Rotors, Caps and Other Accessories

Rotors, Caps, and Other Accessories

For those not familiar with MAS:
A high precision ceramic rotor (sample tube) with plastic turbines is spun at extremely high speed
on air bearings at the Magic Angle (54.7

Volume Discounts
For Rotors, Caps and
Other Small Items
Price Per Item
Quantity Per Line Item
under $ 100
under $ 100
10 or more
$100 – $ 400
$100 – $ 400 
10 or more
$401 – $1000
$401 – $1000
10 or more
Material information can be found after the spinner accessories links (chart below).

**NOTE: DI, XC, SuperSonic, High Speed, and Standard accessories are not interchangeable unless specified. (For example, 7 mm “standard” rotors are only about 2/3 the length of our 7 mm XC rotors.) If unsure about type, contact us with the probe DSI-serial number and we can help. 

Click Links to Accessories pages
(Rotors, Caps and Other Spinner accessories)
For 3 mm spinners
For Drop-In (DI) 4 mm spinners

4 mm, 5 mm, and 7 mm&
SuperSonic (SS) MAS
5 mm, and 7 mm

Sealing Cells
(for DI and XC)

For High Speed (HS)MAS
5 mm and 7 mm
For Standard Speed (Std.) MAS
5 mm and 7 mm
For WideLine (WL)probe – sample container & cap accessories
For 10 mm MAS
Link to 10 mm MAS

Doty Spinner Assembly Materials

Doty spinners utilize super-precision, wear-resistant ceramic stators of silicon nitride or zirconia.   MAS spinner materials must be chosen carefully based on background signals and temperature ranges. Ceramic rotors and plastic caps of various materials are available to provide fast spinning with limited background problems.


Material Specifications

Turbine Cap Specifications

Upper Temp



Minor Elements

Recommended Use

VT Operation Range

Silicon Nitride

1400°C *

98% Si3N4

2% Y2O3 , .005 Al

High Temp probe (750°C)

21 to 750°C


650°C *

94 ZrO2, 4 Y2O3

Hf, 0.3% Si, .02 Al




650°C *

Al, Si, O, B, K

2% F, Mg

for High Speed and Standard probes only

– Macor o-ring caps

-60 to 250°C








160°C *

F, C, Cl


proton & carbon studies

-20°C to 70°C.

GF Torlon


H, C, O, Si

Ti, N, F

fast spinning,

wide temperature range,

wear resistant

-120°C to 160°C

(glued with epoxy
-170°C to 250°C)


240°C *

H, C, O


fast spinning and  

low 29Si or low 19F

-30°C to 80°C



H, C, O

Ti, N

fast spinning and  

low 29Si or low 19F

-30°C to 80°C


300°C *

H, C, O


special extended VT caps

-270 to 240°C

* Note 1: Non-spinning parts can tolerate different temperatures than caps spinning on rotors.
* Note 2: The above chart represents only material characteristics. Check the Probe Specifications

Material Considerations

New Silicon-nitride Rotor Material Identified.

Kyocera has developed a very promising, new grade of Si3N4 , SN240, that appears to have better strength and toughness than any previous grade.   We are optimistic that this new material, along with improved processing, will allow us to offer thick-walled rotors rated to higher spinning speeds with greatly reduced chances of failure.

Improved MAS Turbine Caps.

Glass-fiber-reinforced torlon grade 5030 will now be used on new MAS turbine caps (except for low proton Kel-F caps) for greatly improved VT performance and all-around better reliability and performance. This new material stands out from the rest with respect to isotropic thermal expansion (only 16E-6/0°C), tensile strength at 200°C (120 MPa), and heat distortion temperature (282°C). It also has rather low moisture absorption, high wear resistance, and high impact strength. These caps will be phased in. DI, XC4 and XC5 will be the first probes to use this new turbine cap material.

We have also made changes in 4 and 5 mm XC and SS turbine caps to further improve spinning stability. The XC/SS thick wall Kel-F caps and XC/SS thin wall rotor caps of all materials will have 7 flutes.


Silicon Nitride:  With a density of about 3.18 g/cm3 and a (working) tensile strength of 700 MPa, silicon nitride has the highest strength-to-weight ratio of any ceramic available today.   Its hardness and toughness make it very difficult to grind, but it has the lowest dielectric loss and lowest permittivity of any engineering ceramic, making it the best choice for high frequencies. A HIPed (Hot Isostatic Pressed) variety is available with improved strength and dielectric properties. Its superior electrical properties make it the preferred material for most applications (often, even for silicon and nitrogen), because of silicon’s long T1 and nitrogen’s low natural abundance. The color is black. The only additive or impurity greater than 200 ppm in this new material is yttria. Silicon nitride stators, housings, and rotors are available in all sizes. This material is required for fastest spinning.

Zirconia:  The yttria-stabilized, high-purity material is glossy white and has a density of about 6 g/cm3and a (working) tensile strength of 700 MPa.   Alumina content can be kept below 100 ppm. Zirconia is less expensive than silicon nitride, but the safe spinning speed for zirconia rotors is lower than that of silicon nitride.

Macor:  This white, machineable, boro-silicate glass-ceramic is loaded with synthetic mica to inhibit crack propagation.  It is easily machined with conventional tooling.  Macor housings may be provided for carbon and proton studies at temperatures over 160°C in our standard speed MAS probes.  Macor is usable up to 650°C, but it has very poor thermal shock tolerance.  Macor rotors are only available for the high speed and standard spinners.  Macor rotors are made with a thicker wall and are machined with an integral turbine at one end.  Standard speed rotors require a plug-cap at the open end, while high-speed rotors require a rear turbine.  Macor rotors are recommended for wet samples, air sensitive samples, and temperatures from -150°C to 250°C.  Major constituents:  Al, Si, O, B, K, F.

Boron Nitride:  The hexagonal hot-pressed variety, with 6% calcium borate binder, is easily machineable and is used for disposable inserts in the high-temperature ceramic rotors.  The material is soft enough to scratch easily and may absorb up to 1% moisture.


Improved MAS Turbine Caps.

Glass-Fiber-reinforced Torlon (GFT) grade 5030 will be used for some MAS turbine caps for greatly improved VT performance and all-round better reliability and performance.   This new material stands out from the rest with respect to isotropic thermal expansion (only 16E-6/°C), tensile strength at 200°C (120 MPa), and heat distortion temperature (282°C). It also has rather low moisture absorption, high wear resistance, and high impact strength. These caps are the most wear resistant and have the widest temperature range. GFT is not recommended for proton studies, or for some silicon and some carbon studies. Caps may be used from -120°C to 160°C repeatedly (or when glued in with epoxy from -170°C to 250°C). GFT caps are being phased in. DI probes, XC4 and XC5 are the first probes to use this turbine cap material. Note: For the present, customers will receive either Aurum, torlon, or glass-fiber-reinforced Torlon (determined by stock).

Kel-F:  This is our standard housing material for Standard and High Speed probes.  A translucent white plastic, Kel-F is background free for all nuclei except F, Cl, and C.   Kel-F is also excellent for carbon studies since the strong fluorine coupling effectively broadens the Kel-F carbon signal, and there are no protons to cross polarize. Unfortunately, Kel-F is not as strong as the other cap materials and is thus restricted to lower spinning speeds. Kel-F turbine caps are used with silicon nitride and zirconia rotors.  The turbine caps can be used at temperatures from -20°C to 70°C. (In parts of the spinner assembly that do not spin, the usuable temperature range is -100°C to 150°C.)

Aurum: This dark brown to black thermoplastic polyimide has excellent dielectric properties. Aurum can be used for low silicon applications when fast spinning is desired. Aurum is supplied for most turbine caps and spinner parts on probes designed for fluorine studies and other applications where carbon was not a problem. Turbine caps may be used from -30°C to 80°C repeatedly. (In non-spinning parts of the spinner assembly, the upper temperature limit is 240°C.)

Aurum is no longer available in appropriate forms for our purposes, so Aurum is being replaced by Torlon

Torlon: Torlon is used for fastest spinning of DI3 turbines. This green thermoplastic polyamide-imide, has exceptional chemical resistance. Torlon is now the standard material for fastest spinning turbine caps and can be used as a substitute for Aurum as the NMR characteristics are similar. Torlon is not recommended for proton studies or for some carbon studies. Caps may be used from -30°C to 80°C repeatedly. The caps may be used once to higher temperatures but they will be too loose after that. (In non-spinning parts of the spinner assembly, the upper temperature limit is 260°C.)

Vespel:  This brown plastic is used for the extended temperature caps described below and for nonspinning spinner assembly parts that will reach temperatures over 200°C.  Vespel is not recommended for proton studies or for some carbon studies.

•  Glass-fiber-reinforced Torlon (GFT): ………… Temperature range:   -120°C to 160°C.
GFT glued in : ………… Temperature range:   -170°C to 250° C

• Kel-F Turbine Caps:      ………….. Temperature range:   -20°C to 70°C.

• Torlon Turbine Caps:     …………. Temperature range:   -30°C to 80°C.

• Aurum Turbine Caps:     ………… Temperature range:   -30°C to 80°C.


O-Ring Caps 

For wet samples, air sensitive samples, and variable temperatures

O-ring Caps:  Turbines and plug caps with dual Viton o-ring seals are available for Macor, silicon nitride, and zirconia rotors.  Macor rotors, (available only for standard and high speed probes) are recommended for wet samples, air sensitive samples, and temperatures from -60°C to 250°C.  A single (rear) cap with o-rings is used with a Macor rotor.  However, if faster spinning is critical, VT and air-sensitive experiments can be done in silicon nitride or zirconia rotors using o-ring-sealed cap pairs.

O-ring turbine caps are normally inserted and removed by hand.  Turbines with threaded holes can be ordered (with a threaded insertion tool) for use when loading samples in a glove box.  (A threaded insertion tool is always required to insert and remove the plug cap of standard speed cap pairs.)  Caps can be ordered with axial holes for out-gassing during higher temperature work or to remove air bubbles from wet samples.

•  Kel-F O-ring Caps:   …………….. Temperature range with o-rings:  -45°C to 80°C.

•  Torlon or Aurum O-ring Caps: …Temperature range with o-rings:  -45°C to 120°C.

•  Note:   Although the supersonic o-ring caps can be used for air sensitive samples in XC5 and XC7 probes, XC sealing cells are usually prefered.

Extended Temperature Caps  

DI, XC4 and XC5 probes (and some supersonic) use Glass-fiber-reinforced Torlon (GFT) – glued in. GFT – if glued in:……. Temperature range:  -170°C to 250°C.

• XC, SuperSonic, and high-speed rotors require a front turbine and a rear turbine.
• Standard speed rotors require a front turbine and a plug.

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