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Tag: titanium

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

Benitoite

Benitoite is a barium-titanium-silicate mineral rarely found in serpentinites that are hydrothermally altered. Benitoite fluoresces when exposed to short-wave ultra violate light. It usually appears bluish white or light blue under UV light. The rarely found white Benitoite fluoresces under long wave ultra violate light appearing red in color. It is the Official State Gem of the state of California since 1985.

Composition of Benitoite

This barium-titanium-silicate mineral contains:

  • Barium Oxide (BaO): 36.3%
  • Titanium Dioxide (TiO2): 20.2%
  • Silicon Dioxide (SiO2): 43.5%

Chemical Formula of Benitoite

The chemical formula for this mineral is BaTiSi3O9.

Benitoite Picture


Picture 1 – Benitoite

History of Benitoite

Benitoite was first found in Dallas Gem Mine in California. This blue mineral was thought to be sapphire when it was first discovered. Dr. George Louderback was the first person to identify it as a completely different and new mineral in 1907. He named it “Benitoite” as it was found in San Benito County in California, near the headwaters of San Benito River.

Properties of Benitoite

Here are some of the basic properties of this mineral:

Appearance: The crystals of this mineral have a transparent or translucent appearance.

Color: This mineral is usually blue in color; however, colorless crystals of this mineral can also be found.

Molecular Weight: The molecular weight of this mineral is 413.5 gm/mol.

Crystal Habits: It has tabular dipyramidal crystals.

Crystal System: It has a hexagonal crystal system.

Fracture: The crystals of Benitoite have conchoidal fractures.

Hardness: The hardness of this mineral ranges between 6 and 6.5 on Mohs scale.

Luster: These crystals have vitreous luster.

Solubility: It is insoluble in Hydrochloric acid (HCl) and Sulfuric acid (H2SO4)but soluble in Hydrofluoric acid (HF).

Density: It has the density of 3.6 gm/cm3.

Specific Gravity: Its specific gravity is 3.6.

Streak: The streak of this mineral is white.

Optical Property: Benitoite has uniaxial optical property.

Refractive Index: nω = 1.756 – 1.757 nε = 1.802 – 1.804

Birefringence: δ = 0.046

Mining of Benitoite

It is an extremely rare mineral found in very few locations such as the San Benito County in California, Japan and Arkansas. In San Benito, this mineral occurs in many natrolite veins in glaucophane schist within serpentinite bodies. In Japan it is found in magnesio- riebeckite- quartz- phlogopite- albite dikes that cut a serpentinite body. The gemstone quality Benitoite is only found in California.

Minerals associated with Benitoite

This mineral usually occurs along with different types of minerals. These minerals compose the host rock for Benitoite. Its associate minerals include:

  • Natrolite
  • Neptunite
  • Joaquinite
  • Serpentine
  • Albite

Uses of Benitoite

Benitoite is used for some different purposes; however, its rarity limits these uses.

  • This beautiful mineral is used as a gemstone for making jewelry.
  • Another important use of Benitoite is as a mineral specimen. The unique crystals of this mineral are highly valuable as collectable specimens.
  • It is also used as a minor barium and titanium ore.

Benitoite Jewelry

The hardness of this mineral makes it quite useful as a gemstone. However, its rarity makes it quite an expensive gem. Rings, earrings, pendants and bracelets made using Benitoite gems are very popular. The fact that it resembles the finest sapphires in appearance makes it more appropriate for making jewelry.

Availability of Benitoite

One can buy this gemstone in jewelry shops as well as online. There are many companies offering Benitoite jewelries and gemstones online at proper prices. It is also available in its rough mineral form. The prices vary according to the quality and purity of the product.

Benitoite is highly valued for its beautiful crystalline appearance. Its uses as an ore for some other materials are limited due to its rarity. However, the fact that it is only found in California makes it even more valuable and precious as a gemstone and mineral specimen.

References:

http://www.minerals-n-more.com/Benitoite_Info.html

http://www.wolframalpha.com/input/?i=benitoite

http://www.galleries.com/Benitoite

http://webmineral.com/data/Benitoite.shtml

http://www.benitoitemine.com/benitoite/benitoit.shtml

http://www.mindat.org/min-624.html

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