diethanolamineSee ethanol-
amine.diethyl etherSee ethoxyethane.differential scanning calorime-
try(DSC)See thermal analysis.differential thermal analysis
(DTA) See thermal analysis.diffusion 1.The process by which
different substances mix as a result
of the random motions of their com-
ponent atoms, molecules, and ions.
In gases, all the components are per-
fectly miscible with each other and
mixing ultimately becomes nearly
uniform, though slightly affected by
gravity (see also graham’s law). The
diffusion of a solute through a sol-
vent to produce a solution of uni-
form concentration is slower, but
otherwise very similar to the process
of gaseous diffusion. In solids, diffu-
sion occurs very slowly at normal
temperatures. See also fick’s law.
2.The passage of elementary parti-
cles through matter when there is a
high probability of scattering and a
low probability of capture.diffusion constant See fick’s law.
diffusion gradient See concen-
tration gradient.diffusion limited aggregation
(DLA)A process of aggregation domi-
nated by particles diffusing and hav-
ing a nonzero probability of sticking
together irreversibly when they
touch. The clusters formed by DLA
are *fractal in type.diffusion pump (condensation
pump)A vacuum pump in which oil
or mercury vapour is diffused
through a jet, which entrains the gas
molecules from the container in
which the pressure is to be reduced.
The diffused vapour and entrained
gas molecules are condensed on the
cooled walls of the pump. Pressuresdown to 10–7Pa can be reached by so-
phisticated forms of the diffusion
pump.
diffusive ÛuxSee fick’s law.dihedral(dihedron) An angle
formed by the intersection of two
planes (e.g. two faces of a polyhe-
dron). The dihedral angle is the angle
formed by taking a point on the line
of intersection and drawing two lines
from this point, one in each plane,
perpendicular to the line of intersec-
tion.dihydrateA crystalline hydrate
containing two moles of water per
mole of compound.dihydric alcoholSee diol.
dihydrogen The normal form of
molecular hydrogen, H 2 , used to dis-
tinguish it from hydrogen atoms.1,2-dihydroxybenzene (catechol)
A colourless crystalline phenol,
C 6 H 4 (OH) 2 ; r.d. 1.15; m.p. 105°C; b.p.
245 °C. It is used as a photographic
developer.
1,3-dihydroxybenzene (resorcinol)
A colourless crystalline aromatic
compound, C 6 H 4 (OH) 2 ; m.p. 111°C. It
is made by the fusion of benzene-
disulphonic acid with sodium hy-
droxide and used mainly in the
dyestuffs industry. On fusing with
phthalic anhydride it formsÛuores-
cein dyes. It is also used to make
cold-setting adhesives (with
methanal), plasticizers, and resins.2,3-dihydroxybutanedioic acid
See tartaric acid.diketones Organic compounds that
have two carbonyl (>C=O) groups (see
ketones). There are three kinds, de-
pending on the location of the car-
bonyl groups. 1,2-Diketones (also
called α-diketones), R.CO.CO.R′, have
the carbonyl groups on adjacent
carbon atoms. The aliphatic 1,2-diethanolamine 176d