Products

PHYSICO-CHEMICAL CHARACTERISTICS AND SAFETY DATA

SURFACE AREA

The total surface area of silica is measured according to the method developed by Brunauer, Emmett and Teller (BET), J. Amer, Chem. Soc.60, 309 (1938) and is expressed in m2/g.

The process is based on adsorption of gaseous nitrogen. In practice, the greatly simplified areameter method according to Haul and Dümbgen (ISO 5794/1,annex D) is used.

AVERAGE SIZE OF AGGLOMERATES

In case of spray dried silica, the Alpine air jet sieve is used to determine the particle size.

Spray dried milled products are dispersed in an aqueous suspension through the use of ultrasonic radiation and the particle size distribution is determined with the Coulter Counter or by other laser techniques.

Air Jet Sieve (producer: ALPINE AG, D-8900 Augsburg 1)

The average size of the agglomerates of fillers generally has a great influence on the application engineering behaviour.

pH VALUE

The pH value is determined electrometrically with a glass electrode and a pH meter. Generally, the pH value of silica is in the neutral range.

DRYING LOSS

The spray-dried products contain a small proportion of physically bonded water. After 2 hours of drying in the drying cabinet at 105 ⁰C, the greater part of the physically bonded water is removed.

Weighed Sample in the Weighing Bottle

IGNITION LOSS

After 2 hours of ignition time at 1000 ⁰C, chemically bonded water, in the form of silanol groups is also removed. The ignition loss is determined with the substance that has previously been dried for 2 hours
at 105 ⁰C.

Determining the Ignition Loss

CHEMICAL ANALYSIS

SiO₂ content is determined gravimetrically by fuming off with hydrofluoric acid. The analysis of the metallic oxides Na₂O, Fe₂O₃ and Al₂O₃ is carried out by means of spectrophotometric method from the residue remaining, after the fuming off with hydrofluoric acid.

The sulphate and chloride contents are determined by potentiometric titration.

SIEVE RESIDUE

In order to detect proportions of non-dispersible or sparingly dispersible particles, which are present in very small quantities in spray dried silica, the sieve residue is determined according to Mocker. In this process, a silica suspension is washed through the sieve with 4 bar water pressure. The sieve is then dried and the sieve residue is weighed. 45-micron sieves are used which correspond to 325 mesh (according to ASTM or ISO 787/XVIII).

Filling of Suspension into the Mocker Apparatus

TAMPED DENSITY

This parameter is a measure for the weight of the product in powder form. About 200 ml of silica is tamped 1,250 times in the graduated cylinder of the tamped volume measuring instrument. The tamped density is calculated from the initial weight of the sample and the resulting volume, reported in g/l.

DBP ABSORPTION

The DBP absorption according to ASTM D 2414, similar to the oil absorption, according to DIN 53199, is a numerical value for the absorptive capacity of filler. Owing to the automatic measurement process, however, this method can be carried out more accurately than the determination of the oil absorption.

In addition to the absorptive capacity, the DBP absorption is also influenced by other parameters, such as the
particle size.

HEALTH AND SAFETY DATA

REGULATORY STATUS

Synthetic amorphous silica is neither classified as a dangerous substance under EEC Directive 79/831 EEC, nor amendments as a dangerous goods under transport regulations.

Amorphous silica has been authorized by FDA (USA), PFA (India) for use in selected items, cosmetic and pharmaceutical applications. These products meet the requirements for purity and testing for "colloidal silica" as prescribed in Food Chemical Codex (USA).

TOXICOLOGY

Synthetic amorphous spray-dried silicon dioxide is characterized by the absence of sharp peaks in X-ray power diffraction scans and is therefore considered totally amorphous.

Synthetic amorphous silica is classified as a non-hazardous waste under European, American and Indian regulations. Regular medical examinations of workers employed in the manufacturing and processing of synthetic amorphous silica have been conducted over many years and have shown that no silicosis was caused even under extreme working conditions. The studies of synthetic silica, carried out by means of animal experiments in the past, have largely confirmed the experience acquired from humans during handling with synthetic amorphous silica.