Paul F. Hlava

Intermetallic compound layer formation between copper and hot-dipped 100In, 50In-50Sn, 100Sn, and 63Sn-37Pb coatings

The growth kinetics of intermetallic compound layers formed between four hot-dipped solder coatings and copper by solid state, thermal aging were examined. The solders were l00Sn, 50In-50Sn, 100In, and 63Sn-37Pb (wt.%); the substrate material was oxygen-free, high conductivity Cu. The total intermetallic layer of the 100Sn/Cu system exhibited a combination of parabolic growth at lower aging temperatures and t0.42 growth at the higher temperatures. The combined apparent activation energy was 66 kJ/mol. These results are compared to the total layer growth observed with the 63Sn-37Pb/Cu system which showed parabolic kinetics at similar temperatures and an apparent activation energy of 45 kJ/mol. Both 100Sn and 63Sn-37Pb diffusion couples showed a composite intermetallic layer comprised of Cu3Sn and Cu6Sn5. The intermetallic compound layer formed between In and Cu changed from a CuIn2 stoichiometry at short annealing times to a Cu57In43 composition at longer periods. The growth kinetics were parabolic with an apparent activation energy of 20 kJ/mol. The intermetallic layer growth of the 50In-50Sn/Cu system exhibited extreme variations in the layer thicknesses which prohibited a quantitative assessment of the growth kinetics. The layer was comprised of two compounds: Cu26Sn13In8 which was the dominant phase and a thin layer of Cu17Sn9In24 adjacent to the solder.

Sputter deposition of ZnS:Mn/SrS:Ce multilayered thin film white phosphor

Abstract A full color thin film electroluminescent (TFEL) display can be fabricated by using color filters in combination with a high efficiency ‘white’ phosphor, such as a thin film multilayered stack of ZnS:Mn and SrS:Ce (denoted ZnS:Mn/SrS:Ce). To date, deposition of these multilayers has been limited to vacuum evaporation techniques and atomic layer epitaxy, both of which require different substrate temperatures for growth of high quality ZnS:Mn and SrS:Ce. This repeated thermal cycling during multilayer deposition can adversely affect electroluminescent (EL) performance and manufacturability. Sputter deposition of ZnS:Mn and SrS:Ce produces high quality phosphors for a wider range of substrate temperatures. We have determined a common set of radio frequency (rf) sputter deposition parameters for ZnS:Mn and SrS:Ce that result in high performance, multilayered white phosphors for use in TFEL devices. The EL performance of our samples is comparable to the best performance reported for evaporated multilayered samples. The major improvement is that the rf sputtered ZnS:Mn and SrS:Ce layers were deposited at the same substrate temperature. We report on the effects of sputter deposition parameters on the resultant composition and morphology of ZnS:Mn and SrS:Ce thin films and multilayers. Their EL performance was evaluated and correlated to composition and morphology.

Analysis of the reaction between 60Sn-40Pb solder with a Pd-Pt-Ag-Cu-Au alloy

We present the results of a metallurgical study of a 35Pd-30Ag-14Cu-10Au10Pt-1Zn (wt. %) alloy soldered with 60Sn-40Pb for glass-to-metal sealing applications. Mechanical tests were performed on the Pd-Ag-Cu-Au-Pt-Zn alloy and showed that it retains ductility, with an increase in strength, after heat treatments that simulate the glass-to-metal sealing temperature profile. Wetting characteristics of the alloy with 60Sn-40Pb solder were found to be adequate for pin joining applications. The formation and growth of the interfacial interme-tallic between 60Sn-40Pb and the Pd-Ag-Cu-Au-Pt-Zn alloy were characterized. The matrix of the intermetallic layer consists of PdSn4 with platinum and gold substituting for the palladium in the crystal structure. Also present were precipitates of Cu3Sn and Ag3Sn. Nano-indentation hardness tests showed that the intermetallic layer has mechanical properties similar to the base metal while retaining good ductility. The intermetallic was also found to have good wettability under solder reflow conditions. We conclude from these tests that the Pd-Ag-Cu-Au-Pt-Zn alloy is a suitable option as a pin material for glass-to-metal sealing applications.

Interactions of Simulated Waste Radionuclides and Rocks

In order to predict the long term sorptive properties of common rock minerals in the vicinity of a radioactive waste repository, it is necessary to understand the mechanism of sorption as well as to know which are the active sorptive minerals. This paper describes the results of an electron microprobe study designed to further understanding of these processes and materials. Ion exchange is usually assumed to be the most important mechanism of sorption; therefore, radionuclides are assumed to be associated with minor clay constituents. However Jenne (1) has questioned the role of ion exchange in many geologic sorption processes. Wet chemical studies do not easily lend themselves to the discovery of the active sorptive minerals without the destruction of the rock and the possible altering of the sorption properties. This study is nondestructive and has sought correlations between concentrations of test ions on the surface of the rocks and the associated mineralogy in elemental distribution photomicrographs obtained with the automated electron microprobe. Although individual clay particles are usually smaller than the resolution of the electron microprobe, we have seen that active clays are frequently found in clusters or exist as detrital grains which lend themselves to examination.

Microstructural Characterization of Glass and Ceramic Simulated Waste Forms

Glass is currently the primary waste form candidate for immobilization of Hanford high level radioactive wastes from three generations of nuclear fuel reprocessing. Several chemically varied waste types must be immobilized, including sludges and highly concentrated liquids, and each may require a chemically different but optimum glass composition to fix the appropriate set of radionuclides. Efforts are also underway to evaluate the application of ceramic forms as an alternative to glass for the fixation of Hanford defense waste. Results of laboratory scale studies for fixation of these wastes into glass (1) and ceramic (2) forms have been reported and the studies are continuing.

Microstructural Characterization of Solidified Simulated Reactor Wasteforms

At Hanford the long-term waste management program is considering both glass and ceramics as material with which to immobilize defense waste . (1,2) Hanford defense waste spans three generations of nuclear fuel reprocessing plants. These wastes are chemically quite varied. Currently, glass is the leading candidate for the immobilization of these wastes. Conversion to ceramic materials is the main alternative. In order to ensure good products, thorough microstructural analyses are deemed necessary. Until recently such analyses have not been done and the emphasis has been to characterize the simulated products by studying leach rates.

Interaction of a glass-based nuclear waste simulant and natural rock

An experiment was conducted to determine the interaction between a glass containing simulated radioactive waste from a nuclear reactor and natural rock. (1) This experiment was part of a study to examine the feasibility of disposing of high level radioactive wastes in solid rock bore holes in which radioactive heat would generate a molten zone at depth. As the molten zone cooled by dilution and natural aging of the radioisotopes, it would solidify to form a silicate mass which would hopefully retain the waste elements for a long period of time relative to their half-lives.