US 3744296 A
Piezoelectric and magnetostrictive materials coated with charge transfer complexes of halogens are effective detectors for materials capable of being halogenated, such as olefins.
Description (OCR text may contain errors)
O Umted States Patent 91 [111 3,744,296 Beltzer July 10, 1973 1 COATED PIEZOELECTRIC ANALYZERS  References Cited  Inventor: Morton Beltzer, Westfield, NJ. UNITED STATES PATENTS z 3,194,053 7/1965 Shang 73/23  Asslgnee gz g ifi i g g g f 3,260,104 7/1966 King, Jr. 73 23 3,329,004 7/1967 King, Jr. 73/23  Filed: May 7, 1971  AppL NOJ 141,335 Primary Examiner-Joseph Scovronek Attorney-Manahan & Wohlers and Joseph J. Dvorak  U.S. Cl. 73/23, 23/230 M, 23/232 E,
23/253 TP, 23/254 E, 338/13 [571 ABSTRACT 3 G011! G011 29/22 Piezoelectric and magnetostrictive materials coated  Field of Search 23/232 R, 232 E, with charge transfer complexes of halogens are efiec- 23/254 R, 254 E, 255 R, 255 E, 253 TP, 253 R, 230'l-lC, 230 M; 73/23, 26, 27; 338/13; 310/8, 8.9
tive detectors for materials capable of being halogenated, such as olefins.
l3 Claims, 1 Drawing Figure PAIENIED JUL 1 0191;
EZQELECTRIC CRYSTAL W A SUBSTRATE I. R R ECO DE MERCURY csu. J
Marlon Bel/zer INVENTOR BY'W/ COATED PIEZOELECTRIC ANALYZERS BACKGROUND OF THE INVENTION Coated piezoelectric analyzers have gained considerable commercial acceptance in numerous scientific and industrial applications. For example, in gas chromatography, it is necessary to determine the composition of gaseous effluent. Coated piezoelectric crystal analyzers are particularly useful in such applications, especially where the concentration of the gas to the detector is extremely low. In addition, many simple analyzers have been developed for determining moisture or water content in fuels and in other fluid-feed materials. Other areas of application include the analysisof hydrogen sulfide, aromatics, olefins, and paraffins. These uses, of course, are of particular interest in the petroleum industry.
The fundamental principle of a detection device using a coated piezoelectric crystal is set forth in U.S. Pat. No. 3,164,004 which is incorporated herein by reference. Consequently, only so much of the referenced patent will be repeated as is considered necessary to understand the present invention.
Very briefly, piezoelectric and magnetostrictive materials when coated with a substrate selectively sensitive to changes in their environment can serve as detection devices for use in analyzers. Thus, when a responsive material which is coated with a substrate is placed in a suitable oscillation circuit, it will vibrate at a particular natural frequency. The changes in the environment to which the substrate is sensitive will result in changes in the vibrational frequency of the responsive material.
By the term substrate generally is understood to mean any thin film or coating deposited in a predetermined quantity on a responsive material. The substrate may be either liquid or solid.
Responsive material is, of course, any material which exhibits piezoelectric or magnetostrictive properties.
Very briefly, the operability of such detection devices depends upon the interaction of the substrate with the material to be detected. Interaction is generally understood to mean any physical or chemical relationship between the coating and the material which will tend to increase the resistance of the crystal to the electrical driving force of the oscillating circuit. As will be more fully explained, interaction also may include a physical or chemical relationship between the coating and the material detected which will decrease the resistance of the crystal. Suffice it to say that generally interaction is thought of in terms of weight gain. The greater the weight gain, the less the frequency of the crystal. Illustrative of interactions are adsorption, absorption, chem-adsorption, chemical reactions, and the like.
Ideally, a coated crystal detector should not only be reusable but the frequency of the responsive material should return to a natural stable condition after purging the coating material subsequent to interaction.
Also, substrates employed in crystal detectors are apaccuracy that can be used and reused in the analysis of fluid materials.
The present invention is concerned with such piezoelectric crystal detectors. More specifically, the present invention is concerned with a method and apparatus for detecting materials capable of being halogenated.
SUMMARY OF THE INVENTION According to the present invention, a piezoelectric element for fluid detectors is provided which comprises a responsive material coated with a halogen complex of a charge transfer material.
One embodiment of the inventive piezoelectric detector element comprises a quartz crystal provided with a halogen complex of a charge transfer material. Preferably the charge transfer material is a polymeric mate rial that has an endocyclic nitrogen atom in the repeating unit of the polymer.
In another embodiment of the present invention, a method is provided for detecting materials capable of being halogenated. Fluid materials sensitive to being halogenated are exposed or contacted with the coated piezoelectric detector of the present invention. Upon contact with the crystal, the fluid material is halogenated resulting in a weight change in the substrate. Thus, the responsive material will exhibit a change in its frequency of oscillation. By detecting this weight change, correlation can be established for analytical and detection purposes.
BRIEF DESCRIPTION OF DRAWING The figure is a schematic diagram of a typical oscillator circuit having a detector element of the present invention.
DETAILED DESCRIPTION OF THE INVENTION The particular responsive material" which may be employed in accordance with this invention is defined as any material which exhibits piezoelectric or magnetostrictive properties.
Material which exhibits piezoelectric properties is one which when subject to mechanical pressure develops an electric potential, and vice versa, when subject to an electric potential, mechanically deforms. Several such materials are known, for example, crystal such as quartz, tourmaline, and Rochelle salts and other materials such as barium titanate. Quartz is the particular crystal most often employed in electrical applications; it is the preferred in the instant invention although it is not limited thereto.
A magnetostrictive material is a material which will produce a magnetic field upon mechanical deformation, and vice versa, which will mechanically deform in the presence of a magnetic field. Examples of such types of magnetostrictive materials are nickel and nickel alloys.
A detecor of the present invention comprises a responsive material coated with a halogen complex of a charge transfer material. Charge transfer materials are generally well known in the art. Typically they consist of compounds that may act as electron donors. Thus, a charge transfer complex is an intermolecular addition compound consisting of an electron donor molecule and an electron acceptor molecule. The binding energy of such materials is due mainly to the dispersion type forces such as dipole-dipole forces, accompanied by partial charge. transfer. It is generally understood that electron transfer in such complexes occurs from donor to acceptor without appreciable energy loss since no rearrangement of molecular structure is involved.
Various polymeric materials are known as charge transfer materials. Often these polymeric materials contain a nitrogen atom in the repeating unit of the polymer which forms a charge transfer complex with halogens. More often still, the repeating unit contains an endocyclic nitrogen atom in a ring having conjugated unsaturation. Typical polymers that are known to form charge transfer materials are poly (4- vinylpyridine), poly (2-vinylpyridine), poly (2-vinyl quinoline), poly (N-vinylcarbazole), poly (2- vinylpyrimidine), poly (6-vinylpurine), and poly (2- vinylpyrazine). 1
The halogen complexes of the above charge transfer materials are the specific substrate of the instant invention. By the term halogen is meant bromine, chlorine, and iodine as well as the corresponding interhalogen compounds BrCl, IBr, 1G1, and the like.
One aspect of the present invention is the recognition that such halogen charge transfer complexes can be utilized as a substrate for coated crystal detectors. Coatings or substrates of such charge transfer complexes are not sensitive to moisture and retain the complex halogen rather tenaciously. At the same time the properties of the complex halogen do not differ from that of free halogen substantially. Thus, halogen complexes of charge transfer materials undergo essentially the same reactions as uncomplexed halogens. Thus, a material which is capable of being halogenated can be readily detected by a responsive material containing a coating of this invention. For example, olefins represent a class of compounds that are readily halogenated and to which the substrate of the instant invention is particularly sensitive.
The amount of substrate that is employed is a significant variable in the invention. Its volume in relation to the volume of the crystal and its weight are of particular importance in determining the response of the detector.
The amount of substrate generally used covers the range of from about 1 to about 100 micrograms per square centimeter of responsive material. Larger amounts can be used but difficulty is then encountered in maintaining the responsive material in a condition of stable oscillation. Therefore, the amount often is chosen experimentally for the best compromise.
As stated previously, quartz is the particular crystal most often employed in electrical applications and is the preferred crystal employed in the present invention. Generally, the crystal has a diameter of about 1.2 centimeters and a thickness of about 0.16 centimeters.
it is preferred in the present invention that the coating of substrate be located essentially uniformly in the region or vicinity of maximum oscillation in the responsive material. The particular area of maximum oscillation of the responsive material will be apparent to one skilled in the art. A responsive material of the dimensions previously mentioned and having electrodes that contact opposite faces of the crystal would have a substrate located over one of the electrodes. The substrate, of course, could extend beyond the borders of the electrode and indeed it could cover the entire responsive material. Covering the entire responsive material, however, can be wasteful of substrate and it is not necessary.
There are various techniques for applying the substrate of the instant invention on the crystal. For example, the halogen complex of the charge transfer material can be dissolved in a suitable solvent and painted on the crystal. After applying the solution to the crystal, the solvent can be evaporated. Similarly, suspensions of the substrate can be employed.
Solvents particularly useful in dissolving transfer materials of the type herein specified include the following: propylene carbonate, dimethylsulfoxide and dimethyl formamide. Useful liquids for suspending substrate material include the following: benzene, toluene and water.
The crystal type that is described above can be eniployed in a typical oscillator circuit such as that shown in the figure. Specifically, the circuit is a Pierce oscillator which is essentially a Colpitts oscillator having inductance capacitance tank circuit replaced by the quartz crystal. B+ voltage is applied across the cathode and the plate of the triode. The value may be adjusted by varying the potentiometer R-l so as to obtain ap proximately 1.34 volts across R-3. This voltage opposes the mercury cell resulting in zero potential to the recorder. Thus, the recorder measures a signal proportional to the changes in the grid bias. This grid bias directly reflects changes in amplitude of vibration of the crystal. The radio frequency choke (RFC) and the capacity Cl prevent the radio frequency current from entering the direct current power supply. Capacity C-2 keeps the radio frequency signal out of the recorder. The crystal is connected directly between the grid and the plate, and the amount of feedback is dependent on the interelectrode and stray capacitances between the grid and the cathode and the properties of the crystal. This feedback and the setting of R-l determine the amplitude of vibration of the crystal. The plate to cathode capacitance is shown in the circuit by means of dotted lines. Resistors R-2 and R-3 serve as the grid leak bias. The 10 millivolt recorder (connected to attenuator A) observes only changes in the amplitude of vibration.
In operation materials capable of being halogenated are detected when a fluid containing such materials is contacted with the crystal of the present invention employed in such typical circuit. By measuring the change in frequency of the crystal, change in weight in the substrate is measured. This, of course, indicates that halogenation has occurred. in other words, the material susceptible or capable of being halogenated has been detected in the fluid material.
EXAMPLE l A detection device of the invention with the bromine complex of polyvinylpyridine was tested with respect to its response for detecting olefins.
For the purpose of this test a gas containing 300 ppm of propylene in nitrogen was passed over the detector at a rate of about cc/min. The gas mixture was heated to a temperature of about F. prior to feeding it into the analyzer. The analyzer was similar to that shown in the figure. The detectors initial stabilized frequency was noted and then the flow of test gas was begun. Upon contact with the test gas an immediate increase in the frequency was observed indicating that the olefin was halogenated and the crystal substrate therefore lost weight. The change in frequency with time is shown in Table I below.
TABLE I Contact Time (Minutes) Change in Frequency (Cycles) Start 2 58 4 v 98 6 I17 EXAMPLE 2 The procedure outlined in Example 1 was followed except that 100 percent propylene was the test gas. In this environment a decrease in frequency from the normal frequency of the crystal was observed apparently due to absorption by the substrate of the brominated propylene. Intermittent purging with nitrogen however resulted in an increase in the frequency indicating that halogenation had occurred and demonstrating that the detector could be returned to a stable condition andbe repeatedly used. The results of this test are outlined in Table II below.
TABLE II Gas Time, Minutes Change in Frequency (Cycles) N, Start Propylene l 16 Propylene l 23 N 5 0 Propylene 2 -84 Propylene 7 l00 6 (4-vinyl-pyridine), poly (2-vinylpyridine) and poly(N- vinyl carbazole).
5. The element of claim 1 wherein the charge transfer material is poly (4-vinylpyridine).
6. The element of claim 1 wherein the halogen is se lected from the group consisting of bromine, chlorine, iodine, iodine chloride, bromine iodide and bromine chloride.
7. The element of claim 1 wherein the halogen is bromine.
8. In an apparatus for the detection of fluids wherein an electronic oscillation means is controlled by a responsive material in which the surface of said material is coated with the substrate subjected to contact with the test fluid, the improvement wherein the substrate material comprises a halogen complex of a polymeric charge transfer material having a nitrogen atom in the repeating unit of the polymer.
9. The improvementof claim 8 wherein the halogen is selected from the group consisting of bromine, chlorine, iodine and inter-halogen compounds.
10. The improvement of claim 8 wherein the charge transfer material is selected from the group consisting of poly (2-vinylpyridine), poly (4-vinylpyridine) and poly (N-vinyl carbazole).
11. A method of detecting materials capable of being halogenated comprising contacting a test fluid with a coated piezoelectric detector, said detector having a coating of a halogen complex of a polymeric charge transfer material having a nitrogen atom in the repeating unit of the polymer, and measuring the change in electrical response of such coated piezoelectric crystal detector.
12. The method of claim 11 wherein the test fluid contains an olefin.
13. The method of claim 11 wherein halogen is bromine and the charge transfer complex is poly (4- vinylpyridine).