US3539387A - Single fire glazed ceramic body - Google Patents

Description

United States Patent Oifice 3,539,387 Patented Nov. 10, 1970 3,539,387 SINGLE FIRE GLAZED CERAMIC BODY George D. Kelly and David L. Dean, Zanesville, Ohio, assignors to Ferro Corporation, Cleveland, Ohio No Drawing. Filed Sept. 19, 1967, Ser. No. 668,937 Int. Cl. C04b 41/06 US. Cl. 117-123 13 Claims ABSTRACT OF THE DISCLOSURE The combination of a high strength alumina-nepheline syenite-clay body fired to zero Water absorption, having a glaze applied thereto prior to firing said body, said glaze matured concurrently with said body, said glaze body particularly adaptable to highway road markers and lane dividers.

BACKGROUND OF THE INVENTION There are two types of highway markers or lane dividers, reflective and non-reflective types.

Non-reflective road markers consist of a round or square button of approximately 4 inches in lateral dimension by approximately high. These markers are made from plastic or conventional clayflint-feldspar ceramic formulations with conventional ceramic glazes. Th plastic non-reflecting road markers are blackened by tire marks from moving vehicles and eventually become so discolored that they are diflicult to see. Conventional glazed ceramic road markers are not discolored by tire marks, but it has been found that, when they are mounted, particularly on asphalt roads in hot weather, the road surface is not sufliciently rigid to prevent slight deflection of the markers upon tire impact. This flexing action tends to rupture the conventional ceramic markers and their life is thereby limited. It appears that the ideal marker would be a ceramic marker which does not discolor from tire impact and which is considerably stronger than conventional markers now in use.

Plastic reflective road markers have been tried consisting of a methyl-methacrylate plastic shell, into which a prismatic type reflecting surface has been molded. As a reflector, this type of marker is sufficiently effective; however, since it is made of plastic it has been found that its service life on the road is quite limited, due to abrasion and breakage from tire impact. For reflecting type road markers, it appears that the ideal marker would consist of a glazed, ultra strong ceramic base into which a plastic reflecting surface has been set.

The key to producing both the non-reflecting and the reflecting type road markers of ideal quality is in the de velopment of an ultra strong glazed ceramic base. The object of this invention is to provide such a glazed ceramic base for both reflecting and non-reflecting ceramic road markers.

Conventional ceramic road markers may be manufactured from mixtures of clay, flint, and feldspar. Upon firing of such bodies to vitrification, or the point of zero water absorption, a road marker having a modulus of rupture in the range of 46,000 p.s.i. is obtained. We have found that, if a road marker is made from the composition of this invention and fired to vitrification at Cone 12, the resulting product has a modulus of rupture in the range of 8l3,000 p.s.i. Thus, it can be seen that the new road marker composition is 2. to 3 times stronger than conventional clay-flint-feldspar road markers having a modulus of rupture on the order of 4-6,000 p.s.i.

In the manufacture of conventional ceramic road markers, the usual procedure is to press the so-called green or unfired road marker and then to apply an unfired ceramic glaze by spraying or by dipping. The body and glaze combination is then fired simultaneously to produce a vitrified ceramic body which is covered by a fully matured ceramic glaze. However, in attempting to produce a glazed road marker from the new high strength ceramic body of this invention by this so-called one-fire technique, it was found that, during firing, the body was warped or badly distorted. The cause of this distortion during firing is not fully understood; however, a theory concerning its probable cause has been evolved.

Although we have no wish to be bound thereby, we believe the theory to be as follows: When any ceramic body is fired to the point of vitrification, it will be noted that there is a large decrease in linear dimensions of the body. This decrease in size is commonly referred to as firing shrinkage. It is well known that when a ceramic body is heated, it does not shrink appreciably until a temperature of to 200 F. below its ultimate firing temperature is reached. From this point until the final maturing temperature is reached, the ceramic body shrinks rapidly.

In the manufacture of conventional ceramic road markers, using conventional ceramic glazes, it appears that the melting of the glazes occurs at such a point in the firing cycle that the firing shrinkage of the ceramic body is not interfered with and the body and glaze shrink together to produce a dimensionally accurate road marker. When common ceramic glazes are applied to the new high strength road marker body, and an attempt is made to produce a road marker by the single-fire process, it appears that the glazes melt or react with the ceramic body before the body begins its period of rapid shrinkage. The melted glaze or reaction layer which is formed between the glaze and the surface of the ceramic body, does not shrink uniformly with the body during its period of rapid firing shrinkage. The stresses which are set up in the system during this period cause the road marker to distort.

It is known that the high strength body of this invention can be fired to vitrification, a conventional ceramic glaze applied and the glaze matured in a second firing operation. The economic disadvantages of using a twofire process, however, are obvious. It would be highly advantageous to be able to employ a single-fire process in the manufacture of high strength ceramic road markers.

It has been found that the glaze composition of this invention can be applied to the unfired high strength ceramic body of this invention, and the body and glaze fired to complete maturity in a one-fire process.

It is submitted that the combination of the instant novel high strength body and glaze composition represents a unique approach to the economical manufacture of high strength glazed ceramic road markers.

It is therefore an object of this invention to provide a high strength, single fired, glazed ceramic body.

It is another object of this invention to provide a glaze adaptable to be fired on a high strength green body at Cones 11 to 13.

SUMMARY OF THE INVENTION Broadly stated, the body composition of this invention falls within the following range:

Percent by wt.

Alumina 20-50 Clay 20-50 Nepheline syenite 18-32 The calculated compositional oxide range of the foregoing being:

Percent by wt.

Ignition loss and impurities 1.5

The preferred range of body composition being:

Percent by wt.

The calculated compositional oxide range of the foregoing being:

Percent by wt.

SiO 28-36 Ignition loss and impurities 1.5

The preferred body composition being:

Percent by wt.

325 mesh alumina 45 400 mesh nepheline syenite 25 Ball clay 30 The calculated compositional oxide range of the foregoing being:

Percent by wt.

A1 0 62.6 SiO 32.1 N320 2.9 K 0 1.3 Ignition loss and impurities 1.

The glaze composition (raw) of this invention falls within the following range:

Percent by wt.

Alumina 0-20 Clay 5-35 Nepheline syenite 65-95 Milled zircon 8-14 Talc 0-6 The calculated compositional oxide range of the foregoing being:

Percent by wt.

The calculated compositional oxide range of the foregoing being:

Percent by wt. SiO 54-61 A1 0 20-26 Na O 6-9 K 0 2-4 MgO 0.3-1.5 ZrO 5-7 Ignition loss and impurities L. 1.5

The preferred glaze composition being:

Percent by wt.

Nepheline syenite 79.3 Plastic kaolin 8.8 Milled zircon 8.8 Talc 3.1

The calculated compositional oxide range of the foregoing being:

Percent by wt.

SiO 58.5 A1 0 22.3 N320 8.0 K 0 3.3 MgO 1.0 ZrO 5.9 Ignition loss and impurities l.0

In the preferred body composition, minus 325 mesh alumina, minus 400 mesh nephelinc syenite, and ball clay were used. Kaolin clay can be substituted for at least 50% of the ball clay. It is known that feldspar can be substituted for part or all of the nepheline syenite, but such bodies are more refractory than the preferred composition and must be fired to a somewhat higher temperature depending upon the amount of feldspar employed. Also, it is not necessary to utilize alumina and nepheline syenite of such fine particle size. Coarser starting materials could be employed, but this would require grinding of the body prior to fabrication of road markers.

DESCRIPTION The preferred body of this invention was batch weighed, and mixed according to conventional procedures with water to provide a moisture content of from about 8 to 14 weight percent, based upon the weight of the unfired body, after which, utilizing conventional methods, the body was pressed into a disk-shaped road marker utilizing a conventional ceramic press at pressures of approximately 1000 p.s.i.

However, it is to be understood that the body of this invention is adaptable to be either slip cast or ram pressed, with appropriate alteration in water content.

The preferred glaze composition, milled by conventional methods to the appropriate specific gravity was applied to said road marker by either a splash technique at a specific gravity of 1.70 to 1.72, or by spraying or dipping using conventional methods.

The glaze may be applied to the green body either following complete drying thereof or it may be applied following pressing and partial drying to provide a relatively dry surface to accept the glaze.

For spraying, the glaze slip was adjusted to 1.64 specific gravity. Following glazing and drying, the green glazed ceramic road marker was fired in a conventional kiln to Cone 12, although Cone 11 to Cone 13 inclusive would provide equally good results.

Firing at this range produced a body of zero water absorption having a modulus of rupture of at least 8000 p.s.i., said body covered with an extremely hard, abrasion resistant glazed surface, all accomplished in a single fire.

Although it might be possible to reformulate a glaze using other raw materials to provide a glaze having essentially the same oxide analysis, we believe such glazes would likely not work on the body of this invention since the melting characteristics of any substitute glaze would be sufiiciently different from those of the glaze compounded from our raw materials that such substitute glaze would likely be totally incompatible with our high strength body from both the fusion standpoint as well as its use, utility, and durability.

Conventional porcelain glazes, as known to the ceramic art, were found to react adversely with the body of this invention. Hundreds of glazes of the conventional porcelain type, glazes reformulated to have the same oxide analysis as the subject glaze of this patent, and many other glazes were investigated and all those glazes having satisfactory surface appearance were found to be incom patible with the body of this investigation.

This incompatibility is characterized by a reaction between the body and the glaze which causes deformation Of the glaze-body combination. Incompatible glazes, ap-

plied to the body of this invention, result in a fired combination in which the glazed surface of the road marker assumes a smaller radius of convexity, and the bottom of the road marker becomes concave, rather than remaining fiat as is desired. It is thought that this deformation is due to the melting of at least a portion of the glaze constituents while the body is still in a fairly highly porous condition. The portion of the melted glaze, or melted glaze constituents, is thought to then enter that portion of the body adjacent to the glazed area, causing this portion of the body to assume a dense and vitrified character while the remaining portions of the body are still in a relatively highly porous condition.

As the firing continues, the remaining, unvitrified portion of the body continues to shrink to a considerable degree, while that portion which has been vitrified by glaze constituents shrinks little, if any. The net result is that the portion of the body adjacent to the glaze shows a lower firing shrinkage than the portion of the body which is removed from the glaze. This results in the glazed surface of the road marker assuming a shorter radius of convexity, while the bottom, unglazed surface of the road marker assumes concavity.

It was found that conventional porcelain glazes and other less conventional glazes could be reformulated so as to produce a glaze Which melted very late in the firing cycle, at a time when the body was essentially vitrified. These glazes resulted in road markers which showed no deformation, but, because of the refractory nature of these glazes, the glaze surface was characterized by one or more defects such as pinholes, dullness, or waviness.

And while we produce, by pressing, a body having a modulus of rupture of 8-l3,000 p.s.i., it is contemplated that if we resorted to slip casting or ram pressing, the body of this invention would provide substantially higher modulus of rupture values.

While it is known in the ceramic art generally to produce, utilizing a single fire, glazed bodies such as wall tile and sanitary ware, it should be pointed out that glazed tile are normally not fired to vitrification or zero water absorption as is our body, and tile are furthermore matured at temperatures considerably below Cone 12. Sanitary ware is produced from clay-flint-feldspar type bodies and glazes which are similar in composition to those used to manufacture conventional low strength ceramic road markers.

Neither tile nor sanitary ware bodies exhibit modulus of nlpture values as high as the body of this invention, nor could the glaze of this invention be utilized on either tile or sanitary ware bodies as it is far too refractory, and vice versa.

Nor do we believe that our body would be adaptable to tile or sanitary ware production inasmuch as the large amount of alumina in our body makes it far too costly for this purpose. Furthermore, although our relatively simple bodies can be produced by casting, the complex sanitary ware shapes could be cast only with difficulty from our body inasmuch as the high level of alumina tends to reduce its castability for the complex shapes.

Too, since tile is not fired to vitrification it does not present the large degree of firing shrinkage encountered with our body, hence the problem of distortion and warpage by glaze and body shrinkage differential would not previously have been encountered in these relatively heavy clay bodies.

And, while it is true, as widely practiced, that various other glazes could be applied to our high strength body in a two fire process (bisque and glost), this presents one of the very problems which this invention is designed to solve, i.e., the need for twice firing the relatively thick, heavy shapes of this invention.

Having thus described and illustrated our invention, it is set forth in the following claims which are to be construed in the light of the United States statutes and decisions in such a manner as to give them the broad range of equivalents to which they are entitled.

Percent by wt.

Alumina 20-50 Clay 20-50 Nepheline syenite 18-32 the glaze thereon, prior to firing having the following composition:

Percent by wt.

Alumina 0-20 Nepheline syenite 65-95 Clay 5-35 Milled zircon 8-14 Talc 0-6 2. The glazed body of claim 1 wherein the body prior to firing had the composition:

Percent by wt.

-325 mesh alumina 45 400 mesh nepheline syenite 25 Ball clay 30 and the glaze thereof prior to firing had the composition:

Percent by wt Nepheline syenite 79.3

Plastic kaolin 8.8 Milled zircon 8.8 Talc 3.1

3. The glazed, single fired ceramic body of claim 1, the glaze thereon, prior to firing, having the following composition:

Percent by wt.

Alumina 0-5 Nepheline syenite 75-85 Clay 5-15 Milled zircon 8-10 Talc 1-4 4. The glazed, single fired ceramic body of claim 1, the body thereof, prior to firing, having the following composition:

Percent by wt.

Alumina 40-50 Clay 25-35 Nepheline syenite 20-30 5. The glazed body of claim 1 wherein the body prior to firing had the composition:

Percent by wt.

-325 mesh alumina 45 400 mesh nepheline syenite 25 Ball clay 30 6. The glazed body of claim 1 wherein the glaze thereon, prior to firing, had the following composition:

Percent by wt. Nepheline syenite 79.3

Plastic kaolin 8.8 Milled zircon 8.8 Talc 3.1

7. A glazed, single fired ceramic body having a minimum modulus of rupture of 8000 p.s.i. said body and glaze having been fired to maturity simultaneously, said body, prior to firing, having the following oxide composition:

Percent by wt.

A1203 58-67 sio 28-36 Na O 2-4 K20 1-2 7 the glaze thereon, prior to firing having the following oxide composition:

Percent by wt.

8. The glazed body of claim 7 wherein the body prior to firing had the oxide composition:

Percent by wt.

A1203 626 sio 32.1 N6 2.9 K20 1.3

and the glaze thereof prior to firing had the oxide composition:

Percent by Wt.

SiO 58.5 A1 0 22.3 Na O 8.0 K 0 3.3 MgO 1.0 zro 5.9

9. The glazed, single fired ceramic body of claim 7, the glaze thereon, prior to firing, having the following oxide composition:

Percent by wt.

SiO 47-59 A1 0 2 l-43 Na O 6-10 K 0 24 M g0 0-2 ZrO -1 0 10. The glazed, single fired ceramic body of claim 7, the body thereof, prior to firing, having the following oxide composition:

Percent by Wt.

A1203 45-67 sio 2343 N320 24 K 1-2 11. The glazed, single fired ceramic body of claim 7,

8 said body, prior to firing, having the following oxide composition:

Percent by wt.

A1203 -67 sio 23 43 N320 2 4 K20 1 2 the glaze thereon, prior to firing having the following oxide composition:

Percent by wt.

sio 47 59 A1203 2143 N320 610' K20 2-4 M g0 02 2:0 5-10 12. The glazed body of claim 11 wherein the body prior to firing had the oxide composition:

Percent by Wt.

A1203 626 sio 32.1 N5 0 2.9 K20 1.3

13. The glazed body of claim 11 wherein the glaze thereon, prior to firing, had the following oxide composition:

Percent by wt.

sio 53.5 A1203 22.3 N320 3.0 K20 3.3 MgO 1.0 zro 5.9

References Cited UNITED STATES PATENTS 2,053,244 9/1936 Turk l0648 XR 2,361,376 ill/1944 Athy et al. 106-48 2,370,695 3/1945 Stuft 10648 ALFRED L. LEAVITT, Primary Examiner W. F. CYRON, Assistant Examiner US. Cl. X.R. 117-l25, 169