JPH0768055B2 - Alumina cement and low cement castable binder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an alumina cement that is widely used in the fields of civil engineering / construction and refractories, and more specifically, an amorphous castable used as a steel refractory material. In particular, the present invention relates to a low cement castable binder used in a system called a low cement castable or a high-strength dense castable, which has a very small amount of added alumina cement.

<Conventional technology and its problems> Conventionally, alumina cement, which has been used as a hydraulic binder, is mainly composed of CaO / Al ₂ O ₃ and 12CaO / 7Al.
₂ O ₃ , α-Al ₂ O ₃ and 2CaO ・ Al ₂ O ₃・ SiO ₂ etc. in small amounts,
Most of them were crystalline (eg, Japanese Patent Publication No. 50)
-28090 publication).

And amorphous castable used as a steel refractory material, with this alumina cement as a binder, fused alumina, calcined alumina, fused silica, bauxite, various refractory aggregates such as chamotte magnesia and mullite, if necessary, A hydrated hardened product of alumina cement was obtained by adding a setting regulator, adding water and kneading. The above-mentioned setting regulators include inorganic substances such as boric acid, phosphoric acid and silicofluoride or salts thereof, organic substances such as tartaric acid, citric acid and gluconic acid or salts thereof, generally commercially available fluidizing agents, water reducing agents. Etc., and an appropriate amount is added depending on various conditions such as kneading conditions and curing conditions (Japanese Patent Publication No. 51977/1977, Japanese Patent Publication No. 5950081 and Japanese Patent Publication No. 57-118056). Alumina cement has been used in conventional castables in an amount of about 10 to 30% by weight, and the properties of the castables such as workability, pot life, curing time and strength are largely attributable to alumina cement. It was a thing.

However, in the case of amorphous castable with a large amount of alumina cement, CaO in alumina cement is
SiO ₂・ K ₂ O and Na ₂ O in the aggregate easily react with each other, and 2CaO ・ Al ₂ O ₃・ SiO ₂ (gerenite), CaO ・ Al ₂ O during high temperature use
₃ · 2SiO ₂ (anorthite) and produce low-melting compounds such as fluxes, corrosion resistance and fire resistance of the amorphous castable has a problem of a decrease. For this reason, with the trend toward high corrosion resistance and high fire resistance of steel refractory materials, the amount of conventional alumina cement, which can be said to be the cause of formation of low melting point compounds, is significantly reduced, and ultrafine powder and peptizers and dispersants are used. Due to the densification of the low water flow construction structure made possible by this, low cement castables or high strength dense castables, which have solved the above problems, have been put into practical use and are becoming the mainstream.

However, the amount of alumina cement used is extremely small, and in a system in which ultrafine powder and cement particles are uniformly dispersed in a matrix with a peptizer or dispersant, the function required for alumina cement is It is different from many systems.

In particular, in a system with a large amount of alumina cement used, the hydrate formation itself of alumina cement was deeply linked to the workability of the amorphous castable, characteristics such as pot life and strength, but with the decrease in the amount of alumina cement, Due to the role of alumina cement as a hydraulic binder, Ca ²⁺ and Al that elute from the cement particles due to the reaction between alumina cement and water.
CaO ・ Al ₂ O ₃ which has been used from the past has been replaced by the role of an aggregating agent used for agglomeration of ultrafine powders, such as ³⁺
Other than 12CaO ・ 7Al ₂ O ₃ and 2CaO ・ Al ₂ O ₃・
Alumina cement, which contains SiO _{2 and the} like and is mostly amorphous, has an insufficient aggregation action of the ultrafine powder, resulting in insufficient pot life (aggregation time) and aggregation strength of the matrix.

The present invention, in order to address the problem of this aggregation, as a result of various studies by considering alumina cement as a source of polyvalent ions such as Ca ²⁺ and Al ³⁺ , a specific CaO / Al ₂ O ₃ molar ratio was obtained. The present inventors have completed the present invention by finding that the alumina cement possessed by them is effective.

<Means for Solving the Problems> That is, the present invention is a molar ratio of CaO and Al ₂ O ₃ CaO / Al ₂ O ₃ is 1 / 1.2-
80% by weight of 3/7 amorphous calcium aluminate
The alumina cement contained above is a low cement castable binder containing the alumina cement, ultrafine powder and a deflocculant as main components.

Hereinafter, the present invention will be described in detail.

The amorphous calcium aluminate (hereinafter referred to as A-CA) of the present invention has a molar ratio of a calcia source such as limestone or quick lime to an alumina source such as bauxite or Bayer alumina, similar to ordinary alumina cement (hereinafter referred to as AC). CaO / Al ₂ O ₃
(Hereinafter referred to as C / A) so that it is 1 / 1.2 to 3/7,
The clinker synthesized by the melting method or the firing method is pulverized by a pulverizer such as a vibration mill, a tube mill and a roller mill to prepare a Blaine specific surface area of 3,000 cm ² / g or more.

Amorphization can be achieved by bringing a clinker heated to a high temperature by a melting method or a calcination method into contact with a fluid such as compressed air or a liquid such as water and rapidly cooling the mixture, but the method is not particularly limited. .

For example, a method of firing calcium aluminate hydrate to obtain an amorphous material can be used.

In practice, the method of spraying high-pressure air and / or water on the melt or introducing it into water is easy to carry out. It is also possible to add a small amount of a melting point curing agent in order to accelerate the decrease in melting point when amorphizing. Examples of the melting point depressant include commonly used halogen compounds, boric acid compounds, silicic acid compounds and the like.

The alumina cement of the present invention (hereinafter referred to as the present AC) has a large amount of impurities such as SiO ₂ , TiO ₂ and Fe ₂ O ₃ mixed from the raw materials, which adversely affects the cohesiveness of the matrix. It is preferable to selectively use a source or an alumina source.

Specifically, high-purity limestone (CaCO ₃ 98% or more), quick lime fired based on it, Bayer alumina (Al ₂ O ₃ 99% or more) purified from bauxite can be used.

The amorphization ratio is about 20 to 70% by weight for ordinary AC, whereas in the present invention, 80% by weight or more, particularly 90% by weight or more is more preferable.

When the amorphization ratio is less than 80% by weight, when calcium aluminate (hereinafter referred to as CA) and water are brought into contact with each other, polyvalent ions of Ca ²⁺ and Al ³⁺ (hereinafter referred to as Ca ²⁺ etc.) are not eluted. It is not preferable because it is gradual and the cohesiveness of the matrix deteriorates.

The molar ratio of CaO (hereinafter C) and Al ₂ O ₃ (hereinafter A)
C / A is 1 / 1.2 to 3/7, and particularly preferably 1/2 for alumina cement used for low cement castables.

If the C / A exceeds 1 / 1.2, Ca ^2+, etc. elute quickly and the matrix agglomerates quickly, which is not preferable because the pot life of the low cement castable becomes short. Ordinary AC is C / A in this region, and there are some that contain a small amount of C / A = 1/2, but they are not preferable because they rapidly aggregate. Also, C / A is 3/7
If the amount is less than this, reactivity with water is poor, Ca ²⁺ or the like that aggregates the matrix becomes difficult to elute, and the aggregation strength decreases, which is not preferable.

Especially AC used for low cement castable is C / A
It is preferable that the main component is A-CA consisting of = 1/2 because the matrix agglomerates slowly and the castable pot life is long. The fineness of A / CA is 3,000 cm ² / g or more in terms of Blaine specific surface area.
0 to 12,000 cm ² / g is more preferable. If it exceeds 12,000 cm ² / g, CA particles are likely to become secondary particles and the reactivity with water becomes dull, which is not preferable.

The ultrafine powder used in the present invention is a particle smaller than AC by 1 order, preferably 2 orders of magnitude, and more preferably an average particle size of 2 μm or less. There are no particular restrictions on the constituents of the ultrafine powder, but those that are readily soluble in water are not suitable. The production method is not particularly limited and may be any method such as liquid phase, gas phase, pulverization, classification or a combination thereof, but from the economical aspect, those produced by pulverization or classification or by-products. It is produced in the gas phase as a substance, silicon, silicon-containing alloy and silicic dust (silica fume) which is a by-product at the time of zirconia production and silica dust, and further bauxite is dissolved by caustic soda solution by steam heating, It is obtained by precipitating aluminum hydroxide and firing. Ultrafine alumina powder by the Bayer method (ceramics manufacturing process-powder preparation and molding-edited by The Ceramic Society of Japan, published on January 15, 1986, P99) and the like are effective.

Other calcium carbonate, silica gel, opal silica,
Titanium oxide, zirconium silicate, dimakonium oxide, spinel (MgO ・ Al ₂ O ₃ ), various glasses, viscous minerals such as bentonite and its calcined products, amorphous aluminosilicate, chromium oxide, activated carbon, blast furnace slag and fly ash One kind or two or more kinds of ultrafine powder can be used.

The amount of ultrafine powder used is preferably 10 to 300 parts by weight, and particularly 50 to 150 parts by weight, because of its excellent high-temperature strength.

The deflocculants used in the present invention include phosphoric acids such as hexametaphosphoric acid, tripolyphosphoric acid and pyrophosphoric acid, oxycarboxylic acids such as citric acid, tartaric acid and gluconic acid, boric acids and polyacrylic acids or their Na and K salts. And
Of these, one or more can be used. In particular, sodium tripolyphosphate or a combination of citric acid or sodium citrate and boric acid or borax, which has excellent peptizing action and little delay in curing of the present AC, is preferable.

The amount of the deflocculant used is preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the total amount of the AC and ultrafine powder, which is excellent in deflocculating action, and can be used in a low-cementable castable time of 0.5.
-5 parts by weight are particularly preferred.

Each of the above materials is used as a binder and mixed with various refractory aggregates such as alumina, bauxite, magnesia, and mullite to form amorphous castables.

The amount of this AC is 1 for 100 parts by weight of the castable.
-5 parts by weight is preferable, and 2-3 parts by weight, which is excellent in curing strength and high temperature strength, is particularly preferable.

In addition to the low cement castable binder of the present invention,
If necessary, it is also possible to use an oil pitch, an antioxidant such as metal powder, a foam explosion reducing agent, a thickener and the like in combination.

<Examples> The present invention will be described in detail with reference to Examples.

Example 1 High-purity quicklime (CaO> 98%) and Bayer alumina (Al ₂ O ₃
> 99%) was blended so as to have a predetermined C / A ratio and melted in an electric furnace. The melt is blown off with compressed air of 5 kg / cm ² and rapidly cooled to change the melt charge amount / air pressure ratio.
CA clinker shown in 1 having different relative crystallinity was produced. This clinker is crushed with a batch type ball mill,
AC samples with different Blaine values were obtained by changing the grinding time. This AC was mixed with the formulation shown in Table 2 to prepare a low cement castable.

Water was added to this low cement castable and mixed for 3 minutes with a mixer, and the physical properties of the kneaded product were measured. The results are shown in Table-3.
Shown in. The physical properties were measured by the following methods and measured in an atmosphere of 40 ° C.

Flow: The spread diameter of the kneaded product after 15 taps on the flow table immediately after kneading.

Pot life: The time required from the pouring of water until the fluidity disappeared, and the fluidity was measured with a finger.

Aggregation time: The time from the pouring of water until the surface of the cured body was pressed and no dent was formed.

Cohesive strength: The compressive strength of a 4 × 4 × 16 cm specimen aged at 40 ° C. for 24 hours.

Drying strength: The specimen aged for 24 hours was further dried at 110 ° C. for 20 hours and allowed to cool to room temperature, which was taken as the compressive strength.

Amorphization rate: Calculated from the peak area by the powder X-ray diffraction method.

Amorphization rate (%) = (1-peak area / total area) x 100 (%) As shown in Table-3, the low cement castable using this AC has a large flow value, good workability and sufficient pot life. Moreover, it has an appropriate aggregation time and high aggregation strength, and has excellent performance as an AC for low cement castables.

Example 2 Using AC shown in Table-1, mixed in the formulation shown in Table-4,
Ultra-low cement castables with extremely low AC content were prepared.

A predetermined amount of water was added to this ultra low cement castable and mixed for 5 minutes with a mixer to measure the physical properties of the kneaded product. The results are shown in Table-5. The measurement of physical properties was in accordance with Example 1.

As shown in Table-5, the ultra low cement castable using this AC has good physical properties such as flow and pot life.

Example 3 High-purity quicklime and Bayer alumina were blended so that C / A = 1/2 and melted in an electric furnace. The melt was cooled in air to obtain crystalline CA (CA ₂ ) clinker. This clinker was crushed with a batch type ball mill to give a Blaine specific surface area.
5,420 cm ² / g of crystalline AC was produced.

Water was added to this crystalline AC in an amount such that the water ratio (W / C) was 60%, and the mixture was cured at 20 ° C. and 100 R.H. for 7 days to prepare an AC hydrated cured product. The hydrated cured product was dried at 110 ° C for 20 hours, and then the particle size was 5
Crushed to 1,200 mm or less, calcined the product at 1,200 for 3 hours, and
A-CA with / A = 1/2 was produced. This A-CA was crushed with a batch-type ball mill, and this AC with a Blaine specific surface area of 6,530 cm ² / g
Got

Amorphous and crystalline AC are mixed according to the formulation shown in Table-6,
A low cement castable was prepared.

A predetermined amount of water was added to this low cement castable and mixed for 3 minutes with a mixer, and the physical properties of the kneaded product were measured. The results are shown in Table-7. The measurement of the physical properties was in accordance with Example 1.

As shown in Table 7, when this AC is used, the aggregation time can be lengthened and a low cement castable hydrated product with high aggregation strength can be obtained.

Example 4 The procedure of Example 1 was repeated, except that the peptizers shown in Table 8 were used for A-CA produced in Example 3. Table of results
It is also described in 8.

The deflocculants used were all reagents 1 manufactured by Ishizu Pharmaceutical Co., Ltd.
The grade was used.

<Effects of the Invention> The low cement castable using the present AC can be constructed with a small amount of water, has good workability, and can obtain a sufficient cohesion time and cohesive strength as needed.

Claims (2)

[Claims] 1. A molar ratio of CaO and Al ₂ O ₃ CaO / Al ₂ O ₃ is 1 / 1.2 to ₃ /
Alumina cement containing 80% by weight or more of amorphous calcium aluminate of 7. 2. A low cement castable binder containing the alumina cement according to claim 1 and ultrafine powder and a deflocculant as main components.