Ferromagnetic metals, carbon

Modification of electrical and magnetic properties Conductive, nonconductive, and ferromagnetic metals, carbon fiber, carbon black, and mica Degradabibly Organic fillers starch and cellulosic fibers... 

Nickel is a silver-white, lustrous, hard, malleable, ductile, ferromagnetic metal that is relatively resistant to corrosion and is a fair conductor of heat and electricity. Nickel is a ubiquitous trace metal that occurs in soil, water, air, and in the biosphere. The average content in the earth s crust is about 0.008%. Nickel ore deposits are accumulations of nickel sulfide minerals (mostly pentlandite) and laterites. Nickel exists in five major forms elemental nickel and its alloys inorganic, water-soluble compounds (e.g., nickel chloride, nickel sulfate, and nickel nitrate) inorganic, water-insoluble compounds (e.g., nickel carbonate, nickel sulfide, and nickel oxide) organic, water-insoluble compounds and nickel carbonyl Ni(CO). ... 

In contrast to the ferromagnetic metals, it has been established that carbon solubility in bulk platinum is very low (ref. 46) and probably not a critical factor in the overall carbon deposition process. Carbon will dissolve in platinum, but segregates to the surface on cooling without any apparent disruption of the surface structure (refs. 32,47). 

The accumulation of carbon on metal surfaces when heated in the presence of carbon containing gases is a serious problem encountered in a number of commercial processes. Although carbon appears to deposit on most surfaces there are some materials which are more vulnerable than others since they contain constituents which catalyze carbon formation. The highest catalytic activity is exhibited by the ferromagnetic metals and in particular, iron. Furthermore it is well known that the surface state of such metals can have a dramatic effect on their ability to catalyze the formation of carbon. 

An important simplification results if we can consider the bonding between atoms to be a local phenomenon. In this event, we would need to consider only the immediate neighbours of the adsorbate or defect atoms, and we arrive at the cluster models circled in Fig. 1. Of course, some properties of the system will depend on its extended nature. Others, including the variation in total energy with small displacements of atoms, should be described satisfactorily by a cluster calculation. In such cases, the problem has been reduced to one of molecular dimensions, so that the methods of molecular physics or theoretical chemistry could be used. For many systems of interest to the solid-state physicist, where a typical problem might be the chemisorption of a carbon monoxide molecule on the surface of a ferromagnetic metal surface such as nickel, the methods discussed in much of the rest of the present volume are inappropriate. It is necessary to seek alternatives, and this chapter is concerned with one of them, the density functional (DF) formalism. While the motivation of the solid-state physicist is perhaps different from that of the chemist, the above discussion shows that some of the goals are very similar. Indeed, it is my view that the density functional formalism, which owes much of its development and most of its applications to solid-state physicists, can make a useful contribution to theoretical chemistry. 

With ferromagnetic metals that exhibit superparamagnetism, magnetic measurements can also be used to calculate particle size [2,4,21]. For example, the low-field and high-field Langevin equations were used to analyze the magnetization behavior of Fe particles dispersed on carbon, and the results indicated the presence of 2-4 nm Fe crystallites, a size range consistent with previous measurements [22]. 

The polymorphism of certain metals, iron the most important, was after centuries of study perceived to be the key to the hardening of steel. In the process of studying iron polymorphism, several decades were devoted to a red herring, as it proved this was the P-iron controversy. P-iron was for a long time regarded as a phase distinct from at-iron (Smith 1965) but eventually found to be merely the ferromagnetic form of ot-iron thus the supposed transition from P to a-iron was simply the Curie temperature, p-iron has disappeared from the iron-carbon phase diagram and all transformations are between a and y. 

SWCNTs have been produced by carbon arc discharge and laser ablation of graphite rods. In each case, a small amount of transition metals is added to the carbon target as a catalyst. Therefore the ferromagnetic catalysts resided in the sample. The residual catalyst particles are responsible for a very broad ESR line near g=2 with a linewidth about 400 G, which obscures the expected conduction electron response from SWCNTs. 

Finally, synthetic metals made of polymeric organic molecules may also show the property of ferromagnetism. Organic materials of this kind were first demonstrated in 1987 by Ovchinnikov and his co-workers at the Institute of Chemical Physics in Moscow. The polymer they used was based on a polydiacetylene backbone, which contains alternating double-single and triple-single bonds between the carbon atoms of the molecule (10.2). 

Spectra of four supposedly identical catalysts containing cobalt supported on an activated carbon are shown in Fig. 28. The spectra show that the two good catalysts, B-1 and B-2, contained the cobalt mostly as CoO the poor catalysts, A-1 and A-2, contained the cobalt in the metallic form. This was supported by ferromagnetic comparisons of the... 

Pure iron is a fairly soft silver/white ductile and malleable moderately dense (7.87 gcm ) metal melting at 1,535 °C. It exists in three allotropic forms body-centered cubic (alpha), face-centered cubic (gamma), and a high temperature body-centered cubic (delta). The average value for the lattice constant at 20 °C is 2.86638(19)A. The physical properties of iron markedly depend on the presence of low levels of carbon or silicon. The magnetic properties are sensitive to the presence of low levels of these elements, and at room temperature pure iron is ferromagnetic, but above the Curie point (768 °C), it is paramagnetic. 

Ferrite. Iron which, in pig iron or steel, has not combined with carbon to form cementite (FeaC). It exists in a, /9, y and 8 forms, which vary in magnetism and ahility to dissolve cementite. Name also applied to compd NaFe02 (called Na ferrite), to ferromagnetic oxides having a definite cryst structure (spinels) and the formula M++Fe ++04 of which the divalent metal may be Fe, Ni, Zn, or Mn. The magnetic props vary accdg to the divalent atom present, and ferrites are now tailored for their desired effect, as Ni-Al ferrite ... 

It should be noted that for / Ni2B2C the counterpart without carbon does not exist. Co is, so far, the only transition metal for which both the filled (with C) and the nonfilled structures could be prepared (see table 4). The examples of ferromagnetic GdCo2B2 and antiferromagnetic GdCo2B2C show that the introduction of interstitial carbon has a remarkable effect on the magnetic and, consequently, electronic properties of these compounds. 

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