Production of corundum armored ceramics

The purpose of this study was to develop the compositions and technology of corundum armored ceramics with high ballistic characteristics based on aluminum oxide with an α-Al2O3 content of more than 99 wt.%. The results of the study of the physicochemical processes of obtaining corundum ceramics modified with complex additives consisting of magnesium - aluminosilicate eutectic mixture and oxides of magnesium, yttrium, titanium, zirconium are presented. The introduction of complex additives into the composition of corundum ceramics provides a significant reduction (100-150°C) of the sintering temperature of the product. In this case, additives of yttrium and zirconium oxides contribute to the formation of a uniform-grained microstructure of ceramics, and in the case of adding titanium oxide, a collective recrystallization of corundum grains is noted. The use of small additives (0.3-0.5 wt.%) of magnesium and yttrium oxides together with a eutectic mixture in the compositions of corundum ceramics based on high-quality alumina contributes to the formation of a uniform-grained, dense structure of the material and giving it a high level of physical and mechanical properties as a result of directional the action of each component of the additive on the physicochemical processes of phase formation of the crystalline matrix. A model idea of the mechanism of action of additives on the formation of the microstructure of ceramics during stage-by-stage heating from 1350 to 1650°C in the sintering mode of products is presented. The developed compositions and technologies of corundum armored ceramics have a production focus and implementation in practice.

The retrogradation characteristics of starch in green wheat product Nianzhuan: effects of storage temperature and time

The objective of this study was to reveal the process of starch retrogradation and quality changes of Nianzhuan stored at 4, −18 °C, and freeze-thaw cycles treatment for different lengths of time. XRD revealed that Nianzhuan starch displayed an increasing trend of crystallinity with prolonged storage time and numbers of freezing-thawing cycles, which was likely due to a more orderly crystalline matrix in starch. The Raman full width at half-maximum (FWHM) of the bands at 2913 cm−1 of the three storage methods all decreased. According to DSC analysis, an increase in ∆H was detected, and a significant (P < 0.05) increase in T o and T p were found at −18 °C, and freeze-thaw treated samples, indicating more thermal energy were needed to disrupt re-crystallization. Good correlations between crystallinity, FWHM, ∆H, and hardness, springiness, chewiness were tested. The results of this study would provide useful information for the process of starch-based product Nianzhuan.

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

The aim of this paper is to show, by systematic studies, the influence of γ-Fe2O3 nanoparticles on the physical parameters of the liquid crystalline matrix, exhibiting a ferroelectric phase in a wide temperature range. The detailed research was carried out by using diffraction (PXRD), microscopic (OM, SEM, FCPM, POM), thermal (DSC), optical (TLI), electric and spectroscopic (FTIR) methods. We show that even the smallest concentration of γ-Fe2O3 nanoparticles largely modifies the parameters of the ferroelectric SmC* phase, such as spontaneous polarization, switching time, tilt angle, rotational viscosity, dispersion anchoring energy coefficient and helix pitch. The admixture also causes a significant reduction in the temperature of phase transitions, broadening the SmA* phase at the expense of the SmC* phase and strong streaking of the texture. We present and explain the non-monotonic modification of these parameters with an increase in the nanoparticle concentration. The influence of oleic acid admixture on these parameters is also widely discussed. We have shown that certain parameters of organic-metal nanocomposites can be controlled by the appropriate amount of metal admixture.

Warpage investigation of carbon/PEEK discontinuous long fibre thin panels

Discontinuous Long Fibre (DLF) composites, composed of randomly-oriented strands of chopped unidirectional pre-impregnated tape, have been used in the aerospace industry to produce intricate, net-shape parts with complex features – replacing complicated metallic brackets with single, lightweight parts. Carbon/PEEK DLF composites suffer from warpage problems driven by several factors including their high processing temperatures and semi-crystalline matrix shrinkage. This work aims to characterize warpage of thin-gauge parts and pursue mitigation. Results showed that the magnitude of warpage reduces with decreasing strand size and increasing thickness. At thicknesses greater than 2 mm, warpage appeared relatively stable. The introduction of ribbed features was explored as a mean of mitigating warpage by increasing part stiffness. No significant impact on the magnitude of warpage was observed within parts. However, the addition of ribs helped to control the warped shape of the part.

Effect of 2,4-dinitrophenol dye doping on tristhioureazinc(II) sulfate single crystals: a potential nonlinear optical material

Good quality single crystals of 2,4-dinitrophenol (DNP)-doped tristhioureazinc(II) sulfate (ZTS) were successfully grown by employing the simple and cost effective slow-evaporation solution technique. To study the effect of doping on various device properties, the grown single crystals were subjected to powder X-ray diffraction (PXRD), high-resolution XRD, thermogravimetric analysis (TGA), Vickers hardness testing, and UV–visible, photoluminescence (PL) and Fourier transform IR (FTIR) spectroscopy techniques. The crystal structure of DNP-doped ZTS bulk single crystals remained the same as the crystal structure of ZTS. However, the changes in intensities of the diffraction peaks in the PXRD spectra indicated the incorporation of dopants into the crystalline matrix. FTIR studies confirm the incorporation of dopants into the crystalline matrix, shown by the shifting of certain prominent absorption bands towards higher energy. This also indicated the induced useful strain due to doping, leading to charge transfer and the enhancement of nonlinear optical properties. The cut-off wavelength and optical band gap energy of pure ZTS and DNP-doped ZTS crystals were studied by UV–visible absorption spectroscopy, revealing a slight reduction in the optical band gap energy due to doping, which in turn revealed the enhancement of the optical range. PL studies revealed an enhanced optical range of photoluminescence in ZTS crystals. Second harmonic generation (SGH) studies carried out by the Kurtz powder technique revealed the enhancement of SHG value due to DNP doping. To ensure the thermal stability and mechanical strength of the grown crystals with doping (required from the point of view of device applications), TGA and Vicker's hardness studies were performed.

Probing the characteristics of mush-magma transition: insights from laboratory experiments

&lt;p&gt;The mush-magma transition (MMT) marks a profound change in rheological properties between two of the principal magmatic reservoirs that constitute a magmatic system. Mush behaves as a solid and its rheology is largely dominated by the deformation of the crystals network whereas magma is a liquid and has a rheology dominated by melt.&lt;/p&gt;&lt;p&gt;To better understand the solid-liquid transition in such crystal-rich systems, we present here an experimental study using mixtures of aqueous superabsorbent polymers (SAPs). SAPs are constituted of polymer grains that in water can swell up to 100 times and form gel grains whose size can be controlled by controlling the size of the initial powder. Particle fractions between 60% and 80% are easy to reach, making this system a promising analog of mush. The non-Newtonian rheology of the mixture of water and touching grains combines viscous, elastic and plastic aspects and can be characterized using the free-fall of spheres of different diameters and densities.&amp;#160;&lt;/p&gt;&lt;p&gt;We observe five different regimes of motion for the settling of a sphere: (1) A linear regime where the sphere has a rapid and linear fall and reaches a constant terminal velocity. (2) An irregular regime where the sphere&amp;#8217;s velocity fluctuates around a constant value. (3) A stop&amp;go regime where periods of no-motion and periods of irregular falls follow one another. (4) A slow fall regime where the sphere&amp;#8217;s velocity progressively decreases in a logarithmic way. And (5) a no-motion regime when spheres are not buoyant enough to overcome the yield stress of the mixture or are too small compared to the grain size. So, the Yield number (ratio of the yield stress to the sphere buoyancy-induced stress), critical value Yc above which there is no motion decreases as the sphere to grain diameters ratio becomes smaller than 2. This enlarges the domain of conditions under which the mush strength will lead to the entrapment of the intruder. Moreover, the mixture structure strongly affects the path that a buoyant melt pocket can follow through the mush, and the time it spends motionless. The latter will increase the time available for reactions between melt and surrounding crystalline matrix.&lt;/p&gt;