X-ray Diffraction Grating Crystals

Abstract

The use of structurally layered heavy metal chalcogenides as diffraction grating crystals in X-ray optical assemblies such as X-ray fluorescence spectroscopy, the chalcogen being selected from sulfur, selenium and tellurium, or mixtures thereof. Chalcogenides intercalated with inorganic and organic materials are contemplated.

Description

This invention relates to the use of chalcogenides, either per se or intercalated with various organic and inorganic compounds, as diffraction grating crystals in X-ray optical assemblies. More particularly, the invention relates to the novel use of structurally layered heavy metal chalcogenides where the chalcogen is selected from sulfur, selenium and tellurium or mixtures thereof, and where the heavy metal elements have an atomic number of from 22 to 92, inclusive. The heavy metal elements involved that form layered chalcogenides are selected from certain of the metals included in Groups IB, IIB, IVB, VB, VIIB, VIII, IIIA, IVA, and VA of the Periodic Table of the Elements, or mixtures thereof. In addition, intercalated metals from Group VIB of the Periodic Table of the Elements are also useful in this invention.

It is known that the very close and periodic arrangement of atoms in a small number of crystal structures permit such crystals to act as a diffraction grating for X-ray spectroscopy. Bragg's law, governing the ordered structure of crystals with atoms lying on families of planes that provide a three-dimensional diffraction grating, is as follows:

n.lambda. = 2d sin .theta.

Where n is an integer indicating the order of the spectrum, .lambda. is the wavelength, d the crystal lattice spacing of one set of planes and .theta. the angle between the incident ray and this set of planes. A more complete description of X-ray crystallography is found in the McGraw Hill Encyclopedia of Science and Technology, McGraw Hill, Inc., 1960 Volume 14, at page 567 et seq.

In conventional X-ray fluorescence spectroscopy such as disclosed in the aforementioned encyclopedia commencing at page 576 et seq., the diffracting analyzer (grating) is an integral component of the system. This diffracting analyzer is usually a single crystal which is employed to separate the various wavelengths emitted by the specimen. The better the resolution of such a crystal, the more easily the wavelengths from the specimen are separated into discrete lines characteristic of the elements therein.

One means of improving the resolution of the radiation is to increase the dispersing capability of the diffracting analyzer. The angular separation of the incident wavelengths, and, hence the resolution, is governed by the aforementioned Bragg's law. A broad selection of crystals with a variety of interplanar spacings allows one to select a crystal with high dispersing capabilities in the region of wavelengths of interest.

Because of this requirement for resolution, the choice of diffracting analyzers has heretofor been somewhat limited. Pure and perfect crystals of certain materials have been found to be of little value for this purpose, because many of them cause extinction of the impinging radiation. Furthermore, it is essential that the diffracting analyzer be of good quality to produce sharp, symmetrical peaks representing characteristic wavelengths of the elements in the sample. Defects tend to decrease intensities, causing errors in the analysis. For these reasons, the analyzing crystals of the prior art have been limited to highly purified materials having the desired physical characteristics. These include quartz, and the crystals of the alkali metal halides such as lithium fluoride, sodium chloride, and potassium chloride.

Unfortunately, these materials are subject to certain limitations and disadvantages including (1) unavailability, (2) fragility, (3 ) poor diffracting efficiency, (4) poor capability of diffracting the longer wavelengths of incident radiation, (5) high cost and the difficulty of manufacture, (6) lack of replicability, and (7) characteristic wavelengths of their own that either interfere with wavelengths of the sample or contribute to high background or noise to the analysis. Nearly all of the currently-used analyzing crystals, whether natural or synthetic, are fragile and can be irreparably damaged when dropped or bumped.

It has now been found that certain structurally layered heavy metal chaclogenides can be used as diffraction gratings in X-ray optical assemblies. More specifically, chalcogenides intercalated with various organic and inorganic substances, have been found to possess interplanar spacings heretofor unobtainable in suitable crystal structures. Thus, the use of the aforementioned structurally layered heavy metal chalcogenides as diffraction gratings in X-ray optical assemblies is particularly advantageous because the chalcogenide crystals provide a range of interplanar spacing d extending from 6 to 24 angstroms and even higher. In addition, the crystals are readily prepared in large sizes, are relatively air stable and exhibit high diffracting power.

Among the specific applications of the aforementioned substances to X-ray diffraction grating uses is in fluorescent X-ray spectroscopy, a non-destructive physical method used for the elemental analysis of heavy metal alloys. In that particular application, a primary X-ray beam is directed onto a specimen of interest. Atomic excitations are produced which lead to the emission of secondary X-rays. The energy spectrum of these is characteristic of the atoms involved. Therefore, analysis of the secondary emission will reveal the nature and quantity of constituents in the alloy. The technique is presently limited to heavy metals because light metals produce characteristic X-rays which have much longer wavelengths than the crystal spacings of the conventional crystals used to analyze a secondary emission. The present invention enables such conventional testing to be greatly expanded.

Within the broad concept of the present invention, and as set forth in copending U.S. Patent Application Ser. No. 884,319, filed Dec. 11, 1969, certain of the intercalated chalcogenides are novel compounds, i.e., those in which the sum of the atomic numbers of the heavy metal element and the chalcogen atom are greater than 38.

The compositions useful in this invention include those layered chalcogenides formed from the heavy metal elements having atomic numbers of 22--92, inclusive. Intended to be included in this classification are titanium, vanadium, cobalt, nickel, copper, zinc, gallium, zirconium, niobium, technetium, rhodium, palladium, silver, indium, tin, hafnium, tantalum, rhenium, iridium, platinum, gold, lead, bismuth, thorium, uranium and mixtures thereof. The preferred grouping includes the transition elements defined by Groups IB, IIB, IVB, VB, VIIB and VIII of the Periodic Table of the Elements.

In the preferred embodiment, use of intercalated chalcogenides as diffraction grating (analyzers) is contemplated. The amount of organic or inorganic material intercalated with the chalcogenide can be varied widely and includes weight concentrations of at least 50 percent and higher.

Compounds that are readily intercalated because of their interaction with the aforementioned chalcogenides include ionic compounds such as tetrabutyl ammonium chloride, potassium formate, and sodium chloride and substances that act as Lewis bases. Lewis base compounds intended to be included are those containing at least one non-carbon atom selected from Groups VA and VIA of the Periodic Table of the Elements, preferably oxygen, nitrogen, phosphorous or sulfur.

Among the organic compounds, it is advantageous that the carbon to functional group ratio in the aforementioned compounds be no greater than 50 to 1 and more preferably 15-30 to 1. Although various polymers are contemplated as being useful, generally those molecules having chains of less than 50 carbon atoms are preferred. Nitrogen-containing organic compounds, such as amines, amides, heterocyclic bases and amidines have been found to be especially useful for intercalation. Ketones and aldehydes are also advantageous.

Intercalation of the chalcogenides with various of the compounds set forth above can be accomplished by a number of procedures, as set forth in copending application Ser. No. 884,319, supra. Of these, the most broadly applicable method, when intercalating a Lewis base or an ionic or highly polar molecule has involved immersing the chalcogenide crystals in a liquid bath of the compound for a time sufficient to cause intercalation. Sufficient prolongation of the residence time creates an equilibrium condition. Modifications in pressure or temperature also affect the rate of intercalation, with higher temperatures accelerating the equilibrium condition.

Alternative procedures that can also be used include:

1. Solution Technique: The organic compound to be intercalated is dissolved in a solvent which is itself intercalated less rapidly. The organic crystals to be intercalated are immersed in this solution at an appropriate temperature, that may be elevated.

2. Cointercalation: The chalcogenide crystals are first intercalated with an appropriate compound. The crystals are then treated by one of the above procedures with a second organic compound which then intercalates along with the first compound.

3. Catalytic Intercalation: The chalcogenide crystals are first treated with a compound that intercalates readily. They are then treated with a second organic compound that intercalates at an accelerated rate due to the presence of the first compound. In this process, the first compound is displaced by the second compound.

4. Vapor Phase Intercalation: The chalcogenide crystals to be intercalated are placed in the vapor of the organic compound to be intercalated.

5. Solid Phase Intercalation: The calcogenide crystals to be intercalated are covered and mixed with the compound to be intercalated at an appropriate, perhaps elevated, temperature.

Each of the aforementioned techniques are similar in that the intercalation is allowed to proceed a suitable length of time before the crystals are separated from the excess compound. The suitable time depends on the amount of material one wishes to place inside the crystal.

Other compounds can be utilized to displace or co-intercalate with the Lewis bases or with the aforementioned ionic compounds. Within this definition of useful secondary intercalating materials are Lewis acids; charge transfer acceptors or donors; highly polarizable organic or organometallic substances especially dyes; and compounds containing sulfur, phorphorous, arsenic and heavy metal atoms such as mercury that are capable of engaging in d-orbital bonding.

Other compounds that are suitable for displacement of or co-intercalation with the Lewis bases can be defined as follows:

1. A Lewis Acid or Lewis Base, i.e., compounds with lone pair electrons such as those of nitrogen in amines may donate these in part to the chalcogen in the chalcogenide. Conversely, compounds with unoccupied orbitals, such as are present in many boron compounds, appear to accept electrons from the chalcogen or from the previously intercalated Lewis base;

2. Charge Transfer donors or acceptors, i.e., certain molecules such as tetracyanoquinone, chloranil, and tetracyanoethylene which are very electronegative form charge transfer complexes with the chalcogenide layers or with the intercalated Lewis bases. These are stabilized by the high polarizability of the host. Alternatively, compounds such as tetramethylphenylene-diamine, which have very low electronegativity, form charge transfer complexes with the host, but of the opposite kind;

3. Compounds that have large polarization interactions, i.e., compounds that interact with the chalcogenides, especially molecules that are ionic or that are highly conjugated such as dyes or are highly polar;

4. Compounds capable of d-orbital bonding.

Illustrative examples of the foregoing organic compounds are as follows: ##SPC1##

Within the broad definition of the compositions that exhibit the advantageous use as X-ray diffraction gratings, are a series of intercalated transition metal chalcogenides that include those formed from sulfur, selenium or tellurium and a transition element having an atomic number of from 22 to 92, inclusive. More particularly, those compositions are contemplated where the sum of the atomic numbers of the transition element and the chalcogen are greater than 38. Specific chalcogenides within this definition that have been found particularly useful are the sulfides including specifically TiS.sub.2, ZrS.sub.2, TaS.sub.2, and NbS.sub.2. Compounds particularly suitable for intercalation include aniline, N,N-dimethylaniline, normal aliphatic amines, adamantamine, DABCO, heterocyclic amines, such as pyridine and pyridazine, ammonia, hydrazine, dimethyl formamide, normal aliphatic amides from C.sub.1 to C.sub.18, thiobenzamide, cinnamide, and ionic compounds such as potassium formate, tetrabutylammonium chloride, pyridinium chloride, and sodium chloride.

By way of summary of the preparation of the chalcogenides suitable for X-ray optical materials, the following procedure is considered illustrative. The chalcogenide either in crystal or powder form or stoichiometric (or near stoichiometric) amounts of the transition metal and chalcogen were placed inside a quartz tube. A small amount of elemental halogen, usually iodine, was included to provide a volatile species. After the contents of the tube were displaced to one end, the tube was evacuated and then sealed.

The tube was then placed in a furnace constructed to provide a temperature gradient along the length of the quartz tube. The temperature of the furnace was raised slowly with the temperature of the charged end maintained lower than the temperature of the uncharged end. The gradient was approximately 100.degree. C. When the uncharged end reached 800.degree. C the gradient was reversed. Typically the cool end was maintained between 600.degree. and 800.degree. C. The hot end was typically from 50.degree. to 200.degree. C hotter. The temperature gradient produced a driving force so that the chalcogenide crystals were formed at the uncharged end of the tube. After completion of crystal growth, usually several days later, the tube was cooled sometimes slowly, sometimes rapidly.

Utilizing the foregoing procedure for chalcogenide formation and the previously described preferred method for intercalation, the following compositions were formulated and the indicated interplanar spacings were measured. Each of the compositions demonstrates highly desirable characteristics when employed as X-ray diffraction analyzers.

TABLE I

Intercalated TaS.sub.2 *

Organic Compound D Spacing (A) __________________________________________________________________________ Aniline 18.1 N,N-dimethylaniline 12.4 p-phenylenediamine 12.0 1-aminoaphthalene 21.5 formamide (C.sub.1) 9.2 butyramide (C.sub.4) 11.0 valeramide (C.sub.5) 10.9 hexanamide (C.sub.6) 11.1 caprylamide (C.sub.8) 10.9 stearamide (C.sub.18) 60 cinnamide 12.0, 16.8 benzamide 11.8 urea 9.6, 10.4 dimethylformamide 9.7, 11.8, 12.1 thiobenzamide 11.9 pyridine 11.9 quinoline 12.1 p-dimethylaminopyridine 12.2 ammonia 9.1 hydrazine 9.1 __________________________________________________________________________

TABLE II

NbS.sub.2 Intercalation Compounds*

Compound d (A) __________________________________________________________________________ benzamide 11.3 aniline 18.0 pyridine 12.0 __________________________________________________________________________

TABLE III

TiS.sub.2 Intercalation Compounds

Compound d (A) __________________________________________________________________________ formamide 16.1 acetamide 11.5 propionamide 10.5 butyramide 10.5 valeramide 10.5 caproamide 10.5 hydrazine-water 9.6 N-methylformamide 18.4 N, N-dimethylformamide 9.6 N, N-diethylformamide 9.6 N-methylacetamide 16.3 N, N-dimethylacetamide 9.6 N-ethylacetamide 9.6 N, N-diethylacetamide 9.6 N-methylpropionamide 9.6 urea 12.3 N, N'-dimethylurea 17.7 N,N-dimethylurea 9.6 N, N'-diethylurea 9.6 N, N-diethylurea 9.6 tetramethylurea 9.6 __________________________________________________________________________

Claims

1. In an X-ray optical assembly comprising at least an X-ray source and a diffraction grating, the improvement comprising: said diffraction grating being a structurally layered heavy metal chalcogenide, the heavy metal being selected from at least one of those heavy metal elements having an atomic number of 22 to 92, inclusive, and which is titanium, vanadium, cobalt, nickel, copper, zinc, gallium, zirconium, niobium, technetium, rhodium, palladium, silver, indium, tin, hafnium, tantalum, rhenium, iridium, platinum, gold, lead, bismuth, thorium, and uranium, and the chalcogen being selected from sulfur, selenium and tellurium, or mixtures

2. The X-ray optical assembly of claim 1, wherein said chalcogenide is

3. The X-ray optical assembly of claim 2, wherein said chalcogenide is a

4. The X-ray optical assembly of claim 2, when said chalcogenide has an

5. The X-ray optical assembly of claim 2, wherein said intercalated

6. The X-ray optical assembly of claim 5, wherein said organic compound is

7. The X-ray optical assembly of claim 5, wherein the organic compound contains an atom selected from nitrogen, sulfur, phosphorous and oxygen.

8. The X-ray optical assembly of claim 7, wherein the organic compound

9. The X-ray optical assembly of claim 8, wherein the organic compound is

10. The X-ray optical assembly of claim 5, wherein the organic compound is

11. The X-ray optical assembly of claim 5, wherein the organic compound is

12. The X-ray optical assembly of claim 11, wherein the ionic compound is a

13. The X-ray optical assembly in accordance with claim 4 wherein the organic compound is selected from aniline N,N-dimethylaniline, p-phenylenediamine, 1-aminonapthalene, 1-aminoanthracene, formamide, butyramide, valeramide, hexanamide, caprylamide, capramide, lauroylamide, myristamide, palmitamide, stearamide, cinnamide, benzamide, urea, dimethylformamide, thiobenzamide, pyridine, quinoline, s-triazine, acridine, pyrimidine, pyridazine, p-dimethyl-aminopyridine, butylamine, octylamine, hexadecylamine, octadecylamine, potassium formate, tetrabutyl

14. The X-ray optical assembly of claim 2, wherein the intercalated

15. The X-ray optical assembly of claim 2, wherein the intercalated

16. The X-ray optical assembly of claim 2, wherein the intercalated

17. The X-ray optical assembly of claim 2, wherein the intercalated

18. The X-ray optical assembly in accordance with claim 1, wherein the heavy metals are those classified as transition elements in the Periodic

19. The X-ray optical assembly in accordance with claim 18, wherein the transition element is selected from Group VB of the Periodic Table of

20. The X-ray optical assembly in accordance with claim 1, wherein the

21. The X-ray optical assembly in accordance with claim 20, wherein said chalcogenide is intercalated with an organic compound selected from aniline, N,N-dimethylaniline, p-phenylenediamine, 1-amino-naphthalene, 1-aminoanthracene, amides of from one to 18 carbon atoms, urea, pyridine, quinoline, acridine, pyrimidine, pyridazine, p-dimethylaminopyridine, butylamine, octylamine, decylamine, octadecylamine, potassium formate,

22. The X-ray optical assembly in accordance with claim 20, wherein said chalcogenide is intercalated with an organic compound having a

23. The X-ray optical assembly in accordance with claim 20, wherein said chalcogenide is intercalated with an organic compound consisting of an

24. The X-ray optical assembly in accordance with claim 1, wherein the

25. The X-ray optical assembly in accordance with claim 1, wherein the

26. The X-ray optical assembly in accordance with claim 1, wherein the

27. The X-ray optical assembly in accordance with claim 1, wherein the

28. The X-ray optical assembly in accordance with claim 1, wherein the

29. The X-ray optical assembly in accordance with claim 1 wherein the heavy

30. In an X-ray spectroscope assembly of an X-ray source, a diffracting analyzer, a collimator and detector, the improvement comprising: said diffracting analyzer being a structurally layered heavy metal chalcogenide, the heavy metal being selected from at least one of those heavy metal elements having an atomic number of 22 to 92, inclusive, and which is titanium, vanadium, cobalt, nickel, copper, zinc, gallium, zirconium, niobium, technetium, rhodium, palladium, silver, indium, tin, hafnium, tantalum, rhenium, iridium, platinum, gold, lead, bismuth, thorium, and uranium, and the chalcogen being selected from sulfur, selenium and tellurium, or mixtures thereof.