Search

NATURAL cryolite (Na3AlF6), when fused in a platinum crucible, yields a typical 'wetting' melt, which gradually spreads over the interior of the crucible and may even creep over the edge. When minute amounts of lead, bismuth or thallium compounds are added, a remarkable and practically instantaneous change is observed in the nature of the melt, which becomes 'non-wetting' and forms a single large drop with sharply defined boundaries.

PREVIOUS workers have reported that the tensile strength of nominally identical glass fibres is very inconsistent, with coefficient of variation between 5 and 25 per cent1,2. In an attempt to reduce this variability, I have made and tested ‘E’ glass fibres under carefully controlled conditions. The fibres were drawn from molten glass in a platinum crucible, and were wound around a rotating drum. Only that part of the fibre between the crucible and drum was used for testing. The manipulation technique involved gripping the free length of fibre at its two ends, and mounting it with vacuum wax on a slotted paper mount, which when cut into pieces provided ten test pieces each 1 in. long. Each test piece on its mount was assembled in a special ‘chain-o-matic’ testing machine with controlled rate of loading, and the mount was severed before application of load. By this means it is possible readily to test large numbers of fibres with surfaces which are mechanically undamaged. To reduce atmospheric attack each batch of ten test pieces was tested within two minutes of manufacture, and in an atmosphere of less than 40 per cent relative humidity.