The preparation of high-strength

α

-hemihydrate gypsum (

α

-HH) from dihydrate gypsum (DH) is a potential way to improve the utilization rate of industrial gypsum.

α

-HH with a low aspect ratio was prepared by atmospheric salt solution method

using Mg(NO

3

)

2

solution as the salt medium. The effects of reaction temperature

reaction time

Mg(NO

3

)

2

concentration

pH value

and the solid-to-liquid ratio on the purity

yield and aspect ratio of the product were investigated systematically. Under the optimal reaction conditions of 95 ℃

4 h

40% (mass) Mg(NO

3

)

2

pH 5

and a solid-liquid ratio of 1:5

the yield and purity of the product could reach 89.67% and 99.85%

respectively. Additionally

the average aspect ratio of this product was 2.02

and the compressive strength reached 58.2 MPa. The regulation mechanism was studied by calculating the adsorption energies of Mg(NO

3

)

2

on different crystal planes of

α

-HH

which indicated that Mg(NO

3

)

2

exhibited the strongest adsorption on the (1 1 1) plane

and this preferential adsorption retarded the axial growth of

α

-HH

resulting in a reduced aspect ratio of the crystals. These findings suggest that the Mg(NO

3

)

2

solution is an effective approach for preparing high-strength

α

-HH with controlled morphology.