Does anyone have experience with cyanide-free silver plating? How does it compare?
Second question, does anyone know how to go about getting potassium cyanide in the UK? You used to be able to get it from a chemist's shop by signing a poisons register, but I don't know if that still holds - and chemists don't seem to sell that kind of thing any more.
You'd need to go to a wholesaling laboratory supplies chemists. Have a look in Yellow Pages, they are usually listed in there.
Domestic Chemists have been restricted in what they can carry now by their suppliers like Vantage and Unichem.
Peter
I remember in the dim & distant past (I was about 15 at the time) silvering a mirror for an ancient Thornton Pickard camera using a cyanide-free process - involved the use of silver nitrate, but beyond that, I can't recall the ingredients or recipe.
It produced a usable (but not wonderful) mirror.
Whats the application? I seem to recall that mirrors are mostly made by vacuum deposition of aluminium these days - you may be able to get someone to do it for you fairly cheaply.
Regards, Tony
Recently, in anticipation of working on a boiler, I approached my local chemist, which is part of a large chain, (A "Polymer" of chemists, perhaps?) to enquire about the possibility of getting some conc. sulphuric acid.
They said that they could get me _ANY_ chemical provided that I could provide incontrovertible evidence of who I was and accompanying evidence of my bona-fide need for it. (Although I doubt that membership of Al Q'Aeda would be taken as a bona-fide reason for wanting supplies of sulphur, saltpetre and powdered carbon!)
Interesting. My local chemist is an "Ideal".
That would probably be a chemical deposition, rather than electrochemical, either the dextrose reduction process (which you may have seen demonstrated in chemistry class), or the Rochelle salt process. The latter gives a better film, but takes longer, hours rather than minutes.
Yes. It doesn't stick very well.
Plating the insides of the LOX pump part of a small rocket turbopump. The parts are made of inconel and 316L stainless, so silver plating them is going to be - interesting. The plating has to be rather thick too, about 250 microns, much thicker than any chemical deposition process can manage.
Interesting - why do you need to do that then ?
Because the parts are moving very fast, about 120 m/s. If there are any small particles in the LOX when they hit they can perhaps ignite the metal surface, even stainless steel or inconel - silver won't ignite under those conditions though.
Stainless is okay for the rest, piping and the like, when the LOX isn't moving so fast and the impact energy is lower.
Heck, they make the LOX tanks of rockets out of ally, which is highly reactive - but the impact energy to ignite it isn't there.
Yes, the recipe included dextrose.
Not badly on glass, but I don't doubt that the abrasion resistance would not have been good.
Why the need for the silver plating?
Regards, Tony
Scary stuff...remind me to be a couple of counties away from you when you try it out the first time
Regards, Tony
Given the base material(s) upon which you are depositiing the silver, you might look at multiple layers. For instance, if you can get copper to stick to your base metals, then putting silver onto the copper should be fairly straight forward. Copper has several advantages since you can plate it onto almost anything, it builds quickly, and polishes up reasonably well. Another possibility is to plate nickel onto the base metals and then silver.
While the dextrose reduction process does not adhere to glass very well, nothing else does either. It may be that this process nmay give you acceptable results on top of copper or nickel.
Well I never knew that ! :-)
So why is silver special in this regard dyk ? And where did you find all this significant* esoterica out ?
Bear in mind that silver is a soft metal, so if there are solid particles in the LOX the silver may be abraded fairly quickly.
Cliff Coggin Kent UK
Who's dyk?
Silver is special because it doesn't burn - the reaction with the lox isn't energetic enough to spread. Whereas the reaction between lox and steel is much more energetic, and can be .. spectacular. Ever seen a Bessemer converter going?
Googling, asking on newsgroups, then in libraries. Took a bit of doing, the turbopump mafia like to keep their secrets, but some stuff does get published.
Sadly you can't plate copper directly onto stainless or inconel (or even steel) - but you can use a thin "strike" coating of nickel, and plate on top of that.
Tom wrote:
It doesn't have one.
I considered a volute casing Barske-type impellor pump, but it would be very inefficient as the pump is so small, so I will be using a double Pitot [1] design instead (unless I can't get it to work, when I will fall back to a Barske design, or perhaps try a two-shaft-Quimby-type screw pump).
The Pitot arm is 32 mm dia, there are four pumps [2], a combuster and a turbine on a single 75,000 rpm shaft in an assembly 54 mm max dia and 65 mm long, target weight ~350 grams.
Propellant flow is 175 grams per second. Shaft power is 2.1 kW, pump mechanical efficiency should be ~ 55%, turbopump overall efficiency ~25%, LOX output pressure is 750 psi.
Engine design thrust is 5kN / 100 lb sea level, chamber pressure is 600 psi, expansion ratio is 8.25, Isp is 245 s sea level, 285 s vaccuum.
Note that most of these figures are still theory, and they will almost certainly change a bit in practice. Note also that the design is slightly less demanding than the engineering presently (apart from the pumps) used in small model turbojets, and I hope to improve on those figures.
[1] A Pitot pump is a hollow stationary arm with a Pitot tube inside opening on the end, which is inside a hollow circular casing which spins and accelerates the liquid inside it - the fast-moving liquid enters the pitot and the speed is changed to pressure. Also, the spinning exerts a centrifugal force on the liquid, increasing it's pressure at the outer edge of the casing where the Pitot is located. A double Pitot pump just has two Pitot holes on opposite ends of a single stationary arm.It can be more efficient than an impellor pump because the wetted moving area is smaller, and there are no fast-moving parts in close proximity to give large shear forces - the two main energy wastes are the energy used to move the arm through the liquid, the arm can be shaped and surfaced to minimise that, and the inefficient diffusion recovery (the change of speed to pressure in the Pitot tube - probably only about 60% efficient at best, but recovery only accounts for half the theoretical head, so you lose maybe
20% of the total energy that way).Manufacture makes few demands on close tolerances, the single rotating seal is at low input pressure, vibration is very low and the output is almost entirely pulsation-free, which is important for combustion stability.
[2] two LOX pumps in parallel, and two fuel pumps in series. LOX volume is about twice the kerosene fuel volume. The fuel pressure is nearly double the LOX pressure because it is used to cool the chamber, throat and nozzle before going on to be burnt. An alternative which has some benefits is for the fuel to go through one pump, then cool the nozzle, then the second pump, and then be burnt, but I haven't decided yet.Tom wrote:
It doesn't have one.
I considered a volute casing Barske-type impellor pump, but it would be very inefficient as the pump is so small, so I will be using a double Pitot [1] design instead (unless I can't get it to work, when I will fall back to a Barske design, or perhaps try a two-shaft-Quimby-type screw pump).
The Pitot arm is 32 mm dia, there are four pumps [2], a combuster and a turbine on a single 75,000 rpm shaft in an assembly 54 mm max dia and 65 mm long, target weight ~350 grams.
Propellant flow is 175 grams per second. Shaft power is 2.1 kW, pump mechanical efficiency should be ~ 55%, turbopump overall efficiency ~25%, LOX output pressure is 750 psi.
Engine design thrust is 5kN / 100 lb sea level, chamber pressure is 600 psi, expansion ratio is 8.25, Isp is 245 s sea level, 285 s vaccuum.
Note that most of these figures are still theory, and they will almost certainly change a bit in practice. Note also that the design is slightly less demanding than the engineering presently (apart from the pumps) used in small model turbojets, and I hope to improve on those figures.
[1] A Pitot pump is a hollow stationary arm with a Pitot tube inside opening on the end, which is inside a hollow circular casing which spins and accelerates the liquid inside it - the fast-moving liquid enters the pitot and the speed is changed to pressure. Also, the spinning exerts a centrifugal force on the liquid, increasing it's pressure at the outer edge of the casing where the Pitot is located. A double Pitot pump just has two Pitot holes on opposite ends of a single stationary arm.It can be more efficient than an impellor pump because the wetted moving area is smaller, and there are no fast-moving parts in close proximity to give large shear forces - the two main energy wastes are the energy used to move the arm through the liquid, the arm can be shaped and surfaced to minimise that, and the inefficient diffusion recovery (the change of speed to pressure in the Pitot tube - probably only about 60% efficient at best, but recovery only accounts for half the theoretical head, so you lose maybe
20% of the total energy that way).Manufacture makes few demands on close tolerances, the single rotating seal is at low input pressure, vibration is very low and the output is almost entirely pulsation-free, which is important for combustion stability.
[2] two LOX pumps in parallel, and two fuel pumps in series. LOX volume is about twice the kerosene fuel volume. The fuel pressure is nearly double the LOX pressure because it is used to cool the chamber, throat and nozzle before going on to be burnt. An alternative which has some benefits is for the fuel to go through one pump, then cool the nozzle, then the second pump, and then be burnt, but I haven't decided yet.
Weee :-)
100 lbf = 0.4448 kN has a zero got lost ?
The small jet turbines, eg the Wren 54, run at 120,000 rpm or so. But weee indeed!
Da. Nyet. Added. 500 N/ 100 lbf. foolish me
I thought it didn't look right - too many metric/imperial re-conversions (it actually started out as 500 N ... )
So how big is the impellor going to be in this pump?
Tom
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