JPH04213392A - Method for warm forming and extrusion of metal and composition for metal working useful therein - Google Patents

Abstract

PURPOSE: To protect the surface of a metal worked article from corrosion and abrasion by adding rate earth metal halide to a lubricant compsn. used in the forming and extrusion of a metal at high temp. exceeding about 1100°F.

CONSTITUTION: In a warm forming method for metal adapting a lubricant to the surface of a metal worked article deformed thereafter, rare earth metal halide is added to the lubricant. As rare earth metal halide, especially, rare earth metal trifluoride such as lanthanum trifluoride and cerium trifluoride is pref. Rare earth metal halide is compounded with a metal working lubricant compsn. in an amt. of up to about 30 wt.%, pref., about 10 wt.%. The above mentioned lubricant compsn. contains a liquid substrate, a viscosity raising agent, a lubricant effective at high temp. and rare earth metal halide.

COPYRIGHT: (C)1992,JPO

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to the warm forming and extrusion processing of metals and to improvements in compositions that can be advantageously used in these metal processing operations. More specifically, the present invention provides a temperature range of about 1,100°F. Concerning the warm forming and extrusion processing of metals at temperatures exceeding . In this regard, an important aspect of the present invention relates to the use of rare earth metal halides, such as cerium trifluoride or lanthanum trifluoride, in compositions used in the warm forming and extrusion processing of steel.

Warm forming and extrusion of metals is an operation that typically involves applying a metalworking lubricant composition to the metal surface prior to deforming the metal. The composition itself must meet various requirements. For example, in addition to lubricating properties, the composition must protect metal surfaces from damage such as wear. Furthermore, the composition should not only be relatively easy to apply and remove, but also be compatible with the subsequently applied coating material.

0003

BACKGROUND OF THE INVENTION Many of these metalworking lubricant compositions are homogeneous systems formulated for specific applications in which some properties are preferred over others but are necessarily the product of compromises between conflicting requirements. It is a compound. Heterogeneous metalworking lubricants are also known, such as dispersions of lubricant materials in water or other volatile media. Such heterogeneous lubricants are intended to be applied to a metal workpiece so that, upon evaporation of the volatile medium, a continuous, uniform lubricant film remains on the metal workpiece.

To achieve a balance of properties, compositions useful in the warm forming of metals generally employ a range of oils, waxes, soaps, and sometimes polymeric substances, each of which has a specific application. This has the following advantages. For example, U.S. Pat. No. 4,687,5 to Daglish et al.
No. 87 discloses a metal forming lubricant comprising discrete particles of a waxy material having a softening point above the metal forming temperature in a solid or viscous monomeric organic carrier. Similarly, Parkinson U.S. Pat. No. 3,873,458
No. 5,923,902 discloses a method for cold forming or shaping metals with resin-oil coatings prepared from copolymer dispersions of ethylene and acrylic acid in lubricating oils. Similarly, Cra
U.S. Pat. No. 3,167,511 to Wford et al.
As a lubricant for metal broaching, cutting and rolling.
The use of chlorinated polypropylene in lubricating oils is disclosed. However, these lubricants and other lubricants known in the art have a temperature range of about 1,100°F. cannot provide the necessary lubrication and surface protection to metal workpieces during forming or extrusion processing of metals at temperatures above .

[0005] A primer is often applied to the metal before the lubricant is applied. This basecoat can include, for example, lime, zinc phosphate and/or soap. However, the use of these priming methods also does not allow for warm forming and extrusion of metals at high temperatures, which is desirable for forming and extruding many metal parts, especially metal parts made of hard alloys.

The usefulness of rare earth metal trifluorides, such as lanthanum trifluoride and cerium trifluoride, as solid lubricants has been known for some time. Rare
Earth Fluorides and Ox
ides--An Exploratory St
udy of their use as
Solid Lubricants at Temp
erasures to 1,800°F. (1,
000℃. )NASA TND-5301, 1969
See. Similarly, Aldorf U.S. Pat.
No. 07,214 discloses the use of rare earth metal halides in lubricating greases to create lubricant compositions for lubricating wheel bearings. Pach
olke, US Pat. No. 4,715,972, similarly describes the use of cerium fluoride as one of several solid lubricant particulate additives for gear oils. Also, Larsen U.S. Pat. No. 3,830,280
No. 6,923,911 discloses the use of rare earth metal halides, such as cerium trifluoride or lanthanum trifluoride, as lubricants for die-cast parts. However, none of these prior art disclosures disclose temperatures of about 1,100°F. There is no suggestion of metalworking liquid lubricant compositions suitable for warm forming and extrusion of metals at temperatures above .

[0007]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to operate at high temperatures, particularly around 1,100°F. It is an object of the present invention to provide a method for warm forming and extrusion of metals at temperatures exceeding .

Another object of the present invention is to provide improved compositions useful in the warm forming and extrusion of metals, particularly at elevated temperatures.

Another object of the invention is to provide a stable, about 1,10
0°F. An object of the present invention is to provide a metalworking lubricant composition that does not decompose even at high temperatures exceeding .

Another object of the invention is to provide a metalworking composition that exhibits excellent lubrication properties during metal forming and extrusion at high temperatures and also protects the surface of metal workpieces from corrosion and wear. It is.

Another object of the present invention is to provide a composition for warm forming and extruding metals that not only provides lubrication during forming and extrusion, but also continues to provide lubrication after the metal has cooled. Another object of the invention is that after removal from the mold,
It is an object of the present invention to provide a high temperature metalworking lubricant composition that can be easily removed from metalworks.

Further objects of the invention will become apparent from the description below.

[0013]

SUMMARY OF THE INVENTION The present invention is directed to improvements in the warm forming and extrusion process of metals, and to compositions useful in the process. With this improvement, approximately 1,800°F. It becomes possible to carry out metal processing operations up to temperatures of 100 mL or higher.

According to an important aspect of the invention, the methods and compositions of the invention particularly useful for warm forming and extrusion of metals involve the use of rare earth metal halides in the compositions. The composition has a viscosity of 100°F. Approximately 1,500 in
S. U. S. 100° F. of the liquid substrate, the composition. The viscosity of about 150 to about 1,500S
．． U. S. viscosity increasing agent to increase the viscosity to at least about 400°
F. effective high temperature lubricants; and rare earth metal halides. Optional ingredients include graphite and/or molybdenum disulfide.

[0015] In warm working metal operations, liquid lubricants are typically poured, dipped, brushed or sprayed onto the metal parts, with the overflow preferably collected and returned to a central recirculation tank. Applied to metal by continuous method. Therefore, the lubricant composition is required to be liquid. In order to be able to provide the necessary lubrication, the lubricant must be heated to 100°F. from about 150 to about 1,500 S. U. S. It should be. A liquid composition of this viscosity can be pumped and at the same time provide the necessary lubricity. Following application of the liquid lubricant, deformation of the metal workpiece takes place and then the lubricant is removed from the molding. Metalwork often has a base coat that can include lime, zinc phosphate and/or soap. The inclusion of rare earth metal halides in the lubricant composition increases the temperature at which metal forming can be carried out to about 1,800°F. It was found that the increase was higher than that. This has an upper limit of effective implementation of about 1,100°F. This is a significant improvement over the conventional method. Thus, the method of the present invention can be used at temperatures as low as about 300°F. to about 1,800°F. It can be carried out at a temperature of In many applications, the method operates at temperatures as low as about 900°F. to 1,500°F. carried out at a temperature of

Similarly, in metal extrusion, liquid lubricants are applied such that a lubricant film is present between the extrusion billet and the die. As with warm forming, the viscosity of this liquid lubricant is 100°F. about 150 to about 1
, 500 S. U. S. It should be.

The presence of rare earth metal halides in the lubricant composition reduces the temperature at which extrusion can be effectively carried out to about 1,800°F. rise above. Conventional compositions do not provide the necessary lubricity and metal protection properties at such high temperatures.

The method of warm working and extrusion of metals is about 1,
800°F. Because it can be used to temperatures up to 100 mL or higher, the process is particularly useful in applications using ferrous metals, such as steel, but also other metals such as copper, bronze, brass, and aluminum. The method uses approximately 600
°F. to 1,800°F. It can be carried out at a temperature of However, for molding and extrusion of many objects, temperatures around 900°F. to 1,500°F. temperatures are typically used.

A variety of liquid compositions can be used in carrying out the method of the invention.

One of the compositions is an oily composition. Particularly useful oily compositions contain the following components: 1) a liquid matrix; 2) a temperature of 100°F. The viscosity at 150 to 1,500 S. U. S. Viscosity increasing agent 3
) at least about 400°F. 4) Rare earth metal halides, which are effective lubricants at high temperatures.

Among the optional ingredients of the lubricant compositions of this invention are graphite and molybdenum disulfide.

The amount of liquid matrix component in the composition will vary depending on the particular process being performed and the metal being warm formed or extruded. Generally, this component will constitute from about 40 to about 90 percent by weight of the composition.

Various animal oils, vegetable oils, fats, fatty acid esters and mixtures thereof can be used as liquid substrates in the lubricant compositions of the present invention. Since this non-petroleum-based material constitutes a significant portion of the composition, its selection necessarily has a substantial effect on the physical properties of the composition, such as viscosity and adhesion to metal workpieces.

Preferably, the substrate is a fat, such as a triglyceride. Since triglycerides are produced by esterifying the three hydroxyl groups of glycerin with fatty acids, triglycerides often contain unreacted fatty acids. Fatty acids are generally straight chain compounds containing about 8 to about 18 carbon atoms. Prime burning lard oil is a particularly useful triglyceride.
ard oil) is about 99.5 weight percent triglycerides or substances and less than 0.5 weight percent fatty acids. Other useful substrates are 100°F. The lubricant viscosity at 50S. U. S. or about 1,000
S. U. S. This is soybean oil. Also useful are oleic acid, sulfurized lard oil, fish oil triglycerides, rapeseed oil, tall oil and paraffin oil.

The purpose of the viscosity increasing agent is 100°F. from about 150 to about 1,000 S. U. S.
Various substances can be used to increase the viscosity of the liquid. Particularly useful viscosity increasing agents are asphaltic materials. In addition to increasing the viscosity of the liquid matrix, asphaltic materials improve the adhesion of the composition and also provide lubricity. in general,
The viscosity increasing agent should be present in an amount of about 2 to about 25 weight percent of the composition. Other viscosity increasing agents that can be used in the compositions of the invention are polybutene, aluminum stearate and deglass.

[0026] At least about 400°F. , preferably about 400°F. to about 1,100°F. Many lubricants can be used as the low temperature lubricant composition of the compositions of this invention so long as they provide effective lubrication at temperatures of . A particular class of lubricants of value in the compositions of the present invention are sulfur-containing compounds. Such lubricants are well known in the art and have temperatures up to about 1,100°F. Shows good lubrication properties at temperatures of Sulfurized mineral oils and sulfurized fatty oils are useful as this component. Other examples of such substances are sulfurized fats, mineralized sulfur, sulfurized hydrocarbons,
These include sulfurized castor oil, sulfurized chlorinated oil, etc.

Generally, the sulfurized compound makes up about 50% of the lubricant composition.
Although it can be present in an amount of from about 50 weight percent, for most purposes this amount will be from about 10 to about 20 weight percent.

According to an important aspect of the invention, the metalworking lubricant composition includes a rare earth metal halide, preferably a fluoride. Although other halides such as chloride are known, available and useful, fluoride is more preferred. In particular, rare earth metal trifluorides such as lanthanum trifluoride and cerium trifluoride are preferred. usually,
These rare earth metal halides are present in amounts of about 2 to about 30 weight percent or more of the composition, with amounts of about 5 to 10 weight percent being generally desirable. The particle size of the rare earth metal fluoride should be relatively fine.

Furthermore, other solid lubricants can also be included as optional ingredients in the composition of the present invention. These solid lubricants, including molybdenum disulfide and graphite, can each be present in amounts up to about 10 percent by weight of the composition. Their presence can improve the overall lubricity of the composition. Other optional lubricants that can be included in the compositions of the invention include mica, calcium carbonate and zinc stearate.

Molybdenum disulfide, any other solid lubricants, and rare earth metal halides have a particle size of, for example, about 0.05 mm.
01 microns to about 100 microns, preferably about 0
．． It can be included as a fine powder of 1 to about 45 microns. However, the present invention is not limited to components of any particular particle size.

The compositions of the present invention can be manufactured by standard methods known in the art. Usually, the composition can be manufactured by slightly warming and mixing each component. The rare earth metal trifluoride should be added gradually with stirring to obtain a homogeneous mixture. Sufficient mixing (about 1 hour) should be used to obtain a homogeneous composition. Alternatively, the compositions of the invention can be made by kneading the ingredients.

In addition to oil-based compositions, it is often preferable to have aqueous compositions available, which can reduce cost and toxicity. The composition contains the same ingredients as the oil-based composition, namely, a liquid matrix, a viscosity increasing agent, and a temperature of at least about 400°F. Comprised of rare earth metal halides and low temperature lubricants effective at temperatures of .

As described above, although many of the active ingredients of the aqueous composition are the same as those of the oil-based composition, there are some differences.

[0034] As with oil-based compositions, aqueous compositions also use viscosity increasing agents. Generally, this is one of the compositions.
00°F. from about 150 to about 1,500
S. U. S. It can be any substance that can be enriched in water and is soluble in water. Useful materials include cellulose compounds such as sodium carboxymethyl cellulose, glycols such as diethylene glycol, propylene glycol and butylene glycol, and certain waxes such as Carbowax 3350.

Since it is more difficult to obtain an aqueous homogeneous mixture than an oil-based homogeneous mixture, lubricants and dispersants should also normally be present in the composition. As is common with aqueous compositions containing solid components, lubricants and dispersants help keep the particles in the dispersion so that the composition is uniform. Numerous dispersants and lubricants are known in the art.

Optional ingredients in the aqueous compositions of this invention include antifoam agents, antimicrobial agents, and corrosion inhibitors. These ingredients can perform useful functions in the compositions of the invention.

It is uneconomical to transport the water rather than to produce the water-containing composition, so transporting it as a concentrate to the site of the warm forming or extrusion operation;
It is often desirable to then dilute it with water to produce a concentrate that can be used in metal warm forming or extrusion processes. Glycols such as diethylene glycol, propylene glycol or butylene glycol can be used as viscosity increasing agents in the composition in preparing concentrates that can be diluted into aqueous compositions.

The lubricant compositions described so far have a 1,10
0°F. It has been found that it provides excellent lubricity in warm forming and extrusion of metals at temperatures above . The composition has a temperature of 1,100°F. Stable at temperatures higher than 1,800°F. It is also stable in the above conditions. Additionally, the composition protects metal from corrosion and wear, and can be easily applied and removed by conventional means.

For applications in warm forming and extrusion of metals, the compositions of the invention are applied to the metal by conventional methods such as dipping, flow coating, brushing or spraying. For best results, the composition should be heated to 100°F. has a viscosity of about 500 to about 1,000 S. U. S. It is desirable that This allows the lubricant composition to be easily applied to metals. Among the metals in which the compositions of the present invention can be used are steel, copper, bronze, brass, aluminum, and the like. Other metals may also be used in the warm forming process of the present invention, which involves applying deformation pressure to metal coated with the composition of the present invention. The method is particularly suitable for temperatures up to 1,100°F. and up to about 1,800°F.
It is applicable to metals formed at temperatures above or above.

The composition of the present invention can also be used for metal extrusion. In this method, the compositions of the present invention are applied to metals, including those previously described as applicable to metal forming, at temperatures up to about 1,800°F. Extrusion is performed at a temperature above. The compositions of the present invention provide excellent lubrication and protection of metals from corrosion and wear.

[0041]

EXAMPLES Example 1 The improved high temperature performance of the metalworking composition and metalworking method of the present invention was demonstrated using a commercially available metalworking lubricant (EXTRUDOIL).
519HT), a chemically identical commercial metalworking lubricant that also contains molybdenum disulfide (EXTRUDOIL 519
HT-MOS), and EX containing cerium trifluoride
This was demonstrated by comparing the performance of TRUDOIL 519HT-MOS and chemically identical metalworking compositions. EXTRUDOIL 519HT and EXTRUD
All OIL 519HT-MOS are Witco
Corporation, Allied-Kel
It was obtained from ite Division.

[0042]EXTRUDOIL 519HT product is No. 1 Lard oil (high quality lard containing 99.5 weight percent glyceride derivatives and less than 0.5 weight percent free fatty acids), asphaltic viscosity increaser,
and a lubricant component consisting of sulfurized fatty oil and sulfur-containing mineral oil. EXTRUDOIL 519HT-
The MOS contains the same components in the same relative amounts as EXTRUDOIL 519HT, plus a 10 weight percent molybdenum disulfide dispersion. In addition to containing the same components in the same relative amounts as EXTRUDOIL 519HT, the metalworking lubricant product embodying the invention contained 5 weight percent each of molybdenum disulfide dispersion and cerium trifluoride.

National M with carbide die
Diameter 1 using a 1000 type extrusion molding machine manufactured by Achinery
Each of these metalworking lubricants was tested while extruding 5/16 inch 1050 steel wire to create camshaft lobes. The die is lubricated with constantly recirculating lubricant,
The extrusion temperature was increased incrementally while observing the performance of the lubricant.

EXTRUDOIL 519HT metalworking lubricant, which contained neither molybdenum disulfide nor rare earth metal halides, was tested at 800-900°F. It worked well within the temperature range. 900°F. At higher temperatures, the composition decomposed, and at such high temperatures there was insufficient lubrication to form lobes.

EXTRUDOIL 519HT containing molybdenum disulfide but no rare earth metal halides
-MOS metalworking lubricants operate at approximately 1,000°F. or 1
,100°F. lobe formation was possible at temperatures of . 1,100°F. Raising the temperature above this level caused the composition to decompose, resulting in insufficient lubrication to form lobes.

Metalworking lubricants containing cerium trifluoride can be heated to 1,500°F. Lobe formation was possible at temperatures above, and no decomposition of the metalworking lubricant could be observed.

[0047] Thus, the compositions of the present invention can be used effectively at temperatures not easily lubricated with conventional petroleum-based compositions. This resulted in approximately 1,500
°F. Warm forming and extrusion parts can be efficiently and easily produced at temperatures above.

The following examples illustrate other compositions within the scope of this invention. Examples 2-9 describe oil-based compositions, Examples 10-13 describe aqueous compositions of the invention, and Examples 14 and 15 describe readily dispersible concentrates in water.

[0049]
Example 2 Ingredients
weight percent
No. 1 lard oil
54 Asphalt-based substances
14 Sul-Per
m 181 11
Sulfur-containing mineral oil
6 Molybdenum disulfide dispersion 5 Graphite

5 Cerium trifluoride
51 Sul-
Perm 18 is 100°F. The viscosity of is approximately 2,80
0 S. U. S. to 3,300 S. U
．． S. , with a flash point of 450°F. , the combustion point is 4 9
0°F. , a sulfurized fatty oil weighing 8.4 pounds per gallon and containing 17 weight percent sulfur.

Example 7 Ingredients
weight percent
rapeseed oil
60 Polybutene
20
Pearsall OA 3192 10
lanthanum trifluoride
102 Pearsall OA
319 contains about 17.8 weight percent sulfur and has a viscosity of 210°F. 270 S. U. S. and 10
0°F. 3,000S. U. S. , a synthetic sulfurized sperm whale oil substitute that also weighs 8.6 pounds per gallon.

Example 8 Ingredients
weight percent
tall oil
58 Asphalt
5
Pearsall OA 319 15
Base 3803
5 Graphite

3 Lanthanum trifluoride
143 Base 380 has a sulfur content of 38 percent by weight and a gallon weight of 9.
2 lbs., viscosity 100°F. , 420 S. U
．． S. and 210°F. 60 S. U. S
．． It is a sulfur hydrocarbon.

Example 9 Ingredients
weight percent
sulfurized lard oil
65 Asphalt-based materials
15 Di-tertiary nonyl polysulfide 6 Pe
arsall OA 3774 5
calcium carbonate
3 Cerium trifluoride
64 Pe
Arsall OA 377 typically contains 36 weight percent sulfur and has a viscosity of 210°F. So 5
1 S. U. S. , 100°F. 245 S.
U. S. It is a sulfurized olefinic hydrocarbon with a gallon weight of 8.58 pounds. The substance is completely soluble in naphthenic and paraffinic petroleum.
and has a flash point of 335°F. , combustion point is 360°F
．． It is.

It will be appreciated that the foregoing aspects of the invention are merely illustrative of the invention, and that those skilled in the art may make modifications thereto without departing from the spirit and scope of the invention.

Claims (41)

[Claims] 1. A method of warm forming metal in which a lubricant is applied to the surface of a metal workpiece to be deformed after rolling, characterized in that the lubricant contains a rare earth metal halide. 2. The method of claim 1, wherein the lubricant is a liquid. 3. The rare earth metal halide is present in an amount up to about 30 weight percent of the lubricant composition.
The method described in. 4. The method according to claim 1, wherein the rare earth metal halide is a lanthanum halide. 5. The method according to claim 1, wherein the rare earth metal halide is cerium halide. 6. The method according to claim 4, wherein the rare earth metal halide is a lanthanum trifluoride halide. 7. The method according to claim 5, wherein the rare earth metal halide is cerium trifluoride. 8. The method of claim 7, wherein cerium trifluoride is present in an amount up to about 10 weight percent of the lubricant composition. 9. The method of claim 1, wherein the lubricant composition also includes up to about 10 weight percent graphite. 10. The method of claim 1, wherein the lubricant composition also includes up to about 10 weight percent molybdenum disulfide. Claim 11: Claim 1 wherein the metal is a ferrous metal.
The method described in. 12. The method of claim 1, wherein the metal is steel. 13. The temperature at which the metal workpiece is deformed is about 300°F. to about 1,800°F. The method according to claim 1. 14. The temperature at which the metal workpiece is formed is about 900°F. to about 1,500°F. Claim 1
The method described in. 15. A method of metal extrusion in which a lubricant is applied to the surface of the metal fed to an extrusion die, wherein the lubricant comprises a rare earth metal halide. 16. Claim 15, wherein the lubricant is a liquid.
The method described in. 17. The method of claim 15, wherein the rare earth metal halide is added in an amount up to about 30 weight percent of the lubricant composition. 18. The method according to claim 15, wherein the rare earth metal halide is a lanthanum halide. 19. The method according to claim 15, wherein the rare earth metal halide is cerium halide. 20. The method of claim 18, wherein the rare earth metal halide is lanthanum trifluoride. 21. The method of claim 19, wherein the rare earth metal halide is cerium trifluoride. 22. The method of claim 21, wherein cerium trifluoride is present in an amount up to about 10 weight percent of the lubricant composition. 23. The method of claim 15, wherein the lubricant composition also includes up to about 10 weight percent molybdenum disulfide. 24. The method of claim 15, wherein the lubricant composition also includes up to about 10 weight percent graphite. 25. The method according to claim 15, wherein the metal is a ferrous metal. 26. The method of claim 15, wherein the metal is steel, copper, bronze, brass or aluminum. 27. The extrusion temperature is about 300°F. to about 1,800°F. 16. The method according to claim 15. 28. The extrusion temperature is about 900°F. or 1
,500°F. 16. The method according to claim 15. Claim 29: 100°F. The viscosity of
S. U. S. less than about 1,800°F. A metalworking liquid lubricant composition useful for warm forming and extrusion at temperatures up to The said composition characterized by. 30. The liquid matrix is present in an amount of about 40 to about 90 weight percent of the composition and the viscosity increasing agent is present in an amount of about 2 to about 25 weight percent of the composition to provide effective lubrication at high temperatures. 30. The composition of claim 29, wherein the agent is present in an amount of about 5 to about 50 percent by weight of the composition and the rare earth metal halide is present in an amount of about 2 to about 30 percent by weight of the composition. 31. The composition of claim 29, also containing up to about 10 weight percent molybdenum disulfide. 32. The composition of claim 29, also containing up to about 10 weight percent graphite. 33. The composition of claim 29, wherein the liquid matrix is an oil. 34. The composition of claim 29, wherein the liquid substrate is water. 35. The liquid substrate is an animal oil, a vegetable oil, a fat,
30. The composition of claim 29, selected from the group consisting of fatty acid esters and mixtures thereof. 36. The composition according to claim 29, wherein the viscosity increasing agent is an alphaltoid material. Claim 37: Claim 29 wherein the lubricant contains sulfur.
The composition described in . 38. The composition of claim 29, wherein the sulfur-containing lubricant is selected from the group consisting of sulfurized mineral oils, sulfurized fatty oils, elemental sulfur, and mixtures thereof. 39. The composition according to claim 29, wherein the rare earth metal halide is a fluoride. 40. The composition of claim 39, wherein the rare earth metal halide is lanthanum trifluoride. 41. The composition of claim 39, wherein the rare earth metal halide is cerium trifluoride.