US1578813A - Composite insulating bodies and method of producing them - Google Patents

Description

ice. COMPOSITIONS,

COATING OR PLASTIC.

Patented Mar. 30, 1926.

UNITED STATES Exam? PATENT OFFICE.

CHESTER L. DAWES AND WILLIS A. BOUGHTON, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNORS TO NEW ENGLAND MICA COMPANY, OF WALTHAM, MASSACHUSETTS,

A CORPORATION OF MASSACHUSETTS.

COMZEOSITE INSULATING BODIES AND METHOD OF PRODUCING THEM.

No Drawing.

To all whom it may concern:

Be it known that we, CHESTER L. DAWES and W'ILLIS A. BOUGHTON, citizens of the United States of America, and residents of Cambridge, in the county of Middlesex and State of Massachusetts, have invented new and useful Improvements in Composite Insulating Bodies and-Methods of Producing Them, of which the following is a specification.

Our invention relates to the manufacture of composite insulating plates or other bodies com rising mica flakes or fra ments and a binding mamdheslvely integrates the composite assemblage, and the object of the invention is to produce insulating bodies of this character by utilizing as binding material silicates of the alkali metals either singly or 1 0 s1 ion, an e1 ier with or without mixture with other salts. l/Vhile in some aspects applicable to the production of silicate-bound Inicairaganent insulators capable of service at only moderately high temperatures, our invention has for its main object the production of high-heat and micaflake ins ating bodies, capable of etficient service u pmsintegration temperature of mica such as we have had under observation (about 7 007 50 C.) which sets a maximum temperature limit to insulators comprising m1ca of this variety.

Besides the mica-flake plates bound with an organic material such as shellac, which disintegrates at temperatures considerably below that which mica will endure, micaflake insulators have been produced and used to some extent, in which the flake material is bound with a silicate, such as sodium silicate; but these .have proved d-efectivle Application filed October 26, 1922, Serial No. 597,154.

tegrates, because fluidity of the binder at lower temperatures will be accompanied by mobility of the mica fragments. On the other hand, in order to manufacture an adhesively integrated assemblage of mica fragments, the binder employed must be such as to flow at temperatures below the mica-disintegration point. Thus, in its principal aspect, the means of obtaining a. reconcilia tion between the physical requirements for manufacture on the one hand, and for efliciency in use, on the other, constitutes or characterizes the invention herein described.

The liquefying temperatures of solid or anhydrous alkali-metal silicates, following 5 law of very wide application, become les'. with increase of pressure, usually provided the pressure is not hydrostatic, i. e. equal in all directions. This is true of these silicates whether liquefaction be true fusion, or due to reduction in viscosity of a silicate which retains a small residue of water and may be in a cpndition of colloidal suspension. Thus, Welecting and manipulatingallfi'lLmetal silicates either as single compounds or as mixtures, which under ordinary pressure and at temperatures near to the disintegration point for mica are practically mlid, while they are liquefiable or can be made to flow at or about the same temperature provided increased pressure is applied to them, it is possible to construct a mica-flake insulator, integrated by a silicate binder which at ordinary pressures remains practically solid up to the temperature at which mica disintegrates.

Actual fusion of a silicate involves the expulsion of all water previously retained in association and requires a very elevated temperature. Since they can be made to flow, and thus to manifest all the characteristics of fusion necessary for the practical purposes of manufacture of mica-flake insulators, without expulsion of all water, at more moderate temperatures or pressures than those demanded for true fusion, the alkali metal silicates may in practice be advantageously used in this condition albeit that the water content is reduced to a relatively small percentage.

The simplest constitution of such silicates (represented by Na,SiO,) is seldom realized; the Na O and SiO factors vary widely, and we have found that the silicates of the alkali iielals 1n whichThe silica facEr is hi h (as forii stance a to 1 or 4 to 1 ratio etween SiO and l\a., serve e er or purposes in mg mica-flakes than those in which the If mica flakes of the var-1e y we have employed in our research and a high-silica alkali-metal silicate be assembled in a suitable press (the silicate either in a flowing solution or practically solid at ordinary temperature and pressure, although containing a variable amount of water, and pulverized) and be raised to a temperature, say of 650 WW Y so much water remains in association as is consistent with the temperature condition,

and if pressure be applied'to the assembled materials while maintaining the said tem perature, and be increased, apressure-factor which depends on the temperature actually maintained will resently be developed which represents tie flowing pressure for the given tem erature and the silicate will liquefy and ow, spreading between and over the mica flakes while the whole mass of material becomes condensed by expression of surplus binding silicate if the original quantity was in excess of that required to cover the mica flakes with thin adhesive films. On release of pressure, or subsidence of temperature, or both, the binder solidifies, and a mica-flake plate results which will thereafter retain its integrity in use under any temperatures short of that at which mica itself disintegrates.

Mica-flake plates, comprising silicate binders which, while analogous in composition to those high-silica compounds which require the application of pressure in order to flow at temperatures 'below the disin tegration point of mica, are nevertheless relatively low in silica (by ratio) and capable of flowing at atmospheric pressure at similarly safe temperatures, will be found practically useful in many situations although incapable of retaining practically solid integrity at temperatures approaching that of mica disintegration. In treating the materials for mica-plate manufacture, comprising silicate binders of all the varyingcharacteristics mentioned, these will advantageously be subjected to heat for a period .sufliciently long to allow all except a small residue of watergonfggrtwcape, and then be subjected to press "c l a ,h m all cm serves to give its desired ultimate form and proportions to the micaflake plate and to distribute the binding material over the surfaces of the flakes themselves, and which, in those instances which require pressure to produce a state of flux, serves to render fluid dition. The temperature applied should, in all cases, be substantially higher than that at which water boils; the generation of steam in the silicate binder often causes it to puff up; but if the steam representingvihe water is gradually liberated, there will be left only a smag r idue of water, which is not only harmless under conditions of subsequent use of the mica-flake plate, but also functions usefully in promoting the flow of the binder which is colloidally or chemic ally associated with it? Alkali-metal silicates may be employed either as solutions, or in practically solid and comminuted condition, in the preliminary stages of manufacture of mica-flake plates, or they may be formed in the assemblage of materials by interspersing between the flakes two or more substances which under the conditions of heat, or heat and pressure, react to form the silicate which is ultimately to constitute the binder. instance, a suspension of siliealfiiQ in a solution of alkali hydroxide or carbonate, used as material for preliminary cementation of mica-flakes, drled and heated under pressure will produce a silicate binder. The degree of pressure required to effect flow of the binder-silicate at a safe temperature will depend largely on the silica ratio in the mixture and reaction. A typical illustration of the reaction is:

amon+sio =na siog+n o The s nthetic production of alkali-silicate suitab e for a mica-binder may be effected by heating and compressing admixed alkali salts of suitable nature with silica, by processes very similar to those used in commerce for manufacturing the alkali silicates.

Composite a. alkali metal sz'Zz'cates.Micaflake plates of excellent qualities, such as high electrical resistance high dielectric strength, non-hydroscopicity mechanical strength when cold, resistance to atmospheric conditions, comparative freedom from corrosion or corrosiveness, and relative chemical stability under repeated temperature-fluctuations, are producible by the employment of composite silicates. A mixture otassium silicates, employed manipulated in the manner above described with respect to simple silicates, yields these results. ma with advantage be produced synthetical y by mixing pure potassium hydroxide, or carbonate, with a sodium silicate solution; the me-tathetical reaction which takes place when the mixture is treated by heat, or heat with pressure, is typically represented by:

Na SiO +2KOH:2NaOH+K SiO it being understood that the original quanthe binding material whiclrotmisvwould tity of sodium silicate is in excess, so that rtg aiWy waQi lly, soli l c0n'- there remains after reaction a desired ratio of sodium and as a binder an Such a mixture 106. cdm os'mois; COATING R PLASTIC.

40 will in most cases be resorted to.

of sodium silicate and otassium silicate, not diliicult to apply in manufacturing with free caustic soda. T clatter, however, practice. With unusually powerful preswill of course react with the excess silica in sure apparatus, which may possibly be dethe original silicate to produce an alkali signed, this suggested practical limit of resilicate of somewhat lower silica-alkali ratio. fractoriness to heat may be raised.

Relatively small quantities of salts of the If a binder-substance requires, at atmosalkali metals or alkaline-earth m'g'fils, such plieric pressure, a temperature in excess of as a o en sa s m ra es su a es carbon- 750 C., where mica such as we have had ates OXIC es arsena cs e c., wnci are comunder observation disintegrates, pressure 10 Wfinon-liquefiable when must be applied to make the binding matealone, may be mixed with any of the binding rial flow at safe temperatures below 750 C. materials, represented by the liquefiable If substances are used, as ingredients in salts of the alkali or alkaline-earth bases a composite binding material, which them- (which are characterized by liquefiability or selves are comparatively or actually nonreduced viscosity under various conditions liquefiable or infusible, they should be mixed of temperature and pressure), these fundawith some inorganic salt with which (in tnental binders being used either singly or in solution or liquefaction analogous to fu- 9j'gqombination. alkali metal silicates sion) they will react or dissolve to produce Thus, orates or hos hatm a resultant material which will flow under na"t'1o'n', 'm' lxed with 'fhe relatively hi her pressure, at temperatures consistent with if meltin other salts of the alkali or alkallne the presence of mica. VVater-insoluble salts mm composite binders of may be used either dry and comminuted, or practically any desired liquefiability (with in suspension in water, or in a solution of or a view to temperatures and pressures emsuspension in a soluble binder. ployed) these mixtures with relatively high- Bearing in mind that with some suber melting substances have excellent propstances the temperature of liquefaction or erties of electrical resistance, and are thus flow becomes lower with increase of presadapted to the requirements of insulating sure, while with other substances, infusible plates or other shapespr bodies, and since, at ordinary pressures at a given temperaalsoflthey react with, or become dissolved ture, liquefaction or flow can be produced or su spended in, the predominantflbinder. when sufiicient pressure is applied, it may "material when the application of, heat and safely be stated; that to make a thoroughpres sure produces liquefaction. ly satisfactory high-temperature mica-flake In an case, whether of a simple or complate one should select an inorganic binder posite binder, the manipulation will depend which is effectively adhesive, or becomes so upon the condition in which the material is at an available temperature (which is safe applied. If in solution or suspension, prefor mica) which, at ordinary pressures and liminary drying of the composite assemat the temperature at which the plate is to blage of mica flakes and binding material be used, does not flow, at all events not enough to allow the plate to deform, de-

This is ordinarily done at relatively low compose, or break up, under such use; that temperatures and with pressures only sufone should apply that binder in a disficient to cause the flakes to adhere to one tributed condition to the mica flakes; that another and thus form a plate that holds toone should raise the temperature as closely 'ether and can be handled. After this preto the decomposition point of mica as is liminary drying, the plate is sub'ected to safe, to effect intended and desired chemhigh pressure and temperature. e maxiical or physical changes or both; that one mum limit of temperature is imposed by the should then, or earlier, ap ly sufficient presmica itself, which must not be exposed to a sure to make the binder ow, fill the interdisintegration temperature; the pressure restices, and adhere closely to the mica surquired to produce the requisite liquefaction faces; that one should thereupon, while of the binding material will vary according maintaining the applied pressure, lower the to the liquefaction temperature of the binder temperature to a point where, in spite of at ordinary atmospheric pressure. Tentathe pressure, the binder is in practically a tively, and without more confidence in their solid state; that one should then relax the universal applicability than seems justified pressure and allow the plate to cool.

by the observations and data so far made Examples, which we have found to yield and accumulated by our researches, we sugpracticable binders for high heat micagest the following as guides to the selection flake lates representing several 0 e and manipulation of mica flake binding groups of composite binders hereinabove materials. discussed, are as follows:

If a binding material, at atmospheric Sodium silicate solution (hi 'hl viscous pressure, melts or liquefies at a temperature 7 L cc.; dr sodium carbonate g.; (1" 70- not higher than 800 0., it may be used tassium carbonate Q g.; fused otassiuin liyalone, and be made to flow under pressures droxide, 1.0 g.; water, c

Sodium silicate 72 cc.; )otassium carbonof mica fragments and a silicate of an al- =.W--F- ill ni ra e slum oxide & g.; water 56 cc.

In the foregoing specification, mica-flake 5 plates have been taken as an example of the insulating bodies, the production of which is the object of our invention; micaialges, however, should for the purposes o t specification be taken as an example only, since mica in such comminuted condition as to mgardcd as owdered will respond to treatment with firing materials of the character described. Insulating bodies having shapes or proportions other than those of relatively thin plates are, like true plates, capable of being manufactured by association of {pica fragments and inorganic bind- ,mmmzhtn -z-lfl 'What We claim, and desire to secure by 2 Letters Patent is:

1. An insulating body, mainly consisting g.; magnekali metal containing substantially no water, compressively inte ra-ted.

2. An insulating bod mainly consisting of mica fragments and sodium silicate containing substantially no Water, compressively integrated.

3. An insulating body, mainly consisting of mica fragments and a silicate of an alkali metal high in silica and containing substantially no water, compressively integrated.

4. An insulating body, mainly consisting of mica fragments and sodium silicate high in silica and containing substantially no water, compressively integrated.

Signed by us at Boston, Massachusetts, this nineteenth day of October, 1922.

CHESTER L. DAWES. WILLIS A. BOUGHTON. 7

iii ML"