DD301901A9 - Process for the preparation of hydraulically setting mixtures - Google Patents

Abstract

The process for the preparation of hydraulically setting mixtures assumes that the mixtures, which as a rule consist of an alumina cement and the additives white corundum and / or lignite and / or mullitrohschamotte and / or Tonrohschamotte, preferably alpha Al ind 2 O ind 3, in the presence of up to 1% sulfite waste liquor powder of less than 40 μm m of ground alumina and / or an active, free SiO 2 -containing or forming inert material is added. According to the invention, the proportions to be added should amount to up to 4% highly active inert material which has been ground in the presence of up to 1% sulfite waste liquor and up to 3% less than 63 μm purified SiO 2. Quartz flour, fused quartz, silicon carbide and industrial SiO 2 -containing seizure products such as dust from the production of ferrosilicon and clay leaching residues can be used as the SiO 2 carrier. The operating principle for improving the thermomechanical properties of the mixture and thus of the concrete material is that in the binding matrix, the formation of anorthite - CAS ind 2 - takes place by the SiO ind 2 -containing additive to a limited extent at temperatures greater than 1 300 degrees C. The solid-state reactions can be carried out much more effectively by improving the processing properties of the concrete batch as a result of the addition of sulfite waste liquor powder, preferably via alpha-Al 2 O 3. Furthermore, the morphology of the hexaaluminate formation is influenced to slow the CA ind 6 crystal growth from the reactions between cement and corundum at high temperatures. The formation of anorthite and the altered crystallinity of the CA ind 6 is the prerequisite for the improvement of the thermomechanical properties avoiding the attrition during temperature cycling and the elimination, reducing the irreversible change in length at high temperatures.

Description

Field of application of the invention

The invention relates to a process for the preparation of hydraulically setting mixtures, which are characterized by high mechanical properties, such. B. pressure and abrasion resistance, characterize during or after thermal stress. The mixtures are used as later shaped bricks, finished parts and / or monolithic linings for the delivery of pyrotechnic systems.

Characteristic of the known state of the art

Blends are currently made on the binder side, preferably based on Portland and alumina cements. While the Portland cement for mixtures at Einsat.iemperaturen up to 1200 ⁰ C is used, the alumina cements are used depending on the aggregate up to 1800 ⁰ C operating temperatures. Here, for use temperatures around 1300 ° C, alumina cements based on the raw materials lime and bauxite are used. Such mixtures are then used thermally limited in their application. For this reason, high-purity alumina cements are used as hydraulic binders for the 1400 ^° C. application and / or classification temperatures. In general, it can be found that for classification temperatures of 1400 ⁰ C chamotte and / or raw chamotte, 1 500 ° C fine-grained white corundum and coarse grained chamotte, 1600 ⁰ C normal corundum and for 1 700 ⁰ C OAI ₂ O ₃ in the form of white corundum

be used as an additive. Alumina binders used are pure aluminative binders, where the sum of impurities such as SiO ₂ , Fe ₂ O ₃ , MgO, Na ₂ O and K ₂ O is less than or equal to?%. The Al ₂ O ₃ content of these types of cement is generally between 70 and 80% Al ₂ O ₃ . The amount of concrete produced therefrom, which can be used both for smaller shaped bricks, prefabricated parts and / or for monolithic linings in pyrotechnic plants, is becoming increasingly important since, in particular, the process stages of press molding and product firing are eliminated. In comparison to the fired, classic refractory products with medium and high Al ₂ O ₃ content, however, there are still a number of disadvantages which inhibit a more extensive use, although economic advantages, in particular energy savings, are to be found. Primarily lack of space stability and low strength at the respective classification temperature are mainly the causes for this. For a concrete at 1400 ⁰ C classification temperature, for example, this material would be viewed from the Einsautemperatur forth with a high quality refractory brick or a Korundschamottestein having about 55 to 60% Al ₂ O ₃ comparable include 20MPa in the delivery state and 7MPa by prefiring at 800 ⁰ C for compressive strength according to delivery conditions. In contrast, the fireclay and corundum firebricks have much higher strength values. On delivery, for example, at least 25 MPa must be guaranteed in the case of firebricks and at least 25 MPa in the case of corundum firebrick, both products produced by the non-plastic method. The differences are even more pronounced in high-alumina mixtures where white corundum is used as an aggregate. Compared to a stone quality with 90% Al ₂ O ₃ , the differences are striking. For example, for this high grade alumina stone grade 55.2 MPa as received, after renewed firing at PK171 / 173 56.0 MPa for a qualitatively comparable amount of concrete, consisting of 20% by mass CA / CA2 alumina cement and 80% by mass white corundum. 57.1 MPa as delivered, but measured after thermal treatment at PK171 / 173 15.7 MPa in compressive strength. While the high-alumina stone quality showed no change in length during the re-firing, it is thus room-stable, whereas the concrete material shows an irreversible elongation of + 1.7%. This irreversible strain is due to the formation and crystallization of hexaaluminate in the binder matrix. Due to the irreversible elongation and the resulting very low compressive strength after thermal stress at classification temperature, the poultry booms are the cause of material attrition, where complete linings

must be renewed especially after thermal cycling. Although partial introduction of highly active C1Al2O3 instead of white corundum or raw chamotte as a lager and / or via a mixed cement could indeed achieve an improvement in the space stability especially at high temperatures, but with long-term stress and attrition phenomena can be found. The compressive strength did not reach that of the substitute for the fire food products. It is also known that microfillers in the form of rotary kiln dust, which is obtained in the Rohschamotteproduktion, very finely ground clay minerals and / or fireclay made from raw chamotte or chamotte, are introduced into the hydraulically setting mixture to improve various properties.

Object of the invention

The object of the invention is to produce hydraulically setting mixtures, which are particularly distinguished by high mechanical properties such as compressive and abrasion resistance during or after thermal stress. Another objective is to make the use of necessary refractory materials more productive and cost-effective by reducing process stages.

Explanation of the essence of the invention

The object of the invention is to influence the binding mechanism at high temperatures targeted. The mixes, which are usually off

5-25 Ma .-% alumina cement and 95-75 Ma .-% aggregate such as raw chamotte, sintered mullite, normal corundum and white corundum and possibly

micro fillers

consist, according to the invention up to 4% in the presence up to 1% Sulfitablaugepulver milled highly active inert material, preferably calcined alumina with at least 85% sieve at 40Mm grain diameter and up to 3% smaller 63μιη prepared SiO ₂ added and homogeneously mixed. This ensures that the mixture at low water cement factor good processing and compression properties and thus later in the concrete lower pore ^r aum has. Furthermore, the formation of small amounts of anorthite, CAS ₂ , is achieved at high temperatures. The Anorthitbildung causes the corundum-containing concretes are reduced in the irreversible elongation and that the gumming properties no longer occur under thermal cycling. For a mixture with 20% alumina cement and 80% white corundum, the following directives result after thermal stress at PK 171/175.

Mixed mixture

without additives, with additives, previous solution inventive sol.

linear

Change in length (%) + 1-2.5 <0.5

Compressive strength (MPa) <25> 60

Ausführungsbeispieic

The invention will be explained below in the exemplary embodiments' near.

example 1

A corundum concrete, consisting of

20% by weight of alumina cement with 71.3% Al ₂ O ₃ , CA / CA ₂ base, C, ₂ A _r free 7.5% by mass of white corundum, 0OWS grain

25.5 mass% white corundum, grain 25

17% by weight of white corundum, 63 grain and

30% by weight white cognac, grain 160

were at the expense of Woißkorundkörnung, grain 25.1.5 wt .-% SiC pigment and 1.5 wt .-% highly active CiAI ₂ O ₃ , which was ground in the presence of 0.25% sulfite liquor, residue at 40pm was 2 , 6%, mixed in. The mixing was carried out batchwise in a mixing drum at a ratio of mixture to large-volume mixed bodies of 4: 1. The mixing time was 15 minutes. Of this mixture 2400g were used in a paddle mixer, as usual in the cement industry in the standard testing of cements, with the addition of 240ml of water, equivalent water cement factor of 0.5, prepared to a fresh concrete amount. Thereafter, the prisms were shaped at 2 χ 60 shock on the shock table. The concrete prisms with the dimensions 160 χ 40 χ 40mm were deactivated after 20 hours and stored under water at 20 ± 1 ° C until the 3rd day. After drying at 120 ± 5 ° C, the fire at PK171 / 173 was carried out in a high-temperature tunnel oven. While the batch without the additives reached an irreversible change in length of + 1.9% and a compressive strength of 21.6 MPa, in the batch with the specified additives in the change in length -0.3% and in the compressive strength 94.6 MPa were measured. Increasing the compressive strength more than 4 times is the prerequisite for high abrasion resistance and avoidance of gumming properties.

Example 2

For the production of high-performance burner bricks, the composition was 20% by weight of alumina cement with 71.6% Al ₂ O ₃ , CA / CA ₂ base, C ₁₂ A ₇ -free 1.5% by weight SiC pigment

1.5% by mass of highly active OAl ₂ O ₃ , residue at 40 ppm = 2.6%

8% by weight of white corundum, 0OWS grain

19% by mass white corundum, grain 25 15% by mass white corundum, grain 63 35% by mass white corundum, grain 160

homogenized in a mixing drum in the presence of large-sized hard porcelain balls the mixture. The component used CiAI ₂ O ₃ was, as already set forth in Beispie ¹ 1, batch-wise ground in the presence of 0.25% sulfite waste liquor. Of the mixture again 2400g were prepared in a paddle mixer with a water addition of 240ml, equivalent to a water cement factor of 0.5, to fresh concrete. Thereafter, the prism production was carried out as described in Example 1. After 20 hours, the prisms were switched off and stored under water at 20 ± 1 ⁰ C until the 7th day. Subsequently, the prisms were dried at 120 ± 5 ° C and the high temperature firing at PK175 in a tunnel kiln. Thereafter, the prisms showed a linear change in length of -0.8%, their compressive strength was 127.3 MPa. In comparison, the batch in which instead of 1.5 wt .-% 0.AI ₂ O ₃ and 1.5 Ma .-% SiC pigment 3Ma .-% white corundum, grain 25 was used in the prisms had a linear change in length of + 1.8% and a compressive strength of 19.0 MPa. Again, the material is given a significantly improved thermo-mechanical strength by the altered phase formation in the binding matrix at high temperatures due to limited Anorthitbildung that prevents the usual gumming at Temperatiirwechselbeanspruchung.

Example 3

In this example, amorphous fused silica was used as SiO ₂ additive. The fused quartz material was used in 2 different grinding fineness with a sieve residue of 11.7%, as sample 1 and with a 2.7% at 40μηη as sample 2. The highly active OAI ₂ O ₃ was in the presence of 1% sulfite liquor powder smaller 40μηι milled calcined clay used. Its residue was 5.5% at 40pm.

After the concrete composition

20% by weight of alumina cement, CA / CA ₂ cement with low C, ₂ A ₇ content 1% by mass of fused silica flour

1% by weight highly active OAl ₂ O ₃ , clay ground up with 1% sulphite waste powder additive, 7.5% by weight of white corundum, 0OWS grain

15.5 mass% white corundum, grain 25

20% by mass white corundum, grain 63

35% by mass white corundum, grain 160

were homogenized in a mixing drum in the presence of large volume hard porcelain balls with a mixing time of 15 minutes, the two mixtures. The ratio of mixture to large volume hard porcelain balls in the mixing drum was 4: 1. After homogenization, 2400 g of mixture were again prepared in the mentioned paddle mixer with the addition of water, the Wasserzementfaktor was 0.5, to a fresh concrete. The concrete prisms made from these were fired after 7 days of storage in a tunnel kiln at PK 150 and in the high temperature tunnel kiln at PK 171/175. The results are shown below.

Firing temperature sample 1 sample 2

linear change in length -1.2% -1.4%

Compressive strength 73,8MPa 77,7MPa

Firing temperature PK171 / 175

linear change in length ± 0% + 0.05%

Compressive Strength 82.0MPa 89.9MPa

The results confirm that even when the additive was reduced to a total of 2%, enormous increases in strength due to anorthite formation and reduction of regrowth occurred.

Example 4

As the SiO ₂ -containing component to be added, two industrial production products were used in this embodiment.

Both products contain a high proportion of free SiO ₂ . Their chemical composition is listed below.

Si / SiO ₂ dust vapors Clay residue from the FeSi production chemical extraction SiO ₂ 94.36% 79.50% Al ₂ O ₃ 1.29% 8.13% Fe ₂ O ₃ 0.77% 1.00% CaO not determined 0.09% MgO not determined 0.14% Na ₂ O 0.33% 0.05% K ₂ O 1.68% 0.82% loss on ignition 0.24% 5.85%

In a mixing drum, the components alumina cement, white corundum and the two seizure products were homogenized to give the mixtures. For the mixture with the composition 20% by mass CA / CA ₂ cement, C ₁₂ A ₇ -free

1 or 2Ma .-% accumulation Si / SiO ₂ -Daubbzw. Clay residue 9 or 8% by weight of white corundum, 0OWS grain 20% by weight of white corundum, 25% by weight of corn, 60% by weight of white corundum, grain 63 35% by weight of white corundum, grain 160

was used as a hydraulic binder an alumina cement, which can be characterized by the following data, CA content 38%

CA ₂ content 62%

Sieve residue at 40 mm 24.7%

at 63 pm 8.4%

at 90 pm 1.4%

DCA, Time to 2nd Peak ™ «. 16,7 hours

DCA, heat development rate 37.9 J / gh compressive strength, standard testing

75% standard sand, 25% cement, nachid 48.6MPa

Water cement factor 0.5 after 7 d 86.6 MPa

The preparation of the corundum concrete - test mortar and processing of the same to prisms was carried out according to the known test specification. After 7d, the prisms were dried and then fired in an industrial furnace at PK150 and in a high temperature tunnel kiln at PK173 / 175. The following test results were achieved.

Compressive strength of a CA / CA ₂ cement with the addition of

Addition of Si / SiO ₂ dust from clay leaching - (%) FeSi production residue

firing temperature

PK150 1

firing temperature

PK150 2

firing temperature

PK173 / 175 1

firing temperature

PK173 / 175 2

45,6MPa 51,4MPc 49,7MPa 50,6MPa 45,2MPa 48,3MPa 77.1 MPa 59.4 MPa

Claims (4)

1. A process for the preparation of hydraulically setting mixtures, characterized in that the batch batchwise or in the Gemengehomogenisierung up to 4% in the presence of up to 1% sulfite liquor powder milled highly active inert material, preferably calcined alumina with at least 85% sieve passage at 40 pm grain diameter and up to 3% smaller 63μιτι prepared SiO _{2 is} added and homogeneously mixed. 2. A process for the preparation of hydraulically setting mixtures according to claim 1, characterized in that SiO _{2 is used} in the form of SiO ₂ -forming and / or containing substances. 3. A process for the preparation of hydraulically setting mixtures according to claim 2, de lurch characterized in that SiO ₂ in the form of silicon carbide and / or fused silica and / or quartz sand and / or incurred in FeSi production Si / SiO ₂ dust and / or the residue resulting from the chemical extraction of aluminum silicates is used. 4. A process for the preparation of hydraulically setting mixtures according to claim 1, characterized in that the homogenization batchwise in a mixing drum, preferably in the presence of large volume non-metallic balls whose mass is at least 20% of the Gemengamasse is performed.