# Value of platinum in old aircraft spark plugs?



## hyderconsulting (Jun 8, 2007)

I was contacted tonight by a person who says they have 200 aircraft engine spark plugs of WWII vintage and wants to know how much platinum they have in them. Does anyone have an idea? Regards, Chris Hyder.


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## Harold_V (Jun 8, 2007)

I'm not convinced there's a ready answer. I've processed a number of them, but how they're made varies so much that without having them in my possession, it would be difficult to say. My experience with them was many years ago, and I included the values in my waste materials-----I did not recover them directly. As a result, I have no idea what the yield was. 

I would suggest sorting them by manufacturer, or design, then, using a lathe (if you have one at your disposal), parting off the end of the ground electrode such that you take a little of the steel with the platinum, and then part off the center electrode, same way. As I recall, the platinum in the center is a short piece imbedded in the steel. By cutting them apart as I suggested, you can then dissolve the remaining steel in HCL with ease, leaving behind the values. Do one of each style to determine the yield. 

Don't expect them to contain much platinum----although that's not intended to discourage you. They are worth processing, but it takes a large number of them to yield an ounce. I would expect you'd have about a half ounce in 200 plugs. 

Please let us know what you discover if you explore them. 

Harold


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## aflacglobal (Jun 8, 2007)

Not really sure that the tech programs of that period were really as advanced as today. So alloys and processes of that time may tell you something.

Let's see.

A spark plug is made of a center electrode, an insulator, a metal casing or shell, and a side electrode (also called a ground electrode). The center electrode is a thick metal wire that lies lengthwise within the plug and conducts electricity from the ignition cable hooked to one end of the plug to the electrode gap at the other end. The insulator is a ceramic casing that surrounds much of the center electrode; both the upper and lower portions of the center electrode remain exposed. The metal casing or shell is a hexagon-shaped shell with threads, which allow the spark plug to be installed into a tapped socket in the engine cylinder head. The side electrode is a short, thick wire made of nickel alloy that is connected to the metal shell and extends toward the center electrode. The tips of the side and center electrodes are about 0.020 - 0.080 inch apart from each other (depending on the type of engine), creating the gap for the spark to jump across.

The electrodes in a spark plug typically consist of high-nickel alloys, while the insulator is generally made of aluminum oxide ceramic and the shell is made of steel wire.

Selection of materials for both the electrodes and the insulator have consumed much research and development time and cost. One major spark plug manufacturer claims to have tested 2,000 electrode materials and over 25,000 insulator combinations. As electrodes erode, the gap between them widens, and it takes more voltage than the ignition system can provide to fire them. High-nickel alloys have been improved and thicker electrodes have been used to reduce engine performance loss. In addition, precious and exotic metals are increasingly being used by manufacturers. Many modern plugs feature silver, gold, and platinum in the electrodes, not to mention center electrodes with copper cores. Silver has superior thermal conductivity over other electrode metals, while platinum has excellent corrosion resistance.

The Manufacturing
Process
Each major element of the spark plug—the center electrode, the side electrode, the insulator, and the shell—is manufactured in a continuous in-line assembly process. Then, the side electrode is attached to the shell and the center electrode is fitted inside the insulator. Finally, the major parts are assembled into a single unit.

Shell
1 The one-piece spark plug shells can be made in several ways. When solid steel wire is used, the steel can be cold-formed, whereby coils of steel are formed and molded at relatively low temperatures. Or, the steel can be extruded, a process in which the metal is heated and then pushed through a shaped orifice (called a die) to produce the proper hollow shape. Shells can also be made from bars of steel that are fed into automatic screw machines. These machines completely form the shell, drill the hole through it, and ream it—a process that improves the finish of the drilled hole and makes the size of the hole more exact. 

2 The formed or extruded shells—called blanks until they're molded into their final shapes—require secondary operations to be performed on them, such as machining and knurling. Knurling a shell blank involves passing it through hard, patterned rollers, which form a series of ridges on the outside of the blank. Similarly, machining-—in which machine tools cut into the exterior of the shell blank—generates shapes and contours on the outside of the shell. The shells are now in their final shape and are complete except for threads and side electrodes. 
Side electrode

3 The side electrode is made of a nickel alloy wire, which is fed from rolls into an electric welder, straightened, and welded to the shell. It is then cut to the proper length. Finally, the side electrode is given a partial bend; it is given its final bend after the rest of the plug assembly is in place. 

4 The threads are then rolled on the shells. Now complete, the shells are usually given a permanent and protective silvery finish by an electrolytic process. In this process, the shell is placed in a solution of acids, salts, or alkalis, and an electrical current is passed through the solution. The result is a thin metal coating applied evenly over the shell. 
Insulator

5 Insulators are supplied from stock storage. Ceramic material for the insulator in liquid form is first poured into rubber molds. Special presses automatically apply hydraulic pressure to produce unfired insulator blanks. The dimensions of the bore—the hollow part of the insulator—into which the center electrodes will be pressed are rigidly controlled. 

6 Special contour grinding machines give the pressed insulator blanks their final exterior shape before the insulators are fired in a tunnel kiln to temperatures in excess of 2,700 degrees Fahrenheit. The computer-controlled process produces insulators that are uniformly strong, dense, and resistive to moisture. The insulators may be fired again after identifying marks and a glaze are applied. 
Center electrode

7 The nickel alloy center electrode is first electrically welded to the basic steel terminal stud, a narrow metal wire that runs from the middle of the plug to the lower end (the opposite end from the electrode gap). The terminal stud is attached to a nut, which in turn is attached to the ignition cable that supplies the electric current to the plug. 

8 The center electrode/terminal stud assembly is sealed into the insulator and tamped under extreme pressure. Insulator assemblies are then sealed in the metal shell under 6,000 pounds pressure. After reaming to correct depth and angle, the rim or edge of the shell—called the flange—is bent or crimped to complete a gas-tight seal. Spark plug gaskets from stock are crimped over the plug body so that they won't fall off. 

9 To form the proper gap between the two electrodes, the center electrode of the now completely assembled spark plug is machine-trimmed to specifications, and the ground electrode is given a final bend.

Ralph


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## hyderconsulting (Jun 8, 2007)

Thanks for the replies, guys, and the technical info and estimate on value. I'm not sure if this guy wants to sell the spark plugs or not. If he presses me for a firmer idea on the value I will tell him to list the plugs so they can be identified as to content. From the technical info I think I will start saving plugs and see about breaking them up to recover the electrodes. For one thing nickel and its alloys are realing getting high in price and it would add up some. Regards, Chris Hyder.


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