System containing alkalis

Three conceptual steps can be discerned in the definition of the ionic structure of fluoride melts containing tantalum or niobium. Based on the very first thermodynamic calculations and melting diagram analysis, it was initially believed that the coordination numbers of tantalum and niobium, in a molten system containing alkali metal fluorides, increase up to 8. 

The major technical barrier associated with biomass combustion systems is the formation of tenacious deposits on heat transfer surfaces caused by the unique high-temperature chemistry of biomass ash. Many types of biomass used in combustion systems contain alkali metal species sodium, potassium, and calcium. The ash content of woody biomass is quite low and not a problem. The ash content of agricultural residues such as wheat straw, rice straw, com stover, and alfalfa stems can be quite high, on the order of 5 percent or up to 20 percent for rice straw and rice husks. The presence of alkali metals in conjunction with the high silica content of some biomass ashes can lead to molten ash at combustion temperatures.553-658 In some cases, the K, Si, and A1 contents are such that very low melting-point eutectic mixtures can form. The materials can be fluid at combustion temperatures, but form glasslike deposits on colder downstream surfaces such as heat exchanger tubes. 

Table 2. Catalyst systems containing alkali metals for the hydroamination of ethylene. 

One of the crucial problems in the chemistry of potassium hexafluorotitanate, K2Tip6, is its stability in the environment of different alkali metal fluorides and/or chlorides, since these compounds are usually used as complementary electrolyte components. The cryoscopic measurements in a system containing alkali metal halides and K2Tip6 make it possible to determine the dissociation scheme of K2TiPe, or other reactions taking place between alkali metal halides and K2TiPe. The study of some systems of this type can be found in the literature. 

Systems containing alkali metal and rare-earth fluorides have aroused increasing interest among scientists in recent years. They can be used to make quantum oscillators, optical materials and to predict the behavior of transuranium elements in fuel mixtures for nuclear reactors [1-3]. In view of this, the investigation of the thermodynamics of these mixtures is of not only academic, but also practical interest [4]. 

The homopolymerization of the most popular six-membered cyclic carbonates (TMC and neopentyl carbonate) using nucleophilic initiators based on Li-, K-, Mg-, A1-, Zn-, and Sn-containing compounds were also studied. The systems containing alkali metals. Mg and Sn, were found to afford during polymerization, besides linear, also cyclic oligomers. This shows that for this group of initiators the... 

One of the drawbacks of the systems containing alkali metals is their resistance under hydrothermal conditions and the presence of sulfur. In the first case the activity of soot oxidation drops dramatically for K/CeOs catalysts under water at higher temperatures due to the loss of potassium and a change in the K/Ce optimal ratio, while the formation of sulfates is responsible for activity loss under SOg. 

Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. 

Liquid metals, however, present several disadvantages. Their weights must be considered with regard to equipment design. Additionally, Hquid metals are difficult to contain and special pumps must be used for system safety. Alkali metals react violentiy with water and bum ia air. Liquid metals also may become radioactive whea used for cooling auclear reactors (qv). 

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. 

Analysis of the composition of compounds formed in systems containing Nb02F and alkali metal carbonates reveals several common peculiarities. The first stage of the interaction takes place according to Equation (11) and can be formulated in general as follows ... 

Chai and Zhong [602] investigated the melting properties of molten systems containing K2TaF7 and different alkali metal cations with respect to the optimization of the sodium reduction process. It was shown that the specific... 

A remarkable variety of compounds in the Ca-(B,C,N) system has opened a window for research in related fields. With the elements boron, carbon and nitrogen, substance classes such as borocarbides, boronitrides, and carbonitrides can be considered to contain anionic derivatives of binary compounds B4C, BN, and C3N4. Until now, most compounds in these substance classes have been considered to contain alkali, alkaline-earth, or lanthanide elements. Lanthanide borocarbides are known from the work of Bauer [1]. Lanthanide boronitrides represent a younger family of compounds, also assigned as nitridoborates [2] following the nomenclature of oxoborates. 

This strategy has resulted in entirely new formulations with remarkable benefits. Sustainable Earth (SE) cleaning products combine reagents determined to be safer for human and environmental health with a positively characterized hybrid surfactant system containing a stabilized oxidizing compound. This system eliminates conventional ingredients such as alkyl glycol ethers, alkali builders, alkylphenol ethoxylates, EDTA and ethanolamine. 

Prints containing Alkali Blue are not fast to the standard DIN 16524 solvent mixture, but they are fast to acid, paraffin, butter, and other materials. Tested in accordance with normative testing standards (Sec. 1.6.2.2), the prints unexpectedly also show fastness to alkali. It should be noted, however, that at higher alkali concentrations the tinctorial strength of the system declines and the shade becomes duller. This is a result of the fact that the pigment reacts with alkali. 

Sulfur is weakly soluble in H2O (10 M at 298 K) [33, 34], but Na2S is very soluble [35]. In deaerated aqueous solutions, the alkali-metal polysulfide system contains, in addition to H2O and alkali-metal cations, OH , H+, H2S, HS ,... 

The above use of "stable coexisting minerals" is of course based upon the fundamental consideration that the chemical system is "closed" that is, the chemical components K, Si and OH are "inert", their relative proportions, mass, in the system determines the phases formed. This can be assumed valid for many argillaceous sediments and rocks. However, in some geological environments, aqueous solutions containing alkalis and hydrogen ions in various concentrations (whose activities, therefore, are variables but constant throughout a given system) react with kaolinite or other minerals to influence its stability under otherwise constant physical and chemical parameters. 

We have until now ignored the fact that a system containing only potassium as the alkali ion cannot really represent a natural argillaceous rock. If the correspondence of Na-K and Ca is more or less complete in feldspars and montmorillonites, it is not so in low temperature micas. 

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