IE43792B1 - Method for the manufacture of foamed glass - Google Patents

Abstract

The invention relates to a method for the manufacture of foamed glass wherein a powdery mixture of glass material, a blowing agent and water - if necessary after having been moulded - is dried at temperatures from 20 to 600°C and subsequently 5 foamed at 800 to 1000°C.

Description

The invention relates to a method for the manufacture of foamed glass wherein a powdery mixture of glass material, a blowing agent and water - if necessary after having been moulded is dried at temperatures from 20 to 600°C and subsequently foamed at 800 to 1000°C.

A method of this type is known from U.K. Patent Nos. 623,806 and 623,807. In this known method lamp black is used as blowing agent. To produce foamed glass powder layers of 25 mm thickness are first heated to 800°C for 41 hours and subsequently to 875°C for 35 minutes. The heating period of nearly 2 days precludes an economical manufacture of foamed glass.

Austrian Patent 283,179 describes a method for the manufacture of glass-like, coarse moulded bodies wherein a solution of glass fibres or glass powder in water glass is prepared, the solution evaporated and the residue ground to a powder which can subsequently be processed to porous moulded bodies by heating. In this method a very large quantity of energy is required for the evaporation of the water glass solution, which also renders this method uneconomical.

Attempts to manufacture foamed glass according to the method described at the beginning by the combustion of carbonaceous blowing agents without applying the heat control known from the British Patent Specifications result in an inadequate foam structure, in particular in open-celled foams as well as in bubbles of largely varying sizes.

Accordingly it is an aspect of the invention to provide a method for the manufacture of foamed glass which results in a product with closed cells of small size and which is economically feasible. According to the present invention there is provided a method for the manufacture of foamed glass, comprising the steps of: providing a mixture of a finely divided glass material and a bonding agent, the bonding agent being selected from (1) aqueous solutions of the oxygen acids of beryllium, boron, aluminium, silicon, germanium, arsenic, antimony, telluriu· and phosphorus, (2) aqueous solutions of the anhydrides of the said oxygen acids, and (3) aqueous solutions of the salts formed by said oxygen acids and the basic oxides or basic hydroxides of beryllium, boron, aluminium, silicon, germanium, arsenic, antimony, tellurium and the transistion metals having a variable oxidation number; drying the mixture at a temperature from 20 to 600°C to thereby transform the bonding agent into a gel having water bound thereto; and heating the dried mixture to a temperature from 800 to 1000°C t0 thereby melt the mixture and release the bound water from the gel, the released water forming a vaporous cellulating agent which effects the foaming of the molten glass material. 43^98 The bonding agent used in the method of the invention ensures that very finely dispersed water is present in the gel and this water is subsequently able to act as blowing agent. The fine dispersion of the water in the gel results in the desired pore fineness and uniformity of the foamed glass. In this respect, it is of special importance that the water is set free only when the glass changes into the melted state. This is because the bonding agents are glass formers and during the foaming process in the temperature range from 800 to 1000°C they change into a glass-like state, that is to say they combine with the glass to be foamed and simultaneously release the water in the form of water vapour which acts as blowing agent.

It should be noted that the structure of the bonding agent does not impede the foaming process because, due to the transition of the bonding agent into the glass-like state, the bonding agent structure disappears.

The invention allows the production of very solid moulded bodies in the green state (initial state) which can be foamed without using additional moulds. The continuous application of the method is also possible.

Generally, the weight ratio of glass to bonding agent is 100 : 0.5 to 10.

In the manufacture of foamed glass, the use of the aqueous binder solutions used in the invention has not been contemplated. Obviously, possible applications have not been discovered because glass itself, in the temperature range used for foaming, is generally considered 43?Ο as bonding and fluxing agent and because there seemed to be no use for an additional bonding agent.

The bonding agents to be used in the method of the invention are:(1) Aqueous solutions of the oxygen acids of phosphorus and of the following metalloids; beryllium, boron, aluminium, silicon, germanium, arsenic antimony and tellurium. (2) Aqueous solutions of the anhydrides of the oxygen acids listed in (1) above, and (3) Aqueous solutions of salts formed by the oxygen acids listed in (1) and either (a) the basic oxides or hydroxides of the listed metalloids or (b) the basic oxides or hydroxides of transition metals having a variable oxidation number.

The salts which are contained in this class of bonding agents may, if desired, be produced in situ from compounds which together give the desired salt. An example of forming the salt in situ is shown in Example 1 hereafter.

Preferred examples of oxygen acids for use in the invention are phosphoric acid, boric acid, silicic acid, arsenious acid and antimonious acid. The silicic acid may be in the form of opal, i.e. colloidal silicic acid.

Preferred anhydrides for use in the invention are the anhydrides of the acids of arsenic and antimony.

The bonding agent listed under (3) above may be the salt of a transition metal having a variable oxidation number. Transistion metals which may be used are essentially the transition elements of groups III to VIII of the Periodic Table and preferred examples are manganese, iron, cobalt, and vanadium. The salts which are particularly preferred for use under (3) are phosphates, silicates and borates. 4378s The bonding agent may also include additional components.

For example, a difficulty soluble secondary or tertiary salt of the components of the bonding agent may be added.

It is also possible to use a mixture of an oxygen acid 5 listed under (1) above, or a salt of such an acid and a metal hydroxide, the weight ratio of the acid or salt to the metal hydroxide preferably being from 3:1 to 1:3.

A still further possibility is the use of a transition metal phosphate (component 3a above), in combination with an oxidising agent or reducing agent. Preferred phosphate salts for this purpose are vanadium phosphate and manganese phosphate.

It is decisive for the success of the method according to the invention that, as bonding agent, oxygeh compounds of metalloids are used which have an acid and basic as well as an oxidizing and reducing action, such as the arsenious acid As(0H)3 or its anhydride As203- This compound has the same properties as the various substance combinations which may be used in the method of the invention, for example pyrolusite and phosphoric acid. By comparing arsenious acid and a combination of manganese-(m)-phosphate ahd phosphoric acid, the reactions taking place in the method according to the invention can be explained more clearly.

The arsenious acid is not only able to dissociate as acid but also as base, namely as follows: AsO33'+6H+ = As3++3H20 (I) Analogously, manganese-(III)-phosphate dissociate into phosphoric acid: MnP04 + 2P043- + 9H+ = Mn T + 3H3P04 (2) A corresponding reaction is also MnNaSiO4 + 2NaSiO43 + 9H+ = Mn3+ + 3H3NaSiO4 (3) An appreciable proportion of As3 + or Mn3+ ions is present in strongly acid solutions only. Otherwise the dissociation equilibrium, to a very high degree, is shifted to the left.

All three cases are characterized by the oxidation state 3 which is important for the bonding agents used in foamed glass manufacture.

At most, the oxidation state 4 could also exist, in particular, if silicic acid is used. The same also applies if, instead of manganese oxide, the oxides of other transition metals, such as dioxides or iron or vanadium, are used and instead of acids in the equations(1) to (3) boric acid is used. Here, the equation (1) may always serve as a model. In this connection, the arsenious acid has the following important properties: 1. It has an oxidizing and reducing action. 2. The lowest oxidation state is the state 3. 3. It acts as aqueous bonding and blowing agent. 4. It is a glass former itself.

. It acts simultaneously as acid and base (equation (1)).

The same properties must be required from all utilizable substance combinations, in particular the latter must dissociate according to the equations (1) to (3). This requirement is, for example, met by the use of manganese ore. Due to the manganese ore content the composition of the introduced glass is clearly changed in a manner which is particularly favourable for the manufacture of foamed glass. Mn02 in the form of glass-maker's soap indeed oxidizes the components carbon, sulphides and iron-(II)-silicates contained in the fused glass mass and converts the last-mentioned compound into the three valent state: 2NaP03 + Mn02 + FeSiO3 = 2(Fe,Mn)P04 + Na2SiO3 When heating in the fused glass mass the oxidation also takes place in the presence of the bonding agents which are mentioned in the equations (1) through (3). This control is necessary in order to prevent devitrification with increasing basicity. The arsenious acid meets this requirement by itself because it possesses all the properties which are necessary for this purpose. Wetting, of the batch with a 16.6? H3P04 solution may also be a measure for the control of the reaction.

The use of various types of bonding agent in accordance with the invention will now be considered.

When a silicate is used as bonding agent in combination with manganese oxide the ratio of manganese oxide in the oxidation state 3 to Si02 is preferably 1:3 and in the oxidation state 4 preferably 1:4. Practically, however, the ratio 1:3 is always to be used because Mn02 is always reduced to Mn20.

It is also possible to have free manganese ions in the oxidation state 2 which may be obtained by the reaction Mn3(p04)2 + 4P043‘ + 18H+ = 3Mn2+ + 6H3p04 It is also possible to envisage the reduction of manganese to the oxidation state 0, i.e. down to metallic manganese. This is to a certain degree accompanied by a devitrification which in some cases is desired. In general, the use of tertiary phosphates, for example Ca3(po4)2 or Mg3(p04)2 pr Mn3(p04)2 as well as the reaction product from talcum and phosphoric acid, results in devitrifications, turbidity and, in the presence of sulphur in any form, in sulphides. Due to inadequate oxidation, sulphides which are already present in glasses are not elimifiaced Foaming is thereby reduced the weight per unit volume of the foamed glass is increased and the violet colour of the glass disappears due to three valent manganese. Consequently, this variant of the method according to the invention is of importance in cases where foamed glass with a relatively high weight per unit volume is desired. A particular advantage of this glass consists in that the sensitivity to temperature changes decreases.

In general, it can be stated with respect to the action of the bonding agent according to the invention that very small bubbles are generated the diameter of which, in most cases, is far below 0.5 mm, while the weights per unit volume are in the order of 0.5 through 1.5 g/cm . These bodies show a considerably higher resistance to thermal shocks than normal foamed glass bodies.

As has already been mentioned, opal may be used as the bonding agent. Opal is an amorphous mineral of the class AB2.nH2O in the crystallochemical mineral system, wherein A and B are each different atoms and n is an integer. A mineral of this type can be used as, or as a compound which reacts to give, the bonding agent, the mineral being used in an amount up to approximately 25% by weight related to the total weight of the mixture.

It has been found that the use of these minerals, which belong to the first order of the group II in the crystallochemical mineral system, give foamed glass bodies with a pore size of approximately 1.5 mm without the need to pay special attention to the heat supply control. In fact the mixture containing the powdery glass and the mineral can very rapidly be heated to the fusing temperature which is in the order of 850 to 950°C when using powdery silicate glass. The residence time at this temperature may approximately be 15 minutes. Subsequently, very rapid cooling down to approximately 500°C may follow again, whereupon a slower expansion cooling down to approximately 200°C, . which is generally necessary in the manufacture of glass, must follow. The foamed glass bodies can then be removed from the heating furnace and cooled in the open air.

The excellent action of these amorphous minerals is due to the fact that they give-off their combined water only after the glass has melted so that the subsequently generated water vapour is sufficient for foaming. Since the water is completely given off and immediately converted to vapour, the foaming process is completed 43793 within a short time so that the heating period and a heat gradient in the glass body during the cooling down do not affect the foaming process and the cell formation. The fine-pored structure may be attributable to the fact that the amorphous material is not only particularly finely distributed but also that the mineral dissolved in the fused glass mass so that an almost molecular distribution is achieved.

Amorphous, aqueous minerals of the class stated are available in nature mainly in the form of opal and minerals containing pre10 dominantly manganese oxide.. A synthetic mineral of this type is precipitated, amorphous, water-rich silicic acid. Consequently, this compound corresponds to opal which is aged, colloidal silicic acid.

Minerals containing mainly manganese oxide exist in various forms. MnWQg.nHgO is generally called wad. In addition to manganese, wad may also contain barium, aluminium, lead, nickel, . lithium and /tungsten. Wad rich in copper is also called cupreous manganese ore, - wad rich in cobalt is. called asbolan, ferrous wad is called . reissacherit,. wad rich in barium is' called psilomelan. A..foam particularly suited for the invention is manganese black which, in . addition to manganese oxide, also contains silicon: oxide -and iron oxide. -, - -- For the manufacture of foamed glass with the weight; per unit volume of 150 kg/m3 relatively small quantities of the minerals are required.

If manganese black is used, additions of 0.2 to 2.5% by weight are sufficient. The quantities of the additions in themselves may be increased provided that they do not excessively increase the fusing temperature of the silicate glass. If opal is used, an amount of approximately 5% by weight is preferable. The amount of mineral used may however be up to 25% by weight, provided that a silicate glass with a low fusing temperature is used as the glass material. Additives, such as basalt powder, boric acid, etc., may be added to the silicate glass to adjust the fusion point. Phosphates may also be added as they help to produce small-sized cells.

When a phosphate and a salt formed from phosphoric acid and a metal oxide or metal hydroxide base of which the basicity decreases with increasing valency, is used as bonding agent in combination with an oxidizing or reducing agent, the bonding agents not only allow the manufacture of moulded bodies by a continuous process but also give a particularly fine distribution of the blowing agent.

This fine distribution is due to the formation of complex compounds and furthermore the water is strongly combined in the mixture up to the relatively high temperatures at which the glass is molten. Moreover the metal oxides used for the manufacture of the phosphates release oxygen which, not only immediately serves as blowing agent but also oxidizes impurities in the glass, whereby on the one hand, the glass is clarified and, on the other hand, further gaseous compounds, such as sulphur dioxide, are generated which act as blowing agents.

By the use of these bonding agents it is possible to manufacture very fine-pored uniform foamed glass bodies with a density of less than 0.2 g/cm3.

Phosphates which are particularly suited for the method of the invention are manganese, and zinc phosphates. Among these phosphates, manganese phosphates are particularly suitable because Mn02 which is used for its manufacture is available in large quantities at low costs. The use of vanadium phosphates can also be advantageous because VgOg present in the phosphate additionally contributes to a reduction of the surface tension of the fused glass mass. This favours foaming of the glass.

Owing to their good solubility, sodium phosphates are also particularly suited for use in the bonding agents, sodium metaphosphate being particularly preferred.

When a secondary or tertiary phosphate and an oxidising agent are used in the bonding agent, the oxidizing agent converts these salts to phosphoric acid and metal oxides. It is therefore possible to introduce a secondary and/or tertiary manganese-(II)phosphates and, for example, H202 as oxidizing agent into the mixture so that during the setting of the mixture primary manganese phosphates possibly together with phosphoric acid and manganese dioxide are obtained which immediately form complexes. The formation of pyrophosphates is also possible. For this purpose an alkali can also be added to the mixture to ensure that phosphoric acid generated by the oxidation of the metal to the metal oxide is transformed into soluble phosphates which are suitable as bonding agents.

If an alkali monophosphate is used in the method of the invention then thermal dehydration occurs during the drying of the mixture and high-molecular polyphosphates are formed. If, for example, NaHgPO^ is admixed with a powder of ordinary glass; (glass waste of window panes, bottle glass, etc.) and the mixture subjected to a thermal dehydration there is no difference over the dehydration of pure NaHgPO^ in the free atmosphere. Without side reactions with the glass occurring, a high-molecular polyphosphate is obtained which dissolves in ordinary glass with increasing temperatures. The water given off during the condensation of the primary sodium phosphate in the foamed glass bath causes very fine bubbles to be formed in the fused glass mass. The polyphosphate does not crystallise out after annealing for a long period.

The Graham's salt obtained by the condensation of NaHgPO^ combined with polyvalent ions and therefore the use of NaH2P04 + Mn02 in the bonding agent gives a polyphosphate having combined manganese ions the chain length of which depends on the temperature and water vapour pressure of the fused mass. In fact, admixed metal oxides, for example Mn02, are easily dissolved to complex polyphosphates which are extremely stable so that, for example, a tertiary phosphate cannot be precipitated with any precipitant. The polyphosphate solidifies to a glassy mass.

The condensation product from NaH2PO4 + Mn02 + 4H2SiO3 is particularly useful in the method of the invention, since it gives !0 off its residual quantity of water for foaming only at 840°C, i.e. at a foaming temperature which is favourable for the usual batch, and gives a uniform foaming process.

For these embodiments the use of amphorous aqueous wad MnO2 . xH20 together with silica gel SiO2 . xH20 is very appropriate.

The mixture of glass and bonding agent used for producing the foamed glass is preferably ground, prior to heating, so as to have a surface area of at least 1 m /g.

During the implementation of the method according to the invention the molecules of the bonding agent, already considerably below the reaction temperature proper, in the so-called cover period, cover the surface F of the glass powder with a monomolecular layer. From this a measure for the quantity y in grammes of the bonding agent to be introduced per 100 g of the powdery mixture is obtained, namely: 100 M y =-. 2F (4) fm where M is the molecular weight of the bonding agent, F^ the area of monomolecular layer, which is to be covered by the quantity y and F the BET area of the powdery mixture.

Now, if the temperature is increased the absorbed components react with the absorbent with the formation of surface compounds.

Summarily, the energetic peculiarity of surfaces is covered by the concept of the surface energy σ i.e. the mechanical energy stored in the surface which is larger in the finely divided on state of the substance than in the compact state and which consequently is able to create additional new surfaces during the foaming process. In this connection the only fact that matters is the summary determination of the energetic peculiarities of the 43782 p surface of the finely divided glass, measured in m /g, i.e. it is not the size of the individual particles that matters but the total surface. This allows the manufacture from glass powder with a BET area 0.5 m /g a mixture with a large mean surface energy by adding a small quantity in a particularly finely divided condition, p for example with the BET area of 10 m /g. By covering the total surface of the mixture with a mohomolecular layer of the bonding agent and increasing the temperature to the fusing and foaming point, there is the possibility of creating a number of new surfaces corresponding to the higher surface energy, i.e. foaming at a higher temperature. A larger quantity of the bonding agent than required for a monomolecuTar covering of the surface results in an additional increase of the surface of the films i.e. the undesired larges bubbles or cells of the foamed glass.

The equation (4) therefore specifies the-maximum bonding agent quantity in g per 100 g of the starting material with a BET area F which is required in cases where a thin and hard supporting layer is simultaneously to be generated on the surface of the moulded bodies.

This layer obviously develops as a result of an enrichment of the bonding agent on the surface of the moulded body from wetted masses during the drying process. The production of a hard layer is for example of considerable practical technical importance in the flat roof construction.

Instead of the addition of a small quantity of glass powder in a particularly finely divided state, i.e. instead of the mechanical method for the production of starting products with a high BET area less expensive chemical methods can be used. For example, when a 43793 silicate is used as a bonding agent, the silicate may be mixed with the glass material and water, and the soluble components may be precipitated to increase the surface area of the mixture. Methods of this type are described in the Examples 6 and 7. The covering consists of condensed surface films having a considerable cohesion. According to known relations the surface pressure of condensated films is equal to the reduction of the surface tension.

It is also possible to increase the BET area of the starting substance by adding approximately 1% by weight of a lamellar mineral (e.g. mica) which forms an aggregate of two dimensional crystals when heated at 600 - 800°C.

The moist mixture prepared with the bonding agents are easily mouldable and hardenable after moulding by heating to approximately 200°C. The hardening is of special importance because, during this process, a firm layer forms on the surface of the moulded body, preventing the penetration of gas, which later on, during the foaming process, favours the expansion in the vertical direction. However, special advantages of the hardening consist in the easy handling of the hardened plates owing to high green strength and in the saving of moulding boxes.

This results in the following continuous process sequence: mixing and grinding of the batch to the fineness predetermined by the bonding agent quantity, with wetting of the mass, filling of the mass into the receiver of an extruder the outlet openings of which determine the shape and cross-section of the emerging endless strand which then is successively passed through drying, foaming and expanding ovens without 43782 interruption. As is known in the powder process, prior to the foaming, the powders sinter to sintered plates which are liable to burst into pieces. This is not the case in the method according to the invention. The hardened ribbon remains intact at the sinter temperature.

The same mixtures can also be processed in the dry condition according to the powder process by producing them by means of dry mixing and dry grinding. As a function of the surface of the ground material they contain the same bonding agent quantities as in the case of the wet process in the dry form.

The invention will be further described, by way of example only, with reference to the following Examples.

Example 1 100 g glass powder with additions of 6.12 g sodium metaphosphate i (NaP03)6, 0.36 g soot and 0.135 g iron sulphate FeSO^HgO are ground in the ball mill to a fineness of 1 m /g and mixed with sufficient water to yield a workable mass. From this mass a plate is formed which is dried and hardened at 200°C. The quantity of 6.12 g sodium hexametaphosphate has been calculated according’to the equation (1). The solid plate is heated to foam at approximately 880°C and kept at this temperature for 15 to 30 minutes. Subsequently follows cooling down to approximately 500°C in the air and further slow cooling down for expansion in the expansion oven. 43793 Example 2 A mixture of 80 g glass powder and 20 g basalt powder with addition of 8.26 g (NaP03)g, 1.2 g SiC (particle size 3 urn) and 0.135 g FeS04.2H20 is ground in the ball mill to a fineness of 1.35 m /g BET area and further treated as per Example 1.

Example 3 A mixture of 80 g glass powder and 20 g basalt powder with additions of 0.80 g boron phosphate, 4.60 g (NaP03)6> 0.36 g soot, and 0.135 g FeSO^HgO is ground to a fineness of 1.5 m2/g and further treated as per Example 1.

Example 4 Mixtures according to the Examples 1-3 with the corresponding powder fineness are mixed with sufficient water to become easily mouldable. They are filled into the receiver of an extruder, moulded to an endless strand of the desired plate cross-section and, for drying, slowly passed through a continuous heat-treatment oven of 200°C and subsequently through a continuous heat-treatment oven the annealing zone of which is set between 880 to 900°C. The product leaving the oven is cut to respectively desired lengths.

Example 5 Dry mixtures corresponding to the fineness and composition given in the Examples 1-3 are heated to 880°C in metal moulds and cooled down in the expansion oven after a residence time of 15 to 30 minutes. 43793 Example 6 A mixture of 50? ground basalt with a fineness of 0-0.1 mm 20? sodium metasilicate-5-hydrate 5 7.5? H3B03 22.5? water is prepared in the ball mill. During this step, first the watersoluble components are dissolved and by reaction with one another precipitated to very finely divided products with a large surface so ? that on the dried mixing product a surface of approximately 20 m /g can be measured.

The humid mixture is mixed in a kneader with sufficient p glass powder (ordinary glass) with a surface of 0.5 m /g so that a mouldable mass is obtained which is further processed in the same manner as in Example·4. The proportion of glass in the mixture may be optionally increased in the case of further water addition and foaming agents such as SiC with a maximum particle size of 3 pm may be added to the total mixture.

Example 7 2θ The mixing product from the ball mill according to Example 6 can be dried, crushed to flour fineness, treated with foaming agents and heated in a metal mould to 800°C. This results in a finecellular foamed product. The dry product can previously be mixed with an optional quantity of glass powder.

Within the framework of the present invention glass powder is preferably defined as the crushed product from ordinary glass, in particular waste glass which is available in large quantities in the form of waste bottles.

In the Examples 6 and 7 use is made of the fact that, as a function of the mean surface size of the solid components, the required bonding agent quantity is respectively determined according to the relation 100 M y =- .2F FM since by the addition of glass powder, the mean surface size is regularly decreased with a decrease of the bonding agent quantity. ο The figures given on surface sizes are always BET surfaces (m /g).

The activation by lattice disturbances of layer lattices also belongs to the summary determination of the energetic pecularities of surfaces. From this results the possibility of manufacturing powder mixtures with larger mean surface energy by adding activated substances with layer lattices in order to generate a number of new surfaces corresponding to the higher surface energy, i.e. to foam at a higher level when foaming the mixture.

The tests have shown that the effects with additions of ground mica and talcum are very great; additions of 1% are completely sufficient. By heating these minerals to temperatures above 800°C an aggregate of two-dimensional crystals is obtained since by the expelling of the crystal water the coherence of the layers by means of van der Waal's forces is no longer ensured. The minerals are only active in the aforementioned sense if their crystal structure has not previously been destroyed by fine-grinding. The used mineral substances with layer lattice had a particle size of 0.1 mm and more. Moreover, the escaping crystal water increases the quantity of the swelling gases.

Example 8 A mixture of 85% glass powder and 15% ground basalt is treated with respectively 1 g boron phosphate, silicon carbide and talcum. Silicon carbide has a particle size from 0 to 1 pm, talcum had particles sizes 50% of which were above 0.1 mm. The foamed glass manufactured from this mixture in the powder process had a weight per unit volume of 0.15 g/cm .

The mixture was ground in the ball mill to a BET surface of 1 m2/g.

Example 9 First, 98.00 g glass powder with a fineness or surface of 0.5 cm2/g, 2.00g basalt powder, 2.30 g (NaP03)x, 9.20 g Na-trisilicate with a water content of 20% and 1.20 g sodium metasilicate-5-hydrate are mixed in dry condition.

Subsequently the mixture is wetted with 20 g water and finally dried at approximately 200°C. Drying after previous wetting is necessary for the combination of the water required for foaming at 840°C. Subsequently the solid mass was finely ground while adding 4.00 g manganese ore (FUS 788 - 100 of Messrs. Frank & Schulte, Essen).

The processes of dehydration, condensation and fusion taking place when the abovementioned minerals are used are the same if the phosphates are mixed with powder of ordinary glass, the polyphosphates being dissolved in the glass when the basic glass is in the fusible state. The foaming reaction, protected from the atmosphere, takes place in a monomolecular envelope from polyphosphate glass.

In contrast to this tertiary and secondary phosphate such as Ca3(P04)2 are only difficultly soluble in the glass and are therefore also used as opacifiers in opal glasses. With respect to the production of glass ceramics it would therefore be interesting to eliminate metaphosphates dissolved in the glass from the fused mass by means of a devitrification reaction.

It is not possible to eliminate soluble complex Na3(P04)2 from the fused glass mass in order to render the glass less sensitive to temperature changes by devitrification. However, a phosphate separation can be forced by the addition of talcum if partly pure phosphoric acid is added to the batch instead of NaPOg.

Example 10 A dry mixture of 98.00 g glass powder, 2.00 g ground basalt, 1.15 g NaPO3> 9.20 g sodium trisilicate and 1.20 g sodium metasilicate-5-hydrate is prepared and then successively wetted with g water, dried at 200°C., finally ground under the addition of 4 g manganese ore and 1 g talcum and finally only slightly wetted wtih 5 ml of a 16.6% H3P04 solution.

The reaction of talcum is very complete, i.e. the entire phosphoric acid can thus be precipitated; for this reason only a fraction of the specified talcum quantity is recommended. A quantity of 0.3gtalcum is sufficient. Instead of the phosphoric acid solution refractory binder 32 of the Metal!gesellschaft can also be used after appropriate dilution. 437θ3 Example 11 Of special importance is the relation of the additives to the basic substance glass powder and the quantitative relation of the additives with one another. This in particular applied to the relation phosphate to metal oxide to silicate. Expressed as molar ratio PgOgiMnOgrSiOg it should approximately be 1:2:8. This is substantiated in the following: In the humid mixture the powder surface of the glass is coated with a layer of manganese phosphate if the mixture is prepared in the following manner: 100 g glass powder and 9 g sodium trisilicate are mixed in the dry state, first leaving the phosphate and the metal oxides out, then wetted with 20 g water at the most and finally dried at approximately 200°C. Subsequently, the solid mass is finely ground and finally only slightly wetted with 5 ml of an approximately 20% manganese phosphate solution obtained by dissolving MnOg in phosphoric acid under the addition of H202 as reducing agent. The composition of the manganese phosphate solution is such that the equilibrium 2MnHP04 + H202 = Mn02 + Mn(H.2P04)2 is maintained.

The solution acts as bonding agent by coating the powder surface of the mixture with a layer of manganese phosphate. From the equation the molar ratio P20g : Hn02 = 1:2 is obtained. The properties of the phosphate layer - as is to be expected with topochemical reactions correspond to the properties of the solid starting substance, hence they are depending on the surface state of the glass powder, i.e. the phosphate layer is amorphous and aqueous.

Assuming that an approximately monomolecular layer develops on the powder surface, the addition quantities of Mn02 and P20g can be calculated. The calculation has shown that the required addition quantities are in accordance with the quantities which have been determined as optimal by means of tests.

The above-mentioned preparation of the manganese phosphate solution was based on the reaction 2H3P04 + Mn02 + H202 + Mn(H2P04)2 + 2H20 + 02 For this purpose 7 g manganese dioxide MnO2 have been dissolved in 100 g of a 16.5% H3P04 solution under the addition of HpO2 and subsequently the same quantity of Mn02 has once more been suspended in the solution.

The wetted mixture was slowly heated to a foaming temperature of 840°C in a ceramic mould provided with a dried parting compound consisting of an alumina suspension. The heating time may last 2to 6 hours, the foaming time 15 to 60 minutes and the gradual cooling down 6 hours and more.

In the following some examples are explained in more detail, wherein the solution of the oxygen acid of a metalloid or, more exactly, of its anhydride is exclusively introduced as bonding agent.

Example 12 g glass powder with a fineness at which the glass powder has a surface of 0.5 cm2/g, 3.5 g Sb203 (anhydride of the antimonious acid) and 6.5 g 80% sodium trisilicate are mixed in the dry state, then wetted with 15 g water and finally dried at 43793 approximately 200°C. Subsequently, the solid mass was finely ground and heated to 875¾ for 15 minutes in a ceramic mould. The result was a fine-pored foamed glass body with a weight per unit volume of 0.20 g/cm^.

Example 13 The procedure was the same as in Example 1, however, the ground product was heated to 875°C for a period of 30 minutes in a ceramic mould. The fine-pored foamed glass body obtained in this manner had a weight per unit volume of 0.15 g/cm .

Heating of the ground product over a period of more than minutes will not result in a reduction of the weight per unit volume. However, a further reduction of the weight per unit volume can be achieved by the addition of blowing agents.

Example 14 Prior to the wetting with water 0.3 g soot were added to the mixture according to Example 1. The mass which has been wetted with 15 g water was subsequently dried again at 200°C, subsequently finely ground and heated to 875°C for 30 minutes in a ceramic mould. The result was a fine-pored foamed glass body with a weight 3 per unit volume of 0.10 g/cm .

Example 15 The procedure was the same as in Example 3, however, 0.15 g FeS were added instead of soot. The result again was a fine-pored foamed glass body with a weight per unit volume of 0,10 g/cm.

To increase the weight per unit volume, volcanic glass material or glass-containing basalt can be added to the mixture. 43793 Example 16 Prior to the wetting with water, 15 g of glass-containing basalt were added to the mixture according to Example 1. The material which has been finely ground after drying was heated to 875°C for 30 minutes in a ceramic mould. The fine-poured foaned glass body obtained had a weight per unit volume of 0.20 g/cm3.

Example 17 The procedure was the same as in Example 5, however, 15 g volcanic glass material were introduced instead of 15 g of basalt.

The foamed body obtained again had a weight per unit volume of 0.20 g/cm3 after the finely ground powder has been heated to 875°C for 30 minutes.

Basically, it must be mentioned that in the case of the introduction of larger quantities of basalt or volcanic glass material, the weight per unit volume of the foamed glass can be further increased.

The increase of the weight per unit volume is regularly associated with an increase of the compressive strength. The use of basalt or volcanic glass material has the advantage that these materials are available at lower prices than glass powder.

Conversely, when using additional blowing agents, in particular soot, foamed glass bodies can be obtained the weight per unit volume of which is even below 0.10 g/cm . It is expedient to use as blowing agents soot types, such as cement black, which are known because of their fineness and their wettability by water.

The use of arsenious acid essentially yields the same results as described in the preceding Examples 11 through 16. The hydroxides of ASgOg or SbgOg contained in the wetted mixture are gels with varying water contents which show a similar behaviour as silica acids. However, the hydroxides of arsenic are more water-soluble than the hydroxide of antimony. The bonding agent used in Example 12 which consists of watpr glass and antimony trioxide is particularly advantageous, since, during the drying, the difficulty soluble NaSbOg is formed which contains three molecules of water which are only reluctantly given off. The water is therefore fully available in the foaming process.

In the case of a content of 2 to 3.5% AsgOg or SbgOg carbon, sulphides and iron-(II)-silicates contained in the fused glass mass are oxidized, In case soot or another type of carbon is added as blowing agent, 0.3% carbon are advantageously introduced. A correspondingly adjusted quantity of AsgOg is 2%. The use of arsenious acid or of its anhydride is harmless if the necessary precautions are taken in the processing of this component. However, the foamed glass containing arsenic can be processed without any precautionary measure because, it is completely unpoisonous.

Claims (16)

1. A method for the manufacture of foamed glass comprising the steps of: providing a mixture of a finely divided glass material and a bonding agent, the bonding agent being selected from (1) aqueous solutions of the oxygen acids of beryllium, boron, aluminium, silicon, germanium, arsenic, antimony, tellurium and phosphorous, (2) aqueous solutions of the anhydrides of the said oxygen acids, and (3) aqueous solutions of the salts formed by said oxygen acids and the basic oxides, or basic hydroxides of beryllium, boron, aluminium, silicon, germanium, arsenic, antimony, tellurium and of the transition metals having a variable oxidation number; drying the mixture at a temperature from 20 to 600°C to thereby transform the bonding agent into a gel having water bound thereto; and heating the dried mixture to a temperature from 800 to 1000°C to thereby melt the mixture and release the bound water from the gel, the released water forming a vaporous cellulating agent which effects the foaming of the molten glass material.

2. A method according to Claim 1 wherein the oxygen acids are selected from phosphoric acids, boric acids, silicic acids, arsenious acid and antimonious acid.

3. A method according to Claim 1, wherein the anhydrides are selected from the anhydrides of the acids of arsenic and antimony.

4. A method according to any one of Claims 1 to 3, wherein the basic oxides and hydroxides are selected from the oxides or hydroxides of vanadium, manganese, iron and cobalt.

5. A method according to Claim 4, wherein the bonding agent is a manganese phosphate or a vanadium phosphate.

6. A method according to Claim 1, wherein the bonding agent 5 contains a sodium phosphate.

7. A method according to Claim 6, wherein the sodium phosphate is sodium metaphosphate,

8. A method according to any one of Claims 1 to 7, wherein secondary and/or tertiary manganese phosphates and H 2 0 2 10 are introduced into the mixture.

9. A method according to any one of the preceding claims, wherei an acid oxide of a transition metal or a difficultly soluble secondary or tertiary salt of the components of the bonding agent are additionally introduced into the mixture. 1 5 10. A method according to any one of Claims 1 to 9, wherein an amorphous mineral of the class AB 2 .nH 2 0 of the cristallochemical mineral system, in which A and B are different atoms and n is an integer, is introduced into the mixture as, or as a compound which reacts to form, the bonding agent, the mineral being 20 added in an amount up to 25% by weight related to the total weight of the mixture. 11. A method according to Claim 10, wherein said amorphous mineral is a mineral mainly containing manganese oxide (Mn0 2 ), and is used in an amount of 0.2 to 2.5% by weight. 12. A method as claimed in Claim 11, wherein the mineral containing manganese oxide is manganese black. 13. A method according to Claim 10, wherein the amorphous mineral is opal and is used in an amount of approximately 5% by weight. 5 14. A method as claimed in any one of the preceding claims, where the weight ratio of glass to bonding agent is 100 : 0.5 to 10. 15. A method as claimed in any one of the preceding claims, wherein a mixture of one of said oxygen acids and a metal hydroxide is used as bonding agent and the weight ratio of oxygen acid to metal

10. Hydroxide is from 3:1 to 1:3. 16. A method according to any one of the preceding claims, wherein prior to the heating, the mixture is ground so as to have a BET area of at least 1 m^/g. 17. A method according to any one of the preceding claims,

11. 15 wherein the bonding agents are introduced in an amount Y expressed in g per 100 g of the glass and given by the expression M Y = 100___2 F F H where M is the molecular weight of the bonding agent, F is the BET area of the glass, and F^ is the area of 20 monomolecular layer which is to be covered by the quantity Y.

12. 18. A method according to Claim 1, wherein an alkali metal silicate is mixed with the glass material and water, and soluble components are precipitated with boric acid to increase the surface of the mixture. 43793

13. 19. A method according to any one of the preceding claims, wherein for the increase of the BET area of the starting substances, approximately 1? by weight of a lamellar mineral is added to the mixture, said lamellar minerals forming an aggregate of 5 two-dimensional crystals when being heated in the temperature range from 600 to 800°C.

14. 20. A method according to Claim 19, wherein the lamellar material is mica.

15. 21. A method according to any one of the preceding claims, 10 wherein the mixture of glass and bonding agent is continuously extruded to an endless strand, said strand then being dried and subsequently foamed.

16. 22. A method of producing foamed glass as claimed in Claim 1 and substantially as hereinbefore described in any one of the Examples. 15 23. Foamed glass when produced by the method of any one of Claims 1 to 22.