Crucibles comparison

Figure 4.24 N and B coimplanted in 4H-SiC and annealed in an inductively heated furnace at 1,600°C for 10 minutes within a SiC crucible and high-purity Ar atmosphere, (a) Comparison between as-implanted and annealed N and B profiles, (b) Comparison between the N annealed and simulated profile these were computed under the hypothesis of an N FED diffusion. (From [91]. 2002 Material Science Forum. Reprinted with permission.)...

Oxalo-niobates or niobo-oxalates correspond to the vanado-oxalates, and contain both oxalic acid and niobic add radicals in the complex anion. The only known series possesses the general formula 3R aO. Nb 205.6C203.a H20, where R stands for an alkali metal. The sodium, potassium and rubidium salts are prepared by fusing one molecular proportion of niobium pentoxide with three molecular proportions of the alkali carbonate in a platinum crucible. The aqueous extract of the melt jjs poured into hot oxalic add solution concentration and cooling, or addition of alcohol or acetone, then brings about precipitation of the complex salt. Comparison of the dectrical conductivity measurements of solutions of the alkali oxalo-niobates with those of the alkali hydrogen oxalates determined under the same conditions indicates that the oxalo-niobates are hydrolysed in aqueous solution, and that their anions contain a complex oxalo-niobic acid radical.6... 

Data reporting (i.e., the statement of the results of the proximate analysis test methods) usually includes (in some countries but not in all countries) descriptions of the color of the ash and of the coke button. As an interesting comparison, the test for determining the carbon residue (Conradson), the coke-forming propensity of petroleum fractions and petroleum products (ASTM D-189 ASTM D-2416), advocates the use of more than one crucible. A porcelain crucible is used to contain the sample, and this is contained within two outer iron crucibles. This corresponds to the thermal decomposition of the sample in a limited supply of air (oxygen) and the measurement of the carbonaceous residue left at the termination of the test. 

For this reason, a standard crucible test has been devised in which the chief features, compared with other tests, are the use of a leveled coal surface, a crucible of special shape and unidirectional heating by a gas flame. As a result, regularly shaped coke buttons are obtained and the degree of swelling is assessed by comparison with profiles of standard buttons. 

Instrumental neutron activation analysis was used to determine concentrations of several major and trace elements in samples of heavily corroded residues found in crucible fragments excavated at Tel Dan, Israel. The residues were mostly hard, metallic phases admixed with nonmetallic inclusions that appeared to be ceramic material from the loose porous interior of the crucible itself The objective was to identify the metals that had been melted in these crucibles. A method is described that attempts to separate nonmetallic and metallic phase data. In comparison to previous reports on analyses of source materials thought to have been used at Dan in this period (Late Bronze II Age-Early Iron I Age 1400-1000 B.C.), high gold concentrations were found. These appear to be correlated to arsenic and antimony concentrations. This finding is discussed in relation to possible changes in the source of tin at this period. 

The chemical composition of the German Klingenberg clay has been given for comparison inasmuch as it represents one of the best known bonding clays known, especially for the manufacture of graphite crucibles. 

Fritted-glass crucible A filtering crucible equipped with a porous glass bottom also called a sintered-glass crucible. Fronting Describes a nonideal chromatographic peak in which the early portions tend to be drawn out compare with tailing. F-test A statistical method that permits comparison of the variances of two sets of measurements. 

The last method is similar in its principle to that developed by Kleppa (1960) in his pioneering and extensive calorimetric investigation of molten salts. In his arrangement, salt B was placed in an ampoule made of a pyrex tube fitted with a break-off tip (Figure 4.8b). In comparison with the break-off bubble method, a slight shift in composition due to the effect of surface tension and the wetting of the crucible and the ampoule... 

From Equation 1.1, it follows that the temperature difference between sample and reference is a measure of the difference in heat flow due to the presence of the sample in one of the crucibles, provided that the furnace and heat paths are truly symmetrical. Consequently, this differential heat flow is a measure of the properties of the sample, with all other influences (heat adsorption by the crucible, heat losses through convection, etc.) having been eliminated by use of the comparison with the reference. The AT signal requires calibration to provide a heat flow as a function of temperature, and this is usually carried out by use of standards that are usually pure metals with known enthalpies of melting and materials with known heat capacities (see Section 2.4 in Chapter 2). 

Figure 8.12 Optical micrographs showing a comparison of nickel specimens heated 24 h at 1000 °C in a sealed quartz tube which contained Na2S04 in an AI2O3 crucible. The nickel specimens did not touch the Na2S04. (a) The quartz tube was evacuated and sealed. A layer of nickel sulphide (arrows) has formed on the metal beneath a dense continuous layer of NiO. The nickel sulphide has been etched electrolytically with NaNOs. (b) The qnartz tnbe was backfilled with oxygen to give a pressure of 0.9 atm at 1000 °C. A dense layer of NiO has been formed. No evidence of sulphide formation was observed.

FigureS.IO Evaporation of supported IL ([EMIMJiNTfj], 174°C. HV. porous silica, Kieselgel 100, Merck, 0.06-0.2 mm) and comparison with the simulations by five models Model I effitsion from external surface of the silica particles is r.d.s., Eq. (6.23) Model II pore d rffusion in the particles is r.d.s. Knudsen diffitsion, shrinking core, Eq. (6.29)), Model III mass transfer in the sample is r.d.s. Knudsen diffusion infixed bed of crucible, Eq. (6.34)), Model IV effusion from face surface of sample is r.d.s. and p = p = constant, Eq. (6.37), and Model V effusion from face surface is r.d.s. " Fvap = PBET Psat...

Table I. Comparisons between experimental and theoretical alloy quantity and composition obtained for sea nodules smelting on 500 g scale at 1400 °C in recrystallise alumina crucible.

The use of bonded AZS refractories as paving blocks in glass furnace bottoms for the past several years suggests that these refractories can indeed be used, in place of fused-cast AZS, in some furnaces. However, this study clearly showed the inadequacy of common finger corrosion test and the use of below metal line data in accurate comparison of different bonded AZS refractories. Crucible test used in this study could not differentiate between different bonded AZS refractories available commercially. 

Oxygen. Analyses are ordinarily made by vacuum fusion with Fe or Pt [22,23,27] or by inert gas fusion [28]. The sample is dissolved in the molten metal saturated with carbon in a graphite crucible at 1900°C and the evolved CO converted to CO2 in a CuO column and measured gas-volumetrically. More reproducible results are said to be obtained by neutron activation analysis for oxygen. With this method the sample is exposed a few minutes to 14 MeV neutrons to activate the oxygen by the nuclear reaction 0(n,Y) 0 and the amount of oxygen is obtained from the 0 activity having the half life of ty = 29.1 s [29] by comparison with that of a standard. The technique of isotopic dilution which has been used to analyze for oxygen in Ti should be applicable too [30]. 

In addition to the above glass equipment, the corresponding items made of porcelain and quartz should be on hand. Among the porcelain items there should be white and black crucibles, dishes, classical spot plates and also sets of comparison spot plates as described by Skalos. ... 

Procedure. A drop of the neutral test solution is mixed with a drop of a barium carbonate suspension in a micro crucible and evaporated to dryness. A drop of 1 % solution of phenolphthhalein in 1 1 ethyl alcohol is added. A pink or red color indicates sulfates. A blank comparison test is essential because water suspensions of barium carbonate almost invariably show a slight alkalinity. 

Procedure. The test solution is diluted with water if necessary and then one drop is mixed in a porcelain micro crucible with several milligrams of methylene-disalicylic acid. The ciucible is then kept in a drying oven at 150 C for three minutes. A dark- or light red residue remains, the color depending on the quantity of free sulfuric acid present. It is advisable to conduct a comparison blank test. 

Procedure II. A drop of the test solution containing sulfuric acid is well mixed on a spot plate or in a micro crucible with 6 drops of the reagent solution. A violet color indicates the presence of titanium. For very dilute solutions, comparison with a blank test is advisable. 

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