Dalfratex ceramic textiles

Dalfratex is a range of asbestos free, inorganic fibres and textiles in the form of ceramic cloths and insulators. The ceramic cloths and fibres are capable of operating continuously at 1000°C and up to 1600°C for limited periods. They will not melt or vaporize until the temperatures exceed 1700°C, and have a very high resistance to thermal shock. ™Dalfratex products also provide flexible electrical insulation at temperatures as high as 1000°C.

Originally developed for the thermal insulation of gas turbine jet pipes, Dalfratex products have played a vital role in the European aerospace industries since the 1960's. asbestos free, it achieves an improved, higher temperature performance than asbestos and glass fibre in many applications. Dalfratex products are also widely employed in nuclear reactor applications.

Dalfratex products are composed of continuous filaments of amorphous silica, which combine the flexibility of fibres and textiles, with the refractory properties of silica. In order to service the needs of a wide range of applications the majority of Dalfratex products are available in two basic forms: standard and pre-shrunk. The standard form shrinks during initial heating and products of this type have letter ‘U’ incorporated into the code number. As their name implies, the pre-shrunk forms have been factory treated to confer better dimensional stability in high temperature use. In addition to these forms a wide range of sacrificial organic finishes are available which may be applied to particular products where required for specific end uses. Dalfratex product are available as textile broadcloth5, tapes, sleevings, cords, braided packings, ropes and yarns and also as bulk fibres and batts.

All Dalfratex products have associated adsorbed water, and some products have special organic finishes to impart particular physical properties.

The following chemical composition values assume that all water and special coatings have been removed by ignition at 1000 deg C.

Composition	%
SiO2	98.57%
TiO2	0.3%
AL2O3	0.47%
Fe2O3	0.08%
B2O3	0.06%
CaO	0.05%
MgO	0.07%
Alkalis	0.13%

Total	99.73%

Balance	H2O and trace elements

Special low chloride product

Dalfratex products with a lower level of chlorides are available by special arrangement.
They find application when temperature and humidity conditions conducive to stress corrosion cracking of stainless steel are likely to be encountered.

High Temperature Performance

Maximum Continuous Use Temperature: 1000 deg C
Progressive devitrification eventually leading to brittleness will occur above this temperature.

Maximum Short Term Use Temperature
Dalfratex products can be used up to the softening point if the exposure is of limited duration. The actual duration of exposure is a function of temperature and mode of use. Advice on the suitability of a Dalfratex product for a given application may be obtained from Ceramisis. Some examples of this type of use are: Manufacture of flexible fire barriers and curtains. Fire stopping of pipe penetrations through rigid fire walls. Protection of personnel and plant from liquid metal splash.
Softening Point: approx 1600 deg C.
Thermal Shock Resistance : excellent

Shrinkage / Time / Temperature relationship

Standard products have an initial high rate of shrinkage which is irreversible, and occurs when they are first heated. The following graph is given for guidance only, and is based on measured values for broadcloth.

For certain applications, shrinkage of Dalfratex in-situ during the first heating may be undesirable. For these applications, most Dalfratex products are available in a pre-shrunk form. Further limited shrinkage may still occur in use, depending upon the temperature and time conditions prevailing, but typically will be less than 2% at 1000 deg C.

Thermal Properties

Thermal Conductivity

The following values of thermal conductivity shown on the graph, below, were determined using the water calorimeter procedure described in BS 874: 1973, paragraph 4.2.5. Units are Wm/m2 °C.
The thermal conductivity values of ball in a slightly compressed condition (density 96kg/rn3) are reported, being the most common application form. In the fully relaxed, as supplied, condition the thermal conductivity is 10% to 15% higher at elevated temperatures.

Specific Heat

250 C= 0.80 j/g deg C, 500 C= 0.88, 750 C= 0.96, 1000 C= 1.09

Electrical Properties

Dalfratex fibre is a good electrical insulator, with high electric strength and low electrical conductivity.
For most design purposes it may be assumed that the electrical breakdown strength of a region filled with Dalfratex, is essentially that of atmospheric air.
The dielectric properties of Dalfratex at room temperature are adversely affected by the presence of associated water. This can substantially be removed by heating the material to 100 deg C to 200 deg C, when the losses are significantly reduced.
The electrical properties of Dalfratex have been measured by an independent testing laboratory, and their report is available upon request from Ceramisis Limited.

Chemical Properties

The chemical properties of Dalfratex are similar to those of vitreous silica (silica glass).
In general Dalfratex is compatible with mineral acids except phosphoric and hydrofluoric and is also compatible with a wide range of substances including air, chloride, carbon monoxide, ammonia, sulphur dioxide.
Dalfratex products are compatible with silica refractories at high temperatures. As there is no possibility of forming a SiOz’Al203 eutectic, Dalfratex can safely be used in conjunction with silica
refractories in coke ovens, glass melt tanks etc.
Dalfratex products are not recommended for use in contact with bases such as sodium and calcium hydroxides or substances giving the reaction of these, e.g. sodium silicate.

This data set out in this publication are for information purposes only and their accuracy is not warranted or guaranteed. These particulars do not constitute an offer or any part of an offer.

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