Nextel® 312 and Nextel® 440 are two similar materials - compositions of ceramic specially developed for the production of continuous filament yarns which are sufficiently flexible to manufacture conventional textile articles such as fabrics and sewing threads whilst retaining much of the high temperature and chemical resistance typical of ceramics. Nextel® 440 has somewhat better tensile properties and higher upper working temperature but is less flexible than Nextel® 312. Nextel® 312 is available from Goodfellow as a yarn, a narrow fabric and sewing thread sizes. Sewing threads are made from individual yarns, known as “singles”, wrapped around the outside with rayon and then twisted together in two stages to give a balanced, non-snarl, construction. The rayon comprises about 20% of the initial weight of the thread and will “burn” out by about 300°C if/when the sewn article is subsequently heated.

The fibres are coated with finishes during manufacture which can be removed, if desired, by "heat cleaning" at about 550°C. If the best possible properties are required, further heat treatment at about 920°C should be used. More details of the recommended methods of treatment are available on request.
Key Properties

Chemical Resistance










Acids – concentrated


Fair

Acids – dilute


Good

Alkalis


Poor-Fair

Metals


Good

Electrical Properties










Dielectric constant


5.2 @ 9.4GHz

Mechanical Properties










Tensile modulus ( GPa )


140

Tensile strength ( MPa )


1700

Physical Properties










Apparent porosity ( % )


0

Density ( g.cm-3 )


2.7

Refractive index


1.57

Water absorption - saturation ( % )


0

Thermal Properties










Coefficient of thermal expansion ( x10-6 K-1 )


3 @ 20-1000°C

Specific heat ( J.K-1.kg-1 )


1100 @ 25°C

Sublimation point (°C )


1800

Upper continuous use temperature (°C )


1200-1400

Properties Alumina/Silica/Boria Fibre




Property








Value

Coefficient of thermal expansion - Longitudinal


x10-6 K-1





3.0

Density


g.cm-3





2.7

Extension to break


%





1.2

Modulus


GPa





140

Tenacity


GPa





1.7