Structure electrical resistance

Experiments on N ion implantation in ZrN thin films were performed in order to investigate the process of N atom incorporation in this material and its influence on the structure, electrical resistivity, and superconductivity. Polycrystalline stoichiometric thin films of ZrN with thicknesses of about 250 nm deposited on single-crystal sapphire substrates by RF sputtering using Ar and Nj gas were used for the implantation samples. The partial pressure was 2 X 10 torr for Ar gas and in the range 1.7 to 8 X 10" torr for Nj gas, and the substrate temperature was maintained at 1000°C during the deposition. Samples had a well-developed polycrystalline structure and had values of the lattice parameter (Co) around 4.572 A, around 9.5 K, and residual resistivity (at UK) around 30 pQ cm. 

The electrical-resistance method involves passing an electric current through the structure and exploring the surface with voltage probes. Flaws, cracks, or inclusions will cause a disturbance in the voltage gradient on the surface. Railroads have used this method for many years to locate transverse cracks in rails. 

There are different concrete replacement systems available for renovating reinforced concrete structures. They range from sprayed concrete without polymer additions to systems containing conducting polymers (PCC-mortar). Since with the latter alkalinity is lower, more rapid carbonization occurs on weathering [59] and the increased electrical resistivity has to be taken into account, so that with cathodic protection only sprayed concrete should be used as a repair mortar. 

The cost and economics of cathodic protection depend on a variety of parameters so that general statements on costs are not really possible. In particular, the protection current requirement and the specific electrical resistance of the electrolyte in the surroundings of the object to be protected and the anodes can vary considerably and thus affect the costs. Usually electrochemical protection is particularly economical if the structure can be ensured a long service life, maintained in continuous operation, and if repair costs are very high. As a rough estimate, the installation costs of cathodic protection of uncoated metal structures are about 1 to 2% of the construction costs of the structure, and are 0.1 to 0.2% for coated surfaces. 

Some physical properties of the elements are compared in Table 10,2. Germanium forms brittle, grey-white lustrous crystals with the diamond structure it is a metalloid with a similar electrical resistivity to Si at room temperature but with a substantially smaller band gap. Its mp, bp and associated enthalpy changes are also lower than for Si and this trend continues for Sn and Pb which are both very soft, low-melting metals. 

The low electrical conductivity of PET fibers depends essentially on their chemical constituency, but also to the same extent on the fiber s fine structure. In one study [58], an attempt was made to elucidate the influence of some basic fine structure parameters on the electrical resistivity of PET fibers. The influence of crystallinity (jc) the average lateral crystallite size (A), the mean long period (L), and the overall orientation function (fo) have been considered. The results obtained are presented in the form of plots in Figs. 9-12. 

The modern procedure to minimise corrosion losses on underground structures is to use protective coatings between the metal and soil and to apply cathodic protection to the metal structure (see Chapter 11). In this situation, soils influence the operation in a somewhat different manner than is the case with unprotected bare metal. A soil with moderately high salts content (low resistivity) is desirable for the location of the anodes. If the impressed potential is from a sacrificial metal, the effective potential and current available will depend upon soil properties such as pH, soluble salts and moisture present. When rectifiers are used as the source of the cathodic potential, soils of low electrical resistance are desirable for the location of the anode beds. A protective coating free from holidays and of uniformly high insulation value causes the electrical conducting properties of the soil to become of less significance in relation to corrosion rates (Section 15.8). 

Contact with steel, though less harmful, may accelerate attack on aluminium, but in some natural waters and other special cases aluminium can be protected at the expense of ferrous materials. Stainless steels may increase attack on aluminium, notably in sea-water or marine atmospheres, but the high electrical resistance of the two surface oxide films minimises bimetallic effects in less aggressive environments. Titanium appears to behave in a similar manner to steel. Aluminium-zinc alloys are used as sacrificial anodes for steel structures, usually with trace additions of tin, indium or mercury to enhance dissolution characteristics and render the operating potential more electronegative. 

A lomic Atomic Crystal structure Melting point (°C) Density Thermal conduc- tivity (W/m K- ) at 20 C Electrical resistivity Specific heat Thermal expansion Magnetic susceptibility Electrode potential w.r.i. sal calomel (V) z c 2... 

Atomic number Atomic weight Crystal structure Melting Density Thermal Electrical resistivity (at 20°C) Temperature coefficient of resistivity Specific Thermal Standard electrode potential Thermal neutron absorption cross-section. 

Paints used for protecting the bottoms of ships encounter conditions not met by structural steelwork. The corrosion of steel immersed in sea-water with an ample supply of dissolved oxygen proceeds by an electrochemical mechanism whereby excess hydroxyl ions are formed at the cathodic areas. Consequently, paints for use on steel immersed in sea-water (pH 8-0-8-2) must resist alkaline conditions, i.e. media such as linseed oil which are readily saponified must not be used. In addition, the paint films should have a high electrical resistance to impede the flow of corrosion currents between the metal and the water. Paints used on structural steelwork ashore do not meet these requirements. It should be particularly noted that the well-known structural steel priming paint, i.e. red lead in linseed oil, is not suitable for use on ships bottoms. Conventional protective paints are based on phenolic media, pitches and bitumens, but in recent years high performance paints based on the newer types of non-saponifiable resins such as epoxies. 

Low-voltage electric resistance heater cables fixed to the structural floor slab and then protected within a 50 mm thickness of cement and sand to give a suitable surface on which the floor vapour barrier can be laid. The heating is thermostatically controlled, and it is usual to include a distance reading or recording thermometer to give visual indication of the temperature of the floor at several locations below the insulation. 

Homogeneous alloys of metals with atoms of similar radius are substitutional alloys. For example, in brass, zinc atoms readily replace copper atoms in the crystalline lattice, because they are nearly the same size (Fig. 16.41). However, the presence of the substituted atoms changes the lattice parameters and distorts the local electronic structure. This distortion lowers the electrical and thermal conductivity of the host metal, but it also increases hardness and strength. Coinage alloys are usually substitutional alloys. They are selected for durability—a coin must last for at least 3 years—and electrical resistance so that genuine coins can be identified by vending machines. 

The compact structure of diamond accounts for its outstanding properties. It is the hardest of all materials with the highest thermal conductivity. It is the most perfectly transparent material and has one of the highest electrical resistivities and, when suitably doped, is an outstanding semiconductor material. The properties of CVD and single-crystal diamonds are summarized in Table 7 2.[1][18]-[20]... 

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