Introduction
An
understanding of phase equilibria in ceramic systems is central to the
utilization and development of materials in refractories, glass, and other high
temperature technologies. Phase equilibria address significant questions
related to the flexibility and constrains, dictated by forces of nature, on the
evolution of phase assemblages in ceramic. Phase boundaries also assist in the evaluation of the service
stability of a ceramic materials, both in the long and short time frames. Thus,
knowledge of the stability of a ceramic or glass component in high temperature
or in high pressure environments can often be obtained from an appropriate
stable or metastable phase diagram. In the processing and manufacture of
ceramic products, the reactions which occur are understood more clearly if the
phase relations under equilibrium conditions are known. The chemical and
physical properties of ceramic products are related to the number, composition,
and distribution of the phases present. Temperature, pressure, and
concentration are the principal variables which determine the kinds and amounts
of the phases present under equilibrium conditions. To ceramists, who must
understand the effects of these variables on both the processing and the
properties of the finished product, the phase equilibrium relations (usually
presented in the form of phase diagrams) provide the necessary fundamental
information. The study of phase relations is based on the assumption that the
system under consideration is at equilibrium. In the development of reliable
information on phase relations, this condition must be satisfied. In a
practical sense, however, as in the manufacture or service of a ceramic
product, circumstances may not permit a condition of equilibrium to be
established. In many cases, it is known that the system is driving toward or
approaching equilibrium, and knowledge of the direction in which the reaction
is progressing or the direction by which it deviates from equilibrium can be of
great value. In some instances involving ceramic processing, the approach to
equilibrium actually may be quite close. The progress of a ceramic system
toward its stable equilibrium state can often be halted for kinetic reasons,
resulting in a phase assembly which can persist metastably for an extended
period. The arrest of the equilibrium phases, either inadvertently or by
deliberate processing, has given rise to some useful new materials in recent
years. Thus, a study of stable and metastable phase equilibrium relations is
particularly relevant to ceramic and glass compositions. While most phase
equilibrium diagrams have been and continue to be determined by experimental
laboratory techniques, there is a growing trend toward calculation of
multicomponent equilibria from thermodynamic data. The validity of many classic
ceramic phase equilibrium diagrams, while not basically in doubt, continues to
be questioned and revised because the experimental techniques and
interpretation of data can vary from one study to another. Nevertheless, the
student needs to be aware of both experimental and theoretical methods of
determining phase diagram. The principles of thermodynamics are at the core of
much important phase equilibrium information. It is thus appropriate for us to
begin with a brief review of the definitions and principles of thermodynamics
that pertain to phase relations. (Bergeron and Risbud, 1984). Introduction
An understanding of phase equilibria in ceramic systems is central to
the utilization and development of materials in refractories, glass, and other
high temperature technologies. Phase equilibria address significant questions
related to the flexibility and constrains, dictated by forces of nature, on the
evolution of phase assemblages in ceramic. Phase boundaries also assist in the evaluation of the service
stability of a ceramic materials, both in the long and short time frames. Thus,
knowledge of the stability of a ceramic or glass component in high temperature
or in high pressure environments can often be obtained from an appropriate
stable or metastable phase diagram. In the processing and manufacture of
ceramic products, the reactions which occur are understood more clearly if the
phase relations under equilibrium conditions are known. The chemical and
physical properties of ceramic products are related to the number, composition,
and distribution of the phases present. Temperature, pressure, and
concentration are the principal variables which determine the kinds and amounts
of the phases present under equilibrium conditions. To ceramists, who must
understand the effects of these variables on both the processing and the
properties of the finished product, the phase equilibrium relations (usually
presented in the form of phase diagrams) provide the necessary fundamental
information. The study of phase relations is based on the assumption that the
system under consideration is at equilibrium. In the development of reliable
information on phase relations, this condition must be satisfied. In a
practical sense, however, as in the manufacture or service of a ceramic
product, circumstances may not permit a condition of equilibrium to be
established. In many cases, it is known that the system is driving toward or
approaching equilibrium, and knowledge of the direction in which the reaction
is progressing or the direction by which it deviates from equilibrium can be of
great value. In some instances involving ceramic processing, the approach to
equilibrium actually may be quite close. The progress of a ceramic system
toward its stable equilibrium state can often be halted for kinetic reasons,
resulting in a phase assembly which can persist metastably for an extended
period. The arrest of the equilibrium phases, either inadvertently or by
deliberate processing, has given rise to some useful new materials in recent
years. Thus, a study of stable and metastable phase equilibrium relations is
particularly relevant to ceramic and glass compositions. While most phase
equilibrium diagrams have been and continue to be determined by experimental laboratory
techniques, there is a growing trend toward calculation of multicomponent
equilibria from thermodynamic data. The validity of many classic ceramic phase
equilibrium diagrams, while not basically in doubt, continues to be questioned
and revised because the experimental techniques and interpretation of data can
vary from one study to another. Nevertheless, the student needs to be aware of
both experimental and theoretical methods of determining phase diagram. The
principles of thermodynamics are at the core of much important phase
equilibrium information. It is thus appropriate for us to begin with a brief
review of the definitions and principles of thermodynamics that pertain to
phase relations. (Bergeron and Risbud, 1984).
Introduction
An
understanding of phase equilibria in ceramic systems is central to the
utilization and development of materials in refractories, glass, and other high
temperature technologies. Phase equilibria address significant questions
related to the flexibility and constrains, dictated by forces of nature, on the
evolution of phase assemblages in ceramic. Phase boundaries also assist in the evaluation of the service
stability of a ceramic materials, both in the long and short time frames. Thus,
knowledge of the stability of a ceramic or glass component in high temperature
or in high pressure environments can often be obtained from an appropriate
stable or metastable phase diagram. In the processing and manufacture of
ceramic products, the reactions which occur are understood more clearly if the
phase relations under equilibrium conditions are known. The chemical and
physical properties of ceramic products are related to the number, composition,
and distribution of the phases present. Temperature, pressure, and
concentration are the principal variables which determine the kinds and amounts
of the phases present under equilibrium conditions. To ceramists, who must
understand the effects of these variables on both the processing and the
properties of the finished product, the phase equilibrium relations (usually
presented in the form of phase diagrams) provide the necessary fundamental
information. The study of phase relations is based on the assumption that the
system under consideration is at equilibrium. In the development of reliable
information on phase relations, this condition must be satisfied. In a
practical sense, however, as in the manufacture or service of a ceramic
product, circumstances may not permit a condition of equilibrium to be
established. In many cases, it is known that the system is driving toward or
approaching equilibrium, and knowledge of the direction in which the reaction
is progressing or the direction by which it deviates from equilibrium can be of
great value. In some instances involving ceramic processing, the approach to
equilibrium actually may be quite close. The progress of a ceramic system
toward its stable equilibrium state can often be halted for kinetic reasons,
resulting in a phase assembly which can persist metastably for an extended
period. The arrest of the equilibrium phases, either inadvertently or by
deliberate processing, has given rise to some useful new materials in recent
years. Thus, a study of stable and metastable phase equilibrium relations is
particularly relevant to ceramic and glass compositions. While most phase
equilibrium diagrams have been and continue to be determined by experimental
laboratory techniques, there is a growing trend toward calculation of
multicomponent equilibria from thermodynamic data. The validity of many classic
ceramic phase equilibrium diagrams, while not basically in doubt, continues to
be questioned and revised because the experimental techniques and
interpretation of data can vary from one study to another. Nevertheless, the
student needs to be aware of both experimental and theoretical methods of
determining phase diagram. The principles of thermodynamics are at the core of
much important phase equilibrium information. It is thus appropriate for us to
begin with a brief review of the definitions and principles of thermodynamics
that pertain to phase relations. (Bergeron and Risbud, 1984). Introduction
An understanding of phase equilibria in ceramic systems is central to
the utilization and development of materials in refractories, glass, and other
high temperature technologies. Phase equilibria address significant questions
related to the flexibility and constrains, dictated by forces of nature, on the
evolution of phase assemblages in ceramic. Phase boundaries also assist in the evaluation of the service
stability of a ceramic materials, both in the long and short time frames. Thus,
knowledge of the stability of a ceramic or glass component in high temperature
or in high pressure environments can often be obtained from an appropriate
stable or metastable phase diagram. In the processing and manufacture of
ceramic products, the reactions which occur are understood more clearly if the
phase relations under equilibrium conditions are known. The chemical and
physical properties of ceramic products are related to the number, composition,
and distribution of the phases present. Temperature, pressure, and
concentration are the principal variables which determine the kinds and amounts
of the phases present under equilibrium conditions. To ceramists, who must
understand the effects of these variables on both the processing and the
properties of the finished product, the phase equilibrium relations (usually
presented in the form of phase diagrams) provide the necessary fundamental
information. The study of phase relations is based on the assumption that the
system under consideration is at equilibrium. In the development of reliable
information on phase relations, this condition must be satisfied. In a
practical sense, however, as in the manufacture or service of a ceramic
product, circumstances may not permit a condition of equilibrium to be
established. In many cases, it is known that the system is driving toward or
approaching equilibrium, and knowledge of the direction in which the reaction
is progressing or the direction by which it deviates from equilibrium can be of
great value. In some instances involving ceramic processing, the approach to
equilibrium actually may be quite close. The progress of a ceramic system
toward its stable equilibrium state can often be halted for kinetic reasons,
resulting in a phase assembly which can persist metastably for an extended
period. The arrest of the equilibrium phases, either inadvertently or by
deliberate processing, has given rise to some useful new materials in recent
years. Thus, a study of stable and metastable phase equilibrium relations is
particularly relevant to ceramic and glass compositions. While most phase
equilibrium diagrams have been and continue to be determined by experimental laboratory
techniques, there is a growing trend toward calculation of multicomponent
equilibria from thermodynamic data. The validity of many classic ceramic phase
equilibrium diagrams, while not basically in doubt, continues to be questioned
and revised because the experimental techniques and interpretation of data can
vary from one study to another. Nevertheless, the student needs to be aware of
both experimental and theoretical methods of determining phase diagram. The
principles of thermodynamics are at the core of much important phase
equilibrium information. It is thus appropriate for us to begin with a brief
review of the definitions and principles of thermodynamics that pertain to
phase relations. (Bergeron and Risbud, 1984).