deionized water
potassium hydroxide (Baker 0222, pellets, 86.8% KOH)
alumina (Baker 0005, 98.6% AI(OH)₃)
silicic acid (AKZO SM 604, 90% SiO₂) ^a
strontium nitrate (Fluka 85900) ^b

(1) [50.00 g water + 29.76 g potassium hydroxide + 15.80 g alumina], heat to boiling until clear; cool to room temperature and correct weight loss due to boiling
(2) [96.97 g water + 66.77 g silicic acid], mix until smooth (approximately 6 minutes)
(3) [75.08 g water + 2.124 g strontium nitrate], mix until dissolved
(4) [(2) + (3) + 25.12 g water (rinse)], mix for 6 minutes
(5) [(4) + (1) + 25.08 g water (rinse)], mix for 6 minutes ^c

Vessel: 300 mL stainless steel autoclave ^d
Time: 115 hours ^e
Temperature: 150⁰C ^f
Agitation: none

(1) Cool to room temperature ^g
(2) Filter and wash (5 times) with 650 mL water; the pH of the last wash water = 10.5
(3) Dry in a 150⁰C oven for 16 hours
(4) Yield: 57.2 g (97% on Al₂O₃)

XRD: KFI (only crystalline product) Elemental Analysis: SiO₂/Al₂O₃ = 6.6
Crystal Size and Habit: ~ 0.5 um
Click here to view XRD pattern

[1] J. P. Verduijn, US Patent 4 944 249 (19 February 1991)

a. Colloidal siicas such as Ludox HS-40 are also suitable silica sources.

b. The Sr²⁺ sources used were Sr(OH)₂ and Sr(NO₃)₂; there is no preference.

c. The final gel is (visually) very homogeneous and pourable.

d. No Teflon liner was used.

e. Crystallization times (at 150⁰C) are not critical (90-140 hours).

f. The autoclave was placed in a room temperature oven. The oven was heated within 2 hours to 150⁰C and kept at this temperature for 115 hours.

g. The synthesis magma (after treatment has an amorphous appearance; no free mother liquor can be seen. This is typical for this type of synthesis.