The characterisation of aqueous silicon slips

Nitride-bonded silicon nitride from slip-cast Si + Si3N4 compacts

“…The experimental details and the results of such studies were presented elsewere. 16,17 For slurry characterization, the powders were dispersed in DIW with continuous magnetic stirring for 5-20 min depending upon the required total solid loading (in the range 5-50 wt.%). The pH of the slurry was adjusted to various values ranging from 2 to 12 using HNO 3 (70% sol.)…”

“…Some of the physical characteristics of the Si (HQ and RQ) and Si 3 N 4 (S1) powders are presented in Table I along with their chemical composition (as provided by the supplier). Figure 1 depicts the particle-size distribution curves at the optimum dispersion condition of pH ‫ס‬ 8 for two Si 16 powders and pH ‫ס‬ 10 for Si 3 N 4 17 . The results of Fig.…”

“…1 and Table I indicate The metallic Si as well as the nonoxide Si 3 N 4 powders are usually found to be surface oxidized, and the fine (submicron) particles contain a superficial layer of silica on their outer surfaces. [16][17][18][19][20] When these powders are dispersed in water, the oxidized surfaces get hydrolyzed to form amphoteric silanol (Si-OH) groups. 16,21 In addition, Si 3 N 4 particles also contain basic amine groups viz.…”

“…[16][17][18][19][20] When these powders are dispersed in water, the oxidized surfaces get hydrolyzed to form amphoteric silanol (Si-OH) groups. 16,21 In addition, Si 3 N 4 particles also contain basic amine groups viz. silazane (Si 2 -NH) and silylamine (Si-NH 2 ) on their surfaces.…”

“…17,19,20 In aqueous medium the silanol and amine groups undergo acid/base reactions depending on the pH of the medium and develop positive or negative surface charges depending upon the adsorption of either of the potential detemining OH − or H + ions. [16][17][18][19][20][21] These surface charged particles adsorb a layer of opposite charged ions resulting in an electrical double layer and an electrical potential developed at the shear plane between the bound and free liquid and is called the ZP. On close approach, these particles repel each other due to the overlapping of the electrical double layer.…”