GB2304105A

GB2304105A - Method of manufacturing aluminium nitride

Info

Publication number: GB2304105A
Application number: GB9616430A
Authority: GB
Inventors: Hiroaki Kotaka; Hidenori Yamaoka; Shuitsu Matsuo; Masahiro Ando; Mikiya Fujii; Hiroyuki Terada; Yasuo Misu
Original assignee: Toshiba Monofrax Co Ltd; Toshiba Ceramics Co Ltd
Current assignee: Coorstek KK; Saint Gobain TM KK
Priority date: 1995-08-11
Filing date: 1996-08-05
Publication date: 1997-03-12
Anticipated expiration: 2016-08-05
Also published as: DE19632080A1; GB2304105B; GB9616430D0; DE19632080C2; JPH0952769A

Description

1 1 2304105 "METHOD OF MANUFACTURING ALUMINUM NITRIDE" This invention

relates to a method of manufacturing aluminum nitride, and in particular to a method of manufacturing solid aluminum nitride or aluminum nitride fibers, which enables a nitrification reaction of alumina to be effected with ease, thereby making it possible to manufacture solid aluminum nitride or aluminum nitride fibers in high yield and at low cost.

Aluminum nitride has been used for the manufacture of a filler to be used in a resin sealant for semiconductor element, or for the manufacture of a composite thereof with another kind of metal.

As for the manufacture of aluminum nitride fibers, a method has been proposed in Japanese Patent Unexamined Publication Hei/2-300,319, wherein alumina fibers comprising 90% by weight or more of a-A'203 and less than 10% by weight of S'02 are heat-treated in a mixed gas atmosphere comprising ammonia and hydrocarbon gas at a temperature of 1,300 to 1, 700'C thereby to manufacture aluminum nitride fibers.

However, according to this known method, a sufficient nitrification reaction of alumina could hardly be effected at a temperature of less than 1,300'C, or even at a higher temperature of not less than 1, 300'C.

Therefore, it has been required according to this known method to perform the nitrification reaction at 2 a much higher temperature, taking a time. If the nitrification reactior such a higher temperature and taking time, it is inevitable to invite an for the manufacture of the product.

Even if such a nitrification reaction is performed at such a high temperature, taking a long period of time, it is impossible to achieve a sufficient nitrification reaction of alumina, and hence it has been impossible as a matter of fact to obtain aluminum nitride fibers whose nitrification degree is substantially 100%.

Japanese Patent Unexamined Publication Hei/6-330,412 discloses a technique of nitrifying the surface of alumina-silica fibers wherein the aluminasilica fibers were heat-treated in a mixed gas atmosphere comprising an ammonia and a hydrocarbon gas at a temperature of 1,200 to 1,600'C. It is however impossible with this prior art to effect a sufficient nitrification down to the center of the alumina-silica fibers.

Accordingly, an object of the present invention is to provide a method for manufacturing an aluminum nitride solid body with ease and in high yield, wherein a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas is prepared and then a solid y-A'203, a precursor of longer period of is performed at a longer period of increase in cost 3 y-A'203, or a mixture of said solid y-A'203 and the aforementioned precursor is heat-treated in the aforementioned mixed gas at a temperature of 1,200 to 1, 7 0 OC.

Another object of this invention is to provide a method for easily manufacturing an aluminum nitride solid body whose alumina moiety can be substantially completely nitrified, wherein a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas is prepared, and a solid y-A'2031 a precursor of y-A'203, or a mixture of said solid yA1203 and the aforementioned precursor is calcined at a temperature of 300 to 1,100'C in the aforementioned mixed gas and then heat-treated in the aforementioned mixed gas at a temperature of 1,200 to 1,700C.

Another object of this invention is to provide a method of manufacturing aluminum nitride fibers, wherein a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas is prepared; a liquid precursor of y-A'203 is dispersed in an aqueous solution containing a binder and one material selected from the group consisting of colloidal silica, colloidal alumina and colloidal zirconia; the aqueous solution containing the precursor dispersed therein is concentrated; short fibers are spun from the concentrated aqueous solution placed in a centrifugal spinning machine by rotating the 4 centrifugal spinning machine; the spun short fibers are dried; the dried short fibers are calcined at a temperature of 300 to 1,100'C; and the calcined short fibers are heat-treated in the mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas at a temperature of 1, 200 to 1,700'C.

A still further object of this invention is to provide a method of manufacturing aluminum nitride fiber mat, wherein a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas is prepared; a liquid precursor of -y-A'203 is dispersed in an aqueous solution containing a binder and one material selected from the group consisting of colloidal silica, colloidal alumina and colloidal zirconia; the aqueous solution containing said precursor dispersed therein is concentrated; short fibers are spun from the concentrated aqueous solution placed in a centrifugal spinning machine by rotating the centrifugal spinning machine; the spun short fibers are dried; the dried short fibers are calcined at a temperature of 300 to 1,100C; a mat is formed with the calcined short fibers; and the mat is heat-treated in said mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas at a temperature of 1,200 to 1, 7 0 O'C.

Other objects of this invention will be apparent from the following description.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph showing both X-ray diffraction of y-alumina particles prior to the nitrification thereof which are employed in the examples of this invention and X-ray diffraction of aluminumnitride particles obtained according to this invention; FIG. 2 is a graph showing both X-ray diffraction of y-alumina precursor fibers prior to the nitrification thereof which are employed in the examples of this invention, and X-ray diffraction of aluminum nitride fibers obtained by the nitrification of the y-alumina precursor fibers; and FIG. 3 is a graph showing both X-ray diffraction of alumina (a mixture of a-alumina and 6-alumina) which is not to be employed in this invention, and X-ray diffraction of the above-mentioned aluminum which has been subjected to a nitrification treatment.

This invention provides a method of manufacturing aluminum nitride, which comprises a step of heattreating y-A1203 or a precursor of T-A1203 in a mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas.

The term of "a precursor of -y-A'203" employed herein should be understood to mean a material before being converted into y-A'2031 or mean, if this material 6 is heat-treated in advance at a temperature of 1,000'C to 1,100'C, a gelled material before being converted into y-A'203. The y-A'203 can be manufactured by thermally decomposing an organic or inorganic aluminum compound. Examples of such an organic or inorganic aluminum compound are aluminum alkoxide, aluminum sulfate, aluminum alum, ammonium aluminum carbonate and aluminum hydroxy chloride. These aluminum compounds are specific examples of the precursor of y-A'203", Further, the term of "a solid body of 7-A'203 or the precursor thereof" employed herein should be understood to mean particles or flakes of y- A'203 or the precursor thereof.

After extensive studies made by the present inventors with respect to the conventional manufacturing method for aluminum nitride, it has been found that the reaction temperature and time required for the nitrification of alumina vary greatly depending on the kinds of raw alumina material to be used for the nitrification reaction.

For example, when a-alumina or 8-alumina is employed as a raw alumina material for the nitrification reaction, such a high reaction temperature as more than 1,500'C and such a long reaction time as not less than 5 hours are required. Moreover, even if the heat treatment is conducted at such a high temperature and for a long period of time, it is hardly possible to 7 substantially completely nitrify the raw alumina material.

Whereas, it has been found that if y-A'203 is employed as a raw alumina material, the reaction temperature required for the nitrification reaction can be lowered remarkably, and at the same time the reaction time can also be greatly reduced.

The reason of this has been studied by the present inventors to find out that this can be attributed to the inherent large specific surface area of y-A1203.

Namely, it has been found that the specific surface area of y-A'203 is about 10 times as large as that of a-alumina, so that when an ammonia gas is contacted with this large specific surface area of -y-A'2031 the nitrification reaction of y-A'203 can be prominently promoted.

It has been found that in the process of producing,y-A'2031 prominent dehydration is caused to occur, thus leaving a large number of fine pores 10 to 100 angstroms in diameter in the particle of y-A'203, whereby enlarging the specific surface area of y-A'203, When this y-A'203 is further heated, it is converted into a-A12031 concurrently losing a large number of fine pores, thus sharply decreasing the specific surface area of a-A'203.

In this invention, y-A'203 having a large number of fine pores and an extremely large surface area as 8 explained above is taken notice of and utilized for promoting nitrification reaction in the manufacture of aluminum nitride via a process of contacting the -y-A'203 with a mixed gas consisting essentially of a hydrocarbon gas and ammonia gas.

As for the y-A'203 to be employed in this invention, the y-A'203 that can be obtained by the thermal decomposition of an organic or inorganic aluminum compound or all kinds of precursors thereof would be useful. In particular, the y-A'203 that can be obtained by the thermal decomposition of aluminum hydroxy chloride as an alumina source, or the precursor constituted by this aluminum hydroxy chloride is more preferable for use as a y-A'203 or the precursor thereof to be employed in this invention, since these compounds are highly reactive with nitrogen and excellent in moldability.

The mechanism of the thermal decomposition of the aluminum hydroxy chloride can be expressed as follows.

H20, HCl gas H2C) - Al 2(OH)5C'-2-9H20 1 (300 to 400'C) A'2031'20 1 (600 to 700'C) -y-A'203 I 1200C) a-A'203 As seen from above drawing, when aluminum hydroxy 9 chloride is heated at a temperature of 300 to 400'C, the aluminum hydroxy chloride is converted into an alumina hydrate (A'203-H20) while emitting HC1 and H20. When this alumina hydrate is further heated to 600 to 700C, it is then converted into y-A'203 while emitting H20, When this T-A'203 is further heated to 1200'C or more, it is then converted into a-A'203, As explained above, the production of this intermediate product of y- A'203 is accompanied by the release of H20 and HCI gas, resulting in the formation of a large number of pores in the y-A1203, thus giving a large specific surface area to the y-A'203.

When this y-A'203 is heat-treated as it is or after being calcined at a temperature of 300 to 1,100'C in a mixed gas atmosphere consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas, it can be easily converted into an aluminum nitride.

In this reaction, y-A'203 is reduced by an ammonia gas to produce aluminum nitride. A raw material to be subjected to the nitrification reaction may be y-A'203 per se or may be a precursor of -y-A1203 which can be transformed into -y-A'203 as it is heated to 1,000 to 1,100'C in the reaction of forming aluminum nitride.

The reason for limiting the content of a hydrocarbon gas to not less than 0.5% by volume in the feed gas to be supplied to the nitrification reaction is as follows. Namely, if the content of a hydrocarbon gas is less than 0. 5% by volume, the partial pressure of hydrocarbon gas may become insufficient so that the rate of nitrification reaction of y-A'203 may become extremely low. The hydrocarbon gas serves to remove H20 generated from the reaction between y alumina and ammonia. In view of suppressing an excessive generation of carbon, the content of a hydrocarbon gas should preferably be controlled to not more than 20% by volume. As for the hydrocarbon gas, any of propane gas, methane gas, ethane gas and butane gas may be employed. However, propane gas is most preferable because it is available at low cost.

The nitrification reaction is performed at a heating temperature of 1,200 to 1,700C. If this heating temperature is less than 1,200C, the reaction rate becomes too low, thus taking a long period of time, and at the same time it would be hardly possible, to completely achieve the nitrification reaction of Y-A'203 With respect to the upper limit for the heating temperature, although a temperature of 1,460'C may be sufficient for completely achieving the nitrification reaction, a higher temperature than 1,460C may be employed in view of accelerating the reaction. The heating temperature higher than 1,700'C is not preferable, since it will lead to an increase in manufacturing cost. Therefore, the preferable range 11 for the heating temperature is from 1,300C to 1,460'C.

It is also possible according to this invention to manufacture aluminum nitride fibers by employing yA1203 fibers as a raw alumina material to be nitrified. In this case also, a mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas is prepared at first as mentioned above. As a starting material for alumina, a liquid precursor of y-A'203 can be employed. As mentioned above, the precursor of y-A1203 should preferably be constituted entirely or partially by aluminum hydroxy chloride.

This liquid precursor is dispersed in an aqueous solution containing a material selected from the group consisting of colloidal silica, colloidal alumina and colloidal zirconia to obtain a dispersion. Any of colloidal silica, colloidal alumina and colloidal zirconia functions as a binder for combining particles of -y-A'203 with each other. In addition to these binders, another binder for spinning such as polyvinyl alcohol may be added.

The dispersion thus obtained is then concentrated with a rotary evaporator to obtain a viscous gel-like material. The viscosity of this gel-like material may be about 30 poise in general. This viscous solution i then introduced into a centrifugal spinning machine provided on the outer peripheral wall thereof with a large number of fine openings, and thereafter the S 12 centrifugal spinning machine is rotated in a chamber filled with a dry hot air heated to about 100'C. As a result, the viscous solution is extruded out of these fine openings formed on the outer peripheral wall of the spinning machine thereby producing short fibers. The surfaces of the short fibers thus spun are then immediately dried by the hot air in the chamber. Subsequently, the short fibers are dried entirely including the core portion of the fibers thereby to obtain ordinary short fibers.

Subsequently, the short fibers are collected and calcined at a temperature of 300 to 1,100'C, thereby removing volatile matters such as H20 or HC1 that have been kept in the precursor. If the temperature of calcination is less than 300C, the calcination can not be fully effected. On the other hand, if the temperature of calcination exceeds over 1,100'C, the precursor may be converted via y-A'203 to a-A'203. The precursor (short fibers) thus calcined is then heat-treated in the aforementioned mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas at a temperature of 1,200 to 1,700C thereby accomplishing the nitrification of the short fibers.

Even in the manufacture of the aluminum nitride fibers, it is preferable to select one or more kinds of the hydrocarbon gases from propane gas, methane gas, ethane gas and butane gas.

The heating temperature in the nitrification reaction in this case should preferably be in the range of 1,300'C to 1,460'C as in the case of preparing the aforementioned aluminum nitride solid body.

It is also possible to form a mat by making use of the aforementioned process, wherein the short fibers are simply gathered as they are extruded from a large number of fine openings formed on the outer peripheral wall of the spinning machine to form the mat. In this case, the mat is calcined at a temperature of 300C to 1,100'C, and then heat- treated in a mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas to form a mat composed of aluminum nitride fibers.

Even in the manufacture of a mat composed of the aluminum nitride fibers, it is preferable to select one or more kinds of the hydrocarbon gases from propane gas, methane gas, ethane gas and butane gas.

The heating temperature to be employed in the heat-treatment of the mat composed of the calcined short fibers should preferably be in the range of 1,300C to 1,460'C as in the case of preparing the aforementioned aluminum nitride solid body. (Example 1) A -y-A'203 powder (Trade name: AKP-GO15; average particle diameter: 0.1 pm; available from Sumitomo Kagaku Co.) was calcined in air at a temperature of 9WC for 2 hours. The y-A'203 powder thus calcined was then heat-treated in mixed gas consisting essentially of 5% by volume of propane gas and an ammonia gas at a temperature of 1,400C for 1 hour to perform the nitrification of the y-A'203 powder.

When the y-A'203 powder thus nitrified was examined by means of X-ray diffraction, the complete nitrification of the -y-A'203 powder was confirmed. Further, when the y-A'203 powder thus nitrified was examined by an electron microscope, the diameter of the powder was found to be still as small as 0.1 pin or less. FIG. 1 shows an X-ray diffraction of aluminum nitride particles obtained in this example. (Example 2) To 3,200g of a solution of aluminum hydroxy chloride (the content of Al therein was 23.5 wt.% when calculated as A1203) were added 697g of 10 wt. % conc. polyvinyl alcohol solution and 116g of 20 wt.% conc. colloidal silica to obtain a mixed solution. After stirring, this mixed solution was concentrated by making use of a rotary evaporator to obtain a gel- like material having a viscosity of 35 poise at a temperature of 20'C (a precursor of y-A'203), This viscous liquid was dripped on a disk rotating at a rotational speed of 1,000 r.p.m. in a chamber filled with dry air. As a result, the liquid thus dripped was immediately spread out in the form of disk and blown away by the centrifugal force of the disk, thus forming small particles. These particles were collected and dried at a temperature of 100'C. When these dried particles were examined by an electron microscope, these particles were found to have a flakelike shape about 5 pn in thickness and 10 to 50 pin in both width and length.

Then, these flake-like y-A'203 particles were calcined in air at a temperature of 900C for 2 hours in the same manner as in Example 1. Thereafter, these flake-like y-A1203 particles thus calcined were heattreated as in the case of Example 1 in mixed gas consisting essentially of 5% by volume of a propane gas and an ammonia gas at a temperature of 1,400C for I hour to perform the nitrification of the yA1203 powder. As a result, flakes of aluminum nitride were obtained. (Example 3 and Comparative Example 1) To 3,200g of a solution of aluminum hydroxy chloride (the content of Al therein was 23.5 wt.% when calculated as A1203) were added 697g of 10 wt. % conc. polyvinyl alcohol solution and 116g of 20 wt.% conc. colloidal silica to obtain a mixed solution. After stirring, this mixed solution was concentrated by making use of a rotary evaporator to obtain a gel- like material having a viscosity of 35 poise at a temperature of 20'C (a precursor of y-A1203).

This viscous liquid was introduced into 16 a cylindrical centrifugal spinning machine having a length of 600 mm, a diameter of 200 mm and provided on its outer peripheral wall with a large number of small openings each having a diameter of 0.5 mm. This spinning machine was allowed to rotate at rotational speed of 2,000 r.p.m. in a chamber filled with dry air, thereby extruding the viscous liquid through the small openings formed on the outer peripheral wall of the spinning machine to obtain short fibers. After being dried at a high temperature in the chamber, these short fibers were collected and calcined at a temperature of 900'C for 2 hours to obtain short fibers of y-A'203 The short fibers were then heat-treated in mixed gas consisting essentially of propane gas and an ammonia gas at a temperature of 1,400C for 1 hour, with the content of the propane gas in the mixed gas being changed variously, to obtain aluminum nitride fibers.

When the crystalline phase of aluminum nitride fibers thus obtained were examined by means of X-ray diffraction, the results shown in Table 1 (No. 3 to No. 5) were obtained.

The crystalline phase of aluminum nitride fibers which was subjected to the nitrification treatment without incorporating propane gas in the gas atmosphere (No. 1), as well as the crystalline phase of aluminum nitride fibers which was subjected to the nitrification treatment in the gas atmosphere where the content of 17 propane gas was decreased to smaller than the lower limit as defined by this invention (No. 2) are also shown as Comparative Examples in this Table 1.

Table 1

Change in crystalline phase A1N depending on the content of LP gas No. Content of Crystalline phase of LP gas nitrified x-ray (vol.%) diffraction peak strength (1) Not included a-A1203 (Strong) + A1N (Weak) (2) 0.3 a-A1203 (Medium) + A1N (Broad.medium) 3 0.5 A1N (Broad) 4 1.0 A1N (Strong) 3.0 A1N (Strong) (Example 4)

The short fibers of y-A1203 obtained from the sample No. 5 in Example 3 (Table 1) were collected to form a mat 40 mm. in width, 100 mm in length and 25 mm in thickness. This mat was composed of 94 wt.% of fibers and the balance of a mixture of particles and flakes, both having a size smaller than 0.5 mm mesh.

6 pieces of the mat were prepared, and they were separated into three pairs. These pairs of mats were subjected to heat treatment at a temperature of 300'C, 650C and 800'C, respectively for 30 minutes, thereby obtaining three kinds of calcined mats. All of the 18 calcined mats were found to be amorphous, and specific surface area of fibers constituting these calcined mats was 54.2 m2/g.

Each pair of mats was further heat-treated for 30 minutes in air atmosphere at a temperature of 1,000'C and 1,100'C, respectively. When the resultant mats were examined by means of X-ray diffraction, all of them were found to have been converted into -y-A'203 so that they were suited for the manufacture of aluminum nitride through nitrification reaction.

Then, these calcined mats were subjected to a nitrification treatment. This nitrification treatment was performed by introducing the calcined mats into an alumina boat, and then by heat-treating the calcined mats in a mixed gas atmosphere comprising 3% by volume of propane and the balance of ammonia gas at a temperature of 1,200 to 1,400'C for 3 hours. Thereafter, these nitrified mats were subjected to a decarbonization treatment by further heating them at a temperature of 700'C for 5 hours. The resultant mats were examined regarding the composition thereof by means of X-ray diffraction. The results are shown in Table 2 as No. 6 to No. 11.

Table 2

Relationship between calcining temperature/nitrification temperature and crystalline phase of product Material to be nitrified (A) Heating Nitrification treatment temperature of A in air No. Ratio of Calcination After When When Nitrification A1203 temp. 'C calcination heated heated temp. 'C (anal. %) at at 1000-C 1100-C 6 97 300 Amorphous y -A1203 y -A1203 1200 7 97 300 Amorphous y-A1203 y -A1203 1400 8 97 650 Amorphous y -A1203 y -A1203 1200 9 1 97 1 650 Amorphous y -A1203 -V -A1203i 1400 Af ter nitrification treatment of A A1N A1N A1N 1 As will be clear from Table 2, all of the mats obtained according No. 6 to No. 11 indicated the formation of AlN. FIG. 2 shows graphs of X-ray diffraction of the mat of No. 9 before the nitrification treatment and after calcined at 650C, and of the mat which had been nitrified. (Example 5 and Comparative Example 2) The short fibers of Y-A'203 obtained in the same manner as in the case of the sample No. 5 in Example 3 (Table 1) were calcined to obtain y-A'203 fibers.

The T-A'203 fibers were then heat-treated in mixed gas stream comprising 2% by volume of propane gas and the balance of ammonia gas, with the temperature for heat treatment being changed variously, to obtain aluminum nitride fibers.

The crystalline phase of aluminum nitride fibers thus obtained were examined by means of X-ray diffraction, and then the content of oxygen in the fibers was measured using an oxygen/nitrogen simultaneous analyzer. The results obtained are shown in Table 3 together with Comparative Examples (No. 12 to No. 13).

Table 3

Relationship between nitrification temperature and content of 02 in AlN fibers No. Nitrification Crystalline Content temp. (0C) phase of Of 02 in nitrified fibers Fibers (Vol.%) (12) 1000 -A1203 34 (13) 1100 -Al-203 23 14 1200 AlN 16 1300 AlN 11 16 1400 AIN 3 17 1460 AlN 3 1650 AlN 3 As seen from Table 3, the nitrification treatment of -y-A'203 is required to be performed at a temperature of not less than 1,200C. Namely, when the nitrification treatment of T-A1203 is performed at a temperature of not less than 1,200C, the content of oxygen in the resultant aluminum nitride fibers can be minimized. If the content of oxygen in the fibers is high, the heat conductivity of the fibers increases undesirably. The nitrification treatment at a temperature of not less than 1,400C is particularly preferable in view of minimizing the content of oxygen in the fibers.

In Comparative Examples (No. 12 to No. 13), the temperature for the nitrification treatment was 22 performed at a temperature of 1,000C and 1,100C respectively, thus failing to produce aluminum nitride and at the same time exhibiting a high oxygen content, i.e. 23 vol.% and 34 vol.% respectively in the fibers.

The aluminum nitride obtained in No. 14 to No. 18 of Example 5, and the products obtained in Comparative Examples (No. 12 to No. 13) were measured in-terms of nitrification degree by making use of a thermobalance. Table 4 shows the results obtained. As seen from Table 4, all aluminum nitride samples obtained according to this invention indicated a nitrification degree of 100%.

Table 4

Relationship between nitrification temperature and nitrification degree NO. Calcination Nitrification Nitrification temp. (OC) temp. (C) degree (%) (12) 650 1000 0.1 (13) 650 1100 87.4 14 650 1200 100 650 1300 100 16 650 1400 100 17 650 1460 100 18 650 1650 100 Nitrifaction degree = (Increment of oxide as measured with thermobalance)/ (theoretcal increment as AlN is oxidized) (Example 6)

The short fibers of y-A'203 obtained in the same manner as in the case of the sample No. 5 in Example 3 23 is (Table 1) were calcined to obtain T-A'203 fibers.

The -y-A'203 fibers were then heat-treated in four kinds of mixed gas stream, each consisting essentially of an ammonia gas and 2% by volume of methane gas, ethane gas, propane gas or butane gas at a temperature of 1, 400C for one hour to obtain aluminum nitride fibers.

The crystalline phase of these aluminum nitride fibers thus obtained were examined by means of X-ray diffraction. The results obtained are shown in Table 5 (No. 19 to No. 22).

Table 5

Relationship between kinds of hydrocarbon gas and crystalline phase of nitrified fibers No. Kinds of gas Crystalline phase of nitrified fibers 19 Methane (CH4) AlN Ethane (C2H6) AlN 21 Propane (C3H8) AlN 21 Propane (CO10) AlN As seen from Table 5, any substantial difference regarding the crystalline phase of these aluminum nitride fibers could not be recognized irrespective of the difference in the kinds of hydrocarbon employed. Therefore, the employment of most inexpensive propane gas is preferable. (Example 7) The short fibers of T-A1203 obtained in the same 24 manner asin the case of the sample No. 5 in Example 3 (Table 1) were calcined with the calcination temperature being variously changed in the range of 300 to 1,000C as shown in Table 6.

The calcined short fibers were then heat-treated in mixed gas stream consisting essentially of 2% by volume of propane gas and the balance of ammonia gas at a temperature of 1,400C for one hour to obtain aluminum nitride fibers.

The crystalline phase of aluminum nitride fibers thus obtained were examined by means of X-ray diffraction, and then the content of oxygen in the fibers was measured using an oxygen/nitrogen simultaneous analyzer. The results obtained are shown in Table 6. Table 6 Relationship between calcination temperature and content of 02 in AlN fibers No. Calcination Crystalline Content of temp. (OC) phase of 02 in nitrified fibers fibers _23 300 AlN 11 _24 500 AlN 8 _25 900 AlN 3 26 1000 AlN 3 (27) 1300 a-A1203 26 AlN As seen from Table 6, there was not recognized any substantial difference in crystalline phase of aluminum nitride fibers as long as the calcination temperature was selected from the range of 300 to 1,000C. However, as far as the content of oxygen in the aluminum nitride fibers is.concerned, the higher the calcination temperature was, the lower the content of oxygen in the aluminum nitride fibers could be controlled.

As sample of Comparative Example (No. 27), the same fibers as those of above Example was calcined at a temperature of 1,300'C to find out that the resultant fibers were consisted of a mixture of a-A1203 and 6-A'203. When the fibers were subjected to a nitrification treatment at the same temperature and treatment time as those of above Example, the resultant fibers were consisted of a mixture of a-A'203 and AlN. FIG. 3 shows a graph of X-ray diffraction as measured on the calcined product obtained in prior to the nitrification treatment and the nitrified product obtained after the nitrification treatment. (Example 8) To 3,200g of a solution of aluminum hydroxy chloride (the content of Al therein was 23.5 wt.% when calculated as A1203) were added 697g of 10 wt. % conc. polyvinyl alcohol solution and 200g of 18 wt.% conc. colloidal silica to obtain a mixed solution. After stirring, this mixed solution was concentrated by 26 making use of a rotary evaporator to obtain a gel-like material having a viscosity of 35 poise at a temperature of 20C (a precursor of y-A'203).

This viscous liquid was spun in the same manner as in Example 3 to obtain short fibers.

The short fibers were then heat-treated in mixed gas consisting essentially of 2% by volume of propane gas and am monia gas at a temperature of 1,450'C for 2 hour to obtain aluminum nitride fibers. When the crystalline phase of aluminum nitride fibers thus obtained were examined by means of X-ray diffraction, only the AlN phase could be recognized.

The fibers thus obtained were more or less lower in elasticity as compared with that of the fibers obtained in No. 3 to No. 5 of Example 3.

The same procedures as illustrated above were repeated except that 100g of 10 wt.% conc. colloidal zirconia was employed in place of 18 wtA conc. colloidal silica and the nitrification temperature was selected to be 1, 350'C instead of 1,450C to obtain aluminum nitride fibers. When the crystalline phase of aluminum nitride fibers thus obtained were examined by means of X-ray diffraction, only the AlN phase could be recognized.

The fibers thus obtained were found to be more or less shorter in fiber length as compared with that of the fibers obtained with the employment of 27 aforementioned colloidal alumina, or that of the fibers obtained in No. 3 to No. 5 of Example 3. (Example 9) In the same manner as explained in Example 3, short fibers comprising 97% by weight of A1203 and 3% by weight of S'02 was spun. After being calcined in air atmosphere at a temperature of 650'C for 30 minutes 200g of the resultant calcined fibers were dispersed in 200 liter of water together with 15g of soluble starch and 50g of colloidal silica, both being employed as a binder, and the resultant mixture was fully stirred to obtain a slurry.

A mold for vacuum molding was dipped into this slurry, and the interior of the mold was sucked to allow the fibers and binders in the slurry to adhere onto the surface of the mold to obtain a molded product. The molded product was then dehydrated and dried. As a result, a board 150 mm in length and width, 20 mm in thickness, 0.2g/cm3 in bulk density was obtained. The board was then introduced into an electric furnace and calcined at a temperature of 600'C. Thereafter, this board in the furnace was heat-treated in an ammonia gas atmosphere containing 3% volume of LPG at a temperature of 1,200C for 3 hour to obtain an aluminum nitride board.

The board thus obtained exhibited a high mechanical strength. After being subjected to 91 28 a decarbonization treatment at a temperature of 700C for 5 hours, the resultant board was examined by means of X-ray diffraction, finding that the formation of A1N in the board was recognized.

29

Claims

Claims:

1. A method of manufacturing an aluminum nitride solid body, which comprises the steps of:

(a) preparing a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas; and (b) heat-treating a solid y-A1203, a precursor of,y-A1203, or a mixture of said solid T-A1203 and said precursor in said mixed gas at a temperature of 1,200 to 1,700'C.

2. A method of manufacturing an aluminum nitride solid body, which comprises the steps of:

(a) preparing a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas; (b) calcining y-A'203 or a precursor of T-A'203 at a temperature of 300 to 1,100'C; and (c) heat-treating said y-A'203 or said precursor of -y-A'203, thus calcined, in said mixed gas at a temperature of 1,200 to 1,7009C.

3. The method of manufacturing an aluminum nitride solid body according to claim 1, wherein said hydrocarbon is at least one compound selected from the group consisting of propane, methane, ethane and butane.

4. The method of manufacturing an aluminum nitride solid body according to claim 2, wherein said hydrocarbon is at least one compound selected from the group consisting of propane, methane, ethane and butane.

5. The method of manufacturing an aluminum nitride solid body according to claim 1, wherein said temperature for heat treatment is in the range of 1,300 to 1460C.

6. The method of manufacturing an aluminum nitride solid body according to claim 2, wherein said temperature for heat treatment is in the range of 1,300 to 14WC.

7. The method of manufacturing an aluminum nitride solid body according to claim 1, wherein either said y-A'203 or said precursor of T-A1203 is in the form of particle, flake or a mixture of particle and flake.

8. The method of manufacturing an aluminum nitride solid body according to claim 2, wherein either said T-A'203 or said precursor of y-A1203 is in the form of particle, flake or a mixture of particle and flake.

9. The method of manufacturing an aluminum nitride solid body according to claim 1, wherein said precursor of -y-A'203 is selected from the group consisting of aluminum alkoxide, aluminum sulfate, aluminum alum, ammonium aluminum carbonate, aluminum hydroxy chloride and boehmite.

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10. The method of manufacturing an aluminum nitride solid body according to claim 2, wherein said precursor of y-A'203 is selected from the group consisting of aluminum alkoxide, aluminum sulfate, aluminum alum, ammonium aluminum carbonate, aluminum hydroxy chloride and boehmite.

11. nitride -y-A1203 part of

12. nitride y-A1203 part of

13. nitride The method of manufacturing an aluminum solid body according to claim 1, wherein said is formed using, as a sole alumina source or as alumina source, aluminum hydroxy chloride.

The method of manufacturing an aluminum solid body according to claim 2, wherein said is formed using, as a sole alumina source or as alumina source, aluminum hydroxy chloride.

The method of manufacturing an aluminum solid body according to claim 1, wherein said precursor of y-A'203 is entirely or partially constituted by aluminum hydroxy chloride.

14. The method of manufacturing an aluminum nitride solid body according to claim 2, wherein said precursor of y-A'203 is entirely or partially constituted by aluminum hydroxy chloride.

15. A method of manufacturing aluminum nitride fibers, which comprises the steps of:

(a) preparing a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas; 32 (b) dispersing a liquid precursor of y-A'203 in an aqueous solution containing a binder and one material selected from the group consisting of colloidal silica, colloidal alumina and colloidal zirconia; (c) concentrating said aqueous solution containing said precursor dispersed therein; (d) spinning short fibers from the concentrated aqueous solution placed in a centrifugal spinning machine by rotating the centrifugal spinning machine; (e) drying the spun short fibers; (f) calcining the dried short fibers at a temperature of 300 to 1, 100'C; and (g) heat-treating the calcined short fibers in said mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas at a temperature of 1, 200 to 1, 7 0 O'C.

16. The method of manufacturing aluminum nitride fibers according to claim 15, wherein said hydrocarbon is at least one compound selected from the group consisting of propane, methane, ethane and butane.

17. The method of manufacturing aluminum nitride fibers according to claim 15, wherein said temperature for the heat treatment in said mixed gas is in the range of 1,300 to 1,460'C.

18. The method of manufacturing aluminum nitride fibers according to claim 15, wherein said precursor of 33 y-A'203 is entirely or partially constituted by aluminum hydroxy chloride.

19. A method of manufacturing aluminum nitride fiber mat, which comprises the steps of:

(a) preparing a mixed gas consisting essentially of an ammonia gas and at least 0.5% by volume of a hydrocarbon gas; (b) dispersing a liquid precursor of y-A'203 in an aqueous solution containing a binder and one material selected from the group consisting of colloidal silica, colloidal alumina and colloidal zirconia; (c) concentrating said aqueous solution containing said precursor dispersed therein; (d) spinning short fibers from the concentrated aqueous solution placed in a centrifugal spinning machine by rotating the centrifugal spinning machine; (e) drying the spun short fibers; (f) calcining the dried short fibers at a temperature of 300 to 1,100C; (g) forming a mat with the calcined short fibers; and (h) heat-treating the mat in said mixed gas consisting essentially of a hydrocarbon gas and an ammonia gas at a temperature of 1,200 to 1,700'C.

20. The method of manufacturing aluminum nitride fiber mat according to claim 19, wherein said 34 hydrocarbon is at least one compound selected from the group consisting of propane, methane, ethane and butane.

21. The method of manufacturing aluminum nitride fiber mat according to claim 19, wherein said temperature for the heat treatment in said mixed gas is in the range of 1,300 to 1,460C.

22. The method of manufacturing aluminum nitride fibers according to claim 19, wherein said precursor of,y-A'203 is entirely or partially constituted by aluminum hydroxy chloride.

23. A method of manufacturing aluminum nitride, substantially as hereinbefore described with reference to the accompanying drawings.