煅烧工艺对纳米氧化镁粉体活性的影响

采用柠檬酸法测定了均匀沉淀法制备出的纳米氧化镁粉体活性,并与普通氧化镁粉体活性进行了比较.探讨了煅烧温度和煅烧时间对纳米氧化镁粉体活性的影响.结果表明,煅烧温度和煅烧时间对纳米氧化镁粉体活性的影响很大,煅烧温度为450 ℃和煅烧时间为3 h得到的纳米氧化镁粉体活性较大.普通氧化镁粉体的活性要低于纳米氧化镁粉体的活性.     

纳米氧化镁制备工艺的研究

以六水硝酸镁和氨水为原料,合成氢氧化镁,研究了制备纳米氧化镁的煅烧及球磨工艺,并用X-射线扫描仪(XRD)、扫描电子显微镜(SEM)进行表征.结果表明:分步煅烧制备的纳米氧化镁比一步煅烧的晶粒尺寸小、团聚少,制备出晶粒尺寸为24.1 nm纳米氧化镁.     

纳米氧化镁的制备

研究了制备纳米氧化镁的方法。以碳酸铵和氯化镁为主要原料,加入有机表面活性剂,经过反应、过滤、水洗、醇洗、干燥和灼烧制得纳米氧化镁。经堆积密度、比表面积、孔容积、粒径及透射电镜的测定,试验样品的粒子大小均在10 nm左右。试验结果证明,试验工艺路线及测定方法均适合纳米氧化镁制备。主要原料碳酸铵和氯化镁来源广泛,价格低廉,对纳米氧化镁的工业生产具有重要的意义。     

流变相-前驱物法制备纳米氧化镁粉体

以普通氧化镁和邻苯二甲酸为原料,采用流变相-前驱物法制备了纳米氧化镁粉体,用元素分析和红外光谱表征了前驱物的组成和结构,通过热重分析确定了煅烧温度,分别用X射线粉末衍射、透射电镜对纳米氧化镁粉体的结构及形貌大小进行表征。用该法制备出的纳米氧化镁粉体为立方晶型,形状近似球形,分散性好,平均粒径约为10 nm。     

草酸镁分解法制备纳米氧化镁

以草酸和氯化镁为原料，采用固液法制备了纳米级氧化镁粉体。优化了试验条件，并用TEM和XRD对纳米氧化镁的粒子结构和形貌进行了研究。结果表明，在600℃焙烧，得到的纳米氧化镁粒度分布均匀，平均粒径为15nm。并对固液法生成纳米氧化镁的机理进行了初步探讨。     

纳米氧化镁的制备研究

研究了由碳酸铵和氯化镁制备纳米氧化镁的方法。以碳酸铵和氯化镁为主要原料，加入有机表面活性剂，经过反应、过滤、水洗、醇洗、干燥和灼烧制得纳米氧化镁。经表观密度、比表面积、孔容积、粒径及透射电镜的测定，粒子大小均在纳米范围。试验结果证明，试验工艺路线及测定方法均适合纳米氧化镁制备。主要原料碳酸铵和氯化镁来源广泛，价格低廉，对纳米氧化镁的工业生产具有重要意义。     

一种利用白云石制备花瓣状纳米氧化镁的方法

一种利用白云石制备花瓣状纳米氧化镁的方法,直接利用丰产矿物白云石为原料,采用二段酸浸法和EDTA-氨水络合沉淀反应相结合的方法,制备高纯度的菱面片层类似花瓣状结构的纳米氧化镁。本发明解决了中间产物纳米氢氧化镁沉淀及过滤困难的难题,生产成本较低,工艺简单。     

立方体纳米氧化镁的可控合成及其粒度影响因素的探究

采用溶胶-凝胶法,以Mg(CH_3COO)_2·4H_2O为原料,草酸为络合剂和酸性试剂,从晶体形成机理入手,详细研究了不同粒径立方纳米氧化镁的制备工艺。采用XRD和SEM分别表征了纳米氧化镁的结构和形貌。结果表明,通过改变工艺条件可以制备出粒度可控的纳米氧化镁,反应温度是影响纳米氧化镁粒度与形貌的关键因素。     

直接转化法制备纳米氧化镁的研究

本文以氧化镁和碳酸铵为原料.以表面活性剂A17为分散剂,采用直接转化法成功地制备了平均粒度为60nm的氧化镁粉体.通过热力学核算,从理论上证明该方法是可行的.单因素实验及正交实验表明,制备纳米氧化镁的最优化工艺条件为:反应温度76℃,反应时间90 min,碳酸铵溶液的浓度为0.35 mol/L,氧化镁与碳酸铵摩尔比1:1.3,表面活性剂A17加入量为反应溶液质量的0.5‰,并用激光粒度分析仪、XRD、TEM和比表面积分析仪对最终产物纳米氧化镁进行了表征.结果表明,样品粒径分布窄、分散性良好,平均粒径为65nm.该工艺流程简单,制备条件温和,产品质量稳定,适宜于工业化生产.     

沉淀转化法制备不同粒径的纳米氧化镁

以氧化镁和碳酸铵为原料,采用沉淀转化法研究了不同粒径纳米氧化镁的制备,讨论了加料方式、反应物配比、反应温度、煅烧温度等条件对其粒径的影响。实验结果表明:用沉淀转化法制备出不同粒径的纳米氧化镁颗粒;加料方式对纳米氧化镁的平均粒径有影响,滴加加料法比一次加料法制备的氧化镁粒径大;反应条件对粒径也有显著影响,反应物配比越大,纳米氧化镁粒径越大;反应温度越高,其粒径越小;煅烧温度越高,其粒径越大。     

The use of mixing-sensitive chemical reactions to study mixing in dispersed fibre systems: Adsorption of reactants and product dyes on the dispersed phase

Mixing-sensitive chemical reactions conducted under controlled conditions can be used to qualitatively and quantitatively assess mixing in aqueous systems. These reactions are typically competitive reactions where the distribution of products is used to quantify mixing. This technique is valuable for studying both mixing and local energy dissipation in dispersed systems where the opacity of the suspension prevents the use of other techniques. However, correct interpretation of the test results requires that adsorption of reactants and product dyes on the dispersed phase be known. The adsorption of the reactants and product dyes formed in the mixing-sensitive azo coupling between mixtures of 1- and 2- naphthol and diazotized sulfanilic acid was measured in aqueous suspensions of nylon, polyethylene, fibreglass and kraft pulp fibres. The polyethylene fibre did not adsorb the reactants or product dyes. The nylon, fibreglass and kraft fibres adsorbed both reactants and product dyes, with adsorption described by Langmuir isotherms. Accounting for the adsorption of dye on the dispersed phase allowed correct interpretation of mixing in the aqueous phase of the dispersions. This technique is evaluated for mixing assessment in suspensions of nylon fibre and fully bleached kraft (FBK) pulp in a medium-intensity mixer.     

Forced oscillations of concentration in transport reactors

The performance of a transport catalytic reactor is analysed for an adsorption/desorption type model with Eley-Rideal surface kinetics with square wave oscillations in the feed concentration. The inlet average concentration of both the reactants over a period is assumed to be constant. Significant improvement in the yield of product is obtained by increasing the feed concentration of both the reactants in the first fraction of a period. The effect of adsorption capacity of the catalyst, reaction rate constants, and inlet feed mean concentration of the reactants are evaluated. The deactivation of active sites, due to product inhibition, introduces resonance in the yield versus cycle split. The yield of product shows a minimum with respect to cycle split for the type of forcing where one of the reactant concentrations increases and the second reactant concentration decreases in the first fraction of a period.     

Integral Models of Turbulent Micromixing in Processes with Complex Chemical Reactions

Turbulent mixing during an irreversible isothermal competitive–consecutive reaction is considered. The sensitivity of the calculated results to the choice of micromixing model is analyzed. The upper- and lower-bound estimates of the average concentration of the desired product and selectivity are obtained for integral models of micromixing. The initial concentrations of the reactants affect the process characteristics. Simple analytical expressions are derived for the conditions for complete conversion of the initial reactants. Calculations for portionwise adding of the reactants are also performed.     

Controlling reaction selectivity in the oxidation of methanol at Cu(110) surfaces

When deuterated methanol (CD₃OH) and dioxygen mixtures are coadsorbed at Cu(110) surfaces at room temperature and above, the main reaction product can be switched between formaldehyde and formate by changing the mixture composition. For oxygen-rich mixtures formaldehyde is the major product but when methanol is in 5 : 1 excess only formate is produced. It is proposed that the reaction mechanism is controlled by the microscopic structure of the surface: when the reactants are adsorbed sequentially, separate islands of oxygen and methoxy develop which inhibit further oxidation but when reactants are coadsorbed a homogeneous mixture of adsorbates is produced creating a facile pathway to formate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-linear interactions of dynamic reactive interfaces in porous media

Viscous fingering of reactive miscible flow displacements in a homogeneous porous media is examined. A general model where the two reactants and the chemical product have different viscosities is adopted. The problem is formulated using the continuity equation, Darcy's law, and volume-averaged forms of convection–diffusion–reaction equations for mass balance, and is solved using a pseudo-spectral method. A parametric study was performed to examine the effect of the Peclet number and the log-mobility ratios between the chemical product and the reactants. It is shown that the development and growth of the instability as well as the efficiency of the reaction expressed in terms of the amount of chemical product can be predicted based on the mobility ratio at the initial front between the two reactants and effective mobility ratios between the chemical product and either one of the two reactants. Furthermore, it is reported that larger Peclet numbers lead to slower rates of chemical production.     

维生素K3的合成研究

利用 2 -甲基 -1,4萘醌和亚硫酸氢钠为原料 ,合成维生素K3,考察了原料物质的量比、温度、时间对反应的影响。对结晶母液进行了重复利用试验。产品收率可达 75 %以上。     

A kinetic model of membrane formation by CVD of SiO2 and Al2O3

Silica and alumina layers deposited onto the walls of porous Vycor tubes by chloride hydrolysis in an opposing reactants geometry have been characterized by scanning electron microscopy and electron microprobe analysis. The layers are asymmetric, having a long tail toward the side of the chloride flow and a sharp boundary at the other side. The deposit thickness is several tenths of microns, while the totally plugged region is of order of 1 micron. A model has been developed describing reaction, diffusion and evolution of the porous structure in the Vycor substrate due to the accumulation of the solid product. The deposition reaction is described by transient kinetics in terms if the concentrations of silanol and chloride groups in the product layer, as well as the concentrations of the gaseous reactants. The model is capable of generating deposit profiles in good agreement with those measured by electron microprobe analysis.     

2-呋喃基-4,4,6-三甲基-1,3-二噁烷的合成

以MnSO4.H2O为催化剂,呋喃甲醛与2-甲基-2,4-戊二醇为反应物合成了题示化合物。考查了催化剂用量,反应物的物质的量及反应时间对产物产率的影响。产物的结构由FTIR,1H-NMR和13C-NMR给予确认。     

Variations in Solution Chemistry During the Low-Temperature Formation of Hydroxyapatite

Both the kinetics and the microstructure of monolithic hydroxyapatite formed by a low-temperature dissolution and precipitation reaction strongly depend on the conditions in solution during the reaction. The relationships between the molar ratio of the particulate reactants (dicalcium phosphate and tetracalcium phosphate), the solution chemistry, and the rates of formation of hydroxyapatite are examined. During reaction, steady-state solution conditions are rapidly achieved. However, the steady states attained are not those associated with the metastable invariant point involving the reactants. Rather, the steady-state condition varies depending on the molar ratio of the reactants. The ultimate product of the reactions investigated is calcium-deficient hydroxyapatite. Hydroxyapatite formation occurs in two stages: initial formation of nearly stoichiometric hydroxyapatite followed by its conversion to calcium-deficient material. Microstructural evidence indicates that the formation of hydroxyapatite occurs in association with dicalcium phosphate, eventually causing the dissolution of the hydroxyapatite reactant to become diffusionally controlled. Effects of common ions, sodium chloride and magnesium chloride, on the chemistry of the aqueous phase and on microstructural development are investigated.     

相转移催化合成1，4-双（咪唑-1-基）丁烷的研究

以四丁基氢氧化铵作为相转移催化剂制备了1,4-双（眯唑-1-基）丁烷。通过单因素实验得到了合成该产物的最佳条件：氢氧化钾浓度90％,催化剂用量0．3mmol,反应温度℃,反应物摩尔比2．2,反应时间6h。通过核磁共振波谱、红外光谱对所得产物进行了结构表征。