Morphological Growth of Sputtered MoS2 Films

Sputtered MoS₂ films from 300 Å to 20,000 Å thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment, and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. The type of surface finish (topography) as related to scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film, and various complex surface overgrowths on the film. These nodular growth features have progressively more undesirable effects on the film behavior as the film thickness increases.     

Frictional and morphological properties of AuMoS2 films sputtered from a compact target

AuMoS₂ films 0.02–1.2 μm thick were sputtered from a target compacted from 5 wt.% Au plus 95 wt.% MoS₂ to investigate the frictional and morphological film growth characteristics. The gold dispersion effects in MoS₂ films are of interest to increase the densification and strengthening of the film structure. Three microstructural growth stages were identified on the nano-micro-macrostructural level. During sliding both sputtered AuMoS₂ and sputtered MoS₂ films have a tendency to break within the columnar region. The remaining or effective film, about 0.2 μm thick, performs the lubrication. The AuMoS₂ films displayed a lower friction coefficient with a high degree of frictional stability and less wear debris generation compared with pure MoS₂ films. The more favorable frictional characteristics of the AuMoS₂ films are attributed to the effective film thickness and the high density packed columnar zone which has a reduced effect on the fragmentation of the tapered crystallites during fracture.     

Morphological and frictional behavior of sputtered MoS2 films

From the texture and growth patterns of sputtered MoS₂ films deposited onto substrates, three regions can be distinguised: (1) a ridge formation region, (2) an equiaxed transition zone and (3) a columnar-fiber-like structure. The lubricating properties of sputtered MoS₂ films can be visually identified with respect to optical changes before and after rubbing. The orientation of the surface microcrystallites is identified, and the change in optical properties is explained. In sliding contact the sputtered film tends to break up at the base of the columnar region. Effective lubrication occurs with the film remaining on the substrate. This film is 0.18–0.22 microm thick.     

Impact of electronic waste disposal on lead concentrations in landfill leachate

Lead is the element most likely to cause discarded electronic devices to be characterized as hazardous waste. To examine the fate of lead from discarded electronics in landfills, five columns were filled with synthetic municipal solid waste (MSW). A mix of electronic devices was added to three columns (6% by weight), while two columns served as controls. A sixth column contained waste excavated from an existing MSW landfill. Leachate quality was monitored for 440 days. In columns with the synthetic waste, leachate pH indicated that the simulated landfill environment was characteristic of the acid phase of waste decomposition; lead leachability should be greater in the acid phase of landfill degradation as compared to the methanogenic phase. Lead concentrations ranged from 7 to 66 microg/L in the columns containing electronic waste and ranged from < 2 to 54 microg/L in the control columns. Although the mean lead concentrations in the columns containing electronic devices were greater than those in the controls, the difference was not found to be statistically significant when comparing the data sets over the entire monitoring period. Lead results from the excavated waste column suggest that lead concentrations in all columns will decrease as the pH increases toward more neutral methanogenic conditions.     

Microstructural and wear properties of sputtered carbides and silicides

Sputtered Cr₃C₂, Cr₃Si₂ and MoSi₂ wear-resistant films (0.05–3.5 μm thick) were deposited on metal and glass surfaces. Electron transmission, electron diffraction and scanning electron microscopy were used to determine the microstructural appearance. Strong adherence was obtained with these sputtered films. Internal stresses and defect crystallographic growth structures of various configurations within the film have progressively more undesirable effects for film thicknesses greater than 1.5 μm. Sliding contact and rolling element bearing tests were performed with these sputtered films. Bearings sputtered with a duplex coating (a 0.1 μm thick undercoating of Cr₃Si₂ and subsequently a 0.6 μm coating of MoS₂) produced marked improvement (more than 10.5 × 10⁷ cycles) over straight MoS₂ films.     

Comparison of Metals Leaching from CCA- and ACQ-Treated Wood in Simulated Construction and Demolition Debris Landfills

Pressure-treated wood is often disposed of in landfills in the United States, very frequently in construction and demolition (C&D) debris landfills. C&D debris landfills in many states are not equipped with liner systems to protect groundwater. With the voluntary withdrawal of chromated copper arsenate (CCA) treated wood for most residential applications in January 2004, copper-based wood preservatives, including alkaline copper quaternary (ACQ), are more widely used. To evaluate the impact of metal losses from ACQ-treated wood disposed in C&D debris landfills and compare to those of CCA-treated wood under similar conditions, leachates from three simulated C&D debris landfills (lysimeters) were collected and analyzed for over a period of one year. The wood component in one lysimeter (the control lysimeter) contained pallet wood; the second lysimeter contained CCA-treated wood, and the third contained ACQ-treated wood. Each lysimeter was buried in an active landfill for temperature control. Several batch leaching tests [including the standardized toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP)] were also conducted for comparison purposes. Although the two lysimeters containing treated wood had elevated copper concentrations within the waste matrix, the concentration in the leachate samples from these lysimeters was below detection for Cu (<4?μg/L) throughout the duration of the experiment, likely a result of precipitation as copper sulfide mineral in the reducing conditions of the simulated C&D landfills. As expected, the lysimeter containing CCA-treated wood showed elevated concentrations of arsenic and chromium, with maximum concentrations of 1.16 mg/L and 0.2 mg/L respectively. Greater amounts of boron (B) leached from ACQ-treated wood than CCA-treated wood or pallet wood debris. The results suggest that copper leaching will not be a major concern upon the disposal of ACQ-treated wood in C&D debris landfills. Arsenic leaching from CCA-treated wood remains a concern for unlined C&D debris landfills.     

Coatings for wear and lubrication

In this paper we review the recent advances in the tribological uses of r.f.-sputtered and ion-plated films of solid film lubricants (laminar solids, soft metals, organic polymers) and wear-resistant refractory compounds (carbides, nitrides, silicides). The sputtering and ion-plating potentials and the corresponding coatings formed are evaluated relative to the friction coefficient, wear endurance life and mechanical properties. The tribological and mechanical properties of each kind of film are discussed in terms of film adherence, coherence, density, grain si morphology, internal stresses and thickness and substrate conditions such as temperature, topography, chemistry and d.c. biasing. The ion-plated metallic films in addition to improved tribological properties also have better mechanical properties such as tensile strength and fatigue life.     

The X-ray photoelectron spectroscopy depth profiling and tribological characterization of ion- plated gold on various metals

An investigation was conducted to examine, by X-ray photoelectron spectroscopy analysis and depth profiling, the atomic nature of such tribological properties as friction and microhardness of ion-plated gold. Friction properties were measured with (1) a gold film, (2) the graded interface between gold and nickel substrate and (3) the nickel substrate. All sliding was conducted against hard silicon carbide pins in two processes. The first is the adhesive process in which friction arises primarily from adhesion between sliding surfaces, and the second is a non-adhesive process, namely abrasion, in which friction occurs as a result of the hard pin sliding against the film, indenting into it and plowing a series of grooves. The other substrates used in this study included copper and 440C stainless steel. Reference experiments were also conducted with vapor-deposited gold on the substrates. A vacuum environment is used in order to maximize the adhesion effect, while oil is used to minimize the adhesion effect. The results of the investigation indicate that the friction related to adhesion as well as the friction related to abrasion are influenced by the coating depth. The trends in friction behavior as a function of film depth are, however, just the opposite. The graded interface exhibited the highest adhesion and friction, while the graded interface resulted in the lowest abrasion and friction. The coefficient of friction due to abrasion is inversely related to the hardness. The greter the hardness of the surface, the lower are the abrasion and friction. The microhardness in the graded interface exhibited the highest hardness due to an alloy hardening effect. Almost no graded interface between the vapor- deposited gold film and the substrates was detected.     

Lubrication with Sputtered MoS2 Films

Sputtered MoS₂films (2000–6500 Å) were deposited on highly polished metal surfaces. These films have a low coefficient of friction (0.03–0.04) at speeds of 40–80 rpm and loads of 250–1000 grams. At loads of 250 grams the wear lives are over 0.5 million cycles, but at 1000 gram loads, it decreases to 38,000 cycles. Friction experiments and tensile tests have indicated that sputtered films have a strong adherence to metal surfaces. Electron transmission, diffraction and scanning electron microscopy show that these films have an extremely small particle size, less than 30 Å in diameter, and are very dense and free from observable pinholes. The high kinetic energy of these sputtered species, the submicroscopic particle size and the sputter-etched substrate surface is responsible for strong adhesion and cohesion of the sputtered film.