DE2116476B2 - Method and device for measuring contact angles and heat of wetting between poorly wetting liquids and powders - Google Patents

Description

25 is dispersed as finely as possible so that no air

vesicles are enclosed in agglomerates and

allow the powder to float up a little so that the entire surface is not completely wetted.

The invention relates to a method and a pre-This would lead to erroneous measurement results.

direction for measuring edge angles and wetting. Strong agglomerate formation is generally

Congregation heat between poorly wetting liquids cannot be avoided if the measuring liquid is the

and powders. Powder not completely wetted, so the edge angle

The surface tension of a powder (Pigmen- is greater than 0 °. This occurs when the surface

tes) is generally not known. It would be the surface tension of the liquid greater than that

¹ 11! tunable if contact angle measurements on the surface tension of the powder.

would be feasible. The known methods The invention is based on the object of a

to measure edge angles all require larger methods and a device for measuring

flat surfaces of the solid to be examined, _{χ of the edge angle and}

to z. B. Plussigkenstropfen on the surface - _{2 d} wetting heat

or add vertically into the liquid at 40 °

dipped plates to measure the capillary rise. to create between powders and liquids, and

Try to place powder on a flat surface - for combinations of substances in which the pigment

mating are only possible in a few special cases, only incompletely wetted.

because the generally very high levels of sublimation.

temperatures decomposition of the sample or the organ 45 according to the invention characterized in that the

niche molecules (color pigments) are used. Every pressure is measured with which a liquid is applied

if in such sample preparations, the cause of the capillary forces in the pore volume of a

Structure, modification, etc. penetrating into uncontrollable bulk powder or powder compact.

Way to be changed. Attempts to under- This pressure is, according to equation 1, proportional to the

the powder to be pressed into solid tablets, 50 wetting tension a, cos &

around edge angles on them (e.g. by placing

of a liquid drop) fail to measure- __ 2a _t -cosu _n ,

^assume that Ap ~ " ^(L)

1. the unavoidable microscopic or

submicroscopic roughness defective edge 55 between liquid and capillary wall and

angle delivers and returns proportionally to the capillary radius r. If you know

2. the pores and capillaries that are always present in the ⁿ ! ^s _{u of} ^the capillary radius and the liquid upper compact suck up liquids and thus a surface tension can make contact angle measurement impossible from the measured pressure. _β ^ er contact angle between liquid and solid

60 can be determined. On the other hand, when measured

Another way of making a statement about the capillary pressure and known liquid surface size of edge angles with the help of the maximum tension the capillary rise responsible for the pressure can be determined with a considerable measuring radius if the contact angle is 0 ° niche difficulties associated. To this would be amounts. This condition is fulfilled if the Possibly pigment-powder-beds with liquid surface tension equal to or lower than 65 A height of 10 m is necessary to achieve the maximum increase than the solid surface tension. Will altitude (pressures of 2.5 atmospheres), the capillary pressure was already temperature-dependent measured). In this case the would be correct, which is equivalent to the determination

the temperature coefficient of the wetting tension, the heat of wetting between Liquid and solid can be determined. The device for executing the method according to the invention comprises a sample container to which a pressure gauge and a device, by means of which a pressure can be specified, are connected. Furthermore, the device for Exercise of the method according to the invention by ifine lifting or lowering device, by means of which the powder sample and the measuring liquid can be brought into contact with one another, and through a heatable housing, by means of whose sample, measuring liquid and the entire measuring system are tempered can be advantageously trained.

The invention is illustrated below with reference to the schematic drawing of an exemplary embodiment additionally explained.

The device comprises a container 1 for holding the powder 2 to be examined. The container 1 can be open at the bottom when the powder is pressed in at high pressure. When using it is closed off by a permeable frit at the bottom from spills of powder. At the upper end of the container 1, a pressure gauge 3 is connected in a gas-tight manner. The pressure can be on a display device 4 - if necessary with a recording device - can be read. To the pressure gauge 3 a device 6 (e.g. a pump or a pressure vessel) is also via a three-way valve 5 connected, with which a form can be given to the system. This can be done via a tap 7 Measurement system ventilated or sealed gas-tight from the environment. The measuring liquid 8 can be in contact with the sample container 1 by means of a lifting table 9 or a lowering device 10 to be brought.

The entire measuring system is located in a housing 11, which is controlled by an adjustable heating device 12 can be tempered.

The container 1 with the powder 2 is connected to the pressure gauge 3 in a gas-tight manner.

The system is operated by taps 5 and 7

Heating device 12 on the

and the sample size

throw the taps 5 and 7 so set. 'aaa no connection to the atmosphere and the fore-aft

with aem nanu j s-w - °,

device 6 and pressure gauge 3 to produce

The form is dimensioned so that it is close to the pressure that may be expected The connection between de? Device6 and the pressure gauge again

so interrupted by means of the valve 5. _vk v _nsity

After a certain time, the ™ ^ ™ * ° *** depends on the liquid to be measured, turns out to be more ationary The final pressure, which corresponds to the capiUar pressure to be measured, is displayed on the display unit 4

geS and, if necessary, by means of the register

viSe ^ and the device offer the Advantage that contact angles and wetting warmth through a simple pressure measurement directly on powders

Furthermore, Konneu and d.teer Vornch tion ^ outflows of adsorption layers on the powder surface can be determined with regard to wetting.

In the claimed method, the m

The ^ ffg ™ ^ ™ * known measuring systems mentioned in the introduction are avoided. It is a stau cal process. The hydrodynamics in the bulk powder and thus the viscosity of the fluid play no role. The maximum height required

not to be measured. By the possibility Giving form can significantly reduce the measuring time shortened and the amount of powder limited.

1 sheet of drawings

Claims (3)

Measurement times over several days and weeks. stretch. In dynamic measurement methods, e.g. B. Measurement 1. Method of measuring contact angles of wetting speed, d. H. determination and heat of wetting between poorly 5 of the amount of liquid that ends in a given time network Liquids and powders, as a result of which uniformly flows into a bulk powder, cannot characterized in that the pressure measured directly determines the maximum height of rise and thus with which a liquid can be calculated on the basis of no contact angles. It is not Capillary forces in the pore volume of a powder possible with such dynamic measurements bulk or a powder compact penetrates. io which hydrodynamics play an essential role 2. Device for performing the procedure plays, directly to infer the edge angle,
according to claim 1, characterized by einfen _? There are also special methods for determining sample containers (1), on which a gas-tight wetting tub for powders in liquids, pressure measuring device (3) and a device (6) are known. For example, the calorimetric measurement of the amount of heat by means of which a pressure can be specified can be measured that is released when a powder is connected. from a gas or vapor space into a liquid 3. Apparatus according to claim 2, is stirred in marked. In order to be able to measure measurable temperature changes through a lifting (9) or a lowering process in the calorimeter, the measuring liquid must be in contact with each other in the very direction (10) by means of which the powder sample and large surfaces (many square meters) are wetted. In order to evaluate the measurement it must still be possible to bring, and by means of a heatable wetted surface (specific surface in res housing (11,12), by means of its sample, measuring m ² / g) known, which again with other liquid as well the entire measuring system temperature must be determined. In addition, it must be possible to guarantee. makes it possible that the powder in the measuring liquid