The need for increasing the working temperature and thermal loads in modern technical equipment calls for the use of materials with excellent thermal stability and high melting temperatures.
Anderman Ceramics porous fused silica ES99P material combines a very high maximum working temperature of 1680°C with an utmost thermal shock resistance. This combination is extremely beneficial in thermal applications above 1200°C, where we often get common ceramic materials offering one or the other but not both properties. ES99P fused silica material could be manufactured in various shapes including plates, crucibles and saggers. ES99P fused silica material belongs to the refractory “family” requiring a minimum wall thickness of 10mm for small parts and up to (around) 20 mm or more per meter for longer parts. Large parts can also be manufactured with dimensions around one cubic meter.
Although silica crystallisation occurs above 1050°C leading to a reduced thermal shock resistance in operation after several cold-cold cycles Anderman Ceramics ES99P fused silica material assures a long life service thanks to its coarse grains structure lowering and postponing crystallisation poor effects.
Main applications are silicon melting, platinum melting, metal melting, calcination of ceramic and rare earth powders, heat treatment of metallic powders and glass melting. All applications requiring a fast heating process (induction heating, gas heating, torch flame heating and fast tunnel furnace) where the contact of the product to be treated with the pure silica is sought can potentially use ES99P fused silica material.
Existing moulds for round or square crucibles and saggers avoid limited tooling charges. Parts are really competitive comparing with other expensive ceramics such as zirconium oxide used in platinum melting.
At Anderman Ceramics we’ll be pleased to receive and analyse your application making sure you can profit from our top quality ES99P fused silica material or otherwise recommending another ceramic solution.
For more information please send us an enquiry here
Chemical purity, thermal shock resistance, light transmission and other advanced performance characteristics are superior properties demanded by labware applications.
Quartz offers excellent thermal, electrical, mechanical and optical properties that provide a very high performance for an extensive range of applications through industry.
Fused quartz purity levels are unmatched in the glassware industry and superior to borosilicate products.
The chemical purity and inertness of quartz are essential to many laboratory applications. For example, it can be highly problematical if a lab vessel reacts with its contents and affect the outcome of test. Therefore, the chemical purity is critical and one of the main reasons why many users choose fused quartz vessels.
Supreme thermal properties
Fused quartz beats borosilicate when it comes to heat. Fused quartz is a very stable material at room temperature. At high temperatures, it behaves like all glasses. It does not experience a distinct melting point as crystalline materials.
Fused quartz products can be heated to 1150C under minimal load conditions. It can be quenched into cold water without cracking, due to its high thermal shock resistance. The annealing point is 1140C; strain point is 1070C and fusion point is between 1700C and 1800C.
Quartz flasks are used routinely in petrochemical industry for heating materials such as gasoline. If borosilicate flasks were used instead the borosilicate flasks could break and create a fire.
Because of the exceptional high temperature properties and the low coefficient of expansion flasks made of fused quartz do not break due to the heat or temperature shock. It saves time and money. The initial cost is more expensive but is much safer and will also last longer making them a cost effective solution.
Quartz is also very inert and then, extremely chemical resistant.
A glass cup, for instance, can react with the solution it contains and may corrupt the solution contained. Fused-quartz labware is highly resistant to attack by almost all acid and alkaline solutions, even at high temperatures.
Quartz is also an excellent electric insulator. Both electrical insulation and microwave transmission properties are retained at very high temperatures in many applications.
We can actually say that due to the fused quartz properties it can be used and it’s ideal for many industrial applications.
To many businesses, purchasing ceramic tubes can be a difficult task. However, this can be made very simple if the exact material and size of the tube are known. If this however is not readily available, the more information the supplier receives then they stand a much better chance of meeting the requirements set. As with all applications involving ceramics, the selection process for the material and production method is critical if you are to achieve the most cost effective solution. If you know the exact material and size then this is easy – if not then, here is some information you need to give your supplier to make sure you will get a tube that meets your requirement.
a. Outside diameter
b. Inside Diameter
c. Number of bores (Single or multi hole tube)
e. Tolerance (Normal is around +/-5% but if better required let the supplier know)
2. Quantity required
a. Standard sizes can be purchased in small quantities
b. Special sizes may require a minimum order
c. One off requirement or repeatable business
d. Yearly usage estimate
Also important to remember is that the quantity will depend on an estimate of how much the tubes will be used in a year and the expected life of each tube. One-off orders may produce a larger quantity than a repeatable business due to a less consistent flow of deliveries. Standard tube sizes can be purchased in smaller quantities but more irregular sizes, while specific sizes may usually require a minimum order.
a. Tube – open at both ends
b. Tube – Closed at one end (Sheath)
c. Shape of closed end (Flat ended or round ended.
d. Any additions (Tubes can be made with flanges at one or both ends)
4. Porosity – Dense or porous
a. Dependent on material – porous tubes tend to have better thermal shock characteristics
a. If known but if not then working environment details are very important
6. Working environment
a. Max working temperature
b. Variations in temperature expected and time to change from Max to min temp
c. How tube is supported
d. Vertical or Horizontal in use
e. Elements in contact with tube
f. Use (Thermocouple protection, element support etc)
g. Life expectancy
A. Tubes can be made by a variety of methods in a selection of different ceramics.
B. Both the way the tube is made and the material can affect the performance characteristics
C. Price is effected by
a. Method of manufacture
b. Material chosen
c. Finish requirements (Tolerances etc.)
Again, the more information of the environment and requirements given to the supplier, the greater chance they have of producing the correct product.
Lava, known scientifically as Pyrophyllite, is one of the most promising natural solid materials in the world of industrial ceramics as a substitute to Steatite. Pyrophyllite can be used by customers who are in need of precision machined parts of Steatite in very small volumes for stocks, prototyping, and machinery, where it is not economically viable to manufacture the tooling necessary to produce the steatite parts. This material would an ideal substitute, primarily due to its similar properties, to Steatite. The fact that Pyrophyllite can withhold a maximum temperature of 1300oC as a refractory part means that it would be ideal for furnace parts. Lava is also capable of withstanding up to 700oC as an electrical insulator. Similarly to Steatite, it also starts to show leakages in electrical current at temperatures above700oC through a decrease in insulation.
Although many of the mechanical, electrical and thermal properties are similar for both Lava and Steatite, this does not necessarily mean that the reactionary corrosion of each material will be the same. This is primarily due to the different chemical compositions of the two materials. These are because while Steatite is 65% SiO2 with 34% MgO, Lava has got 60% SiO2 with 35% Al2O3. These different compositions may result in two different reactions to the environment where the part is to be used.
There are two different types of Pyrophyllite, PYRO-13 and PYRO-11. Of the two, PYRO-13 is the most similar to general Steatite, therefore this material could very easily be used to replace Steatite items, bushing, bolts, seals, nuts and insulators, in industrial applications. Another positive fact of PYRO-13 is that it's capable of working under vacuum conditions. In comparison, PYRO-11 is more similar to a porous Steatite. This means that it could be used for similar applications to PYRO-13, but when stronger thermal shock resistance is needed. This is due to the higher 3% porosity in PYRO-11, which also works well in contact with non-ferrous metals. Lava design is limited to a maximum wall thickness of 15mm, if greater the material may crack during firing. Therefore it may be required to lighten the more solid areas when close to the 15mm thickness by drilling close to one end or rounded oblong bores.
The typical time for a quotation of Pyrophyllite is between 1-2 weeks and production is usually within 4-6 weeks, but the parts are provided finished, already precision machined and fired for industrial ceramics use. Typically the lead time to make tooling and produce steatite parts runs several weeks longer and requires a higher volume of parts to make it economically viable.
Measurement of high temperatures, greater than 1000 C, using ceramic based thermocouples is a well established process. In order to do this successfully the resistance wires within the thermocouple need to be insulated and protected.
The use of Ceramic materials to protect the platinum based wire is a method that has been used for many years, due to the exceptional heat resistant properties of these materials. The thermocouple is the most commonly used heat measurement implement and is used for measuring the temperature inside of a furnace, typically being used for the melting or heat treatment of metal or indeed for manufacturing ceramic products.
The ceramic components in a typical thermocouple device are the outer protection tube that is exposed to the furnace. In some cases multiple tubes are used inside each other to provide the level of insulation and protection required.
Ceramic insulators (Tubes with 2 or more core holes through them) are also used to isolate the two or more wires that go to the bi-metallic joint at the head which is the point from which the temperature is measured.
The typical material used for the tube is a 99.7% alumina material, impervious tube, which is attached typically to a metal thermacouple head, containing a terminal block which is used to connect to a standard wire to the instrumentation. In a less demanding heat atmosphere a mullite tube may be used as a cheaper alternative, which will work sufficiently up to 1600 'oc. The mullite tube is also an impervious tube and has 60% alumina content.
Ceramic materials are ideal for many high temperature applications but are also ideally suited to aggressive wear and chemical situations.
The link between metals and ceramics is a long one. Archaeologists have found evidence linking the use of ceramics to contain molten metal as far back as 6000BC. Ceramic containers (Crucibles) continue to be used to this day.
Whereas the basic principals of casting have remained the same over the years, the technology has changed significantly. Methods of melting have changed with the advent of mains power although believe it or not there are still a small number of foundries in the UK melting on an open fire. The ceramics used are also much more technically advanced.
As more stringent requirements for castings such as jet engine components and other high-tec applications have developed then the ceramics used for these materials and the methods to produce the ceramics have continued to evolve.
Alumina and Zirconia are the materials of choice for these high end applications. Crucibles made from these materials can be formed in a variety of ways giving differing performance characteristics. It is often the case that high end zirconia crucibles are used as a matter of course as this is the safest option to prevent contamination. The problem with this is that in a lot of cases this results in a crucible spend considerably higher than necessary.
As with all applications involving ceramics, the selection process for the material and production method is critical if you are to achieve the most cost effective solution.
With the current state of the industrial economy around the world this is an ideal time to consider the use of alternative materials for your applications and processes. Industrial ceramic materials, for example, offer a vast array of compositions and performance characteristics and can be a cost effective alternative in many harsh environments such as high temperature, electrical resistance, wear applications and chemical contact.
One thing however should be considered carefully in the design of ceramic alternatives. The tolerance of a dimension on a metal part may only have minor effect on cost. The same can not be said about ceramic and the cost difference for a slightly tighter tolerance can be significant. Very tight tolerancing can be achieved on ceramic components. The question you should always ask yourself is “Do we need it?”. This should also be the case for any standard tolerances listed on the drawing. If you need precision this can be achieved, but where you don’t need it, money can be saved.
As the accuracy of formed ceramics can vary greatly, it is important to chose the correct forming method. Careful selection of the process used to make the part or indeed to form the base part for later machining will keep the costs to a minimum. The use of a slightly more expensive forming process can at times save a considerable amount of machining. For improved tolerance the parts can be machined “green” (before firing) but for very tight tolerances then the parts must be machined after firing. Finish machining is often difficult and slow. This can add significant cost so should only be used when necessary.
The removal of unnecessary tolerancing and features such as chamfers can often result in massive savings. It is not uncommon for a part with excessive tolerance requirements to cost several times as much as a part correctly designed to be made in ceramic and to suit the application.
In conclusion, it is worth fully exploring alternatives materials such as industrial ceramics , to determine what cost savings, or product life and performance enhancements can be achieved. Remember however, alternate materials may necessitate a change of design thinking in order to maximise the advantages they can offer.
It is often possible to improve the performance by changing one or more of these but as with all ceramic applications thermal shock is only part of the equation and changes must be looked at in context of all the performance requirements.
When designing any product in ceramic it is necessary to look at the overall requirement and often then to find the best compromise that will work.
In high temperature applications, thermal shock is often the main cause of failure. It is comprised of a combination of thermal expansion, thermal conductivity and strength. Rapid changes in temperature both up and down cause temperature differentials within the part, not unlike a crack occurring by putting an ice cube against a hot glass. Movement through differing expansion/contraction leads to cracking and failure.
There are no simple answers to the thermal shock issue however the following guidelines do tend to be beneficial.
- Select a material grade that has some inherent thermal shock characteristics but meets the needs of the application. Silicon carbides and silicates are excellent. Alumina based products are less good but can be improved with the right design.
- Porous products are generally better than impervious and will take larger changes in temperature.
- Thin walled products perform better than thick wall. Also avoid large transitions in thickness throughout the part. Sectional parts may be better as this provides less mass and offers a Pre cracked design alleviating stress raisers.
- Minimise the use of sharp corners as these provide ideal starting points for cracks. Avoid tension loading of the ceramic. Parts can be pre stressed through design to help alleviate this problem.
- Where possible look at the application process to see if it is possible to provide a more gentle change in temperature. Pre heating the ceramic or reducing the rate of temperature change.
The above points will help alleviate thermal shock problems but it is always best to discuss the situation with experts in the field.