硅酸及其盐的研究——ⅩⅢ.单硅酸胶凝作用中的离解常数

硅酸的离解常数是表征硅酸基本性质的重要数据,前人已有不少工作,但由于测定的方法和条件不同,所得数据很不一致.本工作用“N”曲线法测求了硅酸的各级离解常数.     

硅酸及其盐的研究 ⅩⅩⅠ.三甲基硅烷化-气相色谱法测定单硅酸的离解常数

单硅酸的离解常数是表征其基本性质的重要数据,前人已有不少工作,但由于测定的方法和实验条件不同,所得数据很不一致。本实验室曾用“N’曲线法测得了单硅酸的各级离解常数,由于这些常数系在单硅酸到达多硅酸直至凝胶的过程中所测得,故和公认的单硅酸标准离解常数差别很大,只能称为胶凝离解常数。     

硅酸乙酯

硅酸乙酯是最早被工業生產的有機硅化合物之一。在有機硅化合物中,雖然聚烃基硅氧烷現在亦已廣泛用於工業材料,並在應用上有一部分已代替了硅酯乙酯,但是硅酯乙酯在工業上仍然有重要的價值。這是由於硅酸乙酯和聚烃基硅氧烷在應用上有所區別,它的重要的工業應用在於它在適當條件下能够經過水解縮合而析出有高度粘結性及高度耐熱性(1600℃)的二氧化硅的性質。     

硅酸及其盐的研究 ⅩⅪ.三甲基硅烷化-气相色谱法测定单硅酸的离解常数

由于硅酸的聚合性质,单硅酸易发生聚合,溶液中硅酸总量不能代表单硅酸的含量,因而其离解常数不易测准,各家所得数据不一.本文用三甲基硅烷化-气相色谱法测得硅酸溶液中单硅酸含量以求得不同时间下单硅酸的最快聚合点的pH,并以时间外推法求得单硅酸的标准离解常数.本文还用离子强度外推法,求得了单硅酸热力学离解常数。这些常数和公认值一致.     

硅酸及其盐的研究 ⅩⅪ. 三甲基硅烷化-气相色谱法测定单硅酸的离解常数

由于硅酸的聚合性质,单硅酸易发生聚合,溶液中硅酸总量不能代表单硅酸的含量,因而其离解常数不易测准,各家所得数据不一.本文用三甲基硅烷化-气相色谱法测得硅酸溶液中单硅酸含量以求得不同时间下单硅酸的最快聚合点的pH,并以时间外推法求得单硅酸的标准离解常数.本文还用离子强度外推法,求得了单硅酸热力学离解常数.这些常数和公认值一致.     

硅酸凝胶的制备

硅酸凝胶,可用硅酸钠溶液和酸性物质反应的办法来制取。硅酸钠溶液采取20%的溶液,即把20克化学纯的偏硅酸钠晶粒溶解在80毫升热蒸馏水中。     

硅酸镓镧族非线性光学晶体

中红外非线性光学晶体可以实现中红外激光频率转换、拓展激光波长,在民用和军用领域中有至关重要的应用价值。其中,硅酸镓镧族晶体具有透过范围宽、激光损伤阈值高、晶体质量好等优势,引起了国内外同行的广泛关注。在这篇综述中,我们基于现有的实验数据,研究和分析了三种重要的硅酸镓镧族晶体La_3Ga_5Si O_(14)(LGS)、La_3Ga_(5.5)Nb_(0.5)O_(14)(LGN)、La_3Ga_(5.5)Ta_(0.5)O_(14)(LGT)的综合性能,详细总结了它们在电光调Q开关和中红外光参量振荡以及差频激光输出方面的应用。最后,本文还讨论了今后硅酸镓镧族中红外非线性光学晶体的重点发展方向。     

硅酸及其盐的研究——Ⅹ.单硅酸聚合反应动力学

本文用一方程逼近钼硅黄显色的消光-时间曲线,求得了双硅酸的显色速度常数,从而建立了一个在多种聚合度的硅酸水溶液体系中测定单硅酸的方法.利用这个方法,确定单硅酸聚合反应的初速度对其自身浓度是二级反应.根据本实验室提出的硅酸聚合理论,计算了速度常数和相应的活化能,进一步证明了以前所提机制的正确性.     

硅酸及其盐的研究 Ⅴ.氟离子和硅酸的聚合作用

在較广的pH范围內,测定氟离子对硅酸(酸化的水玻璃和单硅酸鈉)胶凝作用的影响。在中性和微碱性溶液中,氟离子促进硅酸胶凝,而且这作用随所加氟离子数量而加大。在酸性溶液中,氟离子也有促凝作用,并随氟离子增多而增加。但只增加到一定限度,过此限度,促凝作用卽行減退。所生凝胶的离浆溶液合氟量亦已测定。在碱性溶液,氟离子全部在离浆液中,表示氟离子不参加凝胶的組成而仅起催化作用。在酸陸溶液,氟离子全部或大部分在凝胶內,这表示它不仅参与反应而且是产物的組成部分。根据以前所提硅酸聚合的机制,对所观測到的結果作初步的解释。     

制取硅酸溶胶的改进

在制取硅酸溶胶的过程中,所加盐酸或水玻璃的浓度和用量都是很重要的;若所加盐酸或水玻璃中的任一种浓度过浓,都容易形成凝聚,甚至生成高聚物而产生沉淀。     

Étude d'équilibres en solution à l'aide des échangeurs d'ions : I Dissociation du perchlorate d'argent et de l'acide nitrique dans les mélanges eau—acide acétique—acide perchlorique ou acide nitrique

A theoretical relationship postulated between the distribution coefficient of a monovalent element and the parameters upon which it depends (acid concentration in solution, dissociation constants of the acid and the salt, selectivity coefficient of exchanged ions) has been verified for the dissociation of silver perchlorate in water—acetic acid—perchloric acid mixtures. The dissociation constants found have been compared with the experimental values obtained by potentiometric measurements. The relationship established has been employed for the determination of nitric acid dissociation constants in water—acetic acid-nitric acid mixtures containing less than 25 % by weight of water. From the results the pK value for nitric acid in pure acetic acid has been evaluated by extrapolation. The theoretical relationship might be used to determine an acid dissociation constant when the dissociation constant of a salt is known and vice versa.     

邻苯二甲酸在异丙醇-水混合溶剂中电离热力学性质的研究

有机酸在混合溶剂中电离热力学性质的研究,无论在化学还是在生物领域中都有十分重要的意义。长期以来,人们对其进行了大量的研究,但对芳香族酸在混合溶液中的电离热力学性质的研究还只限于单取代苯甲酸在乙醇-水等少数几种混合溶剂中的热力学性质。为此,我们在278.15—318.15K范围内测定了无液接电池:     

On the acid behaviour of the alcoholic group of serine

The behaviour of l-serine in strongly alkaline solution was studied at 25 degrees C and in 3.00 mol/l NaClO(4), as a constant ionic medium, to obtain quantitative information about the eventual dissociation of its alcoholic group. A spectrophotometric method was employed to measure the free concentration of hydrogen ions. Two indicators, methyl thymol blue and eriochrome blue type R, were used. Their values as protonation constants and absorbance coefficients were determined in advance. The method here proposed has been validated beforehand by applying it to d-mannite and glycerine and by comparing results so obtained with those previously provided by literature. The investigation showed weak acid properties of the -OH of serine and its dissociation constant was determined. Polynuclear species or further dissociation were not observed.     

Dissociation constant of aqueous trifluoroacetic acid by cryoscopy and conductivity

The dissociation constant of trifluoroacetic acid in aqueous solution has been determined at 25°C by electrical conductivity (0.65 mol-l^–1) and at 0°C by cryoscopy (1.05 mol-l^–1) and electrical conductivity (0.98 mol-l^–1). The good agreement between the values of the constant determined by cryoscopy and conductivity at 0°C lends confidence to the value at 25°C determined by electrical conductivity. The constant determined at 25°C is in reasonable agreement with values determined by differential refractometry (0.92 mol-l^–1) and from acidity function data (0.80 mol-l^–1) reported by other workers. This work renews confidence in the electrical conductivity method for determining dissociation constants of moderately strong acids.     

Acids in dimethylformamide. III. Ionic equilibria of dicarboxylic acids

Dissociation and homoconjugation constants of succinic, malonic, and dimethylmalonic acids have been determined potentiometrically at 25°C. Conductometric studies on the tetraethylammonium salts of the acids permitted the evaluation of the corresponding dissociation constants, which allowed a better fit of calculated curves with experimental data. Homoconjugation of two monovalent anions with a divalent anion was pointed out in all cases. No appreciable homoconjugation of the monovalent anion with the diprotic acids was found. In order to standardize the glass electrode at high paH values, the dissociation constant of diethylbarbituric acid has also been determined.     

ASCORBIC ACID AS A PHOTOOXIDATION INHIBITOR

Abstract— The rate constant for total quenching of singlet oxygen by ascorbic acid has been determined using the inhibition of the bleaching of 9, 10-dimethylanthracene by AA in pyridine. The rate constant was 8.4 × 10^-6 M ^-1 s^-1, as determined photochemically, and 1.06 10^-7 M ^-1 s^-1 as determined in a dark reaction.     

The effects of high concentrations of aqueous tetramethylammonium chloride and other salts on the dissociation of phenylphosphonic acid and on the enolization of acetone

The dissociation constants of benzoic acid and phenylphosphonic acid have been determined in aqueous solutions containing tetramethylammonium chloride at concentrations up to 15 and 13 molal, respectively. The second dissociation constant of phenylphosphonic acid has also been determined in concentrated solutions of alkali halides. Whereas the organic electrolyte increases the observed pK values of the acids, the inorganic electrolyte idecrease them. The rate of enolization of acetone, catalyzed by phenylphosphonate dianion is increased by the presence of tetramethylammonium chloride, but is decreased by the presence of inorganic salts, in accordance with the changes in the apparent acidity constants of phenylphosphonate monoanion that the two different kinds of electrolyte bring about. The slope of the Brónsted plot for the inorganic salts is 0.76; that for the organic electrolyte is 0.46. Non-quaternary ammonium salts also increase the rate of the phenylphosphonate dianion catalyzed enolization of acetone, but this appears to be due to a considerable extent to the formation of reactive iminium ion intermediates.