IEC 60754-2-2011 pdf free download – Test on gases evolved during combustion of materials from cables – Part 2: Determination of acidity (by pH measurement) and conductivity.
4Test method principle
The material under test shall be heated in a stream of dry air. The evolved gases shall betrapped by bubbling through wash bottles filled with distilled or demineralized water.
The acidity of the resulting solution shall be assessed by determination of its pH value.Theconductivity of the solution shall also be determined.
5 Test apparatus
5.1General
The apparatus is shown in Figures 1 to 5.
The assembly of the components which constitute the test apparatus shall be leak-tight. Theconnecting distances between the quartz glass tube and the first bottle and betweensubsequent bottles shall be as short as possible.Glass or silicone rubber tubing shall be usedfor these connections.
NOTE 1 At the exit side of the quartz glass tube,as close to the end as possible, it is permitted to place a plug ofsilica wool to aid collection of condensates.
NOTE 2 A third empty bottle,of the same size as the gas washing bottles, placed before the gas washing bottlesmay be used to improve safety, i.e. to prevent suck back of water into the quartz glass tube,
5.2Tube furnace
The length of the heating zone of the furnace shall be within the range 480 mm to 620 mmand its inside diameter shall be within the range 38 mm to 62 mm. lt shall be equipped withan adjustable electrical heating system.
5.3Quartz glass tube
For the test, a quartz glass tube shall be introduced into the tube furnace.The tube shall beapproximately concentric to the furnace. lt shall be resistant to the action of corrosive gases.
The inside diameter of the tube shall be within the range 30 mm to 46 mm.The tube shallprotrude on the entrance side of the furnace by a length of between 60 mm to 200 mm, andon the exit side by between 60 mm to 100 mm.The initial clearance shall allow for thermalexpansion.For the purposes of measurement of the protrusion distances, the tube shall beregarded as that part of essentially constant diameter.
NOTE The outer diameter of the tube should be chosen with due regard to the inside diameter of the tubefurnace.
Prior to each test the tube shall be cleaned throughout its length by being calcined atapproximately 950“c.
5.4Combustion boats
The combustion boat shall be made of porcelain, fused quartz or soapstone and shall havethe following dimensions:
– external width: within the range 1 2 mm to 30 mm;
– internal depth: within the range 5 mm to 1 0 mm.
NOTE The dimensions of the boat should be chosen with due regard to the inside diameter of the quartz tube.
The preferred method for insertion of the combustion boat into the quartz glass tube is shownin Figure 1.
Prior to each test, the combustion boat shall be washed and calcined in a muffle furnace atapproximately 950 °C for 4 h after which it shall be introduced into a desiccator and cooled toambient temperature.The combustion boat shall then be weighed to an accuracy of 0,1 mguntil two identical consecutive weights are obtained.This weight mshall be recorded.
5.5 Bubbling devices for gases
At the exit of the quartz glass tube, the evolved gases shall be trapped by bubbling throughtwo wash bottles (see Figure 2), each containing approximately 450 ml of distilled ordemineralized water of a purity at least Grade 3 in accordance with iso 3696.
The pH value of the water shall be between 5,5 and 7,5, and the conductivity less than0,5 uS/mm.
A magnetic stirrer shall be introduced in the first gas washing bottle to get a good swirlingmotion and an effective absorbtion of the combustion gases.The tubes into the wash bottlesshall have a maximum internal diameter at their tip of 5 mm in order to aid absorption.
The height of the liquid above the end of the tube shall be (110 ±10) mm in each bottle.
NOTE Use of a standard laboratory glass bottle of internal diameter approximately 75 mm will enable thisrequirement to be met.
5.6Air supply system
The gas used for combustion shall be air.
The flow rate of air introduced into the quartz tube shall be adjusted according to the actualinternal cross-sectional area of the tube, such that the speed of air flowing across the sampleis approximately 20 ml/mm2/h.
The speed of air shall be regulated by reference to the flow rate of air.The flow rate of airshall be (0,0157 x D2) l/h with a tolerance of±10 %.IEC 60754-2 pdf download.