As any regular read of my posts on ACW will know, I have a love/hate relationship with jet vanes. That is partly why I was so attracted to the hypothesis that the Iranian furnace that is the subject of this proliferation case study (or PCS; you have Theresa Hitchens to thank for my over-use of acronyms) is used for their production. Yesterday, I considered the hypothesis that the furnace shown in the video on the production of the Iranian Safir rocket was used for brazing together the inner and out shells of the Safir’s liquid propellant engines. Today, I want to take up the alternative hypothesis, that the furnace is used at some step in the production of graphite reinforced ceramic composite jet vanes. But first some background.
Historical Examples of Production Problems
The image above shows Iraqi fabricated graphite jet vanes used in a static test of the Al Samoud II, which uses a single SA-2/Volga liquid propellant engine. But they were not totally indigenous. In particular, Iraq was not able to manufacture the graphite but instead imported graphite blocks that it then machined into shape. This test, where vane material imported from one country were compared with vane material imported from another, was intended to show that the quality (density? purity? monolithic integrity?) from one source was not sufficient to allow them to be used for jet vanes. The two jet vanes of the acceptable batch survived the test while those from the country that exported the unacceptable batch completely failed. They could have failed for any number of reasons, all of which might fall under the heading of thermal shock or corrosion. The interesting thing, though, is that Iraq was apparently not able to test this quality nondestructively. That implies that they had not issued, and probably not able to issue, a specification that could have been used for the graphite manufacture and quality acceptance. We can conclude that Iraq’s pre-existing knowledge, to borrow a term from tomorrow’s posting, was not very great.
Jet vane suitable for use in solid-propellant rocket exhaust made from carbon-ceramic composites.
If, as rumored, Iran is using carbon-ceramic composite jet vanes, then they have opened the door to a material that is much, much more resistant to thermal shock and oxidation etc. than simple graphite jet vanes. In fact, they could be using the same type of jet vanes for both their liquid propellant rockets and the Sajil solid-propellant missile if they use what is know as Chemical Vapor Deposit (or CVD) using silicon and carbon, SiC. Jet vanes for solid propellant missiles operate in a particularly difficult environment considering the eroding effects of molten aluminum blobs hitting the vanes. If the Iranians are manufacturing their own, then they have almost certainly assimilated an important adjunct technological base. (Again borrowing terminology from tomorrow’s post.)
Details of Jet Vane Production Process
Let’s assume, for the moment, that they are using CVD-SiC. What would that production process look like? First, the vanes would not have to be manufactured in a single step. In fact, they almost certainly would be manufactured in two or more steps. The first steps could be grouped together as fabricating the fiber “pre-form,” which have essentially the final shape of the jet vanes. Since these vane pre-forms are fairly complex shapes, they are probably formed in high pressure/high temperature molds. This is not the step that is shown in the video. The next step could be to remove the pre-form’s temporary matrix, essentially burning it out by a process known as pyrolysis. This could be the step shown in the video but it is more likely that the video shows the next step, deposition of a ceramic matrix in the place of the temporary matrix removed in the last step. This step most likely involves, especially for complex shapes, placing the pre-form in a very low pressure atmosphere of methyltrichlorosilane (MTS or ) with hydrogen as a “carrier” gas. This is typically done with temperatures between 800 to 900 degrees C and pressures on the order of 0.1 atmospheres. This explains the cylindrical shape of the furnace “insert:” it supports the nearly one atmosphere pressure outside the cylinder. (See Chapter 6 of the Handbook of Ceramic Composites.)
The typical temperatures are lower than we determined yesterday for the furnace but not excessively so. Interestingly, based on the ribs on the end caps of the cylinder, it is clearly intended to support a pressure difference between the inside and outside. However, the outer rim of the cylinder, which has little reinforcement, indicates that the pressure difference is probably no greater than a single atmosphere, consistent with the vapor deposition parameters.
This doesn’t prove that the furnace is used for producing jet vanes; only that it is consistent with that use. We will continue this discussion on Thursday, when we talk about Iran’s pre-existing knowledge related to composites. However, we will need some theoretical background before that; background that I will present tomorrow as the theoretical underpinnings for how successful proliferators acquire the know-how to produce technologically sophisticated WMD and the means to deliver it.
This series of posts consists of:
0) Do You Know What This Thing Is?