Mechanism of Development of Pigment Value in Zinc Sulfide Part 11. Development of Pigment Value in Calcination LIRCOLN T. ~ Y O R KA
m
I. HERBERTODELL,Columbia
rniversity, New York, N. Y.
S ORDER to observe the
serving a? a boiler. The temZinc suljide precipitated f r o m sodium sulfide behavior of zinc sulfide durperature, measured with a rare and zinc sulfate has a gel type qf structure, and ing calcination, a group of metal thermocouple, was 11 eld it holds appreciable amounts of touter in sorbed experiments was made upon a constant, usually within 5" and condition, w e n at 100" C. and above. W h e n single precipitate. They covered always within 10" C. pigment ralue is developed by calcination, this both time and temperature as T h e following calcinations variables. The pigment t e s t s were m a d e : at 150" C., 1.5, water is largely eliminated, and the porous gel already enumerated in Part I (6) 3, a n d 6 h o u r s ; a t 300" C., structure oJ the precipitate is lost. The chief mere used on each product, and 3 hours; a t 450" C., 3 and 6 in the decelopment of pigment t d u e in factor cross comparisons of the resulthours; a t 600" C., 0.5, 1.5, 3, 6, zinc sulJide lies in the growth of particles into ing d a t a reveal significant 12, and 24 h o u r s ; at 750"C., the visible range of sizes. T h i s occurs above features of this process. A gel 1.5 and 3 hours; and at 900" C., type of precipitate, c a l c i n e d 3 hours. Before being tested the about 450" C., and the particle size developed i s under a wide range of time and samples Jyere ground to break a ,function primarily of temperature, but also temperature c o n d i t i o n s , was up any l u m p s or a g g r e g a t e s 750" C. the grain growth beof time. Aboce used in order to observe, in formed in calcination. comes excessice and the pigment calue decreases. accentuated form, the changes In t h e d e t e r m i n a t i o n s of From these obserred facts a hypothesis has been taking place in calcination. w a t e r c o n t e n t , t h e loss i n In the precipitation an aqueweight i n d r y n i t r o g e n a t set u p as to the mechanism of crystal growth. ous solution of s o d i u m sulfide 900" C. ( T a b l e I, c o l u m n 1) The experimental data agree quite well with the ( a p p r o x i m a t e l y 1.25 -I[) is a v e r a g e d with the w e i g h t theory of a growth by vaporization of zinc sulfide was added slowly to an aqueof mater removed by calcium f r o m the finer particles and condensation on those ous solution ( a p p r o xi m a t e 1y chloride (column 2 ) , and the of larger size, owing to the higher capor pressure 1.25 +If) of zinc s u l f a t e , a t resulting average values about 75" C. The total quanti(column 3 ) are c a l c u l a t e d to of the smaller particles. ties of the two salts were equivat h e i g n i t e d basis (column 4), lent. giving figures which represent The precipitate was washed by decantation \Tit h hot mater the ratio of water to zinc gulfid& However, in the case until no test for sulfate was found. The solids were then of the samples calcined at 150" and 300" C., the values filtered off and dried in air at room temperature. The prod- for loss in weight of sample are considerably higher than uct, a hard, gel-like material, was ground to pass a KO. 200 those of water absorbed in calcium chloride, the difference sieve in order to secure a homogeneous sample for calcination. being due, as explained later, to the presence of sulfate. The calcinations were carried out by placing 20- or 25- Therefore, in these cases the weight absorbed in calcium chlogram samples of dried precipitate in a quartz Florence flask ride is given as the average for water content, and these values which was immersed in a molten metal bath heated in a pot are marked with superscript letter '. furnace. The atmosphere of superheated steam was mainThe percentage of total zinc as zinc oxide (column 15) tained by continuous passage of steam from another flask represents that portion of all the zinc in a given sample which TABLEI.
,----.
1
Total loss
-
CALCIKATIONwt.
2
3
-
WATERCOSTEKTWt.
increase of CaCln
+
Temp.
Time
sample
wt. sample
C. 150
Hours 1.5 3 6 3 3 6 0.5
%
%
7.68 5,64 7.64 5.69 7.59 5.93 300 3.92 2.40 450 1.48 1.51 1.50 1.34 600 0.91 1.04 1.5 0.75 1.08 0.84 1.02 3 6 0.77 1.00 12 0.78 0.95 24 0.87 1.04 750 1.5 0.57 0.68 3 0.61 0.80 900 3 0.40 0.52 a Dilution for 10-om. reading. b Five grams in 4 cc.
4 v . of 1 and 2
70
PIGUEST
TESTSAXD
ASALYSES
4
5 6 MOISTVRE SORPTIOK 8 WT. SAMPLE I REL.A10 At 2.5. C. At 35'C. OIL TIYE 9 Txrrign
