Crystallization of potash alum: effect of power ultrasound.

The influence of power ultrasound on the crystallization of potash alum was investigated. Experiments have been carried out in a batch stirred vessel. It was found that ultrasonic waves decrease the supersaturation limits and modify the morphology of the crystals produced. The average crystal size decreases with an increase of ultrasonic power. To investigate also the action of ultrasound on already existing crystals, crystals produced in silent conditions were suspended in saturated potash alum solution at various ultrasonic powers. The results show that ultrasound has also an abrasive effect on potash alum crystals for high power inputs.     

Optical limiting and its mechanism in potash alum

Optical power limiting is the increase of optical absorption with light intensity. Pure crystalline potash alum was grown and optical absorption in dependences of the light intensity and thickness of the crystal was studied using laser light. The transmission of the crystals was found to increase with increasing light intensity. However, at higher light intensity, an increase of optical absorption with intensity was observed. The power limiting characteristics, e.g. linear transmission/dynamic range and saturation point, were found to be varied with thickness of the crystal. The findings resulting from this investigation might have potential applications in optical limiting.     

Growth,structure, thermal,electrical and optical properties of potassium aluminum sulfate dodecahydrate (potash alum) single crystal

Single crystal of potassium aluminum sulfate dodecahydrate (potash alum) was grown by the slow evaporation technique of supersaturated aqueous solution at room temperature. The obtained crystal was characterized by using powder X-ray diffraction, DSC, TGA, electrical conductivity, optical transmittance and optical reflectance measurements. Structural and thermal analyses were performed on potash alum crystal. The electrical conductivity of potash alum as electrolyte sample was 1.894 × 10⁻⁶ S/cm. The optical transition and optical band gap energy of potash alum crystal were studied for the first time. Direct and indirect optical band gap energies were 5.75 and 4.50 eV respectively. Extinction coefficient, refractive index, real and imaginary dielectric constants and optical conductivity were calculated for potash alum crystal at a range of photon energies between 1.4 and 6.2 eV. Normal dispersion parameters of potash alum crystal were calculated for the first time.     

New OSL detectors based on LiMgPO4 crystals grown by micro pulling down method. Dosimetric properties vs. growth parameters

Rod-shape crystals of the LiMgPO₄ compound were grown by micro pulling down technique under the different growth conditions. Influence of the different growth rates, thermal setups and gaseous atmospheres on the crystals dosimetric properties was investigated. Samples were irradiated with ⁹⁰Sr/⁹⁰Y β particles and optically stimulated luminescence spectra were measured with the automatic Risø TL/OSL-DA20 reader. The sensitivity level, repeatability, dose–response dependence and short-time fading were compared for all grown crystals. It was found that the crystal grown from the iridium crucible was about three times more sensitive to radiation as compared to the crystal grown from the graphite crucible. Also the radio-sensitivity measured for the crystals grown from the graphite crucible was higher in case of higher growth rates. It was also shown that the residual OSL signal measured one and two weeks after the irradiation was higher for the crystals grown with higher growth rates. There was also no correlation observed between the growth conditions and the level of dose–response nonlinearity. Over the studied dose range the response nonlinearity of the studied samples fluctuated around over a dozen percent, regardless of the applied growth parameters. The obtained results tend to suggest that LiMgPO₄ crystals may be considered as promising dosimeters in different fields of research.     

The influence of a magnetic field on the mosaic spread and growth rate of small Rochelle salt crystals

The growth rates of small (length <1 mm) crystals of Rochelle salt grown with and without a magnetic field have been measured at constant supersaturation (4%). It has been shown that some crystals grown in the presence of a magnetic field exhibit a decrease in the linear growth rate in the [010] direction relative to that shown under normal conditions. It was further noticed that a few crystals of the total number showed slight increases in growth rate. The fact that a majority of crystals showed a decrease in growth rate has given rise to speculations that this should be caused by an increase of strain (mosaic spread), resulting from a change of the mode of incorporation of the growth units into the crystal surface brought about by the applied magnetic field. The results show that most of crystals grown in the magnetic field have a higher mosaic spread and lower growth rate than observed during growth without an applied field. An increase in growth rate in the presence of the magnetic field, observed for a few crystals, might be explained by the relaxation of this strain by formation of dislocations, which in turn enhance the growth rate.     

Growth and size control in anti-solvent crystallization of glycine with high frequency ultrasound

Antisolvent crystallization of glycine was performed under ultrasonic irradiation of 1.6 MHz. The irradiation enhanced both the growth of α-glycine crystal and the uniformity in the crystal size. The degree of both enhancement effects increased with increasing ultrasonic power. While under the irradiation of 20 kHz ultrasound, no growth enhancement was observed, but the crystal size reduced as was reported in the literature. To elucidate the mechanism of growth enhancement, another experiment was designed and conducted to avoid the effect of nucleation from the sonocrystallization. The result suggests that the ultrasound enhances the incorporation of microcrystals to larger crystals. Probably, the collision between solid particles is intensified by the disturbance characterized by the high frequency ultrasound. The crystal growth was modeled with an apparent reaction of microcrystal and larger crystal. The result of the growth experiment was successfully predicted with a rate equation for pseudo first order reaction with a single parameter of rate constant. The rate constant linearly increased with the ultrasonic power. The analysis enables quantitative evaluation of the ultrasonic effect on the crystal growth.     

Ultrasound-assisted crystallization of high purity of 2,4-dinitrotoluene from spent acid

The high purity crystal of 2,4-dinitrotoluene (DNT) could be successfully recovered from spent acid in a short period through diluting method assisted with ultrasonic irradiation. The sonication tests were carried out to elucidate the influence of various ultrasonic powers on the performance of crystallization of 2,4-DNT. It is remarkable that under the supersaturated condition ultrasonic irradiation could significantly accelerate the crystal formation, in which the purity of 2,4-DNT reaches to approximate 98.9 wt%. Based on the particle size distribution of crystals, it is proposed that the enhancement on recovery rate of 2,4-DNT crystals by ultrasound is mainly ascribed to the elevation of mass transfer rate for crystal growth. According to the spectra examined by field emission scanning electron microscope (FESEM), the above hypothesis is further verified by the appearance of smoother surface of crystals. Furthermore, the results of metallurgical microscope measurements show that ultrasound has also an abrasive effect on 2,4-DNT crystals under high ultrasonic power inputs.     

Sonocrystallisation of ZIF-8 in water with high excess of ligand: Effects of frequency,power and sonication time

A systematic study on the sonocrystallisation of ZIF-8 (zeolitic imidazolate framework-8) in a water-based system was investigated under different mixing speeds, ultrasound frequencies, calorimetric powers and sonication time. Regardless of the synthesis technique, pure crystals of ZIF-8 with high BET (Brunauer, Emmett and Teller) specific surface area (SSA) can be obtained in water after only 5 s. Furthermore, 5 s sonication produced even smaller crystals (~0.08 µm). The type of technique applied for producing the ZIF-8 crystals did not have any significant impact on crystallinity, purity and yield. Crystal morphology and size were affected by the use of ultrasound and mixing, obtaining nanoparticles with a more spherical shape than in silent condition (no ultrasound and mixing). However, no specific trends were observed with varying frequency, calorimetric power and mixing speed. Ultrasound and mixing may have an effect on the nucleation step, causing the fast production of nucleation centres. Furthermore, the BET SSA increased with increasing mixing speed. With ultrasound, the BET SSA is between the values obtained under silent condition and with mixing. A competition between micromixing and shockwaves has been proposed when sonication is used for ZIF-8 production. The former increases the BET SSA, while the latter could be responsible for porosity damage, causing a decrease of the surface area.     

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface.     

Use of ultrasound irradiation during acid etching of the 2024 aluminum alloy: Effect on corrosion resistance after anodization

While aluminum alloys are widely used in industrial applications, their protection by anodization as surface treatment always requires a preparation step by alkaline or acid etching. In this paper, use of ultrasound during the acid etching step on the 2024 aluminum alloy was investigated. Etching rate, calculated as of weight loss, was measured under ultrasound irradiation, and compared to silent conditions. The etched surface was characterized by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDS) and X-Ray Diffraction (XRD). Surface treatment was performed up to the final anodization step samples, and their final properties were evaluated as a function of various pre-treatments, including acid etching under ultrasound. The main evaluation concerned anticorrosion properties through electrochemical tests: polarization measurements and electrochemical impedance spectroscopy (EIS) in NaCl solution. Finally, use of ultrasound irradiation during acid preparation induced a beneficial effect on the corrosion performance of the anodic layer.     

籽晶尺寸对宝石级金刚石单晶生长的影响

本文在国产六面顶压机上,在5.6 GPa, 1250—1450℃的高压高温条件下,分别选用边长0.8, 1.5和2.2 mm三种尺寸的籽晶,系统开展了Ib型宝石级金刚石单晶的生长研究.文中系统考察了籽晶尺寸对宝石级金刚石单晶生长的影响.首先,考察了籽晶尺寸变化对宝石级金刚石单晶裂晶问题带来的影响.研究得到了籽晶尺寸变大,裂晶出现概率增加的晶体生长规律.其次,在25 h的生长时间内,考察了上述三种尺寸籽晶生长金刚石单晶时,生长时间与单晶极限生长速度的关系.得到了选用大尺寸籽晶,可以提高优质单晶合成效率、降低合成成本的研究结论.借助扫描电子显微镜和光学显微镜,对三种尺寸籽晶生长金刚石单晶的表面形貌进行了标定.最后,傅里叶微区红外测试,对三种尺寸籽晶生长宝石级金刚石单晶的N杂质含量进行了表征.研究得到了选用大尺寸籽晶实现快速生长金刚石的同时,晶体的N杂质含量会随之升高的晶体生长规律.     

Photoluminescence of ZnTe crystals grown under deviation from thermodynamic equilibrium

Crystalline textured and columnar structures, as well as needlelike ZnTe single crystals, were grown from the vapor phase and in a tellurium melt under deviation of the growth conditions from equilibrium. Low-temperature photoluminescence and x-ray structural studies showed the samples thus grown to exhibit high structural perfection, a uniform impurity distribution, and weak interaction between impurities and defects of the crystal structure. Polariton scattering from neutral donors was detected in structures having a noticeable residual concentration of donors in the substituted state. It is shown that the spectrum of samples grown under nonequilibrium conditions exhibits transitions that are not typical of equilibrium crystals. Measurements of the luminescence spectra as a function of temperature, excitation level, and annealing conditions made it possible to draw tentative conclusions about the nature of these transitions.     

Beryl: Regeneration crystal growth and morphology of regeneration surfaces

The specific features of the regeneration growth of colored varieties of beryl (emerald and bixbite) grown under hydrothermal conditions are studied. Habits and crystallographic features of the faceting of crystals grown on seeds of different orientations are analyzed. Micromorphology of the growth surfaces of emerald and bixbite single crystals is examined using optical and atomic force microscopy. Fractal dimensions of the regeneration surfaces were evaluated for beryl single crystals.     

Polymer-mediated and ultrasound-assisted crystallization of ropivacaine: Crystal growth and morphology modulation

The objective of this research was to modify the crystal shape and size of poorly water-soluble drug ropivacaine, and to reveal the effects of polymeric additive and ultrasound on crystal nucleation and growth. Ropivacaine often grow as needle-like crystals extended along the a-axis and the shape was hardly controllable by altering solvent types and operating conditions for the crystallization process. We found that ropivacaine crystallized as block-like crystals when polyvinylpyrrolidone (PVP) was used. The control over crystal morphology by the additive was related to crystallization temperature, solute concentration, additive concentration, and molecular weight. SEM and AFM analyses were performed providing insights into crystal growth pattern and cavities on the surface induced by the polymeric additive. In ultrasound-assisted crystallization, the impacts of ultrasonic time, ultrasonic power, and additive concentration were investigated. The particles precipitated at extended ultrasonic time exhibited plate-like crystals with shorter aspect ratio. Combined use of polymeric additive and ultrasound led to rice-shaped crystals, which the average particle size was further decreased. The induction time measurement and single crystal growth experiments were carried out. The results suggested that PVP worked as strong nucleation and growth inhibitor. Molecular dynamics simulation was performed to explore the action mechanism of the polymer. The interaction energies between PVP and crystal faces were calculated, and mobility of the additive with different chain length in crystal-solution system was evaluated by mean square displacement. Based on the study, a possible mechanism for the morphological evolution of ropivacaine crystals assisted by PVP and ultrasound was proposed.     

The effect of sonication on microbial disinfection using hypochlorite

Ultrasound alone is capable of killing bacteria when sufficient power is applied but ultrasound at low powers can also be used to improve the effectiveness biocides. In this paper, we explore the effect of the timing of the ultrasonic treatment at 20 and 850 kHz on the biocidal efficiency of sodium hypochlorite solution towards Escherchia coli suspensions. A remarkable frequency effect has been noted. At the lower frequency of 20 kHz the improvement in biocidal activity is greatest when the ultrasound is applied at the same time as the hypochlorite. At the higher frequency of 850 kHz the improvement is best when ultrasound is used as a pre-treatment immediately followed by hypochlorite addition under normal (silent) conditions. The kill rate achieved for pre-treatment using 850 kHz and simultaneous treatment using 20 kHz are very similar. However the former involves less acoustic energy and so is considered to be the more efficient.     

碳气凝胶薄片的制备及表面密度致密层去除工艺

研究了不同密度和厚度的碳气凝胶薄片的制备及其表面致密层去除工艺。在以间苯二酚、甲醛为原料制备有机及碳气凝胶块体材料的基础上,结合自制活动式微模具成型工艺,制备了厚度在80~350 μm,密度在50~600 mg·cm-3范围内变化的碳气凝胶薄片。采用场发射扫描电镜、X射线相衬成像和表面轮廓仪-台阶仪等手段对其表面和内部微观结构进行了表征。测试结果表明,碳气凝胶薄片与块体的内部结构相同,但薄片表面存在一层和内部结构截然不同的致密层。采用不同粗糙程度的材料对薄片进行了表面微处理,成功去除该致密“皮”层。     

Growth,characterization and upconversion properties of erbium-doped potassium lithium tantalate niobate single crystals under 975 nm laser excitation

Potassium lithium tantalate niobate single crystals doped with erbium ions are grown by top-seeded solution growth method. The crystals are characterized by X-ray diffraction and differential thermal analysis. The refractive indices of the crystal are measured using ellipsometry method and fitted by Sellmeier equation. The as-grown crystals are tetragonal phase tungsten bronze-type structure with Curie temperature of 271.3 °C. Characteristic Er^3 + absorption bands are observed from 350 to 1100 nm in ultraviolet–visible-near infrared absorption spectra. These crystals emit brightly green and red upconversion fluorescence under 975 nm LD laser excitation, and the steady state upconversion spectra are obtained at room temperature. The red emission intensity increases as the erbium ions concentration increases in crystals. Processes of excited state absorption and energy transfer are responsible for upconversion luminescence. The emission intensities are quadratic dependences on pump power from pump power dependence analyses and deduction of transition rate equation model.     

Faceting of sapphire crystals grown from a melt by the Stepanov method

The appearance of faces on cylindrical sapphire single crystals grown from a melt by the Stepanov method is studied by photogoniography and optical microscopy. The crystallographic indices of the detected faces are established, and the microstructure of the growth layers is investigated. A relationship between the faceting and the growth conditions is found. The experimental results are compared with data on the faceting of the sapphire crystals grown from a solution-melt and with the calculated specific free surface energies of the faces.     

ZnSe单晶的生长及其激子光谱

本文描述了甩升华法生长ZnSe单晶的生长情况和晶体品质。为了获得高纯高完整性单晶,由高纯Zn和Se反应合成了ZnSe,设计了特殊形状的成核室,保证了在一个晶核上单晶的生长;同时在生长过程中控制组分分压,减小了化学计量比的偏差。通过偏光显微镜的观察和He-Ne激光散射的形貌分析表明,在生长速率小于0.5(毫米/天)情况下,在块状单晶体中观察不到生长带纹的条纹,但观察到位错缺陷。在液氦温度的光致发光光谱中首次观察到强的自由激子光谱和激子激发态的光谱;观察到典型的反射光谱和精细的束缚激子谱线,没有观察到2.4eV以下的深能级发光谱带。这些结果表明单晶的纯度和完整性是良好的。     

Concentration and structural inhomogeneities in highly doped GaSb(Si) single crystals

Concentration and structural inhomogeneities in highly doped GaSb(Si) single crystals grown under various conditions of heat and mass transfer are studied by methods of X-ray topography, high-resolution X-ray diffractometry, and digital image processing. It is established that the inhomogeneity of crystals is determined by specific features of impurity microsegregation during growth under conditions of nonstationary convection in a melt and by peculiarities of the dislocation structure of crystals. The processes related to the initial stage of the decay of the Si supersaturated solid solution in GaSb contribute considerably to the inhomogeneity of crystals on the micro- and macrolevels.