Лекция № 11 ФХС .
Theme: Силикаты in высокодисперсном a condition. Concept about дисперсных systems. A measure дисперсности. Classification дисперсных of systems. The characteristic and methods of reception коллоидных of systems. Коллоидные of the form кремнезема. Гели of a silicon acid.
Lecture №10.
Силикаты in высокодисперсном a condition
1. Concept about дисперсных systems. A measure дисперсности. Classification дисперсных of systems
2. Characteristic and methods of reception коллоидных of systems. Коллоидные of the form кремнезема. Гели of a silicon acid.
Золь кремнезема, is суспензия кремнезема
Гель soft weight
Concept about дисперсных systems. A measure дисперсности.
Дисперсные of system - heterogeneous systems with the strongly advanced internal surface between phases consisting of two or greater numbers of phases, and, at least one of them (named дисперсной by a phase), has enough high дисперсностью and is distributed(allocated) in environmental continuous дисперсионной to environment(Wednesday) as fine particles.
In process of reduction of the sizes of particles дисперсной phases the surface undressed of phases grows. Thus, the concept " дисперсные of system " unites systems containing particles small in all measurements, and system with particles having the significant sizes (down to microscopic).
Дисперсность - characteristic of heterogeneous system back proportional to the size (diameter) of particles дисперсной of a phase. Дисперсность defines(determines) size of a specific surface Sудv, i.e. attitude(relation) of a surface of a particle S1 to its(her) volume V1:
Sудv = S1/ V1
In practice it is necessary to deal in overwhelming majority of cases with полидисперсными by systems, the size of particles in which changes from several ангстрем (10-10м) up to hundreds микрометров (10-4м).
The large interest to дисперсным to systems on the part of the theorists and практиков is called by a wide circulation them in a nature and engineering. The mountain breeds, грунты and ground, fogs and clouds, rain and snow, space dust and fabrics alive организмов are дисперсными systems. Дисперсной structure have the majority of materials of modern engineering - the alloys, polymeric and fibrous materials, concrete and composites.
Classifications дисперсных of systems
There are many classifications дисперсных of systems to various attributes. Elementary is the division all дисперсных of systems on 3 groups on a degree дисперсности: высокодисперсные, or ультрамикрогетерогенные, the size of which particles lays in limits from 10-9 up to 10-7м (1-100 нм), microheterogeneous with the size of particles from 10-7 up to 10-5 м (1-10 microns) and грубодисперсные with particles, which size exceeds 10-5м.
On a modular condition дисперсные of system are divided into three groups - with firm (т), liquid (ж) and газообразной (г) дисперсионными by environments(Wednesdays). Everyone of willows of these groups can be divided(shared) but three subgroups - according to a modular condition дисперсной of a phase. Practically are realized only 8 of 9-ти of theoretically possible(probable) combinations, since the gas in gas in usual conditions forms homogeneous system. Only in особах cases (for example, in space space) the non-uniform areas with флуктуациями of density such as Г-Г are possible(probable).
In technology refractory not metal and силикатных of materials the greatest meaning(importance) have the systems such as Т/Ж with high concentration дисперсной of a phase (суспензии, paste), Т/Г (diluted of a dust, smokes; концентрировенные - powders), Ж/Ж. - эмульсии. Суспензии in an industry have the various names: in technology of knitting materials - шламы, in technology of ceramics and огнеупоров - шликеры, in technology of inorganic substances -пульпы. Высококонцентрированные суспензии name by paste, test (for example, известковое тесто).
On intensity of molecular interaction between phases on their surface of the unit дисперсные of system are divided(shared) лиофильные and лиофобные (from греч. "лиос" - a liquid, "фило" I like ", фобо " - I hate). With reference to water дисперсионной to environment(Wednesday) such systems name гидрофильными and гидрофобными. Лиофильные of system (for example, clay) show strong interaction with дисперсионной by environment(Wednesday) at the expense of small distinction in their molecular nature (polarity and are capable диспергироваться spontaneously, forming термодинамически steady коллоиды. In лиофобных systems this interaction is weak owing to the large difference полярностей of substances, forming them, therefore such systems термодинамически are unstable. The fine particles having raised(increased) free superficial energy, is spontaneous коагулируют (stick together) or коалесцируют (merge). For increase of stability of similar systems enter stabilizers (ions, superficial - active substance to other), адсорбирующиеся on a surface of particles дисперсной of a phase and forming blanket interfering accusation of particles with each other.
On a degree структурирования дисперсные the systems can be divided(shared) into 3 basic groups. To first concern свободнодисперсные (unstructured) systems (золи), in which particle дисперсной of a phase are free, are not connected with each other and can independently move in дисперсионной to environment(Wednesday) by gravity or броуновского of movement. Some concern лиозоли, to them суспензии and эмульсии, aerosol. The second group make связнодисперсные systems described by presence of spatial structure (of a grid, skeleton), made by particles дисперсной of a phase, for example: гели to graze, powders, some суспензии etc. Частички, forming structure, are not capable to mutual moving and can make only oscillatory movements. At enough strong структурпой to a grid such дисперсные of system get a number(line) of properties of firm bodies (high structural viscosity, elasticity etc.), irrespective of a modular condition дисперсионной of environment(Wednesday) and дисперсной фгеы, П.А.Ребиндер of system of the first group has named жидкообразными, and second - твердообразными. The intermediate rule(situation) is borrowed(occupied) by(with) the structured liquids - дисперсные of system the separate particles дисперсной of which phase are connected with each other in friable units, but do not form continuous structure. These units can be considered(examined) as обрывки of a spatial grid, which for whatever reasons has not received complete development or partially has broken up. At complete destruction of structure structured дисперсные of system pass in unstructured (свободнодисперсные). If such transformation occurs is convertible, speak about presence тиксотропии in system.
The characteristic and methods of reception коллоидных of systems.
Heterogeneous высокодисперсные (коллоидные) of system are widely distributed in a nature and have the extremely important meaning(importance) in engineering. Коллоидное the condition is characterized certain(determined) дисперсностью (degree of crushing) firm phase, Depending on the size of particles all дисперсные of system classify as follows: грубодисперсные of system (суспензии, эмульсии), consisting from particles is larger 10-6 м; systems intermediate дисперсности (thin suspensions, smokes, porous bodies), consisting from particles by the sizes 10-6... 10-7 м; высокодисперсные of system (actually коллоиды), consisting from particles by the sizes 10-7.. 19-9 m. As the crushed substance usually is in any environment(Wednesday), from which it to a greater or lesser extent cooperates, the properties are necessary it(him) for considering(examining) in aggregate with this environment(Wednesday). As a result of interaction коллоидных of particles with each other and with дисперсионной by environment(Wednesday) are formed коллоидные of structure with a specific complex of properties. The variety of properties высокодисперсных of systems is caused by the following factors: by chemical structure of separate components, sizes of particles дисперсной of a phase, modular condition of initial products, molecular forces in superficial межфазных layers, and also properties and structure of these layers.
Коллоидные of system are formed in result or splitting of large pieces of substance up to required дисперсности, either association of molecules or ions in units коллоидных of the sizes. According to it exist диспергационные and конденсационные methods of reception дисперсных of systems.
Диспергационные methods. On these methods above system make job for overcoming intermolecular forces and accumulation of free superficial energy. Mechanical диспергирование provides crushing a material at the expense of mechanical job. The electrical way of reception коллоидных of systems is based on education of a volt arch between electrodes from диспергируемого of metal placed in cooled water. This method to диспергационным concerns conditionally, as the metal of an electrode is sprayed at temperature of an arch with education паров, which subsequently are condensed in a cold liquid. Also is conditional to methods диспергирования a concern - method пептизации: to свежеприготовленному to a friable deposit диспергируемого of substance add a solution of the электролита-stabilizer, under which action of a particle of a deposit are separated from each other and pass in the weighed condition, forming золь. Диспергационными by methods to reach(achieve) high дисперсности usually it fails.
Конденсационные methods. By these methods subdivided on physical and chemical, receive systems with the sizes of particles about 10-8... 10-9 m.
Major physical methods of reception дисперсных of systems - condensation from паров and replacement of the solvent. At change of parameters of system, in particular, at downturn of temperature, pressure pair above a liquid (or firm body) can Become above equilibrium and in a gas phase will arise new liquid (or firm) phase; the system becomes heterogeneous, the condensed particles form with a gas phase дисперсную system a fog (or smoke). For education дисперсной of system on a method of replacement of the solvent to a true solution any the substances add in large volume other liquid being for this substance the bad solvent, but well mixing up with the initial solvent. The methods of chemical condensation are based on конденсационном allocation of a new phase from пересыщенного of a solution, thus substance forming дисперсную a phase, occurs as a result of chemical reactions of an exchange, окислительно-восстановительных, гидролиза etc.
Коллоидные of the form кремнезема. Гели of a silicon acid.
The majority of changes, which occur with кремнеземом in a nature, is caused by interaction with water. By the basic characteristic of system кремнезем - water is the tendency it оксида to form коллоидные solutions or гидратированные of weight. Assume, that at education quartz lived осаждение геля кремнезема sometimes precedes development of crystals of quartz. At education аморфного the disgrace кремнезем in the beginning is allocated as soft гелеобразной of weight, which gradually hardens and begins to show peculiar to her дифракционные of property.
To typical natural коллоидным the forms кремнезема posess disgraces; метаколлоидный character have халцедоны and part of quartz.
Коллоидный кремнезем, or золь кремнезема, is суспензия кремнезема, the sizes of which particles are in коллоидной of area. The following ways of preparation water золей кремнезема are known: neutralization of a solution силиката натрия and диализ through полупроницаемые of a membrane; application электродиализа; dissolution of elementary silicon in water solutions of ammonia or амина; neutralization силиката натрия by an acid; пептизация гелей at raised(increased) temperature; application ионообменной of pitch for removal(distance) натрия from a solution силиката натрия. After mixing силиката натрия and hydrochloric acid the silicon acid turns out in высокодисперсном, probably, molecular, condition; she gradually becomes коллоидной at continuous growth of particles. Even at careful further clearing the relative viscosity золя is increased down to education геля. If пересыщенный a solution of a monosilicon acid to leave to grow old, a firm phase аморфного кремнезема at the end is defined(determined). This кремнезем can appear in the form коллоидных of particles, deposit or геля. It was supposed, that the transformation of a monosilicon acid occurs through the intermediate forms of a polysilicon acid up to one of these forms аморфного кремнезема, - as the change represents returning system to a condition adequate(answering) the minimal superficial energy. But this rule(situation), on Р. Айлеру, does not explain the mechanism полимеризации of a silicon acid and does not predict, what form will accept the final polymer. The general(common) equation полимеризации can be submitted as follows:
n Si (OH) 4 > (SiO2) n + 2nH2O
In opinion In. And. Вейля, the process полимеризации entails distribution HE - ions between various atoms of silicon conducting to education of polymeric cells, in which each atom Si4 + is surrounded октаэдрически with six HE - ions. At the presence of small quantity(amount) of alkali the silicon acid can полимеризоваться before education steady дисперсных коллоидных of particles, while in a sour solution is formed гель кремнезема.
The surface of particles коллоидного кремнезема is so great, that гидратация becomes measurable and it is possible to speak about коллоидном гидратированном кремнеземе.
The education геля кремнезема proceeds in two stages. In the first stage originally formed(originally educated) Si (HE) 4 is condensed before education коллоидных частичек. In the diluted solution the further slow increase of the sizes of particles is unique(sole) change, but at the contents about 1 % (May). SiO2 these initial particles are capable to be condensed before education of continuous structure, which provides the certain degree of its(her) rigidity.
The mechanism of both stages полимеризации is identical, namely: condensation before education of communications(connections) Si-О-Si. The irreversibility of process of formation геля is explained by irreversibility of reaction of condensation accompanying with education силоксановой of communication(connection).
Коагуляционные of structure are formed by coupling particles ван-дер-ваальсовыми by forces through layers of a liquid in parts, chains, spatial grids - friable skeletons. The systems with коагуляционными by structures have, as a rule, small durability known plasticity, and also some elasticity. Specific property коагуляционных of structures is тиксотропия - the ability of structures after their destruction as a result of any of mechanical influence spontaneously to be restored in time.
Конденсационно-кристаллизационные of structure arise or as a result of education of strong chemical communications(connections) between particles (конденсационные of structure), or owing to merging кристалликов in process выкристаллизовывания of a new phase. The structures with such character of communications(connections) between particles show упругохрупкие of property. The durability them usually considerably is higher than durability коагуляционных of structures.
Questions
1. Characteristic дисперсных of systems? What is a measure дисперсности?
2. To what attributes классификацируются дисперсные of system?
3. What methods of reception коллоидных of systems exist?
4. Гели of a silicon acid.