GUNNAR0. ASSARSSON
626
T-ol. 64
which crystal perfection, crystal size and crystallographic orientation are controlled, and in which resulting surface morphologies are specified. In particular, it is important to determine the spacings I of monatomic ledges on evaporated or condensed crystals as functions of temperature and supersaturation, because differing variations of the spacings INFINITE E have been p r e d i ~ t e d . ~ . ~ ~ ~ . ~ ~ TEMPERATURE RATURE RESERVOIR I T 1, VOIR AT T, Summary.-1. Surface diffusion of adsorbed CRYSTAL CRYSTAL 6 atoms is shown to limit both crystal growth from Fig. 4.- Thought experimeiit on thermal accommodation the vapor phase and evaporation at low supercoefficient. saturations and undersaturations, leading to condensation or evaporation coefficients less than Volmer and S c h ~ l t z egive ~ ~ a result for condensa- unity. 2. When other factors such as entropy tion of iodine which fits equation 2 with the pre- restraints, surface contamination, diffusion in the dicted value of a2 = l/3, and which fits the form of vapor phase, or activation a t the interface limit Fig. 3; Wyllielg provides convincing evidence condensation or evaporation, surface diffusion also ~ ~ * ~ . affects ~ that 6 := a3 = a4; several a ~ t h o r s ~ suppose the kinetics. I n such a case the condensaconfigurational entropy contributions to evapora- tion coefficient or evaporation coefficient mill be tion which here correspond to equations 14 and 15; less than unity, and will be a function of both evaporation corresponding to equation 16 has been surface diffusion and the other limiting factor. 3. observed for arsenic oxidez6and other materials; Son-thermal accommodation of atoms impinging and finally Bradley and c o - ~ o r k e r obtain s ~ ~ correla- on a growing crystal and/or elastic reflection of tion with the spherical coordinate form of equations such impinging atoms is shown to be unlikely ex17 and 19 for. evaporation of liquid droplets, using cept when marked impurity adsorption on the surthe ~orrect~ion. of E'uchsS0for small droplets in t'he face obtains. 4. Experimental evidence is cited that limit. is consistent with the predicted crystal growth and It seems important t,ocarry out, further Langmuir evaporation kinetics. 5 . It is extremely unlikely evaporation and condensation experiments in that any two of the three coefficients (the condensation coefficient, the evaporation coefficient and the (46) 31. Volmer and W. Schultze, 2. p h y s i k . Chem.. i66A, 1 (1931). (47) E. 'lideal and P. A I . Wiggins, Proc. Roy. SOC. (London),2108, accommodation coefficient) will be equal for a given material except when conditions are such that two 291 (195?, (48) R. IS. Bradley a n d P. Volans, ibid., 2178, 508 (1953). of the coefficients are equal to unity. (49) R . t i . Bradley. M. G. E v a n s and R. W. Whytlaw-Gray, i b i d . , Acknowledgment.-This research was sponsored 7868, 368 (1946). by the U. S. Office of Naval Research. ( 5 0 ) N. F u c h i , I'hys. Z. Sozajei, 6,225 (1934). AOlABATlC
WALLS
m 1 -
I
HY DIZOTHIERMAL REACTIONS BETFTEES CALCIUM HYDROXIDE ,1XD MUSCOVITE AKD FELDSPAR AT 180-%%Oo BY GUNNAR 0. ASSARSSON Chmnicrrl Lnboratory, Geological Survey, Slockholwi 60, Sweden Recewed November IS. 1969
The aut,oclave reactions between calcium hydroxide and minerals containing alkali-alumina-silica a t 120-200° are characterized by a formation of monocalcium silicate monohydrate (the tobermorite phase) and m-dicalcium silicate monohydrate, 1he reactions be ng similar in nature to those of the system calcium hydroxide-quartz. By a simultaneous combination of the alumina of the minerals is formed mainly cubic tricalcium aluminate hexahydrate, having 1 5 - 6 7 , of its lat,tice hydroxyls replaced by silica radicals. The boundary between t'he monocalcium and dicalcium silicate ranges lies a t about 100 mg. CaO/m.2mineral surface for the feldspar and at somewhat less than 30 mg. CaO/m.* for the muscovite. IVhen a relatively rapid combinat,ion of calcium hydroxide-silica takes place at a silicat,e surface of disordered structure (ignited muscovite) the silica radical replaccs hydroxyls in the cubic tricalcium aluminate hydrate in all degrees up t o thr percentage mentioned, as registered in the X-ray photographs as bands or set,s of lines. .4t slow reactions at t,he mineral surface the aluminate phase consists almost exclusively of crystals containing a maximal silica repl$cement'. Small amounts of a compound not posit,ively identified but having a characteristic X-ra,v diffraction line a t 10 A. occur among the autoclave products of ignited muscovite and of feldspar. Its occurrence is established in the products autoclaved at 120-140' independent of the mineral and of the supply of calcium hydroxide. Some other phases not identified also occur. Because of t,he relatively complicated system the equilibrium conditions of the phases cannot be forecast; it must be Pupposed that t~hephases first formed are transformed successively into phases poorer in lime, as t,akes place in t>hesystem calcium hydroxide-quart,z.
Iii n previous paper results were given from an investigation on hydrothermal reactions between cizlcium hydroxide and quartz. Only ternary phases could be formed by these reactions. In ( 1 ) G. 0. .issawson,
TJIIS J O U R X A L64, , 328 (1960).
those between two- or three-component silicates and calcium hydroxide other compounds will also appear. From results of experiments with silicate minerals containing only alumina, alkali and silica it should be possible to estimate the general
behavior of other minerals under similar conditions. h formation of quaternary compounds could be expected since ternary calcium silicates are produced, and some alumina remains; the alkali takes no essential part in the crystallization of the principal phases of the system. The present paper is intended to give an account of the formation of calcium silicate hydrates and other compounds, when calcium hydroxide reacts under hydrothermal conditions with some common ternary silicates containing alumina (muscovite, feldspar). These reactions are of importance for the explanation of certain technical processes and procedures and for elucidation of the occurrence of some m.neralogica1 paragenesis, and the investigation thr reforc covers the natural minerals as \\(>I1 as the dehydration products. The Hydrothermal Reaction Calcium Hydroxide-Muscovite The Muscovite Material.-Purest muscovite feliite from L: large deposit at Boliden, Sweden, u a s uqed ior the preparation of the mica powder. Tnipurities of corundum and sillimanite lvere removed. A q is ne11 known, the mineral is very difficult to grind t o a fine powder in the agate mortar, but after repented grinding and sieving it was possible to get n homogeneous powder. The sainple of muscovite was ground and homogenized in sufficient quantity to provide a uniform sample for all experiments. The composition givcn in Table I corresponds well to the theoretical composition. Samples mere heated during 24 hr. to the required temperatures, and sufficient was talcen for all experiments. After the heating, liinips occurring in the material were crumbled by a slight pressing, so that the grain surface are2 was not modified.
1,150 and 1,200", the principal change in structure took place between 1,000 and 1,050'. This 24 hr. period was sufficient to guarantee a complete transformation of the mineral grains into aggregates corresponding to a plausible equilibrium at the relevant temperatures without residual structures. The X-ray measurements of preparations heated to l,OOOo, showed a small extension of the distance between the atoms. At temperatures of 1,050" and higher, new phases crystallized. They were identified as mullite and 01- and B-corundum. The essential part of the heated products \vas an optically isotropic mass, consisting of an alkali-aluminaglass. Because of the composition of the mineral, accessory compounds (spinel and others) n w e not formed. The present muscovite sample can he considered to have the transition temperature between 1,000 and 1,050", which is a little h i g h ~ r than that found for other samples (Roy". Heated samples of the muscovite were alqo autoclaved a t 160 and 200" for 2-1-hr. The X-ray photographs of these preparations showed the same spacings as the preparations not autoclaved. This autoclave treatment, solely, therefore, does not cause a formation of new phases ill amounts discernible in the X-ray photographs.
The Surface Area per g. of the Muscovite Powder The manner in which the mineral niuscovitp changes its properties on heating is known from earlier investigations.? The results will be summarized in the following. When heated up to about 900" the muscovite crystal loses its water while retaining its outer habitus as well as the general pattern of the remaining atoms. The change in properties is, however, connected principally with small disTABLE I placements in the positions of the atoms without a formation of new phases (Grim and Bradley?). CHEMIC .4 L C(0RII'OGITION O F THE RfINERAL 1'OWDERS; Above about 980" (Roy2) some new phases are yG ITEIGHT ('oinposition, c*:ilctl from thr analyses; Aluscovite: (OH. formed, slowly a t low temperature, more rapidly F)p.re(KXa )?. [(Si'ri)6.,,0-A12.00](A41, Fe)a.00~020. Feldspar: a t higher temperatures and after continued heating. microlinc 78'r, itlhitt. 22cc. The phases that have been reported in the heated Feldspar, Mica, product are mullite, some types of alumina, crismicrocline muscovite tobalite, leucite, and in addition a glass formed 61.9 45.6 by silica, alkali and alumina. 19.2 37.7 To this short description may be added that the 0 2 0.3 thermal dehydration process as well as the forma... ... tion of the new phases is to some degree connected 0.06 0.1 with some properties of the sample used: the rate 0.05 0.1 of heating up and the period of heating time in 12 9 !).2 relation to the size of the grain3 of the mineral, '2 .'I 2.2 the chemical composition, and the earlier treat... 4.5 ment of the sample (heating, repeated grinding). 0.02 0.1 The report given below on the behavior of the The X-r:iy photographs of the untreated mineral muscovite sample is limited to results of interest showed all the same diffraction lines reported by for the hydrothermal reactions. other investigators (Grim, Bray and Bradley2). There are questions of importance for the hyWhen the present muscovite sample was heated drothermal reactions that must be studied before for periods of 24 hr. to 500, 900, 1,000, 1,050, the main problem can be treated: the change in the grain surface area per g. of the mineral brought (2) R . C. 1Iackensie a n d A . -1. Milne, M i n e r a l Mag., SO, 178 11953); N. buiiclius a n d A. XI. Bystrom, Trans. Brit. Ceram. Soc., 52, about by dehydration arid autoclave treatment 653 (1953); R. E. G r i m a n d W.F. Bradley, J . Amer. Ceram. Soc., 23, and the change in mineralogical property. 248 (1943); R . Roy, i b i d . , 32, 202 ( 1 9 1 9 ) ; R . E. Grim, R. H. Bray The heating of the muscovite powder is aca n d W. F. Bradley, A m i . A f i u r r a ! , 22, 815 (1937); R. E. Grim a n d companied by an essential change in grain surface. JV. I?. Bradley ioid., 33, 30 (1948).
It could be expected that removal of the lattice hydroxyls followed by an autoclaving should cause a splitting up of the layer structure and in this way increase the grain surface area considerably. The grain surface areas of the samples determined by the BET-method are listed in Table 11.
hydroxide mg./m.z of the mixtures used for the autoclave experiments is listed in Table 111; it is referred to t,he grain surface area of the autoclaved samples (Table 11). The rate of the combination of lime could not be studied in detail, some general observations only were made. Compounds Formed.-The calcium silicate hyTABLE I1 drates belonging to the system hare been mentioned MUSCOTITS GRAINSCRFACE AREAm.2/g. MINERAL POWDER,in earlier papers.' The quaternary synthetic coinAUTOCLAVED A N D NOT AUTOCLAVED, DETERMINED pounds containing lime, silica, alumina and water IiCCORDING TO THE BET h I E T H O D have been studied by some authors. Hitherto Phase symbols: hf = musvovite; Mr = muscovite, ign. known are the synthetic compounds : gehlenite lxdow 1000'; CO new phaw (corundum mullite, glass) hydrate, hydrogarnet, and the compound 4Ca0. Not Autocl. Ign. temp. Al2O3.SiO2.12H20, some minerals : gismondite, 24 hr., autocl., 2000, QC. m.Vg. m.'/g. Phase lawsonite and scolesite, and some other compounds Not ign. 7 90 13 0 31 of zeolitic type.3 500 1000 1050 1100
1150 1200
5.15 3.55 4 50 4 00 3 65 2 90
9.35 4.30 4.30 4 110 3 90 3 no
hlr hlr ( h l r ) CO CO
co CO
These measurements on the heated samples show a diminishing of the area when the mineral powder is heated to about 1,000". After a small increase at 1,050" the area decreases when the ignition temperature rises to 1,200" or more. This course of change is in agreement with the dehydration and recrystallization of the muscovite established with X-ray measurements and with the microscope. On the other hand, the dehydration causes an ext~iisionof the cell dimensions; the effect of this shculd be a small increase of the area. A splitting up of the layer structure of the muscovite acconip:uiied by an increase of the grain surface area, may in fact occur. Other reactions of an opposite character however, predominate. The muscovite ignited up to 1,000" and then autocl:ivctI showed an increase of grain surface caused hy the autoclave treatment but no change in structure. The most probable explanation of these facts might be sought in a building up of the crystals. If the crystals are formed by crystallites of dimensions just below the microscopical ones, the phenomena in question have a clear explanation. For the problems of this report, howeve1, the results of importance are that the structure of the crystallite remains intact in spite of autoclave treatments and that the grain surface area increases t,o a certain degree because of these treatme,its, the former referring to the structure, the latttr to the tc'sturc. The Formation of the Ca-compounds I3ecause thr properties of the muscovite samples 1-ary a(-cording to the treatment, with subsequently far-reaching variations in the experimental conditions, the autoclave experiments were limited to three preparations, the unheated mineral and the mineral heated to 1,050 and 1,150". The first sample represents the substance of the original structure, the second one corresponds to the very labile structure before final recrystallization, a n d t h r l third oii( the rc~crystallixcd,glass-containing structur~~, the tw) hamples last mentioned having about tiic sanic grain surface area. The calcium
TABLE I11 hluscovite, not ignited (M), ignited a t 1050' ( h l l ~ 5 0and ) at 1150" ( N I I l m ) mixed with calcium hydroxide, autoclaved for 4-24 hr. Symbolsfor thephases: Hy = hydrogarnet; T = tobermorite; Y = unknown 10-A compound; 2A = a-dicalcium silicate monohydrate .411tOclave
CaO.
ar
Phase formed
temp., OC.
rngJm.2
120-140 160-200
21-44
Hy, 2.4, T
21-82
T, Hy, 2A
CaO,
%.lioao, hlitsa
mg./m.z
Phase farmed
5ti :ti-110
T, Hy, 2A, Y T, Hy, 2A
The investigation of the autoclave products under the microscope gave very little information concerning the compounds formed by the autoclave reactions. The crystallites w r e too small to permit an exact determination of the crystallographic properties. Some lumps formed were optically isotropic, some of them showed a general birefringence with a general optical refraction of about l.G. The principal exmiination of the suhstances was limited to X-ray investigations. The mineral muscovite gives X-ray photographs rather rich in diffraction lines. Certain important parts of the photographs, however, are free from such lines and permit an establishment of the presence of compounds formed. The first three diffraetipii lines of muscovite are a t 10, 4.98 and 4.47 h.; most of the identification lines of the compounds possibly formed a t the reaction are to be found a,t Bragg-angles corresponding to d-values higher than 2.0 8. On t'he other hand, the niuscovit'e sa,mples heat.ed to 1,050 and 1,150" give photographs Lather poor in diffraction lincs; a1)ove all, the 10 11. line of the. untreatcd niuscovitc does not occur in these preparations. Sub-X-ray crystallites are formed within the first two hours of autochving. They slowly grow t,o products easily identified (Table 111). After t,he complete combination of lime t,hc reaction products formed are very similar to one another; products somewhat deviating are mentioned below. Autoclaved mixtures rich in lime show generally (3) E. P. Flint and L. S. Wells, Bur. S t a n d a d J . Research, 27, 171 (1941): 33, 471 (1944); I,. S. Wells, W. F. Clarke and 1% F. &IChlurdie. ibid., 3 0 , 30 (1943); H.Bur Strassen, Zemetlf-Kaik-Gips, 11, 137 ( 1 Y 4 3 ) ; F. 11. Ddrr, Unters. i i i i Syst,t.iii Ck0-:4LOh -SiOrIlrO. Diru., 1I:Linz l ! l X ; IT. Zwii, U n t e v . i i n i?isenfrt.i~n Al*os-SiO?-CilSO,-Ii.0, I)iss., hIainz, 1 Y N ; E. Tililu, E. > I , \Viciim;wn, .Ibli. d. Ueutschen .Ihad. e i i I k r l i n
Nr. 4 .
more distinctly crystallized compounds than those turbed crystal structure mixed with lime and autopoor in lime, although the composition of the phases claved a t 120-200" and also the undisturbed muscois the Sam('. vite crystals autoclaved a t 160-200" show the The tobermorite compound is considered to be characteristic spacing of the silicate mentioned. present in the reaciion products when the dif- The lines are distinct without any broadening. fraction line 11.3 A. can be established. The Other Compounds.-There occur in the X-ray compound occurs in almost all of the preparations. photographs some diffraction lines that do not At low temperature (120-140"), however, the belong to the compounds mentioned above. One natural muscovite reacts rather slowly so that the of them (10 -pi.) appearing in the photogr:iphs of tobermorit,e phase could be shown only after a some preparations is noticeable becauye it swm\ rather extended reaction period. The compound to be a characteristic line for the present qystem; occurs rather well crystallized among the products it occurs also in the system feldspar-calcium of ignited muscovite (1,050, 1,150') treated in the hydroxide. Spacings- not identified are gii en in same way At an autoclave temperature of 160" Table IV. The 10 A. line is shown only in thc natural muscovite mixed in the same proportion photographs of mixtures autoclaved a t 120-140" also showd an initial crystallization of the tober- arid prepared from muscovite ignited at 1,030 and morite ph:ise nftpr only 2 hr. In the other auto- 1,150". The photographs of the uiiignited mu\clave productp the diffraction lincs of the tober- covite contain primarily a muscovite spacing of morite 11.3 A. as well as others c:~n be easily 10 8. which makes it impossible to establish the established. occurrence of the compound in question. The The H&ogarnet.--As mentioned above the spacing 10 A. has not been shown in the system alumina released by the attack of the calcium calcium hydroxide-amorphous silica nor in that of hydroxide 012 thc silicale must be combined in some calcium hydroxide-quartz within the temperature way. It is known from earlier investigation on range of the present experiments. It is therefore the system CaO-A120y-I120 that the cubic tri- plausible that the presence of the special conicnlcium aluminate hexahydrate is the stable phase TABLE IV a t higher temperature^.^ This compound does 1)IFFRACTION LINES,NOT IDENTIFIED IU ?rfIYTURES hlVSnot occur pure in the mixtures of the present in- COVIrE (TJNIGN , IGN 1050°, 1150°)-c4LCI~T~1HYDROXIDE, vestigation but 8s a solid solution with some mole21-120 mg. CaO/cin *, 120-200' cules of witer in the crystal structure replaced by --100-140°-180-?00°silica (hydrogarnet 3CaO~AlsO3.3Si0~/6W2O~. I d CA.) I d(L) The law of T-egard is here assumed to be valid for \V 10 0 4 83 the crystztls, namely, that there exists a linear TV 4.19 m 4 5t correlatior between the unit-cell dimensions and ww 4 O!) \v i 01 the chemical composition (garnet 3Ca0.A120s.3m 3 !lS m 3 71) \v 3 3!) \V 3 70 %On, a == 11.86 K . ; calcium aluminate 3CaO. \v 3 4; Al2O3.6H2O,a -x 12.56 A.). This relation is an w 3 17 approxima tioii. The calculations and consideraw 3 u3 tions belov, however, are based on the above assumption. At low temperatures (120, 140") ponents of the system, containing the component the unignitod muscovite reacts with lime to yield alumina are responsible for its appearance. It j s the cubic compound giving diffraction lines that are very distinct. The position of the lines shows probable that the phase represented by the 10 A. an aluminate in which the lattice hydroxyls are line is one of the zeolites mentioned above. A. replaced t o 40-5070 by silica. No difference be- the concentration of calcium ions at the surface of tween the preparations a t 120 and 140" was found. the mineral is rather high the conclusion may be Muscovite ignited at 1,050", mixed with lime and drawn that the ieolite consists of lime, nliiminn autoclaved a t 120-140" yields products that show and silica. A calculation of the spacing. of the groups of successions of distinct diffraction lines. reolites mentioned leads to the result that the The rangc of these groups represents a composi- mineral gismondite is the most plausible. In the photographs from preparations autotion of about 15 and 50% of the hydroxyls replaced hy silica in the pattern. The preparations auto- claved at 180-200" other unidentified spacings claved a t 16O-2OO0 show bands in the photographs occur. Generally d l these spacings show rather. instead of lines, commonly with diffuse edges, weak intensities probably representing relatively the bands obviously originating from lines of the low content of the Corresponding compoundi. I t same character as above. The measurements of may also be noted that the thorough emmination those bands show a constant of 15-5070 silica. In of X-ray photographs provided no evidence for no case are bands observed corresponding to a the occurrence of aluminum hydroxide (hydrargillite, diaspore) or other calcium aluminate hydrate3 higher content of silica. among the reaction products. a-Dicalvium silicate monohydrate was found in The Hydrothermal Reaction most of ihe preparations. At low temperature Calcium Hydroxide-Feldspar (120-130) and with muscovite of undisturbed structure this compound was formed ~lowly. All The Feldspar Material.-A selected piece of the X-ray photographs of the preparations of dis- microcline was ground in the manner deqcribed earlier for quartz.' The powder was not mashed (4) 0 . 4ss:rssm, 2. anorg. a l l g e m . C h r i n , 214, 138 ilea?); J. but purified with a magnet and with a blast of :iir D A n s and 11. Ewk, Z a m ~ i i f - K a l k - G i p s6, , 197 (1953). \ . ?
GUNNAR 0. .~SS.\RRSSOX
630
T'ol. 61
TABLE V MIXTGRES FELDSPAR-CALCIUM HYDROXIDE, AUTOCLAVED AT DIFFERENT TEMPERATURES Symbols for the crystallized phases, see Table 111; CaO calc. mg./m.2 mineral surface area Autoclave
temp., OC.
120 140
160 180
-
-
-----is mg. CaO CaO Time, vomh., hr. nig / m . 2 Phase
170 500 24 170 8 24 2 0 94
2
200
-I
24
--
ii)
75 75 75 50 70 is 50 75 75
fly
(T, Hy) T, Hy
--
+ 310 x 15s
Ik
Y 1,T, Hy Y I-,T, T1y
75 175
165 mg. CaO -CaO Time, comb., hr. mg./m.*
---
(T, Hy)
T, Hy
170 500 24 170 4 24 G 9 24 2 3 24
130 165 165 165 95 165 140 165 165 145 165 165
Phase
11
160" /*-
_Ic(_=H
10
.. ..
..
...
..
...
Y (Hy) Y, T,Hy, 2-4 Y , T , Hy, (2h) Y, T, Hy, 2.1
..
..
...
..
...
Hy, 2A
4 24
I35 190 155 220 220 195 220 220
, ,
ti
(T, Hy) T, Hy, 2A (T, Hy) T, Hy, 2A
mg Ca 0 per sq m. 1)
220 mg. CaO-CaO Time, comb., hr. mg./m.* Phase
7-
J
-t-ucC-cx-
20
Autoclaving time, h r s Fig. 1.--The extraction of the feldspar alkali in the course of the autoclavf treatment of mistures feldspar-calcium hydroxide
and finally ground t o a powder of the required grain size. The composition of the feldspar is given in Table I. The grain surface area was 1.5 m.2/g. measured by the BET-method. The Combination of Lime.-Of special interest is the courise of the boundary reaction in which the lime is combined, in relation to the autoclaving temperature and time. Some experiments were performed in order to determine in an indirect way the attack of the calcium hydroxide on the feldspar. A. the calcium hydroxide dissolves silica and alumina from the feldspar, a corresponding amount of alkali will be set free. By this reaction the successively proceeding destruction of the feldspar could be studied. However, as a consequence of the heterogeneous character of the reaction mixtures the results have only a rather low degree of accuracy. Results of this kind con-
8 24 2 4 24
mg. CaO---CaO Time, comb., hr. mg./m.z Phase
---330
1TO 500 24 170
150 330 160 330
Y, Ily Y, Hy, (2A) Hy, (2.4) Y, T, Hy,(2A)
210
IIy, :2A
.. fly, 2.i
(Hy, 2.4) T, Hg, 2'1 (Hy, 2 a ) T, Hy, 2.4
24
. .
..
..
24 48 24 48 73
3.10 330 330 330 330
. . (TI?;, 2.1) T, Hy, 211 (Hy, 2AI T, Hy, 2.4 rr,
HY
cerning the autoclaving of three mixtures between 160 and 200" are given as a diagram in Fig. 1. The experiments show that the total amount of alkali that it is possible to extract during the autoclave treatment is not reached after 24 hr., although the whole amount of calcium hydroxide is consumed after this period of time (cf. Table V, corresponding experiments). The progress of the attack on the feldspar does not only depend upon the supply of uncombined lime but also upon the compounds which are formed, obviously in more than one stage. The Phases Formed.-The microscopical examination of the samples is made ~ Y ' J 'difficult by the small size of the aggregates formed. The feldspar powder itself was autoclaved at 160 and 220" for i 2 hr.; no new compound could be est:ihlished. The low-temperature treatment (1 20-160") of mixtures feldFpar-calcium hydroxide (165-330 nig. CaO/m.2) for a period of 48 hr. yielded only some spherolites without any birefringence. Specimens autoclaved a t 220" for 7 2 hr. showed the same reaction products; some of the spherolites, however, indicated a low-moderate birefringence, some were obviously optically isotropic; most of them seem to have an optical mean index of about 1.6. The X-ray photographs of feldspar,., in the present case a perthitized microcline, contain a very large number of diffraction lines Illat can be measured only when a camera of vt.ry good dispersion is used. Coincidences of the fcldspar can therefore be possible. The products formed by the autoclave treatment a t lower temperatures (120-140") arc' very poorly crystallized. During the first period of reaction compounds are formed which show no crystallinity, although all or the greater part of the calcium hydroxide is consumed (Table V . After more extended periods of time a crystallinity of the phases appears gradually. The tobermorite compound ib formed, even a t low temperatures (120-140"), as is clcar by the diffraction line 11.3 A. gradually appearing in the X-ray photographs; a t higher temperatures the intensity of this line increases. The spacings of the hydrogarnet deriving from
pounds depend essentially on the state of the surface of the alumina-silicate and on the proportion alumina-silica. The fourth member (e) therefore represents compounds produced when the conditions for the attack are such that the coinpounds of transition type or compounds corresponding to the special supply of components can be formed. During these reactions the tobermorite phase always seems to be formed sooner or later, probably because of its being one of the more stable compounds of the system. I n those cases where it is not shown, the a-dicalcium silicate is formed as a first product and later transformed by extended autoclave treatment into the tobermorite compound. The formation of the tobermorite phase is to be referred to the rate of the dissolving attack on the surface of the silicate in relation to the rate of the diffusion of calcium hydroxide through the layer a t the phase boundary silicate-solution. The formation of different products has always to be referred to the periods of reaction time and to the varying amount of calcium hydroxide a t the surface of the silicates present. The character of the mineral determines the type of calcium silicate. With feldspar the monocalcium silicate was observed to be an initial product when the supply of lime corresponds to 75 mg./m.2 mineral surface; when the concentration is 165 mg./ni.2 the dicalcium silicate is formed. TABLE VI With different samples of muscovite a concentraDCrFR4CTIOU L I Y E C , YOT IDESTIFIED, I N MIXTURES tion of 33 mg. CaO/m.2 of the mineral surface TWS FI:LDSPAR-CALCILY HYDROXIDE, $5-220 mg. CaO/m 2, shown to be above the lower concentration boun120-200 dary for the formation of the dicalcium silicate. 120-1.100 180-2000 I d (K., I d (A., The boundary concentration for the formation of monocalcium-dicalcium silicates could be apn10 0 m 5 58 proximately st 100 mg. for the feldspar and 20 m 6 i0 W 5.16 mg./m.2 for the muscovite preparation. WW 5 06 W 5.12 m 1 w 4.98 When calcium hydroxide attacks the surface ww 4 75 W 4.43 of the silicates the alumina of the cC:mpound is R' 4 12 W 4.26 very active and reacts with uncombined calcium w 3 49 W 3.71 hydroxide immediately. Being a stable phase in m 3 34 m 3 68 pure calcium hydroxide solutions at the autoclave m 3 03 m 2.95 temperatures of the present experiments, the cubic m 2 74 m 2.92 tricalcium aluminate hexahydrate is formed, its m 2.73 composition to a certain degree depending on the character of the surface of the silicate. It is Discussion of Results from the experiments with feldspar as well The above results show that different kinds of evident as natural muscovite that at a mild attack on the overlapping reactions take place between the alkali- surface of the minerals (low temperature, relatively alumina-silicates muscovite and feldspar and the undisturbed crystal structure) the cubic aluminate calcium hydroxide. The essential characteristic formed contains constant d i c a in the of these reactions, however, is independent of the pattern. Assuming 45yo ofproportion the hydrogen to mineral. The conditions a t the surface of the sili- be replaced by Si ions the cubic aluminateions correca tes can be rendered in the following way sponds to the formula 3Ca0.rll2O3.1.3Si02,3..1H20. This content of silica seems to be the highest silica proportion of the system within the present KbH + ( b ) CaO.SiO2.HzO(tobermorite) experimental conditions, requiring for its formation (c) o - ~ C ~ O ~ S ~ + O (~d ~) 3Ca0.AlzOa.( H~O Si02/2H~O)d one atom AI for 0.6 atom Si depending only slightly ( e ) mCaO~nSiO~~oA1zO~~zH~O on the autoclave temperature within the range The &st three silicate-aluminate members on 120-200". The feldspar contains one atom A1 the right part of the formula (b, c, d ) are known and for three atoms Si, the muscovite one atom AI can generally be identified with X-ray photographs. for one Si. The supply of alumina in relation to They are the principal compounds. When the that of silica is therefore larger at the phase boundcalcium hydroxide attacks the surface of the ary of muscovite-solution than that of feldsparsilicate the conditions for the formation of the com- solution. If the reaction runs its courw slowly the
the autoclaved feldspar-lime mixtures have a different character from those from the muscovitelime mixtures. At low temperatures (lZO", 140") only one set of lines occurs in the X-ray photographs, corresponding to a silica content of 4050%. At higher temperatures and with mixtures rich in lime there appear in the X-ray photographs some other distinct lines belonging to the hydrogarnet, corresponding to about 20-30% silica: because of coincidence with other lines it is impossible to estimate the boundary of the lowest silica content. The bands observed in the photographs of the muscovite-lime mixtures do not occur. The different lines of a-dicalcium silicate monohydrate are clearly absent from the X-ray photographs of mixtures poor in lime (75 mg. CaO/m.2) autoclaved a t 120-200". In photographs of mixtures richer in lime (165-330 mg. CaO/m.2) autoclaved at these temperatures, on the other hand, lines belonging to the compound do occur. In the X-ray photographs autoclaved a t 120200" some lines also occtr that have not been identified. The line a t 10 A. is discovered in these mixtures but not in those autoclaved a t 160-200". The use of this line for identification purposes is discussed above in connection with the muscovite and the same considerations are valid. Other unidentified lines of weak intensity occur in the photographs (Table TI).
O
+
+
45yo-silica containing cubic tricalcium aluminate will crystallize. The excess of silica will I)e conibined a s calcium silicate hydrates as the tobermorite phase or as mixtures of the dicalcium silicate and this phase. A more intensive attack of the calcium hydroxide effected either by increased temperature or by a disordered pattern of the surface of the mineral, causes a more rapid formation of the calcium aluminate. The muscovite therefore yields an aluminate, crystallizing with successively less silica as the reaction proceeds; the hydrogarnet is recorded in the X-ray photographs as bands. The more resistant pattern of feldspar contains more silica so that the formation of the hydrogarnet is retarded and the aluminate compound reaches a composition with more silica. The rate of forniation of the Ca-silicate hydrates obviously regulates the successive change in composition of the solid solution. The compound represented in the X-ray photographs by the 10 8.line shows in the present investigation an upper existence limit between 140” and 180”. Similar considerations must be applied to the compounds shown in the preparations autoclaved a t 180-200”. There also seems to be a difference between the unidentified phases of the muscovite and the feldspar preparations; the propertiea of the phases could probably account for the relationship.
The conditionc of cquilihrium hetiwen thc p11itsc.s of tlit sy5teni iir(’ difficult to ost:ildi4, as somc of them are not ~uffici~iitly l\i101v11 (;merally it can be anticipated that tho compound^ at the boundary silicate-cnlcium hydroxidc solution will be transformed into those with the lowest content of calcium attainable within the system under the given experimental conditions. Several types of calcium compounds can result from the attack a t the silicate surface, and these will later be transformed into others by further extraction of the components of the silicate. One may also be reminded of the varying composition of some compounds. The amount of alkali released by the attack a t the mineral surface results in an increase of pH of the solutions, thus causing a change in the equilibrium conditions. The compounds can therefore not be predicted from knowledge of the reactions of the ternary systems lime-quartz-water and lime-alumina-water. Acknowledgments.-The investigations on the hydrothermal reactions between calcium hydroxide, quartz, muscovite and feldspar have been performed with the financial support of The Swedish Technical Research Council, Stockholm. The author also wishes to express his gratitude to International Ytong Co., Stockholm, for placing a t his disposal instruments required for the invest iga ti on.
ACIDITY MEASUREMENTS JYITH THE GLASS ELECTRODE IS H,O-D,O MIXTURES BY KIRSTENMIKKELSEN AKD SIGURI) OLAFNIELSEN* Carlsberg Laboratory, Copenhagen, Denmark Received November 16, 1060
Determinations a t 22’ of the thermodynamic dissociation constant of acetic arid in ordinary water and in deuteriumenriched water (98.0 volume ?, D20) demonstrate that an ordinary Radiometer glass electrode type G 202A under convenient experimental conditions exhibits the theoretical response to variations in the hydrogen-ion concentration in both solvents M . The acidity determinations involve standardization and storage of the in the range between 2 X and 2 X glass electrode in solutions in HzO and subsequent drying of the glass electrode with mercury before immersing it in the 0.5ml. deuterium enriched samples. From the electromotive forces observed with a saturated KC1-H20 calomel electrode at 22’ the relation between true p(DH) and apparent pH in 98% D,O is derived. p(DH) = apparent pH 0.44. A possibility of determining the activities, an and a D , separately is considered from the point of view of extrapolating rate data obtained in HzO-DzO mixtures to pure DzO.
+
Introduction As the data, in the literature appeared conflicting and not sufficiently accurate to serve as basis for precise acidity measurements with a calomelglass electrode couple in mixtures of HzO and D?O, it was decided to reinvestigate the behavior of this electrodt. couple in H20 and in water containing 98.0 volume % DzO, Le., 0.980 volume of DzO per volume of water. For this purpose two calomel electrodes were used, one “light” made up with HzO saturated with KCl and the other “heavy” made up with 98 volume yo D 2 0 water saturated with KC1. Previously Hart’ studied the relation
of true to apparent pH of solutions in D20 as measured with a calomel-glass electrode couple and found the correction for DC1 solutions in DzO to be $0.4 pH unit. This result deviates from that of an earlier investigation2 in which the same correction was given as +0.26 pH unit. Lumry, et u Z . , ~ gave the difference between true pD and glass electrode apparent pH as +0.4 pH unit in 99.8% D20. That the glass electrode a t least under certain experimental conditions exhibits the theoretical response to variations in hydrogen ion concentration is also apparent from a number of investigations, not specifically concerned with
* Danish Atomic Energy Commission, Research Establishment, Chemistry Dept., RisZ, Denmark (1) R , G H a r t , Nat. Research Council Canada Report CRE-423, J u n e (1949); C. A . , 46, 2887 (1952).
(2) R . B. Fischer and R . A. P o t t e r (RIDDC-715) ADD ( 7 ) , 1. 458 (1947); C. A., 46, 2887 (1952). (3) R. Lumry E. L. Smith and R. R. Glantz, J A m . Chem Soc., 73, 4330 (1951).
