JPH0557357B2 - - 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 relates to a method of accelerating the thermite reaction and improving the performance of ceramics. (Prior art) Composite pipes made by coating the mother 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 inner surface of the main tube 1 is heated as shown in Fig. 2. Then, a desired ceramic layer 4 is coated with a generated metal layer 3 interposed therebetween. Fe ₂ O ₃ +2Al→Al ₂ O ₃ +2Fe +199 Kcal/1 mol of Al ₂ O ₃ (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=2.96:1. However, if only thermite base material is used, which has a stoichiometric mixing ratio of metal oxide and metal reducing agent, the resulting ceramic layer will become porous.
As disclosed in Japanese Patent No. 34470, 5 to 15% by weight of SiO ₂ (silicic acid) is added to the base material to make the ceramic densified. (Problem to be solved by the invention) However, when SiO ₂ is added, corundum (α-Al ₂
A glass phase of SiO ₂ and a compound phase of SiO ₂ and FeO (Fe ₂ SiO ₄ ) are formed at the grain boundaries of O ₃ ), resulting in a decrease in the proportion of corundum in the ceramic, resulting in a decrease in strength and hardness. do. In addition, in acidic liquids (especially at high temperatures), the Fe content in the Fe ₂ SiO ₄ phase is eluted, so
The drawback was that sufficient corrosion resistance could not be obtained.
Incidentally, when 7% SiO ₂ is added, the resulting ceramic contains about 14% FeO. In view of the above-mentioned problems, the present invention was made with the aim of reducing FeO in ceramics without impairing the densification of ceramics using the centrifugal thermite method, and thereby improving strength, hardness, and corrosion resistance. be. (Means for Solving the Problems) In order to achieve the above object, the means of the present invention is to add SiC to the thermite main material which is theoretically mixed with iron oxide and Al.
The point is that the added thermite agent added in an amount of 1.5 to 4.0% by weight per minute is used as the thermite agent in the centrifugal thermite method. (Example) The present inventor believes that the reason why a large amount of FeO remains in the produced ceramics is that the reducing power of the metal reducing agent in the thermite agent is weak, and furthermore, the thermite reaction is carried out in the atmosphere, so the metal oxide is It was thought that this was because it was not effectively reduced by the metal reducing agent. As a result of intensive research based on this idea, we have discovered a method that allows the thermite reaction to be conducted in isolation from the atmosphere, increases the reducing power of the metal reducing agent in the thermite agent, and further contributes to the densification of the resulting ceramics. Ivy. That is, an additive thermite agent in which SiC is added to a thermite main agent consisting of theoretically mixed iron oxide and Al is used as a thermite agent in the centrifugal thermite method. The heat of formation due to thermite reaction is, for example, Fe ₂ O ₃
In the case of Al-based materials, the temperature reaches up to 3000℃. On the other hand, SiC
Since the decomposition temperature of is 2600°C, SiC easily decomposes into Si and C during the thermite reaction. Si
acts as an excess reducing agent, reducing the amount of unreacted iron oxide remaining in the ceramics, and also forms SiO ₂ (glass phase) during the solidification process, filling the corundum grain boundaries and contributing to the densification of the ceramics. On the other hand, C is oxidized and burned to become CO ₂ and CO gas, which isolates the entire reaction system from the atmosphere and forms a more favorable reducing atmosphere to reduce the amount of unreacted iron oxide remaining. In order to isolate the reaction system from the atmosphere, attempts were made to conduct the reaction in an N ₂ gas or Ar gas atmosphere, but this resulted in only the formation of a gas flow on the surface layer of the thermite agent with both ends of the main tube open. However, it was difficult to sufficiently block it. In addition, by placing the entire main tube inside a chamber and filling it with the inert gas after vacuum degassing, it is possible to completely isolate it from the atmosphere, but in such a case, special equipment is required and production They are forced to degrade their sexuality. In order to find a suitable addition amount of SiC, the present inventor added metal Si to the thermite base material in various proportions, and determined how the addition amount of Si affects the porosity of the ceramic and the adhesion shear force between the ceramic and the produced iron. We investigated whether it would have an impact. The result is the third
It is shown in FIG. FIG. 3 is a graph showing the relationship between the amount of Si added and the porosity of ceramics. When Si is not added, the porosity of ceramics is extremely porous at about 25%, but with Si: 1 to 5%. It becomes dense with 5%
If it exceeds , a porous tendency will appear. FIG. 4 is a graph showing the relationship between the amount of Si added and the adhesion shear force between the produced iron and the produced ceramics. As shown in Fig. 5, the contact shear force is measured by using a composite pipe (using steel pipe as the main pipe) manufactured by the centrifugal thermite method, placing the main pipe 1 and the produced iron layer 3' on a punching table 5, and It was calculated based on the pressing force when only the ceramic layer 4 was pressed through the punch 6 and the produced ceramic layer 4 was punched out. According to the figure, it can be seen that when Si exceeds 4%, the adhesion shear force is considerably lower than when no Si is added (approximately 120 Kg/cm ² ). At this time, as a result of cross-sectional observation of the composite tube, it was observed that a considerable number of voids were generated at the boundary between the produced ceramic layer 4 and the produced iron layer 3'. The above is (Fe ₂ O ₃ + 2Al) as thermite main agent.
Although we have explained the case where Fe ₃ O ₄ and FeO were used as the metal iron oxide, substantially the same results were obtained. Based on these facts, the theoretically formulated iron oxide and
Si is added at a weight ratio of 1.5 to the thermite main material of Al.
For those with ~4% addition, ceramic porosity is 2~3% Adhesive shear force between produced iron and produced ceramics
It shows 250-100Kg/ ^cm2 , and good ceramic lining tube can be obtained. Note that when 1.5 to 4% Si was added, the FeO content in the produced ceramics was about 5%. From the above, SiC has a Si content of 1.5 to 4% (2.1 to 5.7% for SiC alone) relative to thermite base material.
It can be seen that by adding this, a composite pipe that is dense and has a good lining condition can be obtained. In addition, the method of loading the added thermite agent into the main tube is to spray a mixture of thermite base agent and SiC onto the main tube, or to sprinkle SiC powder onto the mother tube and then apply the thermite base agent on the top surface. May be sprayed. Further, the mother pipe is not limited to metal-based pipes such as steel pipes, but may also be inorganic pipes such as concrete pipes and ceramic pipes. Next, other specific examples will be described together with conventional examples and comparative examples. In addition, the conventional example is SiO ₂
The comparative example is one in which metal Si is added. (1) Mix and prepare the additive thermite agent shown in Table 1, load it into the main pipe (steel pipe) listed in the table so that it has an almost uniform thickness, and rotate it at high speed (1400 ~
1500 rpm) to cause a thermite reaction. (2) After the thermite reaction was completed, the tube was sufficiently cooled to obtain a composite tube. A ceramic layer of about 4 mm was formed on the inner surface of each of the composite tubes. (3) Table 2 shows the results of investigating the composition and physical properties of the produced ceramics. The corrosion resistance is expressed as an index based on the conventional example, and was calculated by immersing it in a 10% H ₂ SO ₄ (sulfuric acid) solution and measuring the corrosion loss.

【table】

[Table] (Effects of the Invention) As explained above, according to the present invention, in the centrifugal thermite method, SiC is added to the aluminum/iron oxide based thermite main material at a Si content of 1.5 to 1.5 to
Since the additive thermite agent containing 4.2% by weight is used, SiC decomposes due to thermite reaction and becomes Si,
CO ₂ gas and CO gas are generated, and Si acts as an excess reducing agent, reducing the residual amount of unreacted iron oxide in the ceramics, and also forms SiO ₂ during the solidification process, filling the corundum grain boundaries and reducing the amount of iron oxide in the ceramics. Makes densification possible. On the other hand, CO ₂ gas etc. encapsulate the reaction system and cause the Al in the added thermite agent and the atmosphere to
By blocking O ₂ , the thermite reaction can proceed according to theory, and the production of unreacted iron oxide can be reduced as much as possible. This not only densifies the resulting ceramics, but also reduces the Fe ₂ SiO ₄ phase as much as possible since the ceramics contain almost no iron, thereby increasing the strength of the ceramics.
Both the hardness and the corrosion resistance can be improved, and a composite tube can be obtained with a produced ceramic layer of very high quality.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main tube showing the loading state of thermite agent in the centrifugal thermite method, FIG. 2 is a cross-sectional view of the main tube (i.e., composite tube) after the thermite reaction,
Figure 3 is a graph showing the relationship between Si addition amount and porosity, Figure 4 is a graph showing the relationship between Si addition amount and adhesive shear force, and Figure 5 is a cross section shown in the adhesive shear force test method. It is an explanatory diagram. 1... Mother pipe, 2... Thermite agent layer, 3... Produced metal layer, 3'... Produced iron layer, 4... Produced ceramic layer.

Claims (1)

[Scope of Claims] 1. A method in which a thermite agent is loaded onto the inner surface of the mother tube, a thermite reaction is performed in a centrifugal force field, and a ceramic layer is coated on the inner surface of the mother tube via a metal layer formed, comprising: SiC is added to the thermite main material consisting of iron oxide and Al in a Si content of 1.5 to 1.5 to the main material.
A method for manufacturing a composite pipe, characterized in that an additive thermite agent containing 4.0% by weight is used as the thermite agent.