Melting Temperature Of Ag Research Articles

Gold and silver: Noble solvents for the synthesis of superconducting boron-doped diamonds

The synthesis of diamonds in traditional growth systems based on Fe, Co and Ni does not allow overcoming the semiconductor level of boron doping of diamond, presumably because of a high affinity of boron to boride-forming metals. For the first time, noble metals that do not form borides—silver and gold—are used as growth media for the synthesis of heavily boron-doped diamonds at 8–9 GPa. Gold and silver are not catalysts for the transformation of graphite to diamond, whereas elemental boron is catalytically active at eutectic melting temperatures above 2500 K. It is found that the synthesis of diamond in AgB and AuB growth media starts at temperatures close to the melting temperatures of Ag and Au, 1600 and 1800 K, respectively. Calculations show that molten Au and Ag dissolve boron atoms without a significant change in the electronic structure of the solution, suggesting that the metal melts serve as a carrier for the boron catalyst. The resulting polycrystalline diamond contains dispersed inclusions of Ag and Au, as well as traces of boron carbide; the formation of borides is not detected. The transport measurements of the diamond samples reveal a transition to a superconducting state in the temperature range from 4.5 to 2.5 K. Raman spectroscopy confirms the heavy boron doping of diamond. Thus, we show that melts of “non-catalytic” metals that do not form borides can be effectively used to synthesize boron-doped conductive/superconducting diamonds at relatively low temperatures.

Microstructure and brazing properties of a novel Ag–Cu-Ga solder

In this study, a novel low-silver Ag-xCu-5Ga (x = 28, 34, 39, 49 and 55) solder with high strength was designed and prepared. The effect of element composition on microstructure evolution, thermal behavior, and the mechanical performance of Ag–Cu-Ga solders were investigated in detail. The results indicated that the melting temperature of Ag–Cu alloy could be reduced effectively with Ga addition, and the typical joint consisted of the block-shaped Cu-rich phase in the welded seam and the ribbon-shaped Cu-rich phase adjacent to the interface. The shear strength of joints brazed with Ag-xCu-5Ga (x = 28, 34, 39 and 49) filler metals can be improved significantly compared to that of commercial Ag–28Cu solder, with a maximum value of approximately 445 MPa in Ag–39Cu–5Ga solder. The best mechanical properties are obtained as the second-phase strengthening and interfacial strengthening reach a balanced coexistence state, determined by the block-shaped Cu-rich phase in the welded seam and the ribbon-shaped Cu-rich phase adjacent to the interface, respectively. This study can provide insights to investigate strengthening mechanisms and develop high-strength solders for vacuum brazing.

Ag droplets nano-shape design on SiC: Study on wetting and energetics

This work describes the effect of the annealing temperature on the size and wetting of nanostructures obtained on 4H–SiC substrate by the dewetting process of a deposited nanoscale-thick Ag film. The work focuses, in particular, on the difference between solid-state dewetting (below Ag melting temperature) and liquid-state dewetting (above Ag melting temperature). Following the deposition of a 58 nm-thick Ag film on the SiC substrate, annealings were perfomed at 800 °C, 850 °C and 885 °C so to induce the Ag film solid-state dewetting. In addition, annealing at 1040 °C was performed so to induce the Ag film liquid-state dewetting. The dewetting processes led to the formation of nanostructures on the SiC surface. Plan-view and cross-view scanning electron microscopy analyses were carried out to quantify the evolution of the average planar size and of the average contact angle (to the SiC surface) of the Ag nanostructures versus the annealing temperature. These analyses allowed us to extract information on the wetting behavior of the nanostructures on the SiC surface by calculating the temperature-dependent adhesion work. In fact, the nanostructures obtained by the 800 °C and 850 °C processes show mean contact angle of 118,9° and 117,4°, respectively, and mean work of adhesion of 0,45 and 0,48 J/m2, respectively. On the other hand, the nanostructures obtained by the 885 °C and 1040 °C show mean contact angle of 48,3° and 52,2° respectively, and work of adhesion of 1,45 and 1,40 J/m2, respectively. The variation of the wetting properties is identified in Si diffusion from the SiC substrate to the Ag nanostructures at the higher temperatures, as confirmed by energy dispersive x-ray analyses. Finally, the optical properties of the Ag nanostructures/SiC systems were probed by absorbance and transmittance measurements allowing to recognize the occurrence of a peak around 460 nm which is attributed to localized surface plasmon resonances due to the Ag nanostructures.

Diffusion and wetting behaviors of Ag nanoparticle and Ag nanowire pastes for laser brazing of Inconel 718

Ag nanomaterials have been investigated as a filler material for brazing Inconel 718 well below the bulk melting temperature of Ag using both vacuum and laser brazing. However, Ag nanoparticles and Ag nanowires exhibit different bonding strengths. In this study, we focus on different diffusion and wetting behaviors of two kinds of nanopastes. At 550 °C, the areal coverage of the nanopaste decreases as a result of shrinkage in the nanopaste. The shrinkage is followed by rapid wetting and spreading on the Inconel 718 surface. A deeper investigation to the diffusion behavior of Ag nanoparticle and Ag nanowire pastes during laser brazing provides a clear correlation between the diffusion distance and the bonding strength. The diffusion of the base material into the Ag joint is shown to result in a concentration “hump” near the Ag-Inconel 718 interface of different base material elements which is likely caused by a difference in diffusivity of Ag and the Inconel 718 constituent elements. Ag NW joints were found to have a thicker diffusion zone, but also exhibit some Nb/Mo segregation when brazed using 300-W laser power. This may lead in different metallurgic bonding.

Effects of rare earth La on microstructure and properties of Ag–21Cu–25Sn alloy ribbon prepared by melt spinning

Abstract Ag–21Cu–25Sn alloy ribbon as a promising intermediate temperature alloy solder (400–600 °C) was prepared by melt spinning technique in this paper. Rare earth La was added into Ag–21Cu–25Sn alloy to refine the microstructures and improve the wettabilities of as-prepared alloy solders. The phase constitutions, microstructures, melting temperatures and wettabilities of selected specimens were respectively tested. The results showed that the dominant phase constitutions of Ag–21Cu–25Sn– x La alloy ribbons were Ag 3 Sn and Cu 3 Sn. The grain size of Ag–21Cu–25Sn– x La alloy decreased with the addition of La increasing. La addition reduced the melting temperatures of Ag–21Cu–25Sn– x La alloy ribbons, and effectively improved the wettabilities of the alloy ribbons. When the addition of La was 0.5 wt%, the wettability of as-prepared alloy solder achieved the optimal value of 158 cm 2 g −1 under brazing temperature 600 °C and dwell time 15 min. In addition, raising brazing temperature and prolonging dwell time could improve the wettability of Ag–21Cu–25Sn– x La alloy ribbon.

(Invited) Solid-State Z-Scheme Photocatalysts for Overall Water-Splitting Under Visible Light

We fabricated an Ag-inserted hetero-junction photocatalyst for water-splitting under visible light, similar to a Z-scheme system but is not required for a redox mediator. In this system, Ag acts as a solid electron mediator for water-splitting. We selected ZnRh2O4 (Eg=1.2 eV) and AgSbO3 (Eg=2.5 eV) as H2- and O2-photocatalysts, respectively. Ag could be inserted between these photocatalysts using a thermal-decomposition reaction of Ag2O and following melt reaction of Ag. In short, commercially available powder of Ag2O and prepared powders of ZnRh2O4 and AgSbO3 were thoroughly mixed and heat-treated at 900oC, which is slightly lower than the melting temperature of Ag. Then, the obtained powder was washed with HNO3 aqueous solution to remove excess Ag, forming the solid-state photocatalyst, ZnRh2O4/Ag/Ag1-xSbO3-y. The Ag1-xSbO3-y and ZnRh2O4 particles were connected to each other with their particle sizes of ~1000 and ~200 nm. In this system, Ag acted as the solid-state electron mediator for the transfer of electrons from the conduction band of Ag1-xSbO3-y to the valence band of ZnRh2O4. Utilizing the constructed photocatalyst, the simultaneous liberation of H2 and O2 from pure water at a molar ratio of ~ 2:1 was achieved under irradiation with visible light at ~ 545 nm. Utilizing the same strategy by changing the O2-evolution photocatalyst, we recently succeeded in pure water-splitting under visible light up to 600 nm. Detailed investigations will be discussed at the conference.

Self-organized patterned arrays of Au and Ag nanoparticles by thickness-dependent dewetting of template-confined films

In this work we report on the formation of self-organized and multimodal sized patterned arrays of Au and Ag nanoparticles on SiO2 surface exploiting the thickness-dependent solid-state dewetting properties of template-confined deposited nanoscale films. In this approach, the Au and Ag surface pattern order, on the SiO2 substrate, is established by the template confined deposition on a micrometric scale, while the solid-state dewetting phenomenon is induced by thermal processes (below the Au and Ag melting temperature). The deposited films have not an uniform thickness. They, instead, present a controlled thickness due to shadowing mask effects during depositions. Such an inhomogeneity can be further controlled by changing the deposition angle. After the dewetting process, scanning electron microscopy analyses allowed us to correlate the mean diameter 〈D〉 and spacing 〈s〉 of the formed nanoparticles by the thickness h of the deposited films. Despite the dewetting process of the Au and Ag films occurs in the solid state, relations describing the evolution of 〈D〉 and 〈s〉 with 〈h〉 typical of the linear hydrodynamic spinodal dewetting process of liquid films, 〈D〉 ∝ h 5/3 and 〈s〉 ∝ h 2, were verified within a 20 % experimental error. As a consequence we call this process “pseudo-spinodal dewetting”.

Effect of oxygen environment on formation of modulated Ag nanostructures along the interface of a Ag-Si heterostructure

Ag nanostructures were formed along the interface between Ag foil and Si wafer. These structures form when heated in the presence of air below the melting temperature of Ag, while heating above the melting temperature results in Ag foil melting with no nanostructure growth. Nanostructure morphology is determined by Si wafer orientation, while the size and periodicity of the structures depend on the duration of thermal processing. Electron backscatter diffraction (EBSD) analysis shows an epitaxial relation between Ag nanostructures and Si. Annealing specimens in vacuum above the Ag-Si eutectic but below pure Ag melting temperature results in solidification of melted foil without any interfacial nanostructure growth.

Fabrication of Ag Nanoparticles Embedded in Al:ZnO as Potential Light-Trapping Plasmonic Interface for Thin Film Solar Cells

Incident photon conversion efficiency of the absorbing materials at either side of a thin film solar module can be enhanced by integrating a plasmonic interface. Silver nanoparticles represent a good candidate that can be integrated to a thin film solar cell for efficient light-trapping. The aim of this work is to fabricate plasmonically active interface consisting of Ag nanoparticles embedded in Al:ZnO that has the potential to be used at the front surface and at the back reflector of a thin film solar cell to enhance light-trapping and increase the photoconversion efficiency. We show that Ag can readily dewet the Al:ZnO surface when annealed at temperatures significantly lower than the melting temperature of Ag, which is beneficial for lowering the thermal budget and cost in solar cell fabrication. We find that such an interface fabricated by a simple dewetting technique leads to plasmonic resonance in the visible and near infrared regions of the solar spectrum, which is important in enhancing the conversion efficiency of thin film solar cells.

Solid State Bonding of Silicon Chips to Silver Buffer on Copper Substrates

A solid state bonding technique was designed and developed to bond silicon (Si) chips to silver (Ag) buffer layer electroplated on copper (Cu) substrates at a temperature (260°C ) far below the melting temperature of Ag (961°C ). This is possible because Ag atoms in Ag buffer are brought in contact with the gold (Au) atoms in Au layer coated on Si chip. The close proximity in atomic scale allows the Ag and Au atoms to see each other, to share electrons and to bond to each other. The possibility of mating between Au and Ag surfaces relies on the deformation of Ag. Ag, with proper annealing, is ductile and has low yield strength. Its surface can thus deform to conform to and to follow the surface of Au layer coated on Si chip. Its ductile property can also help accommodate large mismatch in coefficient of thermal expansion between Si (2.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> °C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and Cu (17×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> °C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ). Ag also has the highest electrical and thermal conductivities among all metals. It is the dream bonding medium. The challenge is to bond Ag to other materials at a temperature compatible to electronic packaging processes, 260°C. In this research, Si chips are coated with thin chromium (Cr) and Au layers and then bonded to Ag buffer plated on Cu substrates. To make Ag buffer ductile, Ag buffer together with Cu substrate is annealed to increase its grain size by a factor of 25. The bonding was performed at 260°C with 1000 psi (6.89 MPa) static pressure. There is no molten phase involved in the bonding process. Scanning electron microscope evaluations show that on the revealed cross section no voids or gaps are observed on Si/Ag and Ag/Cu bonding interfaces. The bonded structure consists of only Si/Cr/Au/Ag/Cu and can sustain at high operating temperature due to high melting temperature of Ag.

Enhancement of electrical properties of anisotropically conductive adhesive joints via low temperature sintering

AbstractThe electrical properties of anisotropically conductive adhesives (ACAs) joints through low temperature sintering of nano silver (Ag) particles were investigated and compared with that of the submicron‐sized Ag‐filled ACA and lead‐free solder joints. The nano Ag particles used exhibited sintering behavior at significantly lower temperatures (&lt;200°C) than at the bulk Ag melting temperature (960°C). The sintered nano Ag particles significantly reduced the joint resistance and enhanced the current carrying capability of ACA joints. The improved electrical performance of ACA was attributed to the reduced interfaces between the Ag particles and the increased interfacial contact area between nano Ag particles and bond pads by the particle sintering. The reduced joint resistance was comparable to that of the lead‐free (tin/3.5 silver/0.5 copper) metal solder joints. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1665–1673, 2006

Effect of tin on melting temperature and microstructure of Ag–Cu–Zn–Sn filler metals

To develop low melting point filler metals for brazing TiNi shape memory alloy (SMA) and stainless steel (SS), a series of Ag–22Cu–Zn–Sn (wt-%) filler metals have been studied. Using differential thermal analysis (DTA) analysis, the melting temperatures of Ag–22Cu–Zn–Sn filler metals were determined. The results show that the increase of zinc and tin contents drastically decreases the solidus and liquidus temperatures of the Ag–22Cu–Zn–Sn filler metals and the melting temperatures of the Ag–22Cu–18Zn–Sn filler metals with 5–8 wt-%tin are < 650°C. Metallographic observations indicate that the increase of zinc and tin in the Ag–22Cu–Zn–Sn filler metals helps the formation of eutectic structure and inhibits the formation of α-Ag and α-Cu solid solutions, but the increase of tin also causes the formation of Ag3Sn and Cu41Sn11 brittle compounds. The results of mechanical property tests of the laser brazed joints of TiNi SMA and SS show that the proper increase of zinc and tin in Ag–22Cu–Zn–Sn filler metals is favourable for improving the strength of the laser brazed joints of TiNi SMA and SS.

Large enhancement in room-temperature magnetoresistance and dramatic decrease in resistivity in La0.7Ca0.3MnO3–Ag composites

A ferromagnet-metal-type composite, La0.7Ca0.3MnO3 (LCMO)–Ag, was fabricated by a two-step chemical route which can avoid the doping of Ag into the lattice of LCMO. The grain size of Ag can be reduced by increasing calcination temperature, which favors the penetration of Ag into LCMO matrices. A large enhancement in magnetoresistance (MR) near room temperature and a dramatic decrease in resistivity are observed for the samples calcined at above the melting temperature of Ag. We suggest that the shift of metal–insulator transition up to Curie temperature in melted-Ag-added LCMO and magnetic inhomogeneity are responsible for the enhanced MR.

X-ray diffraction experiments on Ag and Ge in normal and supercooled liquid phase

While there are a lot of experiments to investigate the structure of elements or binary alloys above the melting point, respectively the liquidus, there are only few measurements concerning the metastable state of supercooled liquids of such samples. Investigations on supercooled Ag show, in contrast to measurements on supercooled Ge, a strange temperature dependence of the structure factor S( Q). While cooling down below a certain temperature, that is already smaller than the melting temperature of Ag, the form of the structure factor rapidly changes. In a range of approximately 10 K, first the height of the first maximum doubles and afterwards becomes even smaller than 1 for lower temperatures. On the other hand the height of the second maximum similarly heightens but afterwards lessens only a bit. Further investigations on Cu, which has an electron configuration comparable with Ag, show a likewise behaviour.

Melting curve of NaCl0.5Br0.5up to 4.5 GPa

Abstract The melting curve of NaCl0.5Br0.5 has been measured under pressure up to 4.5 GPa. The melting temperatures of Ag and NaCl have been used to determine the pressure in the sample at its melting temperature.

Processes of atom mixing at the boundary in Ag-Cu and Ag-Mo systems under argon ion bombardment

Analysis of some aspects for dynamic ion mixing at the film-substrate boundary in Ag-Cu and Ag-Mo systems under argon ion bombardment during Ag film growth has been carried out. Evaluations of vacancy concentration formed in unit time under ion beam action show that without taking into account recombination and annealing the low energy ions are capable of creating a defect concentration in the film-substrate interface 1-2 orders of magnitude smaller than high energy ions. In this case the concentration is comparable with the thermo-dynamical equilibrium concentration at temperatures close to the Ag melting temperature. Proceeding from the comparison of diffusion activation energies, vacancy migration rates as well as taking into consideration mechanical characteristics of material, a conclusion has been drawn about mutual penetration and preferential penetration of substrate material into Ag coating as the result of radiation enhanced processes. Experimental results have confirmed these estimations revealing the considerably larger Ag films adhesion to Mo substrate than to Cu under the same conditions of film formation. The friction tests have shown that wear of Ag-Cu and Ag-Mo solid solutions produced under Ar ion bombardment of the growing Ag film is much lower than the wear of Ag film without ion irradiation.