DYNAMIC PRECIOUS METAL ASSAY DEVICE

Abstract: A dynamic precious metal assaying device comprising a syringe (4) containing a reference cathode half cell (6) at a first end of the syringe and an electrolyte (3), an anode which is the specimen under test, a plunger (1) attached to a piston (2) located within the syringe at a second end of the syringe, an exit nozzle (9) located at the first end of the syringe below the cathode half cell, and wires connecting the cathode and the anode to a current generator and a voltage monitor respectively.

Description: Dynamic Precϊous Meta I Assay Devicβ BACKGROUND OF THE INVENTION Though there are many quantitative and qual itative techniques employing physical and general chemistry to assay precious metals, these are al l too sophisticated for most jewelers. For example, a method employed by most jewelers to determine the purity of the gold al loy is to use a series of standard gold penci ls and compare the results of a scratch test using said penci ls with a gold specimen to be assayed. In such a technique, the jeweler has gold rods of 8 karat, 10 karat, 12 karat, 14 karat, 16 karat, and 18 karat compos ition and an abrasive stone. He scratches the gold specimen under test on the stone and adjac nt to that scratch he scratches the gol d penci l s on said stone . After treating the stone with an acid and comparing the color of the specimen scratch with the color of the gol penci l scratches, he visual ly estimates the qual ity of the specimen in karats. This highly inaccurate system is strongly dependent on th t chnique and abi l ity of the j e ler employing the test. In contrast, the proposed invention employs t e latest e lectronic devices to make a chemica l l y dynami c test of the pur ity of prec ious eta l s . Op rator techn i que i s a m i nor consid ration. The proposed invention uses electro¬ chemistry in combination with current metering and ti e dependent circuits in a simple, hand-held device. The anode of this e lectro-che ical system is the material under test and the cathode is the reference material . A metered current causes an electro-chemical reaction at the anode and after the curr nt-induced electro-chemical r action is terminated , the e lectromotive force is monitored as a function of ti e. The time dependent decay of the potential difference of the ce l l so created is indicative of the purity of the precious metals under test. Though the embodiment of the proposed system is to assay gold , it has been determi ned that the same techn ique can be used for a l loys of other pr cious metals. The system is s l f-contained and uses an acid- f i l led syr inge for testing whi ch a l so contains the reference catnoce. Said syringe is wired to control e l ctronics which as appropri ate circu i try for accurately metering a current and activating electronic switches to terminate said current and to monitor the potential decay. In addition, the electronics has micro-processors and memory circuits to conveniently operate either an analog or digital display indicating the purity in units of measure fami l iar to the operator. SUMMARY OF INVENTION As mentioned above, this dynamic testing system is amenable to the assay of al l precious metals, but the embodiment is directed to the testing the purity of gold. The invention uses an electric c l l comprised of a reference cathode of platinum and an- anode which is the specimen under test. The electrolyte Is a 1- 1 /T. HCL solution. The electrolyte and the reference cathode is contained in a syringe. A wire is connected to the reference cathode. Th syringe has a 2 mi l l imet r diameter hole at its bottom. The bottom of the syringe Is placed so the hole contacts the anode specimen In such a mann r that t electrolyte wets said anode through the hole. The specimen Is wired by means of a cl ip to the circuitry. After the electrochemical cel l is completed by making wet contacts between the syringe and the specimen anode with cl ip attached to said anode, the circuitry is initiated by pressing a start switch. A current pu ls of 3.5 mi l l lamps of about 4 seconds duration Is driven Into the system at an appropriate voltage level . On a microscopic level , el ctrons from the current generate ions between the electrodes and cause simultaneous oxidation and reduction to occur on said electrodes. The amount of oxidation and reduction which occurs is a function of t e purity of the e lectrod s. The precious metal s are re lative l y Inactive. The elements added to al loy the precious metals are copper, tin and other such metals which are chemica l l y active. W en the cur nt pu l se is terminated, the ions that are present in the solution is indicative of the electrochemical ly induced reaction with the specimen anode. The system is now charged up. The electronics then switches from the current mode to a voltage monitoring mode. As showing in figure 1 , the voltag d cays xponential ly during the first few seconds to its equi l ibriur- asy otote. Figure 1 shows the curves for gol of particular purities. The upper curve, curve number 1, shows the dynamic behavior for gold with a higher purity than for the gold in curve number 2. By sampl ing the voltages as a function of time and comparing the potential values and the slope of the voltage decay versus ti e with an electronic look-up table, a microprocessor can interpolate the decay curves to evaluate the percentage of gold in the specimen and display its evaluation in units of karats. Because of the critical interdependence of the current pulse and the electronic look-up tables, it has been determined that a current level in the range of 3 to 4 mi I I lamps wi l l produce voltage curve for high purity gold which decays from 5 volts to 1.4 volts and a voltage curve for low purity gold which decays from .7 volts to 0.2 volts. The current pulse is maintained for about 3.5 seconds. The test probe, shown in figure 2 comprises a syringe of glass or plastic. When the plunger of the syringe is depressed, a drop of electrolyte acid emerges from the tip to wet the test sample and complete the cel l . The fundamental control and measuring circuits are block d iagrammed in Figure 3. Figures 4 and 5 are modifications of Figure 3. There is a start button which resets al l the circuits and initiates the timer. There is a timer that controls the current pulse. A current generator l imits the value of the current. When the current pulse is terminated, a timer monitors the voltage decay. There are Sample and Hold circuits which work in conjunction with the analog to digital voltage converter. The analog to digital voltage converter has an output which is compared with memory, and a microprocessor i nterpo l ates the resu l t. The interpolation is then fed into the digita l display system which displays the assay of the material . B cause this is a dynamic testing system with many variables, the memory information must be obtained empirical ly for each precious metal . As asymptotic test point at about 1 second after the current pulse has been terminated has been determined for several materials relative to a platinum cathode which is shown in table. 1 below. It is also possible increase the accuracy by using several referenced points. TABLE 1 SILVER or GOLD PLATING 250 TO 380 6-7 Kt. 420 to 460 8 Kt. 470 to 515 9 Kt. 520 to 560 10 Kt. 570 to 610 11 Kt. 615 to 630 12 Kt. 635 to 660 13-14 Kt. 680 to 830 14 Kt. Plumb 840 to 870 18-20 Kt. 1000 to 1200 P I at I num 1300 to 1400 DESCRIPTION OF DRAWINGS FIGURE 1 shows a profi le of voltage versus time of the lectrochemical cel l . FIGURE 2 shows the mechanical parts of the test probe. FIGURE 3 shows the detai led box diagram of the c I rcu i try. FIGURE 4 shows a version of the electronics without logic processing. FIGURE 5 shows a version of the electronics with logic processing. EMBODIMENT The embodiment of a Dynami c Go l d Assay Device consists of the test syringe, the specimen anode, and the electronic circuitry. In Figure 2, the test syringe is i l l ustrated. The test syr inge has a p l unger , 1 , which is attached to the piston, 2, which is snuggly fitted to the inside diameter of the cyl indrical wal ls, 4, of the test syringe. A 1 \ J7% hydroch loric acid so l ut ion i s used as an e l ectro l yte , 3 , wh i ch i s contained within the cyl indr ica l wa l ls , 4, and the piston , 2, of the p l unger . At t lower end of the syringe is the cathode half-cel l , 5. The hal f-cel l is shown to have a reduced diameter cyl indrical wal l and to contain a platinum cathode, 6, with a wire, 7, attached and penetrating said half-cel l wal l through a seal , 8, which is impervious to the electrolyte. The platinum cathode, 6, Is a thin cyl inder of high purity platinum which is approximately 8 mi l l imeters long and about 1 centimeter i n diameter . At th bottom end of the syringe there is a hole on axis which serves as aa nozz le , 9. The nozz le is about 2 mi l l imeters in diameter. The nominal length of the syringe with the plunger fu l ly depressed is about 10 centimeters, and of such a diameter as to be conveniently he ld, as one holds a penci l . By a sl ight depression of the plunger, 1 , a sma I I amount of electrol yte, 3, is exp l led from the nozz le, 9, to wet a specimen anode. The wire lead, 7, is connected into the electroni'cs to be described later. The specimen anode is also connected to said e lectronics and the speci en anode, when made wet by the electrolyte which is maintaining a contact through the nozz le with the half-cel l , produces an electro-chemical reaction which is monitored by the electronics. Figure 3 shows a box diagram of the electronics. There are many we I I known circuits which wi I I generate the functions i l lustrated in Figure 3, examples of these are shown in Figures 4 and 5. The chassis, 15, contains the ci rcu itry for the invent ion . There i s a start switch, 16, which resets al l th circuits and initiates a timer , 17. The timer a l so contains e lectronic switches. The timer activates the current generator , 18, which wi l l output a 3.5 mi l l iamp current for 4 seconds. At the end of said 4 seconds, the timer, 17, then initiates the voltage monitor, 19, to fol low the aforementioned voltage decay of the specimen under test, 20, In respect to the reference cathode connected to wire lead, 7. The specimen anode is connected to the voltage monitor by a cl ip lead wire, 21, 1 second after the current pulse was terminated by the timer, 17, a Sample and Hol circuit, 22, opens a window and an analog to digital conv rter, 23, processes t e information through a digital format which may then be compared with information stored In the look-up table, 24. The results of the interpolation that occurs in the look-up table, 24, is transmitted to the digital display, 25. Th digital display reads out in som convenient metric. The circuit referred to as the look-up table, 24, can contain a icro-processor in conjunction with the dedicated memory which not only interpolates, but can also compute time derivatives for comparison with the memory system. By such information processing, both the values of th voltages and the slop of the voltage decay may be used as a dynamic sampl ing of the electro¬ chemical reactions. The Figures 4 and 5 show different configurations of electronic chassis components which have been produced. Figure 4 shows a system without a data processing circuit, 24, and Figure 5 shows a configuration with said logic processing system, 24. To determine the purity of a gold sample, the specimen is connected to the cl ip lead wire which goes into the chassis. The nozzle of the test syringe which is also connected to the chassis Is placed in contact with the specimen under test. By a sl ight depression of the plunger a drop of electrolyte is expel led from the nozzle of the test syringe which makes a wet connection of the test specimen Into the half-cel l within the syringe. The contact of the nozzle to the specimen is maintained whi le the start switch is depressed. The electronics puts the curr nt switch from anode to cathode for about 4 seconds. The cel ls is thus charged up by the current pulse and the decay of the potential difterence that exists between the anode and cathode is monitored for another 1 second. At the end of the 1 second monitoring p riod, the asymptodic voltage is compared in a memory device within the chassis and a digital read-out displays the purity of the gold sample under test.

Claims: CLAIMS We claim a Dynamic Precious Metals Assaying Device compr i s i ng: 1. A syringe, a electrolyte, a reference cathode, a specimen anode, and ci rcu itry with a pai r of lead wires in said syringe, a plunger which acts as a piston within a cyl indrical wal l on one extremity and at the distal end a half-cel l with said reference cathode and a exit nozzle and one of the pair of wires connected to sa i d reference e l ectrode sa i d e l ectro l yte be i ng contai ned i n said syri ng and another ha l f-ce l l of specimen anode which is wetted by sai d e lectrol yte within said syringe by depressing said plunger and said specimen anode connected to the other wire pai r, both wires connected to said circuitry of a timer, a current generator, a analog to digital converter, and a display sai d t i er meter i ng a current from sa i d current generator into said reference cathode and test anode, then said timer switching off said current generator and switchi ng on said ana log to di gi ta l converter , said analog to digital converter sampl ing a voltage decay relative to said reference cathode and specimen anode and converting said information for a display on said digital display wherein values displayed is indicative of the pur ity of sai d specimen anode re l at ive to reference cathode.

Inventors: MEDVINSKY BORIS, RADOMYSHELSKY LEONID, MEDVINSKY, BORIS, RADOMYSHELSKY, LEONID
Applicants: TRI ELECTRONICS INC, TRI-ELECTRONICS, INC.
Application year: 1988
Main classification: G01N27
IPC codes: G01N17, G01N27, G01N33