JPH029451A - Coated layer for self-cleaning - Google Patents

Abstract

PURPOSE:To obtain a self-cleaning coated layer which enables catalytic activity to be maintained for a long time by forming the coated layer of a composite oxide consisting of Ce, Cu and Mn with a specific composition on a base using a plasma flame spraying method so that the density gradient of Ce, Cu and Mn is obtained in a film thickness direction. CONSTITUTION:After an aqueous solution of nitrate containing Ce, Cu and Mn and a precipitate is obtained using a coprecipitation method, a composite oxide expressed by CeA, CuB, MnC OD (where A=1, B+C=1.0<B<1.0<C<1.0>0) through pyrolysis. The obtained catalytic powder is plasma-sprayed on a stainless steel base so that the density gradient of Ce, Cu and Mn is obtained in the thickness direction of the coated layer. Since a self-cleaning coated layer is obtained as described, which is made only of catalyst, the contact area between the catalyst and an oily component is large. In addition, since the plasma-flame sprayed film is a porous film with an optimum porosity, an adequate amount of oxygen is supplied to a reaction surface between the catalyst and the oily component. Consequently, the catalytic activity can be maintained for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a coating layer having a catalytic action for oxidizing hydrocarbon compounds.

BACKGROUND OF THE INVENTION Conventionally, oxides of noble metals and transition metals have been used as hydrocarbon-based oxidative decomposition catalysts. For example, when considering triglycerides of higher fatty acids containing carboxyl groups, which are found in oil stains on cooking utensils, Mn and Cu are examples of hydrocarbon compounds.

Metal oxides such as F, Co, N1, etc. or mixtures of metal oxides are known as oxidative decomposition catalysts, and catalytic materials mainly composed of these oxides are coated on the inner wall of the cooker. There are also catalytic coatings added to glassy films. These are made by dispersing a catalyst in an inorganic binder and applying it to the internal wall surface of the refrigerator to form a coating layer.
It attempts to catalytically decompose oil, food residue, etc. at high temperatures, but because the catalytic material is covered in a film of enamel, glass, paint, etc., the surface exposure is reduced.
A high temperature of 50''C or higher is required, and a coating layer that has catalytic activity at even lower temperatures is desired.

Problems to be Solved by the Invention In the above prior art, for example, each metal oxide has a low catalytic activity for the oxidative decomposition reaction of triglyceride;
Further, when used as a film, the catalyst is dispersed in a heat-resistant binder, so the catalyst surface is not exposed and the activity is reduced, which is a problem. In addition, in order to increase the exposure of the catalyst surface, the coating layer must be made as porous as possible, but on the other hand, making it porous reduces the adhesion with the base material and the corrosion resistance and abrasion resistance of the coating layer. was there. C These problems become the main cause, and secondary problems such as difficulty in practical application occur.

The present invention aims to solve the above problems, and provides a self-cleaning coating layer that lowers the reaction temperature by increasing the activity of the catalyst itself and also when the catalyst is formed as a coating layer on a base material. It is something.

Means for Solving the Problems In order to solve the above problems, the present invention coats the surface of a heat-resistant base material with a coating layer of a composite oxide of rare earth element Ce and transition metals Cu and Mn by plasma spraying. The layer is formed with a concentration gradient of Ce, Cu, and Mn in the thickness direction, and is intended to decompose the oil scattered from the cooked food on the surface of this coating layer.

Function The function of the catalyst coating layer having the above configuration will be explained. First, the catalyst of the present invention, CeACLIBMlICOD (Idanshi A=1, B10=1, O<day<1.O<C<1
, D>0) is an unprecedented compound and exhibits higher activity for oxidizing vetriglyceride than single oxides of each component. For example, CeO2, Cu
It has higher oxidizing activity than O, Cu2O, Mn2O3, and Mn02. This is C. and Cu.

This is because in ternary Mn oxides, the elements on the surface of the oxide have many valences (for example, Mn is trivalent and tetravalent, Cu is monovalent and divalent, etc.), that is, it is a single component. This is because valence control between different elements, which cannot be seen in other materials, is achieved, creating a surface more suitable for reactions. This is recognized in xPS.

In the present invention, a single catalyst film is formed by plasma spraying using the above catalyst. The film itself is a catalyst, so unlike enamel, glass, or paint, the catalyst is not covered and hardened with frit or binder. Therefore, in the coating layer of the present invention, direct contact between the catalyst and oil and sufficient supply of oxygen to the reaction interface can be achieved, thereby improving the catalyst performance. Furthermore, Ce, Cu, Mn are added in the thickness direction of the coating layer.
Therefore, for example, by increasing the content of C on the surface side of the heat-resistant base material of the coating layer, the surface area of the heat-resistant base material can be increased, and the surface area of the heat-resistant base material can be increased.
By increasing the Mn content, a coating layer with higher oxidation activity can be formed.

Example An embodiment of the present invention will be described below.

First, the method for preparing the catalyst will be explained.

An aqueous solution containing nitrates of Go, Cu, and Mn at a predetermined molar ratio was prepared, a precipitate was obtained by a coprecipitation method, and then thermally decomposed to form CeACuBMnCOO (where A=1.B
10=1, O<8<1, O<Cku1. A composite oxide represented by D>0) was used. For comparison, single and dual component transition metal oxides were prepared by precipitation method.

Using the catalyst powder prepared by the above method, plasma spraying was performed on a blast-treated stainless steel substrate (plate thickness: 1 rnm) to form a sprayed catalyst coating with a thickness of 20 μm.

For plasma spraying, an NT30 type DC plasma spray device manufactured by Mizuta Iron Works was used.

This was used as a test piece to confirm its ability to purify oil at 370°C. Drop a certain amount of salad oil onto the test piece and
Changes in the salad oil were observed after it was kept in the oven in C. The results are shown in Table 1.

From the results in Table 1 and above, it can be seen that the coating layer obtained by plasma spraying the Ce--Cu Mn composite oxide has an extremely large accelerating effect on the oxidation reaction of triglycerides.

Approximately 1 ttl of salad oil was dropped onto the catalyst powder and heated, and the temperature at which combustion of the salad oil started was confirmed.

Approximately 240 to 250°C for Co Cu-Mn system
The start of combustion was observed.

With Mn oxide and Cu oxide, this phenomenon does not occur even at 300"C, and the difference in catalytic activity is clear.
It can be seen that the -Mn system is particularly suitable for decomposing oil. Since it is a composite oxide, it exhibits high activity against oil decomposition due to its combined effect of promoting oxidation reactions and acting as a source of oxygen to Mn, etc., especially in R-lux. It seems that this has been done.

Furthermore, if we consider the functions of each element in Co-Cu-Mn complex oxides, as shown in Table 2, Cm oxide has a large surface area as a single oxide, and Cu-
It can be seen that a catalyst with an even larger surface area is created by combining it with a Mn-based composite oxide. As already mentioned above, Ce oxide serves as a source of oxygen to Mn and the like in the bulk.

Table 2 Ce0) (, Mn0) prepared by the same precipitation method
(.

For CLIOX (X: undetermined), each powder and salad oil were mixed at a constant weight ratio, and changes in the weight of the salad oil due to temperature rise were monitored using a thermobalance. Figure 3 shows the results.

From Figure 3, for the oxidation of salad oil, M is better than Ce01.
It can be seen that the catalytic activity of n0) (and Cu OX is higher than that of C.-CuMn-based composite oxides, which has an even more synergistic effect when combined and shows unprecedented high activity. be.

Based on the above results, we attempted to utilize the advantages of plasma spraying to form a more highly active coating layer. In plasma spraying, two or more types of powder can be simultaneously sprayed onto the same substrate from separate spray ports to form a film. Therefore, as shown in Fig. 1, Ce01 and Cu-Mn
A coating layer 4 was formed by thermally spraying 0) (from separate thermal spray ports 2°3 onto a heat-resistant substrate 1. At this time, each thermal spray 1 was changed over time as shown in FIG. 2, and T After a period of time, the thermal spraying was stopped, and a concentration gradient of Ce, Cu, and Mn was created in the thickness direction of the coating layer. Salad oil was dropped onto the coating layer 4 formed with a concentration gradient of Co, Cu, and Mn. When the temperature was increased, the oil completely decomposed after approximately 20°C at 350°C and no residue remained.In the coating layer formed without a concentration gradient, the oil decomposed at approximately 30°C at 370°C as shown in Table 1. The oil is decomposed in ~35 minutes.

This means that by increasing Cll0X on the base material side, a catalyst layer with a larger surface area can be formed, and Cu with high catalytic activity can be used.
This is probably because by increasing the amount of -Mn in the surface layer, overall catalytic activity against oil oxidation is exhibited.

As described in the detailed description of the invention, according to the present invention, a self-cleaning coating layer of a catalyst alone is formed on the surface of a base material by plasma spraying using a Ce-Cu-M n-based composite oxide catalyst with extremely high catalytic activity. Therefore, the contact area between the catalyst and the oil is large, and since the plasma sprayed coating is a porous film with suitable porosity, oxygen is sufficiently supplied to the reaction interface between the catalyst and the oil. Therefore, since the oxygen consumed in the oxidation reaction is replenished from inside the film and from the air, the catalyst activity can be maintained for a long period of time without deterioration of performance.

Furthermore, since the concentration gradient of Ce, Cu, and Mn can be freely leveled in the direction of the film, a more highly active film can be formed. In addition, Ce01 has good adhesion to the base material and is resistant to acids, so it is placed on the base material side of the coating layer.
By increasing the content of (), the adhesion to the base material is improved, and even if it comes into contact with acid, the base material can be prevented from being corroded by the acid.

By applying the self-cleaning coating layer of the present invention to the inner wall surface of an oven, etc., it is possible to reduce the temperature of 500 to 550°C, which was required to be maintained at a temperature of 500 to 550°C in the case of thermal self-cleaning in a conventional burn-off type oven. It is possible to lower the temperature below ℃, which has great effects in terms of energy saving and heat insulation. Also, since oil stains can be completely broken down, the inside of the oven can be kept in a new condition for a long time.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional conceptual diagram of a coating layer according to an embodiment of the present invention;
FIG. 2 is a correlation graph showing an example of a spray amount control method in plasma spraying, and FIG. 3 is a thermogravimetric change curve of a mixture of various oxides and salad oil. 1... Heat-resistant base material, 2, 3... Plasma bath injection port, 4... Plasma sprayed catalyst coating. Agent's name Patent attorney Toshio Nakao Figure 18 Figure 4 I&Jt thermal spraying 1 Atsushi #eye WR (serving eye Δ)

Claims (1)

[Claims] A coating layer of a composite oxide consisting of Ce, Cu, and Mn formed on a base material by a plasma spraying method, and the composite oxide is composed of C
e_ACu_BMn_CO_D (However, A=1, B+C=
1, 0<B<1, 0<C<1, D>0), and the coating layer further includes Ce, Cu, M in the thickness direction.
A self-cleaning coating layer formed by a plasma spraying method characterized by having a concentration gradient of n.