JPH0224660B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an improvement in a method of forming a ceramic layer on the inner surface of a main tube using a thermite reaction, and more specifically, it promotes the thermite reaction and densifies the ceramic layer. Regarding how to. (Prior art) Composite pipes made by coating the inner surface of the pipe with a ceramic layer are used as transportation pipes for various fluids and industrial piping because the ceramic layer exhibits good properties such as heat resistance, abrasion resistance, and corrosion resistance. It has a wide range of applications as a member. Various methods have been used to manufacture this type of composite tube, and recently, the so-called centrifugal thermite method, which utilizes centrifugal force and thermite reaction, has been proposed as a suitable manufacturing method. That is, this method, as shown in Figure 1,
A thermite agent made of a mixture of a metal reducing agent such as Al and Fe ₂ O ₃ and a metal oxide at a certain ratio is loaded into the main tube 1 to form a thermite agent layer 2, which is then subjected to centrifugal force due to high speed rotation. A fire is ignited in the field to cause a thermite reaction as exemplified by equation (1), and the molten metal and molten ceramic produced by this exothermic reaction are separated by specific gravity, and the main tube 1 is separated as shown in Figure 2. The inner surface is coated with a desired ceramic layer 4 via a metal layer 3. Fe ₂ O ₃ +2Al→Al ₂ O ₃ +2Fe +199 kcal/ ₃ moles of Al ₂ O (1) The mixing ratio of the metal oxide and the metal reducing agent is usually adjusted to the theoretical mixing ratio. For example, the above
In the example of Fe ₂ O ₃ and Al, the molar ratio is Fe ₂ O ₃ :Al=1:2, and the weight ratio is Fe ₂ O ₃ :Al=2.959:1. (Problems to be Solved by the Invention) However, when the ratio of metal oxide and metal reducing agent is adjusted to the stoichiometric mixing ratio, the purity of the reaction product decreases. For example, when a mixture of Fe ₂ O ₃ and Al is used as the thermite agent, the produced oxide is mainly
It consists of Al ₂ O ₃ but contains about 10wt% FeO, while the produced metal mainly consists of Fe but contains 5wt% Al.
It will contain some amount. Therefore, by changing the theoretical mixing ratio with Fe ₂ O ₃ and over-blending Al so that the weight ratio is Fe ₂ O ₃ :Al = 2.959 or less: 1, the metal reducing agent Al in the thermite agent
The reducing power of is increased, and the thermite reaction shifts to the right side of equation (1).
It does not help improve the density of the resulting ceramics. SUMMARY OF THE INVENTION In view of these problems, an object of the present invention is to provide a method for manufacturing a composite tube that promotes the thermite reaction, densifies the resulting ceramic, and improves the quality of the ceramic. (Means for Solving the Problems) In order to achieve the above object, the production method of the present invention is characterized in that a silicon compound that does not participate in the reaction is added to the thermite main ingredient consisting of a metal reducing agent powder and a metal oxide powder. An additive thermite agent mixed with a powder of In the method of forming a ceramic layer through a layer, the metal reducing agent in the thermite main ingredient is composed of Al and Mg, and the amount of the metal reducing agent is larger than the amount theoretically required to reduce the metal oxide. The composition of the invention is that it is blended with. (Function) According to the above means, since the amount of the metal reducing agent in the Thermite base agent is blended in a larger amount than the amount theoretically required to reduce the metal oxide, in other words, it is over-blended.
The reducing action of the metal oxide in the thermite base material is strengthened, the thermite reaction is promoted, and unreacted metal oxides in the thermite base material or metal oxides with reduced oxidation numbers generated during the reaction process can remain in the thermite base material. It is possible to effectively prevent these from being contained in the produced ceramics. In addition, since the overmixed metal reducing agent was composed of Al and Mg, MgO−Al ₂ O ₃ was formed by thermite reaction.
Spinel-based ceramics can be produced, thereby significantly improving the corrosion resistance of the ceramic layer to acidic solutions. In addition, due to the silicon compound in the added thermite agent,
The densification of the produced ceramics is achieved, and together with the prevention of the inclusion of the oxides, the quality of the ceramics can be improved. (Examples) Examples of the present invention will be described in detail below. The additive thermite agent used in the present invention is prepared by adding and mixing powder of a silicon compound that does not take part in the reaction to the thermite main agent which is the main component of the thermite reaction. Thermite main agent is a metal reducing agent composed of Al and Mg, Fe ₂ O ₃ , Fe ₃ O ₄ , Cr ₂ O ₃ , NiO,
It is a mixed powder with metal oxides such as MnO ₂ , CoO, CuO, and SnO ₂ , and the metal reducing agent is added in excess of the metal oxide. Generally, Al
is considered to be the amount theoretically required for the reduction of metal oxides, and Mg is considered to be the excess amount. Since Mg has higher oxidizing properties than Si, which is known as a metal reducing agent, when an iron-based metal oxide is used, it is effective in reducing unreduced FeO. It is effective to add Mg in an amount of 15% by weight or less in the added thermite agent, but 3 to 5% is sufficient, and addition of 3 to 5% can reduce FeO to 3 to 4%. However, when Mg is oxidized, it becomes MgO, which becomes part of the composition of ceramics. The content of MgO in ceramics is proportional to the amount of Mg added, and for example, the content of MgO in ceramics is 7 to 10% by adding 3 to 5% Mg.
The composition is MgO. In addition, when MgO is included in Al ₂ O ₃ , if MgO is 8% or more, it becomes α-Al ₂ O ₃ .
It does not form a eutectic structure with MgO−Al ₂ O ₃ and has a white color.
It becomes MgO−Al ₂ O ₃ spinel ceramics. Therefore, in terms of physical properties, it exhibits the properties of MgO-Al ₂ O ₃ spinel ceramics, and has a hardness of 1000 Hv and a bending strength of 1200 Kg/cm ² compared to α-Al ₂ O _3- based ceramics.
Although the ceramic is somewhat soft, its durability against acidic solutions is excellent, about five times that of conventional ceramics, and about twice that of the Si-added ceramics. Silicon compounds such as SiO ₂ , Si ₃ N ₄ and SiC, which do not participate in the thermite reaction, are added to the thermite main ingredient. These compounds have the effect of lowering the fluidity of molten ceramics and densifying the ceramics. However, addition of a large amount is not preferable because it takes away too much reaction heat and acts to inhibit the thermite reaction. In the case of _SiO2 , the amount added may be up to 20% by weight in the added thermite agent, with best effects being obtained between 2 and 8%. The main pipe applicable to the present invention is not limited to a metal pipe such as a steel pipe, but may be a non-metallic pipe such as a concrete pipe as long as it can withstand the thermite reaction. Next, more specific examples will be described. (1) Load the added thermite agent shown in Table 1 onto the inner surface of the main pipe (steel pipe) shown below, rotate the main pipe at the rotation speed shown below, and then ignite the added thermite agent to cause a thermite reaction. brought about. Furthermore, No.1
is an example, and Nos. 2 and 3 are comparative examples. In addition, in No. 3, after first spraying SiO ₂ on the inner surface of the main tube,
In some cases, thermite main agent is loaded thereon, and in other cases, an added thermite agent, in which each component is added and mixed all at once, is sprinkled on the inner surface of the main tube. Γ Bus tube size (mm) Outer diameter 101.6×4.2t×250 Γ Bus tube rotation speed (rpm) No. 1: 1600 No. 2, 3: 1500

[Table]
(2) After the reaction, a second
The outer ceramic layer was lined.
In the same table, the crystal phases were identified by X-ray diffraction. In addition, the thickness of the metal layer is 2
It was about mm.

【table】

[Table] (3) Using the obtained ceramic layer,
Corrosion resistance was investigated by immersing in % _{H2SO4 solution} . For comparison, we also investigated the corrosion resistance of the ceramic layer of a composite pipe manufactured using a thermite agent containing Al and Fe ₂ O ₃ in the theoretical mixing ratio as a conventional example. Corrosion resistance was determined by measuring corrosion weight loss. The results are shown in Table 3 below. The data value is an index when the weight loss of the conventional example is set as 100, and the smaller the value, the better the corrosion resistance. From the same table, in No. 1 according to Example, the crystal phase is mainly MgO-
Since it is Al ₂ O ₃ spinel, it was confirmed that it has extremely good corrosion resistance compared to other materials.

[Table] (Effects of the Invention) As explained above, according to the present invention, an additive thermite agent is used in which a silicon compound is added and mixed into a thermite main agent in which a metal reducing agent is added in excess of the amount of metal oxide. Therefore, the thermite reaction can be promoted, the residual unreacted or reaction intermediate oxides can be reduced as much as possible, and the quality of the ceramic lining the main tube can be significantly improved by densifying the ceramic. Can be done. Furthermore, in the present invention, since the metal reducing agent in the thermite main material is composed of Al and Mg, MgO-Al ₂ O ₃ spinel ceramics can be produced by the thermite reaction, thereby reducing the thickness of the ceramic layer. Corrosion resistance against acidic solutions can be significantly improved.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the main tube in the manufacturing process of the centrifugal thermite method, showing the state in which a thermite agent (added thermite agent in the present invention) layer is formed, and Figure 2 is a cross-sectional view of the main tube in the manufacturing process of the centrifugal thermite method. 1 is a cross-sectional view of a certain composite tube, showing a ceramic layer coated with a metal layer. 1... Mother pipe, 2... Thermite agent layer, 3... Metal layer, 4... Ceramics layer.

Claims (1)

[Scope of Claims] 1. An additive thermite agent made by adding and mixing powder of a silicon compound that does not participate in the reaction to a thermite main agent consisting of powder of a metal reducing agent and powder of a metal oxide is loaded onto the inner surface of the main tube, and centrifugal force is applied to the thermite agent. A method in which the added thermite agent is ignited in a field to cause a thermite reaction to produce molten metal and molten ceramics, and a ceramic layer is coated on the inner surface of the main tube via a metal layer, the method comprising: reducing the metal in the thermite main agent; 1. A method for producing a composite tube, characterized in that the agent is composed of Al and Mg, and the amount of the metal reducing agent is greater than the amount theoretically required to reduce the metal oxide.