Hydrothermal growth of willemite single crystals in acidic solutions

Journal of Crystal Growth 29 (1975) 123—124 © North-Holland Publishing Co.

HYDROTHERMAL GROWTH OF WILLEMrI’E SINGLE CRYSTALS IN ACIDIC SOLUTIONS KOHEI KODAIRA, SHIGERU ITO and TORU MATSUSHITA Department of Applied Chemistry, Faculty ofEngineering, Hokkafdo Upiversity, Kita-13 Nishi-8, Sapporo, 060 Japan

Received 11 December 1974; revised manuscript received 29 January 1975 Willemite single crystals were grown from MCI solutions under hydrothermal conditions. Typical crystals were colorless and transparent with a maximum size of 0.1 mm diameter x 3 mm length. The crystals were hexagonal prisms with rhombohedral termination. The growth direction was the cne, axis.

Willemite (Zn2SiO4) single crystals have been grown 1). Basic solutions were by the hydrothermal method used as solvents. Since A1 2) and chalcogenides3’4) 203 acidic solutions, we athave been crystallized from tempted the use of H 2S04 and HCI solutions as solvents for the growth of willemite single crystals by the hydrothermal method. ZnO blocks sintered at 1000 °C for 3 hr were used as nutrient. A small piece of fused silica or synthetic quartz was used as the Si02 nutrient. The sintered ZnO and Si02 blocks with acid of desired concentrations were sealed into a gold capsule or a

pressure soThe as internal to prevent the fused tube from from rupturing. pressures weresilica estimated the temperatures of the pressure vessel and its degree of filling5). The temperature of the vessel was measured by a chromel—alumel thermocouple strappedto the skin of the vessel and was held within ±4 °C.After hydrothermaltreatmentatthe desired conditions, thevesselwas quenched to room temperature by immersion in water. Table 1 shows the results obtained with hydrothermal treatments at 350 to 500 °Cfor 7 to 10 days. When solvents of 8 to 16 N H2S04 were used, all of the ZnO

fused silica tube. The gold capsule or fused tube nutrient treatment. blocks werePreliminary changed to experiments ZnSO4 after showed hydro3 pressure vessel whichsilica could be thermal was placed in a 5.5 cm up to 2000 kg/cm2 at 700 °C. that willemite single crystals could be grown by the use pressurized with water

The pressure vessel was maintained at the desired pressure and temperature in a tubular furnace. In experiments where a fused silica tube was used, a pressure was applied to the outside of the silica tube which was always higher by about 200 kg/cm2 than the internal

of HC1 solutions as solvents. With the use of a fused silica tube as the reaction container with 2 to 8 N HC1 solutions, needle-like single crystals of willemite were grown radially from the fused silica tube wall. Though the crystals were small in the case of 2 N HC1 solu-

TABLE

1

Representative runs for hydrothermal growth of willemite single crystals in acidic solutions

Q:

Solvent

Temperature (°C)

2 N HC1 4 N MCI 4 N HCI 8 N HCI

400 400 500 400

8 N HCI 8N H 2S04 8 N H2S04

Pressure (kg/cm2)

Duration (days)

Capsule

400 400 1000 400

7

Q Q

500

1000

7

0

400 500

350 1000

10 10

Q

7 7 7

G

Q

G

fused silica tube; 0: gold capsule.

123

Remarks on the willemite single crystals Small and fine Needle like crystals, 1 mm length Small and fine Needle crystals with hexagonal prisms, 3 mm length and 0.1 mm diameter Needle like crystals, 0.5 to 1 mm length No growth, transform to ZnSO4 No growth, transform to ZnSO4

124

KOHEL KODAIRA, SHIGERU ITO AND TORU MATSUSHITA

Fig. 1.

2 for 7 days.

Willemite single crystals grown from 8 N HCI solutions at 400 °Cand 400 kg/cm

tions, the grown crystals became larger with an increase of the concentration of HC1. The crystals obtained at 400 °Cand 400 kg/cm2 for 7 days were colorless and transparent having a maximum size of 1 to 3 mm length and 0.1 mm diameter as shown in fig. 1. The shape of the crystals was hexagonal prisms with rhombohedral termination. However, the crystals ob-

±4mg after hydrothermal treatment at 400 °Cand 4 N HCI solutions for 10 days. Therefore, it is concluded that the willemite single crystals were grown by the reaction of silica with dissolved ZnO. The lattice parameters were calculated from the (006) and (630) reflection lines of the powder X-ray diffraction patterns with Ni-filtered Cu K~c 1radiation by using silicon powders as an internal standard. The lattice parameters as shown in table 2 were found to be almost identical with those reported by Chin’Hang et al. 6)~ It was also concluded from the analysis of X-ray oscillation photographs that the crystals were grown along the Chex axis. A Kurata Research Grant was partly used to finance in this study.

tamed with the use of a gold capsule were small in comparison with those obtained with the use of a fused silica tube. It might be expected that silica is not very soluble in acidic solutions under hydrothermal conditions. However, willemite single crystals were grown by the use of HCI solutions in the present experiments. The silica weight loss in the absence of ZnO was measured to confirm whether silica is soluble or not in HC1 solutions under hydrothermal conditions. A weight loss of References silica could not be determined within the range of 1) B. N. Litvin and 0. 2 Lattice parameters of the willemite crystals TABLE

Source

Lattice parameters

(A)

2) 3) 4)

Cj,~

Present wprk 6) Chin’Hang et al.

13.932 13.931

9.311 9.307

5) 6)

K. Melnikov, in: Growth of Crystals, Vol. 4, Eds. A. V. Shubnikov and N. N. Sheftal (Consultants Bureau, New York, 1966) p. 139. D. F. Weirauch and R. Kung, J. Crystal Growth 19(1972)139. H. Rau and A. Rabenau, Solid State Commun. 5 (1967) 331. Y. Morimoto, K. Wakino, F. Kanamaru and M. Loizumi, J. Am. Ceram. Soc. 54 (1971) 171. G. C. Kennedy, J. Sci. 248 (1950) Chin’Hang Cryst. 15 (1970) M. Am. A. 387.Simonov and N. V.540. Belov, Soviet Phys.-