These are notes regarding my own use of and experiments with Recrystallized Sugar Propellant. I follow the basic formulation and preparation developed by James Yawn.

Contents 1 Preventing KNO3 crystal formation by the addition of a second salt 1.1 KNO3 Crystallization Test 1.1.1 Materials 1.1.2 Procedure 1.1.3 Results 1.1.4 Improvements 1.2 Skillet Propellant Test 1.2.1 Procedure 1.2.2 Results 1.2.2.1 Texture 1.2.2.2 Burn Rate 1.2.2.3 Hygroscopicity 1.3 Test Stand 1.3.1 Voids 1.4 Results 2 Effects of Propellant Processing on Recrystallized Fuel 2.1 Theory

Preventing KNO3 crystal formation by the addition of a second salt

I believe that the KNO3 forms small crystals in the finished propellant as the water is boiled out, and that these crystals are responsible for the grainy texture of the finished propellant. My thought is that the addition of a second salt to the solution will interfere with the KNO3 crystal formation, resulting in:

• An improved texture, less grainy and more glassy
• A better burn by reduction of KNO3 particle size

KNO3 Crystallization Test

This test is to determine if table salt, added to a solution of KNO3 in water, will disrupt crystal formation.

Materials

• KNO3 Stump Rot
• Kosher Salt
• Boiling Water

Procedure

1. Add 7g KNO3 to Test and Control dishes
2. Ad .7g Table Salt to Test dish
3. Dissolve Add several CC boiling water to each dish
4. Stir each dish until dissolved (first control and then test to avoid contamination)
5. Add ice (3 cubes) to each dish and stir until KNO3 precipitates
6. Filter precipitate from each dish
7. Compare amount of precipitate left in filter

Results

The control precipitate was made of grains not much finer than the KNO3 grains that were dissolved in the first place, comparable to a fine granulated (not powdered) sugar.

The test precipitate was made up of finer grains (to the touch). More importantly there was much less solid precipitate, under a quarter, than in the control sample.

These results tentatively confirm that the additional ions disrupt crystal formation in KNO3.

Improvements

• More precise measuring of water volume and temperature
• Dry and weigh retentate
• Boil down filtrate and weigh KNO3 in filtrate
• Compare grain size of precipitated crystals
• Quantitative test of different amounts of salt

Skillet Propellant Test

This test determines the effect that the addition of table salt has on recrystallized sugar propellant prepared in an electric skillet.

Procedure

1. Measure 2 sets of ingredients (with sucrose), test and control (Details left out)
2. Add table salt to test equaling 10% of KNO3 weight
3. Prepare as normal

After the bulk of the water in each batch boiled out the skillet temperature was reduced to 250F and the propellant was gathered, spread and kneaded repeatedly until it passed the 'snap test'. Several strands and fuel grains were cast from each.

I added RIO to a leftover test sample.

Results

Texture

The control sample reached what I would call the texture of mashed potatoes, as I am used to with this method. I cooked 2 batches of the control formula and they turned out identical to each other.

The texture of the test batch was very different from what I am used to. It was much thinner, more of a royal icing or pancake batter. Where the normal sample will mold into a pile in the skillet at 250F the test batch would flatten out and flow into a puddle. The texture made it much nicer to spread around the pan and mix.

The test propellant was a little easier to load into grains.

After thorough cooling I snapped the strands. The control had the slightly grainy texture I am used to from recrystallized propellant. The test strand had a glassy texture, the fracture surface was smooth and shiny. I could not dent the outside of the grain or the fracture surface with a fingernail; I normally can with recrystallized fuel.

Burn Rate

I marked an inch on each strand and recorded video of the burn.

The test shows a slightly retarded burn rate compared to the normal sample.

Sample	Burn Rate	%
Control	2.4mm/s	100%
Test	1.8mm/s	75%
Test + RIO	3.7mm/s	150%

Hygroscopicity

The addition of salt caused the propellant to become much more hygroscopic.

I stored the grains and test strands in a plastic container with silica desiccant. The surfaces of the propellant still grew damp and sticky, while the normal propellant stayed the same or grew drier.

I snapped a .5" diameter strand. It broke cleanly and was still dry, hard and glassy on the inside.

Test Stand

A batch each of the control and test fuels described above is prepared and cast (case bonded) into a 26mm ID 75mm Length PVC pipe with a 7mm core. An additional batch of test plus .7g (~1%) RIO prepared in same manner.

Samples are cored with a 7mm threaded rod through PVC end caps. The rod is left in for cooling which is accelerated by 15 minutes in the freezer (Outside temp is 90 and it would take forever to cool.

Samples vacuum sealed with silica desiccant until testing.

Voids

I have some concern about voids in the packed propellant. I am not sure how to best avoid this.

Results

The addition of table salt to recrystallized sugar propellant does improve the texture, but reduces the burn rate and increases water absorption.

Effects of Propellant Processing on Recrystallized Fuel

After cooking out the moisture in skillet processed recrystallized fuel (KNSU) I scrape it out of the pan. I have both packed it directly into grain molds and I have mixed, pulled and kneaded it by hand until the consistency is putty liked before packing it into the molds. The kneaded version is more pleasant to work with and cures faster and harder. The unkneaded fuel takes longer to cure and stays stickier and softer.

In EX_Motors#PVC9 I tested three motors of the same design, two of which used the unkneaded fuel and one of which used the kneaded fuel. The fuel was case bonded into PVC, which I have seen warnings against, and test fired. The motor with the harder kneaded fuel CATOed, ejecting the nozzle and raining fire down upon the test site (always take precautions!).

Theory

Something about the mixing and kneading process has a significant effect on the flexibility of the final product.