English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Crystallization or devitrification is the most important limitation to the development of new glasses. The significance of this fact has been recognized by many investigators including Littleton [1]2 in 1931 and Preston [2] in 1940, who emphasized the need for further study of devitrification in glass. Any such study must take inLo account two factors: (1) the liquidus temperature or maximum temperature at which equilibrium coexists between the glass and the primary crystalline phase; and (2) the rates of crystal growth at various temperatures. Such data are an important aid not only in the development of new glasses but also in the manufacturing processes of melting, forming, and annealing. Most of the data that could be used in devitrification studies are expressed as phase equilibria diagrams, such as those compiled by Hall and Insley [3], which indicate the liquidus temperatures for various compositions but which present no information as to rates of crystal grovvLh. The classical method for obtaining the liquidus temperature is the quenching method, which was used at the Geophysical Laboratory of the Carnegie Institution of Washington in phase studies of silicate systems. In this method a small powdered sample of glas or crystals, encased in a sui table container, usually a platinum foil envelope, is heated at a given temperature until equilibrium is attained and Lhen quenched in air or some suitable liquid. The sam pIc is examined with the petrographic microscope for crystals, and the process repeated at other temperature until the highest temperaLure j found at which crystals persist. In 1914 Tammann [4] deLer-mined the maximum rate of crystal growth of glass rods that had been heated in a known tempemtul"e gradient. Zschimmer and Dietzell [5] determined rates of crystal growth by placing a piece of glass on a platinum plate in a furnace and maintaining a given temperatme for a specific time interval. After the sample was removed from the furnace, it was sectioned and the crystal size measured with a micrometer microscope. This procedure was repeated for each temperature at which data were desired, and from a graph of temperature and crystal size the temperature of maximum devitri-

An improved apparatus for the determination of liquidus temperatures and rates of crystal growth in glasses