Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2000-06-09
2003-05-27
Dawson, Robert (Department: 1712)
Compositions: ceramic
Ceramic compositions
Refractory
C252S601000, C252S604000, C252S609000, C252S610000, C428S920000, C428S921000, C501S008000, C501S153000, C501S154000, C524S404000, C524S405000, C524S431000, C524S433000, C524S588000
Reexamination Certificate
active
06569794
ABSTRACT:
The present invention relates to compositions for use as thermal insulation or barriers in articles that are required to function under transient elevated temperature conditions, such as are experienced during a fire. Articles in which compositions according to the invention may be used include electrical and optical cables which have fire resistant properties, electrical fittings such as terminals and cable clips, and void-filling compounds which are required to act as fire barriers.
Various materials are used as thermal barriers in articles that have to withstand, or continue to function at, elevated temperatures, such as, for example, may occur during a fire. Such materials include, for example, certain metal oxides which have been fused to form a ceramic coating and inert minerals which remain in a stable solid state up to temperatures in excess of the highest temperature under which the article is required to perform. For example, magnesium oxide, which remains essentially inert at the temperatures achieved by a normal organic matter fuelled fire, may be used. The magnesium oxide may be contained within a metallic housing.
Polymer materials have been used. Some polymers, such as silicon rubber, are stable at temperatures up to around 300° C. but above these temperatures decompose to form an insulating ash of silicon dioxide which then remains stable to higher temperatures. The silicon dioxide ash is however fragile and may fall away or fracture. Other polymers, such as polyamides, fuse at temperatures around 300-400 ° C. and tend to flow away with a resultant loss of insulation from part of the article where it is required.
In the electrical and building industries, articles may have to comply with the standards laid down by ISO 834 Part I which requires an article to remain functional when subjected to heating according to a specified time/temperature curve. In many cases the performance of materials under such conditions is compromised by the temperatures at which the component materials change state or react chemically. One class of materials that is used in various forms is the aluminosilicates. In general, as the silicate content of aluminosilicates decreases the fusion temperature increases. Pure alumina fuses at approximately 2,050° C. whereas the naturally occurring muscovite form of aluminosilicate fuses at approximately 1,100° C. In most fire situations, the temperature does not reach 1,100° C. and therefore if muscovite forms part of the fire barrier system, it remains in the solid phase throughout the fire. Such a system is prone to mechanical failure because the barrier system is in a non-ductile state during the fire. If the muscovite is in particle form and held in place by other components of the barrier system which lose integrity as the temperature increases, it is liable to fall away. If the muscovite is in sintered form it is liable to be fractured due to movement caused by thermal expansion, mechanical shock and vibration experienced during the fire. Fracturing allows the fire front and hot gaseous products of combustion to penetrate the barrier system. In applications where the composition is used as a void-filling fire barrier, failure may enable combustion to penetrate and spread the fire, for example from one room into the next or from one floor to the next in a building. In electrical applications, failure of the fire barrier is likely to result in loss of electrical integrity.
There is need for a composition having thermal insulating properties, that is ductile or flexible at the elevated temperatures experienced during a fire and retains integrity so as to stay in place throughout the fire enabling it to continue to function as a thermal barrier.
According to the present invention in a first aspect, a composition for use as thermal insulation or barrier in articles that are required to function under transient elevated temperature conditions, comprises at least two components, a first of the two components, at temperatures within a first lower temperature range, being ductile or flexible, but undergoing a physical or chemical change at temperatures above the lower range but below an upper temperature limit required for fire resistance performance, a second of the two components being dispersed within the first component, and the first component being cohesive in the lower temperature range so as to retain the second component and to stay substantially in place, the second component undergoing a physical or chemical change in transition to a second upper temperature range, the second component being ductile or flexible in the upper temperature range, and being cohesive so as to stay substantially in place at temperatures in the upper temperature range, the lower limit of the upper temperature range being below the upper temperature limit for fire resistance performance.
In the compositions, the first and second components are mixed together. In the event of a fire, the first component or the reaction products of the first component are dispersed throughout the second component at the upper temperature range.
The change of state of the first component may be fusion or decomposition. The change of state of the second component may be fusion or decomposition.
The first component may comprise a polymer. In this context the term polymer is used to include the polymer itself and/or reagents that may be reacted together to form a polymer. The polymer may be a silicon rubber. Silicon rubber is stable at temperatures up to approximately 300° C. but above these temperatures it decomposes to form an ash of silicon dioxide. The silicon dioxide ash is fragile and, on its own, would tend to fall away or fracture. Other polymer such as polyamides and polyesters fuse at temperatures around 300-400° and, on their own, would tend to drip away thereby losing insulation from the article.
In the case where the first component is a polymer which fuses at temperatures above the first temperature range, the presence of the second component in the polymer may serve to increase the viscosity of the fused polymer and thereby enable it to stay in place at temperatures above, say 400° C.
The second component may comprise a glass, a mixture of materials which when fused form a glass or a crystalline material. The second component fuses at a temperature below the maximum temperature which the article is required to withstand. The second component may start to fuse at temperatures above the melting or decomposition of the first component. Where the first component is a material that decomposes to a solid phase residue, the residue may be dispersed within the fused second component and serves to increase its viscosity helping it to remain in place as the temperature increases.
The composition may include a third component which remains stable in a solid phase throughout the upper temperature range so as to increase the viscosity of the fused second component. The third component may be included where there is no solid residue as a result of decomposition of the first component or it may be included where there is a solid residue in order to increase the viscosity of the fused second component further.
The third component may be an oxide of aluminum, silicon or magnesium or a combination of such oxides, such as an aluminosilicate. The third component may remain in a solid state at temperatures up to and above the upper temperature limit required for fire resistance performance, for example 1000° C., it may fuse at temperatures below this upper temperature limit but above the lower limit of the upper temperature range. In this way, the third component may form a ductile system which provides cohesion in a second upper temperature range. For example, aluminosilicate may be treated to reduce its fusion temperature to lie within the upper temperature range and below the upper limit at which the composition is required to perform.
As stated above, aluminosilicates have temperatures of fusion lying in the range from 1,100° C. to 2,050° C. We have found that by treating aluminosilicat
Letch Lawrence Stanley
Reid Gregor Joseph
Rickman Hazel Jennifer
Dawson Robert
Draka U.K. Limited
Flynn ,Thiel, Boutell & Tanis, P.C.
Robertson Jeffrey B.
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