CA1048229A - Production of a ceramic material containing silicon, aluminium, oxygen and nitrogen - Google Patents
Production of a ceramic material containing silicon, aluminium, oxygen and nitrogenInfo
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- CA1048229A CA1048229A CA74216037A CA216037A CA1048229A CA 1048229 A CA1048229 A CA 1048229A CA 74216037 A CA74216037 A CA 74216037A CA 216037 A CA216037 A CA 216037A CA 1048229 A CA1048229 A CA 1048229A
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
- C04B35/111—Fine ceramics
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
- C04B35/597—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon oxynitride, e.g. SIALONS
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- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
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Abstract
A method of producing a ceramic material includes the step of heating at a temperature between 1200° and 2000°C
a mixture containing silicon nitride in an amount up to 98% by weight of the mixture together with between 1% and 60% by weight of aluminium nitride, between 0.5% and 50% by weight of silica, and between 0.05% and 60% by weight of alumina, some but not all of the silica in the mixture at said temperature being present as an impurity contained by the silicon nitride. The silicon nitride, aluminium nitride, alumina and silica produce at said temperature a reactable composition which constitutes at least 95% by volume of the mixture and in which the silica is present in a molar ratio of 1:2 with part of the aluminium nitride and the alumina is present in a molar ratio of 1:1 with the remainder of the aluminium nitride, and the constituents of the reactable composition react together to produce the required ceramic material.
a mixture containing silicon nitride in an amount up to 98% by weight of the mixture together with between 1% and 60% by weight of aluminium nitride, between 0.5% and 50% by weight of silica, and between 0.05% and 60% by weight of alumina, some but not all of the silica in the mixture at said temperature being present as an impurity contained by the silicon nitride. The silicon nitride, aluminium nitride, alumina and silica produce at said temperature a reactable composition which constitutes at least 95% by volume of the mixture and in which the silica is present in a molar ratio of 1:2 with part of the aluminium nitride and the alumina is present in a molar ratio of 1:1 with the remainder of the aluminium nitride, and the constituents of the reactable composition react together to produce the required ceramic material.
Description
This invention relates to a method of producing a ceramic material.
A method, according to one aspect of the invention, includes the step of heating at a temperature betwe~n 1200C
and 2000 C a mixture cont~nin~ silicon nitride in an amount up to 98~o by weight of the mixture together with between 1~ and60~c weight of ~l~m~ nitride, between 0.5~ and 50~-by weight of silica, and between 0.05% and 60~o by weight of alum-na, some but ~ :-not all of the silica in the mixture at said temperature being 10. present as an impurity contained by the silicon nitride, and the silicon nitride, all n~- nitride, ~ ~;n~ and silica producing at said temperature a reactable composit.ion which constitutes at least 95f~o by weight of the mixture and in which the silica is present in a molar ratio of 1:2 with part of the al- tn; nitride and the el n~ is present in a molar ratio of 1:1 with the r~m~n~er of the aluminium nitride, the constituents of the reactable composition reacting together to :.
produce the required ceramic.material. . --Preferably, the relative proportions of the silicon -20. nitride, al~l ~ni~ nitride, silica and alumina are such that in.said composition the atomic ratio of silicon~ nl : .
i .
nitrogen: oxygen is 6-z:z:8-z:z respectively where z ls :-greater than zero and less than or equal to 5.
A method, according to a further aspect of the in~ention, - .
includes the step of heating at a temperature between t200 C and - .
2000 C a mixture from which silicon nitride is ab~ent but ;
which contains between 40~ and 600~o by weight of all-~; n~
nitride, between 15~o and 45~o by weight of silica, and between "~
0~05~o and 50~ by weight oP ~1- in~ ~ the relative proportlons of _ 2 -~., , -,:
~ - .. , ~- :, the ~1l2~;nium nitride, alumina and silica being such as to produce at said~temperature a reactable composition which constitutes , . :.
at least 95% by weight of the mixture and in whic~ the silica is present in a molar ratio of 1:2 with part of th~ aluminium nitride and the alumina present in a molar ratio of 1:1 with ~ -the remainder of the aluminium nitride, the atomic ratio of silicon:aluminium: nitrogen: oxygen in said composition being :.-.
6-z:z 8_z:z where z is greater than 4 and less than or e~ual to 5, and the constituents of said reactable composition reacting 10. together to produce the required ceramic material. -; ~-Con~eniently, at least part of the ~11 'n~ in the mixture -at said temperature is pre~ent as an impurity contained by the - -.
aluminium nitride.
Con~eniently, at least one of the constituents present in the mixture at said temperature is introduced into the -- -starting materials used to produce the mixture as a compound ~-. .
which reacts to produce the required constituent or constituents -:
during the heating step.
Conveniently, said compound is silicon oxynitride, ---20. aluminium oxynitride, ethyl silicate, or all-m;nillm hydroxide.
t' ~
Preferably, pressure is applied to the mixture during ~.
said heating step.
Preferably, a molten glass is also present in the mixture ~~
at said temperature. A' ''"-~' .
Conveniently, the molten glass is an aluminosilicate glass, or manganese glass or a lithium glass. ~-Alternatively, the molten glass is a magnesium glass. - ~ ^
~ . .
i;
'' ' , ` ' ' ~
~'t ' . ', -::e ~ , ,., X
1048229 -~ -Conveniently, the magnesium glass i~ produced by reaction - -during the heating step between magnesium oxide and a glass- ~ --~
forming compound, both of the latter being present in the ..
mixture. ,;
.~
Cor;veniently, the gla$s forming compound is silica. ~ -In the accompanying drawings:-"~
Figure 1 is a quaternury phase diagram illustrating by way of example compositions of various mixture of al~ ;nil~ '., nitride, silica, alumina and silicon nitride which can be 10. employed in the method of the invention, and " . ,~
Fi~ure 2 is a graph illustratin~ the unit cell dimensions :-.'' '~'', of ceramic materials produced according to the examples -~-.-~ ::.
- hereinafter described. ----~-.. ~,, Referring to the dra~ings, in a first example a ceramic ~-material was produced from a starting mixture consisting of 78.48~ by weight of silicon nitride powder, 14.76% by ~eight of :
aluminium nitride powder aLid 6.76% by weight of silica powder.
In this mixture, the silicon nitride powder emp~oyed contained 89~ by weight of the ~-phase material and had a mean particle -~-20- size of 3 microns, whereas the aluminium nitride powder was that supplied by Koch-Light as type 8006H with a mean particle size ^ -.. . -of 11.5 microns, but, which prior to use, was co ;n~ted to an average value of 6 microns. The silica powder employed wa~ - `
that -~upplied by Hopkin and Williams-Limited as pure ~rQclpirQT~ -silica. -Of the starting materials employed in the above mixture, the silicon nitride powder inherently contained a silica -impurity a~ a coating over the particles of silicon nitride, and the all~min;llm nitride powder inherently contained an -~-3. impurity of alumina. Thus, it will be understood that the ~-- 4 _ ~
: :' ',~ ''"
.- :,., - :., ,~ ~ '"'',: ~.,.
~ .~
......
-~tarting mixture of the first example contained ~11 n~ in -addition to aluminium nitride, silica and silicon nitride. -- ~
Moreover, since the impuritie~ contained by the silicon --nitride and al~lm;n;ll~ nitride starting materials were clearly - ^
going to take part in the subsequent reaction to produce the -~
required ceramic material, before production of the abo~e ~--. -:
mixture the impurity levels in these starting materials were ~
determined by fast neutron activation analysis. Then~ as will -~-become ap~arent below, allowance was made for these impurities 10. in arriving at the composition given above for the starting mixture. Using the particular starting material described~
, .. .
it was found that the silica content of the silicon nitride powder was 4% by weight and the ~12l~;n~ content of the al7~m;~;lm ~ ~
nitride was 6yo by weight. Thus, the overall compoRition of ~`
~ ~, the mixture was in fact 75.34~o by weight silicon nitride~ ~-13.87p by ~eight ~ ~;nium nitride, 0.89yo by weight ~11 ; n~ ~ -and 9.9~o by weight silica. This composition is defined by point A in Fi~ure 1, it being appreciated that in the drawing -~-the axes correspond to the pure materials with no impurities ....
20. present.
To produce the above mixture, the required amount of tho - --starting materials were introduced-into a colloid mill where ~ine was effected using i~o-propyl alcohol as the carrier liquid and was continued until the mean particle size of the ~-: . ,, mixture was less than 3 microns. The mixture was then dried ~- -and subsequently was sieved to remove any powder aggregates.
Thereafter an impurity determination was performed on the mixture to ascertain whether the processing had had any effect ~ -on the impurity lerel~ of the starting material, but it was ~ ~
.~ - -.
30. found that the latter had not been altered by the colloid ~ . ..
- 5 _ :~
~. ~A
. f, .~' ~ . '"' 10~8229 milling or the drying and sieving operations. ~ --The mixture was then loaded into the die cavity of a ~
g~aphite die onto a graphite plug clasing one end of the die ~-cavity. A graphite punch was then assembled onto the powder charge, aLl graphite surfaces in contact with the powder charge ~-~
having previously been spray coated with boron nitride to a depth-of the order of 0.01". The assembly was then introduced into a press, where the temperatura and pressure were simultaneously increased over a period of 30 mir~ltes to 1800C
10. and 1.5 tons/sq. in. respectively. The mixture was then --maintained at this temperature and pressure for 1 hour and, under these conditions the constituents of the mixture reacted to ~;
produce the required ceramic material. On cooling, the reaction product was removed from the die and the cryst~11;ne phases in the product were detected by X-ray d~ffraction using- ;---a Unicam Spectrometer with Cr-K~ monochromatic radiation. The X-ray analysis showed that the reaction product consisted -~
substantially entirely of a single crystalline phase ceramic ~ -material obeying the formula~
20. Si6-z Al N8 where z was equal to 1. The ceramic material was also found to have a crystal structure based on that of ~-phase silicon nitride, but with the a and c unit cell dimensions being 7.648 and 2.938 respectively as compared with values of 7.623 and 2.914 ~-respectively for ~ -hase silicon nitride (see Figure 2) -~, It is to be appreciated that using the mi~ture of the above e~ample and allowing for the impurities in the ~tarting materials~ then at the elevated temperature of the reaction the mi~ture consisted entirely of a reactable composition ~,. . . .
- 6 - ~-." ~
:- gl~ ~ .
cont~;!n;ng 51.3 mole ~ silicon nitride, 0.8 mole % ~ e~
32.2 mole % alllmin;llm nitride and 15.7 mole ~/o silica. Thus - ~-in the reactable composition the silica was present in the ~:
required molar ratio of 1:2 with part of the aluminium nitride(31.4 mole ~o), while the alumina wa~ present in the -~ ~;
required molar ratio of 1:1 with the rem~;n~er o~ the :~ :
aluminium nitride (0.8 mole 7~). In the phase diagram of Figure 1, the shaded triangular area B define4 the limits of ~
the various possible mixtures of ~ m;n~, al~ m nitride~ ~-10. silica and silicon nitride which, on heating consist entirely of a reactable composition in which the alumina~ silica~- -and ~lllm;n;ll~ nitride are present in the requlred molar ratio~
Thus in arriving at the stated composition for the mixture -~
of the above example, the amounts of the various s*arting ~ -materials were calculated so that~ allowing for impurities~ ~
the overall composition of the mixture (as indicated by point A) -was within the limits defined by the triangular area B.
It can readily be calculated that in the reactable composition produced by the mixture of the above example the - -~
20. atomic ratio of silicon~ ;n;llm:nitrogen:oxygen was 6-z:z; 8-z:z respectively where z was equal to 1. Thus the silicon, ~lll~;n; ~ nitrogen and oxygen were present in this reactable composition in the proportions required in the resultant ceramic material. It is, however, to be understood -that other mixtures could have been used which at the hot --pressing temperature would have consisted entirely of a -~
reactable composition having the required atomic proportions of silicon, ~lllm;n;um~ nitrogen and oxygen, such suitable : ,' ~, mixtures lying on the line C in Figure 1.
- 7 ~
-- ., :
1~482Z9 - ~:
In a second example of the invention, it was required to produce a ceram~ic material. obeying the formula~
Si Al N 0 - -6-z z 8-z z ~ with z being equal to 2.1. In producing this ceramic material the starting material5 of the first example were2gain employed but were mixed together in ~uch proportions that the starting mixture consisted of 30.88% by weight of alumin-um nitride, - 50.44~ by weight of silicon nitride, and 18.68% by weight of silica. Thus~ allowing for the impurities in the al~ in~
10. nitride and silicon nitride starting materials, the overall composition of the mixture was 29.03C//o by weight of ~ m ~-nitride~ 48.425~ by weight of silicon nitride, 20 .7C/o by weight of silica and 1.85qo by weight of alumina, this composition being indicated by point D in Figure 1. The procedure of the first - -example was then repeated and, at the elevated temperature .
of the hot pressing process, the mixture consisted entirely of : ~
a reactable composition containing 50 mole% aln~;n;llm nitride, 24.35 mole c/O silicon nitride, 24.35 mole /c silica and 1.3 mole - ~o alumina. Thus~ it will be seen that in the reactable .
20. composition the silica was present in a molar ratio of 1:2 with-part. of the allm~n;llm nitride (48.7 mole %), while the alumina was present in a molar ratio of 1:1 with the ,~ -inder of the al~lm;n;l~m nitride(1.3 mole %). Moreover, it can . -readily be calculated that the atomic ratio of silicon:
.~
alnm;n;ur: nitrogen:oxygen in the reactable composition was . ~ Z
6-z:z:8-z:z where z was equal to 2.1. Thus the silicon~
:'.' ~'~`~
- all in;llm, nitrogen and oxygen were present in the reactable :~ -composition in the proportions required for the ceramic material to be produced. Again, other mixtures could havebeen _ 8 - ~:
., , .
:: .
. . ._._. ~r .
. ~
'. 11 ~ , '' '`
: -~.
~ 1~48ZZ9 ~ ~
employed which at the hot pressing temperature would have consisted entirely of reactable compositions having the atomic proportions required-in the ceramic material of ~-this example, the line E in Figure 1 indicating the possible ~
compositions for such mixtures. As can be seen from Figure 2, ~ -the ceramic material obtained by the method of the second example had a and c unit cell dimensions of 7.674 and 2.962 .
respectively.
In a third example of the invention, the procedure of 10. the first example was again repeated, but in this case the -starting mixture consisted of 43.980,~ by weight of al~
nitride, 27.65~ by weight of silicon nitride and 28~37% by , ~-weight of silica. Thus, allowing Por the i~puritie~ in the ~ -starting materials, the actual composition of the mixture was 41~34% by weight alllmin;~lm nitride, 26~54~o by weight of ~--, silicon nitride, 29~48~o by weight of silica and 2~64% by -~-weight of ~1~ ;n~ this mixture being indicated by the point -~','''' in Figure 1. At the eleYated temperature of the hot ~
,, -, pressing process, the mixture produced a reactable composition 20~ consi~ting of 11~4 mole~p silicon nitride, 58,80 mole~ ~1llmin;
nitride, 28~64 mole% silica and 1.52 mole% alum~na. Thus~
as in the previous examples it will be seen that the ~11 tni nitride, silica and alu~mina were accurately in the required ~ ~
molar ratios, although using the mixture of this example ~--the atomic ratio of silicon~ m;nium: nitrogen: oxygen in the reactable composition were equal to 6-z:z:8-z:z where z was equal to 3. Thus, as will be expected, the components of the reactable composition reacted together at the elevated : . -.
temperature of the hot pressing reaction to produce a ¢eramic 30. material obeying the above formula with z being equal to 3.
_ g ~
''''~ `'''`' 7~ :', ,~, ' ,.-, .~ ~.
'~ ~
1048Z2~ ~
, ~, As sh~own in Figure 2~ the a and c unit cell dimensions of the ceramic material were 7.70 and 2.986 res~eFtively.
In a fourth example~ the same procedure was again carried out, but in this case the starting mixture consisted of 48.33~/ by weight of aluminium nitride. 20.12,~ by weight ~ -of silicon nitride and 31.55% by weight of silica. Thus, allowing for the impurities in the starting materials, the actual composition of the mixture was ~5 .L~30~o by weight Of ~ m~n;um nitride, 19~31~o by weight of silicon nitride, ;-10. 32.36yo by weight of silica and 2~90~o by weight of ~1nmt~A, ~-thi3 mixture being indicated by the point G in Figure 1. -~
As can readily be calculated, at the elevated temperature of the hot pressing process, this mixture consisted entirely of a reactable composition in which the silica was present in a molar ratio of 1:2 with part of the aluminium nitride, while the ~ m;n~ was present in a molar ratio of 1:1 with ~-the rem~;nder of the ~ min;1l~ nitride. Moreover~ in this --reactable composition the atomic ratio of silicon:al~ ~n;-: ', nitrogen: oxygen was equal to 6-z:z:8-z:z where z ~as equal ~- -20. to 3 .3 . Thus, as expected, the ceramic phase of the product -of the hot pressing reaction consisted substantially entirely of a single crystalline phase ceramic material~ -obeying the above formula with z being equal to 3 .3 .~ ~
. .
As shown in Figure 2, the a nnd c unit cell dimensions of the ceramic material were 7,703 and 2.991 respectively.
In a fifth example, the -~tarting materials used above were mixed with alumina powder as supplied by the Al- ;n; .
Company of America as type XA16 to produce a mixture cont~;n;ng 60.6yo by weight of silicon nitride, 20.3% by 3~. weight of alu~;nill~ nitride, 7.9~o by weight of silica and -:: .
''', 104822~
11.2,~ by weight of alumina. Thus, allowing for the impuritie!s in the starting materials, the actual composition of this mixture was 58.180,b by weight of sllicon nitride, 19.08Co by weight of alu~.inium nitride, 10.32G,~ by weight of silica and 12.420/~o by weight of alumina. This mixture is indicate~
by the point H in Figure 1. The mixture was ;crepared and hot ~.
pressed as in the previous examples and, at the hot pressing .:~
temperature, consisted entirely of a reactable composit.ion having ~.
the required molar ratios of ~1u~inium nitride, silica and ~l7l~;
10, ~'oreover, it can readily be shown that in the reactable composition ~ .
the atomic ratio of silicon:aluminium:nitrogen:oxygen was equal to 6-z:z:8-z:z where z was equal to 2. Once again, therefore, the resultant ceramic material obeyed the above formula with :~:~
z being equal to 2.
In a modification of a fifth example, a ceramic material obeying the above formula with z being equal to 2 was produced from the same starting materials, although in this ca~e the -initial mixture contained 64.75C/o by weight of the silicon- -nitride, 15.35~o by weight of the aluminium nitride~ 2.65~ by : .-20. weight of the silica and 17.25~ by weight of the ~ nium. .. :~
Allowing for the impurities in the starting materials~ this .:-:
composition is indicated at I in Figure 1.
It i9 to be appreciated that the method ~ the abo~
examples can also be performed with starting mixtures consisting only of silica, alumina and aluminium nitride. It is~ however, - --found that using such mixtures, where of course silicon nitride is absent, hot pressing produces reactable compositions which --contain silicon, aluminium, nitrogen and oxygen in the ~.
proportions required to provide the atomic ratio given abo~e, ~--30. but with the z value al~ays being greater than 4. Thus~ the --- .
:::
. ~ "~, ,. .~ ~, ~ -:
1048Z29 ~:
ceramic materials obtained from mixtures in which silicon .- -nitride is absent always e~hibit z values in excess of 4 in the above formula. The reason for this can readily be ~
seen by reference to the line J in ~igure 1, it bsing - ~-appreciated that in the mixtures which have composition~ lying on this line the silicon, aluminium~ nitrogen, oxygen are present in the required atomic proportions to produce a ceramic material obeying the above formula when 2 is equal to -:
4. Thus, it will be noted that the line J passes through the al~ ;njl nitride/silica axis, which of course corresponds to the situation where there is no silicon nitride present.
Moreover, it will bc understood that as the silicon nitride .
content of mixture~ lying within the shaded area B:is decreased, ~-.
then the ceramic materials obtained frorn these mixtures have . . . .
increasing z values in the above formula. Hence, if a mixture lies on the triangular area defined between the AlN, A12 03 and -SiO2 apices, which area of course corresponds to a zerQ Si3N4 content-~ then the mixture necessarily produces a ceramic mat.erial having a z ~alue in excess of 4. - -To illustrate the effect of omitting the silicon nitride, in a sixth example, the starting materials of the previous example were used to produce a mixture consisting of 51.45% .
by weight aluminium nitride, 19~1~% alumina, and 29.37% by weight silica. Thus~ allowing for the impurities in the starting materials, the actual composition of the mixture wa~
48.75C~ by weight (62.78 mole %) aluminium nitride, 21~73~ ~
by weight- (11.25 mole ~ lmin~ and 29.52~ by weight (25.97 mole ~) silica. The mixture was processed as in the -preceding examples and was hot pressed at 1850 C, at which .'~
- 12 ~
~, ~-rr ' ~ ~y ~ ~
~048Z29 temperature the mixture consisted of more than 95~ by weight o~
a reactable composition in which the silica was present in a molar ratio of 1:2 with part of the ~ m;n;um nitride and the alumina was present in a molar ratio of 1:1 with the re~ er - of the aluminium nitride. Moreover, at the hot pressing ~-temperature the components of the reactable composition reacted together to produce a ceramic material obeying the above -formula and having a z value equal to 4.6. The a and c unit cell dimensions of the ceramic material were 7.745 A
10. and 3.~12 A respectively. -- It will of course be understood that ceramic materials -~
having z values in excess of 4 in the above formula can also be produced from starting mixtures containing silicon nitride. ~--Thus~ in a seventh example, a ceramic material again having a z value of 4.6 was produced by hot pressing at 1850 C a ~-starting mixture consisting of 10.19,b by weight silica, 40.77 by weight alumina, 33 .98~o by weight aluminium nitride and -~
15.06C~ silicon nitride, all the starting materials again being those employed in the fifth example. Thus, allowing for the 20. impurities in the starting materials, the mixture consists of 12.15 Mole ~ silica, 28.36 moIe ~ mina, 52.46 mole ~ al~ n;l-nitride and 7.03 mole ~ silicon nitride. From these figures it can readily be calculated that the mixture consisted at the hot pressing temperature of ln excess of 95~ by weight of a reactable composition in which the sllica, alumina and aluminium nitride were in the required molar proportions. The resultant --ceramic material had the same a and c unit cell dimensions as -the material of the preceding exa~ple.
, .
. . .
,,~ ,"
' ~'',.
'' ~', It is to be appreciated that in each of the above examples, hot pressing of the ~tarting mixture produced .. reactable composition which not only had the required molar ratios of ~l~minium nitride, alumina and silica, but which also -~ -constituted the entire volume of the starting mixture, It is, however, to be understood that, provided the reactable -compo-~ition constitutes at least 95~ of the weight of the ~ -~ixture, other materials can be present in the mixture at - -the hot pressing temperature. The other materials can be 10. in the form of excess quantities of one or more of the startin~ --materials and preferably are arranged so as to produce a molten glass to aid densification ~ the ceramic material -~
produced during hot pre-~sing. Conveniently, the molten glass ~- `
is an al~lminotboro-~ or iron-silicate glass, or alternatively ~-is a magnesiùm glass, a manganese glass or a lithium glass.
In the case of a magnesium glass the starting mixture would be arranged to contain magnesium oxide and a glass-forming agent, the latter preferably being in the form of silica.
In each of the above examples, the starting mixture~ were 20. produced by i~ing together the actual constituents required for the reactable composition. It is, however,to be appreciated ~ --that one or more of the constituent~ required in the reactab1e ~
. ~ . ,, composition could have been introduced into the starting -" :-, materials as a compound which decomposed during the hot -pressing operation into the required constituent or constituents.
Thus, for example, aluminium hydroxide could have been added to the -~tarting materials t-o provide alumina in the reactable composition while the addition of ethyl silicate to the - ~-starting materials would have provided the necessary silica 30. for the reactable composition. Other such suitable additives to - 14 _ -.''~ ~,,`, ~". '`, ,. .,. - ,~ '' ~, v`' ", lV48Z2~
the starti ~ materials are silicon oxynitride (to pro~ide silica and silicon nitride) and al~ 71ill~ oxy~itride (to provide alumina and aluminium nitride).
By way of illustration of the statements in the preceding - paragraph, in an eighth example of the invention a ceramic ~-material having a z value of 2 in the above formula was - -~
produced by hot pressing for 1 hour at 1700 C a starting weight mixture consisting of 8.94~o by/silicon nitride, 29.36~ by weight ~lu~;njum nitride, 1~ by weight silica and 60.7~
10. silicon oxynitride. In this mixture, the silicon oxynitride had a mean particle size of 2 microns and was supplied by ..
- the Norton Company of America, whereas the other starting ~ -materials were the same as those emplo~ed in the pre~ious eYanple. The silicon oxynitride was found to contain free --silicon nitride and also a surface impurity of silica, but ~
analysis showed that these were present in the molar proportion~ ~ -required to produce silicon oxynitride. Thus, for the purposes of calc~ating the composition of the starting mixture, it was po-sible to regard the silicon oxynitride as the pure 20. material. Moreover, it can readily be shown that 2 moles of silicon oxynitride are equivalent to 1 mole of silicon - ~
nitride and 1 mole of silica so that, allowing for this ~ ~
equivalent and also catering for the impurities in the silicon nitride and s71 inil nitride, the effective overall ~m~
composition of the starting mixture was 51.09yo by weight (26.42 mole %) silicon nitride, 27~57~o by weight (4~.69 mole ~) -al~lmin~ nitride, 1.76~ by weight (1.25 mole ~0) al ~ns7 and 19.58~ by weight ~23.63 mole ~o) -~ilica. At the elevated ~-temperature of the hot pressing process, this mixture consisted 30. of more than 95~o by weight of a reactable composition in which ;
- 15 - ~ -1~)48ZZ9 the silica was present in a molar ratio of 1:2 with part of the aluminium nitride, while the alumina was present in a molar ratio of 1z1 with the remainder of the ; nitride.
It is to be understood that in performing the method of the invention~ sintering of the starting materials should be effected at or above 1200 C since below this temperature there is little or no reaction to produce the required ceramic material. The sintering temperature should not, however, 10. exceed 2000 C since above this temperature at least some of the species present ~how a marked tendency to dissociate .
The optimum temperature i9 normally between 1500C and 1800C
since this gives a reasonable reaction rate without leading to large waight losses. However, l~hen it is required to ~ ~
produce ceram.ic materials having z values approaching 5 in the ~ .
above formula, it is believed that sintering should be - ~
effected at temperatures above this optimum range so as to :
increase the solid solubility of the reacting species. ~.
For this reason, in producing the high z value materials 20. of the sixth and seventh examples, hot pressing was effected at 1850 C.
Further it is to be appreciated that, although in the above examples the heating step has been accompanied by the application of pressure, the heating can also be performed :.~ ~~
in the absence of pressure.
A method, according to one aspect of the invention, includes the step of heating at a temperature betwe~n 1200C
and 2000 C a mixture cont~nin~ silicon nitride in an amount up to 98~o by weight of the mixture together with between 1~ and60~c weight of ~l~m~ nitride, between 0.5~ and 50~-by weight of silica, and between 0.05% and 60~o by weight of alum-na, some but ~ :-not all of the silica in the mixture at said temperature being 10. present as an impurity contained by the silicon nitride, and the silicon nitride, all n~- nitride, ~ ~;n~ and silica producing at said temperature a reactable composit.ion which constitutes at least 95f~o by weight of the mixture and in which the silica is present in a molar ratio of 1:2 with part of the al- tn; nitride and the el n~ is present in a molar ratio of 1:1 with the r~m~n~er of the aluminium nitride, the constituents of the reactable composition reacting together to :.
produce the required ceramic.material. . --Preferably, the relative proportions of the silicon -20. nitride, al~l ~ni~ nitride, silica and alumina are such that in.said composition the atomic ratio of silicon~ nl : .
i .
nitrogen: oxygen is 6-z:z:8-z:z respectively where z ls :-greater than zero and less than or equal to 5.
A method, according to a further aspect of the in~ention, - .
includes the step of heating at a temperature between t200 C and - .
2000 C a mixture from which silicon nitride is ab~ent but ;
which contains between 40~ and 600~o by weight of all-~; n~
nitride, between 15~o and 45~o by weight of silica, and between "~
0~05~o and 50~ by weight oP ~1- in~ ~ the relative proportlons of _ 2 -~., , -,:
~ - .. , ~- :, the ~1l2~;nium nitride, alumina and silica being such as to produce at said~temperature a reactable composition which constitutes , . :.
at least 95% by weight of the mixture and in whic~ the silica is present in a molar ratio of 1:2 with part of th~ aluminium nitride and the alumina present in a molar ratio of 1:1 with ~ -the remainder of the aluminium nitride, the atomic ratio of silicon:aluminium: nitrogen: oxygen in said composition being :.-.
6-z:z 8_z:z where z is greater than 4 and less than or e~ual to 5, and the constituents of said reactable composition reacting 10. together to produce the required ceramic material. -; ~-Con~eniently, at least part of the ~11 'n~ in the mixture -at said temperature is pre~ent as an impurity contained by the - -.
aluminium nitride.
Con~eniently, at least one of the constituents present in the mixture at said temperature is introduced into the -- -starting materials used to produce the mixture as a compound ~-. .
which reacts to produce the required constituent or constituents -:
during the heating step.
Conveniently, said compound is silicon oxynitride, ---20. aluminium oxynitride, ethyl silicate, or all-m;nillm hydroxide.
t' ~
Preferably, pressure is applied to the mixture during ~.
said heating step.
Preferably, a molten glass is also present in the mixture ~~
at said temperature. A' ''"-~' .
Conveniently, the molten glass is an aluminosilicate glass, or manganese glass or a lithium glass. ~-Alternatively, the molten glass is a magnesium glass. - ~ ^
~ . .
i;
'' ' , ` ' ' ~
~'t ' . ', -::e ~ , ,., X
1048229 -~ -Conveniently, the magnesium glass i~ produced by reaction - -during the heating step between magnesium oxide and a glass- ~ --~
forming compound, both of the latter being present in the ..
mixture. ,;
.~
Cor;veniently, the gla$s forming compound is silica. ~ -In the accompanying drawings:-"~
Figure 1 is a quaternury phase diagram illustrating by way of example compositions of various mixture of al~ ;nil~ '., nitride, silica, alumina and silicon nitride which can be 10. employed in the method of the invention, and " . ,~
Fi~ure 2 is a graph illustratin~ the unit cell dimensions :-.'' '~'', of ceramic materials produced according to the examples -~-.-~ ::.
- hereinafter described. ----~-.. ~,, Referring to the dra~ings, in a first example a ceramic ~-material was produced from a starting mixture consisting of 78.48~ by weight of silicon nitride powder, 14.76% by ~eight of :
aluminium nitride powder aLid 6.76% by weight of silica powder.
In this mixture, the silicon nitride powder emp~oyed contained 89~ by weight of the ~-phase material and had a mean particle -~-20- size of 3 microns, whereas the aluminium nitride powder was that supplied by Koch-Light as type 8006H with a mean particle size ^ -.. . -of 11.5 microns, but, which prior to use, was co ;n~ted to an average value of 6 microns. The silica powder employed wa~ - `
that -~upplied by Hopkin and Williams-Limited as pure ~rQclpirQT~ -silica. -Of the starting materials employed in the above mixture, the silicon nitride powder inherently contained a silica -impurity a~ a coating over the particles of silicon nitride, and the all~min;llm nitride powder inherently contained an -~-3. impurity of alumina. Thus, it will be understood that the ~-- 4 _ ~
: :' ',~ ''"
.- :,., - :., ,~ ~ '"'',: ~.,.
~ .~
......
-~tarting mixture of the first example contained ~11 n~ in -addition to aluminium nitride, silica and silicon nitride. -- ~
Moreover, since the impuritie~ contained by the silicon --nitride and al~lm;n;ll~ nitride starting materials were clearly - ^
going to take part in the subsequent reaction to produce the -~
required ceramic material, before production of the abo~e ~--. -:
mixture the impurity levels in these starting materials were ~
determined by fast neutron activation analysis. Then~ as will -~-become ap~arent below, allowance was made for these impurities 10. in arriving at the composition given above for the starting mixture. Using the particular starting material described~
, .. .
it was found that the silica content of the silicon nitride powder was 4% by weight and the ~12l~;n~ content of the al7~m;~;lm ~ ~
nitride was 6yo by weight. Thus, the overall compoRition of ~`
~ ~, the mixture was in fact 75.34~o by weight silicon nitride~ ~-13.87p by ~eight ~ ~;nium nitride, 0.89yo by weight ~11 ; n~ ~ -and 9.9~o by weight silica. This composition is defined by point A in Fi~ure 1, it being appreciated that in the drawing -~-the axes correspond to the pure materials with no impurities ....
20. present.
To produce the above mixture, the required amount of tho - --starting materials were introduced-into a colloid mill where ~ine was effected using i~o-propyl alcohol as the carrier liquid and was continued until the mean particle size of the ~-: . ,, mixture was less than 3 microns. The mixture was then dried ~- -and subsequently was sieved to remove any powder aggregates.
Thereafter an impurity determination was performed on the mixture to ascertain whether the processing had had any effect ~ -on the impurity lerel~ of the starting material, but it was ~ ~
.~ - -.
30. found that the latter had not been altered by the colloid ~ . ..
- 5 _ :~
~. ~A
. f, .~' ~ . '"' 10~8229 milling or the drying and sieving operations. ~ --The mixture was then loaded into the die cavity of a ~
g~aphite die onto a graphite plug clasing one end of the die ~-cavity. A graphite punch was then assembled onto the powder charge, aLl graphite surfaces in contact with the powder charge ~-~
having previously been spray coated with boron nitride to a depth-of the order of 0.01". The assembly was then introduced into a press, where the temperatura and pressure were simultaneously increased over a period of 30 mir~ltes to 1800C
10. and 1.5 tons/sq. in. respectively. The mixture was then --maintained at this temperature and pressure for 1 hour and, under these conditions the constituents of the mixture reacted to ~;
produce the required ceramic material. On cooling, the reaction product was removed from the die and the cryst~11;ne phases in the product were detected by X-ray d~ffraction using- ;---a Unicam Spectrometer with Cr-K~ monochromatic radiation. The X-ray analysis showed that the reaction product consisted -~
substantially entirely of a single crystalline phase ceramic ~ -material obeying the formula~
20. Si6-z Al N8 where z was equal to 1. The ceramic material was also found to have a crystal structure based on that of ~-phase silicon nitride, but with the a and c unit cell dimensions being 7.648 and 2.938 respectively as compared with values of 7.623 and 2.914 ~-respectively for ~ -hase silicon nitride (see Figure 2) -~, It is to be appreciated that using the mi~ture of the above e~ample and allowing for the impurities in the ~tarting materials~ then at the elevated temperature of the reaction the mi~ture consisted entirely of a reactable composition ~,. . . .
- 6 - ~-." ~
:- gl~ ~ .
cont~;!n;ng 51.3 mole ~ silicon nitride, 0.8 mole % ~ e~
32.2 mole % alllmin;llm nitride and 15.7 mole ~/o silica. Thus - ~-in the reactable composition the silica was present in the ~:
required molar ratio of 1:2 with part of the aluminium nitride(31.4 mole ~o), while the alumina wa~ present in the -~ ~;
required molar ratio of 1:1 with the rem~;n~er o~ the :~ :
aluminium nitride (0.8 mole 7~). In the phase diagram of Figure 1, the shaded triangular area B define4 the limits of ~
the various possible mixtures of ~ m;n~, al~ m nitride~ ~-10. silica and silicon nitride which, on heating consist entirely of a reactable composition in which the alumina~ silica~- -and ~lllm;n;ll~ nitride are present in the requlred molar ratio~
Thus in arriving at the stated composition for the mixture -~
of the above example, the amounts of the various s*arting ~ -materials were calculated so that~ allowing for impurities~ ~
the overall composition of the mixture (as indicated by point A) -was within the limits defined by the triangular area B.
It can readily be calculated that in the reactable composition produced by the mixture of the above example the - -~
20. atomic ratio of silicon~ ;n;llm:nitrogen:oxygen was 6-z:z; 8-z:z respectively where z was equal to 1. Thus the silicon, ~lll~;n; ~ nitrogen and oxygen were present in this reactable composition in the proportions required in the resultant ceramic material. It is, however, to be understood -that other mixtures could have been used which at the hot --pressing temperature would have consisted entirely of a -~
reactable composition having the required atomic proportions of silicon, ~lllm;n;um~ nitrogen and oxygen, such suitable : ,' ~, mixtures lying on the line C in Figure 1.
- 7 ~
-- ., :
1~482Z9 - ~:
In a second example of the invention, it was required to produce a ceram~ic material. obeying the formula~
Si Al N 0 - -6-z z 8-z z ~ with z being equal to 2.1. In producing this ceramic material the starting material5 of the first example were2gain employed but were mixed together in ~uch proportions that the starting mixture consisted of 30.88% by weight of alumin-um nitride, - 50.44~ by weight of silicon nitride, and 18.68% by weight of silica. Thus~ allowing for the impurities in the al~ in~
10. nitride and silicon nitride starting materials, the overall composition of the mixture was 29.03C//o by weight of ~ m ~-nitride~ 48.425~ by weight of silicon nitride, 20 .7C/o by weight of silica and 1.85qo by weight of alumina, this composition being indicated by point D in Figure 1. The procedure of the first - -example was then repeated and, at the elevated temperature .
of the hot pressing process, the mixture consisted entirely of : ~
a reactable composition containing 50 mole% aln~;n;llm nitride, 24.35 mole c/O silicon nitride, 24.35 mole /c silica and 1.3 mole - ~o alumina. Thus~ it will be seen that in the reactable .
20. composition the silica was present in a molar ratio of 1:2 with-part. of the allm~n;llm nitride (48.7 mole %), while the alumina was present in a molar ratio of 1:1 with the ,~ -inder of the al~lm;n;l~m nitride(1.3 mole %). Moreover, it can . -readily be calculated that the atomic ratio of silicon:
.~
alnm;n;ur: nitrogen:oxygen in the reactable composition was . ~ Z
6-z:z:8-z:z where z was equal to 2.1. Thus the silicon~
:'.' ~'~`~
- all in;llm, nitrogen and oxygen were present in the reactable :~ -composition in the proportions required for the ceramic material to be produced. Again, other mixtures could havebeen _ 8 - ~:
., , .
:: .
. . ._._. ~r .
. ~
'. 11 ~ , '' '`
: -~.
~ 1~48ZZ9 ~ ~
employed which at the hot pressing temperature would have consisted entirely of reactable compositions having the atomic proportions required-in the ceramic material of ~-this example, the line E in Figure 1 indicating the possible ~
compositions for such mixtures. As can be seen from Figure 2, ~ -the ceramic material obtained by the method of the second example had a and c unit cell dimensions of 7.674 and 2.962 .
respectively.
In a third example of the invention, the procedure of 10. the first example was again repeated, but in this case the -starting mixture consisted of 43.980,~ by weight of al~
nitride, 27.65~ by weight of silicon nitride and 28~37% by , ~-weight of silica. Thus, allowing Por the i~puritie~ in the ~ -starting materials, the actual composition of the mixture was 41~34% by weight alllmin;~lm nitride, 26~54~o by weight of ~--, silicon nitride, 29~48~o by weight of silica and 2~64% by -~-weight of ~1~ ;n~ this mixture being indicated by the point -~','''' in Figure 1. At the eleYated temperature of the hot ~
,, -, pressing process, the mixture produced a reactable composition 20~ consi~ting of 11~4 mole~p silicon nitride, 58,80 mole~ ~1llmin;
nitride, 28~64 mole% silica and 1.52 mole% alum~na. Thus~
as in the previous examples it will be seen that the ~11 tni nitride, silica and alu~mina were accurately in the required ~ ~
molar ratios, although using the mixture of this example ~--the atomic ratio of silicon~ m;nium: nitrogen: oxygen in the reactable composition were equal to 6-z:z:8-z:z where z was equal to 3. Thus, as will be expected, the components of the reactable composition reacted together at the elevated : . -.
temperature of the hot pressing reaction to produce a ¢eramic 30. material obeying the above formula with z being equal to 3.
_ g ~
''''~ `'''`' 7~ :', ,~, ' ,.-, .~ ~.
'~ ~
1048Z2~ ~
, ~, As sh~own in Figure 2~ the a and c unit cell dimensions of the ceramic material were 7.70 and 2.986 res~eFtively.
In a fourth example~ the same procedure was again carried out, but in this case the starting mixture consisted of 48.33~/ by weight of aluminium nitride. 20.12,~ by weight ~ -of silicon nitride and 31.55% by weight of silica. Thus, allowing for the impurities in the starting materials, the actual composition of the mixture was ~5 .L~30~o by weight Of ~ m~n;um nitride, 19~31~o by weight of silicon nitride, ;-10. 32.36yo by weight of silica and 2~90~o by weight of ~1nmt~A, ~-thi3 mixture being indicated by the point G in Figure 1. -~
As can readily be calculated, at the elevated temperature of the hot pressing process, this mixture consisted entirely of a reactable composition in which the silica was present in a molar ratio of 1:2 with part of the aluminium nitride, while the ~ m;n~ was present in a molar ratio of 1:1 with ~-the rem~;nder of the ~ min;1l~ nitride. Moreover~ in this --reactable composition the atomic ratio of silicon:al~ ~n;-: ', nitrogen: oxygen was equal to 6-z:z:8-z:z where z ~as equal ~- -20. to 3 .3 . Thus, as expected, the ceramic phase of the product -of the hot pressing reaction consisted substantially entirely of a single crystalline phase ceramic material~ -obeying the above formula with z being equal to 3 .3 .~ ~
. .
As shown in Figure 2, the a nnd c unit cell dimensions of the ceramic material were 7,703 and 2.991 respectively.
In a fifth example, the -~tarting materials used above were mixed with alumina powder as supplied by the Al- ;n; .
Company of America as type XA16 to produce a mixture cont~;n;ng 60.6yo by weight of silicon nitride, 20.3% by 3~. weight of alu~;nill~ nitride, 7.9~o by weight of silica and -:: .
''', 104822~
11.2,~ by weight of alumina. Thus, allowing for the impuritie!s in the starting materials, the actual composition of this mixture was 58.180,b by weight of sllicon nitride, 19.08Co by weight of alu~.inium nitride, 10.32G,~ by weight of silica and 12.420/~o by weight of alumina. This mixture is indicate~
by the point H in Figure 1. The mixture was ;crepared and hot ~.
pressed as in the previous examples and, at the hot pressing .:~
temperature, consisted entirely of a reactable composit.ion having ~.
the required molar ratios of ~1u~inium nitride, silica and ~l7l~;
10, ~'oreover, it can readily be shown that in the reactable composition ~ .
the atomic ratio of silicon:aluminium:nitrogen:oxygen was equal to 6-z:z:8-z:z where z was equal to 2. Once again, therefore, the resultant ceramic material obeyed the above formula with :~:~
z being equal to 2.
In a modification of a fifth example, a ceramic material obeying the above formula with z being equal to 2 was produced from the same starting materials, although in this ca~e the -initial mixture contained 64.75C/o by weight of the silicon- -nitride, 15.35~o by weight of the aluminium nitride~ 2.65~ by : .-20. weight of the silica and 17.25~ by weight of the ~ nium. .. :~
Allowing for the impurities in the starting materials~ this .:-:
composition is indicated at I in Figure 1.
It i9 to be appreciated that the method ~ the abo~
examples can also be performed with starting mixtures consisting only of silica, alumina and aluminium nitride. It is~ however, - --found that using such mixtures, where of course silicon nitride is absent, hot pressing produces reactable compositions which --contain silicon, aluminium, nitrogen and oxygen in the ~.
proportions required to provide the atomic ratio given abo~e, ~--30. but with the z value al~ays being greater than 4. Thus~ the --- .
:::
. ~ "~, ,. .~ ~, ~ -:
1048Z29 ~:
ceramic materials obtained from mixtures in which silicon .- -nitride is absent always e~hibit z values in excess of 4 in the above formula. The reason for this can readily be ~
seen by reference to the line J in ~igure 1, it bsing - ~-appreciated that in the mixtures which have composition~ lying on this line the silicon, aluminium~ nitrogen, oxygen are present in the required atomic proportions to produce a ceramic material obeying the above formula when 2 is equal to -:
4. Thus, it will be noted that the line J passes through the al~ ;njl nitride/silica axis, which of course corresponds to the situation where there is no silicon nitride present.
Moreover, it will bc understood that as the silicon nitride .
content of mixture~ lying within the shaded area B:is decreased, ~-.
then the ceramic materials obtained frorn these mixtures have . . . .
increasing z values in the above formula. Hence, if a mixture lies on the triangular area defined between the AlN, A12 03 and -SiO2 apices, which area of course corresponds to a zerQ Si3N4 content-~ then the mixture necessarily produces a ceramic mat.erial having a z ~alue in excess of 4. - -To illustrate the effect of omitting the silicon nitride, in a sixth example, the starting materials of the previous example were used to produce a mixture consisting of 51.45% .
by weight aluminium nitride, 19~1~% alumina, and 29.37% by weight silica. Thus~ allowing for the impurities in the starting materials, the actual composition of the mixture wa~
48.75C~ by weight (62.78 mole %) aluminium nitride, 21~73~ ~
by weight- (11.25 mole ~ lmin~ and 29.52~ by weight (25.97 mole ~) silica. The mixture was processed as in the -preceding examples and was hot pressed at 1850 C, at which .'~
- 12 ~
~, ~-rr ' ~ ~y ~ ~
~048Z29 temperature the mixture consisted of more than 95~ by weight o~
a reactable composition in which the silica was present in a molar ratio of 1:2 with part of the ~ m;n;um nitride and the alumina was present in a molar ratio of 1:1 with the re~ er - of the aluminium nitride. Moreover, at the hot pressing ~-temperature the components of the reactable composition reacted together to produce a ceramic material obeying the above -formula and having a z value equal to 4.6. The a and c unit cell dimensions of the ceramic material were 7.745 A
10. and 3.~12 A respectively. -- It will of course be understood that ceramic materials -~
having z values in excess of 4 in the above formula can also be produced from starting mixtures containing silicon nitride. ~--Thus~ in a seventh example, a ceramic material again having a z value of 4.6 was produced by hot pressing at 1850 C a ~-starting mixture consisting of 10.19,b by weight silica, 40.77 by weight alumina, 33 .98~o by weight aluminium nitride and -~
15.06C~ silicon nitride, all the starting materials again being those employed in the fifth example. Thus, allowing for the 20. impurities in the starting materials, the mixture consists of 12.15 Mole ~ silica, 28.36 moIe ~ mina, 52.46 mole ~ al~ n;l-nitride and 7.03 mole ~ silicon nitride. From these figures it can readily be calculated that the mixture consisted at the hot pressing temperature of ln excess of 95~ by weight of a reactable composition in which the sllica, alumina and aluminium nitride were in the required molar proportions. The resultant --ceramic material had the same a and c unit cell dimensions as -the material of the preceding exa~ple.
, .
. . .
,,~ ,"
' ~'',.
'' ~', It is to be appreciated that in each of the above examples, hot pressing of the ~tarting mixture produced .. reactable composition which not only had the required molar ratios of ~l~minium nitride, alumina and silica, but which also -~ -constituted the entire volume of the starting mixture, It is, however, to be understood that, provided the reactable -compo-~ition constitutes at least 95~ of the weight of the ~ -~ixture, other materials can be present in the mixture at - -the hot pressing temperature. The other materials can be 10. in the form of excess quantities of one or more of the startin~ --materials and preferably are arranged so as to produce a molten glass to aid densification ~ the ceramic material -~
produced during hot pre-~sing. Conveniently, the molten glass ~- `
is an al~lminotboro-~ or iron-silicate glass, or alternatively ~-is a magnesiùm glass, a manganese glass or a lithium glass.
In the case of a magnesium glass the starting mixture would be arranged to contain magnesium oxide and a glass-forming agent, the latter preferably being in the form of silica.
In each of the above examples, the starting mixture~ were 20. produced by i~ing together the actual constituents required for the reactable composition. It is, however,to be appreciated ~ --that one or more of the constituent~ required in the reactab1e ~
. ~ . ,, composition could have been introduced into the starting -" :-, materials as a compound which decomposed during the hot -pressing operation into the required constituent or constituents.
Thus, for example, aluminium hydroxide could have been added to the -~tarting materials t-o provide alumina in the reactable composition while the addition of ethyl silicate to the - ~-starting materials would have provided the necessary silica 30. for the reactable composition. Other such suitable additives to - 14 _ -.''~ ~,,`, ~". '`, ,. .,. - ,~ '' ~, v`' ", lV48Z2~
the starti ~ materials are silicon oxynitride (to pro~ide silica and silicon nitride) and al~ 71ill~ oxy~itride (to provide alumina and aluminium nitride).
By way of illustration of the statements in the preceding - paragraph, in an eighth example of the invention a ceramic ~-material having a z value of 2 in the above formula was - -~
produced by hot pressing for 1 hour at 1700 C a starting weight mixture consisting of 8.94~o by/silicon nitride, 29.36~ by weight ~lu~;njum nitride, 1~ by weight silica and 60.7~
10. silicon oxynitride. In this mixture, the silicon oxynitride had a mean particle size of 2 microns and was supplied by ..
- the Norton Company of America, whereas the other starting ~ -materials were the same as those emplo~ed in the pre~ious eYanple. The silicon oxynitride was found to contain free --silicon nitride and also a surface impurity of silica, but ~
analysis showed that these were present in the molar proportion~ ~ -required to produce silicon oxynitride. Thus, for the purposes of calc~ating the composition of the starting mixture, it was po-sible to regard the silicon oxynitride as the pure 20. material. Moreover, it can readily be shown that 2 moles of silicon oxynitride are equivalent to 1 mole of silicon - ~
nitride and 1 mole of silica so that, allowing for this ~ ~
equivalent and also catering for the impurities in the silicon nitride and s71 inil nitride, the effective overall ~m~
composition of the starting mixture was 51.09yo by weight (26.42 mole %) silicon nitride, 27~57~o by weight (4~.69 mole ~) -al~lmin~ nitride, 1.76~ by weight (1.25 mole ~0) al ~ns7 and 19.58~ by weight ~23.63 mole ~o) -~ilica. At the elevated ~-temperature of the hot pressing process, this mixture consisted 30. of more than 95~o by weight of a reactable composition in which ;
- 15 - ~ -1~)48ZZ9 the silica was present in a molar ratio of 1:2 with part of the aluminium nitride, while the alumina was present in a molar ratio of 1z1 with the remainder of the ; nitride.
It is to be understood that in performing the method of the invention~ sintering of the starting materials should be effected at or above 1200 C since below this temperature there is little or no reaction to produce the required ceramic material. The sintering temperature should not, however, 10. exceed 2000 C since above this temperature at least some of the species present ~how a marked tendency to dissociate .
The optimum temperature i9 normally between 1500C and 1800C
since this gives a reasonable reaction rate without leading to large waight losses. However, l~hen it is required to ~ ~
produce ceram.ic materials having z values approaching 5 in the ~ .
above formula, it is believed that sintering should be - ~
effected at temperatures above this optimum range so as to :
increase the solid solubility of the reacting species. ~.
For this reason, in producing the high z value materials 20. of the sixth and seventh examples, hot pressing was effected at 1850 C.
Further it is to be appreciated that, although in the above examples the heating step has been accompanied by the application of pressure, the heating can also be performed :.~ ~~
in the absence of pressure.
Claims (11)
1. A method of producing a ceramic material, including the step of heating at a temperature between 1200°C and 2000°C a mixture containing up to 98% by weight of silicon nitride together with between 1% and 60% by weight of aluminium nitride, between 0.5%
and 50% by weight of silica, and between 0.05% and 60% by weight of alumina, and the aluminium nitride, alumina, silica and any silicon nitride producing at said temperature a reactable composition which constitues at least 95% by weight of the mixture and in which the silica is present in a molar ratio of 1:2 with part of the aluminium nitride and the alumina is present in a molar ratio of 1:1 with the remainder of the aluminium nitride, the relative proportions of the constituents of the reactable composition being such that the atomic ratio of silicon:aluminium:nitrogen:oxygen in said composition is 6-z:z:8-z:z respectively where z is greater than zero and less than or equal to 5, and the constituents of the reactable composition reacting together to produce the required ceramic material.
and 50% by weight of silica, and between 0.05% and 60% by weight of alumina, and the aluminium nitride, alumina, silica and any silicon nitride producing at said temperature a reactable composition which constitues at least 95% by weight of the mixture and in which the silica is present in a molar ratio of 1:2 with part of the aluminium nitride and the alumina is present in a molar ratio of 1:1 with the remainder of the aluminium nitride, the relative proportions of the constituents of the reactable composition being such that the atomic ratio of silicon:aluminium:nitrogen:oxygen in said composition is 6-z:z:8-z:z respectively where z is greater than zero and less than or equal to 5, and the constituents of the reactable composition reacting together to produce the required ceramic material.
2. A method a claimed in Claim 1, wherein silicon nitride is absent and the mixture contains between 40% and 60% by weight of aluminium nitride, between 15% and 45% by weight of silica, and between 0.05% and 45% by weight of alumina, the atomic ratio of silicon:aluminium:nitrogen:oxygen in said composition being 6-z:z:8-z:z where z is greater than 4 and less than or equal to 5.
3. A method as claimed in Claim 1 or Claim 2, wherein at least part of the alumina in the mixture at said temperature is present as an impurity contained by the aluminium nitride.
4. A method as claimed in Claim 1, wherein at least one of the constituents present in the mixture at said temperature is introduced into the starting materials used to produce the mixture as a compound which reacts to produce the required constituent or constituents during the heating step.
5. A method as claimed in Claim 4, wherein said compound is silicon oxynitride, aluminium oxynitride, ethyl silicate, or aluminium hydroxide.
6. A method as claimed in Claim 1 or Claim 2, wherein pressure is applied to the mixture during said heating step.
7. A method as claimed in Claim 1, wherein a molten glass is also present in the mixture at said temperature.
8. A method as claimed in Claim 7, wherein the molten glass is selected from the group consisting of an alumino-silicate glass, a boro-silicate glass, an iron-silicate glass, a manganese glass and a lithium glass.
9. A method as claimed in Claim 7, wherein the molten glass is a magnesium glass.
10. A method as claimed in Claim 9, wherein the magnesium glass is produced by reaction during the heating step between magnesium oxide and a glass-forming compound, both of the latter being present in the mixture.
11. A method as claimed in Claim 10, wherein the glass forming compound is silica.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2733174A GB1482465A (en) | 1974-06-20 | 1974-06-20 | Method of producing a sintered ceramic product |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048229A true CA1048229A (en) | 1979-02-13 |
Family
ID=10257837
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA74216037A Expired CA1048229A (en) | 1974-06-20 | 1974-12-16 | Production of a ceramic material containing silicon, aluminium, oxygen and nitrogen |
Country Status (13)
| Country | Link |
|---|---|
| JP (1) | JPS6041025B2 (en) |
| AT (1) | AT367386B (en) |
| BE (1) | BE823935A (en) |
| CA (1) | CA1048229A (en) |
| CH (1) | CH622231A5 (en) |
| DE (1) | DE2461740A1 (en) |
| DK (1) | DK659974A (en) |
| FR (1) | FR2275423A1 (en) |
| GB (1) | GB1482465A (en) |
| IT (1) | IT1026183B (en) |
| NL (1) | NL7416980A (en) |
| SE (1) | SE404182B (en) |
| SU (1) | SU799640A3 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1123862A (en) * | 1978-09-20 | 1982-05-18 | J. Thomas Smith | Oxidation resistant silicon nitride containing rare earth oxide |
| EP0100380B1 (en) * | 1981-02-05 | 1987-06-16 | Sumitomo Electric Industries Limited | Method for plastic deformation of non-ferrous metals |
| DE3216308A1 (en) * | 1982-04-30 | 1983-11-03 | Feldmühle AG, 4000 Düsseldorf | Sintered moulding based on silicon nitride |
| US4790560A (en) * | 1984-09-06 | 1988-12-13 | Honda Giken Kogyo Kabushiki Kaisha | Independent rear suspension for use on motor vehicles |
-
1974
- 1974-06-20 GB GB2733174A patent/GB1482465A/en not_active Expired
- 1974-12-16 CA CA74216037A patent/CA1048229A/en not_active Expired
- 1974-12-18 DK DK659974A patent/DK659974A/en not_active Application Discontinuation
- 1974-12-24 CH CH1732374A patent/CH622231A5/en not_active IP Right Cessation
- 1974-12-27 IT IT5479074A patent/IT1026183B/en active
- 1974-12-27 FR FR7443071A patent/FR2275423A1/en active Granted
- 1974-12-27 BE BE152000A patent/BE823935A/en not_active IP Right Cessation
- 1974-12-27 NL NL7416980A patent/NL7416980A/en not_active Application Discontinuation
- 1974-12-27 SE SE7416277A patent/SE404182B/en not_active IP Right Cessation
- 1974-12-27 JP JP49149117A patent/JPS6041025B2/en not_active Expired
- 1974-12-27 SU SU742095758A patent/SU799640A3/en active
- 1974-12-28 DE DE19742461740 patent/DE2461740A1/en active Pending
- 1974-12-30 AT AT1039474A patent/AT367386B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| BE823935A (en) | 1975-04-16 |
| SE7416277L (en) | 1975-12-22 |
| FR2275423B1 (en) | 1978-10-13 |
| DK659974A (en) | 1975-12-21 |
| AU7646874A (en) | 1976-06-17 |
| CH622231A5 (en) | 1981-03-31 |
| SE404182B (en) | 1978-09-25 |
| IT1026183B (en) | 1978-09-20 |
| FR2275423A1 (en) | 1976-01-16 |
| JPS6041025B2 (en) | 1985-09-13 |
| JPS51508A (en) | 1976-01-06 |
| SU799640A3 (en) | 1981-01-23 |
| DE2461740A1 (en) | 1976-03-25 |
| ATA1039474A (en) | 1981-11-15 |
| GB1482465A (en) | 1977-08-10 |
| AT367386B (en) | 1982-06-25 |
| NL7416980A (en) | 1975-12-23 |
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