Synthesis of YAG∶Ce^(3+) Phosphor by Polyacrylamide Gel Method and Promoting Action of α-Al_2O_3 Seed Crystal on Phase Formation

YAG： Ce^3 ＋ phosphor particles were prepared using polyacrylamide gel method. The structure evolution of powders during annealing process was followed by X-ray diffraction determination. It is found that some intermediate phases, including θ-Al2O3, YAM and YAP, are formed when calcining polyacrylamide gel, however, the pure YAG phase can be formed directly when calcining polyacrylamide gel with α-Al2O3 as seed crystal. These facts show that the existence of α- Al2O3 seed crystal can block the formation of θ-Al2O3, YAM and YAP, and accelerate its reaction with Y2O3 to form YAG phase directly at lower temperature. The emission peak of prepared YAG ： Ce^3 ＋ phosphor is wide with maximum at 550 nm and the exitation band has two peaks, the major one is around at 460 nm, which matches the blue emission of GaN LED and is suitable for the assemble of white LED. Some fluxes can enhance the photoluminescence intensity of phosphor particles, that can be attributed both to the improvement of crystallization processes of YAG and to the stabilization of trivalence cerium ion in YAG：Ce^3 ＋.

Formation and dispersal of rod-like α-SiAlON seed crystals synthesized by combustion method

Rod-like single-phase seed crystals of yttrium-α-SiAlONs were synthesized by combustion synthesis method. The XRD patterns, the morphologies of products and formation mechanism were investigated. The SEM observation of crystals exhibits well developed elongated hexagonal crystals with highly agglomerative features, assigned to pure and well-crystallized α-SiAlON. After special chemical treatments and water washing, the powders are well dispersed and still keep elongated hexagonal crystals, and the XRD pattern shows that the rod-like structure is crystalline yttrium-α-SiAlON with only a trace of β-SiAlON.

Polycrystalline ZSM-5 Aggregates Induced by Seed and Catalytic Performance in Methanol to Hydrocarbon

Synthesis of ZSM-5 zeolite typically utilizes small molecule polyamines or quaternary ammonium salts as organic structure guiding agent(OSDA).By contrast,the OSDA-free hydrothermal synthesis system eliminates the use of organic templates and the subsequent calcination procedure.This not only reduces the cost of synthesis,but also prevents environmental pollution from the combustion of organic templates,representing an eco-friendly approach.Despite this,literature suggests that even so-called template-free synthesis systems often involve trace amount of organic substances like alcohol.In the present work,a calcined commercial ZSM-5 zeolite was served as seed,with sodium aluminate as aluminum source and silica sol as silicon source,ensuring an entirely template-free synthesis system.Polycrystalline ZSM-5 aggregates consisted of rod-like nanocrystals were successfully prepared in the completely OSDA-free system.Effects of the Si/Al ratio in ZSM-5 seed,dosage and crystallization conditions such as crystallization temperature and crystallization time on ZSM-5 synthesis were investigated.The results show that a highly crystallinity ZSM-5 aggregate consisting of primary nano-sized crystals less than 100 nm is produced from a gel precursor with 5.6%(in mass)seed after hydrothermal treatment for 48 h.Furthermore,the Si/Al ratio in ZSM-5 seed has little effect on the topological structure and pore structure of the synthesized samples.However,the seeds with a low Si/Al ratio facilitate faster crystallization of zeolite and enhance the acidity,especially the strong acid centers,of the catalyst.The catalytic performance of the synthesized polycrystalline ZSM-5 was evaluated during dehydration of methanol and compared with a commercial reference ZSM-5r.The results exhibit that as compared with the reference catalyst,the fabricated sample has a longer catalytic lifetime(16 h vs 8 h)attributed to its hierarchical pores derived from the loosely packed primary nanoparticles.Additionally,the prepared polycrystalline catalyst also exhibits a higher aromatics selectivity(28.1%-29.8%vs 26.5%).

Improved length of calcium sulfate crystal seeds and whiskers via ball milling and hydration treatment

Elucidating the effect of growth periods on the quality of calcium sulfate whiskers(CSWs)prepared from calcium sulfate dihydrate(DH)is imperative.Herein,crystal seeds and whiskers were prepared from DH in a water–glycerol system.Longer whiskers were obtained from crystal seeds prepared via hydration of DH for 30 s than via ball milling for 5 min followed by hydration for 20 s.The attachment of cetyltrimethyl ammonium bromide and glycerol additives to the whisker tops promoted whisker growth.The whisker sponges exhibited good thermal barrier properties and compression cycle stability.

Role of Crystal Seed in Aluminum Hydroxide Crystallization from Ammonia System with Added NH_(4)Al(SO_(4))_(2)·12H_(2)O

A method to promote aluminum hydroxide crystal growth through pickling Al(OH)_(3)as seed in the ammonia system was proposed to overcome these defects.The experimental results show that,under the conditions of pickling time of 15 min,the acid concentration of 10%,the addition of 70 g/L pickling-Al(OH)_(3)seed,and the coarse granular Al(OH)_(3)products(d0.5=85.667)can be obtained.The characterization results show that the phase of the product is gibbsite,consistent with the seed.Moreover,the steps and ledges can be formed on pickling Al(OH)_(3)seed surface under the ammonia system,effectively promoting crystal growth.During crystal growth,the roughness of the crystal surface was first increased and then decreased,and the lamellar structure was deposited on the crystal seed surface.The final particles are approximately round,the surface is compact and dense.The growth of the product is surface reaction controlled.In addition,the content of the AlO_(6)unit is increased and contributed to Al(OH)_(3)crystal growth.

Seed selections for crystallization of calcium phosphate for phosphorus recovery

Seed induces and promotes the crystallization of calcium phosphate, and acts as carrier of the recovered phosphorus （P）. In order to select suitable seed for P recovery from wastewater, three seeds including Apatite （AP）, Juraperle （JP） and phosphate-modified Juraperle （M-JP） were tested and compared. Batch and fixed-bed column experiments of seeded crystallization of calcium phosphate were undertaken by using synthetic wastewater with 10 mg/L P phosphate. It shows that AP has bad enduring property in the crystallization process, while JP has better performance for multiple uses, and M-JP is a hopeful seed for P recovery by crystallization of calcium phosphate.

Influence of Synthesis Parameters with Low Seed Addition on the Crystallinity of ZSM-5

ZSM-5 zeolite microparticles （MPs） were synthesized under hydrothermal condition using a low crystal seed addition approach without template. The synthesis parameters such as the seed addition amount, the SiOJA1203 ratio, the aluminum source, the feeding addition method, aging, and crystallization were investigated. The structure, morphology and composition of the as-synthesized ZSM-5 zeolite MPs were characterized by X-ray powder diffraction （XRD）, scanning electron microscopy （SEM）, laser particle size distribution （PSD） measurements, and inductively coupled plasma-atomic emission spectrometry （ICP-AES）. The SIO2/A1203 ratio of ZSM-5 zeolite MPs was in the range of 20~80. The low seed addition was beneficial to improving the crystallinity and shortening the crystallization time, and the suitable amount of seed was 0.25% （SIO2）. The ZSM-5 zeolite MPs synthesized with aluminium nitrate nonahydrate used as the aluminum source exhibited a relatively high crystallinity. An appropriate aging time could eliminate the effect of feeding addition method and effectively adjust particle size. The particle size of ZSM-5 zeolite obtained at an aging time of 20 h was around 2.0 I.tm. Prolonging the aging time appropriately could also shorten the high-temperature crystallization time. The suitable aging time was 24 h, and the relative crystallinity of ZSM-5 zeolite could reach up to 99% after crystallization for 24 h at 180 ℃

Characterization of CdZnTe crystal grown by bottom-seeded Bridgman and Bridgman accelerated crucible rotation techniques

The growth of CdZnTe crystals with diameter up to 60 mm using bottom-seeded Bridgman method as well as Bridgman accelerated crucible rotation technique (ACRT-B) was investigated. Both ingots exhibit high yields, where single crystal with the volume exceeding 200 cm3 is produced. The crystal properties of two ingots were compared in the aspects of yields, crystalline quality and composition uniformity. For CdZnTe ingot grown by bottom-seeded Bridgman method, the full width at half-maximum (FWHM) of X-ray rocking curve was determined to be 36″, indicating a better crystalline quality than ingot grown by ACRT-B method, which gave FWHM of 56″. The composition distribution of Zn and In in CdZnTe was determined by using electron probe microanalysis (EPMA) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The effective segregation coefficients of Zn kZn and In kIn in the two ingots were evaluated by fitting the experimental data with the Pfann equation.

Kinetics of crystal growth on seeded precipitation of sodium aluminate solutions with new device

A new device was designed,which can effectively avoid the undesired nucleation and agglomeration of fine particles on the experimental results during the sead ed precipitation of sodium aluminate solution,and moreover,the experimental co nditions are nearly kept constant during the experiment. With the new device,it is proven that a good result can be obtained on the kinetics study of the cryst al growth in seeded precipitation of sodium aluminate solution.Experiments were carried out with the concentration of Na2O （Nk）170 g/L,the mole ratio of Na2O to Al2O3 （αk） all between 1.52 to 2.01,at 65,70,75 ℃,respectively. And the kinetics equation of crystal growth of gibbsite was deduc ed.

Production of Sucrose Crystals of Uni-Modal Size Distribution by Seeded Batch Cooling Crystallization

From sucrose aqueous solution of high viscosity, sucrose was crystallized by seeded cooling in a batch crystallizer. At low seed loadings, the product crystal size distribution (CSD) was wide-spread because of enormous secondary and primary nucleation. However, at high seed loadings, it became uni-modal, where the crystallization was dominated by seed growth with practically no secondary nucleation. Enough seeding was thus effective in suppressing nucleation even during batch crystallization with high viscosity solution. The volume mean size of the product crystals obtained at high seed loadings agreed with that calculated by a simple mass balance assuming growth-dominated crystallization with no change in the number of crystals.

Characterization of the Crystal Structure of Sesame Seed Cake Burned by Nd: YAG Laser

This paper reports obtaining of useful and high-value materials from sesame seed cake (SSC). For this purpose, SSC sample was burned for 30 s using Nd: YAG laser with output power 60 W. The products of this process and non-burned SSC were characterized by X-ray diffractometer (XRD), energy dispersive x-ray (EDX) and Fourier transform infrared (FTIR) so as to investigate its crystal structure and chemical components. XRD results of the SSC before burning process showed amorphous silica, rhombohedral phase of carbon, monoclinic phase of aluminum chloride, the hexagonal phase of moissanite-4H, (yellow, black) and hexagonal phase of graphite-2H, C (black). While the results of the burned SSC sample showed that the burning process using the power of Nd: YAG laser cased in appearing of crystalline hexagonal phase for silica and Carbon Nitride and converting the rhombohedral phase of Carbon into hexagonal phase. FTIR showed a number of absorbance peaks assigned to silica.

Preparation and characterization of AlN seeds for homogeneous growth

Large size AlN bulk crystal has been grown on SiC heterogeneous seed by physical vapor transport (PVT). The properties of AlN wafer were characterized by high resolution X-ray diffraction (HRXRD), Raman spectroscopy, etched method and atomic force microscope (AFM). Growth mechanism of AlN crystal grown on heterogeneous SiC seeds was proposed. Crystallization quality of AlN samples were improved with the growth process, which is associated with the growth mechanism. AlN single wafer has excellent crystallization quality, which is indicated by HRXRD showing the (0002),(1012) XRD FWHM of 76.3,52.5 arcsec, respectively. The surface of the AlN wafer is measured by AFM with a roughnessof 0.15 nm, which is a promising seed for AlN homogeneous growth.

Experimental Study on Preparation of Natural Gas Hydrate by Crystallization

In this paper, the saturated solution crystallization method is proposed to promote the formation of hydrate by means of the known similarities between the hydrate formation process and the crystallization process. In this method,adding the second phase crystals was used to replace the spontaneous formation of hydrate crystal nuclei to form hydrate.The effects of saturated Na_2SO_4, MgSO_4, NH_4HCO_3 and CuSO_4 solutions on the formation rates of natural gas hydrate and gas storage capacity were investigated. The results showed that the saturated solution had an influence on the hydrate formation process. Under the given experimental conditions, the saturated Na_2SO_4 solution showed a highest increase in the hydrate formation rate, and the average hydrate formation rate in its presence was 11.8 times higher than that obtained in the deionized water. Moreover, the largest formation rate of gas hydrates observed in the saturated Na_2SO_4 solution was 386 times bigger than that in the deionized water, and the gas storage capacity increased by 10 times. In addition, the average hydrate formation rate in the saturated Mg SO_4 solution was faster than that in water by 20 times. The largest formation rate of gas hydrates in the saturated MgSO_4 solution was 165 times faster than that obtained in the deionized water, and the gas storage capacity increased by 6.2 times. The saturated NH_4HCO_3 and saturated CuSO_4 solutions also influenced the formation process of hydrate. Therefore, the crystallization method of saturated solution can be used to achieve a highefficiency preparation of natural gas hydrates, which provides theoretical guidance for the storage of natural gas in the form of hydrate.

The Early Strength of Slag Cements with Addition of Hydrate Microcrystals

The effect of hydrate microcrystals such as calcium silicate hydrates ( CSH) and ettringite on the early strength of slag cements was studied. The authors explored the possibility of improving the early strength of the slag cement by applying crystal seed technology. It is shown that slag crystal seeds make the early strength of the cement increased due to the action of hydrate crystal seeds , which speed up the hydration of clinker minerals in the nucleation of ettringite. Therefore, the early strength of the slag cement is obviously improved.

Research on Dihydrate Calcium Sulphate Crystallization during the Production of Phosphoric Acid by Wet Process

Simulate the production of phosphoric acid by wet process is conducted in batch experiments facilities by adopting phosphorus concentrate as raw material from Wengfu, Dazhou city, with a view to study sulfuric acid concentration, reaction time, crystallization temperature of calcium sulfate, active additive, the influence of seed crystal on the size and shape of calcium sulfate crystal under conditions of Wet process phosphoric acid productive process. The research results show that under the conditions of the liquid-solid ratio of 4:1, the sulfate acid stoichiometric ratio of 1.1, phosphoric acid mass fraction of 21%, the crystallization temperature of 75&degC, crystallization time of 120 min, when (NH4)2SO4 taken as active additives, Mg-doped calcium sulphate crystal as crystal seed can obtain rodlike crystallization of stability, thickness, uniformity.

Feasibility of integrated seed making and directional solidification of TiAl alloy using cold crucible

A new seed making method with cold crucible by power off technique was proposed. The cold crucible quenched seed with columnar structure has a similar cross-section shape as that of the cold crucible,and can be directly used for the directional solidification processes. The proposed method can significantly simplify the seeded directional solidification process and avoid the contamination from the seed machining.

Growth of KCl_1–xBr_xMixed Crystals with Different Composition Percent and Study of KBr Concentration Effect on Optical Characteristics of Mixed Crystals

In the present research, mixed crystals KCl1–xBrx (x = 0.1, 0.3, 0.5, 0.7 & 0.9) were grown by Czochralski method. Then some analysis such as chemical etching, XRD, and absorbing spectrum were established on the irradiated crystals by γ-ray. The results of this research show that configuration of defects in mixed crystals in contrast with pure crystals is different. Somehow that type and percentage of cumulative composition cause to changing in lattice parameter and lattice defect density in alkali halide crystals and finally change optical properties of crystal.

以碳酸钾为原料制备碳酸锂晶体团聚现象及调控方法的研究

以氯化锂与碳酸钾为原料进行反应结晶制备碳酸锂,以提高碳酸锂收率、降低其钾含量及获得良好粒径分布为目标,考察反应温度、搅拌转速、晶种加入量及晶种加入的粒径大小对实验的影响。实验结果表明,氯化锂与碳酸钾反应结晶存在着明显的晶体团聚现象,反应温度不同,对晶体形貌有显著影响,低温下晶体呈片状团聚体,较高温度下晶体呈棒状团聚体。剪切力的增加可以减小团聚体尺寸,晶种的加入有利于抑制爆发成核,减轻晶体团聚和黏壁现象。实验结果表明,在反应温度为85℃、搅拌转速为400 r/min、氯化锂浓度为3.2 mol/L、晶种加入量为3.0 g/L、晶种粒径控制在小于54μm、超声功率为100 W、超声时间为150 min条件下,获得的碳酸锂收率高、晶体不易发生聚结、钾含量较低且拥有较好的粒径分布。以碳酸钾为原料制备的碳酸锂与以碳酸钠为原料制备的碳酸锂收率相当,但杂质含量有一定的降低。且在反应结晶过程中加入超声后可有效避免出现大团聚体,在保证碳酸锂收率无明显降低的情况下,钾含量明显降低。通过研究获得的实验条件可以为碳酸锂生产调整工艺参数提供依据,并为产品质量的提高提供指导。

Study on Formation Mechanism of Defects in Monoclinic KLu(WO₄)₂Crystals

The laser host crystals of KLu(WO4)2(KLuW) with large sizes up to 43 × 35 × 16 mm3 have been grown along, [110], b, and c crystallographic directions, respectively, by the top-seeded solution growth (TSSG) slow-cooling method. The macro defects are observed using optical microscopy. The main defects found were cracks, inclusions, growth striations, sector boundaries and twin boundaries. The formation mechanism and approaches to reduce or eliminate the defects have been analyzed.