RHODIUM ALLOYS

Abstract

Disclosed is a rhodium alloy including: rhodium; one or more elements selected from the group consisting of iridium, platinum, palladium and ruthenium; and one or more elements selected from the group consisting of yttrium, zirconium and samarium. The alloy includes a greater quantity of rhodium as compared to any other individual element of the alloy. Also disclosed is an electrode, as well as a spark plug, including the claimed rhodium alloy.

Claims

1-9. (canceled)

10. A rhodium alloy comprising: a) rhodium; b) one or more elements selected from the group consisting of iridium, platinum, palladium and ruthenium; and c) about 0.01 to about 0.5 wt % each of any one or more elements selected from the group consisting of yttrium, zirconium and samarium; wherein the alloy comprises a greater quantity of rhodium as compared to any other individual element of the alloy.

11. A rhodium alloy according to claim 10, wherein the alloy comprises: a) about 50 wt % or more of rhodium; b) up to about 49.99 wt % each of any one or more elements selected from the group consisting of iridium, platinum and palladium; c) up to about 35 wt % of ruthenium; d) up to about 5 wt % each of any one or more elements selected from the group consisting of niobium, tantalum, titanium, chromium, molybdenum, cobalt, rhenium, vanadium, aluminium, hafnium and tungsten; and e) about 0.01 to about 0.5 wt % each of any one or more elements selected from the group consisting of yttrium, zirconium and samarium; wherein the rhodium alloy comprises at least one of iridium, platinum, palladium or ruthenium; and wherein the total wt % of the rhodium alloy adds up to 100 wt %.

12. A rhodium alloy according to claim 11, wherein the alloy comprises: a) about 75 to about 95 wt % of rhodium; b) about 15 to about 25 wt % each of any one or more elements selected from the group consisting of iridium, platinum and palladium; c) 0 wt % of ruthenium; d) about 0.01 to about 5 wt % each of any one or more elements selected from the group consisting of niobium, tantalum, titanium, chromium, molybdenum, cobalt, rhenium, vanadium, aluminium, hafnium and tungsten; and e) about 0.01 to about 0.50 wt % each of any one or more elements selected from the group consisting of yttrium, zirconium and samarium; wherein the total wt % of the rhodium alloy adds up to 100 wt %.

13. A rhodium alloy according to claim 11, wherein the alloy comprises: a) about 50 to about 95 wt % of rhodium; b) up to about 45 wt % each of any one or more elements selected from the group consisting of iridium, platinum and palladium; c) about 1 to about 35 wt % of ruthenium; d) up to about 5 wt % each of any one or more elements selected from the group consisting of niobium, tantalum, titanium, chromium, molybdenum, cobalt, rhenium, vanadium, aluminium, hafnium and tungsten; and e) about 0.01 to about 0.50 wt % each of any one or more elements selected from the group consisting of yttrium, zirconium and samarium; wherein the total wt % of the rhodium alloy adds up to 100 wt %.

14. A rhodium alloy according to claim 11, wherein the alloy is selected from the group consisting of: TABLE-US-00004 Rh Ir Ru Cr W Zr Alloy (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 1 80 19.86 0 0 0.1 0.04 2 90 0 9.86 0 0.1 0.04 3 80 19.46 0 0.20 0.30 0.04 4 70 9.86 20 0 0.10 0.04

15. A spark ignition electrode comprising a rhodium alloy according to claim 10.

16. A spark plug comprising an electrode according to claim 15.

17. A spark ignition electrode comprising a rhodium alloy according to claim 11.

18. A spark ignition electrode comprising a rhodium alloy according to claim 12.

19. A spark ignition electrode comprising a rhodium alloy according to claim 13.

20. A spark ignition electrode comprising a rhodium alloy according to claim 14.

Description

[0064] The invention will now be described by way of the following non-limiting Examples and with reference to the accompanying figures in which:

[0065] FIG. 1 illustrates the oxidation performance of rhodium alloys of the present invention at 850° C.

[0066] FIG. 2 illustrates the oxidation performance of rhodium alloys of the present invention at 1000° C.

[0067] FIG. 3 illustrates the oxidation performance of rhodium alloys of the present invention at 1100° C.

[0068] FIG. 4 illustrates the oxidation performance of iridium at 1100° C.

[0069] FIG. 5 illustrates the overall weight loss per hour of the rhodium alloys of the present invention at temperatures between 800° C. and 1100° C.

EXAMPLES

Example 1

Alloy Preparation

[0070] The rhodium alloys detailed in Table 1 below are prepared by argon arc melting. All values are given in weight percent (wt %) based on the total weight of the alloy.

TABLE-US-00002 TABLE 1 Rh Ir Ru Cr W Zr Alloy (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 1 80 19.86 0 0 0.1 0.04 2 90 0 9.86 0 0.1 0.04 3 80 19.46 0 0.20 0.30 0.04 4 70 9.86 20 0 0.10 0.04

[0071] Each alloy is subsequently processed to produce wire having a 2 mm diameter.

Example 2

Oxidation Testing

[0072] The oxidation performance of the alloys is assessed as followed: [0073] 1. Wire at 2 mm diameter is cut into straight lengths of approx. 120 mm. [0074] 2. The wire samples are weighed to 4 decimal places on an enclosed set of scales and diameter measured at 5 points along each length. The average diameter is noted. [0075] 3. Wire samples from several different alloys are placed in a notched alumina based ceramic furnace tray. [0076] The positional order is randomised with the slot number for each sample being noted. [0077] Two samples are tested from at least some of the batches. [0078] Both measures are intended to check for any effect due to positional variation within the test furnace. [0079] 4. A laboratory heat treatment furnace (in this case of work zone 150×150×200 mm) is set to the required test temperature. [0080] 5. Once stabilised, the furnace tray is placed into the centre of the furnace; date and time are noted. [0081] 6. After a suitable interval the furnace tray is removed from the furnace and allowed to cool naturally. [0082] 7. Each wire sample is weight checked and the weight noted. [0083] 8. The furnace tray is returned to the heat treatment furnace maintaining the same orientation. [0084] 9. Sample weights are checked at least 3 times over the duration of the test: typical duration is 350-400 hrs.; date and time are noted. [0085] 10. On completion the final diameter is measured, calculated and noted as above. [0086] 11. Times and measurements are transferred to spread sheet and the oxidative weight loss curves calculated using weight change and weight change per unit surface area.

[0087] The results of the oxidation performance of the rhodium alloys of the present invention at temperature of 850° C., 1000° C. and 1100° C. are shown in FIG. 1-3. FIG. 5 illustrates the overall weight loss per hour of the rhodium alloys of the present invention at temperatures between 800° C. and 1100° C.

[0088] Metal loss through vaporisation occurs for iridium and this is clearly shown in FIGS. 4 and 5 for the Ir graph which has the steepest negative gradient.

[0089] The rhodium alloys of the present invention exhibit comparable or improved properties in comparison to rhodium metal. The rhodium alloys also demonstrate a resistance to weight loss at higher temperatures, unlike iridium metal which exhibits a weight loss of over an order of magnitude greater than the present alloys.

Example 3

Electrode Studies

[0090] The rhodium alloys of the present invention, an iridium standard and a rhodium standard are cut into electrode wire having 1 mm diameter. The wires are fixed into a four station test cell together with matching 3 mm diameter Ir earth electrodes and the gap between them adjusted and set with a vernier calliper. The test electrodes are set at negative polarity and the earth electrode as positive to concentrate erosion on the appropriate electrodes.

[0091] Testing commences with a 10 kV electric pulse driven by an automotive ignition coil being applied to each pair of electrodes at 200 Hz. This initiates a continuous series of rapid spark discharges between the electrodes as generated in a typical automotive engine. The test cell is visually checked at intervals to confirm functionality and after approximately 250 hr. the discharge is stopped and the electrode gap re-measured. A counter initiated at test commencement is used to measure elapsed time from which the number of spark discharges can be calculated.

[0092] The electrodes are reset in the test cell and discharge re-initiated. After a further approximately 250 hr. (approx. 500 hrs discharge time in total) the test is stopped and the same procedure of gap measurement and electrode inspection completed.

Test Duration

[0093] The test duration and approximate number of sparks were calculated. Therefore, for a 20 day test: [0094] 20 days×24 hrs/day=480 hrs [0095] 480 hrs×3600 seconds/hr=1,728,000 seconds [0096] 1,728,000 seconds×200 sparks/second=345,600,000 sparks (per test point)

TABLE-US-00003 Measurements of Gaps Test gap - negative electrode Startpoint Midpoint Endpoint Gap Growth Gap (mm) Gap (mm) Gap (mm) (mm) 100% Ir 8.2 8.6 8.9 0.7 (comparative) 100% Rh 8.1 8.2 8.4 0.3 (comparative) Alloy 1 8.2 8.3 8.5 0.3 Alloy 3 8.1 8.2 8.3 0.2 Alloy 4 8.0 8.1 8.2 0.2

[0097] The 100% Ir electrode exhibits the worst (greatest) erosion, the gap measurement changing by 0.7 mm+/−0.1 mm over the test duration.

[0098] The 100% Rh and Alloy 1, 3 and 4 electrodes exhibit less erosion that the 100% Ir electrode. The Alloy 1 electrode exhibits comparable erosion to the 100% Rh electrode, the gap measurement changing by 0.3 mm+/−0.1 mm over the test duration.

[0099] Alloys 3 and 4 exhibit the least erosion as the gap measurement changed by 0.2 mm+/−0.1 mm for each alloy over the test duration. Alloys 3 and 4 therefore are more resistant to erosion and demonstrate greater resistance than both 100% rhodium and 100% iridium electrodes.