Angular 7: Material Button Icon doesn't work in the header of a datatable

I'm trying to add a refresh button to a Material Data Table on Angular 7, but the name of the icon, refresh is shown in italic instead of the icon.

The relevant code is shown below:

<table mat-table [dataSource]="myDataSource">
  <!-- other rows... -->

  <ng-container matColumnDef="buttons">
    <th mat-header-cell *matHeaderCellDef>
      <button (click)="reload()" mat-icon-button>
        <i class="material-icons" alt="reload">refresh</i>
      </button>
    </th>
    <td mat-cell *matCellDef="let row">
      <!-- buttons for each row here -->
    </td>
  </ng-container>
</table>

Is it not possible to add a material icon to the header of a datatable?

It did work with a normal table.