Infrared absorption in thick film resistors

Infrared absorption in polymer and glass-based thick film resistors has been measured between 400 and 1500 cm^–1. Sample structures are discussed on the basis of X-ray, Fourier transform-infrared and resistance-temperature data. It is shown that in polymer-based thick film resistors, the particulate phase is mostly responsible for the infrared absorption between 400 and 900 cm^–1, whereas the infrared absorption at higher wave numbers is related to the continuous phase. In glass-based thick film resistors, absorption is mostly determined by the highly doped glass. The results indicate that thick film resistors can be used as an absorbent coating in the 400–1500 cm^–1 region by suitable selection of the continuous and particulate phases.     

Friction and wear studies of bulk polyetherimide

Polyetherimide, ULTEM 1000, was studied as a neat resin for investigating its friction and wear behaviour while sliding against mild steel, under unlubricated conditions on a pin on disc machine. Experimental parameters selected were different loads, sliding distances and counterface roughness. It was observed that unlike other semicrystalline highly linear thermoplastics and some thermoplastic thermosetting polyimides, this polyimide does not transfer a film on the counterface under the conditions of the study. It seems that it wears mainly by fatigue mechanism but crack propagation could not be observed in SEM micrographs of pin surfaces. The frictional coefficient was low as compared with other polyimides and varied with contact pressure from 0.4 to 0.22, although the initial value was high. The cycles required to initiate wear particles were around 90 kcycles at 13 N cm^–2 contact pressure. Once the wear started, the specific wear rate was high (K ₀=10^–13m³N^–1 m^–1).     

Wear behavior of carbide coated Co–Cr–Mo implant alloy

The wear behavior of a new type of metal carbide surface coating on Co–Cr–Mo implant alloy was studied. The coating was created using a microwave plasma-assisted reaction. Codeposition of impurity diamond film, diamond particles, and soot was prevented by controlling process conditions. Wear tests were carried out using a sapphire ball-on-Co–Cr–Mo disc unidirectional sliding configuration with harsh conditions of high contact stress and slow sliding speed in both no-lubrication, and deionized water lubrication environments. In the case of uncoated Co–Cr–Mo discs, the effect of deionized water lubrication was remarkable and reduced the wear factor by one order of magnitude compared to the no-lubrication tests. The wear factor of carbide coated Co–Cr–Mo discs was slightly smaller than that of uncoated Co–Cr–Mo discs with deionized water lubrication (2.7×10^–6 mm³N^–1m^–1 vs. 4.2×10^–6mm³N^–;1m^–1). The addition of deionized water lubrication did not greatly affect the wear factor of carbide coated Co–Cr–Mo discs. The influence of surface geometry resulting from the brain coral-like surface morphology of carbide layers on wear behavior was analyzed considering stress concentrations and effective contact area.     

Effect of sliding speed on friction and wear of uni-directional aramid fibre-phenolic resin composite

A previous study on the tribological performance of a compression-moulded aramid fibre-phenolic resin composite, containing 30% continuous fibre, showed that this composite provides a reasonable combination of the friction coefficient and wear rate to be used as a friction component, such as a brake shoe. In the present work, the effect of sliding speed on the friction and wear behaviour of this composite has been investigated. The sliding experiments were conducted in a speed range of 0.1–6 m s^–1 at two normal pressure levels of 1.0 and 4.9 MPa. The coefficient of friction was found to be stable over a wide range of sliding speeds and normal pressures. The wear of the composite was found to be insensitive to changes in the speed in the higher speed range. The results have been supplemented with scanning electron micrographs to help understand possible friction and wear mechanisms.     

A novel route for the synthesis of processable conducting poly(m-aminophenol)

Polymerization of m-aminophenol (mAP) in aqueous NaOH solution was done chemically by using ammonium persulfate (APS) as an oxidative initiator. The product poly(m-aminophenol) (PmAP) was found to be highly soluble in aqueous sodium hydroxide, dimethyl sulfoxide (DMSO) and N,N-dimethyl formamide (DMF). From the intrinsic viscosity measurement, the optimum condition for the polymerization was established with 0.6 M NaOH medium with the ratio of monomer to oxidant as 1:1.5 (mol:mol). The polymer was characterized by FTIR and ¹H NMR spectroscopy, elemental (CHNS) and thermogravimetric (TGA) analyses. From the spectroscopic analysis the structure of the polymer was found to resemble that of hydroxy polyaniline as the polymer contains free –OH groups attached to o/m position in the phenyl ring. The elemental analysis of the polymer also confirmed the same. From TGA study, the polymer was found to be thermally stable. A freestanding film of poly(m-aminophenol) was cast in DMSO solution followed by solvent removal and drying of the film at 100 °C for 7–8 h in an oven. A dc conductivity of 4.8 × 10⁻⁴ S cm⁻¹ was obtained for the synthesized polymer film after doping with H₂SO₄ solution.     

Friction and wear properties of monolithic silicon-based ceramics

Friction and wear properties of two forms of silicon nitride (reaction bonded and hot pressed) and two of silicon carbide (reaction sintered and sintered) are reported. The materials were slid against themselves under unlubricated conditions. Tests were run using a simulated inertial sample dynamometer. Sliding speeds ranged from 0.5 to 5.5 m sec^–1 with applied loads of 225 or 450 N. Friction coefficients were found to be in the range of 0.15 to 0.8 for both types of material. Friction response was qualitatively correlated with changes in surface chemistry at the sliding interface. Wear rates were of the order of 10^–14 to 10^–13m³ (Nm)^–1, in order-of-magnitude agreement with previous pin-on-disc results reported in the literature. Wear surfaces exhibit plastic deformation, ploughing, and oxide film formation and removal.     

Formation of UHMWPE polymeric transfer films on sliding glass counterfaces: early and steady-state wear studied by transmission electron microscopy

At a temperature of 30°C polymeric transfer films were generated on glass counterfaces during small-amplitude oscillatory sliding contact with an ultra-high molecular weight polyethylene (UHMWPE) pin under a constant load of 6.5 MPa. Early discontinuous and continuous (steady-state) transfer films were studied with vertical platinum-carbon replication and transmission electron microscopy (TEM). Nanometre-scale UHMWPE deposits in these transfer films have been visualized for the first time. Nanometre-scale particles averaging 20.6 ±6.3nm (5–40nm) were deposited on glass in the early stages of UHMWPE film transfer. After formation of a continuous transfer film, UHMWPE particles of slightly smaller dimensions, 13.5±6.1 nm (2–41 nm), were deposited on the transfer film surface. In addition, micrometre-scale particles (0.1–6.4 m) were found at the ends of the wear track. At high magnification, a fraction of the UHMWPE polymer chains observed in particle surfaces and in the transfer film surface nearby were not oriented in the sliding direction. Some crystal- or plate-like particles of UHMWPE were seen in the transfer film. Plate-like and micrometre-scale spherulitic inclusions were also identified on the mostly amorphous UHMWPE pin surface fractured at liquid nitrogen temperatures. The high frequency of nanometre-scale UHMWPE particles in contrast to the less numerous micrometre-scale deposits near the ends of the wear track suggests that the nanometre-scale deposits contribute significantly to transfer film formation and to the wear characteristics of UHMWPE.To whom correspondence should be addressed.     

Enhancement of the ionic conductivity of poly(ethylene oxide) electrolyte film by polyaniline addition

To improve the electrical conductivity of LiClO₄–poly(ethylene oxide) (PEO) complex, nonconductive polyaniline (NPANI) was employed as an additive. The electrical conductivity of the PEO–LiClO₄–NPANI electrolyte was at least ten times that of the original PEO–LiClO₄ electrolyte. The amine and/or imine nitrogen atoms in the NPANI polymer chain as well as the oxygen atoms in the PEO poly-merchain attracted the Li⁺ ions, and ion-dipole interaction occurred. The interaction enhanced the mobility of the ClO₄ ^– ions. The positively charged nitrogens were electronically stabilized in the entire polymer chain because NPANI had conjugated electrons. The mechanism is unique and different from those of other polymer additives. It is the very first example in which NPANI was employed as the additive for the PEO solid electrolyte and in which NPANI was found to be an effective additive. In addition, the NPANI addition hardly affected the physical properties of the PEO matrix such as the glass transition temperature and the melting temperature.     

Grain size, grain boundary sliding, and grain boundary interaction effects on nanocrystalline behavior

A dislocation–density grain boundary (GB) interaction scheme, a GB misorientation dependent dislocation–density relation, and a grain boundary sliding (GBS) model are presented to account for the behavior of nanocrystalline aggregates with grain sizes ranging from 25 nm to 200 nm. These schemes are coupled to a dislocation–density multiple slip crystalline plasticity formulation and specialized finite element algorithms to predict the response of nanocrystalline aggregates. These schemes are based on slip system compatibility, local resolved shear stresses, and immobile and mobile dislocation–density evolution. A conservation law for dislocation–densities is used to balance dislocation–density absorption, transmission and emission from the GB. The relation between yield stresses and grain sizes is consistent with the Hall–Petch relation. The results also indicate that GB sliding and grain-size effects affect crack behavior by local dislocation–density and slip evolution at critical GBs. Furthermore, the predictions indicate that GBS increases with decreasing grain sizes, and results in lower normal stresses in critical locations. Hence, GBS may offset strength increases associated with decreases in grain size.     

Superplastic deformation of the Pb-Sn eutectic

Dynamic observations of grain-boundary sliding during superplastic flow of the Pb-Sn eutectic are reported. These observations confirm the postulate that the dominant deformation mode during superplastic flow is grain-boundary sliding with localized deformation necessary to maintain grain coherency. Extensive grain-boundary sliding is also observed when the strain-rate and/or grain size is outside the superplastic flow regime. Stress relaxation tests were also carried out on the Pb-Sn eutectic. These tests provide data on the activation energy (45±5 kJ mol^–1), grain-size dependence (d ^–3), and stress dependence of superplastic flow in this alloy. A threshold stress of 1.3×10⁶N m^–2 for the onset of superplastic deformation is also observed.     

Superplastic behaviour of YBa2Cu3O7−x /Ag superconductors

High-temperature deformation characteristics of YBa₂Cu₃O_7–x oxide (YBCO) and YBa₂Cu₃O_7–x /Ag composite (YBCO/Ag) in uniaxial compression have been investigated. A compression test was carried out at temperatures from 780–930°C at initial strain rates between 10^–6 and 10^–4 s^–1. YBCO/Ag composites with fine, dense and equiaxed grains were compressed over 120% with no indication of failure at higher temperatures, and the strain-rate sensitivity exponent, m, was found to be about 0.42–0.46 between 890 and 930°C. They are considered to be one indication of superplasticity. The activation energy for deformation was 500–580 KJ mol^–1. The specimens suffered grain growth slightly during the deformation at 930°C and the majority of growth might be a function of exposure time, temperature and silver content, but each grain maintained the equiaxed shape after extensive superplastic deformation. This is consistent with a grain-boundary sliding mechanism. The silver at grain boundaries acts to decrease the activation energy for deformation and promote the grain-boundary sliding.     

Fatigue crack propagation in polymeric materials

In order to gain a better understanding of matrix-controlled fatigue failure processes in non-metallic materials a series of fatigue tests were performed on several different polymer materials representing different classes of mechanical response. Fatigue crack propagation rates between 5×10^–6 in. cycle^–1 (127 nm cycle^–1) and 4×10^–4 in. cycle^–1 (10 300 nm cycle^–1) were measured in nylon, polycarbonate, ABS resin, low-density polyethylene and polymethyl methacrylate. A strong correlation was found between the fatigue crack propagation rate and the stress intensity factor range prevailing at the advancing crack tip. Whereas metals exhibit comparable fatigue growth rates for a given stress intensity range when normalised with respect to their static elastic modulus, the polymer materials exhibited a 1300-fold difference in crack growth rate for a given normalised stress intensity range. This observation dramatically illustrates the importance of understanding molecular motion and energy dissipation processes in polymer materials as related to their chemistry and architecture. The relative behaviour of the different polymer materials could be generally correlated with their reported damping characteristics.     

Preparation of cobalt oxide films by plasma-enhanced metalorganic chemical vapour deposition

Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O₂ flow rate of 7cm³ min^–1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min^–1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O₂ flow rate of 20–50 cm³ min^–1, high crystalline spinel-type Co₃O₄ films were formed at a substrate temperature of 150–400°C. The Co₃O₄ film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co₃O₄ films were 20–41 nm min^–1. Both Co₃O₄ films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co₃O₄ film and a hexagonal shape and 60 nm for (111)-oriented film, respectively.     

Properties and interaction of cement with polymer in the hardened cement pastes added absorbent polymer

Ordinary Portland cement mixed with various amounts of absorbent polymer in the form of sodium acrylate ((–CH–)_nCOONa) have been studied. As the content of absorbent polymer increased, heat evolution of samples decreased up to 1.15 wt % of absorbent polymer addition and conversely increased over 1.75 wt %. Flexural strength of cement paste with absorbent polymer was improved more than 20%. As the content of absorbent polymer increased, the porosity values decreased and mean pore diameter shifted to small pore diameter region. Flexural strength of ordinary Portland cement paste had a linear correlation with non-evaporable water content but, that of cement paste with absorbent polymer deviated from a linear correlation with non-evaporable water content. The chemical difference between cement pastes with and without absorbent polymer was found by the inductively coupled plasma-atomic emission spectroscopy and the infrared spectroscopy. For the infrared spectra of absorbent polymer, bands at 1416 and 1560 cm^{– 1} were assigned to C–O single bond and C=O double bond respectively, namely, unidentate complex. As the curing time increased, the absorption bands near 1416 cm^{– 1} shifted to longer wave number and the absorption bands near 1560 cm^{– 1} to shorter wave number and finally bidentate complex was formed. Absorbent polymer released sodium ions to pore solution under the basic condition of pH 12.5–13.5 and became polyacrylic acid. Then some of these polyacrylic acid were crosslinked with others by calcium ions leached from cement grains. Calcium ion was regarded as a central charge connecting the negative parts in carbon-oxygen polarization of absorbent polymer' functional groups.     

Dielectric relaxation of vegetable-based polyurethane

Vegetable-based polyurethane (PU) was prepared in the thin film form by spin coating. This polymer is synthesised from castor oil, which can be extracted from the seeds of a native plant in Brazil called mamona. This polymer is biocompatible and is being used as material for artificial bone. The PU was characterised by dielectric spectroscopy in a wide range of frequency (10^–5 Hz to 10⁵ Hz) and by thermally stimulated discharge current (TSDC) measurements. The glass transition temperature (T _g = 39°C) was determined and using the initial rise method the activation energy was found to be 1.58 eV.     

Flow behavior in surface-modified microchannels with polymer nanosheets

The paper describes water flow behavior in surface-modified microchannels. We prepared straight-type microchannels which had rectangular cross sections with four different combinations of microchannel surface wettability; cleaned glass substrates served as hydrophilic microchannel walls and the microchannel walls coated with polymer Langmuir–Blodgett (LB) films were used as hydrophobic surfaces. The polymer LB films were successfully transferred onto glass substrates by vertical dipping method. The flow rates and the water meniscus shape strongly depended on the microchannel surface wettability. The decrease in flow rate with the increasing number of hydrophobic (polymer LB film) surface was attributed to the higher adhesion energy of hydrophobic surface. The Reynolds number was also characterized to be in the order of 10^− 1, implying a specific feature of microchannel; laminar flow.     

Sliding wear of self-mated Al2O3-SiC whiskerreinforced composites at 23–1200°C

Microstructural changes occurring during sliding wear of self-mated Al₂O₃-SiC whiskerreinforced composites were studied using optical, scanning electron microscopy and transmission electron microscopy. Pin-on-disc specimens were slid in air at 2.7 m s^–1 sliding velocity under a 26.5 N load for 1 h. Wear tests were conducted at 23, 600, 800 and 1200°C. Mild wear with a wear factor of 2.4 x 10^–7–1.5 x 10^–6 mm³ N^–1 m^–1 was experienced at all test temperatures. The composite showed evidence of wear by fatigue mechanisms at 800°C and below. Tribochemical reaction (SiC oxidation and reaction of SiO₂ and Al₂O₃) leads to intergranular failure at 1200°C. Distinct microstructural differences existing at each test temperature are reported.Resident Research Associate at NASA Lewis Research Center.     

Effect of electrization and small direct currents on the wear of metals in sliding friction

It was shown that the magnitude and direction of thermally induced electric currents depend on both the friction conditions (loads, sliding speeds) and the friction pair material, and that the character of the influence of electrization on wear is complex. It was established that currents of the order of 10^–6–10^–4 A may have a noticeable effect on wear of metals which is probably due to electro-transfer phenomena taking place in the metal surface layers during friction.     

Low temperature stress relaxation of nanocrystalline nickel

Stress relaxation in nanocrystalline nickel within the temperature range 523–673 K in a uniaxial compression regime is studied in the present investigation. The results obtained for coarser grained nickel are given for comparison. An average strain rate of nanocrystalline nickel within the investigated range of temperatures is 1.75 × 10^–5–3.03 × 10^–5s^–1. The presence of two types of stress relaxation dependencies are shown. The most likely strain mechanism is grain boundary sliding controlled by grain boundary diffusion for temperatures between 623 and 673 K.     

Effects of metal-ion implantation on wear properties of polypropylene

Polypropylene was implanted with 100 keV titanium and silver ions to fluences of 1, 10 and 50×10¹⁹ ions m^–2 using a vacuum arc metal-ion source. The implanted specimens were tested for sliding reciprocating wear properties using a nylon counterface, 1 N normal load, 3 mm stroke length and 10000 sliding cycles. The results of the wear tests showed that there was a dramatic improvement in wear properties for the 50×10¹⁹ ions m^–2 titanium-implanted specimen, to the point that no wear damage was visibly evident after 10000 cycles. A similar wear improvement was not obtained for the lower fluences for titanium implantation or for the silver-implanted specimens. The improvement in wear properties was related to the mechanisms of linear energy transfer from the incident ions to the polypropylene substrate, and consequent effects on cross-linking, which is responsible for changes in properties. The linear energy transfer was quantified using Monte Carlo calculations. In addition, friction coefficient values were also correlated with the wear test results. The significance of high fluences for wear improvements by ion implantation was demonstrated in this study. The investigation showed that metal-ion implantation can be effective in significantly improving wear properties of polymers with a judicious choice of ion type and ion fluence.