Банк рефератов содержит более 364 тысяч рефератов, курсовых и дипломных работ, шпаргалок и докладов по различным дисциплинам: истории, психологии, экономике, менеджменту, философии, праву, экологии. А также изложения, сочинения по литературе, отчеты по практике, топики по английскому.
Полнотекстовый поиск
Всего работ:
364150
Теги названий
Разделы
Авиация и космонавтика (304)
Административное право (123)
Арбитражный процесс (23)
Архитектура (113)
Астрология (4)
Астрономия (4814)
Банковское дело (5227)
Безопасность жизнедеятельности (2616)
Биографии (3423)
Биология (4214)
Биология и химия (1518)
Биржевое дело (68)
Ботаника и сельское хоз-во (2836)
Бухгалтерский учет и аудит (8269)
Валютные отношения (50)
Ветеринария (50)
Военная кафедра (762)
ГДЗ (2)
География (5275)
Геодезия (30)
Геология (1222)
Геополитика (43)
Государство и право (20403)
Гражданское право и процесс (465)
Делопроизводство (19)
Деньги и кредит (108)
ЕГЭ (173)
Естествознание (96)
Журналистика (899)
ЗНО (54)
Зоология (34)
Издательское дело и полиграфия (476)
Инвестиции (106)
Иностранный язык (62792)
Информатика (3562)
Информатика, программирование (6444)
Исторические личности (2165)
История (21320)
История техники (766)
Кибернетика (64)
Коммуникации и связь (3145)
Компьютерные науки (60)
Косметология (17)
Краеведение и этнография (588)
Краткое содержание произведений (1000)
Криминалистика (106)
Криминология (48)
Криптология (3)
Кулинария (1167)
Культура и искусство (8485)
Культурология (537)
Литература : зарубежная (2044)
Литература и русский язык (11657)
Логика (532)
Логистика (21)
Маркетинг (7985)
Математика (3721)
Медицина, здоровье (10549)
Медицинские науки (88)
Международное публичное право (58)
Международное частное право (36)
Международные отношения (2257)
Менеджмент (12491)
Металлургия (91)
Москвоведение (797)
Музыка (1338)
Муниципальное право (24)
Налоги, налогообложение (214)
Наука и техника (1141)
Начертательная геометрия (3)
Оккультизм и уфология (8)
Остальные рефераты (21697)
Педагогика (7850)
Политология (3801)
Право (682)
Право, юриспруденция (2881)
Предпринимательство (475)
Прикладные науки (1)
Промышленность, производство (7100)
Психология (8694)
психология, педагогика (4121)
Радиоэлектроника (443)
Реклама (952)
Религия и мифология (2967)
Риторика (23)
Сексология (748)
Социология (4876)
Статистика (95)
Страхование (107)
Строительные науки (7)
Строительство (2004)
Схемотехника (15)
Таможенная система (663)
Теория государства и права (240)
Теория организации (39)
Теплотехника (25)
Технология (624)
Товароведение (16)
Транспорт (2652)
Трудовое право (136)
Туризм (90)
Уголовное право и процесс (406)
Управление (95)
Управленческие науки (24)
Физика (3463)
Физкультура и спорт (4482)
Философия (7216)
Финансовые науки (4592)
Финансы (5386)
Фотография (3)
Химия (2244)
Хозяйственное право (23)
Цифровые устройства (29)
Экологическое право (35)
Экология (4517)
Экономика (20645)
Экономико-математическое моделирование (666)
Экономическая география (119)
Экономическая теория (2573)
Этика (889)
Юриспруденция (288)
Языковедение (148)
Языкознание, филология (1140)

Реферат: theory of metal passivation

Название: theory of metal passivation
Раздел: Рефераты по физике
Тип: реферат Добавлен 16:20:22 21 августа 2005 Похожие работы
Просмотров: 186 Комментариев: 2 Оценило: 1 человек Средний балл: 4 Оценка: неизвестно     Скачать

Research concept

Theory of metal passivation

Metal surface contacting with solution of electrolyte in some definite condition transformed to so called passive state. Study of this phenomena on the border of metal – electrolyte plays an important role, as they define the process of destruction of metal. And it is thermodynamically favourable for metal to dissolve as a result of these process. Such phenomenon was first observed by M. Faraday. This is one of the main factor of stability of metal in aggressive environment.

It is known that, there is no unified model of passivation. The most common and in first sight convincing conception of phase oxide is connecting passivation with mechanical formation of thin film on metal surface with oxide layer. However, potential of phase oxide formation differ from critical parameter of polarised curve (pic. 1), specially from potential of activation j a and passivation j П . In case of iron this difference is 0,63 v. For this reason the phase film conception of passivation cannot be taken in that from.

In case of metal passsivation determining role plays water molecule. Some part of water molecule dissociate in the process of adsorption and ion of oxygen breaking the bond with proton firmly block the most active centre of metal surface. This may be considered as start of passivation.

In the theory of passivation some physical factor must be taken in account. Most important of those are stated bellow.

1. Strong electric field. It define the transform of metal to metal oxide: theory of metal passivation.

2. Equilibrium exchange on the border with solution in which take part the ion OH- and Oox .

3. Number of nonequilibrium vacancy in the passivaing oxide lattice.

4. Energetic inhomogeneity of metal surface.

Major factor of the process is inter phase difference of potential, which is defined by composition of the solution. Depending on its value the current of dissolution take the form:

lg ia ( j a )
theory of metal passivation

Breaks on this curve is connected with the formation of thin protection layer in sector II. Reaction of this passive layer formation is

theory of metal passivation

The oxygen undertakes from molecules of water, and half metal from the substrate of metal surface. As a result of formation of this layer the current falls on 4-7 orders in a very narrow interval of potential change j . After formation of a continuous monolayer there occur the state of passivity III.

The question, how this passive layer is formatted was not studied. We shall try to explain the process of passive layer formation and the kinetic of the process.

With this purpose it would be possible to use the thermodynamic theory of Gibbs- Folmer, according to which at formation of a new phase the free energy of system changes in the value theory of metal passivation.

theory of metal passivation,

Where q- the geometrical factor, l- the size of the cluster , M, r- molecular weight and density of a firm phase, theory of metal passivation- chemical potentials of supersaturated solution and firm phase with concentration C1,2 and coefficient of activity f1,2 . In the point of maximum theory of metal passivation the cluster is equilibrium, its critical size lkp surpasses few times the sizes of building particles (molecules) of the layer. The probability of its formation is defined by the work A of this process

theory of metal passivation,

With the condensation of the factor of crystallisation Wc , the probability of crystal cluster formation Wk is

theory of metal passivation.

It is defined by the classical approaches, according to which the formation of equilibrium crystal take place by consecutive connection of building particles to the complexes, already available on surface M.

At calculation of probability it is accepted, that on the surface M spontaneously arise (or on the contrary, break up) twin crystal particles of various sizes of a and with inter nuclear distance r0 . The sizes change as a result of the consecutive elementary acts (transitions) of the type such as theory of metal passivation, i.e. growth or disintegration of crystal particles.

Probability of elementary transitions we shall designate P a ® a ± r0 , theory of metal passivation. Their speeds theory of metal passivation. These values represent quantity of the acts taking place in 1 cm2 of the surface M for 1 sec. They are proportional to superficial concentration na of particles of the given size and probabilities of the elementary acts

theory of metal passivation.

Resulting speed of direct and return transitions

theory of metal passivation.

At balance state

theory of metal passivation

Proceeding from this it is possible to find out

theory of metal passivation

Further we shall define A1 and A2 . Proceeding from this it is possible to calculate the speed of cluster formation

theory of metal passivation

With the help of this formula it is possible to define the laws of formation of the passive layer on the sector II (in pic.1).

Then taking in to account the energetic inhomogeneity of metal surface it is possible to find out the integrated current density

theory of metal passivation

where y- bond energy.

To each pair value of theory of metal passivation corresponds the certain probability I( j , y i ) of formation of twin cluster and the local degree of filling theory of metal passivation by them ith platforms of the surface M. With the growth of potential j formation of cluster becomes more and more intensive. And accordingly grows the integrated degree of its fillingtheory of metal passivation by cluster,

theory of metal passivation

Thus the processing of the first thin superficial layer of metal in oxide is finished. Take place complete passivation of the surface M, the sector II on the curve (fig. 1) is replaced by the sector III, for which the new physical conditions must be taken in account. And further researched may be done.

Оценить/Добавить комментарий
Имя
Оценка
Комментарии:
Где скачать еще рефератов? Здесь: letsdoit777.blogspot.com
Евгений21:42:28 18 марта 2016
Кто еще хочет зарабатывать от 9000 рублей в день "Чистых Денег"? Узнайте как: business1777.blogspot.com ! Cпециально для студентов!
13:46:39 24 ноября 2015

Работы, похожие на Реферат: theory of metal passivation

Назад
Меню
Главная
Рефераты
Благодарности
Опрос
Станете ли вы заказывать работу за деньги, если не найдете ее в Интернете?

Да, в любом случае.
Да, но только в случае крайней необходимости.
Возможно, в зависимости от цены.
Нет, напишу его сам.
Нет, забью.



Результаты(151332)
Комментарии (1844)
Copyright © 2005-2016 BestReferat.ru bestreferat@mail.ru       реклама на сайте

Рейтинг@Mail.ru