Crystal Transformation Temperature Research Articles

Inhibition of dissolution‐induced crystal transformation of ϵ‐Hexanitrohexaazaisowurtzitane in plasticizers by polydopamine coating**

AbstractIn order to avoid the crystal transformation of ϵ‐Hexanitrohexaazaisowurtzitane (ϵ‐HNIW) dissolved in plasticizers, a suitable bonding agent was selected to inhibit the crystal transformation of ϵ‐HNIW. Interfacial interaction simulations were carried out using Materials Studio2017 software for selected neutral polymer bonding agent (NPBA), polyene polyamine bonding agent (LBA) and polydopamine (PDA) and ϵ‐HNIW. Results showed that the interaction order of the three polymers on the ϵ‐HNIW crystal surface is PDA>NPBA> LBA; ϵ‐HNIW@ PDA crystal phase was more stable. Therefore, ϵ‐HNIW@ PDA crystal particles were constructed by the in‐situ self‐polymerization coating technology. Scanning electron microscope (SEM) showed that the ϵ‐HNIW@ PDA was square with smooth surface. The thermal properties of ϵ‐HNIW@ PDA were investigated by differential scanning calorimetry (DSC), which showed that the coating of PDA effectively increased the transition temperature of ϵ‐HNIW crystal. Moreover, the solubility and crystal transformation mechanism and law of ϵ‐HNIW/ϵ‐HNIW@ PDA in four plasticizers were further studied and compared systematically, ϵ‐HNIW@ PDA showed significantly lower solubility compared with ϵ‐HNIW. The solubility size was ranking as isodecyl nonanoate (IDP)>dioctyl sebacate (DOS)>dioctyl adipate (DOA)>paraffin liquid (RH). Variable‐temperature X‐ray diffraction (XRD) tests showed that PDA increased the ϵ‐HNIW crystal transformation temperature by about 35 °C. The small amount of dissolution of ϵ‐HNIW by the four plasticizers had a facilitative effect on the ϵ‐HNIW crystal transformation, which was consistent with the solubility magnitude. These results indicated that PDA‐coated ϵ‐HNIW enhances crystal interfacial interaction, reduces the solubility in plasticizers, and has a significant inhibitory effect on the dissolution‐induced crystal transformation of ϵ‐HNIW.

The Crystal Transformation of α‐HNIW Coated with Different Coatings

AbstractIn this article, varying coatings including rubber binders, plasticizers, and dopamine derivatives have been well coated on the surface of α‐HNIW via the application of water suspension and in‐situ coating method, and the influence of different coatings on the crystal transformation of α‐HNIW has been studied. SEM, DSC, and XRD have been performed for the characterization of the coated α‐HNIW. The results demonstrate that rubber binders have inhibitory effects on the crystal transformation of α‐HNIW, and the inhibitory effect is ranked as NR>BR>EPDM. While the four plasticizers have promoted the crystal transformation of α‐HNIW, and the promoting effect is ranked as DOS>IDP>DOA>RH. Dopamine derivatives have been innovatively used to coat α‐HNIW, which have formed a stable polymer film on the surface of α‐HNIW and result in delayed crystal transformation temperature. In the meanwhile, the inhibitory effect of dopamine derivatives is greater than that of rubber binders with a ranking as PDA>PNE>PLD>POHDA.

Effects of different coatings on the crystal transformation of β-HNIW

In this study, the effects of dopamine, binder and plasticizer on the crystal transformation of β-HNIW were investigated. By a simple preparation method, dopamine, plasticizer and binder were coated on the surface of β-HNIW. The characterization results of SEM, DSC and XRD show that the four dopamine polymers, three binders and four plasticizers form a stable polymer film on the surface of β-HNIW crystal. The crystal transformation temperature of β-HNIW crystal coated with dopamine polymer is delayed to varying degrees, and the crystal transformation temperature is significantly improved about 40 °C. Dopamine polymers effectively inhibit the crystal transformation of β-HNIW, improving the thermal safety of β-HNIW. The three binders have inhibitory effect on the crystal transformation of β-HNIW, and four plasticizers promote the crystal transformation of β-HNIW. Dopamine and binder have an inhibitory effect on the β-HNIW crystal transformation, while the plasticizer has a promoting effect on the β-HNIW crystal transformation.

Enhanced Crystal Stabilities of ε-CL-20 via Core-Shell Structured Energetic Composites

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a widely used high-energy explosive for the application of energetic materials. However, the phase transformation from ε-CL-20 to γ-CL-20 restrains its further application in polymer bonded explosives (PBXs) and propellants. To inhibit the phase transition of CL-20, dopamine was first used in an efficient and facile method of in situ polymerization to passivate CL-20 crystals. The core-shell microcapsule particles were obtained, and the morphological characterization demonstrates the formation of a dense core-shell structure. The differential scanning calorimetry (DSC) and in situ X-ray diffraction (XRD) test results show that the compact and dense coating delays the ε-CL-20 crystal transformation temperature by about 30 °C, which enhances thermal stability. In addition, with the coating via polymers, the friction sensitivity of ε-CL-20 crystals decreases significantly. The findings indicate a successful application of dopamine chemistry in high-energy explosives, which provides an attractive method to modify the properties of CL-20 crystals.

Preparation and Doping Effect of Surface Modified ZnS Nanoparticles on Liquid Crystal Nanocomposite System

A simple method was utilized to synthesize ZnS nanoparticles using mercaptoacetic acid as modifier in aqueous solution. XRD demonstrates that the ZnS nanoparticles have face-centered cubic structure. FT-IR spectroscopy shows that the stabilizer mercaptoacetic acid (MPA) is successfully modified on the surface of ZnS nanoparticles. A nanocomposite system was obtained by mixing the MPA modified ZnS nanoparticles with nematic liquid crystal 4’-pentyl-4-cyanobiphenyl (5CB). The doping effect on liquid crystal texture, liquid crystal transformation temperature, and ultraviolet absorption of the nanoparticles was investigated. The nanocomposite system remains the silky texture of the liquid crystal regardless of the addition of ZnS nanoparticles.

Influences of Heat Treatment on A95 Polycrystalline Alumina Fibers Preparation

In order to discuss chemical and physical reaction of A95 polycrystalline alumina fibers (PAF) during heat treatment and improve the properties, the influences of the protective atmosphere and heat treatment temperature on properties of PAF were researched. DT-TG, IR, XRD and SEM were adopted to characterize the fibers. The results show that in N2 atmosphere, the carbonization and oxidation rates of the gel fibers decrease, the thermal decomposition process of the organics is extended and the crystal transformation temperature of alumina is enhanced. When the heat treatment temperature is lower than 1200 °C, the major phases of A95 PAF are mainly δ-Al2O3 and θ-Al2O3, but no α-Al2O3 appears.

Nitrogen-Doped Carbon Nanotubes Prepared at Different Temperatures for Oxygen Reduction Reaction

The nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor deposition using ethanediamine as a precursor and ferrocene as a growth catalyst under the reaction temperatures of 800°C, 850°C, 900°C and 950°C, respectively. The doped nitrogen aggregated within the bamboo joints of CNTs, and the reaction temperature influenced the amount and type of nitrogen doped into CNTs. The best catalytic activity toward oxygen reduction reaction (ORR) in an alkaline medium was obtained with the N-CNTs prepared at 800°C due to the largest amount of nitrogen being doped into CNTs mainly in the form of pyridinic type. However, the reaction temperature of 900°C is so close to the crystal transformation temperature of iron due to the use of ferrocene that nitrogen would be difficult to be doped into CNTs. Accordingly, the presence of least amount of pyridinic type nitrogen accounted for the poorest ORR activity of N-CNTs prepared at 900°C.

Shape-memorizable styrene-butadiene block copolymer. I. Thermal and mechanical behaviors and structural change with deformation

Thermal properties in the range from room temperature to 150°C, mechanical properties from room temperature to 80°C, and structural changes by drawing and contraction at 80°C followed by crystallization have been studied in a crystalline styrene-butadiene block copolymer, which has the property of shape memory, using differential scanning calorimetry (DSC), mechanical analysis, wide-angle x-ray diffraction (WAXD), and smallangle x-ray scattering (SAXS). This copolymer has the crystal transformation temperature, the melting temperature of the trans- 1,4-polybutadiene domains, and the higher glass transition temperature of the polystyrene domains. When a high strain is adopted for the deformation at 80°C (i.e., between the melting temperature of the polybutadiene [PB] domains and the glass transition temperature of the polystyrene regions) and crystallization conditions with fixed ends are employed, a fibrillar structure with a better regularity of long spacings and a high orientation of crystals forms. When the drawn sample is allowed to contract at 80°C, the high contraction or the shape recovery appears. Nevertheless, crystallization after contraction presents essentially the same supermolecular structure as that before contraction. It is suggested that the molecular chains of polybutadiene were inhibited from flowing freely by the glassy polystyrene molecules and that there must be some structural units separated by amorphous domains that contribute to the elongation and contraction at the high temperature.

Crystal transformation of styrene-butadiene block copolymer

The crystal transformation of styrene-butadiene block copolymer, which has the attribute of shape-memory, has been studied. It is demonstrated from differential scanning calorimetry and wide-angle X-ray diffraction measurements that reversible crystal transformation takes place with temperature; two distinct crystal forms exist above and below the crystal transformation temperature of ∼45°C.

Anisotropic resistivity in the two-dimensional metal (La 1− xSr x) 2CuO 4

Large single crystals of (La 1− x Sr x ) 2CuO 4( x=0.06 and 0.07) of size about 6 mm ( ac-plane) × 40 mm ( a-axis) were grown by the traveling solvent floating zone method. The out of plane resistivity exhibited a distinctive metal-to-semiconductor transition at the tetragonal-to-orthorhombic crystal transformation temperature. The in-plane resistivity was mettalic and showed T α-dependence ( α=1.3−1.5) both in tetragonal and orthorhombic phases. The anisotropy ratio in the resistivity was more than 1000. The conduction mechanisms along both the a- and the c-axes seemed to be quite unique.

Poly(p‐benzamide). II. Thermal behavior and crystal transformations

AbstractThe thermal behavior and crystal transformation of poly(p‐benzamide) are reported. Modification I contains both solvent (N,N‐dimethylacetamide) and LiCl in its crystal lattice. Modification II is likely to form a complex crystal with LiCl, whereas crystalline modification III contains neither solvent nor LiCl in its unit cell. The crystal transformation temperature from modification I to II is 214°C, and the crystal–nematic transition temperatures of modification II and III are 475 and 544°C, respectively. Modification III can be obtained from II by heating above 475°C and cooling, or by washing with water. It can also be obtained from modification I by washing with water and annealing.

Structural studies of the high temperature form of trans-1,4-polybutadiene crystal

Abstract It is known that trans-1,4-polybutadiene shows a crystal transformation at about 76°C. The crystal structure of the high-temperature form of trans-1,4-polybutadiene has been studied by X-ray diffraction. The chain conformation of the high-temperature form is similar to that of the low-temperature form. Above the crystal transformation temperature, the CH2─CH2 bond remains trans, but the internal rotation angles around two CH2─CH bonds are decreased to 80° and −80° from 109° and −109°, respectively. The molecular chains, however, are considered to be in a considerably distorted state due to torsional oscillation about the C─C bonds. It is shown that the X-ray diffraction pattern of the high-temperature form can be explained by taking into account the rotational motion of the chain segments around the molecular axes.

Crystallized state, thickening process, and crystal transformation of single crystal of trans-1,4-polybutadiene

Abstract The effect of heat treatment of trans-1,4-polybutadiene single crystals prepared from dilute benzene solution was studied by dilatometry, X-ray diffraction, and dynamic viscoelastic measurement. The crystal transformation temperature of the single crystal is 55.5[ddot]C, 20[ddot]C lower than that of the bulk crystallized sample. After heat treatment of the single crystal above 55.5[ddot]C, their crystal transformation temperature increases to 69.5[ddot]C. At the same time, thickening of the lamellae suddenly occurs and the viscoelastic primary absorption observed in the single crystal mat disappears. It is suggested that this means that the amorphous region attached to the single crystal rapidly crystallized above this temperature, in particular the loose loops attached to the end surface of the crystal are dragged into the crystalline phase to form tight loops as a result of the sliding diffusion of molecules along their axes. This is accompanied by the sudden thickening of the lamellae at the c...

On the Properties of Powdered and Massive UO2 and U4O9

Samples used in this experiment are as follows.(1) UO2 powder : Ceramic grade UO2 powder produced by Degussa Works. (o/u-2.08)(2) Massive UO2: Eleetrodeposited UO2. (o/u-2.005)(3) Massive UO2: Fused UO2 produced by Spencer Works. (o/u-2.00 3)(4) Massive U4O9 : Electrodeposited U4O9_X (o/u-2.10)(All massive samples were crushed -325 mesh and tested)The difference of oxidation behavior of each sample was detected by X-ray analysis, in-frared spectrophotometry, D.T.A. and microstructure.Main results obtained were as follows.1) The relationship between heating temperature and o/u ratio of samples were shown in Fig.3. The results of X-ray analysis and infrared spectrophotometry of these heated samples were summarized in Table 2. The DTA curves of these samples ware shown in Fig.1. From these results, it seemed that the oxidation behavior of these samples were same substantially, namely, UO2 (cubic) or U4O9_X (cubic) 200-400°C U3O7 (tetragonal) 340-425°C U3O8 (orthorhombic), and the difference of the crystal transformation temperature of individual sample might be introduced from its particle size and surface activity.2) From the results of infrared spectrophotometry, we could recognize a small absorption at about 15.3μ of infrared ray, and it might be caused by the existence of U3O7 phase.3) As shown in Photo. 2, the shape of electrodeposited U4O9_X single crystal was lozenge and very thin, and completely differ from the shape of octahedron of electrodeposited UO2. But this apparent difference of both crystals are not so substantial. The regular triangular etch pits on the lozenge face of U4O9_X crystal showed that this face is identical with (111) face of UO2 crystal.