Amorphous material for regenerator

Disclosed herein is an amorphous material in the form of foil for the regenerator, which is prepared by quenching a melt of a rare earth alloy by injection toward the surface of a roll running at a high speed, said alloy being composed of one or more rare earth elements in an amount of 50-99 atomic %, with the remainder being one or more iron family elements. This amorphous material has a large, stable specific heat capacity at very low temperatures.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an amorphous material which is suitable 
for a regenerator of the refrigerator due to its good mechanical 
properties and thermal properties. 
2. Description of the Prior Art 
Miniature-sized refrigerator are now in general use for the vacuum 
equipment employed in the production of semiconductors by ion implantation 
or sputtering. They fall into two main groups: those equipped with a 
regenerator and those equipped with a heat exchanger. Those belonging to 
the first group, which are based on the Gifford-McMahon cycle or Stirling 
cycle, are commonly used for refrigeration at liquid nitrogen temperatures 
or liquid hydrogen temperatures due to their simple structure and high 
reliability. 
The material packed in the regenerator of the refrigerator is required to 
have a large specific heat capacity and good thermal conductivity in the 
range of operating temperatures. In the past, copper, lead and alloys 
thereof have been used as a regenerator material. They have a disadvantage 
of rapidly decreasing in specific heat capacity at 20.degree. K. or below, 
which presents difficulties in producing very low temperatures in that 
range. 
To solve this problem, there has been proposed a rare earth alloy as the 
regenerator material which has an anomalous heat capacity due to magnetic 
phase transition (Japanese Patent Publication No. 30473/1977). 
Improvements on it have also been disclosed (Japanese Patent Laid-open 
Nos. 310269/1989 and 1050/1991). 
The conventional rare earth alloy used as the regenerator material is an 
intermetallic compound having a low mechanical strength. In other words, 
it is too brittle to be formed into a foil or coil. Therefore, it is used 
mostly in the form of fine powder with a particle diameter of 10 .mu.m-1 
mm. Fine powders of rare earth alloy need great care in handling because 
of extremely high chemical activity. In addition, excessively fine powder 
increases resistance to the flow of the working fluid and escapes from the 
net containing it. 
SUMMARY OF THE INVENTION 
Accordingly, a primary object of the present invention is to provide an 
amorphous material of a rare earth alloy for the regenerator which is free 
of the above-mentioned problems involved in the prior art technology. The 
regenerator material in the present invention is amorphous for the 
improvement of its mechanical strength, so that it can be formed into a 
foil or coil and it maintains a large specific heat capacity over a 
comparatively broad range of very low temperatures. 
The present invention is embodied in an amorphous material for the 
regenerator which comprises one or more rare earth elements in an amount 
of 50-99 atomic%, with the remainder being one or more iron family 
elements. 
According to the present invention, the rare earth element includes one or 
more members selected from Er, Ho, Dy, and Tb, and the iron family element 
includes one or more members selected from Ni, Co, Ru, Pd, Rh, Ir, Os, Pt, 
and Fe.

DETAILED DESCRIPTION OF THE INVENTION 
According to the present invention, the rare earth alloy should contain 
rare earth elements in an amount of 50-99 atomic%. With an amount less 
than 50 atomic%, it has an unduly low specific heat capacity. With an 
amount in excess of 99 atomic%, it is not readily made amorphous. The 
remainder of the alloy constituents should be one or more iron family 
elements selected from Ni, Co, Ru, Pd, Rh, Ir, Os, Pt, and Fe. Owing to 
the combination of rare earth elements and iron family elements, the alloy 
is easily made amorphous and has a high specific heat capacity. 
Incidentally, less than 50% of the iron family elements may be replaced by 
any one or more elements selected from Au, Ag, Cu, Al, Ga, Si, and Ge, so 
as to improve the above-mentioned properties of the alloy. 
An amorphous alloy is usually produced by the single-roll method which 
consists of injecting a melt of an alloy toward the surface of a roll 
running at a high speed, thereby subjecting the melt to rapid quenching. 
This single-roll method can be used to produce the amorphous rare earth 
alloy of the present invention. The resulting product is in the form of a 
foil having a thickness of the order of micrometers to tens of 
micrometers. This foil is by far tougher than those of intermetallic 
compounds and can be wound up easily. Therefore, the rolled foil can be 
packed into the regenerator more densely, while offering less resistance 
to the flow of the working fluid, than the conventional rare earth alloy 
in the form of powder. 
In the case of conventional rare earth alloys, the anomalous heat capacity 
due to magnetic phase transition manifests itself as a narrow peak. By 
contrast, the amorphous rare earth alloy in the present invention gives a 
broader peak with a gentle slope. In other words, it exhibits thermal 
properties (specific heat capacity) most desirable for the regenerator of 
the refrigerator. The effect of the rare earth alloy being amorphous is 
significant when it is used at very low temperatures (4.degree. K. or 
below) in the refrigerator for helium liquefaction. 
According to the present invention, the amorphous rare earth alloy for the 
regenerator has such a high mechanical strength that it can be formed into 
a foil or coil. Therefore, it offers less resistance to the flow of the 
working fluid than the conventional regenerator in the form of a powder. 
In addition, it has a large heat capacity at very low temperatures and 
hence produces a good cooling effect for a long period of time. 
EXAMPLE 1 
A rare earth alloy (Er.sub.65 Ni.sub.35) composed of 65 atomic% Er and 35 
atomic% Ni was prepared by melting 42 g of Er (purity 99.9%) and 7.8 g of 
Ni (purity 99.9%) using an argon arc melting furnace. The alloy was melted 
in a crucible of quartz glass by high-frequency induction heating under an 
argon atmosphere. The melt at about 1000.degree. C. was injected through a 
nozzle by the pressure of argon gas toward the surface of a steel roll 
rotating at about 5000 rpm, so that the melt was quenched. Thus there was 
obtained foil (17 .mu.m thick) of an amorphous rare earth alloy. The 
amorphousness was confirmed by X-ray diffractometry. The specific heat 
capacity of the foil at temperatures in the range of 1.6.degree. K. to 
6.degree. K. was measured. The results are shown in FIG. 1 (solid line 1). 
For comparison, the specific heat capacity of a crystalline rare earth 
alloy (Er.sub.3 Ni+Er.sub.3 Ni.sub.2) of the same composition (Er.sub.65 
Ni.sub.35 ) as above at temperatures in the same range as above was also 
measured. The results are also shown in FIG. 1 (chain line 3). 
It is noted from FIG. 1 that the specific heat capacity of the rare earth 
alloy in this example is less dependent on temperature than that of the 
conventional crystalline rare earth alloy. At very low temperatures below 
2.5.degree. K., the former is greater than the latter. At temperatures in 
the range of 2.5.degree. K. to 6.degree. K., the former remained in the 
range of about 0.8 to 2.5. This indicates that the amorphous rare earth 
alloy of the present invention exhibits good characteristics in specific 
heat capacity at very low temperatures like the above temperatures. 
EXAMPLE 2 
The same procedure as in Example 1 was repeated to prepare a rare earth 
alloy (Er.sub.60 Ni.sub.40) composed of 60 atomic% Er and 40 atomic% Ni. 
The rare earth alloy was made into amorphous alloy foil (22 .mu.m thick) 
by heating to about 1100.degree. C. in the same manner as in Example 1. 
The specific heat capacity of the amorphous alloy foil at temperatures in 
the range of 1.6.degree. K. to 6.degree. K. was measured. The results are 
shown in FIG. 1 (solid line 2). For comparison, the specific heat capacity 
of a crystalline rare earth alloy (Er.sub.3 Ni+Er.sub.3 Ni.sub.2) of the 
same composition as above at temperatures in the same range as above was 
also measured. The results are shown in FIG. 1 (chain line 4). 
It is noted from FIG. 1 that as in the case of Example 1, the specific heat 
capacity of the rare earth alloy in this example is less dependent on 
temperature than that of the conventional crystalline rare earth alloy. At 
very low temperatures below 2.7.degree. K., the former is greater than the 
latter. At temperatures in the range of 2.7.degree. K. to 6.degree. K., 
the former remained in the range of about 1.5 to 2.0. This indicates that 
the amorphous rare earth alloy of the present invention exhibits good 
characteristics in specific heat capacity at very low temperatures like 
the above temperatures. 
EXAMPLE 3 
The same procedure as in Example 1 was repeated to prepare a rare earth 
alloy (Er.sub.70 Ru.sub.30) composed of 70 atomic% Er and 30 atomic% Ru 
(purity 99.9%). The rare earth alloy was made into amorphous alloy foil (8 
.mu.m thick) by heating to about 1250.degree. C. in the same manner as in 
Example 1. The specific heat capacity of the amorphous alloy foil at 
temperatures in the range of 1.6.degree. K. to 6.degree. K. was measured. 
The results are shown in FIG. 2 (line 5). For comparison, the specific 
heat capacity of a crystalline rare earth alloy (Er.sub.3 Ru+Er.sub.3 
Ru.sub.2) of the same composition as above at temperatures in the same 
range as above was also measured. The results are shown in FIG. 2 (line 
6). 
It is noted from FIG. 2 that the specific heat capacity of the crystalline 
rare earth alloy is unstable, greatly fluctuating at temperatures in the 
range of 3.degree. K. to 4.degree. K., whereas that the amorphous rare 
earth alloy in this example is larger than the former and stable in the 
same temperature range. This indicates that the amorphous rare earth alloy 
of the present invention exhibits good characteristics required of the 
regenerator. 
EXAMPLE 4 
The same procedure as in Example 1 was repeated to prepare several kinds of 
rare earth alloys each having the composition shown in Table 1. They were 
formed into amorphous alloy foil, and the specific heat capacity at 
temperatures in the range of 2.degree. K. to 6.degree. K. was measured. 
The results are shown in Table 1. It is noted that the amorphous rare 
earth alloys in this example change in specific heat capacity only a 
little in the specified range of temperatures. They have a large specific 
heat capacity at very low temperatures, which is desirable for their use 
as the regenerator. 
TABLE 1 
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Thick- 
Composition 
ness Specific heat capacity (J/K-mol) 
(molar ratio) 
(.mu.m) 2.degree. K. 
3.degree. K. 
4.degree. K. 
5.degree. K. 
6.degree. K. 
______________________________________ 
67.5Er--32.5Ni 
15 0.69 1.14 1.58 1.97 2.91 
65Er--35Ni 
17 0.67 1.23 1.73 2.16 2.30 
60Er--40Ni 
22 0.56 1.00 1.40 1.82 2.14 
65Ho--35Ni 
22 0.68 0.32 1.08 1.41 1.79 
65Dy--35Ni 
13 0.14 0.24 0.87 0.54 0.71 
60Er--40Co 
15 0.34 0.56 0.82 1.11 1.37 
60Ho--40Co 
13 0.71 0.64 0.78 1.01 1.29 
70Er--30Ru 
8 1.06 2.09 2.70 2.81 2.60 
80Dy--20Ru 
14 0.21 0.25 0.41 0.57 0.75 
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COMATIVE EXAMPLE 1 
The same procedure as in Example 1 was repeated to prepare a rare earth 
alloy composed of 45 atomic% Er and 55 atomic% Ni, and the alloy was made 
into foil by injection toward the surface of a running roll. It was found 
by X-ray diffractometry that the crystalline phase remains in the foil. 
This indicates that the object of the present invention is not achieved if 
the content of rare earth element is less than 50 atomic%.