Modification of alkaline earth silicate fibres

The application is a divisional application and claims the benefit of U.S. application Ser. No. 11/263,655 filed Oct. 31, 2005, which claims the benefit of priority from applicants\' provisional application 60/717,516 filed Sep. 15, 2005 now expired and British patent applications GB 0424190.7 filed Nov. 1, 2004 and GB 0502701.6 filed Feb. 9, 2005, all of which are relied on and incorporated herein by reference.

This invention relates to alkaline earth silicate fibres.

Inorganic fibrous materials are well known and widely used for many purposes (e.g. as thermal or acoustic insulation in bulk, mat, or blanket form, as vacuum formed shapes, as vacuum formed boards and papers, and as ropes, yarns or textiles; as a reinforcing fibre for building materials; as a constituent of brake blocks for vehicles). In most of these applications the properties for which inorganic fibrous materials are used require resistance to heat, and often resistance to aggressive chemical environments.

Inorganic fibrous materials can be either glassy or crystalline. Asbestos is an inorganic fibrous material one form of which has been strongly implicated in respiratory disease.

It is still not clear what the causative mechanism is that relates some asbestos with disease but some researchers believe that the mechanism is mechanical and size related. Asbestos of a critical size can pierce cells in the body and so, through long and repeated cell injury, have a bad effect on health. Whether this mechanism is true or not regulatory agencies have indicated a desire to categorise any inorganic fibre product that has a respiratory fraction as hazardous, regardless of whether there is any evidence to support such categorisation. Unfortunately for many of the applications for which inorganic fibres are used, there are no realistic substitutes.

Accordingly there is a demand for inorganic fibres that will pose as little risk as possible (if any) and for which there are objective grounds to believe them safe.

A line of study has proposed that if inorganic fibres were made that were sufficiently soluble in physiological fluids that their residence time in the human body was short; then damage would not occur or at least be minimised. As the risk of asbestos linked disease appears to depend very much on the length of exposure this idea appears reasonable. Asbestos is extremely insoluble.

As intercellular fluid is saline in nature the importance of fibre solubility in saline solution has long been recognised. If fibres are soluble in physiological saline solution then, provided the dissolved components are not toxic, the fibres should be safer than fibres which are not so soluble. Alkaline earth silicate fibres have been proposed for use as saline soluble, non-metallic, amorphous, inorganic oxide, refractory fibrous materials. The invention particularly relates to glassy alkaline earth silicate fibres having silica as their principal constituent.

International Patent Application No. WO87/05007 disclosed that fibres comprising magnesia, silica, calcia and less than 10 wt % alumina are soluble in saline solution. The solubilities of the fibres disclosed were in terms of parts per million of silicon (extracted from the silica containing material of the fibre) present in a saline solution after 5 hours of exposure. WO87/05007 stated that pure materials should be used and gave an upper limit of 2 wt % in aggregate to the impurities that could be present. No mention of alkali metals was made in this patent.

International Patent Application No. WO89/12032 disclosed additional fibres soluble in saline solution and discusses some of the constituents that may be present in such fibres. This disclosed the addition of Na₂O in amounts ranging from 0.28 to 6.84 wt % but gave no indication that the presence of Na₂O had any effect.

European Patent Application No. 0399320 disclosed glass fibres having a high physiological solubility and having 10-20 mol % Na₂O and 0-5 mol % K₂O. Although these fibres were shown to be physiologically soluble their maximum use temperature was not indicated.

Further patent specifications disclosing selection of fibres for their saline solubility include for example European 0412878 and 0459897, French 2662687 and 2662688, PCT WO86/04807, WO90/02713, WO92/09536, WO93/22251, WO94/15883, WO97/16386 and U.S. Pat. No. 5,250,488.

The refractoriness of the fibres disclosed in these various prior art documents varies considerably and for these alkaline earth silicate materials the properties are critically dependent upon composition.

As a generality, it is relatively easy to produce alkaline earth silicate fibres that perform well at low temperatures, since for low temperature use one can provide additives such as boron oxide to ensure good fiberisation and vary the amounts of the components to suit desired material properties. However, as one seeks to raise the refractoriness of alkaline earth silicate fibres, one is forced to reduce the use of additives since in general (albeit with exceptions) the more components are present, the lower the refractoriness.

WO93/15028 disclosed fibres comprising CaO, MgO, SiO₂, and optionally ZrO₂ as principal constituents. Such fibres are frequently known as CMS (calcium magnesium silicate) or CMZS ((calcium magnesium zirconium silicate) fibres. WO93/15028 required that the compositions used should be essentially free of alkali metal oxides. Amounts of up to 0.65 wt % were shown to be acceptable for materials suitable for use as insulation at 1000° C. WO93/15028 also required low levels of Al₂O₃ (<3.97%).

WO94/15883 disclosed a number of such fibres usable as refractory insulation at temperatures of up to 1260° C. or more. As with WO93/15028, this patent required that the alkali metal oxide content should be kept low, but indicated that some alkaline earth silicate fibres could tolerate higher levels of alkali metal oxide than others. However, levels of 0.3% and 0.4% by weight Na₂O were suspected of causing increased shrinkage in materials for use as insulation at 1260° C. The importance of keeping the level of alumina low was stressed is stressed in this document.

WO97/16386 disclosed fibres usable as refractory insulation at temperatures of up to 1260° C. or more. These fibres comprised MgO, SiO₂, and optionally ZrO₂ as principal constituents. These fibres are stated to require substantially no alkali metal oxides other than as trace impurities (present at levels of hundredths of a percent at most calculated as alkali metal oxide). The fibres have a general composition

Continue reading about Modification of alkaline earth silicate fibres...
Full patent description for Modification of alkaline earth silicate fibres

Brief Patent Description - Full Patent Description - Patent Application Claims

Click on the above for other options relating to this Modification of alkaline earth silicate fibres patent application.
###


How KEYWORD MONITOR works... a FREE service from FreshPatents
1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored.
3. Each week you receive an email with patent applications related to your keywords.  
Start now! - Receive info on patent apps like Modification of alkaline earth silicate fibres or other areas of interest.
###


Previous Patent Application:
Manufacture and use of engineered carbide and nitride composites
Next Patent Application:
Binder for whiteware ceramic mixture and method of using same
Industry Class:
Compositions: ceramic

###