Alumina/Silica/Boria - Al2O3 62/SiO2 24/B2O3 14 - Supplier Data by Goodfellow

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

Key properties of Alumina / Silica / Boria are provided in table 1.

Table 1. Properties of Alumina / Silica / Boria.

Chemical Resistance
Acids – concentrated Fair
Acids – dilute Good
Alkalis Poor-Fair
Metals Good
Electrical Properties
Dielectric constant 5.2 @ 9.4 GHz
Mechanical Properties
Tensile modulus ( GPa ) 140
Tensile strength ( MPa ) 1700
Physical Properties
Apparent porosity ( % ) 0
Density ( ) 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 ( ) 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 2.7
Extension to break % 1.2
Modulus GPa 140
Tenacity GPa 1.7


About Goodfellow

Goodfellow supplies metals, ceramics and other materials to meet the research, development and specialist production requirements of science and industry worldwide.

The Goodfellow group consists of four companies. The main administration, research laboratories and workshops are located at the Company's headquarters in Cambridge, England. The subsidiary offices in America, France and Germany provide an additional service.


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