ion (usually an amine salt or ionized
imino group). They are used for
acrylic Übres and also for wool and
silk, although they have only moderate fastness with these materials.
Direct dyes are dyes that have a
high afÜnity for cotton, rayon, and
other cellulose Übres. They are applied directly from a neutral bath
containing sodium chloride or
sodium sulphate. Like acid dyes, they
are usually sulphonic acid salts but
are distinguished by their greater
substantivity (afÜnity for the substrate), hence the alternative name
substantive dyes.
Vat dyes are insoluble substances
used for cotton dyeing. They usually
contain keto groups, C=O, which are
reduced to C–OH groups, rendering
the dye soluble (the leuco form of the
dye). The dye is applied in this form,
then oxidized by air or oxidizing
agents to precipitate the pigment in
the Übres. Indigo and anthroquinone
dyes are examples of vat dyes. Sulphur dyes are dyes applied by this
technique using sodium sulphide solution to reduce and dissolve the dye.
Sulphur dyes are used for cellulose
Übres.
Disperse dyes are insoluble dyes
applied in the form of a Üne dispersion in water. They are used for cellulose acetate and other synthetic
Übres.
Reactive dyes are compounds that
contain groups capable of reacting
with the substrate to form covalent
bonds. They have high substantivity
and are used particularly for cellulose Übres.
dynamical system A system governed by dynamics (either classical
mechanics or quantum mechanics).
The evolution of dynamical systems
can be very complex, even for systems with only a few degrees of freedom, sometimes involving such
considerations as ergodicity, which
originated in *statistical mechanics.
The evolution of dynamical systems
can be studied using the phase space
for the system. *Chaos is an example
of the complex behaviour that can
occur in a dynamical system.
dynamic equilibrium See equilibrium.
dynamite Any of a class of high explosives based on nitroglycerin. The
original form, invented in 1867 by
Alfred Nobel, consisted of nitroglycerin absorbed in kieselguhr. Modern
dynamites, which are used for blasting, contain sodium or ammonium
nitrate sensitized with nitroglycerin
and use other absorbers (e.g. wood
pulp).
dysprosium Symbol Dy. A soft silvery metallic element belonging to
the *lanthanoids; a.n. 66; r.a.m.
162.50; r.d. 8.551 (20°C); m.p. 1412°C;
b.p. 2562°C. It occurs in apatite,
gadolinite, and xenotime, from
which it is extracted by an ionexchange process. There are seven
natural isotopes and twelve artiÜcial
isotopes have been identiÜed. It Ünds
limited use in some alloys as a neutron absorber, particularly in nuclear
technology. It was discovered by Paul
Lecoq de Boisbaudran (1838–1912) in
1886.
A
• Information from the WebElements site
dystectic mixture A mixture of
substances that has a constant maximum melting point.
189
dystectic mixture
d
www.AzShimi.ir www.AzShimi.com
imino group). They are used for
acrylic Übres and also for wool and
silk, although they have only moderate fastness with these materials.
Direct dyes are dyes that have a
high afÜnity for cotton, rayon, and
other cellulose Übres. They are applied directly from a neutral bath
containing sodium chloride or
sodium sulphate. Like acid dyes, they
are usually sulphonic acid salts but
are distinguished by their greater
substantivity (afÜnity for the substrate), hence the alternative name
substantive dyes.
Vat dyes are insoluble substances
used for cotton dyeing. They usually
contain keto groups, C=O, which are
reduced to C–OH groups, rendering
the dye soluble (the leuco form of the
dye). The dye is applied in this form,
then oxidized by air or oxidizing
agents to precipitate the pigment in
the Übres. Indigo and anthroquinone
dyes are examples of vat dyes. Sulphur dyes are dyes applied by this
technique using sodium sulphide solution to reduce and dissolve the dye.
Sulphur dyes are used for cellulose
Übres.
Disperse dyes are insoluble dyes
applied in the form of a Üne dispersion in water. They are used for cellulose acetate and other synthetic
Übres.
Reactive dyes are compounds that
contain groups capable of reacting
with the substrate to form covalent
bonds. They have high substantivity
and are used particularly for cellulose Übres.
dynamical system A system governed by dynamics (either classical
mechanics or quantum mechanics).
The evolution of dynamical systems
can be very complex, even for systems with only a few degrees of freedom, sometimes involving such
considerations as ergodicity, which
originated in *statistical mechanics.
The evolution of dynamical systems
can be studied using the phase space
for the system. *Chaos is an example
of the complex behaviour that can
occur in a dynamical system.
dynamic equilibrium See equilibrium.
dynamite Any of a class of high explosives based on nitroglycerin. The
original form, invented in 1867 by
Alfred Nobel, consisted of nitroglycerin absorbed in kieselguhr. Modern
dynamites, which are used for blasting, contain sodium or ammonium
nitrate sensitized with nitroglycerin
and use other absorbers (e.g. wood
pulp).
dysprosium Symbol Dy. A soft silvery metallic element belonging to
the *lanthanoids; a.n. 66; r.a.m.
162.50; r.d. 8.551 (20°C); m.p. 1412°C;
b.p. 2562°C. It occurs in apatite,
gadolinite, and xenotime, from
which it is extracted by an ionexchange process. There are seven
natural isotopes and twelve artiÜcial
isotopes have been identiÜed. It Ünds
limited use in some alloys as a neutron absorber, particularly in nuclear
technology. It was discovered by Paul
Lecoq de Boisbaudran (1838–1912) in
1886.
A
• Information from the WebElements site
dystectic mixture A mixture of
substances that has a constant maximum melting point.
189
dystectic mixture
d
www.AzShimi.ir www.AzShimi.com