FR2865471A1 - Glass material, for thermal insulation applications, is hardened chemically to give a structured depth of alkaline ion concentrations from the surface with a given surface stress and core viscosity point - Google Patents

Abstract

The glass material which has been chemically hardened, for thermal insulation applications, has a concentration of alkaline ions from the surface to a depth of at least 100 mu m, a surface stress of at least 200 MPa and a core viscosity point of at least 550[deg]C. The alkaline ions are preferably Na +>, Li +> and K +>. The glass has a thickness of 2-7 mm.

Description

2865471 TEMPERED GLASS FOR THERMAL INSULATION

  The invention relates to a glass or glass having undergone chemical quenching which can be used especially in the field of domestic cooking, as an oven door (more particularly pyrolysis furnaces), stove, stove, fireproof, chimney insert and more generally to separate two gaseous atmospheres at different temperatures.

  The glass used in the field which has just been described must generally be able to: withstand high temperatures, especially up to 530 C, for as long as possible, withstand a hot atmosphere (especially up to 530 C) is on one side of the glass while a cold atmosphere (including ambient temperature, that is to say generally 18 to 40 C) is on the other side, withstand thermal shocks such as those described in standard EN60335-2-6, and in particular that created by spraying cold water (for example 20 C) on one of its main faces even though the other side is in contact with a hot atmosphere ( for example 530 C), withstand mechanical shocks, have sufficient mechanical strength given its use, especially when it is desired to use the glass as a door without the use of a frame to carry it.

  This set of properties can at least partly be brought or approximated by particular glass or ceramic compositions such as certain borosilicate glasses or certain glass ceramics. However, these particular compositions have high costs.

  Thermally or chemically hardened glasses provide good mechanical resistance but they are known to relax rapidly, which means that the advantage conferred by the quenching is too quickly lost in view of the intended applications. In addition, the chemical quenching of some glasses is difficult to achieve and not really considered given the low diffusion coefficient of the ions involved in chemical quenching.

  According to the invention, a particular glass (or glass) having undergone a sufficiently pronounced chemical quenching so that the ion exchange depth (alkaline ions) is at least 100 μm and so that the surface stress is at least 200 MPa and is suitable for the above-mentioned applications. In the context of the invention, the starting glass, that is to say before the chemical quenching, must have the following characteristics: a point of viscosity (strain point in English, which corresponds to the temperature at which the the viscosity of the glass is 1014'5 poise) of at least 550 ° C. and preferably at least 57 ° C., preferably a coefficient of interdiffusion of the alkali ions exchanged at 400 ° C. of at most 9 × 10 -17 m2.s -1, preferably a ratio of the interdiffusion coefficient at 490 C of the alkali ions exchanged on the interdiffusion coefficient at 400 C of the alkali ions exchanged by at least 20.

  The invention therefore uses a glass having a low interdiffusion coefficient at 400 C of the exchanged ions. According to the invention, it is even possible to use a glass having a low interdiffusion coefficient at 49 ° C. of the ions exchanged, in particular a glass whose interdiffusion coefficient at 49 ° C. of the ions exchanged is less than 2.10-15 m.sup.2. 1. From this point of view, the invention goes counter-current in the field of chemical quenching because it uses a glass having a low coefficient of interdiffusion ions, which reflects a low quenchability chemical, nevertheless to chemically soak it.

  The chemical quenching operation is itself known in principle. A conventional chemical quenching technique can be applied to the invention by adapting it because a glass which is initially not very suitable for chemical quenching is used, and on the other hand by taking it long enough for the desired values to be achieved. of ion exchange depth and surface stress are obtained.

  Chemical quenching modifies the surface of the glass. However, the core remains unchanged, so that after chemical quenching, the core viscosity point is that of the glass before chemical quenching.

  Before the quenching treatment, the starting glass must contain an alkaline oxide. This oxide may be Na2O or Li2O, and may be present in the glass for example from 1 to 20% by weight. The chemical quenching treatment consists of replacing alkaline ions initially in the glass with other larger alkaline ions. If the initial oxide is Na2O, chemical quenching is applied by KNO3 treatment, so as to at least partially replace Na 'ions with K + ions. If the initial oxide is Li2O, chemical quenching is applied by NaNO3 or KNO3 treatment, so as to at least partially replace Li + ions as appropriate with Na 'or K ions. Tempering leads to a concentration gradient in K + or Na 'ions perpendicular to at least one of the main faces and decreasing from said main face.

  The final glass according to the invention is a mineral glass based on silica and alkali-mixed, that is to say comprising at least two different alkaline oxides (in particular because of the chemical quenching it has undergone) . It generally contains 50 to 80% silica SiO2. It generally contains 5 to 30% of alkaline oxide of formula M20 in which M is an alkali such as Na, K or Li. Before the chemical quenching, the glass used comprises the same amount of silica and substantially the same total amount of alkaline oxide, the difference with the final glass being that the starting glass may contain only one alkaline oxide. Chemical quenching produces an exchange of alkaline ions, without altering the total molar content of alkaline oxide.

  Generally, the chemical quenching is carried out by immersing the glazing to be treated in a hot bath of the salt chosen (generally NaNO 3 or KNO 3). This bath contains the concentrated salt. The chemical quenching is generally carried out between 380 ° C. and 520 ° C., and in any case at a temperature below the softening temperature of the glass to be treated. Chemical quenching produces an ion exchange at the surface of the treated glass to a depth of, for example, up to 300 μm. This ion exchange is at the origin of alkaline ion concentration gradients. Generally this gradient is characterized by a decrease in the concentration of ions provided by the chemical quenching (usually K + or Na +) from the main face and towards the core of the glazing. This gradient exists between the surface and for example a depth of at most 300 μm.

  The ion exchange depth Pe may be determined a) either by where a represents the mol% of initial alkali oxide in the glass (for example Na2O or Li2O), mi represents the initial total mass (before quenching) of the glass in grams, Mv represents the molar mass of the glass in g / mol, Am represents the weight gain of the glass during quenching in grams, ev represents the thickness of the glass in micrometers, Pe being thus obtained in micrometers, b) either by a microprobe profile in which case it is defined by the depth for which the ion content brought by quenching is equal to that of the glass matrix to within 0.5%.

  It is also noted that chemical quenching gives the glass an improved mechanical strength. This makes it particularly suitable for use with hinges (as a door) directly integrated into the window, without the need for a support frame. However, it is possible to protect the edges of the glass all the same against mechanical shocks, for example by a seal (not necessarily carrier) of metal such as aluminum or stainless steel. Such a seal is placed at the edge of the window.

  The glass or glass according to the invention finds use particularly as external wall (usually part of a door) of pyrolysis furnace or stove or fireplace insert. In the case of a pyrolysis furnace, the window is generally part of a wall (which includes doors) comprising at least two parallel windows and generally not more than five parallel windows, and in most cases three parallel windows, said parallel panes being separated by an air gap. The wall comprising the window according to the invention can be at least one of them and more particularly that in direct contact with the internal atmosphere of the oven, which can be raised between 460 and 530 C. The wall comprising the window according to the invention. the invention may separate the interior of the pyrolysis furnace of which the atmosphere is generally brought to a temperature ranging from 460 to 530 C, from the outside of the furnace in contact with the ambient air . In the case of stoves and fireplace inserts, the glass is usually only to insulate the interior of the stove or fireplace from the atmosphere of the room. In this case, the window according to the invention itself carries out a separation between a hot atmosphere brought to a temperature ranging from 300 to 530 C and a cold atmosphere constituted by the ambient air of a room. In the context of the present application, it is considered that the ambient air is at the average temperature of a room brought between 18 and 40 ° C., in particular about 20 ° C.

  Given the intended use, the window according to the invention can in particular generally withstand at least one of the following conditions without breaking: a) heating at 500 C in the air for at least 300 hours, followed by heating at 300 C for 1 hour, followed immediately (which means that the glass is not allowed to cool) with water spraying at 20 C, b) at 400 C in the air for at least 3 years, followed by immediately (which means that the glass is not allowed to cool) of a water spraying at 20 C on one side of the glass, - c) one of the main faces being in contact with a first atmosphere gaseous (chemically neutral vis-à-vis the glass, such as air) at a temperature ranging from 350 to 530 C, the other face being in contact with a second gaseous atmosphere (chemically neutral vis-à-vis of the glass, such as in particular air) at a temperature of at least 50 ° C., or even at least 100 ° C., relative to the temperature of the glass. the first gaseous atmosphere, these conditions being maintained for at least 2 hours and followed by an immediate sprinkling of water at 20 C on the side having been in contact with the hottest atmosphere. The temperature of the second gaseous atmosphere may be that of the ambient air of a room.

  d) in a glazing unit comprising a plurality of parallel panes (for example 2 or 3 or 4 or 5 panes), the window pane according to the invention being in association with other panes parallel to it, the various panes being separated by glass panes; air, and this so that said glazing separates a first atmosphere (chemically neutral vis-à-vis the glass, such as air) at a temperature ranging from 350 to 530 C, a second a gaseous atmosphere (chemically neutral vis-à-vis the glass, such as air) at a temperature of at least 50 C, or at least 100 C below the temperature of the first gaseous atmosphere, these conditions being maintained for at least 2 hours and followed by an immediate sprinkling of water at 20 C on the side having been in contact with the hottest atmosphere. In this application, the window according to the invention can be in contact with the hottest atmosphere. In this application, all the windows can be according to the invention. The temperature of the second gaseous atmosphere may be that of the ambient air of a room.

  The window according to the invention may have a thickness ranging from 2 to 7 mm.

  The invention is more particularly applicable to panes having a thickness ranging from 2.8 to 5 mm, in particular about 3 mm. The window is usually flat.

  The glass or window according to the invention may be included in a door, in particular comprising hinges directly integrated in said window. The glass or glass or the door according to the invention can be included in a stove or firewall or fireplace insert or stove or oven including the pyrolysis type. More generally, the glass or glass according to the invention can be used to separate two gas atmospheres at different temperatures, the first being at a temperature ranging from 300 to 530 C, the second being at a temperature of at least 50 C compared to the first, or at least 100 C with respect to the first, or even at room temperature, and with reduced risks of breakage due to the good resistance to thermal shock.

  The ability of a window to lend itself to the use targeted by the present invention can in particular be determined by subjecting it to repeated heating cycles at 500 ° C. or 400 ° C. followed by a thermal shock at 400 ° C. by spraying. water at 20 C on one side of the glass, until the glass breaks. The more cycles the window supports, the more suitable it is for the intended use. The window according to the present invention can withstand at least 50 of these cycles, or even at least 100 cycles, or even at least 200 cycles.

  When the duration of such determinations is particularly long, the duration can be estimated from a calculation based on measurements made at a higher temperature in order to accelerate the test. For example, a holding time of 400 C can be estimated from tests carried out at 500 C. To do this, the inventor found that the following formula could be used: Estimated time for 400 C = Time measured at 500 C. CD5001CD400 wherein CD50o is the interdiffusion coefficient at 500 C of the alkaline ions exchanged and CDa 0o is the coefficient of interdiffusion at 400 C of the alkali ions exchanged. This approximation was used for Example 2.

  In the examples which follow, the following terms or abbreviations are used: -Pe: depth of exchange in alkaline ions following the chemical quenching, - Cs: surface stress, - SP: point of viscosity, -CD: coefficient of Interdiffusion of the alkaline ions exchanged, -CD490: coefficient of interdiffusion at 490 C of the exchanged alkaline ions, -CD40o: coefficient of interdiffusion at 400 C of the alkaline ions exchanged, -Tt: Temperature of the chemical quenching -Dt: duration of chemical quenching - number of cycles: number of cycles 500 C / sprinkling of water at 20 C to obtain the rupture of the glass.

  For the examples, the following measurement techniques were used: depth of exchange: measurement by weight gain (equation a), before and after chemical quenching - surface stress: measurement by stratoréfractomètre (device notably described in the thesis of C Guillemet PhD Thesis of Doctor Engineer, Faculty of Sciences, Paris (1968)).

EXAMPLES

  Solidion, Planilux and CS77 branded glasses marketed by Saint-Gobain Glass France were used.

  Table 1 gives the SP (Strain Point) viscosity point values, as well as the values of the CD interdiffusion coefficients of these glasses for the temperatures used in the examples.

  SP CD490ICD400 CD at 400 C: 4.5.10 "15 m2.s- 'at 460 C: 2.3.10-14 m2.s-1 10.5 Solidion 500 C at 490 C: 4.5.10.14 m2.s- 1 to 500 C: 5.8.10-14 m2.s-1 to 400 C: 1.0.10-16 m2.s-1 to 460 C: 1.3.10 "15 m2.s-1 38.0 Planilux 505 C to 490 C: 3.4.10-15 m2.s-1 at 500 C: 4.5.10 "15 m2.s-1 at 400 C: 3.8.10.17 m2.s-1 at 460 C: 4.3.10-16 m2.s-1 24.5 CS77 585 C at 490 C: 9.35.10-16 m2.s-1 at 500 C: 1.4.10-15 m2.s-1

Table 1

  Preparation of the samples for the examples: We take glasses made of each of these glasses, of size 300 x 200 x e, e being the thickness of the panes tested. The edges of these panes are shaped with a P180Y reference belt edge, marketed by 3M. The windows are soaked in a bath of KNO3 heated to the temperature Tt, for a duration Dt. This treatment puts the surface layer of the glasses in compression, which strengthens them.

  The degree of strengthening of the windows can be characterized by measuring their surface compression stress Cs, and their depth exchanged Pe. The higher these 2 parameters, the stronger the reinforcement.

  All the panes were chemically soaked so as to obtain a Pe exchange depth equal to 150 pm for each of them, which corresponds to the treatments indicated in Table 2. It was measured optically with the refractometer and Pe was measured. by the difference in weight before and after quenching.

  2865471 9 e Tt Dt Cs Pe Solidion 3 mm 460 C 17 hours 450 MPa 178 pm Planilux 2.8 mm 460 C 300 hours 370 MPa 180 'am CS77 2.8 mm 490 C 360 hours 350 MPa 176 pm

Table 2

  At the end of these chemical quenching treatments, the CS77 panes are therefore the least reinforced.

  EXAMPLE 1 Stove at 500 ° C. and then 400 ° C. The chemically reinforced samples are then subjected to a repetition of the following cycles: heating at 500 ° C. for 2 hours, followed by heating at 400 ° C. for one hour followed immediately by spraying cold water (20 C) on one side of the glass. The cycles are repeated until the windows break. Table 3 indicates the minimum number of cycles that the windows have supported before breaking.

  Number of cycles Solidion 4 Planilux 7 CS77 250

Table 3

  EXAMPLE 2 Simulation of a Domestic Stove at 400 CA From the results of the preceding example, the behavior of the windows equipping a stove operating continuously at 400 ° C is simulated (use of the previously given formula). the minimum heating time from which breakages occur when the hot windows (400 C) are sprayed with cold water (20 C).

  heat-up time before thermal shock (estimated at 400 C) Solidion 103 hours (ie 4.3 days) Planilux 630 hours (ie 26 days) CS77 18421 hours (2.1 years)

Table 4

2865471 11

Claims (1)

  1. Mineral and alkali-mixed glass having a gradient of concentration of alkaline ions from its surface over an exchange depth of at least 100 μm, a surface stress of at least 200 MPa, and a viscosity point at heart of at least 550 C.