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Tag: nickel

Nitinol

Nitinol metal alloy is one of the most useful alloys used for various purposes. It has numerous important medical applications.

What is Nitinol?

It is a nickel- titanium metal alloy with some unique properties. It is also known as Nickel titanium. This alloy exhibits the superelasticity or pseudoelasticity and the shape memory properties. It means this unique metal can remember its original shape and shows great elasticity under stress.

Composition of Nitinol

This metal alloy is composed of nickel and titanium. It contains these two elements at approximately equal atomic percentages. Nickel is a known allergen and it might also have carcinogen properties. Due to this reason the nickel content of this alloy has raised great concerns about its usefulness in the medical industry.

Production of Nitinol

Extremely tight compositional control is required for making this alloy. Due to this reason it is very difficult to prepare this alloy. The extraordinary reactivity of titanium is another obstacle in its preparation. Two primary melting methods are presently used for this purpose:

  • Vacuum Arc Re-melting: In this method, an electrical arc is struck between a water cooled copper strike-plate and the raw materials. Water cooled copper mold is used for melting the constituents in high vacuum to prevent carbon introduction.
  • Vacuum Induction Melting: The raw materials are heated in a carbon crucible using alternating magnetic fields. This is also accomplished in high vacuum; however, carbon is introduced in this process.
Nitinol Picture
3D view of Austenite and Martensite structures of the NiTi compound.


Picture 1 – 3D view of Austenite and Martensite structures of the NiTi compound.

Source – en.wikipedia.org

There are no considerable amounts of data showing the product of one method to be better than the other. Both these methods have different advantages to offer. Other methods like induction skull melting, plasma arc melting, and e-beam melting are also used for this purpose on a boutique scale. Physical vapor deposition process is also used in laboratories.

Symbol of Nitinol

This metal alloy is denoted by the symbols of its constituent metals. The formula for this alloy is NiTi.

History of Nitinol

This material derived its name from its constituents and its place of discovery. In 1962, William J. Buehler and Frederick Wang first discovered the unique properties of this metal at the Naval Ordnance Laboratory.

Commercialization of this alloy was not possible until a decade later. This delay was mainly caused by the difficulty of melting, machining and processing the material.

Properties of Nitinol

The shape memory and superelasticity properties are the most unique properties of this alloy. The shape memory property allows this metal to “remember” its original shape and retain it when heated above its transformation-temperature. It happens due to the different crystal structures of nickel and titanium. This pseudo-elastic metal also shows incredible elasticity which is approximately 10 to 30 times more than that of any ordinary metal.

Here are some basic physical and mechanical properties of this alloy:

Physical Properties

Appearance: this is a bright silvery metal.

Density: The density of this alloy is 6.45 gm/ cm3

Melting Point: Its melting point is around 1310 °C.

Resistivity: It has a resistivity of 82 ohm-cm in higher temperatures and 76 ohm-cm in lower temperatures.

Thermal Conductivity: The thermal conductivity of this metal is 0.1 W/ cm-°C.

Heat Capacity: Its heat capacity is 0.077 cal/ gm-°C.

Latent Heat: this material has a latent heat of 5.78 cal/ gm.

Magnetic Susceptibility: Its magnetic susceptibility is 3.8 emu- gm in high temperatures and 2.5 in low temperatures.

Mechanical Properties

Ultimate Tensile Strength: The ultimate tensile strength of this material ranges between 754 and 960 MPa.

Typical Elongation to Fracture: 15.5 percent

Typical Yield Strength: 560 MPa in high temperature; 100 MPa in low temperature

Approximate Elastic Modulus: 75 GPa in high temperature; 28 GPa in low temperature

Approximate Poisson’s Ratio: 0.3

Making Nitinol Devices

Hot working of this material is relatively easy than cold working. The enormous elasticity of this material makes cold working difficult by increasing roll contact. This results in extreme tool wear and frictional resistance. These reasons also make machining of this alloy extremely difficult. The fact that this material has poor thermal conductivity does not help in this purpose. It is relatively easy to perform Grinding, laser cutting and Electrical Discharge Machining (EDM) on this metal.

Heat treatment of this material is very critical and delicate. The heat treatment-cold working combination is important for controlling the useful properties of this metal.

Nitinol Wires

Nitinol is used for making shape-memory actuator wire used for numerous industrial purposes. This wire is used for guidewires, stylets and orthodontic files. This wire is ideal for applications requiring high loading and unloading plateau-stresses as well as for eyeglass frames and cell phone antennas. However, the main uses of this wire are in stents and stone retrieval baskets.

Nitinol Stent

This alloy is used for manufacturing endovascular stents which are highly useful in treating various heart diseases. It is used to improve blood flow by inserting a collapsed Nickel titanium stent into a vein and heating it. These stents are also used as a substitute for sutures.

Nitinol Basket

Nickel titanium wire baskets are well-suited for many medical applications as it is springier and less collapsible than many other metals. This basket instrument is highly useful for the gallbladder.

Uses of Nitinol

Here are some of the main applications of Nitinol metal alloy:

Medical Applications

  • This alloy is very useful in dentistry, especially in orthodontics for wires and brackets that connect the teeth. Sure Smile (a type of braces) is an example of its orthodontic application.
  • It is also used in endodontic mainly during root canals for cleaning and shaping the root canals.
  • In colorectal surgery, it is used in various devices for the purpose of reconnecting the intestine after the pathology is removed.
  • Nitinol stents are another significant application of this metal in medicines.
  • Its biocompatible properties make useful in orthopedic implants.
  • Nitinol wires can be used for marking and locating breast tumors.
  • The use of Nitinol tubing for various medical purposes is increasing in popularity.

Industrial Uses

  • Nitinol wires are used in model heat engines made for demonstration purposes.
  • This material is used in temperature controls. Its shape changing properties can be used for activating a variable resistor or a switch for controlling the temperature.
  • This metal is often used in mechanical watch springs.
  • It is used as microphone boom or a retractable antenna in cell phone technology for its mechanical and flexible memory nature.
  • Nitinol spring is used in various industries for the purpose of utilizing the superelastic properties of this metal.
  • Nitinol sheets are used for punching, stamping and deep drawing.

Other Uses

  • It is also used as an insert for golf clubs for its shape changing abilities.
  • It is a popular choice for making extremely resilient glass-frames.
  • Nitinol is used for making self-bending spoons used in magic shows.

Availability of Nitinol

Nickel titanium is available in various forms including wires, tubes, sheets and springs. NDC is one of the leading manufacturer and supplier of this metal alloy. However, there are many other suppliers of Nitinol wires, tubes, springs etc. Different forms of this metal are also available online at reasonable prices.

Nitinol is counted among the most useful metal alloys with numerous industrial and medical applications. It is often the best choice for many applications that require enormous motion and flexibility. However, this material has shown fatigue failure in many demanding applications. Experts are working hard for the purpose of defining the durability limits of this metal alloy.

References:

http://www.nitinol.com/nitinol-university/nitinol-facts/

http://www.memry.com/nitinol-iq/nitinol-fundamentals/physical-properties

http://jmmedical.com/resources/221/Nitinol-Technical-Properties.html

http://www.colorsproject.com/nitinol_articles_science_digest_1982_sanders.pdf

http://www.dynalloy.com/AboutNitinol.html

Manganin

Manganin is the trademarked name for an alloy that consists of three metallic elements – Copper, Nickel and Manganese. This alloy is useful in various industries. Read on to learn more about the composition, properties and uses of this material.

History of Manganin

Edward Weston, an American chemist, was the first person to discover “Manganin” in 1892, while working on the improvement of another metallic alloy. This alloy, which was previously known as “Alloy No. 2”, was discovered by Weston who renamed it as “Constantan”.

Composition of Manganin

This metal alloy consists of the following metals in the following proportions:

  • Copper (Cu): 86%
  • Manganese (Mn): 12%
  • Nickel (Ni): 2%

Chemical Formula of Manganin

The chemical formula of this substance is CuMnNi. It consists of the formulas of all the constituent metals, namely CU for Copper, Mn for Manganese and Ni for Nickel.

Chemical Structure of Manganin


Properties of Manganin

Following are some of the basic properties of this alloy:

  • It has the formula weight (sum of the molecular masses of the atoms in the formula) of 177.18 g/mole.
  • This alloy has a low temperature coefficient of resistance (relative change of the physical properties of a substance with 1 K temperature change).
  • The resistivity of this resistance alloy is 4.55×10-5 ohm centimeters.
  • It is electrically conductive.
  • It has a melting point of 960 °C.
  • The tensile strength of this substance ranges between 300-600 MPa.
  • The electrical resistivity of this alloy varies between 43 and 48 µOhmcm.
  • The density of this alloy is 8.4 g/cm3.
  • It has a specific gravity of 8.5.
  • Its electrical resistance is found to be constant over a range of temperatures.

Uses of Manganin

Manganin has been used for different industrial purposes from the moment of its discovery. The properties of this material make it most efficient for certain applications. It is widely used in industries for manufacturing various substances like:

Shunts

The wire and foil of this material are mainly used to manufacture various resistors – mainly ammeter shunts. Shunt refers to a device that controls the passage of electric current in different points of a circuit. This metal alloy has very low temperature coefficient of resistance. It also has long term stability. These properties make it very useful to be used for making shunts.

A coil of this substance is usually 150 mm wide and 0.025 mm thick.

Gauges

This substance has a low sensitivity to strain (Deformation of a substance due to the stress or strain applied to it) and a high sensitivity to hydrostatic pressure (the pressure applied by a fluid at the state of equilibrium as a result of gravitational force). Due to this reason, it is very useful in gauges to study High-Pressure Shock Waves (an energy carrying wave originated from a variety of mediums like gas, liquid, solid and also through various fields under a high-pressure).

Manganin gauges are extensively used in high-pressure shock wave studies that range from 1 – >400 kilobars (1 bar = 100 000 N/m2 or 14.5 psi). The gauge is bonded in mainstream applications between two flat polymer plates or metallic plates.

Manganin-Constantan Thermocouples are more efficient than Copper-Constantan Thermocouples in the thermometry (temperature measurement) units of Commercial Ultrasound Hyperthermia Systems.

Manganin wire is also seen to be used as an electrical conductor in cryogenic systems. Its use minimizes transfer of heat between points that require electrical connections.

References:

http://www.reade.com/products/4-alloys-metal-inorganic-powder-sheet-a-wire/305-manganin-alloy-manganin-shunt-manganin-strip-manganin-wire-nickel-plated-copper-wire-cu-mn-fe-astm-b267

http://www.isabellenhuette.de/pdf/WIDER_LEG/MANGANIN-ISABELLENHUETTE-R.pdf

http://www.lakeshore.com/temp/acc/am_wirets.html

http://www.ncbi.nlm.nih.gov/pubmed/7714367

http://www.vishaypg.com/docs/11524/mangpatt.pdf

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