Formation Of Ettringite By Hydration Of A System Containing An Anhydrous Calcium Sulfoaluminate.pdf

August 1965

Journal of The American Ceramic Society-Discussions

W. D. Kingery, Introduction to Ceramics; p. 241. John Wiley & Sons, Inc., New York, 1960 6 J. B. MacChesney and J. F. Potter, “Factors and Mechanisms hffccting the Positive Temperature Coefficient of Resistivity of Uariurn Titanate,” .7 Am. Cermn. SOG.,48 121 81-58 (1965).

435

CERAMIC SURFACE

bulk and boundary diffusion are nearly equal. This leads t o the uniform skin development schematically shown in Fig. 2. If the defect concentration is reduced by lowering the La content, then Darainhoundary > D b u l k for oxygen and only a thin reoxidized skin is formed on the surface of each grain. This model may explain “oxidation” of the La-doped BaTiO3 ceramics reported by MacChesney et U Z . ~ and the “blocking layer” for the P T C anomaly proposed by Heywang.G Acknowledgments The authors are greatly indebted to S. Mori for the X-ray analyscs and t o M. Fujimura for technical assistance.

and Notes

GRAIN

Fig. 2. Development of skin by diffusion-controlled reoxidation i n the defect structure B ~ o . & ~ ~ . o ~ ~ ~ o . o ~ ~ TiO3. (Dgrain boundary z5 D b u l k . )

W. Heywang, “Resistivity Anomaly in Doped Barium Titanate,” ibid., 47 [lo]454-90 (1964).

Formation of Ettringite by Hydration of a System Containing an Anhydrous Calcium Sulfoaluminate by P. K . MEHTA and A. KLEIN

A

t o Dana’ the natural mineral ettringite has the probable composition 6Ca0. AlzO3. 3SOa. 33H20 and occurs as colorless, acicular crystals. A hydrate of identical chemical composition and resembling the mineral ettringite in crystal characteristics is important in the chemistry of hydraulic ccmentitious inatcrials. I t s formation during the carly stages of hydration of normal portland cements is generally believed to be responsiblc for the prevention of quick-set which, in the absence of CaS04 in cement, could occur because of the precipitation of calcium aluminate hydrates. In supersulfated cements, the ceincnting action is attributed to the formation of ettringite. Furtlierinore, cttringite is generally believed to be the cause of destructive expansion which occurs when some portland cement coneretcs comc in contact with aggressive sulfate watcrs. The latter conccpt has been used in thc production of expanding cements where the expansion incidental to the formation of cttringitr is hariicssed for shrinkage compcnsation and for chemically prestressing concretc.2 Starting with Candlot3 in 1890, several investigators4 have reported the synthetic preparation of ettringite by precipitation from solutions such as Al,(SO)a, Ca(OH)g, CaS04, and 3Ca0. A1203. The product thus obtained consists of long, slender, needle-shaped hexagonal crystals. In the prcsent investigation, however, ettringitc was prepared by direct hydration of an anhydrous molar composition, 6Ca0 * A1203.3S03, which was made by calcining stoichiometric proportions of high-purity CaC03, Al( OH)3, and CaS04.2HzO a t 1300°C in a Globar furnace. Since 4Ca0.3AIz03.SOa is the only stable ternary phasc known presently,6 the composition of the anhydrous compound 6Ca0. AlzOl.3S03, as determined by quantitative X-ray diffraction analysis, was 30y0 4Ca0.3A1203SOs, 53.5y0 CaSOd, and 16.5% CaO. The material was ground to about 4000 cm2/g* and was subsequently hydrated with a stoichiometric amount of distilled water t o yield 6Ca0. AlzOs. 3S08.33H20. The paste was cast in cylindrical plastic molds 1 in. in diameter. The hardened paste was removed from the molds, wrapped in cotton pads soaked with distilled water, and transferred to an airtight container for further hydration. The progress of hydration was followed by X-ray diffraction analysis; in 7 days the material was completely hydrated to ettringite. CCORDING

X-ray diffraction analysis of the completely hydrated sample did not show carbonation products, hydrated compounds other than ettringite, or nnhydratcd constituents. This procedure for preparing ettringite by hydration is not only less tedious than the conventional techniques involving interaction of solutions with specific ionic concentrations and elaborate filtering and drying procedures in Con-free atmospheres, but it also yields a product of fine particle size, which is more representative of the ettringite phase actually formed in portland cements hydrated with limited amounts of water. In fact the crystals Received March 1, 1965; revised copy received June 1, 1965. This work was sponsored by National Science Foundation Grant No. 616. The writers are, respectively, assistant professor, and research engineer and lecturer, Department of Civil Engineering, University of California, Berkeley, California. E. S. Dana, Textbook of Mineralogy, 4th ed.; p. 770. Revised by W. E. Ford. John Wiley & Sons, Inc., New York, 1932. ( a ) A. Klein and G. E. Troxell, “Studies of Calcium Sulfoaluminate Admixtures for Expansive Cements,” Am. Soc. Testing Muter. Proc., 58, 986-1008 (1958). (.b) Alexander Klein, Tsevi Karby, and Milos Polivka, “Properties of an Expansive Cement for Chemical Prestressing,” J . Am. Concrete Inst., 58 [I]59-82 (1961). ( c ) T. Y. Lin and Alexander Klein, “Chemical Prestressing of Concrete Elements Using Expanding Cements,” ibid., 60 [9] 1187-1218(1963). 3 E. Candlot, Bull. Soc. Encour. Ind. Nut., 102, 682 (1890). ( a ) A. A. Klein and A. J. Phillips, “Hydration of Portland Cement,” Natl. Bur. Std. Tech. Paper, No. 43 (1914). ( b ) H. Kuhl and H. Albert, Zement, 12, 279 (1923). (c) William Lerch, F. W. Ashton, and R. H. Bogue, “Sulphoaluminates of Calcium,” J . Res. Nutl. Bur. Std., 2 [4] 715-31 (1929) R P 54. ( d ) G. L. Kalousek, “Sulfoaluminates of Calcium as Stable and Metastable Phases,” Dissertation, University of Maryland, 1941. 6 P. E. Halstead and A. E. Moore, “Composition and Crystallography of an Anhydrous Calcium Aluminosulfate Occurring in Expanding Cement,” J . Appl. Chem. (London), 12 [9] 413-17 (1962). * ASTM Specification C 204-55, Fineness of Portland Cement by Air Permeability Apparatus. OH. E. Swanson, N. T . Gilfrich, M . I. Cook, R. Stinchfield, and P. C. Parks, “Standard X-Ray Diffraction Powder Patterns, Vol. 8 ” . pp. 3-4 in Nutl. Bur. Std. ( U . S.) Circ., No. 539, 76 pp. (April i959).

Journal of The 1merican Ceramic Society-Discussions

436

Table I.

-

,~_-___ ~_ -, I

d

Vol. 48, No. 8

X-Ray Powder Diffraction Pattern of 6Ca0.A120s.3SOa.33H20

Pi-esent study

h kl

and Notes

Natl. Bur. vf Stds.

_ ~

Present study

,

______A

1

hkl

d

I

9 73 8 86

100 12

323 410 412 324 413

2 2 2 2 2

d

130 124 079 059 033

4 6 3 6 1

2.130 2.124 2.081 2 062 2 033

2 5 4 5 1

1 2 3 9 2

2 027 1.979 1.975 1.946 1.905

1 2 3 10 1

1

1.875 -. 1.853 1.845 1.829 1.812

2

1.786 1.768

2

10 9 8 7 5

71 71 87 23 76

5 100 12 5 11

110 112 200 104

5 4 4 4

61 98 86 70

80 25 7 45

5 4 4 4 4

61 98 86 69 41

81 24 6 36 3

317 325 414 500 407

2 027 2 004 1 971 1 943 1 904

203 114 210 204 212

4 3 3 3 3

02 88 67 60 48

10 70 6 16 32

4 02 3 88

3 67 3 60 3 48

10 51 7 14 31

503 2-1-10 332 42 1 422

1 875 1 854 1 843 1 828 1 806

3 26

10 21 9 6 45

3 3 3 2 2

27 24 02 81 77

4 19 6 6 38

1 1 1 1 1

789 763 748 723 705

2

714 6971 680j 616 564

6 12 7 21 45

1 679 1 663 1 620 1 598 1 574

4 10 A 2 6

1,515 1.510 1,462 1.392

2 2

?J 24

3 02 2 81 2 77

222 310 008 3 12 216

2 712 2 688

5

2 616 2 S66

19 55

2 2 2 2 2

313 224 400 118 306

2 2 2 2 2

5’27 490 430 422 408

6 4 2 4 12

2 2 2 2 2

5’24 487 434 422 401

4 3 2 2 10

208 320 226 32% 316‘

2 2 2 2 2

352 231 210 184 152

5 7

2 2 2 2 2

347 230 209 185 154

4 20 43 8 23

9

50 6

26

wcrc so s i i ~ ~that l l it was impossible t o confirm the acicular habit by petrographic microscopy. Since the iiitciisities of X-ray tliffractioii pcaks arc affcctcd by tlic particle size of thc crystals, it is obvious that the ettriiigite produced by hytlration is better suited for application in quantitative X-ray diffraction analyses.

__^--, I

I

002 100 101 I02 t 03

213 300 116 220 304

Natl. Bur. of Stds.

d

c

5 3 3 5 1

~

6 8 4 4

4

4

J

1

The X-ray diffraction pattern of the ettriiigitc prepared by the authors is shown in Tablc I. I t includes some data, in addition to the data earlier reported by the National Bureau of on a syntlictic specimen of ettringite prepared by precipitation froti1 appropriate solutions.

Thermal Expansion of Polycrystalline Hf0,-ZrO,

Solid S o h tions

b y 0. M. S T A N S F I E L D

OMPIXIE solid

solutioii in tlie I-ifOl- ZrOn binary system lias been reportctl. N o Iiigh-teiiiperature therinal expaiisioii (1:tt:i exist, however, for coiiipositions contaiiiing appreciable :iiiiouiits of both coiiipoIieiits. This iiotc reports the thernial c~sp:msion of polycrystalline IHf02-Zr02 bodies betwceii 900’ ; i t i t l 2600°C as deteriiiined by tlilatometry. Hafiiia w:is o1)t:iiiictl iii two purities: 99,9 \vt% IHOl coiit:iiiiitig 180 ppin Zr and 96 w t % HfOz containing 2.2 w t % %r, 0.2 wtO/, Ti, iiiid 0.2 w t % I’e. The %rOS w:is 98 wt% pure witli less than 50 ppiii Nf. Only the liigli-purity HfO, was used to iil;ikc pure HfOn speciiiieiis. The lcss pure HfO, was used in tiiakiiig HTOz-%rO2bodies since it was deterniiiietl that tlie iiiipurities tiid riot affect the tlierinal expansion. ‘l‘lic t1il:rtonieter :rnd tlic procedure used to fabi-ic;rte the specitiiciis Iiavc heen described elscwhcre.” The :iccuracy of tlic

C

Received April 22, 1965; rcviscd copy received June 14, 1965. Tliis work was sponsored by the (Jnitetl States Air Force, Air Force Materials and Processes I,aboratory, undcr Contract AI’ :13(657)-11269. The writcr is a rcsearch cngineer a t Solar, a 1)ivisioii of Intcrn:itiorial Harvester Cornpany, San Dicgo, California. i C. E. Curtis, L. M. 1)oiiey. and J. I<. Jolitisoii, “Sortie Proyerties o f Hafiiiuni Oxide, Hafniuiii Silicate, Calcium Hafnate, a n d I-Iafniuin Carbide,” J . A m . Cwm?.Soc., 37 [lo] 458-65 (1854). I<. 1’. Domagala, “Study of the Zircotiia-Hafnia System,” Illiiiois Institute of Technology I