High temperature high pressure apparatus

A high temperature high pressure apparatus which comprises: an annular die having a straight cylindrical bore and a substantially conical face in adjacency outwards with each end thereof, a pair of tapered punches which are in opposed and axial alignment with the die so that a conical face of each punch is substantially in parallel with that of the die, a pair of inner gaskets, each of which is made of fired refractory and is arranged in direct abutment on the conical face of the punch and the bore of the die, a pair of outer gaskets, which are made of material of intermediate hardness level and is arranged in adjacency outside the inner gasket, and a pair of stopper rings of readily deformable but highly tough material and arranged in adjacency outwards to the outer gaskets.

The present invention relates to a high temperature high pressure apparatus 
which basically comprises an annular die and a pair of tapered punches in 
opposed and axial alignment therewith and, in particular, to such 
apparatus improved in durability as well as reproducibility of pressures 
on the order of 60 kilobars simultaneously at temperatures of several 
hundreds above 1000.degree. C., conditions required for industrial 
production of synthetic diamond and cubic boron nitride (CBN). 
Punch-and-die apparatuses are favored in industrial manufacture of 
synthetic diamond or CBN for their simplicity in general of construction 
and a relatively large volume available for specimen to be treated. In 
designing an apparatus of this type for attaining such high pressures by 
optimizing the geometry and material of each part, there are two essential 
points to be considered: first, provision of a special pressure resisting 
means to every component under severe load, or the punches and die in 
particular, in order that they can hold effectively a pressure of several 
tens of kilobars within, which is far beyond the highest strength 
obtainable with cemented tungsten carbide, the strongest material so far 
available, and second, confinement of the pressure thus developing within 
the specimen. 
Among known techniques for providing pressure resistance, a high rigidity 
cylinder is employed which consists of alumina sintered so hard as to 
exhibit an apparent density very close to the true one, and which is 
hollow with a space for accomodation of specimen and other reaction parts 
and arranged in peripheral abutment on a middle cylindrical bore of a die 
as shown in, for example, U.S. Pat. No. 3,988,087. Examples illustrated 
therein of the cylinder have at each end a flat surface, perpendicular to 
the axis and in joint inwards with a conical bore face. The cylinder being 
shorter than the bore of the die, there is provided a circular space, 
conveniently referred to as "pocket" hereinafter, which is defined in part 
by an end cylindrical bore of the die on each flat end face of the high 
rigidity cylinder. Gaskets of fired agalmatolite are so arranged as being 
partly accomodated in the pocket and in another space between the punches 
and high rigidity cylinder. This construction is advantageous in 
substantially decreased thrust loads on the die bore due to the high 
rigidity cylinder intervening and properly supported between the specimen 
and die, and in that punches and die of increased dimensions are 
successfully realizable with adequate strength due in part to the 
simplicity especially in contour of the die bore and in part to 
feasibility of such readily workable material as some hard steel grades, 
favorable for not requiring powder metallurgy which otherwise would be 
necessary and essentially limit the mass of such components to be realized 
as seen in a die of cemented tungsten carbide. 
Gaskets are employed in abutting relation with a conical face of punch in 
most high pressure apparatuses for playing a significant role in securing, 
as well as a reasonable durability, a good function with punches, die and, 
occasionally, high rigidity cylinder, such that high pressures should 
develop within a specimen compressed and densified by advancement of 
punches, and thus produced pressures should be confined within a given 
space, that punches should be provided with radial thrust in order to 
oppose a radial tension deriving from the axial compression which occurs 
in punches under load during operation, and further importantly, that the 
high rigidity cylinder should be also compressed to suppress axial 
elongation in order to secure the reduction of stresses on the die. 
Gaskets also have to be so arranged as to provide a proper travel for punch 
advancement in order to establish a pressure of required levels, prior to 
heating, for effecting the synthesis of diamond or CBN, and in order to 
make up for some pressure loss which results from the conversion to 
respective denser crystal morphology of specimen, especially, and 
additional plastic deformation of some material between the punches, by 
further moving the latter in accordance with creeping reduction in volume 
as the conversion proceeds. 
Punch travel is allowed with fired ceramic gaskets principally by axial 
deformation as they are densified, and in part by material flow to lower 
pressure regions within or even without the high pressure chamber defined 
by the punches and die bore. Thus the travel allowance quickly decreases 
as the compression proceeds prior to the heating. 
In a high pressure apparatus with a high rigidity cylinder, gaskets are 
arranged inside the above said pockets, and provide, based on the high 
internal friction, a high gradient in which pressure varies, within the 
high pressure chamber, from over 50 kilobars at an innermost face of 
gaskets to an atmospheric level at the outermost edge which is open in 
conventional designs. Thus a principal pressure drop occurs within the 
gasket portion squeezed between the conical faces of punches and high 
rigidity cylinder, as this portion confines extreme stresses inside, and a 
further pressure drop occurs inside another portion within the spaces 
"pocket", with the final sealing of stresses from the atmosphere and 
confinement of gasket material from flowing out achieved by the very 
portion between the punch face and bore edges. 
Capability of confinement primarily depends upon and in proportion to the 
internal friction, effective length (along the surface of contact) and 
reversely to the thickness of gasket material. Conventionally designed 
apparatuses have essential difficulty, due to the limited length, in 
realizing with components of increased dimensions or in providing 
substantially increased punch travels. 
The space "pocket" also provides a receptacle for gasket material as it is 
compressed and spreads out from between the conical faces of punches and 
high rigidity cylinder, and produces a mild gradient of pressure within. 
In order to attain a reasonable extent of service life with conventional 
apparatuses, where no axial stress support is allowed for the die of 
steel, it has been desired that the pressure in the "pocket" be limited 
under 20,000 atms. 
Pressure is finally sealed at the bore edges of a die, essentially 
providing a steepest pressure drop there. Effective punch travels 
critically depend on the thickness of gaskets at such portion of the die, 
so there are two simultaneous requirements yet to be sufficiently met with 
conventionally designed apparatuses: confinement of pressure and an 
adequate allowance for punch travel in the course of phase conversion. 
Japanese Patent Publication Sho 53-34190 discloses an apparatus arrangement 
in which a gasket in layers of paper, asbestos or the like arranged in 
adjacency outside another gasket of pyrophyllite which is arranged along 
the conical faces of an annular die with a straight cylindrical bore. 
Although this arrangement may allow rather an increased punch travel, it 
apparently is disadvantageous in that effective load for compressing the 
specimen remains low relative to the overall load applied by a hydraulic 
press, due to more part being spent in compression of the outer and inner 
gaskets with an increased effective length (along the conical faces of 
punches and die), an unfavorable feature required for opposing the 
stronger outward thrust occurring along the inner edge of the outer gasket 
on this particular die arrangement without any "pocket" 
Therefore, one of the principal objects of the present invention is to 
provide an apparatus, essentially eliminated of above said drawbacks. 
According to the invention there is provided a high temperature high 
pressure apparatus which comprises: an annular die having a straight 
cylindrical bore and a substantially conical face in adjacency outwards 
with each end thereof, a pair of tapered punches which are in opposed and 
axial alignment with the die so that a conical face of each punch is 
substantially in parallel with that of the die, a pair of inner gaskets, 
each of which is made of fired refractory and is arranged in direct 
abutment on the conical face of the punch and the bore of the die, a pair 
of outer gaskets, which are made of material of intermediate hardness 
level and is arranged in adjacency outside the inner gasket, and a pair of 
stopper rings of readily deformable but highly tough material and arranged 
in adjacency outwards with the outer gaskets. A better performance can be 
achieved with an apparatus characteristically comprising a high rigidity 
hollow cylinder in abutment on the die bore. So there is also provided 
another apparatus which comprises: an annular die having a straight 
cylindrical bore and a substantially conical face in adjacency outwards 
with each end thereof, a pair of tapered punches which are in opposed and 
axial alignment with the die so that a conical face of each punch is 
substantially in parallel with that of the die, a hollow cylinder of high 
rigidity material, which has a flat face at each end perpendicular to the 
axis and is in abutment on the bore of the die, a pair of inner gaskets, 
each of which is made of fired refractory and is arranged in direct 
abutment on the conical face of the punch, the bore of the die, and the 
flat face of said hollow cylinder, a pair of outer gaskets, which are made 
of material of intermediate hardness level and is arranged in adjacency 
outside the inner gasket, and a pair of stopper rings of readily 
deformable but highly tough material and arranged in adjacency outwards 
with the outer gaskets. 
In the invention the outer gaskets may consist, singly or in combination, 
of paper such as cardboard, asbestos, hard rubber or fluorine containing 
resins such as teflon (trade name) in single block, assembly of smaller 
pieces, layers or coil, or molded agalmatolite so fired as to exhibit a 
porosity over 30%. 
In this connection, Japanese Patent Publication Sho 53-34190 utilizes 
cardboard paper as gasket material based on the good pressure resistance; 
and this instant invention takes most of such property of this particular 
material or others of similar property, by using in backup support for 
inner gaskets of ceramic material. 
Thus arranged ring-like outer gaskets may take geometry such that the 
initial ratio, prior to the compression, of radial width to height in 
perpendicular relation amounts over 1, and favorably between 1 and 3, 
inclusive, thus permitting secured maintenance of support from outside the 
inner gaskets, and increased proportion of hydraulic load applied to the 
compression of specimen, by decreasing the part on the gaskets. 
A gap of several millimeters wide (in radial direction) may be allowed 
between the inner and outer gaskets, although they should be better placed 
substantially in abutment on the outer and inner periphery, respectively, 
or occasionally with the outer gaskets resting in contact on or under a 
flat face of the inner gaskets. 
With the outer gaskets of substantially single material intervening, the 
conical faces in opposition of the punch and die are substantially in 
parallel, with an occasional outward divergence at an angle of or smaller 
than 10.degree., favorably for decreased proportion of press load required 
for compression of the gaskets due to the pressure continuously decreasing 
outwards. Such conical faces can be outwards convergent at angles within 
10.degree. if the gasket contsists of two or more materials, with a softer 
material portion outside a harder material portion. 
The stopper ring of the invention is substantially made of either a block 
or a closed loop with the ends joined, of soft rubber, polyethylene, PVC 
or other tough and hard-to-tear materials which are also softer than the 
outer gasket. The ring and outer gasket are arranged in abutment 
immediately or by means of another piece of material of intermediate 
softness between the outer gasket and ring. 
Although applicable in general to a die arrangement comprising the pocket 
at each end of the bore, the above described system of inner and outer 
gaskets and stopper ring are most effectively employed on or in a die with 
a bore straight cylindrical over the length, in combination with a high 
rigidity hollow cylinder shorter in length than the bore so that said 
cylinder is in abutment on a middle portion of the die bore. This 
arrangement permits a secured punch travel for compression to the 
completion of a conversion run, under secured pressure reduction on the 
die due to the high rigidity cylinder which lines the die and which is 
adequately supported by axial load. Improvement in die service life is 
also achievable as a result of thus secured function of the cylinder in 
combination with improved stress condition around die edges, which 
otherwise would be susceptible to cracking. 
The merits set forth above can be achieved equally with a die which has a 
cylindrical bore such that each end portion exhibits a discontinuously 
increased diameter with a flat face at the joint, as shown in U.S. Pat. 
No. 4,097,208. 
Further features and advantages of the invention will be understood from 
the following description, taken in connection with the accompanying 
drawing, in which:

The FIGURE of the drawing shows an elevation in section of a high 
temperature high pressure apparatus designed according to the invention. 
In the FIGURE, a pair of punches 1, 2 of cemented tungsten carbide, such 
as WC-Co, are in opposed and axial alignment with an annular die 3 of 
steel such as high speed or die grade. In abutment on a straight 
cylindrical bore of the die there are provided a high rigidity cylinder 4 
which consists of alumina ceramic sintered so hard as to be substantially 
pore-free and which exhibits a trapezoidal cross section with a length 
shorter than the bore of the die, and an inner gasket 5, 6 of molded and 
fired chamotte (or, grog) ceramic in adjacency to each end of the cylinder 
4. The inner gaskets 5, 6 are surrounded by outer gaskets 7, 8 which 
consist of cardboard in layered structure. The gaskets 7, 8, in turn, are 
surrounded by stopper rings 9, 10 which are made of a strip of rubber 
wound around several times and secured together. The cylinder 4 is lined 
inwards with a sleeve 12 of refractory such as agalmatolite to define a 
reaction chamber 11, closed at each end with a tablet 13, 14 of hard fired 
agalmatolite. Steel rings 15, 16 are arranged outside the tablets for 
conducting through the punches 1, 2 electric current to heat the reaction 
chamber 11. 
In operation of the apparatus, the chamber 11, inner gaskets 5, 6 and outer 
gaskets 7, 8 are subjected to compression. The gaskets 5, 6, although 
fluidized under plastification stay for the most part and densify 
increasingly within the die bore, as the gaps between the punches and die 
are effectively sealed with the outer gaskets and stopper rings. The 
cylinder 4 has a conical face in substantial parallel and opposition to an 
end conical face of the punch, so the gasket portion between the conical 
faces seals, at a quickly increasing efficiency, compressive stresses 
inside and a pressure over 50 kilobars can be reached while the inner and 
outer gaskets still allow a sufficient compression for further advancement 
of punches, thus permitting to make up for the pressure loss in the course 
of conversion process. The die herein shown is less susceptible than 
conventionally to cracking in the bore face, because it is placed under an 
axial compression on the shoulder (or in the vicinity of bore edges), 
which effectively can set off the axial tension deriving from severe 
radial thrusts working on the bore. 
EXAMPLE 
The apparatus employed comprised cemented tungsten carbide punches, each 
tapering at 36.degree. against the axis, with a flat end face 75 mm 
across, and a high speed steel die with a straight cylindrical bore 175 mm 
across and 165 mm long. The high rigidity cylinder of substantially 
pore-free, hard sintered alumina measured 125 mm in length and 75 mm in 
I.D. (minimun), with a conical face inwardly convergent at 36.degree. 
against the axis. Inner gaskets of 50% SiO.sub.2 -50% Al.sub.2 O.sub.3 (in 
weight) chamotte ceramic had a contour to be fitly placed in abutment on 
said cylinder and punches, with a thickness of 11 mm along the conical 
face of the cylinder. The inner gaskets were enclosed with outer gaskets 
of cardboard block which measured 175 mm in I.D., 225 mm in O.D. and 12.5 
mm in thickness, and were wound in four layers with a strip of 3 mm thick, 
12.5 mm wide soft rubber secured at the end by adhesive. The reaction 
chamber was constructed of a fired agalmatolite sleeve of a 35 mm I.D. and 
70 mm length. 
With this arrangement, punch travel of as long as 6 mm were achieved at 
good reproducibility during a conversion process to synthetic diamond from 
graphite, in comparison with an approximately 3 mm long travel achievable 
with a die with a bore of comparable diameter but of conventional design 
without the outer gaskets and stopper rings. 
As may have been apparent by the description given above, the apparatus of 
the invention permits to attain the pressure levels to cause conversion 
runs from graphite and HBN to diamond and CBN, respectively, with an 
additional punch advancement allowed in adequate extent for making up for 
pressure loss occurring in the course of conversion run. Thus with the 
apparatus, 
1. Pressures can be produced, properly controlled until the completion of a 
conversion process, achievable due to the substantially increased punch 
travel allowance, so the crystalline product can be obtained with higher 
and more consistent quality in grain size and morphology, by properly 
regulating the pressure condition with higher precision at critical 
moments, which is now achievable successfully; 
2. The die exhibits an increased service life, due to the support by axial 
compression. Further improvement is also obtained due to decreased 
pressure gradient along the bore and; 
3. Improvement is achievable in stress reduction on the die, or efficiency 
of pressure production inside the high rigidity cylinder, as it is placed 
under proper support by an adequate axial compression which suppresses 
axial elongation.