Chemistry Reference
In-Depth Information
80°
80°
90
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5.8
Cross-section of the sensor housing. Dimensions are given in mm.
company where a maximum bleaching time of 3 h was respected (semi-
continuous bleaching activity). The results are presented in Figs 5.10-5.14
and concern five measurement series over a period of 83 days. It is important
to note that the sensor was calibrated only once, notably at the first point of
the first series of measurements. It must be pointed out that the sensor
remained in bleaching solution when no bleaching activity was occurring
in the company. Those results are represented in Fig. 5.10 (test 1). Hence,
the time axes of Figs 5.11-5.14 are fragments of a continuous time axis. An
important condition that needs to be fulfilled to compare the results of the
subsequent tests (test 2 to test 5, after 6, 15, 57 and 82 days, respectively),
mutually as well as with those of the first test, is that the sensor is continu-
ously maintained in a bleaching solution. It should also be noted that for the
control of the bath composition, particularly for determination of the hydro-
gen peroxide concentration, this company adopts a simple method. Titration
is performed occasionally and then the metering pumps are manually oper-
ated, where timing of the titrations and the added quantities of reagents are
based on experience. It is to be noted here that the titrations indicated in
Figs 5.10-5.14 are all analyses that we performed ourselves.
The results given in Figs 5.10-5.13 indicate that wide fluctuations occur
in the hydrogen peroxide concentration of the bleaching bath, and that the
pattern of the concentration variation changes with the time of the mea-
surements. This suggests a poorly efficient bleaching process; however, it is
