Specific charge

To the above costs must he added hack any unit costs omitted from those to which learning might bring improvement. These will normally include overheads and specific charges on the project such as the unit cost of special tools, jigs, etc. 

Total charge, volumetric charge density, and charge-to-mass ratio (specific charge) are useful parameters in assessing electrostatic hazards. Charge on... 

Compare two different explosive charge weights of the same material. For an observed overpressure of 40 psi from a specific charge using the scaling equation above, the scaled distance is Z = 5 ft/lb /. WTiat is the distance for an overpressure of 40 psi with a charge of 500 lb ... 

Several metals that are farther removed from the noble gases in the periodic table form positive ions. These include the transition metals in Groups 3 to 12 and the post-transition metals in Groups 13 to 15. The cations formed by these metals typically have charges of +1, +2, or +3 and ordinarily do not have noble-gas structures. We will postpone to Chapter 4 a general discussion of the specific charges of cations formed by these metals. 

In the second part of the 20th century, the tantalum capacitor industry became a major consumer of tantalum powder. Electrochemically produced tantalum powder, which is characterized by an inconsistent dendrite structure, does not meet the requirements of the tantalum capacitor industry and thus has never been used for this purpose. This is the reason that current production of tantalum powder is performed by sodium reduction of potassium fluorotantalate from molten systems that also contain alkali metal halides. The development of electronics that require smaller sizes and higher capacitances drove the tantalum powder industry to the production of purer and finer powder providing a higher specific charge — CV per gram. This trend initiated the vigorous and rapid development of a sodium reduction process. 

Significant improvement of tantalum powder properties was achieved by the application of molten alkali halides as solvents for potassium heptafluorotantalate, K2TaF7. Variation of the initial concentration of K2TaF7 in the melt, stirring and rate of sodium loading enable a well-controllable production of tantalum powder with a wide variety of specific charges. Heller and Martin [590] proposed the use of a reactor equipped with a stirrer in 1960. Fig. 142 shows a typical scheme of the reactor [24, 576]. All metal parts of the reactor are made of nickel or nickel alloy. 

Based on available results, it can be summarized that the particle size of tantalum powder increases (specific charge decreases) with the increase in temperature, K2TaF7 concentration and excess sodium. In addition, an increase in the specific surface area of the melt and Na/K ratio also leads to the formation of coarser tantalum powder. The most important conclusion is that for the production of finer tantalum powders with higher specific charges, the concentration of K2TaF7 in the melt must be relatively low. This effect is the opposite of that observed in the electrochemical reduction of melts. 

Modem requirements of the capacitor industry initiate further development of tantalum powder production processes. The tendency is to produce powder of higher purity with a higher specific charge and at lower cost. Further development of the processes can be successfully achieved based on current achievements in the chemistry of tantalum and niobium fluoride compounds. 

From a thermodynamic point of view, apart from charge density and specific charge, the redox potential of lithium insertion into/removal from the electrode materials has to be considered also. For instance, the redox potential of many Li alloys is between -0.3 and -1.0 V vs. Li/Li+, whereas it is only -0.1 V vs. 

Figure 1. Specific charges and charge densities of several lithiated anode materials for lithium batteries, calculated by using data from Refs, [10, 32-35], Li4 denotes a fourfold excess of lithium, which is necessary to attain a sufficient cycle life.

Figure 7. First- and second- cycle constant-current charge/discharge curves of graphite Timrex KS44 in LiN(S02CF3)2/ethylene carbonate/dimethyl carbonate as the electrolyte (CilT irreversible specific charge Crev =reversible specific charge) [2J.

Apart from reactions with the electrolyte at the carbon surface, the irreversible specific charge is furthermore strongly affected by the possible co-intercalation of polar solvent molecules between the graphene layers of highly graphitic matrices [139]. This so-called "solvated intercalation reaction" depends (i) on the crystallinity and the morphology of the parent carbonaceous material, which will be discussed in Sec. 

Both effects resulting from solvent cointercalation, the mechanical destruction and the higher irreversible specific charge losses, seriously complicate the operation... 

The latter, so-called "high specific charge" or "high capacity", carbons have received considerable attention in recent research and development. Usually they are synthesized at rather low temperatures, ranging from -500 to -1000 °C, and can exhibit reversible specific charges from -400 to -2000 Ah kg (x= -1.2 to -5 in... 

Figure 11. Schematic drawing of some mechanisms for reversible lithium storage in "high-specific-charge" lithiated carbons as proposed in Refs, (a) [216], (b) [218, (c) [224], (d) [230], (e) [41], and (f) [238]. The latter figure has been reproduced with kind permission of Kureha Chemical Industry Co., Ltd.

Although the high specific charge carbons exhibit a multiple of the specific charge that is severafold that of graphite, there are still some problems to solve ... 

J Carbons chemically pre-lithiated before the production of the electrode can exhibit specific charges grater than 400 Ahkg 1, too [210],... 

Other explanations lor the increase in specific charge obtained by using hydrogen-containing carbons and for the observation of potential hysteresis were suggested in Refs. [251, 252],... 

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