On this day

On 27th March 1923, James Dewar, the Scottish chemist and physicist died.  He is probably best known for his invention of the Dewar Flask which he used in conjunction with extensive research into the liquefaction of gases. He was also particularly interested in atomic and molecular spectroscopy, working in these fields for more than 25 years.

 (20 September 1842 – 27 March 1923)

By 1891 James Dewar had designed and built machinery which yielded liquid oxygen in industrial quantities. Around 1892 the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask (otherwise known as a Thermos or vacuum flask) – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out that it was found possible to preserve the liquids for comparatively long periods, making examination of their optical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask – he lost a court case against Thermos concerning the patent for his invention. While Dewar was recognised as the inventor, because he did not patent his invention there was no way to stop Thermos from using the design.

The vacuum flask consists of two flasks, placed one inside the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which prevents heat transfer by conduction or convection.  Vacuum flasks are used domestically to keep beverages hot or cold for extended periods of time and for many purposes in industry.

Dewar flasks

Various sizes of Dewar flask are available and are commonly used in Cryogenics for the storage of tissue samples for example.  See also, the safe use of liquid nitrogen by clicking here.

For more information visit:-
http://en.wikipedia.org/wiki/Vacuum_flask
http://en.wikipedia.org/wiki/James_Dewar

The amazing properties of Borosilicate Glass

Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion (~3 × 10⁻⁶ /°C at 20°C), making them resistant to thermal shock, more so than any other common glass. Such glass is less subject to thermal stress and is commonly used for the construction of reagent bottles, flasks, beakers and many other laboratory glassware items. Borosilicate glass is sold under such trade names as Pyrex, Schott & Simax.

 

Borosilicate glass was first developed by German glassmaker Otto Schott in the late 19th century and sold under the brand name "Duran" in 1893. After Corning Glass Works introduced Pyrex in 1915, the name became a synonym for borosilicate glass in the English-speaking world.

Chemical Properties
Borosilicate glass has a very high resistance to attack from water, acids, salt solutions, halogens and organic solvents. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkaline solutions cause appreciable corrosion of the glass.

Hydrolytic resistance For many applications, it is important that laboratory glassware has excellent hydrolytic resistance; e.g. during steam sterilisation procedures, where repeated exposure to water vapour at high temperature can leach out alkali (Na+) ions. Pyrex borosilicate glass for example has a relatively low alkali metal oxide content and consequently a high resistance to attack from water. Pyrex fits into Class 1 of glasses for hydrolytic resistance according to ISO 719 (98°C) and ISO 720 (121°C).

Acid resistance
Glasses with a high percentage weight of silica (SiO2) are less likely to be attacked by acids. Pyrex borosilicate glass is over 80% silica and therefore remarkably resistant to acids (with the exception of hot concentrated phosphoric acid and hydrofluoric acid). Glass is separated into 4 acid resistance classes and Pyrex corresponds to Class 1 in accordance with DIN 12116 and meets the requirements of ISO 1776.

Alkali resistance
Alkaline solutions attack all glasses and Pyrex can be classified as moderately resistant. The alkali resistance of Pyrex borosilicate glass meets Class 2 requirements as defined by ISO 695 and DIN 52322.

High usage temperature

           

The maximum permissible operating temperature for DURAN® borosilicate glass is 500 °C. Above a temperature of 525 °C the glass begins to soften and above a temperature of 860 °C it changes to the liquid state.

DURAN® can be cooled down to the maximum possible negative temperature and is therefore suitable for use with liquid nitrogen (approx. – 196 °C). During such use/ freezing. In general DURAN® products are recommended for use down to – 70 °C. During thawing ensure that the temperature difference does not exceed 100 K.

 

The link below shows how Duran glass is made
http://www.duran-group.com/en/about-duran/how-duran-is-made.html

For more information visit
http://www.scilabware.com/Glass_technical/
http://www.duran-group.com/en/about-duran/duran-properties.html
http://en.wikipedia.org/wiki/Borosilicate_glass