GB2150545A - A process for preparing metamorphosed titanic acid compounds - Google Patents

Abstract

A process for preparing metamorphosed titanic acid compounds comprises heating, under a non-oxidative atmosphere, a mixture of (1) a titanic acid compound or a mixture or eutectic mixture of two or more of titanic acid compounds selected from (a) alkali metal titanate compounds of the general formula:- Ma2O &cirf& nTiO2 &cirf& mH2O (I> wherein Ma is an alkali metal, n is an integer of from 1 to 10 and m is 0 or an integer of from 1 to 10, and (b) alkaline earth metal titanate compounds of the general formula:- MbO &cirf& nTiO2 &cirf& mH2O (II> wherein Mb is an alkaline earth metal and n and m have the same meanings as above; and (2) a carbide or a mixture of two or more of carbides of the general formula:- C(M)z (III> wherein M is an element other than carbon selected from Groups III, IV and V of the Periodic Table and z is an integer corresponding to the valency of M. n

Description

SPECIFICATION A process for preparing metamorphosed titanic acid compounds The present invention is concerned with a process for preparing metamorphosed titanic acid compounds.

Recently, alkali metal titanate compounds and alkaline earth meral titanate compounds have attracted attention as reinforcing materials for ceramics and composites and have found use as various industrial materials. However, there is still a great interest in developing functional composite materials, utilising the heat resistance and reinforcing ability of titanic acid compounds, to give conductivity to and to colour these titanic acid compounds by subjecting them to metamorphosis.

Thus, it is an object of the present invention to provide a new process for imparting conductivity to and for colouring titanic acid compounds by subjecting the compounds to metamorphosis.

Thus, according to the present invention, there is provided a process for preparing metamorphosed titanic acid compounds, which comprises heating, under a non-oxidative atmosphere, a mixture of (1 ) a titanic acid compound or a mixture or eutectic mixture of two or more of titanic acid compounds selected from (a) alkali metal titanate compounds of the general formula: Ma2O nTiO2 mH20 (I) wherein Ma is an alkali metal, n is an integer of from 1 to 10 and m isO or an integer of from 1 to 10, and (b) alkaline earth metal titanate compounds of the general formula: MbO ntO2 mH2O (II) wherein Mb is an alkaline earth metal and n and m have the same meanings as above; and (2) a carbide or a mixture of two or more carbides of the general formula: C(Mlz (III) wherein M is an element other than carbon selected from Groups Ill, IV and V of the Periodic Table and z is an integer corresponding to the valency of M.

The process according to the present invention has the following advantages: (1 ) modification of colour tint and/or metamorphosis providing conductivity of the titanic acid compounds can be carried out effectively, without causing any deterioration in the other properties, such as the heat resistance, of the titanic acid compounds; (2) the metamorphosis treatment is simple and exceedingly safe since heating in an atmosphere of hydrogen is not required; and (3) any step for separating the carbide used as raw material and remaining in the metamorphosed titanic acid compound obtained is not necessary. Substances derived from this raw material have an excellent heat resistance and do not reduce the conductivity and the product containing these substances can be sintered as such.

Alkali metal titanate compounds represented by general formula (I) include, for example, anhydrides and hydrates of lithium titanate, sodium titanate, potassium titanate and the like. Preferred alkali metal titanates for industrial applications include the potassium titanates, especially K20 4 4TiO2; K20 6 TiO2 and K20 8 TiO2, as well as their hydrates, which are in a fine, fibrous crystal form and have an excellent heat resistance and excellent reinforcing ability when used for composite materials.

Alkaline earth metal titanate compounds represented by general formula (II) include, for example, anhydrides and hydrates of calcium titanate, magnesium titanate, barium titanate, strontium titanate and the like.

According to the present invention, compounds represented by geneal formulae (I) and (II) may be used either individually or as mixtures or eutectic mixtures of two or more of them.

Carbides represented by general formula (Ill) which are used according to the present invention include well known ones, such as boron carbide, silicon carbide, titanium carbide, germanium carbide, tin carbide, lead carbide, phosphorus carbide and the like, preferred carbides including boron carbide, silicon carbide, titanium carbide and the like. They may be used either individually or as a mixture of two or more of them.

Although the mechanism of the metamorphosis of the titanic acid compounds in the process of the present invention has not been completely elucidated, it is assumed that, when a mixture of the titanic acid compound and the carbide of general formula (III) is heated under a non-oxidative atmosphere, the carbide may act as a deoxidant and cause a reductive metamorphosis of the titanic acid compound to yield a product having a good conductivity and a modified colour, whereby the carbide may also be dehydrogenated or oxidised without affecting the electroconductivity of the titanic acid compound.

Regarding the ratio of mixing of the titanic acid compound and of the carbide of general formula (Ill), the two components may be mixed in such ratio that the number of carbon atoms in the carbide is 0.01 to 10 times and preferably 0.1 to 3 times per oxygen atom in the titanic acid compound except the oxygen atom(s) present in any water of crystallisation contained therein, although the ratio may vary, depending upon the kind of titanic acid compound and the carbide employed and also upon the intended use of the product obtained. When the amount of carbide is too small, difficulties are liable to occur in attaining the object of the present invention. On the other hand, when the amount of the carbide is too great, the operation of mixing the raw materials becomes difficult and a lot of energy is required for the heating.

If it is necessary to separate excess carbide remaining after the metamorphosis of the titanic acid compound, the separation may be effected by utiiising the difference in specific gravity between the titanic acid compound and the carbide. ido)vever, the remaining carbide in the metamorphosed product usually does not restrict the use of the product.

The non-oxidative atmosphere used according to the present invention is a non-oxidative atmosphere containing substantially more than 90% by volume of one or more reducing gases, such as carbon monoxide, or inert gases, such as nitrogen, helium or carbon dioxide. At atmosphere of nitrogen or carbon dioxide is especially preferred.

The heat treatment according to the present invention is usuaily carried out at 500 to 1 500çC. for 2 to 600 minutes and preferably at 800 to 1200'C. for 5 to 180 minutes, although the conditions for the treatment may vary, depending upon the nature of the raw materials and the intended use of the resultant product. A special furnace is not required for the heat treatment and any conventional furnace can be used for the heating.

Although the heat treatment may be psrformed by heating a simple mixture of the titanic acid compound and the carbide as such, it is preferred to use a uniform mixture of powdered titanic acid compound and powdered carbide so that the titanic acid compound may be well contacted with the carbide. It is also desirable to remove air contained in the mixture, especially in a mixture of powdered titanic acid compound and powdered carbide, or to replace the air with a non-oxidative material, as far as possible. The air contained in the mixture wouid cause consumption of the carbide before completion of the metamorphosis of the titanic acid compound and would require a prolonged time for the metamorphosis and an excessive amount of the carbide and would be liable to give rise to incomplete or non-uniform metamorphosis.

Therefore, when carrying out the process of the present invention, it is preferably to remove air from the mixture of the titanic acid compound and the carbide, for example by: 1) first compressing the mixture under a reduced pressure into a compact form and then heating the compact material or 2) mixing the mixture with a binder which is decomposed into a non-oxidative gases upon heating, compressing the mixture into a compact form, if necessary, and then heating the mixture or the compact material.

The binder which is decomposed into non-oxidative gases upon heating is a compound which contains, as the main component, one or more elements selected from hydrogen, carbon and nitrogen and is decomposed upon heating into water vapour, carbon dioxide. carbon monoxide or nitrogen. The binder may, for example, be selected from water, ammonia, amino coin pounds, nitrogen-containing compounds, hydrocarbons, carbohydrates and various synthetic resins, or may be a mixture of two or more of them, provided that it is in liquid form at ambient temperature or a the time of moulding under pressure and can exert the binding ability necessary for he moulding of the mixture of the titanic acid compound and the carbide.However, from the point of view of economy and of the application of the product, there may be used, for example, water, hydrocarbons, glycerol, ethylene glycol, carbohydrates, such as starch, urea derivatives, polyvinyl alcohol, butyral resin, polyvinyl acetate resin, atactic polyethylene, liquid polypropylene, polybutene, acrylic resin and the like. The amount of these binders to be used may vary without limitation, depending upon the nature of the titanic acid compound and of the carbide, as well as upon the intended use of the product. However, it is preferred to use the binder in an amount of not more than 300 parts by weight (hereinafter, parts by weight are referred to as parts) and more preferably of not more than 100 parts per 100 parts of the total amount of the titanic acid compound and of the carbide.Too large an amount of binder is undesirable because it requires excessive heating during the metamorphosis and removal of decomposition products resulting from the remaining binder By heating under a non-oxidative atmosphere, the above-mentioned binder produces carbides remaining as ash, most of which are, however, harmless to the electroconductive metamorphosis, although they have a black colour.Therefore, it is unnecessary specially to separate and remove the decomposition products of the binder before practical use of the product insofar as the binder is used in an appropriate amount According to the present invention, it is also possible to use a sintering binder, in combination, which sinters and acts as a binder ior the mixture oftitanicacid compound and carbide upon heating.

Furthermore, it is possibie, according to the present invention, to obtain a metamorphosed moulding or compact body having conductivity by moulding a mixture of titanic acid compound, carbide, sintering binder and, if required, a binder necessary for moulding and then heating the moulded article under a non-oxidative atmosphere, metamorphosis of the titanic acid compound and the metamorphosis and moulding by the sintering binder thereby being effected simultaneously.

For moulding the mixture of titanic acid compound, carbide and binder, any conventional moulding method can be used wherein a uniform mixture is prepared by any conventional method at ambient temperature or heated to a temperature which does not cause vaporisation or decomposition of the binder, the mixture being subjected to any one of the following moulding processes: (1) a process using a compression moulding machine, wherein the mixture is filled into a mould and then compressed; (2) a process using a granulating moulding machine, wherein the mixture is put into a granulator to give granules or flakes; (3) a process using a tabletting machine, wherein the mixture is tabletted; and (4) a process using press rollers, wherein the mixture is passed through the rollers to give a sheet.

However, it is preferred, from the point of view of uniformity and efficiency of the heating during the metamorphosis, to effect the moulding in such a way that the moulding obtained has a comparatively large surface area. In general, the thicker is the moulding, the larger is the temperature gradient therein. It is necessary to control the thickness of the mouldings in order to avoid unevenness of the heating, i.e.

unevenness of the metamorphosis.

The following Examples are given for the purpose of illustrating the present invention: Example 1 3 g. of potassium titanate (Otsuka Chemical Co. Ltd., Japan Tismo D) and 1 g. of powdered silicon carbide were well mixed in a mortar. The mixture was put into a boat-shaped 30 ml. crucible made of very pure alumina. Air in the crucible was displaced with nitrogen gas. The crucible was put in a tubular electric furnace made of very pure alumina (inner diameter of the tube 50 mm.; length 1 m.) maintained at 1100 C., heated for 2 hours under a nitrogen stream of 50 ml./minute, cooled to ambient temperature under a nitrogen stream and then taken out. A metamorphosed potassium titanate of pale blue colour was obtained.

For comparison, the process was repeated but without the addition of powdered silicon carbide, the mixture being heated and metamorphosed under the same conditions as above. The resultant potassium titanate was white, there being no change in colour.

Examples 2 to 6 and Comparative Example 1.

A mixture of potassium titanate and powdered silicon carbide, prepared by the same method as in Example 1, was pressed in tabletting machine at a pressure of 150 kg/cm2 for 30 minutes on a vacuum to give tablets of 10 mm. diameter and 1 mm. thickness which consisted of potassium titanate and silicon carbide.

Tablets thus prepared were put on a platinum boat and then into the same electric furnace as was used in Example 1. Air in the boat was displaced with nitrogen for 30 minutes and then tablets were heated at the temperatures and for the periods shown in the following Table 1 under a nitrogen stream.

The properties of the resultant tablets, which consist of mixtures of metamorphosed potassium titanate and silicon carbide, are shown in the following Table 1. For comparison, the result obtained with potassium titanate but without the use of silicon carbide is shown as Comparative Example 1 in the following Table 1.

TABLE 1 Example condition of colour conductivity No. metamorphosis temper- time before after before after ature metamor- metamor- metamor- metamor { C.) (min.) phosis phosis phosis phosis 2 1000 30 greyish- bluish- no yes white violet 3 1050 20 greyish- blackish- no yes white violet 4 1050 30 greyish- blackish- no yes white violet 5 1100 15 greyish- blackish- no yes white violet 6 1150 10 greyish- blackish- no yes white violet Compar ative 1050 30 greyish- greyish- no no Example white white Note 1) In Table 1, the conductivity was evaluated by a Digital Multimeter TR 6841 (made by Takeda Riken Co. Ltd., Japan). The term "no" means the case in which the value of the resistance was not less than 106 Q when the electrodes were contacted with both sides of the tablet.The term "yes" means the case in which the value of resistance was not more than 103 Q.

Example 7.

4 g. of potassium titanate (the same as used in Example 1), 1 g. of silicon carbide and 0.5 g. of liquid paraffin as a binder were well mixed in a mortar, the mixture was filled in a mould and pressed at a pressure of 20 kg/cm2for 3 minutes to give a cylindrical moulded article of 10 mm. diameter and 40 mm. length.

The resultant moulded article was put on a platinum boat. The boat was deaerated for 30 minutes, replaced with nitrogen and heated at 1150"C. for 30 minutes under a nitrogen stream of 50 ml./minute to give a cylindrical product of blackish-violet colour containing some voids. The loss in weight was 15% less than that of the initial material.

Both sides of this cylindrical product were coated with silver paste and the conductivity was measured by the same method as was used in Example 2, the value being 2.8 x 103 n. The volume resistivity was 5.50 x 102form., calculated by the following equation: Volume resistivity measured resistance (Q) x area of electrode (cm2) distance between electrodes (cm) For comparison, Example 7 was repeated but without silicon carbide to give a greyish-white product, which is the same colour as the raw material before heating. When a binder was not used, a cylindrical moulded article was not obtained by pressing at 20 kg./cm2 for 3 minutes, the product easily collapsing.

Examples 8 to 17.

Mouldings were made by the same method as in Example 7 except that the kinds of the titanic acid compounds, the amounts of the silicon compounds, the nature and amounts of the binders, the temperatures and heating periods and the like were varied, as shown in the following Tables 2 and 3. The results of these metamorphoses are shown in the following Table 3.

Examples 16 and 17 were repeated, except that the silicon carbide and liquid paraffin were omitted. The results are shown as Comparative Examples 2 and 3 in the following Tables 2 and 3.

TABLE 2 Example titanic acid carbide binder compound kind amount kind amount kind amount (g.) (g.)(g.) 8 potassium 4 silicon 0.5 liquid 1.0 titanate carbide paraffin (Tismo D) 9 D 4 " 1 " 1.0 10 " 4 " 1 ethylene 1.0 glycol 11 " 4 " 1 water 1.2 12 " 4 titanium 2 liquid 1.3 carbide paraffin 13 potassium 4 silicon 1 poly- 0.6 titanate carbide butene (Tismo L) 14 " 4 titanium 2 acrylic 0.3 carbide resin 15 barium 4 silicon 1 liquid 0.8 titanate carbide paraffin 16 D 4 " 1 " 0.8 17 " 4 " 2 " 1.2 Comparaative " 4 - - - - Example 2 "3 " 4 - - - TABLE 3 Example condition of colour conductivity No. metamorphosis ofthe temper- time before after moulded ature metamor- metamor- article ( C.) (min.) phosis phosis {Q) 8 900 30 greyish- pale 6.9 x 106 white violet 9 1100 30 " bluish- 2.4x104 violet 10 1150 20 " deep 4.7x10 violet 11 1100 60 " bluish- 7.1 x 104 violet 12 1150 30 dark blackish- 1.4 x 100 violet violet 13 1100 30 " bluish- 3.7x104 violet 14 1150 20 D blackish- 1.9x101 violet 15 1000 30 " grey 9.1 x 107 16 1200 30 " dark 4.2x105 brown 17 1200 30 " " 3.1 x 105 Comparative 1200 30 " greyish Example white 2 " 3 1200 30

Claims (16)

1. A process for preparing metamorphosed titanic acid compounds, which comprises heating, under a non-oxidative atmosphere, a mixture of (1) a titanic acid compound or a mixture or eutectic mixture of two or more of titanic acid compounds selected from (a) alkali metal titanate compounds of the general formula: Ma2O nTiO2 mH2O (I) wherein Ma is an alkali metal, n is an integer of from 1 to 10 and m isO or an integer of from 1 to 10, and (b) alkaline earth metal titanate compounds of the general formula:: MbO nTiO2 m mH2O (II) wherein Mb is an alkaline earth metal and n and m have the same meanings as above; (2) a carbide or a mixture of two or more carbides of the general formula C(M)2 (III) wherein M is an element other than carbon selected from Groups Ill, IV and V of the Periodic Table and z is an integer corresponding to the valency of M.

2. A process according to claim 1, wherein the titanic acid compound and the carbide in the mixture are mixed in such ratio that the number of carbon atoms in the carbide is 0.01 to 10 times per oxygen atom in the titanic acid compound except the oxygen atom(s) present in any water of crystallisation contained therein.

3. A process according to claim 2, wherein the titanic acid compound and the carbide in the mixture are mixed in such ratio that the number of carbon atoms in the carbide is 0.1 to 3 times per oxygen atom in the titanic acid compound except the oxygen atom(s) present in any water of crystallisation contained therein.

4. A process according to any of the preceding claims, wherein the non-oxidative atmosphere is one containing substantially more than 90% by volume of one or more of reducing gases, other than hydrogen, or inert gas.

5. A process according to claim 4, wherein the inert gas is nitrogen, helium or carbon dioxide.

6. A process according to claim 4 or 5, wherein the reducing gas is carbon monoxide.

7. A process according to any of the preceding claims, wherein the heating is carried out at 500 to 1500 C.

for 2 to 600 minutes.

8. A process according to claim 7, wherein the heating is carried out at 800 to 1200 C. for 5 to 180 minutes.

9. A process according to any of the preceding claims, wherein the mixture is compressed into a compact form under reduced pressure, prior to the heating.

10. A process according to any of the preceding claims, wherein the mixture contains a binder admixed therewith, which binder decomposes into non-oxidative gases upon heating.

11. A process according to claim 10, wherein the binder is a compound which contains, as the main component, one or more elements selected from hydrogen, carbon and nitrogen and decomposes upon heating into water vapour, carbon dioxide, carbon monoxide or nitrogen.

12. A process according to claim 11, wherein the binder is liquid paraffin, ethylene glycol, acrylic resin, polybutene or water.

13. A process according to any of the preceding claims, wherein the mixture also contains a sintering binder.

14. A process according to any of the preceding claims, wherein the alkali metal titanate compound is potassium titanate, sodium titanate or lithium titanate, the alkaline earth metal titanate compound is calcium titanate, magnesium titanate, barium titanate or strontium titanate and the carbide is boron carbide, silicon carbide or titanium carbide.

15. A process according to claim 1 for preparing metamorphosed titanic acid compounds, substantially as hereinbefore described and exemplified.

16. Metamorphosed titanic acid compounds, whenever prepared by the process according to any of claims 1 to 15.