Explosive initiation of various forms of the Ti/2B energetic system

Clemenson, Michael

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Description

Title

Explosive initiation of various forms of the Ti/2B energetic system

Author(s)

Clemenson, Michael

Issue Date

2012-09-18T21:16:37Z

Director of Research (if dissertation) or Advisor (if thesis)

• Glumac, Nick G.
• Krier, Herman

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Titanium
• Boron
• Explosive Initiation

Abstract

Metal additives, such as aluminum, are commonly added to explosives in order to generate higher energy release and overpressures. However, these types of additives are ineffective in enabling a satisfactory level of control over the weapon’s blast effects. Metal-based reactive materials (RM) are of interest because they will allow weapons to be tailored to suit certain applications. The combination of titanium and boron is a prime example of such a reactive material. The high temperatures and persistent fireball generated by the Ti/2B composite after a weapon’s blast can be utilized in the defeat of biological weapons or destruction of bio-weapon factories. This energetic material can also conceivably be used as a structural reactive casing to enhance damage effects upon penetration of a target. The Ti/2B combination can take many forms, including Ti/2B powder blends and the titanium boride (TiB2) compound. However, most work in the area of Ti/2B reactive materials has focused on the creation and classification of Ti/2B mechanical alloys. Jiang et al. experimentally investigated the creation of these mechanical alloys using an arrested reactive milling procedure [1]. Through these investigations they determined a procedure to mechanically alloy titanium and boron into a metastable Ti/2B nanocomposite energetic material. The performance of Ti/2B composite energetics was analyzed in a methane flame experiment by Trunov et al. [2]. They found that in both wet and dry gaseous environments, the Ti/2B nanocomposite alloy achieved a more rapid and efficient combustion than aluminum powder when ignited in the flame. Yet, there remains a lack of information concerning the relative performance of the various forms of the Ti/2B energetic system when initiated with a high explosive (HE), a more realistic representation of the material’s application. Therefore, the aim of the current study is to investigate, in a controlled environment, the explosive parameter enhancement effects of various forms of Ti/2B energetic materials in air and compare their performance relative to an inert baseline. Experiments for the study were conducted in the large blast chamber located at the University of Illinois at Urbana-Champaign. Each material was initiated in air using single point detonation of a high explosive and a suite of diagnostics was used to gather information during each test. The diagnostics utilized include transient blast pressures, quasi-static pressures, two-color infrared pyrometry, spatially-varying spectroscopy, and high-speed imaging. The forms of the Ti/2B system tested during the experiment are as follows: • TiB2 Compound o -325 mesh • Ti/2B Powder Blend o -325 mesh titanium and boron • Ti/2B UIUC #1 Mechanical Alloy o -325 mesh titanium and boron • Ti/2B UIUC #2 Mechanical Alloy o -325 mesh titanium and nano-boron • Ti/2B NJIT Mechanical Alloy o -325 mesh titanium and nano-boron • TiO2 Inert Baseline Material o -325 mesh The high-speed imaging shows the development of the structure of the reactive material as it breaks out after initiation and begins to react. The imaging is also a useful tool for qualitative comparisons of the reactivity of the various forms of the energetic system. The imaging results show that the UIUC mechanical alloy #2 and the NJIT mechanical alloy have the most reaction emission leading to the qualitative conclusion that these materials are more reactive than the other forms tested. For each image a corresponding spatially-varying spectrum was recorded. The spectroscopic images show both the thermal emission spectrum of the high explosive and the emission spectrum from the reaction of the energetic material being tested. The spectral range is located in the visible spectrum, centered on the bands produced by the BO2 spectrum. The spectra show that the nanocomposite alloys emit the strongest BO2 signature which indicates a larger amount of boron combustion. The transient blast pressure measurements are useful in quantifying the peak overpressures produced by the initiation of the reactive material as well as the impulse contained in the initial blast wave. The reactive materials tested did not produce a significantly higher peak blast pressure when compared to the inert baseline test. This shows the reaction of Ti/2B reactive materials is too slow to drive the initial blast wave. The peak temperature of each reaction was recorded using a two-color infrared pyrometer at 1 and 1.5 μm. The measured temperatures of the various forms of Ti/2B materials were relatively the same within uncertainty. The quasi-static pressure (QSP) measurement is defined as the long-duration gas overpressure in the blast chamber after the explosive event. This data is the main focus of the experiment due to the fact that the energy release of the reactive materials can be calculated using the pressure data and a constant volume ideal gas analysis. These values can then be compared to a theoretical energy release based on enthalpy of reaction calculations. The QSP data shows that the nanocomposite mechanical alloys produce the greatest long-time overpressure and the largest energy release, confirming the qualitative predictions from the collected images and spectra. In conclusion, the imaging, spectral, and QSP data agree by showing that the Ti/2B mechanical alloys containing nano-boron are the most reactive of the materials forms tested and have the most promise when combined with conventional munitions. The peak temperatures were relatively similar and the peak overpressure data shows that the reaction of the energetic materials is too slow to impart a larger impulse to the initial blast wave.

Graduation Semester

2012-08

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Copyright 2012 Michael Clemenson

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