High-temperature fusion

Chemical methods to determine the crystalline content in silica have been reviewed (6). These are based on the solubility of amorphous silica in a variety of solvents, acids or bases, with respect to relatively inert crystalline silica, and include differences in reactivity in high temperature fusions with strong bases. These methods ate qualitative, however, and fail to satisfy regulatory requirements to determine crystallinity at 0.1% concentration in bulk materials. 

Complete dissolution of plutonium residues, especially high temperature calcined plutonium dioxide contained in residues such as incinerator ash, continues to cause problems, despite continued research since the Manhattan Project (9). Methods to improve the Rocky Flats system include the use of additives (e.g., cerium) and electrochemistry, other solvents (HCl-SnCl2) as well as high-temperature fusion methods (10). High pressure dissolution, HF preleaching, fluorination, and other methods are being investigated. 

High temperature fusion (500-700 °C) of alkali or alkaline earth metals with tellurium, e.g., M2Te3 (M = K, Rb, Cs), CsTe4, MTe2 (M = Mg, Ba). 

The high-volatile Liddell bituminous coal (Figure 2 (E)) shows little indication of thermally-activated molecular mobility below 500 K. There is some fusion between 500 and 600 K followed by a major fusion transition above 600 K which appears very similar to the high temperature transition of the Amberley coal. This Liddell coal, however, has only 6% liptinite, has a crucible swelling number of 6.5 and exhibits considerable Gieseler fluidity. We therefore attribute this high temperature fusion event to the aromatic-rich macerals of the coal and associate it with the thermoplastic phenomenon. This implies that a stage has been reached in the coalification processes at which aromatic-rich material becomes fusible. 

Note The Boccess of this prcpMStfon depends entirely on cane fnl temperature eontrol of the high-temperature fusion. It is advisable, but not essential, to keep a clean clamped thermometer (range to 500 0) immersed in the reaction mixture during the experiment. Bear in mind that metallic catalysts and especially organic substances such as dust, paper, or cloth may cause violent and even explosive decomposition of the molten potassium chlorate. He crudble or dish used for the fusion should therefore be scrupulously dean and preferably new. 

Lovering, J. F. High temperature fusion of possible parent materials for tektites. Nature [London] 186, 1028—1030 (1960). 

Salts are used in Dry methods as Dry Menstrua. Just as the liquid menstrua of the Wet Way extract and retain the essentials in Vegetable and Mineral works, the Dry Way achieves the state of total liquefaction of the mineral or metal by high temperature fusion aided by select salts. Much of this technology stems from the very ancient arts of glassmaking and... 

The pyrogenic silicas are formed at high temperatures. The most common type of fume silica , which is produced by the flame hydrolysis of silicon tetrachloride, is widely known as Aerosil. This term has become generic for the fume silicas, although strictly Aerosil is the trade mark of Degussa (Fetch, 1994). Other pyrogenic silicas are made by the high-temperature fusion or vaporization of sand in an arc or plasma. 

Using Acid-Catalyzed High-Temperature Fusion... 

Simple crucibles of nickel, iron, silver, and gold are used as containers for the high-temperature fusion of samples that are not soluble in aqueous reagents. Attack by both the atmosphere and the contents may cause these crucibles to suffer mass changes. Moreover, such attack will contaminate the sample with species derived from the crucible. The crucible whose products will offer the least interference in subsequent steps of the analysis should be used. 

Introduction of contaminants from reaction of the solvent with vessel walls. This source of error is often encountered in decompositions that involve high-temperature fusions. Again, this source of error becomes of particular concern in trace analyses. 

Refractory materials Substances that resist attack by ordinary laboratory acids or bases brought into solution by high-temperature fusion with a flux. 

Energy production in the future could be greatly altered with small, clustered, safe high-temperature fusion reactors burning cheap, abundant fuel. 

As alternatives to the wet chemical methods described above, high-temperature combustion with magnesium sulfate followed by acid leaching or high-temperature fusion with magnesium nitrate have been proposed. The latter method has been shown to decompose phosphonates that are quite refractory. 

Some materials are particularly resistant to acid digestion, e.g., certain rocks, mineral oxides, phosphates, and some iron alloys. For these samples, high-temperature fusion with an acidic or basic flux such as lithium metaborate (LiBOs) in the molten state can be used to render such materials soluble in water or dilute acid. Fusion decompositions are the most rigorous methods available and all silicate materials, including refractory substances like zircon and cassiterite, can be dissolved completely when fused with an appropriate flux. However, there are several disadvantages to this method including the introduction of additional salts into the final solution... 

This method is slow by modern standards, but at the time of its discovery, it greatly speeded up the laboratory preparation of diborane. Earlier workers had used a rather tortuous and wasteful—if historically important—procedure due to Stock, which involved the pyrolysis of higher boranes obtained from magnesim boride (301-303), itself only obtainable from a high-temperature fusion process (305). 

Bulk catalysts comprise mainly active substances, but some binder is often added to aid the forming/shaping operation. This is the case for iron oxide for the water-gas shift (WGS) reaction, iron molybdate for the oxidation of methanol to formaldehyde, and vanadyl pyrophosphate for butane oxidation to maleic anhydride. However, in some cases, bulk catalysts are used as prepared, without the need for addition of the binder. Typically, this involves catalysts prepared by high temperature fusion (eg, the iron-based ammonia synthesis catalyst). The need for the addition of binder, or the requirement for pelleting, solely depends on the strength required for the catalyst under the reaction conditions and the reactor type that is used in. This requires consideration of attrition resistance, and oxide... 

As alternatives to the wet chemical methods described above, high-temperature combustion alone or with magnesimn sulfate followed by acid leaching [58,59] or high-temperature fusion with magnesium nitrate have been proposed [60]. The latter method has been shown to decompose phosphonates, which are quite refractory due to their stable C-P bonds [51]. Nevertheless, these techniques are usually recommended for soils or sediments analysis and appear less used than those above (section a) for determination of TP or TIT in water samples. 

Most tests require that the sample be brought into solution before being tested. Occasionally, a sample may not be readily soluble in most reagents or only very slowly soluble. These may need to be opened up by means of high temperature fusion in a flux such as sodium carbonate. This can also be performed easily on a microscale (i.e., a fine platinum loop) with appropriate fluxes and technique. 

In order to augment the quantity and quality of final synthesis yield as obtained from conventional hydrothermal activation, another modified method has been introduced which utihzes two different steps, an initial high temperature fusion of fly ash-alkah mixture, prior to employing the final stage of hydrothermal activation of the fused product. The main variables have been fusion temperature and time, alkali type and its concentration and crystallization time in hydrothermal synthesis process, which can affect the quahty and yield of final product. As such, it has been confirmed that the final yield can be quantified to exhibit zeolitic conversion up to 62 % together with by production of alkaline waste solution which can become a threat to the environment after disposal. A flowchart of the synthesis process is depicted in Fig. 3.3 [1, 2, 9, 10, 12, 43, 44]. 

---