB), and beaker size had obvious influences on yield. It was found that higher νrot, lower dMB, milling beakers with larger diameter, and a ΦMB of ∼0.3 are advantageous for the reaction. Furthermore, the influence of the type of mill was investigated, including reactions performed in different planetary and mixer ball mills, in a stirred media mill, and with a mortar mill. Comparisons with the other solvent-free synthetic routes showed that ball milling is an effective way of performing the reaction with low energy intensity.

Planetary ball mills are well known and used for particle size reduction on laboratory and pilot scales for decades while during the last few years the application of planetary ball mills has extended to mechanochemical approaches. Processes inside planetary ball mills are complex and strongly depend on the processed material and synthesis and, thus, the optimum milling conditions have to be assessed for each individual system. The present review focuses on the insight into several parameters like properties of grinding balls, the filling ratio or revolution speed. It gives examples of the aspects of grinding and illustrates some general guidelines to follow for modelling processes in planetary ball mills in terms of refinement, synthesis' yield and contamination from wear. The amount of energy transferred from the milling tools to the powder is significant and hardly measurable for processes in planetary ball mills. Thus numerical simulations based on a discrete-element-method are used to describe the energy transfer to give an adequate description of the process by correlation with experiments. The simulations illustrate the effect of the geometry of planetary ball mills on the energy entry. In addition the imaging of motion patterns inside a planetary ball mill from simulations and video recordings is shown.

In order to lay raw materials foundation for increasing the performance of insulating brick with the low grade quartz sand along the Yangtze River, the effect of ball milling methods on the properties of quartz sand powder was researched via the ball milling method in this paper. The results show the mean grain size of quartz powders are 11.25μm via a roller ball milling, the mean grain size of quartz powders are 7.37μm via a planetary ball milling, and the particle size distribution of quartz powders milled via a roller ball milling is wider than that of quartz powders milled via a planetary ball milling. The ball milling strength of planetary ball milling is higher than that of roller ball milling. The planetary ball milling use more electronic energy than the roller ball milling in the same time. The output of powder using the roller ball milling is more than that of powder using the planetary ball milling. when the raw materials of quartz building materials is low particle size remand, and the output is more, the roller ball milling methods is suitable to prepare the raw materials of quartz building materials.