Silica gel, commercial

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Description

The moisture adsorbing properties of silica gels are affected by factors such as capillary pore size or the inclusion of hygroscopic salts, resulting in a wide range of performance. Thus, it is important to compare the buffering capacity of different types of silica gels to determine which has the best performance for a specific application. In 1977, Thomson described the specific moisture reservoir with the variable M where M represents the amount of water (in grams) that is gained or lost by 1 kilogram of silica gel for each 1% change in RH. However for any specific silica gel type, M can vary widely due to the expected RH range and the hysteresis of the adsorption/desorption curve. In order to compensate, a new value called MH has been defined as the average amount of water (in grams) that is gained or lost by 1 kilogram of silica gel for each 1% change in RH. This is determined by repeatedly cycling silica gel between adsorption and desorption within a specific RH range until a constant value is measured.

Table 1: Specific moisture reservoir (g/kg for a 1% RH change) at 20°C *

Moisture sorbent MH 50 ± 10% M 20 → 30% M 60 → 50% Recommended for Recommended for
RH around 50% Keep RH low Keep RH high Temp exhibit case in room with good to moderate climate control Maintenance-free exhibit case
RHapid Gel 6.11 ± 2.16 4.48 ± 0.42 4.38 ± 1.40 2 kg/m3 4 kg/m3
PROSorb 5.42 ± 1.32 4.37 ± 0.10 4.25 ± 0.38
Art-Sorb 4.04 ± 0.80 2.84 ± 0.47 4.18 ± 0.49 4 kg/m3 8 kg/m3
Arten Gel 5.7 5.5
Regular density silica gel (clear, type A) 1.93 ± 0.44 5.48 ± 0.40 1.47 ± 0.16 9 kg/m3 18 kg/m3
Orange silica gel 1.16 ± 0.26 4.92 ± 0.59 0.94 ± 0.14
Bentonite clay (Desi Pak) 1.19 ± 0.07 2.25 ± 0.03 1.11 ± 0.02
Molecular sieves 4A (zeolite) 0.33 ± 0.02 0.47 ± 0.04 0.31 ± 0.01

Resources and Citations

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