US3771974A

US3771974A - Surface-coated metal material having resistance to molten tin

Info

Publication number: US3771974A
Application number: US00070066A
Authority: US
Inventors: K Itakura; Y Ohmae
Original assignee: Nippon Sheet Glass Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd
Priority date: 1969-09-18
Filing date: 1970-09-08
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13

Abstract

A metal material having corrosion resistance against molten tin, said metal material comprising a metal base having iron as a main constituent and a surface coating alloy layer, said surface coating alloy layer composed of an iron alloy and a particulate matter dispersed in said alloy, said alloy consisting of iron and one or both of titanium and aluminium, said particulate matter consisting essentially of at least one of TiO2, Al2O3, ZrO2, CaO, MgO, SrO, BaO and SiO2 and one or both of titanium and aluminium. The metal material is prepared by contacting a powdery mixture of one or both of titanium and aluminium and at least one metal oxide listed above with a metal base having iron as a main constituent, and heating them to an elevated temperature in an inert atmosphere.

Description

United States Patent [1'91 Itakura et a].

' 1111 3,771,974 [451 Nov. 13, 1973 SURFACE-COATED METAL MATERIAL HAVING RESISTANCE TO MOLTEN TIN [75] Inventors: K'iyoshi ltakura, Nishinomiya;

Yutaka Ohmae, Kawanishi, both of I Japan [73] Assignee: Nippon Sheet Glass Co., Ltdt,

Osaka, Japan [22] Filed: Sept. 8, 1970 [21] Appl. No.: 70,066

[30] Foreign Application Priority Data Sept. 18, 1969 Japan 44/71126 Sept. 18, 1969 Japan 44/71127 [52] US. Cl. 29/195 M, 117/107.2 P

[51] Int. Cl B32]: 15/18 [58] Field of Search 29/195 M [56] References Cited UNITED STATES PATENTS 1,775,531 12/1956 Montgomery et a1. 29/195 X 2,900,276 8/1959 Long et a1 29/195 X Primary ExaminerL. Dewayne'Rutledge Assistant ExaminerE'. L. Weise Attorney-Wenderoth, Lind & Ponack [57] ABSTRACT A metal material having corrosion resistance against molten tin, said metal material comprising a metal base having iron as a main constituent and a surface coating alloy layer, said surface coating alloy layer composed of an iron alloy and a particulate matter dispersed in said alloy, said alloy consisting of iron and one or both of titanium and aluminium, said particu late matter consisting essentially of at least one of TiO A1 0 ZrO CaO, MgO, SrO, BaO and SiO and one or both of titanium and aluminium. The metal ma- V terial is prepared by contacting a powdery mixture of one or both of titanium and altiminium and at least one metal oxide listed above with a metal base having iron as a main constituent, and heating them to an elevated temperature in an inert atmosphere.

4 Claims, 1 Drawing Figure SURFACE-COATED METAL MATERIAL HAVING RESKSTANCE T MOLTEN TIN This invention relates to a surface-coated metal material having resistance to molten metal, especially mol ten tin.

in recent years, the glass industry developed a method of producing glass sheet having good flatness by pouring out a molten glass melted in a glass-melting furnace continuously over a molten metal to form a glass ribbon, cooling it by advancing it along a molten metal bath, and then withdrawing it. This method is termed a float glass process in the art. In this process, a molten tin is mainly used as the molten metal, and is palced in a tank of refractory brick. The atmosphere surrounding the molten metal bath is a reducing atmosphere for preventing the oxidation of the metal bath. Because of oxygen and sulfur contained in very small amounts in the glass batch or in the atmosphere, small amounts of oxides and sulfides are formed on the molten metal bath, and adhere to the underside of the glass ribbon advancing on the molten metal bath while being in contact therewith, thereby causing defects on the glass ribbon. A pocket is provided on the side wall of the molten metal bath to remove a floating matter comprising these oxides and sulfides; the floating matter is gathered in the pocket and then scraped out. This scraping means is partly immersed in the molten metal, and undergoes strong corrosion of the molten metal. Of course, any other materials which are in contact with the molten metal undergo strong corrosion of the molten metal. Hence, the material to be immersed in the molten metal need be highly anti-corrosive against the molten metal, and readily processable mechanically, and have high strength and thermal stability at high temperatures. Silicon nitride and graphite (in a reducing atmosphere) can be mentioned as such material from the standpoint of resistance to heat and corrosion, but these materials meet with difficulty in respect of processability and mechanical strength. Stainless steel is a material which is easily workable and heat resistant and has strength at high temperatures, but has the de fect of being susceptible to corrosion by the molten metal.

Generally, even alloys having good thermal stability and corrosion resistance in use in the air do not necessarily have corrosion resistance when being in contact with a molten tin. For instance, platinum and gold are said to be excellent in heat resistance and corrosion resistance in the air, but when immersed for a day in molten tin at 600C., undergo large corrosion. With stainless steel heat-resistant alloys such as l8Cr-8Ni stainless steel or 25 Cr- Ni stainless steel, the main constituents such as nickel, chromium and iron are locally dissolved out and finally disappear when such alloys are immersed in molten tin for a day at 900C. In choosing materials resistant to molten tin, therefore, we cannot rely on the standards for ordinary heat-resistant and corrosion-resistant materials.

It has now been found that iron-aluminium alloys, iron-titanium alloys, iron-aluminium-titanium alloys and the like have good corrosion resistance against molten tin, and that when the surface of a metal consisting predominantly of iron is subjected to calorization, a kind fo the aluminium impregnation method, the corrosion resistance of the metal to molten tin can be enhanced. The calorization is a well-known method of treating the surface of metal which involves packing the metal to be treated into an iron receptacle together with a penetrant consisting of the powders of an aluminium-iron (:50) alloy and a small amount of ammonium chloride, and after sealing, heating the receptacle to 900l ,O00C. thereby to form a coating of the iron-aluminium alloy on the surface of the metal. A marked increase in corrosion resistance is observed when the calorizing treatment is applied especially to such alloys as iron-aluminium, iron-titanium, and ironaluminium-titanium alloys. The corrosion resistances of 5Al-95Fe alloy, 5Ti9SFe alloy and 5Al-9Ti-86Fe alloy (the alloy composition being by weight) were examined, and the results are shown in Table 1 below. The test procedure was as follows: The metal material was immersed in molten tin at 970C. in a reducing atmosphere, and the number of days which elapsed until there was a corrosion perceptible to the naked eye on the surface of the material.

TABLE 1 Materials Not calorized Calorized 5Al-9SFe alloy 7 days 25 days 5Ti-95Fe alloy 7 25 5Al-9Ti-86Fe alloy 8 29 It is clearly seen from the results shown in Table 1 that these alloy materials have corrosion resistance durable for about 25 days when calorized. The corrosion resistance of this degree, if not sufficient, is feasible for practical purposes. These three types of iron base alloys, however, are expensive in addition to having such defects as extreme hardness and difficulty of working. Mild steel and stainless steel which are easy to work mechanically will have an improved corrosion resistaiice when calorized, but the corrosion resistance is durable for less than 7 days, as will be shown later in the Examples. It is necessary therefore to replace such materials frequently.

An object of the present invention is to provide a metal material which has a high resistance to corrosion by molten tin and high strength and thermal stability at high temperatures and which is easy to work mechanically.

According to this invention, there is provided a metal material having corrosion resistance against a molten metal consisting predominantly of tin, said metal material comprising a metal base having iron as a main constituent and a surface coating alloy layer, said surface coating alloy layer composed of an iron alloy and a partieulate matter dispersed in said alloy, said alloy consisting essentially of iron and at least one metal selected from the group consisting of titanium and aluminium, said particulate matter consisting of at least one metal oxide selected from the group consisting of TiO Al- 0 ZrO CaO, MgO, SrO, BaO and Si0 and at least one metal selected from the group consisting of titanium and aluminium.

By the term metal base having iron as a main constituent or metal base consisting predominantly of iron are meant such ordinary iron materials as cast iron, carbon steel, stainless steel, manganese steel, chromium steel, and tungsten steel and also such special iron alloys as Al-Fe alloy, Al-Ti-Fe alloy and Ti-Fe alloy. The term molten metal consisting predominantly of tin or molten metal having tin as a main constituent means tin or tin alloys as molten metal used in the float glass process.

The excellent corrosion resistance against molten tin exhibited by the metal material of the present invention having a surface coating layer is considered to be due to the fact that the iron-titanium alloy layer, ironaluminium alloy layer or iron-titanium-aluminium alloy layer which itself has corrosion resistance against molten tin is maintained for long periods of time on the surface or the base by the presence of the particulate matter. The titanium and/or aluminium, the constituents of the surface coating alloy layer diffuse into the inside of the metal base having iron as a main constituent during use in a high temperature molten tin. When the concentration of the titanium and/or aluminium in the coating alloy layer is reduced and the corrosion resistance of the coating alloy layer against the molten tin is about to decrease, the titanium and/or aluminium present in the particulate matter dispersed in the coating alloy layer diffuse into the alloy layer to restrain the lowering of the concentration of the titanium and/or aluminium in the alloy layer. Thus, the surface coating alloy layer having corrosion resistance is maintained for a prolonged period of time. Since the metal oxides containing the particulate matter are chemically stable at high temperatures to such metal components as tin and iron present around the particulate matter, the particulate matter containing the metal oxides are hardly corroded by the molten tin. Moreover, by the dispersion of the particulate matter in the alloy layer, the net surface area of the alloy part of said layer in contact with molten tin decreases, and the corrosion resistance is further enhanced.

Any metal oxides can be used in the present invention which are chemically stable to the metal components such as tin and iron existing around the particulate material, at high temperatures (600-1l00C.). From the standpoint of feasibility, economy and ease of handling, the use of A1 0,, TiO ZrO CaO, MgO, SrO, BaO and SiO as the metal oxides contained in the particulate matter is particularly preferred.

As previously stated, the particulate matter present in the coating alloy layer of the present invention is stable to molten tin, and reduces the surface area of the alloy part of said layer in contact with the molten tin and serves to supply titanium and/or aluminium component to the alloy layer. Therefore, that part of the particulate matter which is present near the surface of the coating alloy layer acts effectively.

One preferred embodiment of the corrosion-resistant metal material of the present invention is a metal material in which the particulate matter is present only on the surface part of an alloy layer of iron and titanium and/or aluminium and is substantially absent in the deeper part of the alloy layer. Another preferred mode of the metal material of this invention is a metal material in which the composition of the surface coating alloy layer on the base material is not uniform,and the concentration of titanium and/or aluminium is progressively lower from the surface part towards thepart in contact with the base material. It is assumed that by such a concentration gradient, the bonding between the alloy layer and the base material will become firm.

ln order for the surface-coated metal material of this invention to exhibit overall good properties such as corrosion resistance against molten tin, mechanical workability, strength, and thermal stability, the coating layer contain the particulate matter only near its surface, and this part containing the particulate matter have a thickness of at least 30 11.. Furthermore, the alloy layer at its surface portion containing the particulate matter desirably contains 5-50 percent by weight of iron, 40-90 percent by weight of titanium, zirconium, calcium, magnesium, aluminium, strontium, barium and/or silicon, and 23-12 percent by weight of oxygen in the form of oxide, as a total amount of the alloy and the particulate matter.

The particulate matter preferably has a diameter mainly in the range of 10 to 100 u, and preferably consists of 15-55 percent by weight of metal oxides, and -85 percent by weight of titanium and/or aluminium metals. The ratio of the particulate matter mixed in the surface portion of the alloy layer is preferably 15-45 percent calculated as the percentage of the sectional area-of the particulate based on the total sectional area near the'surface of the alloy layer.

The corrosion-resistant metal material of this invention has corrosion resistance more than that of calorized iron-aluminium-titanium alloy, iron-aluminium alloy or iron-titanium alloy. It is easy to work mechanically and is low in cost.

The surface-coated metal material of this invention having corrosion resistance against molten metal is produced by contacting a mixture consisting of the powders of at least one metal selected from the group consisting of titanium and aluminum and the powders of at least one metal oxide selected from the group consisting of TiO,, A1 0,, ZrO CaO, MgO, SrO, BaO and SiO with a metal base consisting predominantly of iron, and beating them to an elevated temperature in an inert atmosphere. In this process, the metal base consisting predominantly of iron reacts with the surrounding mixture of the powders of titanium and/or aluminium and the powders of metal oxides, and the titanium and/or aluminium actively diffuses and penetrate into the metal base to form an alloy. This results in the production of an alloy layer of iron and aluminium and/or titanium on the surface of the metal base, and a particulate matter consisting substantially of the metal oxides and titanium and/or aluminium is dispersed in the alloy layer at the same time. By the term inert atmosphere" is meant an atmosphere filled with a gas of the class which does not substantially oxidize the powders of titanium and aluminium to be contacted with the metal base, and does not substantially reduce the metal oxide powders.

Prior to contacting of the metal base having iron as a main constituent with the powdery mixture of the metal oxides and titanium and/or aluminium in the above-mentioned process, the base metal may be pretreated by coating a thin layer of a metal oxide on it, immersing it in molten aluminium, or bonding a thin layer of aluminium by the spray method. This pretreatment is particularly effective for applying a homogeneous coating layer to the surface of the metal base. It is desired that the powdery mixture described should consist of 65-90 percent by weight of the metal oxides and 10-35 percent by weight of titanium and/or aluminium. The heating temperature need be below a point at which the base metal begins to be deformed, and generally the desired range is from 750 to l,lC. The treating time is generally about 1 to 10 hours, but the employment of high frequency heating makes it possible to shorten the treating time to several minutes.

The present invention will be described further by the following Examples in which all percentages are by weight.

EXAMPLE 1 A ca. 4 percent aqueous starch paste solution containing percent of alumina powders having a size of 10-60 was coated in a thin layer on the surface of a round rod of mild steel, 13Cr stainless steel, 18Cr 8Ni stainless steel, and 25Cr 2ONi stainless steel each having an outer diameter of 10 mm and a length of 100 mm, and dried. Each of the round rods was embedded in a heating chamber containing 25 percent of aluminium powders having a size mainly in the range of 5 y. to 10 p. and 75 percent of alumina powders having a size of not more than 60 u, and while filling the chamber with argon gas, the round rod was heated for 6 hours at a temperature of 950C. After allowing the rod to cool, it was withdrawn from the powder in the heating chamber, and the powder adhering to its surface was removed by brushing. There was obtained a metal material having as a surface coatinglayer on the base material, a layer of iron-aluminium alloy in which the particulate matter consisting of aluminium and alumina was dispersed.

The mild steel-base metal material contained a surface coating alloy layer having a thickness of about 0.7 mm, and an area having the particulate matter dispersed existed between the surface and the point about 0.2 mm deep from the surface in the alloy layer. When the stainless steels such as 13 Cr stainless steel, 18%Cr*8%Ni stainless steel, and 25%Cr2%Ni stainless steel were used as the base metal, the thickness of the surface coating was about 0.5 mm, hardly differing from steel to steel. An area having the particulate matter dispersed was present between the surface and a point about 015mm deep from the surface in any of these products.

The coating alloy layers of the metal materials obtained in this Example had substantially the same structure although differing more or less in thickness depending upon the type of the base metal. Therefore, the structure of the coating alloy layer was observed using the metal material having mild steel as the base. This will be discussed somewhat in detail below with reference to the attached microscopic photograph.

As is shown in the microscopic photograph, a coating alloy layer 1 is superposed on a base material 4 in intimate contact with each other in the corrosion-resistant metal material of this invention. The alloy layer consists of an upper layer 2 in which a particulate matter is dispersed in the alloy and a lower area 3 substantially free from the particulate matter and consisting. only of an iron-aluminium alloy. In this photograph, the thickness of the layer 1 is about 700 ,u, and the area 2 has a thickness of about 200 u. The ratio of the particulate mixed in the area 2 is about 35 percent calculated as the percentage of the sectional area of the particulate matter based on the total sectional area taken near the surface. According to the measurement of an X-ray microanalyzer, the composition of the aluminium-iron alloy layer of the area is 54 percent aluminium and 46 percent iron. This corresponds substantially to the composition Fe Al The particulate matter has a size mainly in the range of 10 u to 100 ,u, and consists of about 55 percent aluminium and about 45 percent alumina. In the area 3 where the particulate matter is not dispersed, the concentration of aluminium is reduced progressively towards the base material 4, and finally, the area 3 is firmly bonded to the base material 4.

The four corrosion-resistant metal materials obtained in this Example were each immersed in molten tin at 970C. in a reducing atmosphere, and the number of days which elapsed until the occurrence of corrosion on the surface was determined with the naked eye. It was found as shown in Table 2 below that irrespective of the type of the base material, all of the metal materials did not undergo appreciable corrosion even after 60 days from the immersion. For comparative purposes, Table 2 also gives the corrosion test results on the untreated base material and the calorized base material.

TABLE 2 Number of days elapsed until the occurrence of appreciable corrosion Base materials Untreated Calorized Metal material obtained in this Example Mild steel 2 hours 5 days more than 60 days 13%Cr stainless 6 hours 7 days more than steel 60 days 18%Cr-8%Cr 4 hours 6 days more than stainless steel 60 days 25%(Jr-20%Ni 4 hours 6 days more than stainless steel 60 days EXAMPLE 2 A ca. 4 percent aqueous starch paste solution containing 10 percent of titanium oxide powders having a size of 10-60 p. was coated in a thin layer on the surface of each of the same round rods as set forth in Example 1, and dried. Each of the round rods was then embed tied in a heating chamber containing percent of titanium oxide powders having a size of not more than 60 p, and 25 percent of titanium powders having a size mainly in the range of 5 y. to 10 .1.. While filling the chamber with argon gas,the round rod was heated for 10 hours at l,l00C. After allowing the rod to cool, it was withdrawn from the powder in the'heating chamber, and the powder adhering to its surface was removed by brushing. There was obtained a surfacecoated metal material having as a surface coating layer on the base material, a layer of iron-titanium alloy in which the particulate matter consisting of titanium and titanium oxide was dispersed.

Each of the metal materials obtained was subjected to the same corrosion resistance test as set forth in Example l, and it was found that even after a lapse of 60 days none of the four metal materials obtained underwent corrosion.

The surface coating layer of the metal material having mild steel as the base metal had a thickness of about 0.4 mm, and an area having the particualte matter dispersed therein was present between the surface and a point about 0.1 mm deep from the surface in the alloy layer. In the case of 13%Cr stainless steel, 18%Cr- 8%Ni stainless steel, and 25%Cr-20%Ni stainless steel, the thickness of the surface coating was about 0.3, hardly differing from steel to steel. An area having the particulate matter dispersed therein was present between the surface and a point about 0.08 mm deep from the surface in the alloy layer.

The mild steel-base metal material obtained will be discussed. Thethickness of the alloy layer of this metal material is about 400 pt, and the particulate matter is dispersed in an area existing between the surfat ie and a point about 100 1. deep from the surface in the alloy layer. The ratioof the particulate material mixed in' this area was about 30 percent as the percentage of the sectional area of the particulate matter based on the total sectional area. According to the measurement of an X-ray microanalyzer, the iron-titanium alloy layer in the area where the particulate matter is dispersed consists of 65 percent titanium and 35 percent iron, which substantially corresponds to the composition Ti Fe. The main size of the particulate matter is -80 ,4, and its composition is about 55 percent titanium and abour 45 percent titanium oxide. The concentration of titanium is reduced progressively towards the base metal in the area not having the particulate matter dispersed which exists between the area having the particulate matter dispersed and the base metal, and finally, the alloy layer is firmly bonded to the base metal.

EXAMPLE 3 Each of the same round rods as used in Example 1 was embedded in a heating chamber containing 75 percent of calcium oxide powders having a size of not more than 60 p. and 25 percent of aluminium powders having a size of 10-60 p.. While filling the heating chamber with argon gas, the rod was heated for 6 hours at 900C. After allowing the rod to cool, it was withdrawn from the powders in the heating chamber, and the powders adhering to the surface were removed by brushing. There was obtained a surface-coated metal materials having as a coating layer on the surface of the base material, an iron-aluminium alloy layer in which the particulate matter consisting of aluminium and calcium oxide was dispersed.

Each of the metal materials obtained in this Example was subjected to the same corrosion resistance test as set forth in Example 1, and it was found that even after a lapse of 60 days, these metal materials did not undergo appreciable corrosion.-

The thickness of the alloy layer of the metal material containing mild steel as the base metal was about 0.65 mm, and an area having the particulatematter dispersed therein was present betw'een'the surface and a point about 0.2 mm deep from the surface. The thickness of the coating alloy layer in the 13%Cr stainless steel, l8%Cr8%Ni stainless steel and 25%Cr-20%Ni stainless steel was about 0.5 mm, hardly differing from steel to steel, and an area having the particulate'matter dispersed therein was present between the surface and a point about 0.15 mm deep from the surface.

EXAMPLE 4 Each of the four round rods same as used in Example 1 was embedded in a heating chamber containing 75 percent of calcium oxide powder having a size of not more than 60 u and 25 percent of the powders of titanium having a size mainlyin the range of 10 p. to 60 a. While filling the heating chamber with argon gas, each of the rods was heated for 8 hours at 1,I00C. After allowing the rod to cool, it was withdrawn from the powders in the heating chamber, and the powders adhering to the surface were removed by brushing. There was obtained a surface-coated metal material having as a surface coating layer on the base metal, an irontitanium alloy in which a particulate matter consisting of titanium and calcium oxide was dispersed.

Each of these metal materials obtained in this Example was subjected to the same corrosion resistance test as set forth in Example 1, and it was found that even after a lapse of 60 days, these metal materials did not undergo appreciable corrosion. The thickness of the alloy layer of the metal material having mild steel as the base metal was about 0.35 mm, and an area having the particulate 'matter dispersed therein was present between the surface and a point about 0.1 mm deep from the surface in the alloy layer. In the case of the l8%Cr8%Ni stainless steel, 13%Cr stainless steel, and 25%Cr-20%Ni stainless steel, the thickness of the coating alloy layer was about 0.3 mm hardly differing'from steel to steel. An area having the particulate matter dispersed therein existed between the surface and a point about 0.08 mm deep from the surface in the alloy layer.

All of the methods used in the foregoing Examples are a kind of the penetrating process, and therefore, the composition of the alloy layer obtained by such methods might be affected by the quality of the steel material usedfFor instance, in the case of stainless steel, very minor amounts of nickel and cobalt may be contained in the layer. However, as will be understood from the results obtained in these Examples, the corrosion resistance does not differ depending upon the kind of the steel material, and it is assumed that very minor amounts of components other than iron present in the steel material, even if incorporated in the alloy layer, would not reduce the corrosion resistance of the resulting metal material.

As will be demonstrated by these specific Examples, the metal material of the present invention exhibits a marked corrosion resistance against molten tin. In the foregoing Examples, the metal materials obtained by the process of the invention have corrosion resistance 10 times or more as high as that of the metal materials whose base material has been calorized. The metal materials of the present invention which is easy to work mechanically and is low in cost have far better resistance to corrosion than calorized iron-aluminium alloy, iron-titanium alloy and iron-aluminium-titanium alloy, and therefore the metal materials of the'present invention are very useful-as metals material having high corrosion resistance against molten tin.

What we claim is:

l. A metal material having corrosion resistance against a molten metal consisting predominantly of tin, which metal material comprises a metal base having iron as the main constituent and a surface coating layer containing 1 an iron alloy consisting essentially of iron and at least one metal selected from the group consisting of titanium and aluminium and 2 particulate matter dispersed in the alloy only in the surface portion of the surface coating layer, which surface portion of the surfacecoating layer has a thickness of at least 30 and consists essentially of 5-50 percent by weight of iron, 4090 percent by weight of titanium, aluminium, zirconium, calcium, magnesium, strontium, barium, silicon or a mixture thereof, and 33-12 percent by weight of oxygen as oxide, the particulate matter consisting essentially of at least one metal oxide selected from the group consisting of TiO,, A1 0,, ZrO,, CaO, MgO, SrO, BaO and SiO and at least one metal selected from the group consisting of titanium. and aluminium, the concentrations of the titanium and aluminium components layer.

3. A metal material according to claim 1 wherein the diameter of the particulate matter is predominately in the range of l0 1;. to p..

4. A metal material according to claim 1 wherein said particulate matter consists of 15-55 percent by weight of said metal oxides and 45-85 percent by weight of titanium and aluminium metals.

Claims

2. A metal material according to claim 1 wherein the portion of the particulate matter mixed in the alloy in the surface portion of the surface coating layer is 15 to 45 percent in terms of the percentage of the sectional area of the particualte matter based on the total sectional area of the surface portion of the surface coating layer.
3. A metal material according to claim 1 wherein the diameter of the particulate matter is predominately in the range of 10 Mu to 100 Mu .
4. A metal material according to claim 1 wherein said particulate matter consists of 15-55 percent by weight of said metal oxides and 45-85 percent by weight of titanium and aluminium metals.