טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentOlga Meikler
SubjectThe Effect of Surface Poisoning Additives on Crystallization
DepartmentDepartment of Chemistry
Supervisors Professor Eichen Yoav
Dr. Denekamp Chagit
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Controlling the morphology (polymorphism, shape, and size) of powders is significant for many industrial applications, as these properties influence the fluidity of both the powder and its compositions.

In polymer-bonded explosives, the influence of powder morphology on sensitivity has been reported repeatedly. Controlling the crystal morphology is therefore a ubiquitous challenge and thus has drawn the attention of many research groups. One way to gain control over crystal morphology is by the use of molecular additives.

Crystal morphology is also relevant in the field of nitroaromatics, some of which are energetic materials. Nitroaromatic 2,4-dinitroanisole (DNAN) is an energetic material that has lately been used as a substitute for 2,4,6-trinitrotoluene (TNT) in melt pour compositions that are less-sensitive replacements for composition B. DNAN was used as a model compound for the study of surface-poisoning effects in crystallization.

In addition to the expected solvent effect, it was found that the concentration of solutions and presence of additives control the formation of polymorphs and crystal habits. In some cases, aromatic and/or nitro- containing additives interact with DNAN, probably competing with intrinsic intermolecular interactions that allow the formation and growth of DNAN crystals. It was also found that single -crystal- to-single-crystal phase transitions take place between γ to β form and from the β form to the α form

An important property for use of material in melt pour compositions is a relatively low melting point, which is required to be far from its initiation point for the process to be safe. We present development of new energetic compositions suitable for extrusion based printing. We explore the possibility of using eutectic mixtures of energetic materials. For example, BTNPTE, a dense TNT analog, forms molten mixtures with DNAN having a >220 ˚C gap between melting and thermal decomposition temperatures. We successfully printed layers using the eutectic mixtures to reach proof of concept.