ADSORPTION AND REACTION. 11* The Setting of Litharge-Glycerine Cement. BY HARVEY A. NEVILLE
A mixture of lead monoxide and glycerine is the answer to many requirements for a practical cement. The set product has considerable strength, is waterproof, and makes a tight joint, since it expands slightly in hardening. There is, however, almost no information available concerning either the type of reaction involved in its setting or the product formed. The reaction between litharge and glycerine, resulting in a cement, was found to be highly exothermic. This suggested that the process could be followed by the method employed to study the setting of plaster of Paris, described in the previous article'. The results when the method is applied to mixtures of litharge and glycerine seem of particular interest because of their complete analogy to those obtained for plaster of Paris. The processes of setting in the two cases are obviously not similar in respect to the type of chemical action which obtains, but they are alike in that they both involve two stages: ( I ) a preliminary adsorption of the liquid phase by the solid; followed by ( 2 ) a chemical reaction between the adsorbed liquid and the adsorbent. Experimental Part The procedure was quite as in the study of plaster of Paris. Small cardboard boxes (about one cu. in.) were used as molds for the cement. The mixture of litharge and glycerine was stirred vigorously in a small beaker for either one or three minutes and then poured into the mold. A thermometer was introduced and the mold was placed in an insulated receptacle. The rise in temperature with time was noted and the curves, as illustrated in Fig. I , closely resemble those for plaster of Paris. The point -S- on the curves indicates the end of the first stage in the setting. At this time the mass is quite stiff and has a dry appearance. The volume change of the mixture in setting was also determined and, as in the case of plaster of Paris, consists in a contraction corresponding to the first stage, followed by a slight expansion as the chemical reaction occurs. The existence of two distinct forms of lead monoxide, yellow rhombic and red tetragonal, has finally been definitely established2. Commercial litharge is usually a buff colored powder, and this form was used in these experiments except where otherwise stated. The litharge was in all cases sifted through a 120-mesh sieve. Some commercial litharge consists of scales or flakes and has a red color. This is the red tetragonal form, produced by crystallization from
* Contribution from the Department of Chemistry of the University of Illinois. 'Keville: J. Phys. Chem., 30, 1037 (1926). * Applebey and Reid: J. Chem. SOC.,121, 2129 ( 1 9 2 2 ) .
H i R V E T A . KEVILLE
I182
the molten stage. If any form of lead nionoside iq heated to dull retlne-, it changes to a canary yellow ponder. Thece form3 have different rate5 of v t ting with glycerine, as noted in Table I. The conirnercial h f f powder -etmost rapidly. It is probably amorphous or incompletely CrySt:illine--Soii1Pwhat a. is plaster of Paris-and hence it. adsorptive aliility 1.; great. The yellow ponder, made hy heating litharge juSt helow it. melting point, ~ I Y J ably hac n more complete crystal structure and it sets less readily. The ret1
5: .YL 1-
:i 2i
, 1
FIG. I
The Setting of Litlmrge and C;I!.cerine-Tlicr.iii~~l Effect
crystalline form, even when finelj- pon.tleret1. tenrls t o settle (Jilt from tlic mixture with glycerine. showing lack of adsorptive cnpacity. It. setting is slow: very little chemical action occurs as is shon-n hy the rrlntivelj- slight rise in temperat,urc. This flaky red form of litharge is hrnce not sntisfnctorj. for use in the cement.
TABLEI Description of 11atc.rinls
Stimd
Eyiri uioleculai: I . Lit harge and glycerine, 2. ” both tlrietl at 1o6Y’. 3. ” nith lor; n.ater ncldrtl !> !l , ,, , 11 1
,1
4.
5. 6.
11
” t
11
”
11
11
11
f 1
7. 8. PbO (yel) ” 9. PbO (red) ”
11
11
I miii.
‘‘4hoiirs *I t1nj-
30
niin.
Stirred 3 inin.
66 min. *A hours 2 0 inin.
1,
to litharge instead 2 0 ‘:1 ” with IO? dil. HC’1 addetl -docs not set” 10~; clil. KOH ” 13 min. ” 105sat. P I I ( T O ~ ) ~ -very slon.--criinil~ly ” 10‘; water 36 min.
’!
1 0 5
* Aipproximntel! , t Rise in temperature only 8‘C. Product
*’ CrllIll~J~\
i$
”
~ -
ADSORPTION AND REACTION
I
183
Proportions Rise i n Temperature mol. PbO : I mol. glycerine 4 4 degrees,C. 66 min. 3 mol. PbO : 2 mol. ” 57 ,’ 5 1 ,) 2 mol. PbO : I mol. ” 54 ” 28 ” Acceleration.-The results set forth in Table I show that the dried materials set very slowly, hence water is a catalyst for the reaction. Furthermore, the catalytic effect of water is more pronounced if the water is used to moisten the litharge rather than added to the glycerine. The setting is also hastened if the mixture is stirred for a longer time a t the start. Acids and salts with neutral or acid reaction, dissolved in water and added to the glycerine, prevent or retard the setting. Alkalies and salts with basic reaction (Na2C03) accelerate the setting. The OH- ion apparently aids the adsorption of the liquid phase by the solid, while the H+ ion prevents it-probably being preferentially adsorbed. Products of the Reaction.-The large amount of heat evolved in the setting of litharge-glycerine cement indicates that a definite chemical reaction occurs. Merwin’ states that well-defined crystals are formed when litharge is suspended in hot glycerine and the mixture agitated. He assigns to the product the formula PbO. C3H602. This would mean that the substances reacted in equimolar proportions and that a molecule of water was eliminated. This may be true when, as in this case, a large excess of glycerine is present. It can be shown that water is actually a product of the reaction; for, if carefully dried materials are allowed to react and the set product is ground and placed in an oven at 106’C., the loss in weight can be determined. If an excess of litharge is used, corresponding at least to the ratio 3 litharge: 2 glycerine, the loss in weight of the product at 106’ is greater by one-fourth than js to be expected from Merwin’s formula. It corresponds more nearly to one and one-half molecules of water from a molecule of glycerine. This mould indicate that the reaction is: 3 PbO 2 C3Hb(OH)3 = P ~ ~ ( C ~ H S O3~HzO )Z Heat. Also leading to this conclusion is the fact that mixtures of litharge and glycerine in the proportion of the equation give the greatest evolution of heat, as illustrated in Fig. I and noted in Table I. This then is the optimum proportion for complete utilization of both litharge and glycerine, The product of the reaction between litharge and glycerine is a very light buff color, sometimes almost white. The material is practically waterproof, a little surface action to produce lead hydroxide apparently occurring. However, if the set material is finely ground and boiled with water, it is completely hydrolyzed to lead oxide and glycerine. If the set product is heated, decomposition occurs to form oxidation products of glycerine and a carbonaceous residue mixed with lead. If the heating is conducted in absence of air and below the melting point of lead, pyrophoric lead is obtained. The carbonaceous matter present aids in keeping the lead in a finely divided form. I
+
Merwin: J. Ind. Eng. Chem., 9, 390 (1917).
+
+
I181
HARTET A . NEVILLE
Summary I. The setting of litharge-glycerine cement, like the ketting of plaster of Paris, is a two-stage process: (a) ;ldqorption of liquid phase hy solid, acconipanied by contraction in voluiiie. (13) Eyothernial chemical reaction h e t n - e m adsorlied liquid and adcorhent. The rate of setting is shown t o tlepend upon the form of PhO u w l and -7. upon the dryness of the glycerine. Kater, OH- ions, ancl .tirrinp accelerate the setting; H' ions prevent setting. 3 . Water ic shown to he a product of the reaction and a definite formuln is as+qwtl t o the other product. 4. The product ic completely hy-clrolyzetl liy hoiling u-ith water. It produces pyrophoric lead if hezttetl in niwence of air. 1-7 borrc1, IllLrlols.
