No abstract

Energy dispersive X-ray fluorescence technique was used to study the elemental composition of some historical paper samples obtained from the National Library of South Africa. Six elements namely Fe, Cu, Mn, Ca, K and S were detected. It was found that older documents had higher concentrations of Ca and hence a considerable alkaline buffer than recent documents. It was also observed that the levels of Ca dropped significantly between 1800 and 1890 coinciding with the period paper making technology also changed. The concentrations of K and S also went down around 1890. Fe remained fairly high and was detected in all samples. Cu and Mn were found to be at very low concentrations compared to Fe. This research shows that Fe has the potential to impact negatively on paper permanency unless de-acidification is undertaken because of its relative abundance compared to Cu.

& A plug-and-play type digital temperature control system was developed and tested. The software designed for the controller implemented 100% duty cycle for temperature errors of 2 C or more and a 25% duty cycle for temperature errors of 1 C. This produced an initial rate of change of temperature of 0.170 C s À1 at a 100% duty cycle and 0.0040 C s À1 at a 25% duty cycle. The temperature rates were invariant for both positive and negative temperature gradients. The system was also able to make the incubator reach the final steady state temperature in less than 70 s.

It has been established that the 1N4148 diode is able to operate as a temperature sensor in the range 0 • C to 160 • C. The steady state response and the dynamic response of the diode are used to support this statement. The linearity of the steady state voltage-temperature characteristics of the diode has been established beyond the range previously investigated. A digital thermometer was then designed using the 1N4148 diode as the sensor. The thermal time constant of the diode was found to be 390 ms. A comparison of the dynamic response of the diode to step temperature changes and that of a type J thermocouple was carried out and it was found that the diode had a larger thermal time constant.

An alternative method was developed to determine the thermal time constant of a relatively cumbersome temperature sensor in still oil. A relationship between the take-off gradient, initial temperature, thermal time constant, and final steady-state temperature was deduced. An experiment was then performed using a Pt100 temperature sensor to test the veracity of the relationship. The Pt100 temperature sensor was subjected to five different step changes in temperature from an initial temperature of 60 °C. This resulted in five exponential curves with five different take-off gradients. The linearization method was used to determine the thermal time constant as a control experiment. The new method was then applied to the same data set. It agrees very well with the linearization method within the limits of experimental error.