FREQUENTLY ASKED QUESTIONS
GENERAL
What is a polysilazane?
A polysilazane (silazane-based polymer) is a material having a polymeric chain structure based on alternating silicon and nitrogen atoms. Polysilazanes have have both linear, cyclic, and fused cyclic chain segments.
How do KiON polymers differ from conventional polysilazanes?
KiON polysilazanes are built from linear chains which crosslink through ladder-like and fused cyclic structures.
Are these materials patented?
Yes. KiON Specialty Polymers has in its portfolio of intellectual property a number of U.S. patents and broad foreign coverage on its basic technologies.
What is the shelf life of a KiON polysilazane?
When stored in capped containers, the shelf life for most KiON polymers is at least a year. KiON Specialty Polymers has retained samples of Ceraset Polyureasilazane which have demonstrated shelf stability of well over three years.
Are any special precautions needed when storing KiON polysilazanes?
Since all polysilazanes will slowly hydrolyze upon exposure to moist air, KiON polysilazanes should be stored in closed containers, preferably with minimum headspace. A nitrogen headspace is not necessary. Glass or polyethylene containers are suitable for most KiON products.
Do I need to use a glove box or other such precaution when using KiON polysilazanes?
No. KiON polysilazanes are typically used on open benchtops; however, adequate ventilation is required.
If polysilazanes react with water, wouldn't a coating or other object made from a KiON polymer gradually degrade over time?
When properly cured, coatings or objects made from KiON polysilazanes or KiON polysilazane "hybrid" polymers are stable to hydrolysis. KiON Specialty Polymers has retained plaques of peroxide-cured Ceraset Polysilazane 20 for years with no degradation. Similarly, urethane "hybrid" flooring material made from KiON's Ceraset Polyureasilazane polymer is still operational in outdoor locations eight years after installation.
Can you do something to eliminate the characteristic "ammonia" odor of KiON polysilazanes?
Unfortunately, no. Much of the odor associated with KiON polysilazanes comes from slight hydrolysis of the polymers when they are exposed to moist air. While the extent of this hydrolysis is rather insignificant relative to the performance of the polymer, the small amounts of ammonia which are generated are readily detected by the human nose. In normal processing environments the amount of ammonia generated is orders of magnitude below the threshhold limits for ammonia exposure in the workplace.
KiON polysilazanes are excellent ceramic precursors. They give 96 wt% ceramic yields at 1,000° C in an air atmosphere. Fire resistant plastics can be made from these polymers. Why do they have a Flash Point?
KiON polysilazanes gradually convert to ceramic material when heated to 1,000° C in either an inert atmosphere or air. As they crosslink and condense upon exposure to higher and higher temperatures, they gradually take on the characteristics of a ceramic (i.e. more brittle, more resistant to fire, etc…) However, until the initial phases of crosslinking occur (i.e. vinyl crosslinking for Ceraset Polysilazane 20), some of the liquid KiON polymer has a molecular weight which is low enough so that some of it is volatilized. In this "uncrosslinked" state silazanes will combust.
Can I heat a 500 ml beaker full of liquid Ceraset Polysilazane 20 to 300° C in air?
No. This is a dangerous situation which could result in a fire. When used as liquids in such large quantities the polymers should be fully cured before they are exposed to such high temperatures.
Can I use benzoyl peroxide or MEKP to cure Ceraset Polysilazane 20 or Ceraset Polyureasilazane?
As a rule, diacyl peroxides such as benzoyl peroxide are not effective in curing Ceraset Polysilazane 20 or Ceraset Polyureasilazane. The vinyl silyl group is generally "sluggish" when it comes to free radical curing. Typically, the peroxide radicals which are formed by the thermal decomposition of diacyl peroxides will deactivate by decarboxylation before they can activate the vinyl silyl groups in Ceraset Polysilazane 20 or Ceraset Polyureasilazane. MEKP can be used, but it is important to test any peroxide on a small scale under the intented cure conditions before proceeding to large-scale processing, since such radical-induced cures can be quite exothermic and create a safety hazard.
Is Ceraset Polysilazane 20 or Ceraset Polyureasilazane UV-curable?
While extensive work has not been done in this area, Ceraset Polysilazane 20 or Ceraset Polyureasilazane can be UV-cured with the addition of UV sensitizers (dimethoxyphenyl acetophenone). Again, the vinyl silyl group is somewhat sluggish, so cure rates are slower than those observed for unsaturated organic compounds.
POLYMER COMPOSITES
Can you send us samples of an acrylic (or urethane, epoxy, polyester, …) KiON hybrid polymer?
As detailed in the Technical Bulletins which can be found on this website, various "hybrid" polymer compositions can be prepared using KiON polysilazanes. Any one version of such a "hybrid" polymer often represents an optimization of certain performance characteristics at the expense of others. The value of any given KiON polymer hybrid is thus extremely application dependent and relies heavily on the complimentary organic starting materials which are employed. For this reason, a sample of any given "hybrid" polymer would not be truly representative of the potential for that hybrid system and KiON Specialty Polymers does not sample such hybrids. It is better to think of KiON polymers as "reactive intermediates" in the formation of application-specific hybrid compositions. While the reactivity of polysilazanes toward various organic moieties is detailed in the Technical Bulletins which are included on this website, KiON Specialty Polymers would be happy to assist any customer who has questions regarding specific KiON polymer "hybrids".
Is the silicon-nitrogen bond in KiON polymers more reactive than a primary amine or a polyol when it is reacted with an isocyanate or an epoxy?
KiON polysilazanes are EXTREMELY reactive at room temperature toward aromatic isocyanates (e.g. TDI, MDI). The reaction is exothermic and a significant amount of heat is evolved. For this reason, it is important to EXERCISE EXTREME CAUTION when reacting KiON polymers with aromatic isocyanates. Cross sections of no more than about 0.5 inches should be attempted in unfilled compositions. Particulate fillers such as silicon carbide and aluminum metal can be used to ameliorate this exotherm. The reaction of KiON polysilazanes with aliphatic isocyanates (e.g. HMDI trimer, IPDI) is less pronounced. While KiON polysilazanes will cure aliphatic isocyanates over the course of several hours, often some heat (60°-70° C) is required to effect a complete cure. The reaction of KiON polymers with epoxy resins is slow and requires significant heating (>160° C). Even so, cure can be incomplete and depends on the exact structure of the epoxy resin.
Does the reaction of a KiON polysilazane with an isocyanate or epoxy group generate a lot of heat?
KiON polysilazanes are EXTREMELY reactive at room temperature toward aromatic isocyanates (e.g. TDI, MDI). The reaction is exothermic and a significant amount of heat is evolved.. For this reason, it is important to EXERCISE EXTREME CAUTION when reacting KiON polymers with aromatic isocyanates. Cross sections of no more than about 0.5 inches should be attempted in unfilled compositions. Particulate fillers such as silicon carbide and aluminum metal can be used to ameliorate this exotherm. The reaction of KiON polysilazanes with other organic moieties is much less exothermic, and often some heating is required to effect full cure.
What is the compatibility of KiON polymers with unsaturated polyester resins or vinyl ester resins?
Since unsaturated polyester resins and vinyl ester resins usually have significant OH functionality, the preparation of hybrid polymers using these resin systems is not usually successful. Reaction is normally accompanied by significant gas (ammonia) evolution.
CERAMICS COMPOSITES
Do I have to use a peroxide to cure Ceraset Polysilazane 20 or Ceraset Polyureasilazane?
No. The use of peroxides or azo compounds as free radical initiators is recommended only to promote vinyl crosslinking (cure) at relatively low temperatures. Technical Bulletin 1 (TB1) on this website gives temperature / time curves for several recommended peroxides. Without the use of a free radical initiator such as a peroxide or azo compound, Ceraset Polysilazane 20 or Ceraset Polyureasilazane will undergo vinyl crosslinking at temperatures of about 180°-200° C.
At what binder level is Ceraset Polysilazane 20 or Ceraset Polyureasilazane effective?
It depends on the composition and particle size of the powder which is used. Acceptable "green" strengths can typically be obtained at about the 2 wt% level. At the 4 wt% level using small diameter ceramic powders, very strong green bodies can be obtained. At approximately the 13-15 wt% level "slurries" which can be injection molded at room temperature can be obtained using sintertable silicon nitride or silicon carbide powders. Whenever Ceraset Polysilazane 20 or Ceraset Polyureasilazane is used as a binder, it is important to remember that green strength will develop only upon thermal curing of the polymer. Also, while Ceraset Polysilazane 20 or Ceraset Polyureasilazane containing relatively high temperature peroxides such as dicumyl peroxide is shelf-stable for many months, once ceramic powder has been added to the mixture, the effect of the peroxide will last for only about one day even though the shelf life of the powder-filled KiON polysilazane is indefinite.
What is the density of pyrolyzed Ceraset Polysilazane 20 or Ceraset Polyureasilazane?
Even though the ceramic yield of cured Ceraset Polysilazane 20 or Ceraset Polyureasilazane is quite high (85-96 wt% depending on the pyrolysis atmosphere) some mass loss occurs. This mass loss is manifest as homogeneous porosity throughout the pyrolyzed polymer rather than shrinkage. Typically, bulk densities are around 2 - 2.5 g/cm3. When pyrolysis is performed below crystallization temperatures (below about 1,400° C to about 1,600° C) an amorphous, non-glassy ceramic is formed.
At what temperature does Ceraset Polysilazane 20 or Ceraset Polyureasilazane convert to a ceramic?
Cured Ceraset Polysilazane 20 or Ceraset Polyureasilazane will GRADUALLY convert to an amorphous, non-glassy ceramic material upon heating to 1,000° C in either air or an inert atmosphere. The exact composition which is obtained at 1,000° C depends on the composition of the pyrolysis atmosphere. The conversion to a ceramic, however, is not precipitous. As a cured sample of Ceraset Polysilazane 20 or Ceraset Polyureasilazane is heated to 1,000° C it slowly condenses, first with the evolution of ammonia, then with the evolution of (mainly) methane, and finally with the evolution of small amounts of hydrogen gas to generate the final ceramic. Within different temperature regimes in this condensation process Ceraset Polysilazane 20 or Ceraset Polyureasilazane will have different degrees of "polymeric" versus "ceramic" characteristics. At lower temperatures, Ceraset Polysilazane 20 or Ceraset Polyureasilazane will behave more like a polymer; at higher temperatures, Ceraset Polysilazane 20 or Ceraset Polyureasilazane will behave more like a ceramic. The exact performance characteristics of the material can thus be tailored to a specific use by carefully choosing the ceiling temperature to which the polysilazane is heated. As a rule of thumb, Ceraset Polysilazane 20 or Ceraset Polyureasilazane is more "ceramic-like" when heated above 600° C and more "polymer-like" when kept at temperatures below 600° C.
Are the ceramics obtained from the pyrolysis of Ceraset Polysilazane 20 or Ceraset Polyureasilazane crystalline materials?
Not necessarily. As described above, the ceramic which is obtained from the pyrolysis of a cured sample of Ceraset Polysilazane 20 or Ceraset Polyureasilazane at 1,000° C is an amorphous, non-glassy ceramic. The chemical composition of this ceramic depends on the pyrolysis atmosphere (see Technical Bulletin TB2 included at this website). Crystallization typically occurs at temperatures between 1,400° C and 1,600° C and depends on the exact chemical composition of the ceramic which is obtained at 1,000° C.
Can I achieve theoretical density for either a silicon nitride or silicon carbide ceramic prepared from Ceraset Polysilazane 20 or Ceraset Polyureasilazane?
Yes. While the bulk density of a cured sample of Ceraset Polysilazane 20 or Ceraset Polyureasilazane which is pyrolyzed at 1,000° C is only around 2 - 2.5 g/cm3 and is manifest as homogeneous porosity throughout the sample, the use of an appropriate sintering aid (either as a reactive chemical or as a particulate powder) will allow for full densification at typical sintering temperatures (ca. 1,700° C for silicon nitride, and above 2,000° C for silicon carbide). Yttria or alumina sintering aids can be used when the final ceramic composition is chosen to be silicon nitride, while conventional boron-containing sintering aids can be used when the final ceramic composition is chosen to be silicon carbide. In either case, a fully dense (3.1-3.2 g/cm3) monolith can be obtained with mechanical properties which are the equivalent to high quality samples prepared using conventional powder consolidation (sintering / densification) techniques.
Can HTT 1800 or Cerasets be used as a powder binder for oxide ceramics such as aluminum oxide?
Yes. In fact, by choosing the correct amount of alumina in relation to the amount of HTT 1800 or Cerasets used as "binder" SIALON ceramics of well-defined stoichiometries can be obtained.