GB2108977A

GB2108977A - Water resistant and thermally insulating silicate articles and compositions and method for the production thereof

Info

Publication number: GB2108977A
Application number: GB08219669A
Authority: GB
Inventors: Marin Alexandrov Popov; Todor Georgiev Georgiev; Bogdan Borissov Klisurski; Georgi Georgiev Malinov
Original assignee: KNIPSM ZAVODPROEKT
Current assignee: KNIPSM ZAVODPROEKT
Priority date: 1981-07-07
Filing date: 1982-07-07
Publication date: 1983-05-25
Also published as: IT1189309B; DE3217260A1; FR2509286B1; IT8248765A0; FR2509286A1; GB2108977B; BG34662A1

Abstract

A water resistant and thermally insulating silicate article is produced using a starting mixture having the oxidic composition: from 62 to 68% SiO2; from 1.5 to 5% Al2O3; from 5 to 10% B2O3; from 0.1 to 0.5% CaO+MgO and from 21 to 26% by weight Na2O, all percentages being expressed on a weight basis, and subjecting the mixture to baking at a temperature of 600 to 700 DEG C. The oxidic composition is suitably provided by a mixture of liquid and solid sodium silicate, borax and perlite.

Description

SPECIFICATION Water resistant and thermally insulating silicate articles and compositions and method for the production thereof This invention relates to water resistant and thermally insulating silicate articles and compositions and method for the production thereof.

Bulgarian Authorship Certificate No. 23622 describes porous silicate articles and a method for the production thereof. These articles are formed of a mixture of sodium hydropolysilicate and finely particulate siliceous fillers such as sand chalcedonolite slag, steryl or perlite in a ratio by weight of from 1:1 up to 1:10. To produce the articles, sodium hydropolysilicate is obtained in a preliminary step by heating a mixture of liquid sodium silicate and solid sodium silicate in a weight ratio of from 5:1 up to 1:1 on a water bath and drying the material so obtained at a temperature of 300C to a dry material content of from 45 to 55%. This product is admixed with silicate filler in a weight ratio of from 1:1 up to 1:10, and the mixture is ground in a ball mill to not more than 10% fraction left on a sieve of 900 screen holes/cm2.The material so milled is subjected to granulation after addition of from 7 to 20% by volume water. The granules obtained are placed in metal moulds (usually steel moulds) of different sizes and the granulate is compressed under a pressure of from 0.2 to 0.5 MPa. The moulds are placed in an electric furnace heated to a temperature of 2000C and baked at a temperature of from 550 to 6000C for 2 hours.

Disadvantages of this procedure are that the final product sticks to the metal mould, and indeed the overall procedure for producing the final product is too complicated. A disadvantage of the thermally insulating articles so prepared are their high bulk density and relatively low heat insulating capacity. When no silicate fillers are used with the sodium hydropolysilicate, the articles possess low bulk density (i.e. from 60 to 200 mg/m3) and low thermal conductivity, i.e.

0.05-0.1 W/m. deg., but their water resistance is so poor that they disintegrate when subject to atmospheric moisture.

According to one aspect of this invention, there is provided a composition for use in the production of a waterproof and thermally insulating silicate material having an oxidic composition comprising from 62 to 68% by weight SiO2; from 1.5 to 5% by weight Al2O3; from 5 to 10% by weight B2O from 0.1 to 0.5% by weight in total of CaO and MgO and from 21 to 26% by weight of Na2O.

This composition can be used to produce a water resistant and thermally insulating material, possessing a low bulk density (from 100 to 300 kg/m3) and improved heat insulating capacity (A=0.04--0.01 W/m.deg.) when it has been used to form an article having a compressive strength of from 0.3 to 1 MPa.

According to a second aspect of this invention, there is provided a method for the production of a waterproof and thermally insulating silicate article, which comprises baking a shaped mixture having the oxidic composition of the first aspect of the invention at a temperature of from 600 to 7000 C.

In carrying out the method of the second aspect of this invention, it is preferred to use, as a source of the oxidic composition, a mixture of from 55 to 65% by weight of liquid sodium silicate having a modulus in the range of from 2.5 to 3.2; from 11 to 22% by weight of solid, particulate sodium silicate; from 7.4 to 14% by weight borax and from 6 to 17% by weight perlite. Green perlite as well as the residual fine fraction obtained when swelling perlite can both be used in the composition of this invention.

When producing shaped articles by the method of this invention, using the preferred starting mixture, in a preferred procedure, the liquid sodium silicate may be placed in a vessel provided with a stirrer of variable speed and is heated on a water bath. Milled solid sodium silicate is added thereto. After heating the mixture to a temperature of about 700C, a boiling 30% by weight solution of borax is added while stirring the mixture at high speed. A homogeneous mixture is produced to which the perlite is added.

The mixture is then heated to a temperature of about 950C after which it is poured onto a polyethylene foil and is cooled to ambient temperature. The homogeneous mixture is then placed in a metal mould previously lubricated with superphosphate and preheated and heated therein to a temperature of 600-7000C in a furnace. Owing to the high temperature, the mixture expands and fills up the metal mould. The heating may last for from 1 to 4 hours, depending on the size of the articles being produced. Then, the mould with the shaped article therein is cooled slowly to ambient temperature and the article is removed. The process of baking can also be accomplished in a conveyor type furnace, with the material to be heated being provided as a continuous strip which when the baking is completed is cut to size.

As will be appreciated from the foregoing, the present invention offers the following advantages: The raw materials are easily available nonmanufactured substances; the overall procedure for producing the shaped articles is simple; the thermally insulating material is prepared at a relatively low temperature, but still possesses properties similar to those of foamed glass; the thermally insulating material is water resistant, fire proof and rot proof and can be employed at temperatures of from -500C to 5500C.

The following Examples illustrate this invention: Example 1 A mixture was prepared consisting of: 64.4% by weight of a 32% by weight solution of sodium silicate having a modulus of 2.96 21.4% by weight of solid sodium silicate 7.7% by weight of borax; and 6.5% by weight of swelled perlite (residual fine fraction).

The mixture obtained was baked at a temperature of 6500C. The article so prepared possessed a bulk density of 200 kg/m3; compressive strength of 0.4 MPa and a coefficient of thermal conductivity A=0.06 W/m.deg.

Example 2 A mixture was prepared consisting of: 64% by weight of a 33% by weight solution of sodium silicate having a modulus of 2.9 1 19/0 by weight of milled solid sodium silicate 8% by weight of borax 17% by weight of swelled perlite (residual fine fraction).

The mixture was baked at a temperature of 6500C. The articles produced possessed a bulk density of 300 kg/m3; compressive strength of 1 MPa and a coefficient of thermal conductivity A=0.08 W/m.deg.

Example 3 A mixture was prepared consisting of: 60% by weight of a 30% by weight solution of sodium silicate having a modulus of 3 20% by weight of milled solid sodium silicate 14% by weight of borax 6% by weight of swelled perlite (residual fine fraction) The mixture was baked at a temperature of 6500C. The articles produced possessed a bulk density of 1 80 kg/m3; compressive strength of 0.5 MPa and a coefficient of thermal conductivity A=0.05 W/m.deg.

Example 4 A mixture was prepared consisting of: 57% by weight of a 30% by weight solution of sodium silicate 19% by weight of milled solid sodium silicate 7.7% by weight of green perlite (milled) 13.3% by weight of borax 3% by weight of swelled perlite (residual fine fraction) The mixture was baked at a temperature of 6800 C. The articles produced possessed a bulk density of 1 50 kg/m3 and a compressive strength of 0.3 MPa. The coefficient of thermal conductivity A=0.06 W/m.deg.

Example 5 A mixture was prepared consisting of: 61.7% by weight of a 35% by weight solution of sodium silicate having a modulus of 2.8 20.6% by weight of solid sodium silicate (milled) 7.4% by weight of borax 10.3% by weight of milled green perlite The mixture was baked at a temperature of 6000C. The articles produced possessed a bulk density of 240 kg/m3, a compressive strength of 0.6 MPa and a coefficient of thermal conductivity A=0.07 W/m.deg.

The water resistance of the articles prepared by the procedures of the foregoing Examples 1 to 5 was tested by boiling the articles in water having a temperature 100-1 050C for a time of 42 hours. After the completion of the test the test samples possessed the same dimensions as initially. No surface cracks and no volume changes were observed after the test and the hardness of the porous silicate structure was preserved. In contrast, test samples, prepared using the sample composition No. 5 disclosed in Bulgarian Authorship Certification No. 23622 and tested under the same conditions, underwent disintegration when in boiling water for a period of 10 to 30 min. yielding pieces of gel composition. This is believed to be evidence that during the respective heat treatments, the presence of perlite (both green and baked one) and of borax in the indicated amounts, promote the progress of favourable chemical reactions which take place after the completion of the expansion process and result in the formation of a waterproof, finely porous silicate structure.

Claims

1. A composition for use in the production of a waterproof and thermally insulating silicate material having an oxidic composition comprising from 62 to 68% by weight SiO2; from 1.5 to 5% by weight Al2O3; from 5 to 10% by weight B203; from 0.1 to 0.5% by weight in total of CaO and MgO and from 21 to 26% by weight of Na2O.

2. A composition as claimed in claim 1, wherein the oxidic composition is provided by a mixture of from 55 to 65% by weight liquid sodium silicate having a modulus of from 2.5 to

3.5; from 11 to 22% by weight of solid sodium silicate; from 7.4 to 14% by weight of borax and 6 to 17% by weight of perlite.

3. A composition as claimed in claim 2, wherein the perlite is green perlite or the residual fine fraction obtained when swelling perlite.

4. A composition for use in the production of a waterproof and thermally insulating material substantially as described in any one of the foregoing Examples 1 to 5.

5. A method for the production of a water proof and thermally insulating silicate article which comprises baking a shaped mixture having the oxidic composition set out in claim 1 at a temperature of from 600 to 7000 C.

6. A method as claimed in claim 5, wherein there is used a composition as set forth in claim 2 which is first heated to a dry matter content of from 55 to 60% by weight.

7. A method as claimed in claim 5 or 6, wherein the mixture is baked in a metal mould which has been preheated and lubricated with superphosphate.

8. A method for the production of a waterproof and thermally insulating article substantially as described in any one of the foregoing Examples 1 to 5.

9. A waterproof and thermally insulating article which has a bulk density of from 100 to 300 kg/m3, a heat insulating capacity, A of 0.04 to 0.1 W/m.deg. and a compressive strength of from 0.3 to 1 MPa, which article has been produced from a composition as claimed in anyone of claims 1 to 3.

9. A waterproof and thermally insulating composition whenever produced by the process claimed in any one of claims 5 to 8.

Superseded Claims 1-9 New or Amended Claims

1. A composition for use in the production of a waterproof and thermally insulating silicate material having an oxidic composition comprising from 62 to 68% by weight SiO2; from 1.5 to 5% by weight Al2O3; from 5 to 10% by weight B203; from 0.1 to 5% by weight in total of CaO and MgO and from 21 to 26% by weight of No 20, which oxidic composition is provided by a mixture of from 55 to 65% by weight liquid sodium silicate having a modulus of from 2.5 to 3.5; from 11 to 22% by weight of solid sodium silicate; from 7.4 to 14% by weight of borax and 6 to 17% by weight of perlite.

2. A composition as claimed in claim 1, wherein the perlite is green perlite or the residual fine fraction obtained when swelling perlite.

3. A composition for use in the production of a waterproof and thermally insulating material substantially as described in any one of the foregoing Examples 1 to 5.

4. A method for the production of a waterproof and thermally insulating silicate article which comprises baking a shaped mass formed from the composition claimed in any one of claims 1 to 2, at a temperature of from 600 to 700"C.

5. A method as claimed in claim 4, wherein the said composition is first heated to a dry matter content of from 55 to 60% by weight prior to undergoing shaping.

6. A method as claimed in claim 4 or 5, wherein the said composition is baked in a metal mould which has been preheated and lubricated with superphosphate.

7. A method for the production of a waterproof and thermally insulating article substantially as described in any one of the foregoing Examples 1 to 5.

8. A waterproof and thermally insulating article whenever produced by the process claimed in any one of claims 4 to 7.