Chromium oxygen content

Mellor, 1940, Vol. 8, 436 1943, Vol. 11, 162 1942, Vol. 12, 32 Pyrophoric chromium attains incandescence in the oxide, while calcium, potassium and uranium need heating before ignition occurs, when combustion is brilliant in the 53% oxygen content. 

For the sake of illustration (15), the relationship between internal stress in chromium deposits and their oxygen content is shown in Figure 16.6. The scatter of points shows the results of many hundreds of experiments. This is not surprising as... 

Another important application is in the refining of steels when the oxygen content must be controlled at the parts per million level and monitored continuously on line and many oxygen sensors are currently used in the steel industry for this purpose. The principle of operation is as described for the lambda sensor and one form is shown schematically in Fig. 4.39. In this case the reference activity is established by a chromium metal/chromium oxide mix rather than being defined by air. 

The sesquioxide, Cr Oa, containing trivalent chromium, is an amphoteric oxide. It yields chromic salts, such as chromic chloride, CrCla, and sulphate, Cr2(S04)a, which are very stable and show great similarity to the ferric salts and to salts of aluminium as, for example, in the formation of alums. Since, however, chromic oxide functions as a weaker base than chromous oxide, the latter having a lower oxygen content, the chromic salts are more liable to hydrolysis than the chromous salts. This is well marked in the case of the chlorides. Again, in spite of the stability of chromic salts, only a slight tendency to form simple Cr " ions is exhibited, whilst complex ions are formed much more readily, not only complex anions, as in the case of iron and aluminium, but also complex cations, as in the extensive chromammine series. In this respect chromium resembles cobalt and platinum. 

It is thought to start with chromium carbide deposits along grain boundaries that leave the metal open to corrosion. This form of corrosion is controlled by maintaining low chloride ion and oxygen content in the environment and use of low carbon steels. 

It was found that chromium alloyed and austenitic steels have high corrosion resistance. The equivalent corrosion rate of two steels such as HT-9 and Fe9CrlMo was measured after their exposure during 4000 hours at 600-650"C temperature, 6 m/s flow velocity and 1 ppm oxygen content. The results of measurements are given in Table 5.3 [5.12, 5.13, 5.14]. 

It was found in the tests performed on the experimental and industrial facilities, that corrosion rate for chromium steels in PbBi alloy is 6-60 mg/m at 450-500°C. It can vary with temperature, coolant velocity, oxygen content and other parameters. In lead, this value is about 0.026 mg/m h at 600°C with no mass transfer [5.20]. 

Samples of SS 316 stainless steel, exposed to flowing sodium at different temperatures, were exalted for diemical and mechanical property dianges. The threshold oxygen contents in sodium forthe formation of KaCrO when in contact with 316SS, 304SS, D9 alloy, 2.1/4Cr- IMo and 9Cr-lMo steels were calculated. The influence of selective leaching of chromium on the carbon actiwty oC socfium in the loop was assessed by a thermorfynamic model... 

Figure 2 shows compositions of the thin films determined by RBS and EELS. The oxygen content of the thin films was increased with increasing Poj. This demonstrates that the oxygen content of the thin films can be controlled by varying / Oj. In addition, not only nitrogen content but also chromium content decreased with increasing Pcj. Therefore, vacancy would be included into chromium sites in the Cr(N,0) thin film. 

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