Refractory sample

Microwave containers for sample digestion are commercially available which can be used for ashing samples at temperatures up to 300° C or pressures to 800 psi, under controlled pressure and temperature. Under these conditions, even refractory samples can be digested successfully in a reason-... 

Flayden [52] conducted a controlled series of alkali corrosion tests of commercial refractories using the crucible cover technique illustrated in Fig. 13. This test involved placing a refractory sample over a crucible containing a premeasured amount of alkali carbonate and heating the assembly to 1350°C for 12 h. A furnace containing a load of test samples is... 

Fig. 14. Furnace setup to react multiple refractory samples with alkali at elevated temperatures.

Basic flux A substance with basic characteristics in the molten state used to solubilize refractory samples, principally silicates. Beam The principal moving part of a mechanical analytical balance. 

Fluxes Substances that in the molten state pos.sess acidic or basic properties used to solubilize the analyte in refractory samples. Focal plane A surface on which dispersed radiation from a prism or a grating is focused. 

Figure 3. Photograph showing the refractory samples in the tube furnace...

SEM analyses of MgO refractory samples containing the calcium silicate binder showed the presence of Na2S04 and free SO3. At higher exposure temperatures, more weight increase was observed and more Na2S04 was detected. The calcium silicate binder was corroded by SO3. Calcium sulfate was formed as shown in the SEM image in Figure 5. 

A SEM image of a forsterite bonded (2) MgO (1) refractory sample is shown in Figure 6. A lower weight gain was observed for the forsterite bonded MgO. Slight corrosion was observed, as the forsterite protects the attack of MgO grains by SO3... 

A refractory sample exposed to a temperature of 1300°C was mounted on a stainless steel shaft with a section of stainless steel tubing placed around the shaft which in turn served as a high temperature "sacrificial anode. Corrosion tests were conducted at rotation speeds of 60 and 120 rpm, along with a few under-static conditions. 

The wear resistance of refractories is determined according to ASTM C-704-01 [56]. This test method measures the relative abrasion resistance of various refractory samples under standard conditions at room temperature. The abrasion resistance of a refractory material provides an indication of its suitability for service in abrasion or erosive environments. 

Refractory samples are often only present as granulates and are hard to grind. Indeed, here the abrasion of the mills (be it even a hard material such as WC) is high and this leads to contamination and consequently to interferences in the AAS determination. In this case, melting with fluxes is the only method of digestion. 

Many types oflasers are used for this analysis technique, including Nd-YAG, ruby, CO2, N2, and excimer. For satisfactory operation, lasers must be capable of sufficient power density to effectively ablate and vaporize refractory sample matrices. Both the Nd-YAG and ruby lasers can be operated in two modes normal (free-running) mode and the fixed Q-switched mode. In the normal mode, ablation craters are created with uniform and reproducible diameters, the depth of which are determined by the number of pulses used. The Q-switched mode is used for samples that are particularly difficult to energy couple because of their transparent nature. Although the Q-switched mode provides more energy and hence a larger amount of material is ablated, performance in terms of efficiency and reproducibihty are usually not a good as operation in the normal mode. 

Another way to develop MOE data is by the sonic test methods. Eundamen-tally, the sonic method evaluates the MOE using the resonant frequency of the refractory sample. However, the sonic method tends to overpredict the MOE value. The primary reason is that the resonating sample is exposed to an... 

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