pH值对BaTiO3纳米粉体性能的影响

本文研究了溶胶-凝胶过程中不同pH值条件下制得钛酸钡纳米粉的性能，从双电层理论及反应机理分析讨论了pH值对胶体的形成及团聚状态的影响，得到了反应的优化条件(溶液的pH值应控制在8以上)，制得粒径小、颗粒分布均匀、少团聚的 BaTiO     

pH值对BaTiO3纳米粉体性能的影响

本文研究了溶胶-凝胶过程中不同pH值条件下制得钛酸钡纳米粉的性能,从双电层理论及反应机理分析讨论了pH值对胶体的形成及团聚状态的影响,得到了反应的优化条件（溶液的pH值应控制在8以上）,制得粒径小、颗粒分布均匀、少团聚的BaTiO₃纳米粉体．     

化学法制备超细陶瓷粉末工艺研究

研究了共沉淀法制备ＺｒＯ２·Ｙ２Ｏ３·Ａｌ２Ｏ３陶瓷粉末工艺过程。通过正交试验，找到了防止粉体团聚的各工艺参数。结果表明，在共沉淀法制粉过程中，母液浓度对粉体粒度无明显影响；滴定ｐＨ值以８－９为佳；表面活性剂与粒子分散剂的正确选择与适时定量加入可明显减弱粉体团聚倾向。在最佳工艺条件下制得粒度为０．５μｍ左右超细陶瓷粉末。     

表面活性剂在制备ZrO2微粉中的作用

研究了在用化学沉淀法制备ＺｒＯ２微粉的过程中,ｐＨ值,Ｚｅｔａ电位,表面活性剂及其添加方式等因素对氢氧化锆胶体的稳定性,分散性及氧化锆粒子尺寸的影响,控制了团聚体形成,得到了无硬团聚体的亚微米级的超细ＺｒＯ２粉末。     

分散剂对纳米碳化硅粉末在水中分散的影响

研究了ｐＨ２－１２范围内分散剂－聚乙烯亚胺（ＰＥＩ）的加入及其浓度对碳化硅粉末在水中的分散情况的影响。发现在浆料中加入分散剂时，碳化硅在ｐＨ＝１０．４时达到最佳分散，此时浆体呈现牛顿流体特征，表现出最小的沉降高度和最大的电位势。在酸性条件（ｈＨ＝２－７）浆体产生很大的团聚，具有较大的沉降高度，较大的粒子尺寸，较低的电位值，呈现非牛顿体特征。对于碳化硅粉末适宜的分散条件是在碱性条件ｐＨ＝８～１０。     

以蔗糖为碳源制备纳米碳化硅粉影响因素的研究

以蔗糖和正硅酸乙酯（ＴＥＯＳ）为前驱体，对溶胶－凝胶法制备纳米碳化硅粉工艺中的几种重要影响因素进行了研究。这些影响因素包括ｐＨ值、去离子水量、蔗糖加入先后顺序等。ＸＲＤ分析结果表明，过量水导致Ｓｉ（ＯＲ）４的充分水解，并形成高度交联的水解聚合物。由于交联程度高使得１４００℃反应时只能得到大粒径的无定型二氧化硅，不能得到β－ＳｉＣ。而无论是在酸碱条件下，ＴＥＯＳ与适量水反应的产物经高温反应后都能得到粒径为１５～２０ｎｍ的β－ＳｉＣ粉。β－ＳｉＣ粉的产率以先用适量水水解，再加入蔗糖溶液的样品为最高。ＳＥＭ和ＴＥＭ分析表明，在酸性环境中水解后制得的纳米碳化硅粉分散性好，粒度均匀；而在碱性环境中水解制得的碳化硅粉团聚程度高。     

EDTA络合法制取稳定ZrO2纳米粉

本文以ＥＤＴＡ为络合剂,使它与无机锆、钇盐 事,生成络合物溶胶。这种化学络合法制得的溶胶结构随着锆、钇离子与ＥＤＴＡ的摩尔配比（ｒ）及其溶液所处介质溶液的ｐＨ值而变化,借助于ＴＧ、ＤＴＡ、ＸＲＤ、ＢＥＴ、ＴＥＭ等方法分析;可得出最后煅烧温度为６００℃。在实验范围内,ｐＨ值恒定时,ｒ大于２时,粒径随ｒ增大而增加;当ｒ〈２时,粒径随ｒ增加而减小。在同一配比下,ｐＨ〉５时,ＳＢＥＴ随ｐＨ值的升高迅速下降     

亚铁盐氧化法合成纺锤形α—Fe2O3微粒条件的研究

硫酸亚铁空气氧化直接合成α－Ｆｅ２Ｏ３是备制均分散异形α－Ｆｅ２Ｏ３微粉的新方法。本研究通过ＸＲＤ、ＴＥＭ、化学分析等方法考察ｐＨ值对合成过程及产物的影响并确定其最佳合成条件。     

纳米级CaO—ZrO2复合氧化物粉体的制备与表征

采用化学共沉淀－超临界干燥技术制备ＣａＯ－ＺｒＯ２纳米粉体，并详细考察了主要制备参数－共沉淀过程的ｐＨ值对产品粉全体性能的影响，实验表明，超临界流体干燥法能很好地保留初始湿凝胶的结构，有效地防止凝胶干燥过程中粒子间硬团聚现象的发生，该法合成的纳米粉体具有粒径小，粒度分布围窄，比表面大等特点，此外，实验还发现，水合凝胶体系ｐＨ值会很大程度上影响产品粉体的性能，在实验范围内，随着体系ｐＨ值的增大，粉体     

液膜技术提取稀土的试验研究

采用煤油－Ｓｐａｍ８０－Ｐ５０－ＨＣｌ组成的液膜体系，研究了自稀土母液中提取稀土的基本原理、制乳条件、油内比、水乳比、ｐＨ值和提取时间等，稀土提高２取率达９８％左右。     

天然热释电材料电气石的微结构及对水的pH值影响机理的研究

以新疆产天然电气石为原料制备了电气石微粉,利用X射线衍射仪、扫描电镜、高分辨电镜、pH酸度计研究了电气石的物相、微结构特点和电气石对水酸度及其随温度变化的影响.结果表明,电气石单个微粒为单畴的铁电体,可视为电偶极子;利用电气石微粉可以使水的酸度呈弱碱性;电气石对水酸度的影响随温度的变化进一步佐证了电气石的热释电性,并探讨了电气石对水作用的可能机理.     

制备条件对NZP族磷酸盐粉体材料物性的影响

用化学共沉淀法配合高温煅烧合成了几种不同化学组成的NZP族磷酸盐粉体材料,从实验结果和对共沉淀反应过程的理论分析两方面入手,着重研究了反应体系的pH值与形成单相NZP族晶体化合物的关系,以及煅烧温度对NZP族粉体比表面积的影响规律.结果表明:控制液相反应过程的pH值=8.5有利于形成单相的NZP族晶体化合物,结晶形态完整的NZP族化合物的比表面积＜30m2/g,在低于晶化温度下煅烧则可以制备大比表面积的NZP族粉体.此外,本研究所合成的NZP族化合物在pH=3～9的水溶液体系中表面带负电荷.     

Defluoridation of groundwater using brick powder as an adsorbent

Defluoridation of groundwater using brick powder as an adsorbent was studied in batch process. Different parameters of adsorption, viz. effect of pH, effect of dose and contact time were selected and optimized for the study. Feasible optimum conditions were applied to two groundwater samples of high fluoride concentration to study the suitability of adsorbent in field conditions. Comparison of adsorption by brick powder was made with adsorption by commercially available activated charcoal. In the optimum condition of pH and dose of adsorbents, the percentage defluoridation from synthetic sample, increased from 29.8 to 54.4% for brick powder and from 47.6 to 80.4% for commercially available activated charcoal with increasing the contact time starting from 15 to 120 min. Fluoride removal was found to be 48.73 and 56.4% from groundwater samples having 3.14 and 1.21 mg l(-1) fluoride, respectively, under the optimized conditions. Presence of other ions in samples did not significantly affect the deflouridation efficiency of brick powder. The optimum pH range for brick powder was found to be 6.0-8.0 and adsorption equilibrium was found to be 60 min. These conditions make it very suitable for use in drinking water treatment. Deflouridation capacity of brick powder can be explained on the basis of the chemical interaction of fluoride with the metal oxides under suitable pH conditions. The adsorption process was found to follow first order rate mechanism as well as Freundlich isotherm.     

聚乙烯亚胺在SiC粉体上的定量吸附研究

利用紫外一可见光谱研究了分散剂聚乙烯亚胺在粉体ＳｉＣ上的定量吸附情况．加入酸性ＰＥＩ后粉体ＳｉＣ表面的电性发生改变,等电点由ｐＨ＝２．０移至ｐＨ＝１０．５．分散剂在粉体上的吸附满足Ｌａｎｇｍｕｉｒ单层吸附方程．对分散剂ＰＥＩ－Ｈ^＋（ｐＨ＝３．５７）来说,单层吸附值为０．０１７２ｍｇ／ｍＬ．对分散剂ＰＥＩ－Ｈ^＋（ｐＨ＝６６１）来说,单层吸附值为０．０２０８ｍｇ／ｍＬ．利用富利叶红外光谱证实了这种吸附作用．     

Anodic Oxidation of Both Particulate and Compact Iron in Chloride-Containing Acetate Buffer Electrolytes

The voltammetric records of Fe powder and compact iron electrode in chloride-free and chloride-containing acetate buffer electrolytes of various pH values were compared in the range 4.0 to 6.0. Owing to the consumption of the powder, the voltammetric current at the powder electrode decreases nearly to zero. Full passivation of the iron surface was observed in the absence of chloride on both electrodes. The differences become clear in chloride-containing electrolytes: with the compact electrode, the dissolution proceeds continuously while with the powder electrode the rate of the process is limited by both the degree of iron conversion and potential applied. Chloride ions not only incorporate into the intermediate species but also form soluble species in the passivation layer, leading to its degradation. The result is an observable anodic dissolution reaction of further Fe powder. The composition of the layer differs in dependence on pH. At lower pH, dissolution proceeds faster and to a larger extent. At higher pH, the thickness of the passive layer is larger and it contains more Fe hydroxides/oxides with higher resistance to the action of chloride. Scanning electron microscopy confirmed deep breakdown of the crystal structure of Fe grains.     

Anodic Oxidation of Both Particulate and Compact Iron in Chloride-Containing Acetate Buffer Electrolytes

The voltammetric records of Fe powder and compact iron electrode in chloride-free and chloride-containing acetate buffer electrolytes of various pH values were compared in the range 4.0 to 6.0. Owing to the consumption of the powder, the voltammetric current at the powder electrode decreases nearly to zero. Full passivation of the iron surface was observed in the absence of chloride on both electrodes. The differences become clear in chloride-containing electrolytes: with the compact electrode, the dissolution proceeds continuously while with the powder electrode the rate of the process is limited by both the degree of iron conversion and potential applied. Chloride ions not only incorporate into the intermediate species but also form soluble species in the passivation layer, leading to its degradation. The result is an observable anodic dissolution reaction of further Fe powder. The composition of the layer differs in dependence on pH. At lower pH, dissolution proceeds faster and to a larger extent. At higher pH, the thickness of the passive layer is larger and it contains more Fe hydroxides/oxides with higher resistance to the action of chloride. Scanning electron microscopy confirmed deep breakdown of the crystal structure of Fe grains.     

溶胶-凝胶法制备TiO2粉体及其光催化性能研究

以钛酸丁酯为前驱物,无水乙醇为溶剂,采用溶胶-凝胶法制备了TiO2粉体,并采用紫外分光光度计、XRD等表征手段对TiO2的粒度、晶型结构进行了表征,分析了煅烧温度、TiO2晶型比例、溶液初始pH值等因素对TiO2结构性能及光催化活性的影响.结果表明:TiO2的锐钛矿晶型与金红石晶型的转相温度为700 ℃左右;采用溶胶-凝胶法制备TiO2时,控制溶液的pH值为4,煅烧温度为600 ℃,所得产物晶型全部为锐钛矿;当无水乙醇与钛酸丁酯的体积比为10:1时,产物的粒径为617 nm;且当配制溶液pH值为4,煅烧温度为600℃条件下,煅烧时间为40~60 min时,所制备TiO2的光催化效果较好,降解率较高;当光催化体系的pH值为9、以质量浓度为10 mg/L的亚甲基兰溶液浸泡2 h,TiO2的用量为0.25 g/L时,产物的降解率高达95.3%.     

Fabrication of a composite powder and its application as an active brazing alloy

A copper-based active brazing alloy containing a high titanium content was produced by an electroless coating technique. Particles with a narrow density distribution were produced by deposition of nano-copper on a fine titanium powder. Both conventional titanium powder and sponge titanium were studied. The effects of pH and time on copper deposition were investiguated.Higher pH was found to increase the quantity of copper deposited. Using multiple depositions, a copper-titanium ratio of 75 wt% copper-25 wt% titanium could be achieved after several platings for pH varying between 12 and 12.8. The particle size distribution of the composite powder shows uniform growth of the copper shell and no agglomeration under pH 12. Major agglomeration of the final powder was observed for a bath pH of 12.8.Complete melting of the composite powder has been studied by DSC and the sessile drop technique. Melting began within the diffusion zone formed at the interface through the Cu₄Ti → Cu(s) + L peritectic reaction that occurs at 885^∘C. The melting process continued by successive peritectic reactions and dissolution of the remaining elements of the diffusion couple. The wetting behavior of this alloy was evaluated on different ceramic substrates (Al₂O₃, Si₃N₄) and found to be similar to literature observations.     

pH值对溶胶凝胶-燃烧合成纳米晶LaMnO_3粉末的影响

以硝酸镧、硝酸锰和柠檬酸为原料,采用溶胶凝胶燃烧合成技术制备了超细LaMnO3粉末。借助XRD、DTA、SEM、FT-IR等分析仪器研究了溶胶凝胶-燃烧合成技术合成超细LaMnO3粉末的过程,着重讨论了前驱体溶液不同pH值对溶胶凝胶燃烧合成过程及合成产物的影响。结果发现,采用溶胶凝胶燃烧合成技术能合成纳米晶的LaMnO3粉末,随前驱体溶液pH值增加,燃烧反应速率增加,合成粉体的平均晶粒尺寸随pH值增加而减小。通过控制前驱体溶液pH值能一步合成超细LaMnO3颗粒(粒径200nm)。