Paper contact resistance

Gardner, K A. and T. C. Carnavas, Thermal-Contact Resistance to Pinned Tubing, Trans, of ASMEJour, of Heat Transfer, Paper No. 59-A-135. 

In contrast with this, Liu, Ko, and Liao [13] and Liu et al. [14] reported the fabrication of CFPs that were carbonized at temperatures between 1,300 and 1,400°C. Carbon black particles or graphite powder can also be added to the resin-based solution that is impregnated in the paper in order to improve the electrical conductivity (and decrease contact resistance) of the CFP. By adding these particles, it is not necessary to perform the final carbonization or graphitization step in order to achieve high conductivity in the paper [9,13]. 

Until recently, the issue of contact resistance was hardly mentioned in papers dealing with OTFTs because the performance of the devices was so low that the current flowing between source and drain was only limited by the resistance of the channel. With improvement of the charge-carrier mobility, this is no longer true limitations by contact resistance are becoming increasingly crucial, and finding ways to reduce these limitations has become a key issue. 

This paper describes some recently completed work on the electrical conductivity of paper. A reliable method of measuring bulk conductivity of paper, where the contact resistance is reduced to negligible values, has been developed. A study of the effect of some papermaking variables, such as the type of pulp, the degree of refining and the fiber orientation, on the bulk conductivity of paper is reported. Finally, an investigation has been made into the current transient phenomena exhibited by paper upon the application of an electric field. These transient currents were interpreted as the transport of ionic species within a water associated fibrous network making up the paper. 

Bulk electrical conductivity has always been controversial for paper since the contact resistance at the paper-electrode interface can be much higher than the resistance of the paper itself. This neglect of contact resistance has produced many erroneous reports of bulk conductivity of paper. 

In the following section, a new bulk conductivity cell is described that significantly reduces the contact resistance to a level where the measurements of paper bulk conductivity can be made with an accuracy that is limited primarily by the anisotropic structure of the paper itself. A small uncertainty in the measured conductivity arises from compaction ( 10%) of the paper sample in the apparatus caused by the application of 13-8 MPa pressure to the stainless steel electrode system in the cell. This pressure is used to eliminate contact resistance. Despite this uncertainty, measurement errors in the new cell are significantly less than the spread in the conductivity values ( 200)t) determined at different points in a single paper sheet. The variability arises from inhomogeneities in the cellulose fiber network within the sheet. 

To measure the surface resistivity of paper, a variant of a four-point probe method proposed by Cronch 15 was used. This approach has proven to be reliable, avoiding the effects of contact resistance by employing an electrostatic voltmeter (utilizing contactless probes) to measure the surface potential of paper subject to a constant current. 

Two important requirements must be met by a technique designed to provide accurate measurements of the bulk conductivity of paper. First, the contact resistance between the electrode and the paper should be either known or negligible and, secondly, the paper should not be significantly modified by the technique used. The in situ pressure bulk conductivity cell satisfies these requirements, as will be shown in the following sections. 

In the study described above, strong evidence was shown that for the case of James River conductive base paper, a pressure of 13.8 Mfa applied to stainless steel electrodes was sufficient to effectively reduce contact resistance to negligibly small proportions. In the study described below the question as to whether the in situ pressure conductivity method would also be appropriate for different types of nonconductive papers which exhibit varied surface morphology is addressed. Consequently, paper samples were prepared, with basis weights of 60, 115, and 190 g/m2, all with a 1 1 ratio by weight of softwood-hardwood pulp, in a centrifugal dynamic vertical sheet former. Each of... 

From all these observations it is concluded that the contact resistance is not a function of the surface roughness when an applied pressure of 13-8 MPa is used. This indicates the possibility that the air gaps between the fibers and the electrode are contributing to the electrode surface area as a result of an electrical breakdown phenomenon. This hypothesis would lead to a very low contact resistance since almost all the electrode area would be effective whether the current is carried directly from the electrode to the paper fibers or through a conductive air gap. 

A study, similar to that described above, was made to compare the results of using optically polished stainless steel electrodes under pressure with Galium-Indium eutectic liquid electrodes in determining bulk conductivity of papers. The Ga-In alloy is believed to make intimate contact with the surface of the paper, thus significantly reducing the contact resistance. 

Figure 14. Resistance vs. thickness for a series of papers with different basis weight. The intercept of the minimum values gives the contact resistance and the slope is proportional to the resistivity of the paper. (Reproduced, with permission, from Ref. 16. Copyright 1981, American Institute of Physics.)...

This article has addressed a number of issues relating to the electrical properties of paper or fibrous structures. It was shown that reliable measurement methods are now available for estimating both the bulk and surface conductivities of paper. In the case of the bulk conductivity, a new in situ pressure conductivity cell was described which significantlyreduces contact resistance. The surface conductivity can be determined by the application of a modified four-point probe method first used on paper by Cronch<15). It was shown that the degree of refining has a small effect on the bulk conductivity of paper. 

The separator used was a Nation membrane. Each electrode was separated by a carbon paper disk (Toray TGP-H-090) from the Ti plate current tap to minimize contact resistance. The assembled cell was immersed into 1M H2S04(aq) to impregnate electrodes by electrolyte. 

F. 6.21 Dummy geometries used to establish the influence of horizontal and vertical contact resistances. Thick horizontal lines indicate the presence of horizontal graphite papers, while thick vertical lines indicate the presence of the vertical graphite papers. Reproduced with permission from [20] by Vanmeensel et al. Cop)right 2005, Elsevier... 

Uses Thermoplastic resin for inj. molding and extrusion applies. for extrusion coatings for plastics films, metal foils, and paper chem.-resist. powd. coatings automotive fuel/hydraulic hoses gears cams bearings raw material for pharmaceuticals absorbent, carrier in personal hygiene prods. vise, control agent, opacifier in cosmetics food pkg. in side seam cements for food-contact containers... 

The sensor arrays considered in this paper are fabricated using a piezoresistive material. Piezoresistive materials are materials which exhibit a change in its resistivity upon an application of a mechanical stress on its surface. This phenomenon is called piezoresistivity. It has been found that the contact resistance could be described by the following equation [10] ... 

This paper introduces the concept of determining the contact resistance of an intercell contact bar interface, and to use this information along with other parameters to develop the most efficient solution in the future. In future work the following additional aspects will be considered ... 

In (10) and (25)-(34) cam-follower experiments are described. In all test rigs the cam radius was of the order of 50 mm, while the cam width was of the order of 10 to 20 mm. Film thickness is estimated from global capacitance in (10), (25), (30) and (31), and from overall contact resistance in (26). Local film thickness measurements, employing the 0.25 mm dia. gauge described in (18), are reported in (29). The loads are rather low. This paper also shows pressure measurements obtained with a 0.25 mm effective dia. piezoelectric transducer. Local pressures and temperatures can also be obtained using miniature thin film transducers, see (27), (28), (32) and (33). These transducers have a minimum width of 10 pm. To find local cam surface temperatures, an infrared scanning system was employed in (34), with a spot size of 0.45 mm. 

In order to determine the effect of stress on contact resistance between sintered materials and carbon paper, the analysis of contact resistance was carried out with the following stress values 20N cm-, 40N cm-2, 60N cm-2, lOON cm-2,140N cm-2,160N cm-2. 

For the characterization of electrical surface properties the measurement of the interfacial contact resistance (ICR) between the surface of a plate or a material sample and a carbon paper representing the gas diffusion media in a fuel cell has been established (Wang, 2003 Nam, 2007 Han, 2009 Joseph, 2005). Since the ICR value is dependent on compaction force, this measurement is often carried out in a range of 0-30 kg cm regarding compaction force for fuel ceU mounting. 

Until today, this method has undergone shght change in setup and a diversification of measured and calculated resistances. Mostly, this measurement is conducted as illustrated in Figure 6.13b where one sample (equal properties on both surfaces assumed, here nitrided chromium on 316L stainless steel) is sandwiched between two carbon papers which are clamped between two gold-plated current collectors which are adjustable in compaction force. In order to calculate the contact resistance between carbon paper and coating, two different measurements have to be performed is the measurement of the... 

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