Mg~(2+)//CO_3~(2-)、HCO_3~-、OH~--H_2O体系相平衡研究

新型碱源脱钙固碳之后的海水中存在的大量镁离子和碳酸氢根,提取其中的镁离子可以实现海水镁资源利用并将海水进一步软化;分离碳酸氢根使固碳彻底,有利于后续海水资源利用.镁和碳酸氢根的提取需要在碱性条件下进行,因此,本实验将CO_2脱钙之后的海水体系简化为Mg~(2+)//CO_3~(2-)、HCO_3-、OH~--H_2O体系.并利用等温溶解平衡法,研究该体系在10℃条件下的相平衡,探索体系的析盐规律.液相组成通过溶液滴定法获得,由X射线衍射分析技术测出固相物质组成得出,并利用origin9.0软件绘制出四元体系相图.相图中得到1个三相共饱点,固相物组成是MgCO_3·3H_2O、Mg(OH)_2和Mg_5(CO_3)4(OH)_2·8H_2O;3条共饱和曲线分别为MgCO_3·3H_2O、Mg(OH)_2的共饱线,Mg_5(CO_3)4(OH)_2·8H_2O、Mg(OH)_2的共饱线,Mg_5(CO_3)4(OH)_2·8H_2O、MgCO_3·3H_2O的共饱线;2个明显的结晶区,MgCO_3·3H_2O结晶区和Mg(OH)_2结晶区,1个Mg_5(CO_3)4(OH)_2·8H_2O的部分结晶区.以上实验数据可为盐化工生产及结晶分离提纯提供参考依据.     

Crystal Growth of[Ca_3Al(OH)_6?12H_2O]_2·(SO_4)_3?2H_2O (Ettringite) Studied Under Microgravity Conditions

On parabolic flights,the growth of ettringite,[Ca_3Al(OH)_6·12H_2O]2·(SO_4)_3·2H_2O,a major reaction product of cement with water which forms instantaneously,was crystallized under microgravity conditions and studied.In the experiments,Ca(OH)_2/Al_2(SO_4)_3 solutions were combined and reacted for 10?s,followed by immediate filtration of the suspension and subsequent quenching with acetone.For the ettringite crystals,the size,aspect ratios,quantity and morphology were determined and the results were compared with those from identical experiments performed under terrestric gravity.Under microgravity,generally smaller crystals (l-2.9 μm) precipitated in larger amount than under normal gravity (l-3.5 μm).The aspect ratios of the crystals grown under terrestric or microgravity condition were comparable at about 5.6.It is assumed that the reason for the smaller ettringite crystals is the absence of convection leading to more initial nuclei,but slower crystal growth which is diffusion limited.Apparently,no preference relative to the ion transport to the different faces of the crystals exists.The results contribute to the understanding of the mineralization of inorganic salts under microgravity conditions for which hitherto only a handful of examples were reported.     

Thermal Behavior Study of Carbonate Inorganic Materials

The thermal decomposition processes of(MgCO_3)_4·Mg(OH)_2·5H_2O(MCH),5ZnO·2CO_3·4H_2O(ZCH),NiCO_3·2Ni(OH)_2·4H_2O(NCH),PbCO_3(LC)and [Cr(OH)_5]_2·CO_3·8H_2O(CC)were studied via TG-DSC.The results of research imply that MCH has the largest capacity of heat absorption and ZCH is second to MCH among the studied materials.The non-isothermal kinetic parameters of MCH and ZCH were calculated by Kissinger and Ozawa methods.Furthermore,thermal decomposition mechanisms of MCH and ZCH were investigated by Coats-Redfern method.Due to the large specific heat capacity,MCH and ZCH are promising to be used as a coolant in extinguishant formulations.     

Synthesis and Structural Analysis of LDH-SO_4-CO_3 Whisker

High-quality LDH-SO_4-CO_3 whiskers were synthesized via liquid precipitation method using MgSO_4·7 H_2 O and Al_2(SO_4)_3·18 H_2O as precursors and Na_2CO_3-NaHCO_3 buffer solution as precipitant. The influence of buffer solution concentration on the characteristics of the samples was investigated. The asgrown whiskers were characterized by X-ray diffraction, transmission electron microscopy, and BrunauerEmmett-Teller N_2 specific surface area measurements. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. The LDH-SO_4-CO_3 whiskers with well-defined geometry, distinct intercalated structure, decent quality, and excellent dispersing capability can be obtained under the following conditions: buffer solution volume ratio of 45%, reaction temperature of 83°C, and reaction time of 182 h. The obtained whiskers are well-crystallized and exhibit homogeneous morphology consisting of fiber bars.     

Synthesis of calcium chloroborate whiskers via sedimentation and sintering process

Single crystalline calcium chloroborate(Ca_2B_5O_9Cl) whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl_2, H_3BO_3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca_2B_5O_9Cl. SEM and TEM results show that the Ca_2B_5O_9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.     

Formation mechanism of barium titanate nanocrystalis under hydrothermal conditions

Growth units and the crystallization habit of BaTiO3 nanocrystals have been investigated. It has been proposed that the growth units of BaTiO3 were surface hydroxylated Ti(OH)62- octahedra. The relationship between crystal morphology and the variation of the current intensity in the solution has been obtained through the measurement of the OH in the solution and the hydrothermal experiment with superimposed direct electric field. Based on the computation of the stability energy of the growth units, the relationship between the crystallized morphology of crystallites and the most favorable growth units under different conditions has been derived. It has been found that there is structure similarity between anatase (TiO2) and BaTiO3 from the crystal chemistry viewpoint, so they are soluble in each other, which can serve as a reasonable explanation for the abnormal phenomenon of the retention of cubic substable phase at room temperature.     

Preparation of mullite whiskers and their enhancement effect on ceramic matrix composites

Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H2O. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H2O and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H2O, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of AlF3·3H2O. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.     

The synthesis of micro-sized silicon carbide whiskers and the application for heat transfer enhancement

This paper presents a simple and cost-effective method for the production of micro-sized silicon carbide whiskers at high yield and the effect on heat transfer enhancement for the whisker laden fluids. For Si C whisker synthesis, the starting powder mixture is obtained by milling short carbon fibers with the white ashes of rice hulls. Calcination in argon, together with the subsequent purification process, results in a high yield of Si C whiskers, which possess a diameter of 200–400 nm and a length of several tens of microns. The formation of the whiskers is discussed according to VS growth mechanism. Convective heat transfer performance in small channel tubes is then studied for fluid systems mixed with those micro-sized Si C whiskers at different concentrations. The heat transfer coefficient of Si C containing fluid can be significantly improved in comparison to the base fluid.     

Theoretical Study of Electron Paramagnetic Resonance Spectra and Local Lattice Distortion for Mn~(2+) in Zn(ClO_4)_2·6(H_2O)Mg(ClO_4)_2·6(H_2O)

The electron paramagnetic resonance(EPR) spectra of trigonal Mn~(2+) centers in Zn(ClO_4)_2·6(H_2O) and Mg(ClO_4)_2·6(H_2O) crystals were studied on the basis of the complete energy matrices for a d~5 configuration ion in a trigonal ligand field. It was demonstrated that the local lattice structure around a trigonal Mn~(2+) center has an compressed distortion along the crystalline c_3 axis, and when Mn~(2+) is doped in the Zn(ClO_4)2·6(H_2O) and Mg(ClO_4)_2·6(H_2O) crystals, there is a similar local distortion. From the EPR calculation, the local lattice structure parameters R=2.183 2 ?, for Zn(ClO_4)2·6(H_2O), R=2.130 2 ?, for Mg(ClO_4)2·6(H_2O) have been determined.     

Biological Effect Studies of Norfloxacin Complexes on Tetrahymena and Escherichia Coli by Microcalorimetry

Norfloxacin complexes Co(nor)_2·8H_2O(nor=norfloxacin) and [Co(nor)(phen)]NO_3·2H_2O(phen=1,10-phenanthroline) were synthesized and their biological activity on Tetrahymena and Escherichia coli(E.coli) was assayed by means of microcalorimetry. Massive experimental parameters such as the growth constant k, inhibitory ratio I, half inhibition concentration IC_(50) and generation time TG were obtained. Data showed that with the increase of exposing complex concentration, both complexes exhibited strong inhibition during the growth of organisms. While toxic degrees were quite different on Tetrahymena and E.coli, due to various toxic mechanisms. And complex molecular volume and the ability of the complex penetrating into cells may be the keys.     

RESEARCH ON THE WATER-RESISTANCE OF MAGNESIUM OXYCHLORIDE CEMENT——I:THE STABILITY OF THE REACTION PRODUCTS OF MAGNESIUM OXYCHLORIDE CEMENT IN WATER

In this paper.the change of the crystalline phasesin hardened magnesium oxychloride cement(MOC)paste inwater was analyzed by XRD.It was developed that the reactionproducts 5 phase or 3 phase of MOC are instable in water andcan be changed into Mg(OH)_2 by the action of water,whichcauses the content of 5 phase or 3 phase to be less and less,thecontent of Mg(OH)_2 to be more and more and the strength to bethe lower the lower,after hardended MOC paste was immersedin water.The change of 5 phase and 3 phase into Mg(OH)_2 isnot a dissolve process,but a hydrolysis process.The hydrolysisproducts of 5 phase and 3 phase are Mg(OH)_2 precipitationand soluble Cl~-,Mg~+ ions and H_2O.The hydrolysis is sponta-neous thermodlynamically and its chemical kinatic equation is C=C_oe~(-kt) Thus,it is suggested that only by enhancing the stabilityof 5 phase or 3 phase in water and preventing 5 phase or 3phase from the hydrolyzing can the water resistance of MOC beimproved well.     

Microstructure and Thermophysical Properties of Mg-Ga Alloys

The microstructure and thermal characteristics of Mg-36%Ga,Mg-43%Ga,and Mg-45%Ga(wt%) alloys were investigated.The experimental results show that the microstructure of Mg-36%Ga alloy is mainly composed of primary a-Mg phase and a-Mg+Mg_5Ga_2 eutectic phase,the microstructure of Mg-43%Ga alloy is mainly composed of a-Mg+Mg_5Ga_2 eutectic phase,and the microstructure of Mg-45%Ga alloy is mainly composed of primary Mg_5Ga_2 phase and a-Mg+Mg_5Ga_2 eutectic phase.The melting enthalpies of Mg-36%Ga,Mg-43%Ga,and Mg-45%Ga are 146.41,171.90,and 113.90 J/g,with the phase change temperature of 422.57,422.70,and 422.90 ℃,respectively.Mg-43%Ga alloy contains the highest melting enthalpy because of the highest content of a-Mg+Mg_5Ga_2 eutectic phase.In addition,the thermal expansion of the three alloys increases with increasing temperature,while the thermal diffusivity and thermal conductivity decreases with increasing content of Ga.     

Hot compressive deformation behavior of an in-situ TiB whisker reinforced Ti matrix composite

An in-situ TiB whisker reinforced Ti matrix (TiBw/Ti) composite is fabricated by powder metallurgy technique followed by hot extrusion. Hot compressive deformation behavior of the composite, in which the TiB whiskers were oriented along the extruded direction, is investigated. The results indicate that the hot compressive resistance of the TiBw/Ti composite is higher than that of the unreinforeed Ti, and hot compressive resistance of the composite in the direction parallel to the whisker orientation is higher than that in the direction perpendicular to the whisker orientation. The hot compressive resistance of the composite increases with increasing strain rate and decreasing temperature. With increasing test temperature, the rate of the decrement of the compressive flow stress of the composite is higher than that of the unreinforced Ti. With increasing amount of compressive deformation, more and more TiB whiskers rotate and break during deformation. The rotation of the whiskers is easier at higher temperature, while, at lower temperature it becomes more difficult and whisker breakage becomes much more serious.     

Comparative study on lattice parameters of HAP nanoparticles with those of HAP whiskers

Hydroxyapatite whiskers are used as reinforcement for biomaterials because of their needlelike morphology and strong strength of single crystal. HAP nanoparitcles are used in drug delivery system, protein separation and anticancer drug besides their implant applications. Many new properties arise from nanoeffects while nanoeffects come from specialty of nanostructure. The Ca（NO3）2·4H2O and （NH4）2HPO4 were used as starting reagents for preparation of HAP whiskers and nanoparticles. The whiskers are 100-200 μm long while nanoparticles are 30-80 nm in size. XRD is applied to characterize the lattice parameter difference of whisker and nanoparticle. Compared with those of HAP whiskers, the a-axis and b-axis of HAP nanocrystals are shortened while the c-axis is elongated. That makes nanoparticles capable of their non-needle-like morphology, higher reaction activity and special bioeffects.     

SiC WHISKER-TOUGHENED ALUMINIUM NITRIDE CERAMICS

Aluminium nitride ceramics containing 15-30 w/o of SiC whiskers can be sintered tofull density(by hot pressing at 1800℃)using2-3 w/o of Y_2O_3,additions.The whiskersincrease the toughness and strength of thecomposite,K_(10) increasing from 2.8 to about5.0 and flexural strength increasing by 30-50%.However,the whiskers must be welldispersed and if the dispersion is notsatisfactory,toughness may increase but thestrength decreases.The hot-pressingtemperature can be reduced by up to 100℃ ifY(NO_3)_3 .5H_20 is used as the sinteringadditive instead of Y_2O_3,but some oxidation ofthe AIN occurs during heating.Isopropan-2-01 is a better dispersing agent thancyclohexane,but again some oxidation of theAIN does occur.The best sample prepared during this work contained 20 w/o of SiC whiskers and 2 w/oY_2O_3 added as Y(NO_3)_3. 5H_2O and mixed inisopropanol.This exhibited a mean strength of453MPa(maximum 522MPa,measured bydisc flexure)and a fracture toughness of5.5MPam~(1/2).     

Si-Al-Y Co-deposition Coatings Prepared on Ti-Al Alloy for Enhanced High Temperature Oxidation Resistance

Si-Al-Y co-deposition coatings were prepared on Ti-Al alloy by pack cementation processes at 1 050 ℃ for 4 h with different halide activators in the packs for enhancing the high temperature oxidation resistance of Ti-Al alloy. The structure, constituent phases, formation process and oxidation behavior of the coatings were investigated. The experimental results showed that the coatings prepared respectively with NaF and NH_4Cl as activators were composed of a(Ti, X)_5Si_4,(Ti, X)_5Si_3(X represents Nb and Cr), and TiSi_2 outer layer, a TiAl_2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi_2 in the outer layer and(Ti, X)_5Si_4 and(Ti, X)_5Si_3 phases were observed in the middle layer of the coating prepared with AlCl_3·6H_2O activator. Among the halide activators studied, the coating prepared with AlCl_3·6H_2O was thicker and denser, which is the only suitable activator for pack Si-Al-Y co-deposition coatings on a Ti-Al alloy. The oxidation results show that the coating can protect the Ti-Al alloy from oxidation at 1000 ℃ in air for at least 80 h. The excellent oxidation resistance of the coating is attributed to the formation of a dense scale mainly consisted of TiO_2, SiO_2 and Al_2O_3.     

Preparation and Performance of Magneto-optical Glasses Doped with Tb3＋/Dy3＋

In order to increase the content of rare-earth oxides in magneto-optical glass and improve the Verdet constant, the rare-earth doped ternary Ga2O3-B2O3-SiO2(GBS) system magneto-optical glasses were prepared by the melt quenching technique. The infl uence of Tb3+ and Dy3+ ions on the structure of GBS glasses was investigated using FTIR, DSC and Faraday rotations. The experimental results showed that the content of rare-earth oxides in the glasses with the double incorporation of Tb2O3 and Dy2O3 was higher. The crystallization parameter β achieved the maximum 0.48 with Tb3+/Dy3+ content of 35mol%. Terbium oxide existed mainly in [TbO3] units in the glasses and [TbO4] units were converted into [TbO3] with increasing Tb2O3 content. As Ga3+ ion is larger than B3+ ion in radius, leading to an increasing of the glass network gap and improvement in the ability of accommodating rare earth ions, Verdet constant increased.     

Preparation,Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials' ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.     

STUDY OF THE MOLECULE VIBRATING SPECTRA OF THE TERNARY SYSTEM La_2O_3-LI_2O-B_2O_3 GLASSES

This paper deals with the ternary xLa_20_2·20Li_2O·(80-x)B_2O_3 glssses in terms of GroupTheory.By means of Raman spectra and Infrared spectra,the effects of La_2O_2 on the structureof the system are found to be similar to that of Li_2O.With the increase of x value,the transfor-ming process of the glass structure is:[B_8O_(12)]~(2-)——[B_4O_7]~(2-)——[BO_2]~(1-)If the content of La_2O_2 is higher,pyroborate and orthoborate groups would come into being.This is very useful to the study of new noncrystalline Li+-fastion conductors.     

MORPHOLOGY AND CRYSTALLOGRAPHY OF ALUMINIUM NITRIDE WHISKERS

The AlN whiskers were composed by the Al_2O_3-C system with some CaF_2 and NH_4Cl addition under the condition of the carbothermal reduction treatment of 1450 C and 2h as well as nitrogenous atmosphere. The composed AlN whiskers were analysed and the results show that some whiskers morphology such as plate cwoed, brached corrugated were observed and the ratios of length to diameter change greatly. The composed whiskers are not even. some surface quality is not high. TEM analyse show that the fiber axes are normal to[0112] and [1101]. The mechanism of the growth of the whiskers is supposed to be VLS(Vapor-Liquid-Solid)