Critical Shock Energy and Shock and Detonation Parameters of an Explosive

The present study deals with the connection between critical shock energy and detonation properties of an explosive. A relation for critical shock energy has been derived in terms of detonation velocity, width of reaction zone, initial density of the explosive, specific heat ratio of detonation products and either constants of linear relation between shock and particle velocity of the explosive or the constants of the Murnaghans type of equation of state of the explosive. These relations have been used to calculate the critical shock energy of RDX, HMX, RDX/TNT (60/40) and TNT explosives. The values of critical shock energies obtained in this study are in close agreement with those reported in the literature.Defence Science Journal, 2009, 59(4), pp.436-440, DOI:http://dx.doi.org/10.14429/dsj.59.154

Metallised Fuel rich Propellants for Solid Rocket Ramjet: A Review

This paper reviews the research work carried out in the field of metallised fuel-rich propellants (FRP). Limitations and merits of various potential metals (Al, Mg, B, Be, or Zr) as a component of FRP are discussed. The paper also includes a discussion on the combustion mechanism of metallised propellants, including problem areas and probable remedial measures. Zirconium and Ti appear to have potential to offer FRP with efficient combustion. Ideal performance is not achieved with current systems based on Al and B and further work is needed to develop FRP having all three desirable attributes, viz., ease of ignition, stable combustion and high specific impulse (I/sub sp/) in a single composition

Strength Degradation of Sapphire Fibers During Pressure Casting of a Sapphire-Reinforced Ni-Base Superalloy

Transient-liquid-phase (TLP) bonding was used to fabricate a Haynes 230 Ni-base superalloy/sapphire fiber composite for high-temperature applications. Boron was used as a melting-point depressant for the Ni, to aid superalloy infiltration of the fibers. Preliminary study of the composite indicated an incomplete TLP bonding cycle. Therefore, microstructural and microchemical analyses were carried out to determine the TLP bonding mechanism. It was found that the TLP process did not occur under local thermodynamic equilibrium conditions at the solid/liquid interfaces, contrary to the primary assumption of conventional models, so a modified model for TLP bonding is proposed. The main differences between the proposed and the conventional models are: (a) the concentration of the melting-point depressant increases with time during isothermal solidification, (b) extensive boride segregation at grain boundaries and boride precipitation occurs within grains adjacent to the interlayer in the initial composite assembly, (c) because of the relatively high boron concentration in the interlayer, the TLP bonding cycle was incomplete, resulting in residual-liquid borides. To achieve ideal TLP bonding, four modifications are recommended: (i) use less boron, (ii) use finer sapphire fibers, (iii) create smaller initial grain sizes in the matrix and (iv) increase the homogenization time

Impact, Friction, Shock Sensitivities and DDT Behaviour of Advanced CMDB Propellants

This paper reports results of impact, friction and shock sensitivities of CMDB propellants containing AP, RDX, PETN and their combinations. Results of impact and friction sensitivities indicate that CMDB propellants containing AP are highly sensitive and AP-based compositions are more impact and friction sensitive than RDX and PETN-based compositions, qnd that these sensitivities are proportionalto oxygen balance of the composition, which is in agreement withearlier findings. Inclusion of high explosives like RDX and PETN increases the shock sensitivity of CMDB formulations, whereas AP-based compositions are least shock sensitive. There exists are lationship between shock sensitivity and VOD of the individual oxidiser/high energy ingredient incorporated in the formulation. Shockamplitude values of 87 and 46 k bar in CMDB and DBP, as determinedby NOL card gap test, suggest that CMDB propellants are much more shock sensitive than DBP. Composite propellants are insensitive toshock, as they did not undergo detonation even at zero card gap.Results of DDT behaviour of CMDB propellants show that they aremore prone to deflagration to detonation transition under adverse conditions

Synthesis and Characterisation of Diaryl Furoxans

The paper discusses the synthesis, characterisation, and performance evaluation of diarylfuroxans namely, bis-phenyl-3,4-furoxan (5) and bis-(4’-nitrophenyl)-3,4-furoxan (6). Themolecules have been synthesised on the lines of reported method by cyclodimerisation of thenitrile oxides generated from benzaldoxime and p-nitro benzaldoxime, respectively. The synthesisedfuroxans (5 ) and (6) were characterised by the elemental analysis, UV, IR, and 1H NMRspectroscopy. The hazard characteristics (impact and friction sensitivity) confirm that thecompounds are safe to handle. The oxygen balance, velocity of detonation and detonationpressure have been computed. The detonation velocity and pressure along with oxygen balanceincreased with the substitution of nitro group in the benzene ring, as expected. Thethermogravimetric studies on promising compound (6) brings out that maximum weight lossoccurs at decomposition temperature of 259–260 °C

Autistic adults’ experiences of managing wellbeing and implications for social prescribing

doi: 10.1080/09687599.2023.2263628Autistic people demonstrate poor outcomes on objective measures of wellbeing, yet research centring lived experience provides a more nuanced picture. There is growing support for person-centred, holistic and community approaches to enhancing wellbeing for autistic people. Social prescribing may be one such approach. This qualitative study explored the concept of wellbeing for autistic adults – including barriers and self-management – and the implications of this for modifying social prescribing. It involved semi-structured interviews with 21 autistic adults in the UK. Reflexive thematic analysis of the data supports research suggesting that self-determination may underlie many aspects of wellbeing for autistic people. The COVID-19 pandemic provided new opportunities to develop wellbeing strategies but also had negative impacts. Social prescribing could promote self-determination by signposting autistic people to peer support opportunities building on intrinsic interests

Thermal Behaviour of AP Based CMDB Propellants with Stabilizers

Stability test results and DTA studies indicate the superiority of molecular sieve (MS) over zirconium silicate (ZrSiO/sub 4/) as the stabilizer for a composite modified double base (CMDB) system. Shelf life as computed from autoignition test results was 30 years for MS-based composition which is almost double the life of ZrSiO/sub 4/, but approximately half the life of resorcinol-based composition which was used as a reference. Higher stabilizing effect of MS as compared to ZrSiO/sub 4/ has been explained on the basis of the presence of channels and cavities in its structure, which makes it an effective adsorbent for decomposition catalysing species. Poor stabilization capability of m-dinitrobenzene as compared to resorcinol suggests the catalytic involvement of acidic decomposition products of nitrate esters in autodecomposition process of CMDB propellants

Transition Metal Carbohydrazide Nitrates: Burn-rate Modifiers for Propellants

This paper discusses the synthesis and characterisation of cobalt (Co), nickel (Ni) andcopper (Cu) carbohydrazide nitrates. In differential scanning calorimetry (DSC), the complexesexhibited exothermic decomposition indicating their energetic nature. The commencement ofdecomposition was observed at 220 °C for Ni complex, and at 160 °C for Co complex whereasthat of Cu complex occurred at 75 °C. In view of the better thermal stability, Ni and Co complexeswere selected for further study. The activation energy of decomposition of Ni and Co complexeswere found to be 47 kcal/mol and 60 kcal/mol respectively. Impact and friction sensitivity testresults revealed relatively lower vulnerability of carbohydrazide cobalt nitrate. Its incorporationin an ammonium perchlorate (AP)-based composite propellant led to 9-19 per cent enhancementwhereas that of carbohydrazide nickel nitrate resulted in 28-74 per cent enhancement in burningrates in the pressure range 1.9 MPa to 8.8 MPa. Exothermic decomposition of the coordinationcomplexes on propellant surface and involvement of metal at molecular level formed ondecomposition of the complexes in combustion environment of composite propellant may beattributed to the catalytic effect of this class of compounds on the lines of reported literature

Combustion Behaviour of Advanced Solid Propellants.

The study reports the effect of incorporation of Al and ammonium perchlorate (AP) individually and in combination with each other on combustion pattern and specific impulse (Isp) of minimum signature propellants. Incorporation of Al obviates the combustion instability problems; however, it has marginal effect on burning rates. The composition containing AP and zirconium silicate combination gives superior performance; however, its Isp is considerably lower than the composition incorporating 9 per cent AP. A combination of 6 per cent Al gave 20 per cent enhancement in burning rate and 12 s increase in Isp as compared to purely nitramine-based composition, cal-val results also reveal increase in energy output on incorporating AP and Al. Hot stage microscopic and propellant combustion studies indicate occurrence of intense decomposition reaction in case of AP-based compositions