Sample-changing wheel

To obtain TRIR spectra with sufficient sensitivity, we typically signal average several thousand laser shots at each IR frequency of interest. A flow cell, therefore, is necessary to prevent excessive sample decomposition, especially when photo-irreversible processes are monitored. A reservoir of solution (typically 10-20 mL) is continually circulated between two calcium or barium fluoride salt plates. To maintain sample integrity for non cyclic systems, one is usually forced in the dispersive TRIR experiment to acquire data in a series of short (e.g., 100-200 cm ) scans rather than in one complete scan. Thus, a substantial amount of sample may be required. Sample integrity is also of significant concern in the step-scan FTIR experiment because data must be collected at each mirror position. To address this concern, very large reservoirs of solution are required alternatively, a sample changing wheel [33] or very focused pump-probe beams in combination with sample translation [34] have been used with thin film samples. 

Stainless steel microelectrodes were prepared by sheathing 100-pm diameter stainless steel wire in glass. Tips were polished on a precision diamond wheel. Electrode response to variation in cathodic depolarizer concentration was confirmed by exposure to solution containing up to 6 mM HjOj. The increase in for the electrode was comparable to the change observed for sample coupons exposed to the same H2O2 concentrations. The electrode was conditioned by exposure to the influent reactor solution for several hours before measuring E, within the biofouling deposits. 

A schematic diagram of the machine is shown in Figure 1. The abrading razor blade bears on the rubber sample which is in the form of a wheel 6.25 cm diameter and 1.2 cm wide. The blade is clamped at one end of a freely pivoted arm which has a simple dashpot damper at the other end. The whole arm is mounted in a spring cantilever the movement of which, and hence the applied force, is detected by a transducer. The geometry of the machine is such that this force is the frictional force developed, and the normal reaction on the blade is equal to the applied vertical load. The abrasion loss is obtained from the weight change of the rubber sample. Abraded rubber... 

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