Last updated: 18/08/2015 13:38:25
Platinum thermocouple wire
A thermocouple is quite simply a sensor for measuring temperature, with many applications from central heating boilers to jet engines. Thermocouples use the reaction of two dissimilar metals to measure temperature variation. The types of metal involved vary according to the temperature range in which the thermocouple operates.
Some thermocouples use relatively inexpensive alloys such as nickel, chrome, iron and aluminium. The thermocouples we’re interested in, known as Types B, R and S, use platinum – a rare and expensive material that is one of the noble metals (which also include silver and gold).
Platinum has the chemical symbol Pt and the atomic number 78, and is twice the density of silver. One of the rarest elements on Earth and extremely valuable, it is mined mostly in South Africa. As an indication of its value, the crown worn by Queen Elizabeth the Queen Mother, as Consort of King George VI, had a frame made of platinum. Though the crown was undoubtedly spectacular, the platinum frame added significantly to its weight; a solid six inch cube of platinum weighs as much as an adult man.
We don’t expect you to send us the Queen Mother’s crown for valuation! However, though the platinum wire used in thermocouples is a relatively small diameter, its value makes it well worth selling to Gold-Traders.
Why platinum? It cannot be oxidised, withstands most acids, has high resistance to corrosion and high temperatures, and is electrically stable and an efficient conductor. In thermocouples, platinum is often combined in an alloy with rhodium, a chemically inert transition metal which is also part of the platinum group.
The ratio of platinum to rhodium depends on the type of thermocouple.
For a Type B thermocouple, one conductor will be 70% platinum, 30% rhodium, while the other will be 94% platinum, 6% rhodium. Type B thermocouples are used for very high temperature measurements, with a usable range of around 800°C to 1800°C.
A Type R thermocouple will have one conductor with 87% platinum, 13% rhodium, and the other conductor 100% pure platinum. It’s used for temperatures up to 1600°C, in applications such as the steel industry.
The Type S thermocouple can also withstand heat up to 1600°C, and has one conductor that’s 90%, 10% platinum and the other 100% pure platinum. A typical application for Type S is providing the calibration standard for the melting point of gold (1064.43°C). It’s also used in pharmaceutical and biotechnology applications.
Unlike other dealers, the prices we quote are the prices we pay. We have no hidden deductions and don’t charge testing or refining fees. If we receive your thermocouples within 3 days, the quoted prices per gram are guaranteed. If global platinum prices drop, we’ll still pay you what we’ve quoted. If we raise our prices, you’ll get the higher amount.
To sell your thermocouple wire, please complete our claim form. Once submitted, you’ll be asked to print a copy for signing and we’ll give you full instruction regarding packaging and postage. All packages are dealt with on the day of receipt, Monday to Friday.
Platinum hallmarking was introduced in the UK in 1975 as a result of legislation brought about by the Hallmarking Act of 1973. Prior to this date, items containing platinum would often carry no markings or simply ‘Plat’ or ‘Platinum’ and would be of varying purity.
A typical platinum hallmark
All platinum items weighing more than 0.5 grams must now carry a valid hallmark when sold in the UK. The photo on the right shows a typical hallmark. A platinum hallmark will consist of 3 compulsory and 3 optional stamps.
This post is a simple platinum hallmark guide, which we hope you find useful. If you have platinum to sell, please see our up-to-date scrap platinum prices. We also publish our scrap gold prices and our scrap silver prices.
Also referred to as the makers mark, the first stamp in the photo indicates who submitted the item for hallmarking. Each sponsor (maker) has their own unique stamp.
The third stamp in our example photo is the fineness mark. This tells you the precious metal content, expressed in parts per thousand. There are four recognised standards of platinum:
When identifying an item as being platinum, it’s important to check the shape and contents of the fineness mark. If the shape is anything other than what is shown below, it isn’t platinum. As you can see, our ring is 950 platinum.
Assay Office Mark
The assay office mark tells you which assay office tested and hallmarked your item. There are now four assay offices in the UK:
The following 3 marks are all optional. Under hallmarking legislation, there is no compulsorary requirement to show these additional marks, however they are often shown.
Traditional Fineness Symbol
If your platinum item has a purity of 950 or 999, it may display the traditional orb mark. In our example photograph, you can see the second stamp is the traditional fineness symbol.
Date letters are optional and therefore not always seen (as in our example photograph). The date letter tells us the year the item was hallmarked. As date letters were standardised across all assay offices from 1975, it’s quite easy to read. Below is a chart of all date letters from 1975 onwards.
Standardised UK hallmark date letters from 1975 onwards
International Convention Mark
An International Convention Mark is sometimes shown within the hallmark. It is a mark recognised by all member countries of the International Hallmarking Convention.
Without a valid hallmark, most jewellers and small scale gold buyers will not be able to accurately test the purity of platinum jewellery. Due to its inherent inertness, traditional ‘acid’ testing can only help determine if an item isn’t platinum, however you can’t for example differentiate 900 and 999 platinum.
High-end and specialist precious metal dealers use XRF (X-ray fluorescence) testing to accurately identify the platinum content of jewellery. Inductively coupled plasma, optical emission spectrometry is used by assay offices during the hallmarking process.
Used in laboratories and in scientific instruments, platinum thermocouple wire is often used for measuring temperatures in-excess of 2000°C.
Due to its high value, thermocouple wire should always be recycled. You can sell your platinum thermocouples to Gold-Traders and receive payment on the day we receive your package.
You can check our scrap platinum prices, which are always up-to-date. The rates we display are the minimum prices per gram that we will pay you. If platinum prices drop once you’ve sent your thermocouple wire, we’ll pay you our original quoted rates (providing we receive it within three days of quotation). If our platinum prices increase, we’ll automatically pay you the higher rate.
To proceed, please fill out our claim form and follow our simple instructions in relation to postage and packing.
A crucible is a container made from a material that doesn’t melt easily and used for high temperature chemical reactions.
Platinum crucibles offer very high temperature strength. Its contents can be heated in excess of 1000°C without the crucible melting.
Being a noble metal, Platinum does not oxidise or corrode, thus does not interfere with the chemical reaction occurring during the heating process.
Inevitably, a Platinum crucible will reach the end of its life at some point. Once it becomes cracked or misshaped beyond repair, it must be replaced.
Gold-Traders purchases unwanted and damaged Platinum crucibles. Our scrap platinum prices page is regularly updated and the rates quoted are guaranteed for 3 days following completion of one of our claim forms.
Unsure of the weight or type of gold you have? No problem! Simply complete our simple online claim form and send us your scrap gold for a free, no-obligation quote.
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