Truth about Zirconia Products

While you are using Zirconia products, you should know how to take care of it. There are some fact that should be known to you about the metal if you are handling it. The products made of Zirconia should be stored in a dry place. Never use a wet crucible, always pay attention to dry it naturally before using it. If you are drying the wet Zirconia crucible then ensure that the process should be slow enough.

Therefore it is significant that you should pay a little attention when you use a Zirconia product. The necessary tips if followed well can enhance the life of your Zirconia products. It has been seen that Zirconia coil products are most fragile in nature. So careful handling is necessary. Always avoid a collision during the process of unpacking, handling, transportation as well as cleaning. Pay attention to identify if any micro-cracks present before using zirconia products. Any product with a micro-crack is not advised to be used. Only put that much material at one time in your zirconia crucibles which can get proper heating. Overloading the crucibles will only result in uneven heating. To minimize the thermal shock of the vessel it is mandatory to maintain a slow ramp rate as well as a sluggish cooling rate.

There may be a possibility that if the crucible is taken immediately out of the direct furnace right away from a high temperature it may cause a crack. So take proper care while you are handling the crucible in a higher temperature. Make sure that the vessel can only be removed from the heat while the temperature is below 100°C.

Uneven heating of the Zirconia crucibles can cause a crack. So do not use it for heating through torch or furnaces where you cannot control the temperature change rate. It is suggested that if you are using an induction furnace to heat the crucible then it should be surrounded through zirconia powder.

However, all the above tips and information is only a guide. The main intention of the topic is to warn you about the behavior of the metal. The metal may behave in a different way depending on its operating technique. The novice users may get benefitted with the help of the tips and advice, while the experienced users, can become more efficient if they follow it seriously. However, this guide is not the final end-all of information.
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What is Cubic Zirconia

Zirconium dioxide (ZrO2) has a cubic crystalline form which is known as cubic zirconia. In many cases, it is found colorless but usually, it has many varieties of colors. It is a hard synthesized material and optically flawless. Zirconia word is famous in jewelry and it is interesting to know that because of its diamond-like appearance, it has remained a strong competitor of diamond in the market. The other reasons why it is used in jewelry is that it is low in cost and durable.

History of Cubic Zirconia:
From the analysis of cubic zirconium coil and by further thermal reactions on it, stabilized zirconia was formed in 1929. Detailed research on zirconia was done in 1937 and it was confirmed by using X-ray technology. According to some theories, on the initial discovery, zirconia was used as a ceramic material in some industries because of its high resistance to heat and electricity.


Technical Aspects:
The both, physical and optical, properties of synthesized cubic zirconia are variable as there could be a difference in the method of production among many manufacturers. It is crystallographically isomeric, which, as an important element, could be used instead of a diamond.

If the hardness of zirconia is measured on the Mohs scale, it is 8-8.5. According to research, it is slightly harder than many natural-gems. Its refractive index is 2.18 which is closer to diamond's refractive index.

Zirconia's value of dispersion is 0.0588-0.066 which is quite higher than that of the diamond. Its structure shows that it has no cleavage and does exhibit a conchoidal structure.

Zirconia shows different color behaviors under UV rays with long or short wavelengths. It was researched that only colored based cubic zirconia is able to show a very complex pattern of colors.

Conclusion:
The above-discussed information is basic which you should know about cubic zirconia and its technical aspects. Understanding and knowledge of this topic can help you differentiate between diamond and zirconium. This is important because there have been many cases of fraud where the jeweler sold zirconia instead of a diamond. It is obvious that you may not be able to identify the difference in the physical appearance of both substances.
However, a closer inspection and some simple experiments can help you to avoid any possible misunderstanding. These experiments can be some tests to judge the color patterns or refractive index of zirconia and diamond under different conditions.

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How To Select Platinum Crucibles

The laboratory vessels are expected to be used in the operations like calculations and melting. So before selecting a vessel, you should be very careful about some features of the vessels those are mandatory. The vessel should possess qualities like high-temperature strength, high melting point, oxidation resistance in air and oxygen, ductility and corrosion resistance ability.

Platinum is highly rarely available material, having a melting point of 1772 Celsius. The main benefit of using the material is that it has outstanding resistance to chemical attack.
Often it has been observed that if platinum is mixed with other material it can be more useful in certain ways. Platinum combined with five percent of gold will provide you greater temperature strength as compared to pure Platinum. Thus it is widely accepted as the best-suited material for the manufacture of crucible, thermal couple wire and casting molds. Sometimes platinum mixed with rhodium for the best result. These alloys provide superior hardness and greater strength than other platinum alloys to make them adjustable in more aggressive conditions. When platinum mixed with iridium content, the mechanical potency and thermal corrosion resistance power also increases with greater iridium content. However, care should be taken off the iridium as it suffers greater weight loss if open to the oxidizing atmospheres. Iridium is an outstanding material with extreme corrosion resistance and greater temperature strength as well as the melting point makes it the chosen material for an inert atmosphere oxide melts.

There are some Fusion Agents that can affect the rare material platinum in its smooth functioning. So be careful if you come across any of these materials. Just have knowledge how this material behalves and act accordingly. When platinum combined with Alkali fluorides, it has been seen that the loss of weight of platinum is very insignificant. If it comes with the contact of Alkali chlorides or alkali earth chlorides, they can attack the material with a1000EC temperature in the presence of air. As a result, it will release chlorine from the fused salt. If combined with Alkali Bisulfates, it can harm the material in slightly above 700EC. However, you can reduce the effect by adding ammonium sulfate.

So it is advisable that do not heat the materials of the unknown combination. There are some material if heated in platinum crucibles may cause the vessel to become brittle. The materials are arsenic, antimony, lead, selenium, phosphorus, tellurium and zinc. The material like all base metals including gold and silver will dissolve platinum when in their molten state.

It is very important to heat platinum crucibles always in an oxidizing atmosphere. And care should be taken to hold them in with the help of platinum-tipped tools only. Make sure that platinum should not be heated with another platinum material it may cause a weld of both the vessel. It is better to avoid a smoky flame. Carbon may cause it damage.

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Can You Solder Thermocouple Wire

Pt-Rh thermocouple is a very important temperature measuring element. It has the advantages of wide measuring range, convenient use, and high precision, so it is widely used in industry, agriculture, national defense and scientific research.

Pt-Rh thermocouples are widely used in various high-temperature furnaces and other heating equipment to detect or control temperature. They are precious metal materials. Correct use of platinum-rhodium thermocouple not only saves materials and funds for the country, but also obtains accurate temperature measurement. One of the main reasons for the errors of platinum-rhodium thermocouples is parasitic potential.

The basic structure of platinum-rhodium thermocouple:

The basic structure of Pt-Rh thermocouple for industrial temperature measurement includes thermocouple wire, insulating tube, the protective tube, and junction box.

Common platinum-rhodium thermocouple wires and their properties:

1. Platinum-rhodium 10-platinum thermocouple (scale S, also known as the single platinum-rhodium thermocouple) whose positive component is the platinum-rhodium alloy containing 10% rhodium.

Negative extremely pure platinum; its characteristics are:

(1) Thermoelectric properties are stable, anti-oxidation is strong, suitable for continuous use in the oxidizing atmosphere, long-term use temperature can reach 1300 C, over 1400 C, even in the air, pure platinum wire will recrystallize, making the grain coarse and fracture;

(2) High accuracy. It is the highest accuracy of all thermocouples and is usually used as a standard or for measuring higher temperatures.

Platinum-rhodium thermocouple is a common temperature measuring element in the temperature measuring instruments. It measures temperature directly, converts temperature signal into the thermoelectric potential signal, and converts temperature of the measured medium through the electrical instrument (secondary instrument). Installation methods of thermocouples are as follows: the main fixing methods are the threaded connection, flange connection, and welding. Their application occasions and requirements are different, mainly based on pressure, temperature and other parameters. So what aspects should we pay attention to when installing and using?

1. When using thermocouple compensating conductor, attention must be paid to the type matching, the polarity cannot be disconnected, and the temperature of the compensating conductor and the thermocouple connecting end cannot exceed 100 C.

2. When the temperature is measured or controlled by a thermocouple with a large time constant, the temperature shown by the instrument fluctuates very little, but the actual temperature of the furnace may fluctuate greatly. In order to measure temperature accurately, thermocouples with small time constants should be selected.

3. After power-on according to the instrument wiring diagram, the instrument first displays the thermocouple indexing number of the instrument, then displays the range of the instrument, and then measures the setting temperature of the digital tube display in the lower row of the instrument, and the digital tube display in the upper row of the instrument.

4. The thermal couple wire cannot be installed in the area where the measured medium seldom flows. When measuring the gas temperature in the tube with the thermocouple, the thermocouple must be installed in the opposite direction of the flow velocity and be in full contact with the gas.

5. In order to make full heat exchange between the measuring end of the thermal couple and thermal resistance and the medium under test, the measuring point should be selected reasonably and the valve should be avoided as far as possible.

6. According to the law of intermediate conductor, in the practical application of thermocouple temperature measurement, hot-end welding and cold-end open circuit is often adopted, and the cold-end is connected with the display instrument through a connecting wire to form a temperature measurement system.

Pt-Rh thermocouples are suitable for high-temperature applications in various production processes. They are widely used in powder metallurgy, sintering furnace, vacuum furnace, smelting furnace, glass, steel-making furnace, ceramics, and industrial salt bath furnace.
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Pyrolytic Boron Nitride: Layered Structure and Simple Quality Assurance

Boron nitride is an interesting advanced ceramic material. Although it’s also an electric insulator, low coefficient thermal expansion and has great corrosion resistance, the hardness is quite low (only 4, similar with graphite). Compared to more conventional alumina and zirconia, it's a machinable material due to the low hardness. Pyrolytic boron nitride is a thin (1~3mm) boron nitride material produced by CVD process.

When normal hot pressed boron nitride acts more like graphite, except for the electric conductivity, pyrolytic boron nitride has quite a lot different properties due to the structure. As the material is “grown” from chemicals around in gas phase, PBN by nature has a layered structure. The strong, thin and paralleled slices of PBN give this material some flexibility, which is abnormal for most of ceramics, including hot pressed boron nitride. Although thin and semi-transparent, PBN is not that brittle as it looks like. It is actually quite hard to break a PBN thick disc.

*It takes the quite large force to take this 3mm PBN disc apart, and it’s significantly layered before broken.



Hot Pressed Boron Nitride material is used to make Boron Nitride crucible for growing single crystals in most cases. For this application, it would be a serious issue if the slices tear apart from each other. As the crystal growth process requires accurate temperate control, the lower thermal conductivity caused by the layered structure will be harmful. During the manufacturing, it is common to build up some internal force inside the PBN material, especially on the tips, and this force is the major reason for layered defects for PBN products. That's why the VGF crucible is harder to make and cost considerably more than simple shape crucibles.

It is quite simple to examine if a PBN part is layered. As the material is usually quite thin, it is semitransparent. Under strong lights, there will be the shadow at the layered area. Though it looks normal from outside, layered products should be treated as unqualified products.

*Layered crucible tip. It can be detected with the LED on a cell phone



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