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Theory and Technique of Precipitation Crystallization.

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applies, where k2 = 7.3 /: l O . . 4 m i x ' , k 3 = 1.2 7 1 0 - 3 min-1,
C = [U4?] [H2tart]/[H3]2, and F = [U4~']2[UO:^]/[H~~]".
Uranium(V) may be formed as a n intermediate.
G. N. Nod- Wnind, Copenhagen (Denmark), found thzt the
slow exchange ofTl in the systemTl"/T13@ / C P a t low chloride
concentrations is due t o the low rate of exchange of the TI3",
which is present a s a complex. On t h e other hand, the faster
TI exchange observed with increasing C l e concentration can
be explained by a n increase in the rates of exchange of both
oxidation states of the TI.
Condensed fluoro-oxo complexes were obtained from monomeric fluoro-oxo complexes by L. Kolrlitz, Berlin (Germany),
by thermal condensrttion. The condensation may be caused
either by dehydration
Catalytic hydrogenation was studied by P. J . Hnlperrr, c'hi,
(U.S.S.R.), J . C .
cago, 111. (U.S.A.), V. A . T i ~ h p o v Moscow
Baikrr, Chicago, 111. (U.S.A.), and L. Simtr/icti, Budapest
(Hungary). Metals, metal ions, and coordination compounds
of the d5-dI0 elements have catalytic activity. T h e hydrogen
appears to be activated either heterogeneously ( P . g. by
RuC163" or Cu23) or homogeneously (e. g. by Co(CN): or
Ag5) o r by addition (e. 5. with lrCI(C0) [C6Hj)3]2). During
the hydrogenation of olefins, generally a metal-olefin complex
is formed first a n d is then hydrogenated, probably yicr intermediate formation of an olefin-hydrido complex. Btriltrr
showed that Pt-Sn compounds can be used for selective hydrogenation, e. g. of soya oil. The configuration of dienes is altered in the presence of these catalyst systems above 30 C .
Halogenoalkanes, particularly CCIJ and CHCI3, can be reduced calalytically by NaBH4 in the presence of Coe(trispy)3;
D. Korrrnd, Prague (Czechoslovakia), found that the reaction
[Co(trispy)3]@ -t CHCI3 + fCoftrispy)3]2a
+ CHCI?'?
o r by cliniinatiJn of IHf
occurs first and that the CHC13 2 reacts further rapidly. The
Co(lI) complex is rcduced again t o the Co(l) complex by the
N a 5 H 4 (trispy = trispyridyl).
The binuclear complexes ( C ~ H ~ ) ~ N [ F S S ~ - O(CzH5)4- S ~ F ~ ~ , Hydroformylation and hydrogenation using C02(CO)s as
a catalyst are inhibited by C ~ H S S H(C*Hj)2S2,
and CS?, but
~ F ~ probably
N[Sb*OzFg] (Zn), a n d K ~ [ A S ~ O (2b)
not by thiophene and (CzHr,).S, according t o K. M t i r k d ,
oxygen-bridged octahedra.
Veszpreni (Hungary). CoS is formed first and then reacts
further i n the presence of the organosulfur coinportnds t o
form Co3(CO)$3 or Co3(CG)gS(SR), so that the reaction
c o n x s to a standstill.
W . Lciizgcribeck, Rostock (Germany), observed a structural
specificity in t h e catalytic action of tridentate Cu?", Co2 '.
and Zn2-', chelates and of the chclates of these ions
F. Mrrjdik, Veszprem (Hungary). reported on the products of
with Schiff bases i n the oxidative activity of the imipyrolysis of alkoxides and aroxides of Al and Ti. Olefins and
alcohols are split o f f and products with 0x0 bridges are
phenylflavin systems. Stereochemical specificity was found
obtained; these sometimes still contain free hydroxyl groups.
with the parahematin of L-histidine and with its CLIcomplex
Thermolysis of compounds of the type AI(OC4H9)2(OCsHS)
with D- and L-DOPA as substrates; L-DOPA was oxidizcd
yields polymeric products which contain the phenoxy group.
43 "',faster than D - D O P A ( D O P A -= diliydroxyphenylalaninc).
Analogous investigations of VO(OCH3)3 were reported by
E. Ti';ilu, Berlin (Germany), found that metal ions catalyse
G.v. Pjeiffer, Veszprem (Hungary). Here methanol and water
the hydrolytic degradation of ccndensed phosphates and of
a r e eliminated lending vicz V407(OH)4(OCH3)2 t o V 2 0 5 .
the SzO;'? ion. The catalytic activity is approximately proInvestigations of gold complexes of the type K[Au(CN)2X2]
portional to the stability of the metal-ion EDTA complexes.
by infrared and Raman spectroscopy were carried o u t by
T h e concentration dependence of the effect on the reaction
L. H . Jones, Los Alamos, Calif. (U.S.A.),who showed that the
the S20729 ion indicated that complex formation
force constant for the ALI-Cbonds decreases from 3.16 t o 2.92
(chclating) occurs prior to the hydrolysis of the S-0-S bond.
nidynes/A in the series X =: CNG, ClC, B r e , I". These values
n K4sFjOH
K,[HO(ASF~-O),~ j
.4sF40t1] . n - 1 H F
imply a strong cr- but only a weak z-interaction in the Au-C
[VB 8821186 I E ]
German version: Angew. Cheni. 77, 349 (1965)
Theory and Technique of Precipitation Crystallization
From November 10th t o IZth, 1964, the Mineralogy Section
of the Geological Society of the German Democratic Republic held a symposium on "Theory and Technique of Precipitation Crystallization".
F r o m the lectures:
R . F. Stricklcrnd-Constnhle (London, England) described four
methods for increasing the number of nuclei in supersaturated
solutions a n d supercooled melts: (1) On addition of a crystal
t o a supersaturated solution or melt, the small particles, adhering t o the crystal, turn into fresh seeds. This may be prevented by first placing the crystal into a solution slightly below the saturation point. The small particles o n t h e crystal
surface are then rapidly dissolved, while the large crystal remains almost undamaged and continues t o grow in a supersaturated solution. (2) New seeds are formed when crystalline
needles a r e broken or crushed. (3) T h e fragments of polycrystals, which frequently show poor cohesion, yield fresh
seeds. Cases (2) and ( 3 ) commonly occur in mass crystalliAiryew. Cherii. iiiterricrf.
Edit. / Vol. 4 (1965) / No. 4
zation. Depending on the type of crystal, the degree of supersaturation a n d the nature of foreign compounds present in
the solution, crystalline needles and polycrystals are formed
instead of ideal crystals with plane surfaces. (4) If ideal crystals are required, the number of nuclei can only be increased
by disintegration of t h e crystals already formed on impact
with o n e another or with t h e stirrer and t h e wall.
These types of seed increase are the only possible ones o n
crystallization in the metastable zone (moderately supersaturated solution). Fundamentally, these types of seed increase
are t o be distinguished from seed formation, the rate of whic:i
markedly increases only at higher degrees of supersaturation.
exp [-Ak/kT] -.C-exp I-- U
rate of seed formation
frequency factor
uork of seed formation
Boltzmann constant
T = tcmperature [ 'K]
d!T3 (In r ) z ]
surface tension
degree of supersaturation, i. e .
cffective concentration/saturated concentration
36 1
J . M y / (Pardubice, Czechoslovakia) discussed the stability of
supercooled liquids. Within the metastable zone, i. e. within
the range between saturation and supersaturation curves in
the solubility vs. temperature diagram, crystal seeds d o not
form spontaneously. The width of the metastable zone of
aqueous solutions increases with their purity and viscosity,
with the duration and degree of superheating, and with the
rate of saturation, i.e. with the increase in saturation per unit
time. This may be proportional to the rate of cooling. Complete degradation of the aggregates of water molecules may
be assumed to take place on prolonged and strong heating,
while their recombination is retarded on rapid cooling.
According to U. Steinicke (Berlin, Germany) aluminum hydroxide may be prepared by a channel process: the solutions
of aluminum salt and ammonia are mixed in a jet and directly
sprayed into the internal tube (a few cm in diameter) of a double-walled glass tube (the “channel”). The basic idea of this
continuous process is to mixtheoriginal solutions inthe absence
of a wall, with subsequent ageing of the precipitate in achannel
system. Ageing is controlled by the rate of flow (slope of the
channel), the pH-value and the temperature profile. The dried
and calcined final product has a high catalytic activity and a
sharp maximum in the particle size distribution curve (particle size can be varied from about 10 to 100 p).
M . J . Koslovski (Tiraspol, U.S.S.R.) examined the influence
of spark discharges o n the formation of seeds in aqueous electrolyte solutions. The rate of seed formation at the surface of
a supersaturated solution is proportional to the square of the
field strength and to the degree of supersaturation. The spark
flashes over from the electrode to the surface of the solution.
Seed formation largely depends on which pole of the power
supply the solution is connected to. In the case of KCI, spark
discharge with the solution as the negative pole produced a
marked crystallization, while crystallization was low with the
solution being the positive pole. The crystallization of halides,
sulfates, nitrates, phosphates, and carbonates of the alkali
metals and alkaline earths was investigated. The rate of seed
formation decreases with increasing viscosity and purity of
the solution.
According to H . J . Meyer (Bonn, Germany) vaterite (CaC03)
is preferentially formed during rapid precipitation from aqueous solutions, especially in the presence of electrolytes. The
proportion of the CaCO3-modifications (calcite, aragonite,
vaterite) at 50 “C and in the presence of uni-univalent electrolytes (e.g. NaCl, NH4N03) depends on the concentration and
nature of the latter. Other solutes present and high degrees of
supexsturation favor the formation of somatoids [*I.
As R. Boistefle and R. Kern (Nancy, France) showed, clumping of sodium chloride crystals can be prevented by spraying the crystalline powder, e . g . with K4[Fe(CN)6] solution.
On evaporation, the Kh[Fe(CN)6] forms small sharp points
on smooth sodium chloride surfaces. These probably prevent
a close fit of the crystal planes and, therefore, the clumping of
[“I Somatoids are small crystals with uneven planes, which,
depending on the conditions of precipitation, are spindle-shaped,
spherical, lenticular, sheaf-like, dumbbell-shaped or snowtextured.
the crystals. From a more than 23 %, supersaturated solution,
sodium chloride does not crystallize in cubes, but in octahedra.
Other solutes present (CdZ+, CO(NH2)2, Fe(CN):-, Fe(CN)i-)
lower the critical concentration and may lead to further
changes in form and habit (e.g. rhomboid dodecahedra and
dendrites are formed).
M . Hille (Berlin, Germany) prepared small NaCl and KCI
crystals of definite form and size for flotation studies. Cubes
of NaCl and KCI as well as octahedra of NaCl (size about 50
to 60 p) are formed by precipitation with methanol/ethanol/
acetone mixtures from aqueous solutions of these salts, saturated at 20°C. The organic solvents added must be miscible
with the solution. Formamide (20%) is required for precipitating octahedra of NaCl. Octahedra of KCl crystallize from
an aqueous solution of KCI, which is saturated at 50 “C, contains urea (50 %), and is supercooled down to 30 “C. The flotability of minerals may be improved or made at all possible by
a definite crystal form.
Ch. Jentsch (Berlin, Germany) carried out adsorption measurements on alkali halide crystals of different forms. The
crystals, 5 to 10 p in size, were obtained by precipitation with
methanol/ethanol/acetone mixtures. The crystal size varies
with the ratio of the organic solvents. The solution contained
PbClz for the precipitation of KCI octahedra, glycine for the
precipitation of NaCl rhomboid dodecahedra. N o adsorption
of the solutes affecting crystal form was noted, but water was
adsorbed in several layers.
M . Kahlweir (Gottingen, Germany) dealt with growth studies.
A temperature jump was used to produce super- or subsaturation in a saturated solution within about 10-5 sec. Growth
and dissolution of the crystals were traced by conductivity
measurements. It is concluded that growth is controlled by
surface reactions (e.g. dehydration) at lower degrees of supersaturation, and by diffusion at higher degrees of supersaturation (above 1
H. Neels and S. Aslajan (Leipzig, Germany) studied the formation of spherolites of sodium hydrogen carbonate from an
aqueous solution by addition of methanol. The size of the
spherolites decreased from 8 to 4 p with increasing degree of
supersaturation (70-100 ”/,). The crystalline needles of the
spherolites showed a step-wise growth. H. Neels and A. Felbinger (Leipzig, Germany) observed that the rate of formation
of sodium hydrogen carbonate seeds on carbonization of an
ammoniacal sodium chloride solution, is related by a n exponential function to the degree of supersaturation. Todes
(U.S.S.R.) used the rate of seed formation to determine the
interfacial energy of CaS04 in aqueous solution as 12 erg/cm2,
and A . E. Nielsen (Copenhagen, Denmark) determined that
of Bas04 as 130- 10 ergjcmz. R . Piwonka, H . Orfmnnn, and
H . Hartmann (Liibenwalde, Germany) precipitated cadmium
sulfide, in the presence of halide ions, in the stable hexagonal
modification, while sulfate ions led to the metastable cubic
modification. St. Zagrodski and 2. Niedzielski (Lodz, Poland)
observed increased seed formation on ultrasonic irradiation
of supersaturated saccharose solutions, reaching a maximum
at a sound frequency of 7.2 kc.
[VB 881/212 IE]
German version: Angew. Chem. 77, 351 (1965)
Chemical Effects Associated with Nuclear Reactions and Radioactive
About 130 scientists from 28 countries attended this symposium which was arranged by the International Atomic
Energy Agency and the I.U.P.A.C. Joint Commission on
Applied Radioactivity and was held in Vienna (Austria) on
December 7th-1 Ith, 1964. Some 60 papers, which are to be
published soon, were presented.
Investigations Using Mass Spectrometry
The chemical effects of internally converted isomeric transitions with subsequent Auger effect [l] could previously be
measured only with compounds of a few nuclides. Due to the
occurence of recoil the results were uncertain to an unknown
Angew. Chem. internat. Edit. I Vol. 4 (1965) 1 No. 4
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precipitation, theory, crystallization, techniques
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