502 research outputs found
Landfill Leaching: an Experimental Investigation Using Column Apparatus
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Detonator using Nickel Hydrazine Nitrate as Primary Explosive
Nickel hydrazine nitrate is an energetic coordination compound having explosiveproperties in between that of primary and secondary. This compound was used to develop a newtype of detonator by replacing the sensitive primary explosive, lead azide in conventionaldetonators and keeping RDX (cyclotrimethylenetrinitramine) as the output secondary explosive.The detonator consists of three regions, viz., initiation, deflagration-to-detonation transition(DDT), and output. The initiation and the electrical rating of 1A/1W no-fire were achieved usinga suitable squib. The DDT and the output were taken care of, by pressing requisite quantitiesof Nickel hydrazine nitrate and RDX, respectively at required densities in a stainless steel stemchannel. The detonator assembly involves crimping the squib and the stem channel in a stainlesssteel housing and applying a suitable resin at the crimped-end for leak tightness. The outputwas assessed from the dent depth on aluminium plate, volume expansion on lead block, and byachieving veloctiy of detonation of 8200 m/s in mild detonating cords, containing 0.95 g/m ofRDX, which indicates full-order detonation. The detonators were tested at system level andfound to perform satisfactorily
QENS and FTIR studies on binding states of benzene molecules adsorbed in zeolite HZSM-5 at room temperature
Fourier-transform infrared (FTIR) spectroscopy and quasi-elastic neutron scattering (QENS) were
employed for monitoring of the binding states of benzene molecules, adsorbed in HZSM-5 zeolite at 300 K and
for loadings of 0.6 to 7 molecules per unit cell. While the in-plane combination C-C and C-H stretching bands
of adsorbed benzene remained una.ected, a splitting was observed in the out-of-plane C-H bending vibrational
bands, a feature reported for the transformation of benzene from liquid to solid phase. Also, the intensity ratio of
the in-plane C-C stretching band (ν19 of adsorbed benzene at 1479
cm-1 and the bands in the region ) 3100-3035 cm-1 due to fundamentals and
combination C-C and C-H stretching vibrations indicated a trend observed typically for a condensed phase of
benzene. No shift was observed in the frequency of the above-mentioned IR bands when zeolite samples
exchanged with Na+ or Ca2+ were employed. QENS results suggest that the
benzene molecules occluded in zeolitic pores (~3 molecules per unit cell) undergo a 6-fold rotation but their
translation motion is too slow. Also, a high residence time of 16.5 ps was observed for the benzene entrapped
in HZSM-5, compared to a time of ~2.5 ps reported for the liquid and ~19 ps for the solid state of benzene.
These results reveal again the compression of the benzene molecules on adsorption in zeolitic pores. It is
suggested that the benzene molecules confined in cavities experience a strong intermolecular interaction, giving
rise eventually to their clustered state depending on the loading. In the clustered state, benzene molecules are
packed with their plane parallel to zeolitic walls and interact with each other through p-electron clouds. No
electronic bonding is envisaged between these clusters and the framework or the extra-framework zeolitic
sites
Three-Dimensional Elastic Compatibility: Twinning in Martensites
We show how the St.Venant compatibility relations for strain in three
dimensions lead to twinning for the cubic to tetragonal transition in
martensitic materials within a Ginzburg-Landau model in terms of the six
components of the symmetric strain tensor. The compatibility constraints
generate an anisotropic long-range interaction in the order parameter
(deviatoric strain) components. In contrast to two dimensions, the free energy
is characterized by a "landscape" of competing metastable states. We find a
variety of textures, which result from the elastic frustration due to the
effects of compatibility. Our results are also applicable to structural phase
transitions in improper ferroelastics such as ferroelectrics and
magnetoelastics, where strain acts as a secondary order parameter
Intermediate states at structural phase transition: Model with a one-component order parameter coupled to strains
We study a Ginzburg-Landau model of structural phase transition in two
dimensions, in which a single order parameter is coupled to the tetragonal and
dilational strains. Such elastic coupling terms in the free energy much affect
the phase transition behavior particularly near the tricriticality. A
characteristic feature is appearance of intermediate states, where the ordered
and disordered regions coexist on mesoscopic scales in nearly steady states in
a temperature window. The window width increases with increasing the strength
of the dilational coupling. It arises from freezing of phase ordering in
inhomogeneous strains. No impurity mechanism is involved. We present a simple
theory of the intermediate states to produce phase diagrams consistent with
simulation results.Comment: 16 pages, 14 figure
Droplet Fluctuations in the Morphology and Kinetics of Martensites
We derive a coarse grained, free-energy functional which describes droplet
configurations arising on nucleation of a product crystal within a parent. This
involves a new `slow' vacancy mode that lives at the parent-product interface.
A mode-coupling theory suggests that a {\it slow} quench from the parent phase
produces an equilibrium product, while a {\it fast} quench produces a
metastable martensite. In two dimensions, the martensite nuclei grow as
`lens-shaped' strips having alternating twin domains, with well-defined front
velocities. Several empirically known structural and kinetic relations drop out
naturally from our theory.Comment: 4 pages, REVTEX, and 3 .eps figures, compressed and uuencoded,
Submitted to Phys. Rev. Let
Disorder-Driven Pretransitional Tweed in Martensitic Transformations
Defying the conventional wisdom regarding first--order transitions, {\it
solid--solid displacive transformations} are often accompanied by pronounced
pretransitional phenomena. Generally, these phenomena are indicative of some
mesoscopic lattice deformation that ``anticipates'' the upcoming phase
transition. Among these precursive effects is the observation of the so-called
``tweed'' pattern in transmission electron microscopy in a wide variety of
materials. We have investigated the tweed deformation in a two dimensional
model system, and found that it arises because the compositional disorder
intrinsic to any alloy conspires with the natural geometric constraints of the
lattice to produce a frustrated, glassy phase. The predicted phase diagram and
glassy behavior have been verified by numerical simulations, and diffraction
patterns of simulated systems are found to compare well with experimental data.
Analytically comparing to alternative models of strain-disorder coupling, we
show that the present model best accounts for experimental observations.Comment: 43 pages in TeX, plus figures. Most figures supplied separately in
uuencoded format. Three other figures available via anonymous ftp
Tweed in Martensites: A Potential New Spin Glass
We've been studying the ``tweed'' precursors above the martensitic transition
in shape--memory alloys. These characteristic cross--hatched modulations occur
for hundreds of degrees above the first--order shape--changing transition. Our
two--dimensional model for this transition, in the limit of infinite elastic
anisotropy, can be mapped onto a spin--glass Hamiltonian in a random field. We
suggest that the tweed precursors are a direct analogy of the spin--glass
phase. The tweed is intermediate between the high--temperature cubic phase and
the low--temperature martensitic phase in the same way as the spin--glass phase
can be intermediate between ferromagnet and antiferromagnet.Comment: 18 pages and four figures (included
- …