CS222675B2 - Method of thermal treatment of glass - Google Patents

Abstract

In a proces for the thermal treatment of glass, the glass is preheated to a predetermined temp. and contacted with a gas-fluidised particulate material. The particulate material comprises a mixt. of several chosen particulate materials, >=1 of which has gas-releasing properties in contact with hot glass. The mixt. of particulate materials is chosen to have the required thermal capacity and fluidity to cause the desired thermal treatment of the glass. The process is esp. useful for hardening flat or curved glass sheets, esp. for car windscreens. The degree of hardening is controlled by the gas developing properties, heat capacity and fluidity of the fluidised particles. The movement of the particles in the vicinity of the hot glass is faster than in the body of the material due to the development of gas, thus improving heat transfer between the hot glass and the fluidised particles.

Description

The invention relates to the heat treatment of glass, in particular to the heat curing of flat glass or bent glass panes, for example glass panes for self-consumption as a vehicle windshield or as part of a laminated windshield of motor vehicles, side lights or rear lights for motor vehicles. vehicles or for use in the construction of windscreen assemblies for aircraft and railway locomotives.

Czechoslovak Patent No. 212 240 describes a method of heat treating glass articles by heating each glass article to a temperature above its lower loading temperature and rapid loading. The glass article is deposited in a gas-fluidized layer of particulate material that is in a uniformly expanded state of particle fluddation by controlling the distribution of the gas in the particulate material at the velocity of gas flow through the particulate material between the clearing initial fluidization and the quenching. Maaimááá exposing the grain material.

This state of fluddation of the layer is such as to induce mixing of the fludooviral granular material on the hot submerged surfaces of the glass when the glass is ejected in the fluidized bed, but asUT transient tensile stresses induced in the surface of the hot glass. Its front first gets in contact with the fluidized bed, they are not so large that Uhr) tilt the glass. Thus, this process has a high yield.

The degree of hardening of the glass sheet which is immersed - in this fluidized bed depends on the heat transfer rate between the fluded grains and the incandescent table, and the rapid transfer of hot particles away from the vicinity of the glass sheet with a concurrent fast supplying cooler particles from the fluidized bed body near the glass sheet.

The movement of the part near the surfaces of the sld-a is more rapid than the movement of the particles in the volume of the layer due to the rapid mixing of the fluidized grains, caused by the heated submerged surfaces of the glass. layer.

The agitation of the granular material at the glass surfaces is greatly increased when a selected granular material is used in which the possibility of gas evolution is concealed so that the gas is rapidly released from the granular material when heated. near the surfaces of the mica.

It has been found that there are three factors which predominate in controlling the thermal curing of glass in a gaseous particulate gas and, in particular, which control the degree of curing of the hot glass sheet when the sheet comes into contact with the grain-containing gas. áattriáltá.

These factors are as follows:

1. the development of gas from the granular aatriary.

2. Thermal capacity per unit volume of granular material at minmmmU fluidization, which is derived from the specific heat of the maatriH measured at 50 ° C and the density of the maatter of the layer measured at the min.

3. The granularity of the granular material, as defined below, is the sum of the four values that are assigned to the malathlu by the four properties of the fluidizable granular mBate-Hlu. The term fluidity, as used herein, has the meaning given above.

These four properties of the granular material material and the method of obtaining the values are described in the article Evaluation of Flow Fluxes of Solids by Rdph L. Caerra Je., Eogioeteiog Volume 72, Number 2, January 16, 1965 and are as follows:

100 (A-A)

1. Compressibility = ------------%,

P where

P = Bulk density in a dense state a

A - loose weight in loose state.

2. Bulk angle: this is the angle in degrees between the horizontal and the slope of the pile of granular material discharged from one point above the horizontal until a constant angle is measured.

3. Flat blade purpose: The flat blade is inserted horizontally into the bottom of the dry granular maaseial mass and lifted straight up and out of the maaseial mass. The average value of u & Lu in degrees to the horizontal on the side of the stack of material on the flat blade is the angle of the flat blade.

4. The particle size distribution (called coeficeene equally in the aforementioned article), which is described in the aforementioned article as a numerical value achieved by dividing the sieve opening width (ie, the sixth size) through 60% of the granular maaterial through the sieve opening only 10% granular material.

All of the particle size distributions reported herein were measured in a manner known per se, using a Coolter computer to determine the particle diameters corresponding to the obtained 40% total weight and 90% corresponding to the 60 mesh apertures through which 60% passed. and only 10% of the grained material.

The numerical values of the compression angle and the angle of the flat blade were measured. using a Hosakawa tester. for powders manufactured by the Hosakawa Labooatory, The Hosakawa Iron Wooka, Osaka, Japan, the powder testing apparatus specifically designed for use in determining the flowability of powders as described above.

The graininess of the granular material is basically dependent on factors such as mean particle size, particle size distribution, and particle shape, sometimes referred to as particle angularity, i.e., whether they have a rounded or angular shape. The fluidity of the hoodiota increases with the growth of the middle veeikossi particle, the narrowing of the veeikossi particle distribution and the reduction of the particle size.

The thermal capacity per unit volume at minimizing fluidization is dependent upon the specific heat of the mattriL and the density of the fluidized bed at minimizing fluidization, and this density increases as the particle size distribution narrows.

The high cured tire is formed in the slurry when the salt is cooled in a fluidized bed having optimum fluidity. Some of the materials that produce the desired curing foam are commercially available. Other commercially available mats may be modified to produce the desired curing stresses through the mat, thereby altering its mean particle size and size distribution.

However, there is a problem that there is a limit to the degree to which it can be controlled by the curing agent induced in the glass by changing the fluidity of the commercially available massagers. Materials with the desired sequence need not be commercially available. Production of a large amount of grain having the desired flowability may involve sieving a large amount of granular material. On the other hand, when one mattrié is used, it is the only way. adjusting the thermal capacity of the fluidized bed to reduce the size distribution. so that there is no way of thermal capaci- tation modification, there is no change in the sequencing that is created by reducing the particle size distribution.

It has now been found that a granular material can be formed having optimal gas-forming properties, heat capacity and flowability to produce the desired curing pressures in the glass article using a mixture of granular materials, each of which contributes to the optimum properties of the composition.

By selecting the granular materials and proportions in which they are mixed, the gas fluidized granular material can be adapted to provide any desired curing stresses within a wide range.

The invention therefore provides a method of heat treating a glass in which the glass is heated to a predetermined temperature, then contacted with a gas-fluidized granular material, wherein the granular material is a mixture of selected granular materials of which at least one is granular. a material having gas-forming properties capable of releasing from 4% to 37% by weight of the gas of its own weight after heating to a constant weight at 800 ° C, wherein the proportions of the individual granular materials of the mixture are selected such that unit of volume at a minimum fluidization ranging from 1.02 to 1.73 MJ · ³ .K · ¹ .

It is advantageous if said granular materials mixed in predetermined proportions which confer fluidity of the mixture in the range 71 to 83 and the thermal capacity per unit volume at minimum fluidisation in the range 1.09 MJ ^"3 .K" ^ 1.38

It is further preferred that the gaseous granular material is gamma-alumina.

It is further preferred that the composition comprises gamma-alumina and alpha-alumina.

It is further preferred that the composition comprises from 7 to 86% by weight of the gamma-alumina and from 14 to 93% by weight of the alpha-alumina.

It is further preferred when the composition contains a gas-generating particulate material and at least one particulate metal oxide whose thermal capacity per unit volume at minimum fluidisation in the range from 1.76 MJ.nT ^ * .K ¹ to 2.01 MJ ^third lT ^1, wherein the mixture has a thermal capacity per unit volume at minimum fluidisation in the range 1.27 MJ.nT ^ * .K ¹ to 1.76 and a flowability in the range 71 to 82 cm.

j

It is further preferred that the particulate metal oxide is spheroidal iron oxide α-FegO 3.

It is further preferred that the composition comprises 30 to 70% by weight of spheroidal iron oxide.

It is further preferred that the composition comprises 70 to 30% by weight of gamma alumina as a gas generating material.

It is further preferred that the composition comprises 28-35% by weight of spheroidal ferric oxide and 45-56% by weight of alpha-alumina, the remainder being gamma-alumina as a gas generating material.

It is further preferred that the particulate metal oxide is zirconium ZrOg.SiOg ·

It is further preferred that the composition comprises from 10 to 70% by weight of Al2 O3 • HgO alumina monohydrate as a gas generating material and from 30 to 90% by weight of zirconium.

It is further preferred that the gas-generating granular material is an aluminosilicate.

It is further preferred that the aluminosilicate is zeolite and the composition comprises from 8 to 10% by weight of zeolite and 90 to 92% by weight of alpha-alumina.

Furthermore, it is advantageous when plymLotvorTým granular material is aluminum monohydrate in ₂ O ₃ .H ₂ O.

Further, it is preferred that the mixture comprises SiC and a gas-forming granular material.

It is further preferred that the mixture comprises 17 wt. % alumina and 33% silicon carbide.

It is further preferred that the gaseous particulate material is alumina trihydrate.

Furthermore, it is preferred that the mixture ob pulls two foam-forming granular materials, Al2 O4H2 O and gamma-alumina in equal proportions.

It is further preferred that the gas-forming granule is sodium hydrogencarbonate NaHCO ₃ .

Finally, it is preferred that the mixture comprises 10% sodium hydroxide and 90% sodium alumina.

These measures of the invention achieve a significant improvement in the thermal curing of the e-glass by contacting the gas with a fludic granular material, since the mixture used in the process of the invention allows better control of the stresses in the glass during thermal curing than can be achieved. of the prior art.

Some embodiments of the examples will now be described with reference to the drawings, in which Fig. 1 schematically shows a vertical section through a device for thermally curing glass sheets. in accordance with the present invention, FIG. 2 is a graph of the mean hot stress versus the proportions of a mixture of granular materials constituting a gas-shed layer indicating changes in the feed rate as these actions change; FIG. 3 is a graph similar to FIG. Fig. 4 is a graph similar to Fig. 3 and shows the variation of the pressure stresses in a glass of thickness.

Fig. 5 is a graph similar to that of Fig. 3 and illustrates the center tensile stress in a 6 mm thick glass; Fig. 6 is a graph similar to Fig. 4 and Fig. 7 is a graph similar to Fig. 3 for 12 mm thick glass; Fig. 8 is a graph similar to Fig. 4 for 12 mm thick glass; and Fig. 7 is a graph similar to Fig. 4 for 12 mm thick glass. Figures 9, 10 and 11 show the change in the central tension in relation to the composition of granular material compositions in three different processes for carrying out the method of the invention.

FIG. 1 shows a vertical curing oven 6 having side walls 2 and a dome J. The side walls 2 and a dome J are made of a conventional bead and a bottom of the furnace has an opening 4 delimited by an aperture in the base plate. J, which has a curing oven j.

The sliding closure, not shown, is adapted to close the mouth 4 in a known manner. The panel to be bent and then thermally excised is suspended in the furnace by pliers 2 which grip the upper edge of the glass panes 6. The pliers 2 hang from a pincer rod 8, which is suspended from a conventional elevator, not shown. and which takes on the vertical guides 2 which run down from the furnace J to guide the shackles and lift the tongs of the rod 8.

The crushing bending tool 60 and 11 is located immediately below the mouth 4 of the furnace 1 in the heating chamber 64. which is maintained at a temperature such that the bending tools 60 are used. 11 have the same temperature as the heat to be burned. The chamber 12 is heated by hot gases guided by the gates. 1_2a. When the bending tools £ 0. The bending tool 10 is a rigid dial mounted on the arm 13 and has a curved front surface that defines the device to be formed on the glazing 6. an annular frame die supported by struts 14 mounted on a back plate 12 * which is mounted on an arm 16. The curvature of the frame die aligns with the curvature of the punch surface.

The guides 2 extend down each side of the bending tools 10, 11 toward the container for the fluidized bed 17 of the granular refractory material in which the glowing curved glass sheet 6 is to be cooled by lowering the sheet 6 down into the layer.

The fluidized bed receptacle 17 comprises an upwardly open rectangular receptacle 18 which is mounted on the lifting platform 12. When the platform 19 is in its raised position, the upper edge of the receptacle 18 is just below the bending tools 10 and 11.

The diaphragm 20, providing a large pressure drop, extends across the base of the tank 18.

The edges of the diaphragm 20 are fixed between the flange 21 on the tank and the flange 22 on the plenum 23 forming the base of the tank. The flanges 21, 22 and the edges of the membrane 20 are screwed together as indicated by reference number 24. chamber 23 and fluidizing air is supplied to the pipeline under controlled high pressure. A high pressure drop of at least 60% across the membrane 20 occurs, resulting in an even distribution of fluidizing air in the granular material at a gas flow rate through the granular material between just suspended in upward air, and at a rate corresponding to the maximum expansion of the granular material at which the dense fluidization phase is maintained.

The expanded layer is substantially in a bubble-free quiescent state of fluidization of particles with a horizontal quiet surface through which the glass sheet 6 enters the layer.

The membrane 20 may comprise a steel plate having a regular hole pattern and multiple layers of thick microporous paper laid on the plate. For example, 15 sheets of paper may be used. The diaphragm 20 is supplemented with a wire mesh screen deposited on layers of paper, such as a stainless steel screen.

The cullet trap may be positioned near the membrane 20 and is designed not to impede the uniform flow of fluidizing gas upward from the membrane 20.

The guides 2 extend down to a position below the bending tools 10, 11 and terminate in the region of the upper edge of the tank. The fixed frame 27 is mounted in the tank 18 and has an upwardly bent foot 28, which engages the lower edge of the glass sheet 6 immersed in the fluidized bed when the tapered rod 8 is lowered under the bending tools 12 * 11 by an elevator.

In order to get the glass sheet 6 into the device, the lifting platform 12 and 8 is lowered by the clamp rod 8 in the lowest position at the bottom of the guides and the glass sheet 6 to be bent and cured is introduced into the pliers 6.

The elevator then lifts the suspended glass sheet 6 into the furnace 1, which is maintained at a temperature of, for example, 850 ° C, so that the glass sheet 6 is rapidly heated to a temperature close to its lower cooling temperature, e.g. When the glass sheet 6 has reached a uniformly desired temperature, the closure closure opening 6 is opened and the hot glass sheet is lowered by lift to a position between the open bending tools 10 and 11. The arms 13 and 16 are actuated and the bending tools 10, 11 are clamped to bend the panel 6 to the desired curvature.

When the pane 6 has the desired curvature, e.g., to allow the pane to be used as a component of a laminated windshield for motor vehicles, the bending tools 10, 11 are opened and the glowing curved pane 6 is rapidly lowered into the fluidized bed. 17 in the tank 18 which has been raised to a cooling position by lifting the lifting platform

19. While the glass sheet 6 has been heated in the furnace 1. The fluidized bed 17 is maintained at a temperature between 30 ° C to 150 ° C by water cooling through a jacket 29 fixed to the flat longitudinal walls of the tank 8.

The fluidized bed 17 is a gas-fluidized particulate material which is a mixture of predetermined proportions of several particulate materials, at least one of which has gas-forming properties and is capable of releasing gas when the fluidic material comes into contact with the hot glass.

A suitable gas-forming granular material is capable of releasing 4.0% to 37% of its own gas mass when heated to a constant weight at 800 ° C. Suitable materials are gamma-alumina γ-Α1 ₂ 0ρ which is porous and contains water adsorbed in their pores; aluminosilicates which are porous and contain water adsorbed in their pores; alumina hydrates such as Al ₂ O ₃ Al ₃ O ₃ trihydrate containing combined crystalline water, and AlgO ₃ H ₂ O monohydrate containing crystalline water, which is porous with water that is also adsorbed in the pores; materials which produce gases other than water, eg sodium bicarbonate NaHCO 3

To produce the desired curing stresses in the glass, the components of the granular material mixture are mixed in predetermined proportions which impart a flowability of from 60 to 86 and a heat capacity per unit volume at a minimum fluidization of from 1.02 to 1.75 MJ. .βγ ·κ · ¹ .

Other components of the mixture that are mixed with the gas-generating granular material are granular materials that are inert in the sense that substantially no gas is released from the material when the material is heated. Examples are alpha-alumina and -Al ₂ 0 ^; zircon ZrOy • Si0 _2; silicon carbide and spherical iron oxide α-FegOy

These granular materials are dense and non-porous and are selected to have a fluidity and heat capacity different from the fluidity and heat capacity of the gas-forming granular material such that, depending on the proportion of dense non-porous material used, they are effective for modifying the fluidity and heat capacity of the mixture to the extent that the required degree of curing stress in the glass is created ·

It is believed that when the hot glass pane cools rapidly in a gas-fluidized layer of the granular material mixture, rapid release and expansion of the gas released from the gas-forming granular material by heating the granular material on glass surfaces will increase local mixing of the granular material mixture on glass surfaces in a manner close to boiling. liquids, resulting in mixed gas and particulate layers flowing over the surfaces of the glass as the glass cools in the fluidized bed.

By mixing the components of the mixture in predetermined proportions, an optimum heat transfer from the glass surfaces to the volume of the layer is achieved, which induces the desired stresses to be introduced into the glass, achieves constant heat dissipation into the more distant parts of the layer. by mixing the fluid granular material immediately surrounding the glass sheet ·

The water-cooled jacket 2J keeps the outermost parts of the layer cool so that they act as heat sinks. Intensive mixing of the granular material on the glass surfaces continues long after the glass has cooled below the lower cooling temperature, ensuring that temperature gradients from the center to the glass surface initially induced in the glass when the glass is in the fluidized bed is maintained when the glass is cooled in the region of the lower cooling temperature, whereupon the desired curing stress is created during continued cooling of the glass while the glass is still immersed in the layer.

The lower edge of the hot glass sheet cools evenly as the lower edge enters the horizontal rest surface of the expanded fluidized bed. Substantially the same tensile stresses are created in different areas of the glass sheet edge surface so that a very low fracture occurs.

During lowering of the lower edge of the glass into the layer, each portion of the lower edge always comes into contact with a fluid material that is in a rest, uniformly expanded state of particle fluidization, and this uniform treatment of the lower edge regardless of the flow of the flowing material. The development of glass surfaces by the development of gas from the gas forming component of the composition largely avoids fracture and the consequent problems of handling glass fragments in the layer, which, together with preventing loss of glass sheets due to glass shape changes and / or surface quality deterioration, desires a commercially advantageous yield.

Some examples of carrying out the invention with selected granular material mixtures are given below. In each example, the numerical value of the product of the particle density in g / cm 2 and the mean particle size in micrometers of each component of the mixture is less than 220. This is a criterion that has proven advantageous to assess whether a particular granular material is suitable for a uniformly expanded state of particle fluidization when air is used at ambient temperature and ambient pressure. The mixture of individual granular materials is then capable of fluidizing in a quiescent, uniformly expanded state of fluidization of the particles.

Example 1

The fluidized bed 11 was formed by a mixture of gamma-alumina as a gas-generating granular material and alpha-alumina.

The gamma-alumina used was a microporous material having pores with a diameter in the range of 2.7 to 4.9 nm and from 20% to 40% of the free porous space. The pores contained adsorbed water, which is released as a gas when the material is heated.

The gamma-alumina used had the following properties:

mean particle size 119 / m particle size distribution 2.34 fluidity 90.25 water content (weight loss at 800 ° C) heat capacity per unit volume at minimum fluidization 4.3 "1.09 MJ ~ ³ · .K

The alpha-alumina used was dense and non-porous and had the following properties:

mean particle size 30 рш particle size distribution 1.22 fluidity 70 heat capacity per unit volume at minimum fluidization (MJ.m ³ .K ¹ ) 1.3

The experiments were performed with mixtures of gamma-alumina and alpha-alumina, which were mixed together in predetermined proportions.

The soda-lime-silica glass sheets of 2.3 mm thickness were cut and their edges treated by rounding with a fine diamond grit disc. Each sheet was heated to 660 ° C in an oven 6 before being bent and cooled in a fluidized bed that was in a resting, evenly expanded state of particle fluidization. Table I summarizes the properties of the various mixtures of these materials in the range of 30% to 90% by weight of alpha-alumina and 70% to 10% by weight of gamma-alumina, as well as the central tensile stress induced in the glass sheets when cooled. By way of comparison, Table I also shows the central tensile stress produced when only alpha-alumina alone and also gamma-alumina are used.

Table I

Percentage in the mixture alpha-alumina 0 30 50 70 90 100 ALIGN! gamma-alumina 100 ALIGN! 70 50 30 10 0 fluidity of the mixture 90.25 81, 5 75 74 72.25 70 heat capacity of the mixture per unit volume at minimum fluidization) 1.09 1.16 1.20 1.24 1, 28 1.3 center tensile stress (MPa) 41 43 49 49 47 32

Giant. 2 shows the variation of the central tensile stress with the composition of the mixture.

The gamma-alumina itself has a fluidity that is too high to create maximum curing stress in the glass sheets, especially due to their large mean particle size and the fact that these particles are relatively smooth, non-angular in shape. The addition of a fraction of alpha-alumina having a lower flowability than gamma-alumina, due to the smaller mean alpha-alumina particle size and the angularity of its individual particles, reduces the flowability of the mixture.

The flowability of the mixture decreases as the amount of alpha-oxide in the mixture increases and there is a proportional increase in the created center tensile stress. A maximum center tensile stress of 49 MPa is achieved when the flowability has been set to an optimum value of 74 and the mixture contains about 70% by weight of alpha-alumina and 30% by weight of gamma-alumina.

Alpha-alumina has a higher heat capacity than gamma-alumina, and as the proportion of alpha-alumina in the mixture increases, the thermal capacity of the mixture gradually increases, contributing to the voltage increase that is achieved.

A further addition of alpha-alumina in excess of 70% by weight increases the heat capacity slightly further and maintains adequate fluidity, but reduces the central tensile stress induced in the glass, since the proportion of the gaseous alumina component has been reduced to a low value.

Example 2

The fluidized bed was formed by a mixture of gamma-alumina as a gas-generating granular material and alpha-alumina.

The gamma-alumina used was a microporous material with a pore size in the range of 2.7-4.9 nm and with 20% to 40% free porous space. The pores contained adsorbed water which was released as a gas when the material was heated.

The gamma-oxiU used had the following properties:

mean particle size 64 цц particle size distribution1.68 fluidity Θ4 water content (loss -homogeneity at 800 ° C) 4% heat capacity per unit volume at linear fluidMi (MJ.m ^-3 . ^ ¹ ) 1,66

The same alpha-alumina as in Example 1 was used.

Experiments were carried out with mixtures of alumina and alpha-alumina, which were mixed in predetermined proportions from 100% gamma-alumina and 0% alpha-alumina to 0% alumina and 100% alpha-alumina.

Table II summarizes the thermal capacities per unit volume of the fluidization and fluidity of the mixtures used.

Table II

Mixture (%) Thermal kapaecta Tetaitost gamma-oxiU alpha-alumina 100 ALIGN! 0 1, 05 84 86 14 1, 09 82.75 61 39 1.15 79 40 60 1, 20 76 22nd 78 ', 25 73.25 7 93 1.29 71 0 100 ALIGN! 1.30 70

Sheets of 2.3 mm thick glass were cut and their cores were trimmed using fine diamond grit discs. The sheet was suspended with pliers J and was heated in the furnace before it was bent and cooled.

The results are shown in Figures 3 and 4. The horizontal line of the kaiUt curve represents the blend of the composition in%. In each of Figures 3 and 4 there are four curves corresponding to the center tensile stress (Fig. 3) and the surface pressure stress (Fig. 3). 4), the inducer in glass sheets of 2.3 mm thickness which have been heated to temperatures of 610, 630, 650 or 670 ° C and then cooled in a fluidized bed which has been maintained in a steady, expanded state of particulate particle fluidization, and at a temperature in the range of 60 to 80 ° C.

The curves show that it was preferable to use about 86% of alpha alumina monooxide mixed with gamma-indium oxide. As the level of alpha-alumina in the mixture increases, the center tensile stress and the surface pressure stress induced in the glass during the thermal curing process increases to the maximum that is achieved when the amount of alpha-alumina is about 70 to -80% by weight. . In general, the highest stress was induced when the alpha-alumina amount was about 55 ° C to 85% by weight. The higher the alpha-alumina content in the mixture causes a reduction in the induced alpha-alumina.

By suitably selecting the proportions of gamma-dioxide and alpha-alumina, the mixture had a gas wave formation, a heat capacity per unit volume at a continuous fluid at 50 ° C, and a fluidity such that remarkably high threefold and thawing values were generated.

For example, when the glass is heated to 670 ° C and then wetted, the desired center tensile stress in the range of 42 MPa to 49 MPa and the corresponding surface pressure stress can be induced. in the range of 83 MPa to 103 MPa in the glass by selecting predetermined proportions of alumina gamma and alpha alumina in the range from 7 to 86% alumina gamma monoxide and from 93 to 14% by weight alpha alumina .

Example _ 3

TabbULe todnová ¹ oeoPn ^t ree ⁰ δitáht sida taouěíce about 6 mm ^b yls h ^ ^h has re refrigerati Ophrah adjusted after being heated and cooled in a fluid bed · in a quiescent uniformly expanded state fuuddace částac consisting of a mixture of the same granular gamg ^ a- Alumina and alumina alpha-oxide as in Example 2.

Giant. 5 and 6 are graphs similar to the graphs of FIGS. 3 and 4, which znászoruuí results obtained for the glass is heated to e ^^ teptáty · 61 ^ 630, ⁶⁵⁰ and ⁶⁷⁰ DEG C., ^and cooled Otom.

The results indicate that the desired curing can be induced in the glass, depending on the proportions of aluminum gamma-oxide and alpha-oxide in the socia. The stresses were obtained when the mixture contained about 65-95% alpha alumina. For example, when the glass was heated to 670 ° C and then cooled in a fluidized bed, 22% by weight of ga? E? And (? 1% of alumina and 78% by weight of alpha-alumina) had a center tensile strength. and a surface pressure of 216 MPa.

This 6 mm thick high strength glass was used to make window assemblies for aircraft and railroads.

Similar results were obtained when the cured sheet ^{stdnovááoenaotř,} emOiitého ska of thickness 10 mm. These glass panes are used in the manufacture of aircraft window assemblies, which may, for example, comprise two 10 mm thick cured glass panes and an external 3 mm thick panes. The tabs are layered together with plastic materials of a known type.

Example 4

Tabule sodnovááoeoPntj ^; The 12 mm thick glass was cut and trimmed, then heated and cooled in a fluidized bed of a mixture of aluminosilicate and alumina in pre-foamed portions in the same manner as in the wall. Example 2. Results were obtained for glass panes heated to 610, 630, 650 and 670 ° C with the subdivisions of gamma alumina and alpha alumina, and the results are shown in the curves in Figures 7 and 8.

Mp values were measured when the fluid mixture contained about 65-85% alpha alumina moles. When the sheet was heated to 670 ° C and cooled in the fluidized bed between 22% alumina and 78% alumina, the center tensile stress in the glass was 124 MPa and the surface pressure opposition was 261 MPa.

Giant. Figures 7 and 8 illustrate how a wide range of three-column voltage values can be induced in the glass, if desired, by selecting the components of the scaled grains and the prills relative to the respective temperature at which the glass looks before cooling.

The results shown in FIGS. 3 to 8, and in common, that higher cure stresses are obtained when increasing the thermal capability (alpha-alumina) component in the mixture according to the point until a greater increase in subsidence decreases the elongation. Olyoteric components (ga ^ e ^ and ^ nit h nit nit nit nit) to an undesirable level.

The proportions of the gas-generating material and the other component or components of the mixture provide a flowability in the range of 60-86, which is such that the nature of the mixing is favorable for cooling the glass to such an extent that the desired glass-strength values are achieved.

The cooling of the glass is due to the rapid mixing of the granular material near the surface of the glass, the mixing being caused by the formation of water vapor from the gamma-alumina in the mixture.

Higher alpha alumina increases the rate of heat removal from the site, as well as modifies the fluidity of the simsi.

Example 5

The fluidic layer was formed by sidOs! .gamma.-alumina as a gas-generating component with the content of spherical iron oxide α-FegO3 and one or two kinds of alpha-alumina.

Aluminum glide has the following ilaientsil:

mean particle size 84 µm particle size distribution 1.94 fluidity

87.25 water content (weight loss at 800 ° C) 6% heat capacity per unit volume at minimum fluidization

1,063

The spherical iron oxide had in fact:

mean particle size particle size distribution fluidity thermal kaaita per unit volume at о1п1о01п1 fluidization pm, 69

76.5

2 ^ 1 MJ. · “ ^3. ^

The first alpha-alumina had the following ^ 1- ^ по £ ^ 1:

mean particle size particle size distribution fluidity pm '25 thermal capacity per unit volume at οΙπΙοΟΙπΙ

1192 MJ. ° ".K ³ · ¹

The 2.3 mm thick glass panes were heated to 660 ° C and cooled in a fluidized bed of the aforementioned particles, which were in the steady-state expanded particle fluidization state.

The Vlaienosia of the blends and the resulting central tensile stresses formed in the glass panes are shown in Table III.

»3

Table III

(1) Mixture concentration (%) (5) (2) (3) (4) clay-aluminum oxide 70 50 30 20 May 16 globular ferric oxide 30 50 70 35 28 aLfa-alumina (1) - - - 45 36 alpha alumina (2) - - - - 20 May fluidity of the mixture 82 79 78 74 73.5 thermal capacity of the mixture per unit volume at оХп1о01пХ fluidmc! MJ. ^m_3 .K ^_1 1,347 1.54 1, 726 1,502 1, 44 central tension tie MPa 45 49 50 57 53.0

Giant. 9 shows the variation of the center-tensile stress with the composition of mixtures (1, 2 and 3) of gamma-aluminum oxide and α-F? GO? In Table III. The central tensile stresses resulting from the swelling of gamma-alumina alone α-α-FegO 3 alone were 41 MPa and respectively. 32 MPa.

As in Example 1, the gamma-alumina that has been attracted in this example has a fluidity that is too high to create a murmur curing stress in the glass sheets. The ferrous iron oxide has a low flowability of non-gamma-alumina, mainly because of the smaller mean particle size. The addition of increasing concentrations of spherical iron oxide to the gammaoxide (III) in the mixtures (1, 2 and 3) of Table III has a gradual effect of reducing the flowability of the mixture by gradually decreasing the average particle size of the mixture as the amount of ferric oxide in the mixture increases.

As the flowability of the mixture decreases, the central tensile stress produced in the glass panes gradually increases. A maximum central tension of 50 MPa is achieved when the mixture contains about 70% spherical iron oxide and 30% gamma-aluminum oxide.

The flowability of the spherical ferric oxide is not as low as that of the alpha-alumina used in Example 1, since the ferric oxide has a larger mean particle size and the particles are smoothly rounded compared to the angular particles of alpha-alumina. Thus, ferric iron oxide is not as effective in reducing the flowability of the composition as the alpha-alumina of Example 1.

The blend (3) of this example, comprising 70% bead of ferric oxide and 30% of gamma alumina, which produces a maximum center tension of 50 MPa, has a flow rate of 78 that is higher than the optimal flow rate of 74% of 70% The alpha-alumina content of 30% and 30% gamma-alumina, which produces a high center tensile voltage in Example 1.

However, the mean tensile stress produced by the mixture (3) in this example is approximately the same as the maximum center tensile stress produced by the mixture of Example 1. This is because the fluidity of the mixture (3) is slightly higher than the optimal fluidity at which For example, the iron oxide used in the mixture (3) has a considerable heat capaci- tate output than the heat capacity of the alpha-oxide used in the first step.

Since it was believed that the flowability of the mixture (3) was too high, a mixture (4) was prepared which contained an alpha-alumina array as used in Example 1. This reduced the flowability of the mixture to about 10%. 74 and the mixture produced a further increase in central tensile stress to 57 MPa despite a decrease in heat capacity.

The composition (4) has the same optimum flowability, i.e. 74, as the composition of Example 1 containing. 30% gamma · alumina and 70% alpha-alumina, which produces a max. Minimum center tension of 49 MPa. The fact that the mixture (4) forms vyěěí central tensile stress of ⁵⁷ .is' caused ^{b y} the ENA EEI ^^ loou Topa ou ^ ⁽⁴ ^ ^{k Ter} is ^{1, 5, 02 M} Jm ~ ³ .K '' in comparison with 1.24 of the mixture of Example 1.

The lowering of the flow resulting from the inclusion of a second alpha-alumina fraction in the mixture (5) was generated by a reduction in thermal capacity. the mixture compared to the mixture (4) with an accompanying small reduction in the central tensile stress.

Example 6

The fluidized bed was composed of a mixture of gas-generating granular carbon monoxide monohydrate of M2O4-Z2O3.Η2Ο and Zr2SiOg.

The monoxide of MoO4 was in the form of boetamate, which is a porous maerial, containing 15% of crystalline water and 13% of water content in its pores. The adsorbed water was released during the glass setting and was particularly effective for. the development of a gas which causes increased agitation of the granular majtrillt near the glass surfaces.

The mono-hydrate of the used oxide < 1 >

mean particle size distribution size, !! particle flowability water content (loss of hmohnonsi at 800 ° C) heat capsule per unit volume at minimum flow rate

5i m »00

28.4%

-1β M ^ .m ^ - ^. K ^-1

Zirconium, which is an inert non-zirconium zirconium having a higher heat capacity than alpha hio (III) oxide, has the following characteristics:

mean particle size 34 jim particle size distribution 1.73 fluidity thermal capacity per unit volume at minimum scaling 67 1 ^, 76 MJ. ^o_3 .K ^ ¹

The 2.3 mm glass sheets were heated to about 660 ° C and cooled in the hemi-hydrate and zirconium monohydrate garments as shown in Table IV, which summarizes the sibOs property. and central tensile apertures 'formed' in the glass sheets.

Table IV

Mono-composition of the mixture monoOh ^r Уrát oxide h.iniéého 100% 70% 50% 20% 10% 0% zircon 0% 30% 50% 80% 90% 100% fluidity of the mixture 78 75.5 74 73. 71 67 heat capacity per unit volume at fluidization rate (MJ ^· m · 3 ^· · · ') 1, 005 1,277 1 .41 1.62 1.70 1.76 center tensile stress 37 42 44 46.5 39 23

Giant. 10 shows the variation of the center pulse tension with the composition of the mixture.

The alumina monohydrate has good gas-forming properties and a lower flowability than the aluminum gamma-oxides listed in Examples 1 and 5. However, the flowability of the alumina mono-hydrate is higher than the optimal flowability that produces a medium tensile stress, and the thermal capacity is relatively low. Zirconium has a lower flowability and higher thermal capacity than the mono-oxide of the oxide and as the zirconium grows as the SiO2 grows, there is a gradual increase in the central tensile stress created in the glass due to both a gradual decrease in the flow and the heat capacity of the mixtures.

Zirconium has a high thermal capacity that significantly contributes to increasing the central tensile stress in the glass sheets in the same way as the spherical iron oxide of Example 5. Since zirconium has a lower flowability than the spherical iron oxide of Example 5, it is more effective in reducing the flow rate. thus, it makes a greater contribution to the increase in the central tensile stress caused by the decrease in the value of the tekutooti blends.

A low tensile stress of 46.5 MPa was tightened when the blend contained about 20% aluminum hydroxide monohydrate and 80% zirconium, the blend having an optimum flowability of 73.

An additional zirconium addition of about 80% by weight increases the thermal capacity of the salt, but results in a reduction in the central tensile stress due to a significant reduction in flowability below the optimum value and a reduction in gaseous component, i.e. % Of aluminum oxide, to a lower effective level.

He said a 7

The fluidized bed consisted of a mixture of alpha-alumina te with the same proportions of each of the four alumina g-cocoxides designated A, B, C and D in Table V, which summarizes the properties of the alumina gaoaaoχirs.

Table V

Gana-oxides of aluminum

AND (B) C D mean particle size (m) 70 61 57 72 particle size distribution 1.47 1.67 1.66 1.65 fluidity 88.5 88 85 86

Gamma-oxides clay continued Table V

AND (B) C D water content (% hmoOnoolic losses at 800 ° C) 7 7 7 7 heat capacity per unit volume at minimum ^ ^f the luidaci ^(MJ .m ^{"3. K)} 1.16 1.16 1'2 1.12

The properties of alpha-alumina were as follows:

mean particle size 22 | particle size distribution 1.69

fluidity heat capacity per unit volume during ainium ^and fluidization

1.24 MJ.rn ^_3 .K

The glass sheets (2.3 mm thick) were heated to 660 ° C and cooled in the gas-fused mixtures of the above-mentioned small particles, which were in the resting, evenly expanded state of the particle foundation.

The properties of the mixtures and the resulting center tensile stresses produced in the glass panes are shown in Table VI.

Table VI

Weight. composition of the mixture a mixture of 4 gamma-alumina 100% 40% 20% 10% 0% alpha-alumina 0% 60% 80% 90% 100% fluidity of the mixture 87 70 67 65 63 heat capacity per unit volume ^P s MiniMini fluiteci (MJ.m ^.K-1) 1.14 1.20 1, 22 1,23 * 1.24 center tensile stress 39 40 35 31 25

Giant. 11 shows the variation of the central tensile stress with the lamella composition.

These examples have shown how higher pressures can be produced by blending a gas-forming granular material with an inert aacerial than can be formed using gas-forming granular material and the cereal itself. However, it may be desirable to produce lower stress values than can be achieved using the gas-forming granular material itself.

In this example, this is achieved by using alpha alumina having a small mean particle size and a relatively broad particle size distribution, resulting in a significantly lower flowability than the alpha alumina used in the previous examples.

The maximum tensile stress that was produced was 40 MPa when using a mixture of 40% alumina aluminum oxide and 60% alpha alumina, which had a flowability of 70. This was slightly higher than the central tensile stress of 39 MPa. formed using gamma alumina alone.

The gradual addition of further alpha-oxide in the garbage rapidly reduces the flowability of the compositions to such low values that the center tensile stress produced in the glass sheets is less than the center tensile stress produced by ingestion of gamma-alumina self-oxides.

Example a d 8

The fluidized bed consisted of a mixture of 9% hmoonnosi zeeoite, which is a porous crystalline aluminum oxide having adsorbed water in its pores, and 91% alpha alumina hmoonnosi. Zeeolt had the following features:

mean particle size 37 / uo particle size distribution 1, 682 fluidity 70

thermal capacity per unit volume at minimum fluidization of 1 ^, 4 MJ.m ^-3 .K “ ¹

Alpha-alumina had the following properties:

mean particle size 37) im layout size, !! of particles 1, 682 fluidity 70 the heat capacity is one unit of volume at minimum fluidization ^{1 3} 4 MJ ~ .K "

Kapaacta heat per unit volume when allowed to fluidize minimáání ^b YLA ¹ 3 ^{4 MJ} .m ^-3 .K ^-1 and fluidity was allowed to 60th

The 2.3 mm glass sheet was heated to 660 ° C and cooled in a fluidized bed, and a central tensile stress of 41 MPa was created in the table. By varying the selected subdivisions of the components, a center tensile stress in the range of 25 MPa to 41 MPa could be generated in the tab.

Example 9

The blend of granular fluidized materials contained 20% by weight of aluminum oxide and 40% by weight of each of the two aluminum oxides which were readily available and used instead of one of the more rare alpha-oxides. oxide

Vllstoooti gaimaoxtdu aluminum were the following:

mean particle size 57 ^^ m particle size distribution 1, 66 fluidity 85 water content (hmoonoot loss at 800 ° C) 7%

1.18 thermal capacity per unit volume while minimizing fluid! (MJ.rn ^-3 .K ~)

The properties of the two alpha-aluminum oxides А and В are given in Table VII.

Table VII

Alpha-alumina

AND В average particle size Cum) 38 24 particle size distribution 1.19 1,25 fluidity 75 66 heat capacity per unit volume at minimum fluidization (MJ.m ³ .IT ¹ ) 1.14 1.19

The flowability of the mixture was 73.5 and its heat capacity per unit volume at minimum fluidization was 1.25

The 2.3 mm glass sheet was heated to 660 ° C and cooled in a fluidized bed, and a center tensile stress of 48 MPa was induced in the sheet. By varying the selected proportions of the blend components, selected center tensile stresses in the range of 34 MPa to 48 MPa could be created in the sheet.

Example 10

The adaptability of the method of the invention is further illustrated by adapting the mixture by mixing some of the gas generating components and some inert components, all of which are available and relatively inexpensive materials, to form a mixture having gas forming properties and optimum fluidity and heat capacity that produces the desired stresses in the glass cooled in this mixture when in the quiescent, uniformly expanded state of fluidization of the particles.

In this example, the blend contained 5% by weight of each of the four gamma-alumina A, V, C and D, whose properties are summarized in Table VIII.

The total amount of 20% by weight of gamma-alumina was mixed with 26.67% by weight of each of the three alpha-alumina E, F and G, the properties of which are summarized in Table IX.

Table VIII

AND Alpha-alumina В C D mean particle size (^ un) 70 61 57 72 Particle size distribution 1.47 1, 67 1, 66 1, 65 fluidity 88.5 88 85 86 water content (% by weight, losses at 800 ° C) 7 7 7 7 heat capacity per unit volume at minimum fluidization (MJ.m · ^. K ¹ ) 1.16 1.16 1.12 1.12

Table IX

E Alpha-alumina F G mean particle size ((rn) 38 30 24 particle size distribution 1.19 1, 22 1.25 fluidity 75 70 66 heat capacity per unit volume ^P s ^ nii huTACI minima. ^ Jn ^ .K ^-1 1, 38 13 1.19

The flowability was 74 and its thermal capacity per unit volume at minimum fluidisation being 1, ²⁶ MJ ^"3 .K ''.

The 2.3 mm glass sheet was heated to 660 ° C and cooled in a fluidized bed and the center tensile stress induced in the sheet was 49 MPa. Changing the selected proportions of gamma-alumina representing 20% of the blend, or changing the proportions of alpha-alumina constituting 80% of the blend, or changing the relative proportions of the total amount of aluminum and aluminum to total Alumina in the mixture of the sea and produced central tensile stresses in the range of 32 to 49 MPa.

Example 11

The fluid granular fraction contained 17% by weight of the alumina monohydrate of Example 6 mixed with 83% by weight. silicon carbide having successor properties;

mean particle size 40 μα particle size distribution 1 .32 fluidity 72.75 heat capacity per unit volume at minimum fluidization 1,21 MJ.m3.K '

The flowability of the mixture was 75 and its thermal capacity per unit volume at minimOlní fluid ^C was ^1, 02 Μ. · ".Κ ³ ''.

The 2.3 mm thick glass sheet was zcl · У ^; at 660 ° C and cooled in the fluidized bed, and the induced central tensile stress in the sheet was 5 MPa. These materials have created the possibility of creating a selected central tensile stress within a wide range of 32 MPa to 51 MPa by selecting predetermined blend components to adapt the blend to the production of glass stresses.

Example 12

In the high-temperature mixture, both granular materials may have gas-forming properties. The mixture was made from equal amounts of gamma-alumina and alumina trilium wire ΙΙΗ. A fraction of the crystalline water from the alumina hydrate was released upon heating, which improves the effect of the water released from the gamma-alumina pores.

jum

1.9%

1.05 MJ · ^3. ^ '

The properties of aluminum and aluminum were as follows:

medium particle size particle size distribution fluidity water content · (hmoonool loss at 800 ° C) heat capacityCta per unit volume while minimizing fluidity

The properties of the trilyAluminium oxide triates were as follows:

mean particle size particle size distribution fluidity water content (hmoSnool loss at 800 ° C) heat capacity per unit volume while minimizing fludcation

1,42%

1.56 MJ · ³ .K ^_1

Teloitost mixture was 85.25 and its thermal capacity ^ the per unit volume at minimum ^and was ^1, 31 MJ ^ .K ^first .

A 2.3 mm thick SIO-10SS sheet was inputted at 660 ° C and cooled in a fluidized bed, and the center tensile stress induced in the tab was 47 MPa. The selected central tensile stress in the range of 42 MPa to 47 MPa could be induced in the glass by appropriately selecting the relative subsections of the two gas-forming materials.

Example 13

Ptyno ^ ornré granular matoeiály, ^kt er ^s uvolnuuí pl ^y n ^y jirté, ^not water vapor at zadívání may also použžt, e.g., sodium hydrogeeohličitco NaHCO ^, which releases adLdiáihičitý as water. A 10% w / w mixture of sodium / sodium hydrogen carbonate with a b88 content of 0.6. 56 hmosnooli ko ^ id ^ í silica to increase its tekitossi 90 56 hrnounoH clfc-sxiUh clays ^ E and Example 9 b ^y la pouužta in this example. ,

TMO hair of a mixture of sodium hydrogeenuiičitgnu koloidndm oxide křemičiýfa b ^y L ^y Followers

mean particle size 70 jum particle size distribution 1, 98 fluidity 75

HgO + COg content (hmoOnool loss)

at 800 ° C) 37 56 heat capacity per unit volume at minimum fluidization 1, 41 a moderate MT.m ^_3

Calves Tost fluidnd composition b ^y la 75 and its thermal capacity ^ the per unit volume at minimum fluid! 1 ^and was ³⁸ MJ ³ .K ^'1. '

The 2.3 mm glass sheet was sealed to ⁶⁶⁰ ° C and then cooled in a fluidized bed and the mean tensile stress induced in the tab was 53.5 MPa. By appropriate selection of the relative proportions of the components of the mixture could. selected central tensile stresses in the range of 34 MPa to about 55 MPa may be induced in the glass table ·

In many instances the data voltage induced in the glass when it cools in the fluidised mixture of particulate ^{maateiálů, d} Uve ene as a voltage in the induction ^and Tabut tloušlce about 2.3 mm from sodnov ^ ^ enatokřemičitčo ska zOn it to 660 ° C and then cooled ^ ejtyo way: the gauze ^p o ^p sucked in examples 2, 3 and 4 may be achieved by varying the different voltages temperature to which the glass is heated, and proportionally higher voltages are induced in the thicker glass.

All examples znázzoriuUí as selecting poddlů maaeeiálu gas generating particulate which is capable of releasing 4-47% hmonnoti gas from its own hmoonnott when a ^{row of} ah eje. to a density at 8 ° C, ^by mixing this material builder in predetermined proportions with other gas generating materials or inert materials, the mixture can be adapted to produce the desired temperature. from 60 to 86 and the thermal Kapaa ^c to ^b ječotku on him when oinioZLní flutoaci in the range of I to ^{02. 1.75} MT.m ^"3. ^ ^{1 What} zaaišťuje that the glass sheet cooling in a thermally cured to the desired degree, indicated in cases of central tensile stress.

As is customary in a thermally cured glass, the ratio of the surface compressive stress to the central tensile stress is of the order of 2: 1 and the surface compressive stress that is induced is usually about twice that of said central tensile stress.

In the method of the present invention, the curing conditions can be easily reproduced, and it is possible to utilize a wide range of granular materials as available and use mixtures cheaper and easier! available granular maize products instead of the more expensive and more expensive individual components with O Ots, so operating costs are reduced.

Furthermore, by selecting the granular malaria and sub-compartments in which they are mixed, it is possible to produce in the glass selected higher curing stresses than those which can be achieved from the components of the compositions when used alone.

Some of the granular material described above were commercially available with a suitable mean particle size, fluidity size distribution, and heat trap.

When these properties of the desired material, such as aluminum ganoxide, were not printed in commercially available malaria, the punching was used to produce the pelletized granular οβ ^ mac macrophages the desired property for mixing with the fusions to form mixtures which, when the fusing curing stresses, vr glass.

The fluid mixtures set forth in Examples 1 to 4 and 13 have been found to be particularly suitable for the thermal curing of glass sheets. for lamination in the manufacture of automooil windscreen. The flowability of these blends is in the range of 71-83, the gas content in the mass loss values when heated to constant humidity at 800 ° C is in the range of 4% to 37%, and their thermal capacity per unit volume at oinimíZní fluidization is in the range of 1.09 to ^1, 38 MJ ^"3. ^ ^1.

By selecting subdivisions of the litter components, it is possible to create lower stresses in the glass than those produced by the gas component itself, as shown in Example 7.

Claims (21)

SUBJECT OF THE INVENTION A method of heat treating a glass, wherein the glass is heated to a predetermined temperature, then contacted with a gas-fluidized granular material, wherein the granular material is a mixture of selected granular materials, at least one of which is a granular material which: has gas-forming properties capable of releasing from 4% to 37% by weight of gas from its own mass when heated to a constant weight at 800 ° C, the proportions of the individual granular materials of the mixture being selected such that the granular material mixture has a heat capacity per unit volume at minimum fluidisation in the range 1.02 to 1.73 MJ.nT .lC ^ ¹ and a flowability in the range of 60 to 86th 2. The method of claim 1, wherein said granular materials are mixed in predetermined proportions to impart a flowability of from about 71 to about 83 and a heat capacity per unit volume at a minimum fluidization rate of about 1.09 IU / ml. K * ¹ to 1.38 Method according to claim 1 or 2, characterized in that the gas-generating granular material is gamma-alumina. 4. The process of claim 3 wherein the mixture comprises gamma-alumina and alpha-alumina. 5. The process of claim 3 wherein the mixture comprises from about 7% to about 86% gamma alumina and from about 14% to about 93% alpha alumina. 6. The method of claim 1, wherein the mixture comprises a gas-generating particulate material and at least one particulate metal oxide whose heat capacity per unit volume at minimum fluidization is in the range of 1.76 MJ / cm < -1 ^& gt ;. 1 MJ.nf * ³ .K ~ ¹ , the mixture has a heat capacity per unit volume at a minimum fluidization in the range of 1.27 MJ.nT.K &^lt; ^-1 > 71 to 82. 7. The method of claim 6 wherein the particulate metal oxide is a spheroidal iron oxide. 8. The method of claim 7, wherein the mixture comprises 30 to 70% by weight of spheroidal iron oxide. The method of claim 8, wherein the mixture comprises 70 to 30% by weight of gamma alumina as a gas generating material. 10. The method of claim 8, wherein the mixture comprises 28-35% by weight of spheroidal iron oxide and 45-56% by weight of alpha-alumina, the remainder being gamma-alumina as a gas generating material. 11. The method of claim 6 wherein said particulate metal oxide is zirconia ZrO ₂ · .sío _second 12. The process of claim 11 wherein the composition comprises from about 10% to about 70% by weight of the alumina monohydrate. 13. The method of claim 1 wherein the gas-generating granular material is aluminosilicate. 14. The process of claim 13 wherein the aluminosilicate is zeolite and the mixture comprises from 8 to 10% by weight of zeolite and 90 to 92% by weight of alpha-alumina. 15. The process of claim 1, wherein the gas-forming granular material is alumina monoalysate. 16. The process of claim 1, wherein the mixture comprises silicon carbide SiC and a gas-permeable material. 17. The process of clause 16, wherein the mixture comprises 17% by weight oxide monohydrate and 83% silicon carbide. 18. The method of clause 1, wherein the full grain granule is a trilyl oxide of Α1 ₂ Οβ.3Η ₂ Ο. 19. The method of claim 1 vyzm-bore formed in that it comprises two gassing SMLS granular mateeiály, trHydrát hlinKého oxide Al ₂ Oy3HgO ga and ^ e ^ (^ 3 ^ 1.d alumina in equal proportions. 20. The method of claim 1, wherein the semitransparent grain material is sodium bicarbonate NaHCO3. 21. The process of claim 20 wherein the mixture comprises 10% by weight sodium bicarbonate and 90% alpha alumina.