DE1571533B1 - BURNED FIREPROOF SILICONE EARTH SHAPED BODY - Google Patents

Description

The invention relates to a fired, refractory silica shaped body of high resistance to abrasion, thermal shock, increased density and good thermal conductivity, from a refractory approach consisting of 90 to 98 percent by weight of silica rock, 1 to 5 percent by weight of calcium oxide and magnesium oxide and a maximum of 1.5 Weight percent Al, 0, and alkali from the rock and Ti02.

By-product coke ovens are long, narrow chambers lined with silica bricks and usually united together in batteries of 100 or more chambers. The chambers are separated by walls of silica bricks, which is also the - include heating ducts which supply the heat for the coking of coal. By virtue of this arrangement, the combustion gases from the heating pipes and the gaseous char products are kept separate from each other at all times.

When operating coke ovens, they are prepared for loading by inserting the doors. The coal is then introduced into the coking chambers and the burn cycle commenced. Coking is typically completed in 14 to 18 hours depending on the width of the oven and the temperature being used. After the coking cycle is complete, the doors are removed and the coke is pushed out of the chambers by an electrically powered ram into the quench cart. The quenching carriage transfers the hot coke to the quenching station, where the coke is cooled by spraying water on it. After the coke has been pushed out of the furnace, the doors are reinserted and the furnace is ready to resume a load. The main refractory material used for the construction of by-product coke ovens is silica stone. Silica stone has two inherent properties that make them suitable for such an area of application. The more important property is their volume stability at working temperatures of the coke oven. The reversible thermal expansion of the silica stones is essentially complete below about 575 ° C. Thus, the continued high temperature expansion noted as with other types of refractory bricks and which must be considered in construction does not occur with the use of silica bricks. The other special property of silica stones is their ability to withstand high loads and to remain rigid within a few degrees of their actual melting point of 1730'C. Conventional, first-class silica stones do not fail in a stress test of 17.5 kg / cm2 until a temperature of around 1635 to 1660'C is reached. As disclosed in USA. Patent 2,351,204, in which the total content of alumina, titania, and alkalis does not amount to more than 0.5 weight percent, consist of a load of 17.5 kg / cm2 up to a temperature of about 1690 or even 1700'C.

The coke oven operation shows that the highest temperatures occur in the furnace walls. These walls are also very rapid in temperature changes subject. However, experience has shown that, although the wall temperature rarely drops below 540'C and therefore no flaking due to thermal shock is a serious problem, but it is a factor that needs to be taken into account The highest temperature normally found in the oven walls amounts to about 1540'C, so that the mechanical strength of the silica does not is questioned.

The walls of the coke oven are subjected to substantial abrasive action during the charging and in which o pushing out of the coke in the quench shuttle. The furnace chamber itself is already tapered in order to reduce the abrasion effect on the wall as much as possible while it is being pushed out. Thus, the ability of the wall bricks to effectively withstand the abrasive effects of coke is directly related to the life of a coke oven battery. As explained above, the heat required for coking is supplied from the heating pipes that are enclosed in the silica walls. Thus, the thermal conductivity of the wall material is an important factor for the heat transfer from these heating lines to this coke. It is understood that a material with a high thermal conductivity would result in a more economical operation of the coke oven than a material with a lower conductivity.

In such a special and other general areas of application it is with regard to fired, refractory moldings based on silica required that they should have a combination of properties, namely high resistance to abrasion and thermal shock as well as increased Density for better thermal conductivity.

In this context, the relevant previously known products were in no way able to satisfy. The relevant quartzite moldings occasionally contained relatively small amounts of titanium dioxide, but only as an impurity. It has become known (French patent 1 410 114) to heat a quartzite material to a temperature above 500 ° C. for the production of refractory linings and then to subject it to a hydrothermal treatment at a temperature of about 200 ° C. Calcium hydroxide is added to the preheated quartzite in a suitable device, with quartz powder, titanium dioxide, sulphite waste liquor or molasses residues also being able to be added in order to achieve better deformability into corresponding shaped bodies. This is then followed by the transfer into the corresponding mold bodies in autoclaves for the purpose of carrying out the hydrothermal treatment mentioned.

Studies have also become known (Brit. Cer. Soe. Volume 59 [1960], pp. 1 to 15) which aim to determine the effect of adding titanium dioxide to silicon dioxide on the crystallite conversion.

There is also a silica stone with a titanium dioxide content 0.1 to 0.5111, become known (USA. Patent 2,662,021). However, such a low percentage of titanium dioxide does not result in any improvement in the corresponding physical properties.

The object of the invention is now to provide a Moldings of the above Kind based on silica too create significant improvements in terms of abrasion resistance and durability to thermal shock as well as to improved density.

The shaped body according to the invention is now characterized in that about 2 to 5 percent by weight of TiO2 is present as a separate batch component.

Further characterizing features emerge from the subclaims.

A particularly valuable stone material shows no more than about 0.5% in terms of the chemical analysis of the batch, in total of the components alumina (A1.0,), titanium dioxide (Ti02) and alkalis (Na, 0 and K, 0). For conventional silica bricks, the amounts of these ingredients in the aggregate can range up to about 0.8 to 1.501 . In the case of a particularly valuable stone material, the composition is further characterized in that, based on the chemical analysis, calcium oxide and / or magnesium oxide are present in the silica stone in a total amount of at least 3.3 times the content of clay, titanium dioxide and alkalis. The contents of calcium oxide (Ca0) and magnesium oxide result from the addition of the binder, usually the commercially available hydrates. The silica rock or quartzite as used in the masses can be of any type commonly used for making silica stones, the degree of purity being determined by whether a regular or particularly valuable stone material is being made target. In the state obtained by mining, the silica material can consist of solid quartzite or an agglomerated quartzite stone. Other forms of the silica rocks used for silica stone manufacture are also suitable.

The applied titanium dioxide (TiO,) of the present invention is added as a separate batch ingredient (i.e., in addition to the TiO which is present as an impurity in the silica rock). According to the invention, a pigment grade product is preferred. Such titanium dioxide is usually precipitated or condensed from a fluid. Preferably the oxide is finely divided to such an extent that virtually all of the particles are 5 microns or smaller in size. This degree of fineness is important to obtain a sufficiently dense stone and can be considered critical for this purpose. It is incorporated into the batch in any number of ways, which results in a thorough dispersion of the titanium dioxide in the batch. There are about 2 to 5 0 / "based on the mixture of titanium dioxide used, with a range of about 3 to 40 /, is preferred.

The calcium oxide employed as the binder can usually be commercially available hydrated calcium oxide. Dolomite calcium oxide (Ca0 - Mg0) can also be used and is usually added as the hydrate in the same way. When only magnesia (MgO) is used, it is preferable to use a lightly burned magnesia (caustic magnesia). With regard to these procedures, all relevant steps in the field of producing silica bricks are known. The calcium oxide or magnesium oxide added to the batch is considered to be a binder since it serves both as a binder in the fired stone and provides mechanical strength to the unfired stone. In the manufacture of silica bricks calcium oxide is usually used in amounts of 1 to 5 0 / (on the basis of Ca0), and less often magnesium oxide is applied.

The silica bricks of the present invention are usually made by means of a press, an impact press, or a manual forming process in accordance with the conventional procedures developed for the manufacture of very high quality and conventional refractories from silica. In the following working examples, the conventional method using a press is used to manufacture the silica bricks. The individual components are crushed and thoroughly mixed together to produce a typical product for making stones in the following way: Silica: percentage -3.2 + 1.65 mm mesh size ...... 10 -1.65 + 0 , 59 mm clear mesh size 30 -0.59 - 0.21 mm clear mesh size 16 -0.21 mm clear mesh size ...... 44 About 5 percent by weight of water and about 10/0 concentrated sulphite liquor are added as a temporary binder. The mass is pressed into stones with dimensions of 22.8 - 11.4 - 7.6 cm under a pressure of 560 kg / cm2. The stone is then removed from the press and dried for about 24 hours at a temperature of 120.degree. The dried stone is then burned in a tunnel kiln for 5 days, with a maximum temperature of 1480 ° C being reached.

The quartzite used in these examples has analytical values of about 99.5 % Si02 with A120, + Fe203 + Ti02 + alkalis as the remaining components. The titanium dioxide added is pigment grade as marketed by the National Lead Company and has an overall particle size of less than 5 microns. Small amounts of iron pyrite charring and alumina with a mesh size of less than 0.105 mm clear mesh size are added to increase the mechanical strength of the stone (with little loss of refractory properties). Any clay and iron ore or iron oxide can be applied in a similar manner. The batch components and the numerical values obtained by means of the stones obtained are summarized in Table 1 : Table 1 1 1 2 Quartzite ..................... 960/0 930/0 Hydrated calcium oxide .... 3.20 /, 3.20 /, Iron pyrite burn off ............ 0.3 () /, 0.30 / 0 Alumina ..................... 0.5010 0.5010 Titanium dioxide .................. - 30/0 Modulus of rupture, kg / cm2 ......... 59.5 100.0 Bulk density, mg / cm3 ......... 1.714 1.95 Apparent porosity, 0 /, ....... 24 18 Cold compressive strength, kg / cm2 .... 518 517 Silica chipping test (degree of cracking when heated to 820 ° C at a given rate) 1 1 2 150'C / h heating speed digkeit ................. considerably none 260'C / h heating speed digkeit ................. strong moderate Measurements of the thermal conductivity of the mixtures are also carried out and are shown in Table 11 : Table II Medium temperature thermal conductivity (0 C) 1 1 2 93 ............. 6.7 9.4 430 ............. 8.4 11.8 650 ............. 9.4 12.9 875 ............. 10.5 11.5 1100 ............. 11.5 15.0 It can thus be seen that the addition of titanium dioxide leads to an improvement in each of the properties tested with the exception of the cold compressive strength, which remains practically the same. The mechanical strength of the stones is significantly improved, as demonstrated by the modulus of rupture. It is well known in the refractory art that the transverse strength of refractory bodies is quite directly related to the abrasion resistance. The modulus of rupture is a standard test for examining refractory materials. It is determined by simple apparatus, has a good degree of accuracy, and is an excellent measure of bond strength. Therefore, its determination is often carried out in lieu of an attrition test which requires much more involved equipment. Therefore, in the present case, the increase in mechanical strength shown for batch no. 2 is an indication of the great improvement in abrasion resistance.

The mechanical strength of silica bricks has always been a problem for the manufacturer of refractories. Considerable work has been done in recent years in developing stronger bonds without seriously adversely affecting the intrinsic properties of the stones. A low modulus of rupture is very likely to result in broken corners and edges during handling and shipping. Small changes in the composition of the batch, blending or grouting of conventional mixtures can result in stones that are too weak to provide satisfactory instruction. The almost twofold increase in mechanical strength, as achieved by adding 3 % titanium dioxide, is a great improvement.

The beneficial effect on the resistance to heat chipping through the addition of titanium dioxide can also be found in Table I. The silica stones must be slowly heated to a temperature of about 820 ° C. , since most of their thermal expansion occurs below this temperature and below this value they tend to flake extremely easily. It can be seen that batch 2 shows no crack formation when heated to 204 ° C./h, while the original stone, which was previously considered to be of high quality, shows considerable crack formation. Even when heated to 260 ° C./h, the stone with the addition of titanium dioxide shows only moderate cracking, while the conventional stone becomes worthless here.

The increase in thermal conductivity, as reflected by the addition of titanium dioxide is readily available on the basis of those reported in Table II Results visible.

High quality coke oven bricks generally have a lower alumina content (i.e. less than 0.3 O / J and iron oxide than conventional silica bricks. For example, a high quality brick consists of 96.50 / 0 quartzite and 3.5 "/, hydrated calcium oxide. Thus, the overall strength of the stone will be lower than that of a conventional stone. The higher mechanical strength is particularly necessary to enable the safe handling and shipping of special coke oven bricks and to reduce the pressure during transport. The A higher content of alumina and iron oxide can be achieved by adding small amounts of alumina and iron ore or iron oxide, as is achieved according to the examples in Table I, or by using a less pure quartzite which contains iron oxide and alumina up to 5% titanium dioxide to an approach such as that used for the production of high-quality silica bricks ird, leads to an improvement in each of the properties tested in approximately the same proportion as was achieved with a conventional stone. It can thus be seen that where the selection of silica stones depends on mechanical strength, high quality stones, i. That is, which originally contain not more than 0.5% , in total Al, 0 "TiO, and alkalis, can be used with a content of additional titanium dioxide.

It thus appears that the addition of titanium dioxide to silica stones results in a stone product having improved resistance to abrasion, improved resistance to thermal shock, greater density and greater thermal conductivity. Additions of titanium dioxide, however, have a somewhat detrimental effect on the refractory properties of the bricks and thus no more than 5 can certainly be used.

In the above, all percentages are based on weight, unless otherwise noted. The stones are made by means of more conventional Working method established, and the numerical values obtained by means of the investigations are standard disclosures in the field of refractory materials.

According to the prior art, the addition of small amounts of titanium dioxide to silica masses is known. However, the relevant publications do not teach that it is critical to add titanium dioxide in an amount of 2 to 5 %, as is the case according to the invention.

Experimental report Coke oven bricks are required to have a combination of properties including chipping and abrasion resistance as well as high thermal conductivity and, of course, structural strength at working temperatures. The applicant has produced the following series of mixtures for the purpose of demonstrating a special combination of such properties, as achieved according to patent application H 57 583. These mixtures have the composition given in Table III. The quartzite has such a size distribution of the individual particles that all the mixtures have a classification which is typical of approaches to the manufacture of refractory bricks and lies within the limit values given in connection with Table III. Table 111 Mixture (in %) A B C 1 DE F G H J- Quartzite ............. 95.95 94.95 93.95 92345 90.95 89.95 96.46 94.5 93.0 Hydrated Ca0 ... 3.2 3.2 3.2 3.2 3.2 3.2 1.47 3.2 3.2 Iron pyrite burn-up ... 0.3 0.3 0.3 0.3 0.3 0.3 0.30 0.3 0.3 Alumina ............. 0.55 0.55 0.55 1 0.55 0.55 0.5 0.55 0 0 Titanium dioxide .......... 0 1 2 3.5 5 6 1.22 2 3.5 - Particle sizes (all mixtures) range -4.76 1.68 mm clear mesh size ........................... 10 to 110 /, - 1.68 + 0.59 mm clear mesh width .......................... 26 to 29 0/0 -0.5 # - ' 0.21 mm clear mesh size ............................ 16 to 17 0 /, -0.21, mm clear mesh size .. ................................ 44 to 47 0/0 - The mixture A is a typical silica-stone mixture for - -Coke ovens and serves as a reference for all mixtures in this series. The mixtures B, C, D, E and F are 9-en 'by means of adding various Men - made of titanium dioxide to the mixture A at the expense of f'einen quartzite. The, GemIsch.e # H and J are similar to the mixtures C and D, but do not contain any clay added. The mixture G is designed in a manner similar to a mixture as suggested by the publication by A cott "(this is a reference which was cited in the USA patent office against the patent application corresponding to the present application). Table '1V mixture A B C DE F derS '# endhnik 11 J la G Volume weight, g / cm3 (D. 10) (AST-M method C 134-41) 1.80 1.83 1.86 1.87 1.89 1.91 1.83 l'87 1.87 Modulus of rupture, kg / cm2 (D-3) (ASTM method C 113-55) 79.0 85.5 82.0 77.6 78.5 79.8 54.6 75.0 69.4 Cold pressure resistance (D. 3), - kg / CM2 - (ASTM method C 113-55) 418 478 454 447 436 483 450 422 404 'Apparent porosity (ASTM method C20-46) 23.00 /, 21.70 / 0 21.60 /, 20.40 / 0 20.20 /, 19.40 /, 22.30 /, 20.80 /, 20.20 /, Attrition Test (Weight Loss) 5.6 g 5.0 g 4.4 g 4.0 g 4.0 g 5.8 g - (Test described in American Ceramic Society Bulletin, '40 [7], pp. 451 to 455 [1961]). Chipping test *) (similar to ASTM Procedure, C439-61) Heating rate 260'C / h ................ no 370'C / h ................ very low 480'C / h ................ considerably none 540 - C / h ................ low no no ht tested Stress test until say (ASf M procedure C 16-32), temperature at Failure, 'C .............. 1660 1658 1 1648 1630 1620 1620 1630 1620 1655 Very low = three stones not affected, others contain a crack. Low = three stones not affected, others contain a crack. Considerable = All four stones contain a large crack and various secondary cracks. None - # All four stones unaffected. All mixtures are, of water, based on the weight of the batch, admixed in a Mueller type mixer with about 10 /, Ligninlauge and 4 to 5 0 /. After the addition, the mixtures are pressed into stones under a pressure of 560 kg / cm 2, dried for 5 hours at a temperature of 120 ° C. and baked at a firing temperature with the marking Cone 17-18 . After firing, X-ray analysis shows that all of the quartz has been converted to crystal, tridymite, or glass, and this means that the stone has been properly fired. The stone is then examined to determine its various properties. The results of these tests are summarized in Table IV.

Volume weight, porosity, apparent specific weight The volume weight of all mixtures in the series is compared against the titanium additions, with an increase in the volume weight achieved by these additions. It is generally known that higher density and higher thermal conductivity are directly related and thus - additions of titanium dioxide lead to an improvement in thermal conductivity. Table IV also shows that essentially the greatest increase in density occurs with the smallest addition of titanium dioxide of 20%. To take full advantage of this result, stones should be made that contain at least about 20% titanium dioxide.

Another advantage of the production of stones results from titanium dioxide additions of more than 20%. For a given slight variation in titanium dioxide addition, the density change achieved is less, resulting in a more uniform product, and uniformity is required in current manufactures. This is done by observing the steep rise in density change until a value of 20 / "titanium dioxide is reached, and then the slope is only slightly inclined. Thus, workers in a production facility could be informed that the preferred addition of 30 / "Titanium dioxide takes place, with a deviation of up to 0.501, from batch to batch, i. H. from 2.5 to 3.5 0 / " and you still get a product with practically uniform density. However, this is not the case if less than 2 ') / 0 are added.

Table IV shows the porosity versus the titanium dioxide additions for the specified series of mixtures . In practice, this is the inverse function of the volume weight. Low porosity is important because of their favorable relationship to other properties, such as mechanical strength, abrasion resistance and thermal conductivity. * Table IV clearly shows an advantageous reduction in porosity due to titanium dioxide additions of more than 20%. It should also be noted that practically uniform porosity is obtained with more than 20 / "'titanium dioxide" although changes are made to the titanium dioxide content.

Abrasion resistance Mixtures A and F and also G, which are similar to the state of the art according to S cott (see the comments above), are subjected to an abrasion test which consists in placing 6.35 kg of silicon carbide grains on a sample This test is described in the publication by D, R, R ee d and Edwin Ruh, American Ceramie Socicherheit Bulletin, 40 (7), pp 452-455 (1960) . The measure of tear resistance is simply the G- = Wi (hts loss of the sample. The results are shown as weight loss in Table IV, which in turn indicate the critical value of the smallest addition of 2T-tanediox -. «d.

Chipping Test The chipping test consists of filling the door of an electric furnace with a plate of four test stones and placing a thermocouple on the end of the plate opposite the furnace. The hot surface of the plate is then heated in several batches at increasing speeds up to 820 ° C. and cooled at half the selected heating speed. The stones are cool to the waste examined for cracks. Numerical values of this test are also given in Table IV. The addition of titanium dioxide significantly increases the chipping resistance. Old mixtures containing at least 2% titanium dioxide resist a heating rate of. about * -54Ö 'C / Ii, which is a very considerable burden. This is further evidence of the 'Schr-well-matched appropriate physical properties which, according to the application , are achieved.

Load test to failure (refractory property) The load test shows with its results that titanium dioxide additives lead to a continuous reduction in the refractory properties, i. H. the Fähigkeit-, - stresses examples erhöhten-- Tern # temperatures to resist. The omission of alumina additives (mixtures H and J) leads to an increase in the breakdown temperature by about 25 ° C. Since the maximum working temperature of the coke oven walls is around 1540'C, the temperature of the failure during the load test of the stones used in 'walls ' should be at least around 500C higher than the maximum working temperature, whereby. An addition of 5 0 /, titanium dioxide is a sächezen upper limit.

Overall, the tests reported above show that an amount of 2 to 5% added TiO2 results in the most expedient combination of physical properties. The curves of the various figure # ep should be a graphic proof of this. Another interesting aspect of these curves is the apparent "maverick" behavior of the refractory # mixture according to "S cot Ü (see the above. Remarks on this), i. i.e., does not appear to coincide with the expected curves. One explanation can of course be the fact that after "S cott" it was not intended to manufacture silica stones. According to this citation, an attempt was made to examine only the effects of the various materials on the conversion of quartz.

Claims (4)

Claims: 1. Fired, refractory silica molded body with high strength against abrasion, thermal shock, increased density and good thermal conductivity, from a refractory mixture consisting of 90 to 98 percent by weight of silica rock, 1 to 5 percent by weight of calcium oxide and magnesium oxide and at most 1.5 per cent by weight A1203 and alkalis from the rock as well as Ti02 testeht, wherein d a d u rch that 2 are available to 5Gewichtsprozent Ti02 in Forinkörper as an additional approach ingredient. 2. Silica molded body according to claim 1, characterized in that the approach contains titanium dioxide -. * D in an amount of about 3 to 4 0 /. 3. Silica molded body according to claim 1, characterized in that the approach contains up to 0.3 percent by weight of iron oxide or Contains iron ore and up to 0.5 percent by weight of alumina or clay. 4. Silica molded body according to claim 2, characterized in that the titanium dioxide is practically completely present with a particle size of 5 microns or below.