Silver Powder Research Articles

Recyclability‐by‐design of Printed Electronics by Low‐Temperature Sintering of Silver Microparticles

AbstractA low‐temperature sintering mechanism of silver microparticles is established and used to enable the design‐for‐recycling of printed electronics. The formation of necks during the initial phase sintering of precipitated and atomized silver microparticles is studied. Temperature‐ and time‐dependent in‐situ analyses indicate the existence of a mobile silver species that provides efficient mass transport. The activation energy of neck formation identifies silver ion formation as the rate‐limiting step of low‐temperature silver sintering. It is demonstrated that resistivities of 271 times that of bulk silver can be attained after 40 minutes at 150°C. Low‐temperature sintering not only reduces the energy required during thermal treatment but it yields layers that are suitable for recycling, too. The resulting layers have conductive necks that are mechanically weak enough to be broken during recycling. Printed layers are redispersed and the recycled silver powder is reused without loss of the electrical performance in new prints. Their conductivities are industrially relevant, which makes this recyclability‐by‐design approach promising for manufacturing more sustainable printed electronics.

Eco-friendly recovery and preparation of high purity nano silver powders from retired photovoltaic solar cells

With the increasing deployment of photovoltaic modules, recycling of waste photovoltaic has become a topic of great concern. Silver (Ag) represents a significant resource in retired crystalline silicon solar cells (RCSSC). However, conventional methods for the recovery of silver are based on the use of harmful inorganic acids, which give rise to environmental concerns. Furthermore, the use of unsuitable chlorine sources may result in the production of target products with a low level of purity. Herein, we reported a new method featured with eco-friendly mixed organic acid to extract and recycle Ag from retired crystalline silicon wafers. Single-factor experiments and response surface optimization experiments were carried out to find the optimal conditions in the leaching step. A process comprising chlorination precipitation, ammonia dissolution, and liquid phase reduction was constructed for the production of silver powder from the leaching solution. This approach resulted in a high silver leaching yield of 97.38 % and silver purity of 99.85 % before purification with an average particle size of 229.7 nm.

Temperature stable (1-x)BaAl2Si2O8-xBa3V2O8 (0.2 ≤ x ≤ 0.5) microwave dielectric composite ceramics for LTCC applications

BaAl2Si2O8 microwave dielectric ceramics possess dielectric properties of low permittivity (εr) and low loss, coupled with low synthesis cost, making them promising for commercialization. However, the hexagonal structure undergoes high-temperature phase transitions that deteriorate thermal shock resistance and durability, hindering its practical use. In this work, we report temperature-stable BaAl2Si2O8-Ba3V2O8 low temperature co-fired ceramics (LTCC). The combination of Ba3V2O8 and G9 glass achieved a near-zero τf and a thermal expansion coefficient of ∼ 8.5 ppm/℃, significantly enhancing the temperature stability of BaAl2Si2O8 ceramics. By employing ion substitution and enhancing lattice disorder, the components of G9 glass were strategically designed to successfully induce hexagonal-to-monoclinic transformation of BaAl2Si2O8 phase. The dielectric properties of 0.5BaAl2Si2O8-0.5Ba3V2O8-9 wt% G9 sintered at 900 ℃ were εr ∼9, Q×f ∼22,000 GHz and τf ∼ +1.9 ppm/℃. Good chemical compatibility with silver powders was confirmed by further investigation of the co-firing behavior. This work provides attractive candidate for BaAl2Si2O8-based LTCCs and an available approach for modifying BaAl2Si2O8 ceramics.

Effect of silver morphology on rheology and photopolymerization characteristics of Silver-Hydroxyapatite slurry for Vat Photopolymerization-based 3D printing process

The present work deals with the processing of HA-silver photocurable slurry to make composites using the Vat-photopolymerization process. Slurries with increasing amount of silver addition in the HA-Ag (0, 5, 10, 15%) slurry have been prepared using monomers with photo-initiators and printed successfully. Silver powder used in this study is in the form of flakes and spheres. A shear thinning behaviour of all the compositions of the slurries has been observed which is essential to fabricate defect-free parts. With increase in silver addition to 15 wt%, the viscosity decreased by around 60 % however curing depth was compromised. From SEM micrographs it was observed that HA with silver flakes showed better sintering with sintering density of 95% compared to only HA and HA with spherical silver samples.

Hydrogen-Rich Syngas Production in a Ce0.9Zr0.05Y0.05O2−δ/Ag and Molten Carbonates Membrane Reactor

This study proposes a new dense membrane for selectively separating CO2 and O2 at high temperatures and simultaneously producing syngas. The membrane consists of a cermet-type material infiltrated with a ternary carbonate phase. Initially, the co-doped ceria of composition Ce0.9Zr0.05Y0.05O2−δ (CZY) was synthesized by using the conventional solid-state reaction method. Then, the ceramic was mixed with commercial silver powders using a ball milling process and subsequently uniaxially pressed and sintered to form the disk-shaped cermet. The dense membrane was finally formed via the infiltration of molten salts into the porous cermet supports. At high temperatures (700–850 °C), the membranes exhibit CO2/N2 and O2/N2 permselectivity and a high permeation flux under different CO2 concentrations in the feed and sweeping gas flow rates. The observed permeation properties make its use viable for CO2 valorization via the oxy-CO2 reforming of methane, wherein both CO2 and O2 permeated gases were effectively utilized to produce hydrogen-rich syngas (H2 + CO) through a catalytic membrane reactor arrangement at different temperatures ranging from 700 to 850 °C. The effect of the ceramic filler in the cermet is discussed, and continuous permeation testing, up to 115 h, demonstrated the membrane’s superior chemical and thermal stability by confirming the absence of any chemical interaction between the material and the carbonates as well as the absence of significant sintering concerns with the pure silver.

Study on the influence factors of the grain growth type of micro-nano silver powders prepared by liquid-phase reduction method

Abstract The preparation was carried out by liquid-phase reduction method with AgNO3 as the oxidizing agent, ascorbic acid (C6H8O6) as the reducing agent, and polyvinyl pyrrolidone (PVPK30) as the dispersing agent. The effects of silver nitrate concentration, ascorbic acid concentration, PVPK30 concentration, solution PH value before and after the reaction, and the temperature of reaction on average particle size (D50), dispersity, and particle size uniformity of silver particles were investigated by orthogonal experiment L18 (36) with six factors and three levels. The spheroid-like silver particles with good dispersity of 400-600nm and the spheroid-like silver particles with suitable particle size uniformity of 80-100nm were successfully prepared by optimal experiments. The results of the orthogonal experiment show that the molar ratio of the reducing agent to the oxidizing agent plays a decisive role in the type of grain growth. The crystal nucleus will coagulate and grow at a higher molar ratio (⩾1.05). With the increase in molar ratio, the nucleation rate is higher, the grain growth rate is faster, and the size of silver particles is smaller.

Synthesis of uniform spherical silver powder without dispersants in a confined impinging-jet reactor

Sliver powder is the most common and extensively utilized precious metal powder in electronics, primarily for electronic paste. Herein, micron-sized spherical silver powder was synthesized via a liquid phase reduction method employing silver nitrate as the source of silver and ascorbic acid as the reducing agent in a confined impinging jet reactor (CIJR). The impact of the molar ratio between silver nitrate and ascorbic acid, the flow rate, and the temperature on the particle size of silver powder was investigated. The optimal process conditions for silver powder are as follows: maintain a molar ratio of 1:1 and control the feeding rate at 10 ml/min while operating at 50 ° C. The confined impinging jet reactor offers enhanced control over reaction conditions during the synthesis of silver powder, surpassing the capabilities of traditional batch reactors. The aforementioned optimized methodology was employed to successfully synthesize uniform and spherical silver powder (with an aspect ratio approaching 1) in the low Reynolds number jet, resulting in an average particle size of d50 = 0.83 μm and a standard deviation of 0.07, without the addition of dispersant. The synthesis method presented here improves the performance of silver powder, simplifies the production process, reduces energy consumption, and minimizes waste generation. These advances yield significant environmental and economic benefits. In the future, with the continuous development and optimization of microreactor technology, this synthesis method is anticipated to play a more prominent role in the commercial-scale production and application of micrometer-sized silver powder.

Silver-Organic Complex in Photosensitive Silver Pastes for Enhanced Resolution and Aspect Ratio.

Traditional screen printing is an easy approach commonly used for conductive pattern fabrication of electronics but lacks high resolution. Photolithography offers better resolution but is complex. Photosensitive silver pastes (PSP) combine the benefits of both but suffer from undercut issues, causing uneven etching, decreased interfacial adhesion, and thus poor resolutions. In this study, we explore the use of molecular precursors (i.e., silver oxalate) to replace metallic silver particles and enhance the depth of light penetration. Our findings demonstrate a successful solution to the undercut issue, achieving an undercut index of 1.0, indicating an undercut-free scenario and enabling higher resolutions in line and pattern formation. Additionally, our research confirms the feasibility of multilayer stacking of photosensitive pastes, achieving unprecedented aspect ratios in line patterns. By replacing 25% of micrometer silver powder with silver oxalate (PSP-25), we achieved optimal line widths as fine as 10 μm. The three-layer stack of PSP-25 reached a substantial aspect ratio with a height of 29.4 μm and an optimal fringe pattern resolution of 10 μm line width with a 15 μm aisle width. Utilization of silver oxalate was observed to slightly expand the line width, likely due to light scattering by the fine silver nanoparticles (∼40 nm) formed during the photodecomposition of silver oxalate.

Insight of Effect of Silver Powders on Silver–Silicon Contacts of Crystalline Silicon Solar Cells through Analysis of Glass Structural Decay

Optimally designed silver–silicon (Ag–Si) contacts, based on silver (Ag) paste screen printing and the rapid sintering process, are widely utilized in mainstream crystalline silicon solar cells, enabling to reduce contact resistance and high photo‐conversion efficiency. Ag powder is the largest conductive component in Ag paste, but its impact on the formation of Ag–Si contacts lacks in‐depth research and comprehensive understanding. In this work, it is demonstrated that the oxygen adsorption capacity of silver powders affects the formation of Ag–Si contacts by enhancing the reactivity of Ag powders with glass frits, and has a significant effect on the performance of devices. The generation of Ag2O introduced by surface‐absorbed oxygen promotes the transformation of [TeO4] triangular bipyramidal into [TeO3] triangular pyramid, thus destroying the network structure of the glass frits. This structural decay accelerates the spreading of glass frits in the bulk, causing the glass frits to come into contact with SiNx layers earlier and facilitating the formation of the Ag–Si contacts. In this work, not only a complete picture of the interaction between Ag powder and glass frits but also a new direction is provided to optimize the Ag–Si contacts.

An efficient numerical method for modeling silver powder heat exchanger in dilution refrigerator

Dilution refrigerator provides continuous ultralow temperature environments as low as 10 mK. It has been widely used in a variety of important applications such as quantum computations. The silver powder heat exchanger in a dilution refrigerator plays a crucial role in realizing ultralow temperatures on the order of 10 mK by precooling the circulation of helium mixtures. To study the silver powder heat exchanger quantitatively, we have proposed an efficient numerical solution method for its thermodynamic model. This method utilizes constraint conditions cleverly to convert the initial value problem of differential equations into a boundary value problem, allowing us to solve the control equations using the existing ODE function quickly. Furthermore, we demonstrate the application of this method in the evaluation and design of silver powder heat exchanger. The research results of this paper have certain significance for the development of dilution refrigerator.

Optimizing Silver Paste Conductivity with Controlled Convection for Nanowrinkle Growth.

Conductive silver paste plays a crucial role as an interconnecting material between electrodes and circuits in electronic circuits and solar cells. The quality of the silver paste is greatly influenced by the preparation of the conductive-phase silver powder and the sintering process. This study investigated the impact of fluid dynamics on the preparation of silver powder. Combined with X-ray diffractometer characterization and molecular dynamics simulation, the formation mechanism of wrinkled silver powder was explained. The wrinkled silver powder replaced the traditional smooth spherical silver powder, and the point contact between the smooth silver powder turned into a line and surface contact. After mixing and sintering with the micrometer flake silver powder, the electrical conductivity and sintering morphology of the silver paste were improved. Compared with the silver content of conventional silver paste (≥75 wt %), the silver paste of (9.23 ± 0.68) × 10-6 Ω cm can be prepared by curing at 250 °C for 45 min when wrinkled powder/flake powder = 1:1 and silver paste content was only 66.7%. This research work provides a new idea for the morphology control of submicrometer silver powder, which has important applications in the field of low-temperature silver paste for new N-type batteries.

Preparation of Gradient Polyurethane and Its Performance for Flexible Sensors.

Flexible sensors are prone to the problems of slow recovery rate and large residual strain in practical use. In this paper, a polyurethane functional composite with a gradient change in elastic modulus is proposed as a flexible sensor to meet the recovery rate and residual strain without affecting the motion. Different hard and soft segment ratios are used to synthesize a gradient polyurethane structure. The conductive percolation threshold was obtained between 45 wt% and 50 wt% of flake silver powder. Both gradient polyurethane and gradient polyurethane composites demonstrated that gradient materials can increase the recovery rate and reduce residual strain. The gradient polyurethane composites had a tensile strength of 3.26 MPa, an elastic modulus of 2.58 MPa, an elongation at break of 245%, a sensitivity coefficient of 1.20 at 0-25% deformation, a sensitivity coefficient of 11.38 at 25-75% deformation, a rate of recovery of 1.95 s at a time, and a resistance to fatigue (over 1000 cycles at a fixed strain of 20% showed a stable electrical response). The sensing performance under different cyclic strain frequencies was also investigated. The process has practical applications in the field of wearable skin motion and health monitoring.

Morphology of 925 Silver Powder Particles Produced From Gas Atomization

Morphology of 925 Silver Powder Particles Produced From Gas Atomization

Effect of Accumulative Roll Bonding Cycles and Postprocessing Heat Treatment Temperature on Shape Memory Properties of Cu–Al–Ag Alloys

Herein, Cu/Al/Ag‐layered composites with two silver powder concentrations (2 wt% and 3 wt%) are fabricated with the aid of accumulative roll bonding (ARB). The ARB‐ed samples are heat treated at different temperatures (750, 850, 950, and 1050 °C), times (30, 45, and 60 min), and cycles (1–9 cycles) to produce Cu–Al–Ag shape memory alloys. The samples are characterized by X‐ray diffraction, scanning electron microscope, and electron backscattering diffraction. Phase transformation temperatures are measured by differential scanning calorimetry. Strain recovery and shape memory behavior are evaluated by bending and tensile tests, respectively. The results indicate that alloys containing 2 wt% Ag, rolled till 9 cycles, heat treated at 950 °C for 60 min, and samples with 3 wt% Ag, fabricated by 9 cycles, annealed at 850 °C for 60 min show maximum β martensite phase amount. The strain recovery ratios of the first and second samples are 71.7% and 71.2%, respectively. Additionally, the tensile test shows that the residual plastic strain and the recovered strain for the first sample with 2 wt% Ag are equal to 0.7% and 3.0%, respectively. These results for the second sample with 3 wt% Ag are 1.2% and 3.4%, respectively.

Physical Properties of Paste Synthesized from Wet- and Dry-Processed Silver Powders.

This study compares the characteristics and low-temperature curing properties of pastes prepared from silver (Ag) powders synthesized by either wet powder (WP) or dry powder (DP) processing. The WP synthesis of electrode particles has the advantage of controlling the average particle size and particle size distribution but the disadvantage of producing low-purity, crystalline particles because they are synthesized through chemical reduction at less than 100 °C. Conversely, the DP synthesis of electrode particles has the advantage of producing pure, highly crystalline particles (due to synthesis at high temperatures) but the disadvantage of a high processing cost. WP and DP were used to manufacture pastes for low-temperature curing, and the physical properties of the pastes and the electrode characteristics after low-temperature curing were compared between powder types. Shear stress as a function of the shear rate shows that the WP paste is a plastic fluid, whereas the DP paste is a pseudoplastic fluid, closer to a Newtonian fluid. Screen printing the Ag pastes and curing for 30 min at 130 °C produces a nonconductive WP paste, whereas it produces a DP paste with a conductivity of 61 mΩ/sq, indicating that the highly crystalline DP paste is advantageous for low-temperature curing.

Pressure-less Ag-Sinter: Necking, Pores Structure and Its Properties

Pressure-less Ag-sinter die-attach structure revealed good-networked silver interconnects along with discontinuous shrinkage porosities. A thin sheet test sample is processed to be evaluated with commercially available test equipment. In this study, test samples are stencil printed to a thickness from 70 to 100 µm and sintered at 200/250°C for 30/60 minutes. A test sample to a thickness of 13mm is processed by stacking a few layers of printed Ag-sinter and sintered at 200°C for 1h. Interestingly, good necking is observed in between the silver powder particles and measured properties for three different porosity levels of pressure-less Ag-sinter are as follows: • Discontinuous porosities of structure are about 15 to 20%, 25 to 35% and 45 to 55% depending on the paste chemistry and formulation (with or without binder) *Density of these pores structure is fro 4.5 to 7.7 g/cc • Electrical sheet resistivity is from 3.7 to 9.2 µΩ.cm • Thermal conductivity is from 80 to 190 W/m°K • Elastic modulus (ultrasonic testing method) is from 7.2 to 38 GPa 1. Lower the porostiy, hight the thermal conductivity and elastic modulus • Coefficient of thermal expansion (CTE) is about 19.2 to 21.5ppm • Specific heat capacity (Cp) is about 0.24-0.25 J/Kg°K *Both CTE and Cp properties of Ag-sinter are not influenced by porosity in the structure

RECEIVING METALS FROM SECONDARY RAW MATERIALS. POWDER OF SILVER

Purpose of research. Powder of silver is one of the most widely used materials in industry. In the free or sintered (compressed) state, it is widely used in medicine as an element of antiseptics, in electronics as the basis of conductive pastes, conductive adhesives and contacts intended for closing and opening electrical circuits, in the production of multilayer ceramic capacitors, etc. Due to its high electrical conductivity, powder of silver is also used as a cathode material in solar cells. In today's conditions, the development of materials for alternative energy sources is quite relevant. Powder of silver can be used as a component of the active mass in chemical current sources. It is known that the characteristics of the active mass are influenced by the properties of the powder, namely, the size and shape of the particles. Materials and methodology. In this work, it was proposed to use boards of radio-electronic equipment as raw materials for the production of powders of silver. The reductant, recovery rate and modes of obtaining finely dispersed powders of silver after processing of secondary raw materials were identified. Results. The influence of the parameters of the reduction of powders of silver, namely, the type of reducing agent and the rate of reduction, was studied. It was established that in the process of forming powders of silver, a developed morphology and space between particles are formed, which increases the surface area, due to which the performance characteristics of various devices, in which powder of silver can be used as a component, will improve. Scientific novelty. Factors that affect the size and shape of powder of silver particles, namely, the type of reducing agent and the rate of reduction, have been established. Conclusions. It was established that the size of particles of silver depends on the speed of recovery. The stronger the reducing agent, the higher the rate of metal reduction, and the larger the particle size. Changing the speed of recovery (slowing down or speeding up) allows you to get particles of silver with the desired size. The indisputable advantage of the method of obtaining powder of silver by reduction is the formation of high-purity metal, which positively affects the properties.

Study on Preparation of High-Performance Flake Silver Powder by Liquid Phase Reduction

Flake silver powder was prepared by liquid phase reduction method with silver nitrate as silver source, ferrous sulfate heptahydrate as reducing agent, citric acid and gum acacia as surfactants. The effects of reducing agent dosage, citric acid dosage, gum acacia dosage, silver nitrate dosage and reaction temperature on the properties of silver powder were studied. The results show that when the dosage of silver nitrate is 0.08 mol·L−1, the molar ratio of silver nitrate to ferrous sulfate heptahydrate is 1:2, the oxidizing solution is added to the reducing solution at the rate of 100 ml·min−1, the citric acid is added to the oxidizing solution at 7.5% of the mass of silver nitrate, the gum acacia is added equally dispersed to the oxidizing solution and the reducing solution, the addition amount is 20% of the mass of silver nitrate and the reaction temperature is 30 °C, the silver powder obtained is flake with good dispersion and narrow particle size distribution.

Patent Literature on Epoxidation of Propylene Over Silver Catalysts Using Molecular Oxygen – A Critical Industrial Review

AbstractWe summarize the patent literature related to the direct oxidation of propylene‐to‐propylene oxide (DOPO) over silver catalysts. Inventions claiming new compositions, preparation methods, and/or alternative process options are illustrated with data sampled from patent documents. Early claims focused on powders of silver (silver oxide) alloyed with and/or surface‐modified with one‐two promoterswhere silver was in large excess (>80 wt%). In the following decades, inventors refined their approach and pursued alternative bulk synthetic methods supplemented with impregnation to produce formulationscontaining lower amounts of silver in combination with various other transition metals, halides, alkalis and/or alkaline earth elements. Simultaneously, process development has facilitated increased PO selectivity via the co‐feeding of water and/or carbon dioxide at volume percent levels combined with smaller ppmV concentrations of organic chlorides and nitrogenoxides. At the end we briefly discuss how non‐catalytic oxidative routes to propylene oxide provide additional insights for new catalyst development. While these approaches hardly exceed 60 % PO selectivity, they may shed light on design criteria for catalysts capable of achieving that goal. Success in the field will require strong fundamental understanding of the activation of dioxygen on catalytic surfaces to define design requirements for silver catalystswith high selectivity to PO via direct oxidation.

Silver-Assisted Hydrogen Evolution from Aluminum Oxidation in Saline Media.

A swarf of aluminum alloy with high corrosion resistance and ductility was successfully converted into fine hydro reactive powders via ball milling with silver powder and either lithium chloride or gallium. The latter substances significantly intensified particle size reduction, while silver formed 'cathodic' sites (Ag, Ag2Al), promoting Al corrosion in aqueous saline solutions with hydrogen generation. The diffraction patterns, microphotographs, and elemental analysis results demonstrated partial aluminum oxidation in the samples and their contamination with tungsten carbide from milling balls. Those factors were responsible for obtaining lower hydrogen yields than expected. For AlCl3 solution at 60 °C, Al-LiCl-Ag, Al-LiCl, Al-Ga-Ag, and Al-Ga composites delivered (84.6 ± 0.2), (86.8 ± 1.4), (80.2 ± 0.5), and (76.7 ± 0.7)% of the expected hydrogen, respectively. Modification with Ag promoted Al oxidation, thus providing higher hydrogen evolution rates. The samples with Ag were tested in a CaCl2 solution as well, for which the reaction proceeded much more slowly. At a higher temperature (80 °C) after 3 h of experiment, the corresponding hydrogen yields for Al-LiCl-Ag and Al-Ga-Ag powders were (46.7 ± 2.1) and (31.8 ± 1.9)%. The tested Ag-modified composite powders were considered promising for hydrogen generation and had the potential for further improvement to deliver higher hydrogen yields.