This paper overviews the relatively new surface engineering discipline of plasma electrolysis, the main derivative of this being plasma electrolytic deposition (PED), which includes techniques such as plasma electrolytic oxidation (PEO) and plasma electrolytic saturation (PES) processes such as plasma electrolytic nitriding/carburizing (PEN/PEC). In PED technology, spark or arc plasma micro-discharges in an aqueous solution are utilised to ionise gaseous media from the solution such that complex compounds are synthesised on the metal surface through the plasma chemical interactions. The physical and chemical fundamentals of plasma electrolysis are discussed here. The equipment and deposition procedures for coating production are described, and the effects of electrolyte composition and temperature on ignition voltage, discharge intensity and deposited layer thickness and composition are outlined. AC-pulse PEO treatment of aluminium in a suitable passivating electrolyte allows the formation of relatively thick (up to 500 μm) and hard (up to 23 GPa) surface layers with excellent adhesion to the substrate. A 10–20 μm thick surface compound layer (1200HV) and 200–300 μm inner diffusion layer with very good mechanical and corrosion-resistant properties can also be formed on steel substrates in only 3–5 min by use of the PEN/PEC saturation techniques. Details are given of the basic operational characteristics of the various techniques, and the physical, mechanical and tribological characteristics of coatings produced by plasma electrolytic treatments are presented.

Plasma electrolysis for surface engineering

Progress in preparation, processing and applications of polyaniline

Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.

Microstructural evolution during film growth

The gas-phase reaction between MoO3-x and H(2)S in a reducing atmosphere at elevated temperatures (800 degrees to 950 degrees C) has been used to synthesize large quantities of an almost pure nested inorganic fullerene (IF) phase of MoS(2). A uniform IF phase with a relatively narrow size distribution was obtained. The synthesis of IFs appears to require, in addition to careful control over the growth conditions, a specific turbulent flow regime. The x-ray spectra of the different samples show that, as the average size of the IF decreases, the van der Waals gap along the c axis increases, largely because of the strain involved in folding of the lamella. Large quantities of quite uniform nanotubes were obtained under modified preparation conditions.

http://science.sciencemag.org/content/sci/267/5195/222.full.pdf

High-Rate, Gas-Phase Growth of MoS2 Nested Inorganic Fullerenes and Nanotubes

Sol–gel coatings on metals for corrosion protection

The use of Raman scattering to study disorder in pulsed laser deposited MoS2 films

PbMoO4 is a potential solid lubricant for use at elevated temperatures in oxidizing environments. Pulsed laser deposition (PLD) was utilized to grow thin films of this material because it allows good control over film chemistry and crystallinity. Films were grown at different substrate temperatures in vacuum and in partial pressures of oxygen. The chemistry and crystallinity of the films were evaluated using X-ray photoelectron spectroscopy, Raman spectroscopy, and glancing angle X-ray diffraction. Friction coefficients and wear lives were measured using a ball-on-flat tribometer at room temperature and 700‡C. Films deposited in vacuum, at room temperature and at 300‡C, were oxygen deficient. To adjust chemistry and crystallinity, films were grown in a partial pressure of oxygen (i.e. 6.7×10−1 Pa). Stoichiometric, crystalline films of PbMoO4 were produced when films were grown at 300‡C in this environment. PbMoO4 films were lubricious (Μ = 0.35) and long lived at 700‡C, but at room temperature had high friction and failed quickly. The properties of the films grown at the different conditions are discussed.

Synthesis and characterization of a high-temperature oxide lubricant

Pulsed laser deposition was used to produce hydrogen‐free amorphous diamondlike carbon (a‐C) and hydrogenated amorphous diamondlike carbon (a‐C:H) from graphite and polycarbonate targets, respectively. Films were grown under identical conditions in high vacuum at low temperatures onto steel and Si substrates. The a‐C films were uniform, while a‐C:H films contained a great number of particles ejected from the target surface. The a‐C films have hydrogen contamination about 0.1 at. %, while a‐C:H have about 25 at. % H and 10 at. % O. High percentages of sp3 bonding were found in both films. Film densities were estimated to be 3.0 g cm−3 for a‐C films and 2.2 g cm−3 for a‐C:H films. Chemical and structural characteristics of the films were correlated with their thermal stability and mechanical properties. Temperatures for starting graphitization were about 500 °C for a‐C and 350 °C for a‐C:H. The presence of hydrogen reduced film hardness from 60 GPa for a‐C films to 14 GPa for a‐C:H films. Hydrogen was also ...

Structure and properties of diamondlike carbon films produced by pulsed laser deposition

Self-assembled NAnophase Particle (SNAP) surface treatments for corrosion protection of AA2024-T3

Two types of conducting polymer composites comprising polypyrrole (PPy) (filler) dispersed in a polyimide (PI) (matrix) and bilayered conducting polymer/PI composites, were successfully formulated Electrochemical deposition of the PPy/PI composite was accomplished by initially depositing PPy onto the working electrode, and then casting a layer of PI onto the modified electrode The PPy/PI composite was also formulated by first casting a PI film onto the bare electrode followed by electrochemical deposition of PPy Poly(N-ethylaniline)/PI composites were prepared by initially depositing a thin layer of poly(N-ethylaniline) onto the substrate (AA 2024-T3) and then casting a layer of PI resin onto the modified substrate The composite coatings were characterised by advanced analytical techniques, such as reflection absorption infrared spectroscopy (RAIR), SEM, dc polarisation studies and electrochemical impedance spectroscopy SE/S275

M.S. Donley

Papers

The use of Raman scattering to study disorder in pulsed laser deposited MoS2 films

Synthesis and characterization of a high-temperature oxide lubricant

Structure and properties of diamondlike carbon films produced by pulsed laser deposition

Self-assembled NAnophase Particle (SNAP) surface treatments for corrosion protection of AA2024-T3

Electrochemical Behaviour of Conducting Polymer/Polyimide Composite