State-of-the-art research on fireworks and pyrotechnics

Titles and Abstracts

Selected Pyrotechnic Publications of Dr. Takeo Shimizu,
Part 1 (1985 to 1994)
from the International Pyrotechnic Seminars

Table of Contents (Shimizu – Part 1)

Hypothesis on the Cause of Serious Accidents Related to Salutes Charges

Abstract: First, we hypothesize that a serious accident related to the use of salutes may be caused by the simultaneous explosion of several salutes or salute components, resulting in an unexpected, abnormally strong shock wave. To prove our theory, we conducted three experiments. In Experiment 1, we examined the transfer of the explosion between salutes with one donor to shed light on the properties of the charges. Experiment 2, which we conducted to examine the transfer in the case of two donors, revealed a localized effect of the transfer. In Experiment 3, we measured the pressure during explosion using a pressure-sensing film, which was used to create pressure contour lines. Our experiments reveal that there is an area of abnormally high pressure, a finding which supports our hypothesis.
Proceedings of the 10th International Pyrotechnic Seminar, July, 1985.

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A Concept and the Use of Negative Explosives

Abstract: In general, a pyrotechnic composition consists of an oxygen donor such as KNO3, KClO3, or KClO4, etc., an oxygen donee such as organic resin and some other inert substances. When substances, CaCO3, AlO3, SiO or CaSO4, etc. are contained in it, they are regarded as an inert substance, because they are full of oxygen and cannot be more oxidized. This type of explosive deflagrates with oxidation reaction and could be called “positive explosives”. However, when some substances, Mg, Al or Si, etc., which have a very large reduction capacity, the inert substances change to active ones. This type of explosives, which consist of Mg, Al or Si, etc., plus a substance which is thought to be inert in conventional explosives, is defined here as “negative explosives”. With the oxygen donee, Mg was concerned as a representative case, because it is very popular and has the largest reduction capacity; it burns even sand or earth. About 50 types of negative mixtures were listed as samples. Their characteristics were examined by several tests. Ignition and burning properties were tested on the ground by using black match. Ignition temperatures were obtained from a heating test in a glass tube. Illuminating capacities were measured by burning consolidated mixtures as a flare. Ballistic characteristics were examined by firing a projectile with a small mortar by using granulated mixtures for the propellant charge. The results were discussed and a proposal for use of negative explosives was made.
Proceedings of the 11th International Pyrotechnics Seminar, July 1986.

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Ballistics of Firework Shells

Abstract: Heretofore we have had four important problems with calculations in this field, i.e., with the interior ballistics when using Black Powder as the propellant: (1) to obtain a suitable form function of the propellant which consists of irregular grains, (2) to obtain solutions when the burning rate of the propellant grains is proportional to P(, where P is an internal pressure of the mortar barrel and ( the pressure exponent, (3) to obtain suitable solutions when the propellant gas escapes from the burning room through the clearance between the wall and the shell in the mortar, and with the exterior ballistics (4) to obtain simply the drag coefficient for various shapes of shells. For (1) a treatment to calculate the surface areas and volumes of grains assuming the propellant grains consist of a mixture of cubes and spheres is proposed. For (2) a method to solve a three order differential equation derived from three basic interior ballistic equations step by step with proper time intervals is proposed. For (3) the nozzle theory used for rocket engines is introduced. For (4) the fact that the maximum height of the projectile in the air is almost the same as that of vacuum when the flying times of the both are equal is applied. These methods are applied to 6-inch shells and examined if they are suitable in practice.
Proceedings of the 13th International Pyrotechnics Seminar, July 1988.

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An Example of Negative Explosives: Magnesium Sulfate/Magnesium Mixture

Abstract: At the Eleventh International Pyrotechnics Seminar, 1986, in Vail, Colorado, I reported on a study of pyrotechnic mixtures with a theme, “A Concept and the Use of Negative Explosives”. A further study has been continued on the same subject as before. In the former report it was known that magnesium sulfate/magnesium mixture detonates on heating. I studied if it is suitable for the noise mixture of fireworks in place of the ordinary one which contains aluminum and potassium perchlorate and which has long been a cause of serious accidents in the firework industry. The chemical reaction of the magnesium sulfate/magnesium mixture on detonation is thought to be: MgSO4 + 4 Mg => MgS + 4 MgO + 353 kcal. From several experiments following results were obtained: (1) The intensity of the explosive noise from the magnesium sulfate/magnesium mixture is almost the same as that from the ordinary aluminum mixture when the weight of the charge of the former is two or two and a half times as large as that of the latter. (2) The magnesium sulfate/magnesium mixture is far more safe on handling than the ordinary aluminum mixture. It was proved by an iron ball dropping test and a fire propagation test. (3) The tone quality of the noise from the magnesium sulfate/magnesium mixture is mild and superior than that from the ordinary aluminum mixture. (4) In practical use it is necessary to protect the noise unit which contains the magnesium sulfate/magnesium mixture from moisture.
Proceedings of the 15th International Pyrotechnics Seminar, July 1990.

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The Effect of Hot Spots on Burning Surface and Its Application to Strobe Light Formation with Mixtures Which Contain No Ammonium Perchlorate

Abstract: The objective of this work was to make clear the effect of hot spots or hot spot materials on burning pyrotechnic compositions and to find practicable strobe light compositions without ammonium perchlorate which is not always popular in the firework field, using the effect of hot spot materials. As the hot spot materials, four types, Japanese oak charcoal, red iron, red lead, and potassium dichromate were selected from many substances. The effect of each was examined by burning tests of compositions which contained rosin, usual oxidizers (ammonium perchlorate, potassium perchlorate, and potassium nitrate), and a small quantity of each hot spot material. In this case, the effects did not clearly appeared except that of potassium dichromate, which promoted the burning rate of compositions in fairly large extent. Secondly, the effect of red lead and potassium dichromate was examined with compositions which consisted of magnesium, guanidine nitrate, and metal sulphates, which had been thought to be suitable for strobe lights. From the results of experiments, examples of four colored light compositions are shown for practical use. It is concluded that the effects of hot spots are not so clear, when using with compositions which contain usual oxidizers. However, when using with the compositions for strobe light, which do not burn so easily, the hot spot materials are very effective in adjusting the strobe reaction and to obtain the compositions in practical use.
Proceedings of the 16th International Pyrotechnic Seminar, June, 1991.

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The Surface Explosion of Pyrotechnic Mixtures

Abstract: In the past we sometimes observed a fairly large burning star caused an explosion with a loud noise at the very moment when it fell onto the ground. The star did not explode totally, but only with the thin surface layer. The burning surface layer of the star may be very sensitive to shock because of the high temperature. This phenomenon is here called the “surface explosion.” The objective of this paper is to investigate the surface explosion by experiments. It may be very important to make clear the mechanism of the transition from burning to explosion or detonation not only with pyrotechnic mixtures, but also with general explosives, especially to avoid accidents. The mechanical sensitivity of the burning surface layer was examined by dropping an iron ball onto it with consolidated mixtures of ordinary stars and illuminants, etc. Most of them showed a higher sensitivity than that of a standard mixture called red explosive at ordinary temperatures. Using small rocket engines, propellant of potassium chlorate and potassium perchlorate comparing with that of ammonium perchlorate were examined. The former two caused the surface explosion or a perfect detonation when ignited and the rocket engines were broken, and only the propellant of ammonium perchlorate worked well. The phenomenon of the surface explosion was discussed in combination with a past accident.
Proceedings of the 18th International Pyrotechnics Seminar, July 1992.

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Stabilizing Firework Compositions 
     I. Minimum Solubility Law to Foresee the Degeneration 
    II. A New Chemical Method of Magnesium Coating

Abstract: These studies concern two important problems at present: one is how to select the component materials of a mixture not to cause degeneration, and another is to find a more effective method of magnesium coating than those at present. A firework mixture generally consists of several solid materials which are closely in contact with each other. The state is not so much natural as artificial. Therefore, the mixture often causes chemical degeneration to remove into a more stable state which is opposite to the purpose. The direction of the change has been unknown without experiences. It has been a great difficulty on selecting materials. I have found a rule to foresee the direction: the component materials in a mixture gradually decomposes with each other to create the most water insoluble material. This tendency should be called the “minimum solubility law”. A table was prepared to foresee the direction of the degeneration reactions arranging materials in the order of their solubilities. When a magnesium flake is soaked in a solution of dichromate and sulfate, the flake is gradually coated with a thin black film. It may be CrO2 and have a high corrosion resistance. The effect was tested with several dichromates and sulphates against mainly ammonium perchlorate using magnesium ribbon and powder. In addition an effect of guanidine nitrate on the coating was observed because it gave a good result of corrosion resistance when it was used as a blinker (strobes) in the past.
Proceedings of the 19th International Pyrotechnics Seminar, February, 1994.

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Burning Rate and Grain Size of Component Materials of Pyrotechnic Mixtures

Abstract: It has been generally believed that the finer the grain size, the faster the burning when we select the component materials of a pyrotechnic mixture. It is not always true because a small explosion occurred in the past when we tested a smoke mixture, although it contained a dye of very coarse grains. The purpose of this paper is to make clear the general mechanism of the burning rate of pyrotechnic mixtures on the standpoint of the grain size of component materials of pyrotechnic mixtures. Experiments on burning rate were carried out with four types of mixtures changing the grain size of the component materials: (a) base mixtures of oxidizer (conventional materials as potassium chlorate, potassium perchlorate or ammonium perchlorate) and fuel (accroides resin), (b) mixtures of the base and an inert material (clay), (c) mixtures of the base and a semi-inert material (barium nitrate), (d) mixtures of an explosive of synthesized simple substance (potassium picrate) and an inert material (clay). All the materials except potassium picrate were sieved to obtain grains of six class sizes. With decreasing the grain size of the component materials, some mixtures increased and some decreased the burning rate. In other cases there were grain sizes which gave the smallest burning rate: the burning rate at first decreased and then increased. In general, the burning reaction seemed to be stabilized as the grain size decreased. These effects will help the designing of pyrotechnic mixtures for various purposes.
Proceedings of the 20th International Pyrotechnics Seminar, July 1994.

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