James E. Krzanowski

Comprehensive Approach toward Understanding Element Speciation and Leaching Behavior in Municipal Solid Waste Incineration Electrostatic Precipitator Ash

A comprehensive approach was used to characterize speciation and leaching behavior of major, minor, and trace elements in electrostatic precipitator (ESP) ash from a Canadian MSW incinerator. Neutron activation analysis (NAA), X-ray powder diffraction (XRPD), scanning electron microscopy/X-ray microanalysis (SEM/XRM), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS) were used to quantify elements, describe particles and phase associations, identify bulk and surface mineral phases, and identify the speciation of elements. SEM/XRM showed a complex polycrystalline material covering aluminosilicate spheres. XPS, as a surface technique, provided information on speciation at the particle surface where leaching first occurs. SIMS showed molecular fragments indicative of speciation and enrichment of volatile species (K, Zn, Cl, S, Pb) in the fine polycrystalline material. Many of these phases readily dissolve during leaching. Dissolution behavior and pH-dependent leaching could be modeled with the geochemical thermodynamic equilibrium model MINTEQA2. The abilityto model leaching behavior provides an opportunity to examine possible disposal or treatment behavior.

Heavy metal stabilization in municipal solid waste combustion bottom ash using soluble phosphate

Abstract Heavy metal chemical stabilization with soluble PO 4 3− was assessed for bottom ash from combustion of municipal solid waste. Bottom ash can contain heavy metals (e.g. Pb) that can leach. An experimental dose of 0.38 mols of soluble PO 4 3− per kg of residue was used without optimizing the formulation for any one heavy metal. The reduction in the fraction available for leaching according to the total availability leaching test was 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn. pH-dependent leaching (pH 4, 6, 8) showed that the treatment was able to reduce equilibrium concentrations by 0.5 to 3 log units for these heavy metals. Bulk and surface spectroscopies showed that both crystalline and amorphous precipitates were present as insoluble metal phosphate reaction products. Dominant reaction products were calcium phosphates, tertiary metal phosphates, and apatite family minerals. Observed phases included, β-Ca 3 (PO 4 ) 2 (tertiary calcium phosphate); Ca 5 (PO 4 ) 3 OH (calcium hydroxyapatite); Pb 5 (PO 4 ) 3 Cl (lead chloropyromorphite); and Pb 5 (PO 4 ) 3 OH (lead hydroxypyromorphite). These are considered to be very geochemically stable mineral phases. The geochemical thermodynamic equilibrium model MINTEQA2 was modified to include both extensive phosphate minerals and simple ideal solid solutions in order to better model pH-dependent leaching. Both end members [e.g. Pb 5 (PO 4 ) 3 Cl, β-Ca 3 (PO 4 ) 2 ] and ideal solid solutions [e.g. (Pb 2 ,Ca)(PO 4 ) 2 ] were observed as controlling solids for Ca 2+ , Zn 2+ , Pb 2+ , and Cu 2+ . Controlling solids were not identified for Cd 2+ because pH dependent concentrations were generally below detection limits. The divalent metal cations in bottom ash were effectively stabilized by treatment with soluble PO 4 3− .

Microstructure and vacuum tribology of TiC-Ag composite coatings deposited by magnetron sputtering-pulsed laser deposition

Abstract Composite titanium carbide–silver films have been co-deposited by magnetron sputtering-pulsed laser deposition (MSPLD) to study their friction and wear properties in vacuum. The films deposited were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The silver content in the films ranged from 6 to 46 at.%. Structural characterization of the films revealed that Ag had a nano-crystalline structure when dispersed in the film, but larger crystallites of Ag (∼50–200 nm) also formed on the surface. Films with higher Ag contents showed evidence of higher diffusion rates, leading to a coarser structure and greater surface coverage. Pin-on-disk friction tests were performed under vacuum to observe the friction and wear behavior of these films. Friction was lower with higher Ag content, but wear was higher; the optimal Ag concentration was found to be 15%. SEM images from the surface of the films and wear tracks were obtained to understand the morphology of this type of composite ceramic coating, and revealed Ag layers in the wear track elongated in the direction of wear. Based on these results, the significance of silver as a friction-reducing agent in vacuum environments was demonstrated.

Deformation and bonding processes in aluminum ultrasonic wire wedge bonding

The ultrasonic wire bonding (UWB) process has been examined using transmission electron microscopy (TEM) and standard wire pull testing techniques. Al-0.5 wt.% Mg wires 75 μm in diameter were bonded to pure and alloyed Al substrates. The bonding parameters, surface roughness, and surface contamination levels were variables in the experiments. Cross-section TEM specimens were made from these samples. TEM analysis was conducted on the wire, wire/substrate interface and substrate. Pull tests showed that for the Al substrates the surface roughness or the presence of contamination did not effect the bond strength, whereas for contaminated stainless steel substrates, a three μm surface finish resulted in the highest bond pull strength. The TEM observations revealed features such as low-angle grain boundaries, dislocation loops and the absence of a high dislocation density, indicating that the wire and substrate were dynamically annealed during bonding. Based on the width of a zone near a grain boundary in the wire which was depleted of dislocation loops, it was estimated that local heating equivalent to a temperature of 250° C for 90 msec was achieved in the wire during bonding. No evidence was found for melting along the bond interface, indicating that UWB is a solid-state process. Based on the TEM observationsof the bond interface and the pull tests, it is concluded that the ultrasonic vibrations clean the surfaces to be joined to the extent that a good bond can be obtained by intimate metal-metal contact in the clean areas.

Structural and mechanical properties of TiC and Ti-Si-C films deposited by pulsed laser deposition

TiC and Ti–Si–C films have been deposited by pulsed laser deposition at substrate temperatures ranging from room temperature to 600 °C onto (111) silicon wafers and 440C stainless steel substrates. X-ray diffraction, x-ray photoelectron spectroscopy, and electron microscopy were employed for structural and compositional evaluation of the films, and nano-indentation hardness testing and pin-on-disk wear tests were used to evaluate the mechanical and tribological properties. All the TiC films were highly crystalline except the one deposited at room temperature, whereas for the Ti–Si–C films the degree of crystallinity increased with temperature, ranging from amorphous for the room temperature deposit to about 50% crystalline at 600 °C. The hardness of the TiC films was relatively constant with deposition temperature at about 25 GPa, whereas the hardness of the Ti–Si–C films increased with deposition temperature from 11 to 33 GPa. The temperature dependence of the hardness is attributed to the degree of crys...

Structure and mechanical properties of Ti–Si–C coatings deposited by magnetron sputtering

Nanostructured coatings consisting of mixed carbide phases can provide a potential means to developing superhard coatings. Heterogeneous nanostructured coatings can be obtained by either deposition of multilayer structures or by depositing film compositions that undergo a natural phase separation due to thermodynamic immiscibility. In the present work, we have taken the latter approach, and deposited films by radio frequency cosputtering from dual carbide targets. We have examined a number of ternary carbide systems, and here we report the results obtained on Ti–Si–C films with a nominal (Ti1−xSix)C stoichiometry and with x⩽0.31. It was found that the nanoindentation hardness increased with Si content, and the maximum hardness achieved was nearly twice that of sputter-deposited TiC. We further analyzed these films using high-resolution transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction. Since cubic SiC has an x-ray pattern almost identical to that of TiC, the extent of phase separation could not be determined by that method. However, XRD did demonstrate a general disordering of the films with increasing SiC content. In addition, a mottled structure was observed in high-resolution TEM images of the Si-containing films, confirming microstructural effects due to the Si additions.Nanostructured coatings consisting of mixed carbide phases can provide a potential means to developing superhard coatings. Heterogeneous nanostructured coatings can be obtained by either deposition of multilayer structures or by depositing film compositions that undergo a natural phase separation due to thermodynamic immiscibility. In the present work, we have taken the latter approach, and deposited films by radio frequency cosputtering from dual carbide targets. We have examined a number of ternary carbide systems, and here we report the results obtained on Ti–Si–C films with a nominal (Ti1−xSix)C stoichiometry and with x⩽0.31. It was found that the nanoindentation hardness increased with Si content, and the maximum hardness achieved was nearly twice that of sputter-deposited TiC. We further analyzed these films using high-resolution transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction. Since cubic SiC has an x-ray pattern almost identical to that of TiC,...

Magnetron sputter deposition of WC-Ag and TiC-Ag coatings and their frictional properties in vacuum environments

Abstract Thin films of WC–Ag and TiC–Ag were deposited by magnetron sputtering for the purpose of analyzing their tribological properties in vacuum. X-ray diffraction was used to determine structural properties, and energy dispersive X-ray analysis was used to determine the relative atomic content of silver in the films. Pin on disk friction tests were performed to obtain the coefficient of friction in vacuum. The deposited films showed a structure containing separate carbide/silver phases, as was desired for providing both high wear resistance and low friction. The tribological test results show a significant decrease in the friction coefficient for both TiC–Ag and WC–Ag, to a minimum value of 0.2, with increasing silver content.

Composite coatings incorporating solid lubricant phases

The concept of incorporating a solid lubricant, silver (Ag), within a hard carbide film for vacuum tribology applications is investigated in this paper. SiC/Ag and HfC/Ag films were deposited by magnetron cosputtering at 200 °C onto Si and 440C steel substrates. The composition, phase structure, and morphology in these films was examined using x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The microstructural analysis showed that Ag was incorporated both within and on the surface of the films. There was a strong tendency for Ag to segregate to the film surface. Vacuum tribology tests were conducted using a ball-on-disk test in a vacuum of 1.33 µPa with a 1 N load for 10 000 cycles. For both the SiC/Ag and HfC/Ag films, the average friction coefficients were reduced when sufficient Ag was present. These tests show that carbide-Ag composite films hold promise for vacuum tribology applications.

Nanostructure and mechanical properties of WC-SiC thin films

The mechanical properties of WC-SiC thin films deposited by dual radio frequency magnetron sputtering were investigated. The films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), and transmission electron microscopy (TEM) to evaluate the details of the microstructure and degree of amorphization. The results indicate that small additions of SiC (<25%) can significantly increase hardness compared to a pure WC film, but higher SiC contents do not strongly affect hardness. XRD studies show the SiC had a disordering effect. TEM results showed that WC films had coarse porous structure, but films with a low silicon carbide content (approximately 10 to 25 at%) had a denser nanocrystalline structure. Samples with greater than 25% SiC were amorphous. The initial hardness increase at lower SiC contents correlated well with the observed densification, but the transition to an amorphous structure did not strongly affect hardness.

Structural and mechanical properties of TiC/Ti and TiC/B4C multilayers deposited by pulsed laser deposition

Multilayers of TiC/Ti and TiC/B 4 C have been deposited by pulsed laser deposition. Ti, B 4 C, and TiC targets were used to deposit multilayer films onto 440C steel and silicon substrates at 40 °C. The structural, compositional, and mechanical properties of the multilayers were examined by x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, and nanoindentation techniques. Tribological properties were also evaluated using a pin-on-disc friction and wear test. The TiC/Ti films were found to have a crystalline structure, and both (200)TiC/(100)Ti and (111)TiC/(101)Ti orientation relationships were found in these films. In the TiC/B 4 C films, only the sample with the largest bilayer thickness (25 nm) had significant crystallinity and only the TiC layer was crystalline. X-ray photoelectron spectroscopy depth profiles confirmed the presence of composition modulations in these films. Nanoindentation tests of the TiC/Ti multilayers showed hardness levels exceeding that predicted by the rule-of-mixtures. The TiC/B 4 C multilayers showed increasing hardness with decreasing bilayer thickness but reached only 22 GPa. The pin-on-disc tests gave friction values ranging from 0.3 to 0.9 for both sets of films. These results were correlated with the degree of crystallinity and grain structure of the films.